By the end of this chapter, students will be able to:
- Describe how water is an integral part of all .
- Explain how chemical and turn into .
- Differentiate the two main categories of sedimentary rocks: rock formed from pieces of weathered ; and chemical rock that precipitates out of by organic or inorganic means.
- Explain the importance of sedimentary structures and analysis of , and how they provide insight into the Earth’s history.
and the processes that create it, which include , , and , are an integral part of understanding Earth Science. This is because the majority of the Earth’s surface is made up of sedimentary rocks and their common predecessor, . Even though sedimentary rocks can form in drastically different ways, their origin and creation have one thing in common, water.
5.1 The Unique Properties of Water
Water plays a role in the formation of most . It is one of the main agents involved in creating the in rock. It also is a and agent, producing the grains that become . Several special properties make water an especially unique substance, and integral to the production of and .
The water molecule consists of two hydrogen atoms covalently to one oxygen atom arranged in a specific and important geometry. The two hydrogen atoms are separated by an angle of about 105 degrees, and both are located to one side of the oxygen atom. This atomic arrangement, with the positively charged hydrogens on one side and negatively charged oxygen on the other side, gives the water molecule a property called . Resembling a battery or a magnet, the molecule’s positive-negative architecture leads to a whole suite of unique properties.
allows water molecules to stick to other substances. This is called . Water is also attracted to itself, a property called , which leads to water’s most common form in the air, a droplet. is responsible for creating surface , which various insects use to walk on water by distributing their weight across the surface.
The fact that water is attracted to itself leads to another important property, one that is extremely rare in the natural world—the liquid form is denser than the solid form. The of water creates a special type of weak called . allow the molecules in liquid water to sit close together. Water is densest at 4°C and is less dense above and below that . As water solidifies into ice, the molecules must move apart in order to fit into the crystal lattice, causing water to expand and become less dense as it freezes. Because of this, ice floats and water at 4oC sinks, which keeps the oceans liquid and prevents them from freezing solid from the bottom up. This unique property of water keeps Earth, the water planet, habitable.
Even more critical for supporting life, water remains liquid over a very large range of temperatures, which is also a result of . Hydrogen allows liquid water can absorb high amounts of energy before turning into vapor or gas. The wide range across which water remains a liquid, 0°C-100°C (32°F-212°F), is rarely exhibited in other substances. Without this high boiling point, liquid water as we know it would be constricted to narrow zones on Earth, instead water is found from pole to pole. Further, water is the only substance that exists in all three phases, solid, liquid, and gas in Earth’s surface environments.
Water is a , meaning it dissolves more substances than any other commonly found, naturally occurring liquid. The water molecules use and to pry ions away from the crystal lattice. Water is such a powerful solvent, it can even the strongest rocks and given enough time.
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5.2 Weathering and Erosion
refers to the solid rock that makes up the Earth’s outer . is a process that turns into smaller particles, called . includes pressure expansion, , , and salt expansion. Chemical includes and , , and .
is a mechanical process, usually driven by water, wind, gravity, or ice, which transports (and ) from the place of . Liquid water is the main agent of . Gravity and processes (see chapter 10) move rocks and to new locations. Gravity and ice, in the form of (see chapter 14), move large rock fragments as well as fine .
resistance is important in the creation of distinctive geological features. This is well-demonstrated in the cliffs of the Grand Canyon. The cliffs are made of rock left standing after less resistant materials have weathered and eroded away. Rocks with different levels of resistance also create the unique-looking features called hoodoos in Bryce Canyon National Park and Goblin Valley State Park in Utah.
5.2.1 Mechanical Weathering
physically breaks into smaller pieces. The usual agents of are pressure, , freezing/thawing cycle of water, plant or animal activity, and salt evaporation.
buried deep within the Earth is under high pressure and . When uplift and brings to the surface, its drops slowly, while its pressure drops immediately. The sudden pressure drop causes the rock to rapidly expand and crack; this is called pressure expansion. Sheeting or is when the rock surface spalls off in layers. is a type of that produces rounded features and is caused when moves along in the .
, also called , uses the power of expanding ice to break apart rocks. Water works its way into various cracks, voids, and crevices. As the water freezes, it expands with great force, exploiting any weaknesses. When ice melts, the liquid water moves further into the widened spaces. Repeated cycles of freezing and melting eventually pry the rocks apart. The cycles can occur daily when fluctuations of between day and night go from freezing to melting.
Like , happens when plant roots work themselves into cracks, prying the apart as they grow. Occasionally these roots may become fossilized. is the term for these roots preserved in the rock record. Tunneling organisms such as earthworms, termites, and ants are biological agents that induce similar to .
Salt expansion, which works similarly to , occurs in areas of high evaporation or near- environments. Evaporation causes salts to out of and grow and expand into cracks in rock. Salt expansion is one of the causes of , a series of holes in a rock. Tafonis, cracks, and holes are weak points that become susceptible to increased . Another phenomena that occurs when salt water evaporates can leave behind a square imprint preserved in a soft , called a hopper crystal.
5.2.2 Chemical Weathering
is the dominate process in warm, humid environments. It happens when water, oxygen, and other reactants chemically degrade the components of and turn them into water-soluble ions which can then be transported by water. Higher temperatures accelerate rates.
Chemical and work hand-in-hand via a fundamental concept called surface-area-to-volume ratio. only occurs on rock surfaces because water and reactants cannot penetrate solid rock. penetrates , breaking large rocks into smaller pieces and creating new rock surfaces. This exposes more surface area to , enhancing its effects. In other words, higher surface-area-to-volume ratios produce higher rates of overall .
Carbonic Acid and Hydrolysis
(H2CO3) forms when carbon dioxide, the fifth-most abundant gas in the , dissolves in water. This happens naturally in clouds, which is why is normally slightly acidic. is an important agent in two reactions, and .
occurs via two types of reactions. In one reaction, water molecules ionize into positively charged H+1 and OH−1 ions and replace in the crystal lattice. In another type of , molecules react directly with , especially those containing silicon and aluminum (i.e. ), to form molecules of clay .
is the main process that breaks down rock and creates clay . The following is a reaction that occurs when silica-rich encounters to produce water-soluble clay and other ions:
+ (in water) → clay + metal (Fe++, Mg++, Ca++, Na+, etc.) + bicarbonate (HCO3-1) + silica (SiO2)
Clay are platy or phyllosilicates (see chapter 3) similar to micas, and are the main components of very fine-grained . The substances may later into rocks like and , as well as amorphous silica or nodules.
is a reaction that dissolves in and leaves the ions in , usually in water. Some and , like salt and , are more prone to this reaction; however, all can be . Non-acidic water, having a neutral pH of 7, will any , although it may happen very slowly. Water with higher levels of acid, naturally or man-made, dissolves rocks at a higher rate. Liquid water is normally slightly acidic due to the presence of and free H+ ions. Natural rainwater can be highly acidic, with pH levels as low as 2. can be enhanced by a biological agent, such as when organisms like lichen and bacteria release organic acids onto the rocks they are attached to. Regions with high humidity (airborne moisture) and experience more due to greater contact time between rocks and water.
The shows rates are associated to rankings in the (see chapter 4). at the top of the Bowen series crystallize under high temperatures and pressures, and chemically at a faster rate than ranked at the bottom. , a that crystallizes at 700°C, is very resistant to . High -point , such as and (1,250°C), relatively rapidly and more completely. and are rarely found as end products of because they tend to break down into elemental ions.
is also noteworthy for the special geological features it creates. In places with abundant , can produce a topography characterized by sinkholes or caves (see chapter 10).
Timpanogos Cave National Monument in Northern Utah is a well-known feature. The figure shows a cave created from followed by — with seeped into the cavern, where evaporation caused the to out.
, the chemical reaction that causes rust in iron, occurs geologically when iron atoms in a with oxygen. Any containing iron can be oxidized. The resultant iron may permeate a rock if it is rich in iron . may also form a coating that covers rocks and grains of , or lines rock cavities and . If the are more susceptible to than the original , they may create void spaces inside the rock mass or hollows on exposed surfaces.
Three commonly found are produced by iron- reactions: red or grey hematite, brown goethite (pronounced “GUR-tite”), and yellow limonite. These iron coat and bind grains together into sedimentary rocks in a process called , and often give these rocks a dominant color. They color the rock layers of the Colorado Plateau, as well as Zion, Arches, and Grand Canyon National Parks. These can permeate a rock that is rich in iron-bearing or can be a coating that forms in cavities or . When the replacing existing in are resistant to , iron concretions may occur in the rock. When is replaced by weaker , this process commonly results in void spaces and weakness throughout the rock mass and often leaves hollows on exposed rock surfaces.
is a mechanical process, usually driven by water, gravity, (see chapter 10), wind, or ice (see chapter 14) that removes from the place of . Liquid water is the main agent of .
resistance is important in the creation of distinctive geological features. This is well demonstrated in the cliffs of the Grand Canyon. The cliffs are made of rock left standing after less resistant materials have weathered and eroded away. Rocks with different levels resistant also create the unique-looking features called hoodoos in Bryce Canyon National Park and Goblin Valley State Park in Utah.
is a combination of air, water, , and organic matter that forms at the transition between and . is made when breaks down and turns it into . If does not remove the significantly, organisms can access the content of the . These organisms turn , water, and atmospheric gases into organic substances that contribute to the .
is an important for organic components necessary for plants, animals, and microorganisms to live. The organic component of , called , is a rich source of bioavailable nitrogen. Nitrogen is the most common in the , but it exists in a form most life forms are unable to use. Special bacteria found only in provide most nitrogen compounds that are usable, bioavailable, by life forms.
These nitrogen-fixing bacteria absorb nitrogen from the and convert it into nitrogen compounds. These compounds are absorbed by plants and used to make DNA, amino acids, and enzymes. Animals obtain bioavailable nitrogen by eating plants, and this is the source of most of the nitrogen used by life. That nitrogen is an essential component of proteins and DNA. range from poor to rich, depending on the amount of they contain. productivity is determined by water and nutrient content. Freshly created , called andisols, and clay-rich that hold nutrients and water are examples of productive .
The nature of the , meaning its characteristics, is determined primarily by five components: 1) the mineralogy of the parent material; 2) topography, 3) , 4) climate, and 5) the organisms that inhabit the . For example, tends to erode more rapidly on steep slopes so layers in these areas may be thinner than in flood plains, where it tends to accumulate. The quantity and chemistry of organic matter of affects how much and what varieties of life it can sustain. and , two major agents, are dependent on climate. Fungi and bacteria contribute organic matter and the ability of to sustain life, interacting with plant roots to exchange nitrogen and other nutrients.
In well-formed , there is a discernable arrangement of distinct layers called . These soil horizons can be seen in road cuts that expose the layers at the edge of the cut. Soil horizons make up the . Each reflects climate, topography, and other soil-development factors, as well as its organic material and . The horizons are assigned names and letters. Differences in naming schemes depend on the area, type or research topic. The figure shows a simplified that uses commonly designated names and letters.
O Horizon: The top horizon is a thin layer of predominantly organic material, such as leaves, twigs, and other plant parts that are actively decaying into .
A Horizon: The next layer, called , consists of mixed with . As soaks down through this layer, it leaches out soluble chemicals. In wet climates with heavy this leaching out produces a separate layer called horizon E, the leaching or eluviation zone.
B Horizon: Also called , this layer consists of mixed with removed from the upper layers. The is where is chemically weathered. The amount of organic material and degree of decrease with depth. The upper zone, called , is a porous mixture of and highly weathered . In the lower zone, saprolite, scant organic material is mixed with largely unaltered .
C Horizon: This is and is a zone of . Here, fragments are physically broken but not chemically altered. This layer contains no organic material.
R Horizon: The final layer consists of unweathered, parent and fragments.
The United States governing body for agriculture, the USDA, uses a taxonomic classification to identify types, called orders. Xoxisols or laterite are nutrient-poor found in tropical regions. While poorly suited for growing crops, xosisols are home to most of the world’s mineable aluminum (). Ardisol forms in dry climates and can develop layers of hardened , called caliche. Andisols originate from deposits. Alfisols contain clay . These two orders are productive for farming due to their high content of nutrients. In general, color can be an important factor in understanding conditions. Black tend to be anoxic, red oxygen-rich, and green oxygen-poor (i.e. reduced). This is true for many sedimentary rocks as well.
Not only is essential to life in nature, but also human civilization via agriculture. Careless or uninformed human activity can seriously damage ’s life-supporting properties. A prime example is the famous Dust Bowl disaster of the 1930s, which affected the midwestern United States. The damage occurred because of large-scale attempts develop prairieland in southern Kansas, Colorado, western Texas, and Oklahoma into farmland. Poor understanding of the region’s geology, ecology, and climate led to farming practices that ruined the .
The prairie and plants are well adapted to a relatively dry climate. With government encouragement, settlers moved in to homestead the region. They plowed vast areas of prairie into long, straight rows and planted grain. The plowing broke up the stable and destroyed the natural grasses and plants, which had long roots that anchored the layers. The grains they planted had shallower root systems and were plowed up every year, which made the prone to . The plowed furrows were aligned in straight rows running downhill, which favored and loss of .
The local climate does not produce sufficient to support non- grain crops, so the farmers drilled wells and over-pumped water from the underground . The grain crops failed due to lack of water, leaving bare that was stripped from the ground by the prairie winds. Particles of midwestern prairie were deposited along the east coast and as far away as Europe. Huge dust storms called black blizzards made life unbearable, and the once-hopeful homesteaders left in droves. The setting for John Steinbeck’s famous novel and John Ford’s film, The Grapes of Wrath, is Oklahoma during this time. The lingering question is whether we have learned the lessons of the dust bowl, to avoid creating it again.
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5.3 Sedimentary Rocks
is classified into two main categories: and chemical. or sedimentary rocks are made from pieces of , , derived primarily by . rocks may also include chemically weathered . rocks are classified by grain shape, , and . Chemical sedimentary rocks are from water with . Chemical rocks are classified mainly by of in the rock.
5.3.1 Lithification and Diagenesis
turns loose grains, created by and transported by , into via three interconnected steps. happens when friction and gravity overcome the forces driving transport, allowing to accumulate. occurs when material continues to accumulate on top of the layer, squeezing the grains together and driving out water. The mechanical is aided by weak attractive forces between the smaller grains of . typically carries cementing agents into the . These , such as , amorphous silica, or , may have a different than the grains. is the process of cementing coating the grains and gluing them together into a fused rock.
is an accompanying process to and is a low- form of rock (see chapter 6). During , are chemically altered by heat and pressure. A classic example is aragonite (CaCO3), a form of calcium that makes up most organic shells. When lithified aragonite undergoes , the aragonite reverts to (CaCO3), which has the same chemical formula but a different crystalline structure. In containing and magnesium (Mg), may the two into dolomite (CaMg(CO3)2). may also reduce the space, or open volume, between grains. The processes of , , and ultimately occur within the realm of , which includes the processes that turn organic material into .
5.3.2 Detrital Sedimentary Rocks (Clastic)
or sedimentary rocks consist of preexisting pieces that comes from weathered bedrock. Most of this is mechanically weathered sediment, although some clasts may be pieces of chemical rocks. This creates some overlap between the two categories, since sedimentary rocks may include chemical . or rocks are classified and named based on their .
rock is classified according to , which is from large to small on the Wentworth scale (see figure 5.26). is the average diameter of fragments in or rock. Grain sizes are delineated using a log base 2 scale. For example, the grain sizes in the pebble class are 2.52, 1.26, 0.63, 0.32, 0.16, and 0.08 inches, which correlate respectively to very coarse, coarse, medium, fine, and very fine granules. Large fragments, or clasts, include all grain sizes larger than 2 mm (5/64 in). These include, boulders, cobbles, granules, and gravel. Sand has a between 2 mm and 0.0625 mm, about the lower limit of the naked eye’s resolution. grains smaller than sand are called silt. Silt is unique; the grains can be felt with a finger or as grit between your teeth, but are too small to see with the naked eye.
Sorting and Rounding
describes the range of grain sizes within or . Geologists use the term “well sorted” to describe a narrow range of grain sizes, and “poorly sorted” for a wide range of grain sizes (see figure 5.27). It is important to note that engineers use similar terms with opposite definitions; well consists of a variety of grain sizes, and poorly has roughly the same grain sizes.
When reading the story told by rocks, geologists use to interpret or transport processes, as well as energy. For example, wind-blown sands are typically extremely well sorted, while deposits are typically poorly sorted. These characteristics help identify the type of process that occurred. Coarse-grained and poorly sorted rocks are usually found nearer to the source of , while fine are carried farther away. In a rapidly flowing mountain you would expect to see boulders and pebbles. In a lake fed by the , there should be sand and silt deposits. If you also find large boulders in the lake, this may indicate the involvement of another transport process, such as caused by ice- or root-wedging.
is created when angular corners of rock fragments are removed from a piece of due to abrasion during transport. Well-rounded grains are defined as being free of all sharp edges. Very angular retains the sharp corners. Most clast fragments start with some sharp edges due to the ’s crystalline structure, and those points are worn down during transport. More rounded grains imply a longer time or transport distance, or more energetic erosional process. is also a factor in .
Composition and Provenance
describes the components found in or and may be influenced by local geology, like and hydrology. Other than clay, most components are easily determined by visual inspection (see chapter 3). The most commonly found is because of its low chemical reactivity and high , making it resistant to , and its ubiquitous occurrence in . Other commonly found grains include and lithic fragments. Lithic fragments are pieces of fine-grained , and include , clasts, or pieces of .
of produces Hawaii’s famous black () and green () sand beaches, which are rare elsewhere on Earth. This is because the local rock is almost entirely of and provides an abundant source of dark colored clasts loaded with mafic minerals. According to the Goldich Dissolution Series, clasts high in are more easily destroyed compared to clasts of like .
Geologists use to discern the original source of or . is determined by analyzing and types of present, as well as textural features like and . is important for describing history, visualizing paleogeographic , unraveling an area’s geologic history, or reconstructing past .
In , sometimes called (SiO2), may be determined using a rare, durable clast called (ZrSiO4). , or zirconium , contains traces of uranium, which can be used for age-dating the source that contributed to the lithified rock (see chapter 7).
Classification of Clastic Rocks
rocks are classified according to the of their . Coarse-grained rocks contain clasts with a predominant larger than sand. Typically, smaller grains, collectively called or matrix, fill in much of the volume between the larger clasts, and hold the clasts together. are rocks containing coarse rounded clasts, and breccias contain angular clasts (see figure 5.31). Both and breccias are usually poorly sorted.
Medium-grained rocks mainly of sand are called , or sometimes if well sorted. grains in can having a wide variety of compositions, roundness, and . Some names indicate the rock’s . contains predominantly grains. is with significant amounts of , usually greater than 25%. that contains , which weathers more quickly than , is useful for analyzing the local geologic history. Greywacke is a term with conflicting definitions. may refer to with a muddy matrix, or with many lithic fragments (small rock pieces).
Fine-grained rocks include , , , and . is a general term for rocks made of grains smaller than sand (less than 2 mm). Rocks that are , meaning they separate into thin sheets, are called . Rocks exclusively of silt or clay , are called or , respectively. These last two rock types are rarer than or .
Rock types found as a mixture between the main classifications, may be named using the less-common component as a descriptor. For example, a rock containing some silt but mostly rounded sand and gravel is called silty . Sand-rich rock containing minor amounts of clay is called clayey .
5.3.3 Chemical, Biochemical, and Organic
rocks are formed by processes that do not directly involve and . may contribute the materials in water that ultimately form these rocks. and organic are in the sense that they are made from pieces of organic material that is deposited, buried, and lithified; however, they are usually classified as being chemically produced.
Inorganic rocks are made of from ions in , and created without the aid of living organisms. Inorganic rocks form in environments where concentration, gasses, temperatures, or pressures are changing, which causes to crystallize.
sedimentary rocks are formed from shells and bodies of underwater organisms. The living organisms extract chemical components from the water and use them to build shells and other body parts. The components include aragonite, a similar to and commonly replaced by , and silica.
Organic sedimentary rocks come from organic material that has been deposited and lithified, usually underwater. The source materials are plant and animal remains that are transformed through burial and heat, and end up as , , and methane ().
Inorganic rocks are formed when out of an aqueous , usually due to water evaporation. The form various salts known as . For example, the Bonneville Salt Flats in Utah flood with winter rains and dry out every summer, leaving behind salts such as and . The order of deposit is opposite to their solubility order, i.e. as water evaporates and increases the concentration in , less soluble out sooner than the highly soluble . The order and percentages are depicted in the table, bearing in mind the process in nature may vary from laboratory derived values.
|Mineral sequence||Percent seawater remaining after evaporation|
|Various potassium and magnesium salts||5%|
Table 5.1: Deposition order and saturation percentages.
Calcium – water precipitates porous masses of called . can form near degassing water and in saline lakes. Waterfalls downstream of springs often as the turbulent water enhances degassing of carbon dioxide, which makes less soluble and causes it to . Saline lakes concentrate calcium from a combination of wave action causing degassing, springs in the lakebed, and evaporation. In salty Mono Lake in California, towers were exposed after water was diverted and lowered the lake levels.
Cave deposits like stalactites and stalagmites are another form of chemical of , in a form called . slowly precipitates from water to form the , which often shows . This process is similar to the growth on faucets in your home sink or shower that comes from hard ( rich) water. also forms at hot springs such as Mammoth Hot Spring in Yellowstone National Park.
deposits commonly formed early in Earth’s history, but this type of rock is no longer being created. Oxygenation of the and oceans caused free iron ions, which are water-soluble, to become oxidized and out of . The iron was deposited, usually in alternating with layers of .
, another commonly found rock, is usually produced from silica (SiO2) from . Silica is highly insoluble on the surface of Earth, which is why is so resistant to . Water deep underground is subjected to higher pressures and temperatures, which helps silica into an aqueous . As the rises toward or emerges at the surface the silica precipitates out, often as a cementing agent or into nodules. For example, the bases of the geysers in Yellowstone National Park are surrounded by silica deposits called geyserite or sinter. The silica is in water that is thermally heated by a relatively deep source. can also form biochemically and is discussed in the subsection. has many synonyms, some of which may have gem value such as jasper, flint, onyx, and agate, due to subtle differences in colors, striping, etc., but is the more general term used by geologists for the entire group.
are among the few forms created by an inorganic chemical process, similar to what happens in . When water is oversaturated with , the precipitates out around a nucleus, a sand grain or shell fragment, and forms little spheres called (see figure 5.41). As evaporation continues, the continue building concentric layers of as they roll around in gentle currents.
sedimentary rocks are not that different from rocks; they are also formed from ions in . However, sedimentary rocks rely on biological processes to extract the materials out of the water. Most macroscopic organisms use , primarily aragonite (calcium ), to build hard parts such as shells. When organisms die the hard parts settle as , which become buried, compacted and cemented into rock.
This extraction and secretion is the main process for forming , the most commonly occurring, non- . is mostly made of (CaCO3) and sometimes includes dolomite (CaMgCO3), a close relative. Solid reacts with hydrochloric acid by effervescing or fizzing. Dolomite only reacts to hydrochloric acid when ground into a powder, which can be done by scratching the rock surface (see chapter 3).
occurs in many forms, most of which originate from biological processes. Entire coral and their ecosystems can be preserved in exquisite detail in rock (see figure 5.42). contains many visible . A type of called originates from beach sands made predominantly of shells that were then lithified. is of loosely-cemented shells and shell fragments. You can find beaches like this in modern tropical environments, such as the Bahamas. contains high concentrations of shells from a microorganism called a coccolithophore. , also known as microscopic mud, is a very fine-grained containing microfossils that can only be seen using a microscope.
Biogenetic forms on the deep , created from made of microscopic organic shells. This , called ooze, may be calcareous (calcium based) or siliceous (silica-based) depending on the type of shells deposited. For example, the shells of radiolarians (zooplankton) and diatoms (phytoplankton) are made of silica, so they produce siliceous ooze.
Under the right conditions, intact pieces of organic material or material derived from organic sources, is preserved in the geologic record. Although not derived from , this lithified organic material is associated with sedimentary and created by similar processes—burial, , and . C Deposits of these fuels develop in areas where organic material collects in large quantities. Lush swamplands can create conditions conducive to . Shallow-water, organic material-rich can become highly productive and deposits. See chapter 16 for a more in-depth look at these -derived energy sources.
Classification of Chemical Sedimentary Rocks
In contrast to , chemical, , and organic sedimentary rocks are classified based on . Most of these are monomineralic, of a single , so the rock name is usually associated with the identifying . rocks consisting of are called rock salt. Rocks made of () is an exception, having elaborate subclassifications and even two competing classification methods: Folk Classification and Dunham Classification. The Folk Classification deals with rock grains and usually requires a specialized, petrographic microscope. The Dunham Classification is based on rock , which is visible to the naked eye or using a hand lens and is easier for field applications. Most geologists use the Dunham system.
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5.4 Sedimentary Structures
Sedimentary structures are visible textures or arrangements of within a rock. Geologists use these structures to interpret the processes that made the rock and the environment in which it formed. They use to usually compare sedimentary structures formed in modern environments to lithified counterparts in ancient rocks. Below is a summary discussion of common sedimentary structures that are useful for interpretations in the rock record.
5.4.1 Bedding Planes
The most basic sedimentary structure is planes, the planes that separate the layers or in sedimentary and some rocks. Visible in exposed outcroppings, each plane indicates a change in conditions. This change may be subtle. For example, if a section of underlying firms up, this may be enough to create a form a layer that is dissimilar from the overlying . Each layer is called a , or stratum, the most basic unit of , the study of sedimentary layering.
As would be expected, thickness can indicate quantity and timing. Technically, a is a plane thicker than 1 cm (0.4 in) and the smallest mappable unit. A layer thinner than 1 cm (0.4 in) is called a . Varves are planes created when and are deposited in repetitive cycles, typically daily or seasonally. Varves are valuable geologic records of climatic histories, especially those found in lakes and deposits.
5.4.2 Graded Bedding
refers to a sequence of increasingly coarse- or fine-grained layers. often develops when occurs in an environment of decreasing energy. A is observed in rock called . are formed by gravity flows, which are underwater flows of . These subsea density flows begin when is stirred up by an energetic process and becomes a dense slurry of mixed grains. The flow courses downward through submarine channels and canyons due to gravity acting on the density difference between the denser slurry and less dense surrounding seawater. As the flow reaches deeper ocean basins it slows down, loses energy, and deposits in a of coarse grains first, followed by increasingly finer grains (see figure 5.49).
5.4.3 Flow Regime and Bedforms
In fluid systems, such as moving water or wind, sand is the most easily transported and deposited grain. Smaller particles like silt and clay are less movable by fluid systems because the tiny grains are chemically attracted to each other and stick to the underlying . Under higher flow rates, the fine silt and clay tends to stay in place and the larger sand grains get picked up and moved.
Bedforms are sedimentary structures created by fluid systems working on sandy . , flow velocity, and or pattern interact to produce bedforms having unique, identifiable physical characteristics. Flow regimes are divided into upper and lower regimes, which are further divided into uppermost, upper, lower, and lowermost parts. The table below shows bedforms and their associated flow regimes. For example, the is created in the upper part of the lower .
|Flow regime (part)||Bedform||Description|
|Lower (lowest)||Plane bed||Lower plane bed, flat laminations|
|Lower (lower)||Ripples||Small (with respect to flow) inclined layers dipping downflow|
|Lower (upper)||Dunes||Larger inclined cross beds, ±ripples, dipping downflow|
|Upper (lower)||Plane bed||Flat layers, can include lined-up grains (parting lineations)|
|Upper (upper)||Antidunes||Hard to preserve reverse dunes dipping shallowly upflow|
|Upper (uppermost)||Chutes/pools (rare)||Erosional, not really a bedform; rarely found preserved|
Table 5.2: Bedforms and their associated flow regimes.
Plane created in the lower are like planes, on a smaller scale. The flat, parallel layers form as sandy piles and move on top of layers below. Even non-flowing fluid systems, such as lakes, can produce plane . Plane in the upper are created by fast-flowing fluids. They may look identical to lower-flow-regime ; however, they typically show , slight alignments of grains in rows and swaths, caused by high transport rates that only occur in upper flow regimes.
are known by several names: marks, cross , or cross . The ridges or undulations in the are created as grains pile up on top of the . With the exception of , the scale of these is typically measured in centimeters. Occasionally, large flows like lake outbursts, can produce as tall as 20 m (66 ft).
First scientifically described by Hertha Ayrton, shapes are determined by flow type and can be straight-crested, sinuous, or complex. Asymmetrical form in a unidirectional flow. Symmetrical are the result of an oscillating back-and-forth flow typical of intertidal swash zones. Climbing are created from high sedimentation rates and appear as overlapping layers of shapes (see figure 5.54).
are very large and prominent versions of , and typical examples of large . happens when or pile atop one another, interrupting, and/or cutting into the underlying layers. Desert sand are probably the first image conjured up by this category of .
British geologist Agnold (1941) considered only Barchan and linear Seif as the only true forms. Other workers have recognized transverse and as well as parabolic and anchored by plants that are common in coastal areas as other types of .
are the most common sedimentary structure found within channelized flows of air or water. The biggest difference between and air-formed (desert) is the depth of fluid . Since the ’s depth is immense when compared to a channel, desert are much taller than those found in . Some famous air-formed landscapes include the Sahara Desert, Death Valley, and the Gobi Desert.
As airflow moves along, the grains accumulate on the ’s windward surface (facing the wind). The angle of the windward side is typically shallower than the leeward (downwind) side, which has grains falling down over it. This difference in slopes can be seen in a cross-section and indicates the direction of the flow in the past. There are typically two styles of : the more common cross with curved windward surfaces, and rarer planar cross with flat windward surfaces.
In tidal locations with strong in-and-out flows, can develop in opposite directions. This produces a feature called herringbone .
Another variant occurs when very strong, hurricane-strength, winds agitate parts of the usually undisturbed seafloor. These are called and have a 3D architecture of hills and valleys, with inclined and declined layering that matches the shapes.
are so named because they share similar characteristics with , but are formed by a different, opposing process. While form in lower flow regimes, come from fast-flowing upper flow regimes. In certain conditions of high flow rates, accumulates upstream of a subtle instead of traveling downstream (see figure 5.59). form in phase with the flow; in they are marked by rapids in the current. are rarely preserved in the rock record because the high flow rates needed to produce the also accelerate .
is the result of organisms burrowing through soft , which disrupts the layers. These tunnels are backfilled and eventually preserved when the becomes rock. happens most commonly in shallow, environments, and can be used to indicate water depth.
occur in clay-rich that is submerged underwater and later dries out. Water fills voids in the clay’s crystalline structure, causing the grains to swell. When this waterlogged begins to dry out, the clay grains shrink. The layer forms deep polygonal cracks with tapered openings toward the surface, which can be seen in profile. The cracks fill with new and become visible veins running through the lithified rock. These dried-out clay are a major source of , small fragments of mud or , which commonly become in and . What makes this sedimentary structure so important to geologists, is they only form in certain —such as that form underwater and are later exposed to air. Syneresis cracks are similar in appearance to but much rarer; they are formed when subaqueous (underwater) clay shrinks.
5.4.6 Sole Marks
are small features typically found in deposits. They form at the base of a , the sole, and on top of the underlying . They can indicate several things about the conditions, such as flow direction or up-direction (see Geopetal Structures section). or are grooves carved out by the forces of fluid flow and loads. The upstream part of the flow creates steep grooves and downstream the grooves are shallower. The grooves subsequently become filled by overlying , creating a of the original hollow.
Formed similarly to but with a more regular and aligned shape, are produced by larger clasts or debris carried along in the water that scrape across the layer. come from objects like sticks carried in the fluid downstream or embossed into the layer, leaving a depression that later fills with new .
Load , an example of soft- , are small indentations made by an overlying layer of coarse grains or clasts intruding into a softer, finer-grained layer.
5.4.7 Raindrop Impressions
Like their name implies, are small pits or bumps found in soft . While they are generally believed to be created by rainfall, they may be caused by other agents such as escaping gas bubbles.
is a of large and usually flat clasts—cobbles, gravels, , etc.—that are aligned in the direction of fluid flow. The clasts may be stacked in rows, with their edges dipping down and flat surfaces aligned to face the flow (see figure 5.66). Or their flat surfaces may be parallel to the layer and long axes aligned with flow. Imbrications are useful for analyzing paleocurrents, or currents found in the geologic past, especially in deposits.
5.4.9 Geopetal Structures
structures, also called up-direction indicators, are used to identify which way was up when the layers were originally formed. This is especially important in places where the rock layers have been deformed, tilted, or overturned. Well preserved , , and can be used to determine up direction. Other useful structures include:
Vugs: Small voids in the rock that usually become filled during . If the void is partially filled or filled in stages, it serves as a permanent record of a level bubble, frozen in time.
- – In places where or pile on top of one another, where one interrupts and/or cuts another below, this shows a cross-cutting relationship that indicates up direction.
- , : Sometimes the are preserved well enough to differentiate between the crests (top) and troughs (bottom).
- : Body in life position, meaning the body parts are not scattered or broken, and like footprints (see figure 5.68) can provide an up direction. Intact fossilized coral are excellent up indicators because of their large size and easily distinguishable top and bottom. , such as ammonites, can be used to age date and determine up direction based on relative rock ages.
- Vesicles – flows eliminate gas upwards. An increase of vesicles toward the top of the flow indicates up.
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5.5 Depositional Environments
The ultimate goal of many studies is to understand the original . Knowing where and how a particular was formed can help geologists paint a picture of past environments—such as a mountain , gentle , dry desert, or deep-sea . The study of is a complex endeavor; the table shows a simplified version of what to look for in the rock record.
|Location||Sediment||Common rock types||Typical fossils||Sedimentary structures|
|Abyssal||Very fine muds and oozes, diatomaceous Earth||Chert||Diatoms||Few|
|Submarine fan||Graded Bouma sequences, alternating sand/mud||Clastic rocks||Rare||Channels, fan shape|
|Continental slope||Mud, possible sand, countourites||Shale, siltstone, limestone||Rare||Swaths|
|Lower shoreface||Laminated sand||Sandstone||Bioturbation||Hummocky cross beds|
|Upper shoreface||Planar sand||Sandstone||Bioturbation||Plane beds, cross beds|
|Littoral (beach)||Very well sorted sand||Sandstone||Bioturbation||Few|
|Tidal flat||Mud and sand with channels||Shale, mudstone, siltstone||Bioturbation||Mudcracks, symmetric ripples|
|Reef||Lime mud with coral||Limestone||Many, commonly coral||Few|
|Lagoon||Laminated mud||Shale||Many, bioturbation||Laminations|
|Delta||Channelized sand with mud, ±swamp||Clastic rocks||Many to few||Cross beds|
|Fluvial (river)||Sand and mud, can have larger sediments||Sandstone, conglomerate||Bone beds (rare)||Cross beds, channels, asymmetric ripples|
|Alluvial||Mud to boulders, poorly sorted||Clastic rocks||Rare||Channels, mud cracks|
|Lacustrine (lake)||Fine-grained laminations||Shale||Invertebrates, rare (deep) bone beds||Laminations|
|Paludal (swamp)||Plant material||Coal||Plant debris||Rare|
|Aeolian (dunes)||Very well sorted sand and silt||Sandstone||Rare||Cross beds (large)|
|Glacial||Mud to boulders, poorly sorted||Conglomerate (tillite)||Striations, drop stones|
Table 5.3: Rock record and depositional environments.
are completely and constantly submerged in seawater. Their depositional characteristics are largely dependent on the depth of water with two notable exceptions, and .
sedimentary rocks form on the . The plain encompasses relatively flat with some minor topographical features, called hills. These small seafloor mounts range 100 m to 20 km in diameter, and are possibly created by . Most plains do not experience significant fluid movement, so formed there are very fine grained.
There are three categories of . Calcareous oozes consist of -rich plankton shells that have fallen to the . An example of this type of is . Siliceous oozes are also made of plankton debris, but these organisms build their shells using silica or hydrated silica. In some cases such as with diatomaceous earth, is deposited below the , a depth where solubility increases. Any -based shells are , leaving only silica-based shells. is another common rock formed from these types of . These two types of are also classified as in origin (see biochemical section).
The third type is pelagic clay. Very fine-grained clay particles, typically brown or red, descend through the water column very slowly. Pelagic clay occurs in areas of remote open ocean, where there is little plankton accumulation.
Two notable exceptions to the fine-grained nature of are and deposits. occur at the base of large systems. They are initiated during times of low sea level, as strong currents carve into the . When sea levels rise, accumulates on the shelf typically forming large, fan-shaped floodplains called deltas. Periodically, the is disturbed creating dense slurries that flush down the underwater canyons in large gravity-induced events called . The is formed by a network of that deposit their loads as the slope decreases, much like what happens above-water at fans and deltas. This sudden flushing transports coarser to the where they are otherwise uncommon. are also the typical origin of sequences. (see chapter 5).
deposits are not common in the rock record. The most notable type of deposits are contourites. Contourites form on the slope between the and deep . Deep-water ocean currents deposit into smooth drifts of various architectures, sometimes interwoven with .
The lower lies below the normal depth of wave agitation, so the is not subject to daily winnowing and . These layers are typically finely laminated, and may contain hummocky cross-stratification. Lower are affected by larger waves, such those as generated by hurricanes and other large storms.
The upper contains within the zone of normal wave action, but still submerged below the beach environment. These usually consist of very well sorted, fine sand. The main sedimentary structure is planar consistent with the lower part of the upper , but it can also contain created by .
5.5.2 Transitional Coastline Environments
Transitional environments, more often called or environments, are zones of complex interactions caused by ocean water hitting land. The preservation potential is very high in these environments because often occurs on the and underwater. environments are an important source of hydrocarbon deposits (, ).
The study of is called . examines depositional changes and 3D architectures associated with rising and falling sea levels, which is the main force at work in deposits. These sea-level fluctuations come from the daily tides, as well as climate changes and . A steady rise in sea level relative to the is called . is the opposite, a relative drop in sea level. Some common components of environments are zones, , , , and deltas. For a more in-depth look at these environments, see chapter 12.
The zone, better known as the beach, consists of highly weathered, homogeneous, well-sorted sand grains made mostly of . There are black sand and other types of sand beaches, but they tend to be unique exceptions rather than the rule. Because beach sands, past or present, are so highly evolved, the amount grain can be discerned using the , tourmaline, and rutile. This tool is called the ZTR (, tourmaline, rutile) index. The ZTR index is higher in more weathered beaches, because these relatively rare and -resistant become in older beaches. In some beaches, the ZTR index is so high the sand can be harvested as an economically viable source of these . The beach environment has no sedimentary structures, due to the constant bombardment of wave energy delivered by surf action. Beach is moved around via multiple processes. Some beaches with high supplies develop nearby.
, or , are sedimentary environments that are regularly flooded and drained by ocean tides. have large areas of fine-grained but may also contain coarser sands. deposits typically contain gradational and may include multi-directional marks. are also commonly seen due to the being regularly exposed to air during low tides; the combination of and marks is distinctive to .
Tidal water carries in , sometimes focusing the flow through a narrow opening called a tidal inlet. Tidal channels, creek channels influenced by tides, can also tidally-induced flow. Areas of higher flow like inlets and tidal channels feature coarser grain sizes and larger , which in some cases can develop into .
, which most people would immediately associate with tropical coral found in the oceans, are not only made by living things. Natural buildups of sand or rock can also create , similar to . Geologically speaking, a is any topographically-elevated feature on the , located oceanward of and separate from the beach. The term can also be applied to (atop the ) features. Capitol Reef National Park in Utah contains a topographic barrier, a , called the Waterpocket Fold.
Most , now and in the geologic past, originate from the biological processes of living organisms. The growth habits of coral provide geologists important information about the past. The hard structures in coral are built by soft-bodied organisms, which continually add new material and enlarge the over time. Under certain conditions, when the land beneath a is subsiding, the coral may grow around and through existing , holding the in place, and thus preserving the record of environmental and geological condition around it.
found in coral is typically fine-grained, mostly , and tends to deposit between the intact coral skeletons. Water with high levels of silt or clay particles can inhibit the growth because coral organisms require sunlight to thrive; they host symbiotic algae called zooxanthellae that provide the coral with nourishment via photosynthesis. Inorganic structures have much more variable compositions. have a big impact on in environments since they are natural storm breaks, wave and storm buffers, which allows fine grains to settle and accumulate.
are found around shorelines and islands; coral are particularly common in tropical locations. are also found around features known as , which is the base of an ocean island left standing underwater after the upper part is eroded away by waves. Examples include the Emperor Seamounts, formed millions of years ago over the Hawaiian . live and grow along the upper edge of these flat-topped . If the builds up above sea level and completely encircles the top of the , it is called a coral-ringed atoll. If the is submerged, due to , , or sea level rise, the – structure is called a guyot.
are small bodies of seawater located inland from the or isolated by another geographic feature, such as a or . Because they are protected from the action of tides, currents, and waves, environments typically have very fine grained . , as well as , are ecosystems with high biological productivity. Rocks from these environments often includes marks or deposits. Around where evaporation exceeds water inflow, salt flats, also known as sabkhas, and sand fields may develop at or above the high line.
Deltas form where enter lakes or oceans and are of three basic shapes: -dominated deltas, wave-dominated deltas, and -dominated deltas. The name comes from the Greek letter Δ (, uppercase), which resembles the triangular shape of the Nile . The velocity of water flow is dependent on riverbed slope or , which becomes shallower as the descends from the mountains. At the point where a enters an ocean or lake, its slope angle drops to zero degrees (0°). The flow velocity quickly drops as well, and is deposited, from coarse clasts, to fine sand, and mud to form the . As one part of the becomes overwhelmed by , the slow-moving flow gets diverted back and forth, over and over, and forms a spread out network of smaller distributary channels.
Deltas are organized by the dominant process that controls their shape: -dominated, wave-dominated, or -dominated. Wave-dominated deltas generally have smooth coastlines and beach-ridges on the land that represent previous shorelines. The Nile River delta is a wave-dominated type (see figure 5.84).
The Mississippi River delta is a -dominated . shaped by levees along the and its distributaries that confine the flow forming a shape called a birdfoot . Other times the tides or the waves can be a bigger factor, and can reshape the in various ways.
A -dominated is dominated by tidal currents. During flood stages when have lots of water available, it develops distributaries that are separated by sand bars and sand ridges. The tidal of the Ganges River is the largest in the world.
are diverse. Water is a major factor in these environments, in liquid or frozen states, or even when it is lacking (arid conditions).
() systems are formed by water flowing in channels over the land. They generally come in two main varieties: or . In , the flow carries grains via a single channel that wanders back and forth across the . The away from the channel is mostly fine grained material that only gets deposited during floods.
systems generally contain coarser grains, and form a complicated series of intertwined channels that flow around gravel and sand bars (see chapter 11).
A distinctive characteristic of systems is the intermittent flow of water. deposits are common in arid places with little development. Lithified are the primary -filling rock found throughout the region of the western United States. The most distinctive sedimentary deposit is the fan, a large cone of formed by flowing out of dry mountain valleys into a wider and more open dry area. are typically poorly sorted and coarse grained, and often found near lakes or deposits (see chapter 13).
Lake systems and deposits, called , form via processes somewhat similar to deposits, but on a much smaller scale. deposits are found in lakes in a wide variety of locations. Lake Baikal in southeast Siberia (Russia) is in a . Crater Lake (Oregon) sits in a . The Great Lakes (northern United States) came from glacially carved and deposited . Ancient Lake Bonneville (Utah) formed in a pluvial setting that during a climate that was relatively wetter and cooler than that of modern Utah. lakes, named for their curved shape, originated in floodplains. tends to be very fine grained and thinly laminated, with only minor contributions from wind-blown, current, and tidal deposits. When lakes dry out or evaporation outpaces , form. deposits resemble those of normal lake deposits but contain more . Certain can have -type deposits as well.
systems include bogs, marshes, swamps, or other wetlands, and usually contain lots of organic matter. systems typically develop in coastal environments, but are common occur in humid, low-lying, low-, warm zones with large volumes of flowing water. A characteristic deposit is a peat bog, a deposit rich in organic matter that can be converted into when lithified. environments may be associated with tidal, deltaic, , and/or .
, sometimes spelled or œolian, are deposits of windblown . Since wind has a much lower carrying capacity than water, deposits typically consists of clast sizes from fine dust to sand. Fine silt and clay can cross very long distances, even entire oceans suspended in air.
With sufficient influx, systems can potentially form large in dry or wet conditions. The figure shows features and various types. British geologist Ralph A. Bagnold (1896-1990) considered only Barchan and linear Seif as the only true forms. Other scientists recognize transverse, star, parabolic, and types. Parabolic and grow from sand anchored by plants and are common in coastal areas.
Compacted layers of wind-blown is known as . commonly starts as finely ground up rock flour created by . Such deposits cover thousands of square miles in the Midwestern United States. may also form in desert regions (see chapter 13). Silt for the Plateau in China came from the Gobi Desert in China and Mongolia.
sedimentation is very diverse, and generally consists of the most poorly-sorted deposits found in nature. The main clast type is called , which literally means two sizes, referring to the unsorted mix of large and small rock fragments found in deposits. Many , glacially derived , include very finely-pulverized rock flour along with giant boulders. The surfaces of larger clasts typically have striations from the rubbing, scraping, and polishing of surfaces by abrasion during the movement of ice. systems are so large and produce so much , they frequently create multiple, individualized , such as , deltaic, , pluvial, , and/or (see chapter 14).
In addition to and process, geologists also classify by its depositional characteristics, collectively called or lithofacies. Sedimentary consist of physical, chemical, and/or biological properties, including relative changes in these properties in adjacent of the same layer or geological age. Geologists analyze to interpret the original environment, as well as disruptive geological events that may have occurred after the rock layers were established.
It boggles the imagination to think of all the sedimentary environments working next to each other, at the same time, in any particular region on Earth. The resulting develop characteristics reflecting contemporaneous conditions at the time of , which later may become preserved into the rock record. For example in the Grand Canyon, rock of the same geologic age includes many different : beach sand, silt, mud, and farther . In other words, each sedimentary or presents recognizable characteristics that reflect specific, and different, that were present at the same time.
may also reflect depositional changes in the same location over time. During of rising sea level, called , the moves inland as seawater covers what was originally dry land and creates new . When these turn into , the vertical sequence reveals beach lithofacies buried by lithofacies.
Biological are remnants (, diatomaceous earth) or evidence () of living organisms. , fossilized life forms specific to a particular environment and/or geologic time , are an example of biological . The horizontal assemblage and vertical distribution of are particularly useful for studying species evolution because , , burial, and processes happen over a considerable geologic time range.
assemblages that show evolutionary changes greatly enhance our interpretation of Earth’s ancient history by illustrating the between sequence and geologic time scale. During the Middle (see chapter 7), regions around the Grand Canyon experienced in a southeasterly direction (relative to current maps). This shift of the is reflected in the Tapeats Sandstone beach facies, Bright Angle Shale near-offshore mud , and Muav Limestone far-offshore facies. organisms had plenty of time to evolve and adapt to their slowly changing environment; these changes are reflected in the biological , which show older life forms in the western regions of the canyon and younger life forms in the east.
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Sedimentary rocks are grouped into two main categories: () and chemical. () rocks are made of clasts or that lithifies into solid material. is produced by the mechanical or of and transported away from the source via . that is deposited, buried, compacted, and sometimes cemented becomes rock. rocks are classified by ; for example is made of sand-sized particles. rocks comes from out an aqueous and is classified according to . The rock is made of calcium . Sedimentary structures have textures and shapes that give insight on depositional histories. depend mainly on fluid transport systems and encompass a wide variety of underwater and above ground conditions. Geologists analyze depositional conditions, sedimentary structures, and rock records to interpret the paleogeographic history of a region.
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Figure 5.1: A model of a water molecule, showing the bonds between the hydrogen and oxygen. Dan Craggs. 2009. Public domain. https://commons.wikimedia.org/wiki/File:H2O_2D_labelled.svg
Figure 5.2: Dew on a spider’s web. Luc Viatour. 2007. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Spider_web_Luc_Viatour.jpg
Figure 5.3: Hydrogen bonding between water molecules. Qwerter. 2011. Public domain. https://commons.wikimedia.org/wiki/File:3D_model_hydrogen_bonds_in_water.svg
Figure 5.4: A sodium (Na) ion in solution. Taxman. 2006. Public domain. https://commons.wikimedia.org/wiki/File:Na%2BH2O.svg
Figure 5.5: The outer layer of this granite is fractured and eroding away, known as exfoliation. Wing-Chi Poon. 2005. CC BY-SA 2.5. https://en.m.wikipedia.org/wiki/File:GeologicalExfoliationOfGraniteRock.jpg
Figure 5.6: The process of frost wedging. Julie Sandeen. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Mechanical_weathering.png
Figure 5.7: The roots of this tree are demonstrating the destructive power of root wedging. Arseny Khakhalin. 2006. CC BY 3.0. https://commons.wikimedia.org/wiki/File:Pine-tree_roots_digging_through_the_asphalt_-_panoramio.jpg
Figure 5.8: Tafoni from Salt Point, California. Dawn Endico. 2005. CC BY-SA 2.0. https://commons.wikimedia.org/wiki/File:Tafoni_03.jpg
Figure 5.9: Each of these three groups of cubes has an equal volume. Kindred Grey. 2022. CC BY 4.0.
Figure 5.10: Generic hydrolysis diagram, where the bonds in mineral in question would represent the left side of the diagram. Unknown author. 2014. CC BY-SA 4.0. https://www.wikiwand.com/en/Hydrolysis#Media/File:Hydrolysis.png
Figure 5.11: In this rock, a pyrite cube has dissolved (as seen with the negative “corner” impression in the rock), leaving behind small specks of gold. Matt Affolter (QFL247). 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:GoldinPyriteDrainage_acide.JPG
Figure 5.12: This mantle xenolith containing olivine (green) is chemically weathering by hydrolysis and oxidation into the pseudo-mineral iddingsite, which is a complex of water, clay, and iron oxides. Matt Affolter. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Iddingsite.JPG
Figure 5.13: Eroded karst topography in Minerve, France. Hugo Soria. 2005. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Karst_minerve.jpg
Figure 5.14: A formation called The Great Heart of Timpanogos in Timpanogos Cave National Monument. Sleeping Bear Dunes National Lakeshore. 2012. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Tica_(7563200350).jpg
Figure 5.17: Grand Canyon from Mather Point. Szumyk. 2004. Public domain. https://commons.wikimedia.org/wiki/File:Grand_Canyon-Mather_point.jpg
Figure 5.18: Sketch and picture of soil. Carlosblh. 2006. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Estructura-suelo.jpg
Figure 5.19: Schematic of the nitrogen cycle. Johann Dréo. 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svg
Figure 5.20: Agricultural terracing, as made by the Inca culture from the Andes, helps reduce erosion and promote soil formation, leading to better farming practices. Unknown author. 2007. Public domain. https://www.wikiwand.com/en/Andean_civilizations#Media/File:Pisac006.jpg
Figure 5.21: A simplified soil profile, showing labeled layers. Wilsonbiggs. 2021. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Soil_Horizons.svg
Figure 5.22: A sample of bauxite. Werner Schellmann. 1965. CC BY-SA 2.5. https://commons.wikimedia.org/wiki/File:Bauxite_with_unweathered_rock_core._C_021.jpg
Figure 5.23: A dust storm approaches Stratford, Texas in 1935. George E. Marsh Album via NOAA. 1935. Public domain. https://commons.wikimedia.org/wiki/File:Dust_Storm_Texas_1935.jpg
Figure 5.24: Geologic unconformity seen at Siccar Point on the east coast of Scotland. dave souza. 2008. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Siccar_Point_red_capstone_closeup.jpg
Figure 5.25: Permineralization in petrified wood. Moondigger. 2005. CC BY-SA 2.5. https://commons.wikimedia.org/wiki/File:Petrified_forest_log_2_md.jpg
Figure 5.26: Size categories of sediments, known as the Wentworth scale. Jeffress Williams, Matthew A. Arsenault, Brian J. Buczkowski, Jane A. Reid, James G. Flocks, Mark A. Kulp, Shea Penland, and Chris J. Jenkins via USGS. 2011. Public domain. https://commons.wikimedia.org/wiki/File:Wentworth_scale.png
Figure 5.27: A well-sorted sediment (left) and a poorly-sorted sediment (right). Woudloper. 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Sorting_in_sediment.svg
Figure 5.28: Degree of rounding in sediments. Woudloper. 2009. Public domain. https://commons.wikimedia.org/wiki/File:Rounding_%26_sphericity_EN.svg
Figure 5.29: A sand grain made of basalt, known as a microlitic volcanic lithic fragment. Matt Affolter (QFL247). 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:LvMS-Lvm.jpg
Figure 5.30: Hawaiian beach composed of green olivine sand from weathering of nearby basaltic rock. Aren Elliott. 2018. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Panorama_of_Papakolea_green_sand_beach_in_Hawaii_2.jpg
Figure 5.31: Megabreccia in Titus Canyon, Death Valley National Park, California. NPS. Unknown date. Public domain. https://commons.wikimedia.org/wiki/File:Titus_Canyon_Narrows.jpg
Figure 5.32: Enlarged image of frosted and rounded windblown sand grains. Wilson44691. 2008. Public domain. https://commons.wikimedia.org/wiki/File:CoralPinkSandDunesSand.JPG
Figure 5.33: The Rochester Shale, New York. Wilson44691. 2015. Public domain. https://en.m.wikipedia.org/wiki/File:Rochester_Shale_Niagara_Gorge.jpg
Figure 5.34: Claystone laminations from Glacial Lake Missoula. Matt Affolter. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:GLMsed.jpg
Figure 5.35: Salt-covered plain known as the Bonneville Salt Flats, Utah. Michael Pätzold. 2008. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Bonneville_salt_flats_pilot_peak.jpg
Figure 5.36: Ooids from Joulter’s Cay, The Bahamas. Wilson44691. 2010. Public domain. https://commons.wikimedia.org/wiki/File:Ooids,_Joulter_Cays,_Bahamas.jpg
Figure 5.37: Limestone tufa towers along the shores of Mono Lake, California. Yukinobu Zengame. 2005. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Limestone_towers_at_Mono_Lake,_California.jpg
Figure 5.38: Travertine terraces of Mammoth Hot Springs, Yellowstone National Park, USA. Frank Schulenburg. 2016. CC BY-SA 4.0. https://en.m.wikipedia.org/wiki/File:Mammoth_Terraces.jpg
Figure 5.39: Alternating bands of iron-rich and silica-rich mud, formed as oxygen combined with dissolved iron. Wilson44691. 2008. Public domain. https://commons.wikimedia.org/wiki/File:MichiganBIF.jpg
Figure 5.40: A type of chert, flint, shown with a lighter weathered crust. Ra’ike. 2014. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Flint_with_weathered_crust.JPG
Figure 5.41: Ooids forming an oolite. Unknown author. 2008. Public domain. https://www.wikiwand.com/en/Oolite#Media/File:OoidSurface01.jpg
Figure 5.42: Fossiliferous limestone (with brachiopods and bryozoans) from the Kope Formation of Ohio. Jim Stuby. 2010. Public domain. https://commons.wikimedia.org/wiki/File:Limestone_etched_section_KopeFm_new.jpg
Figure 5.43: Close-up on coquina. Wilson44691. 2008. Public domain. https://commons.wikimedia.org/wiki/File:CoquinaClose.jpg
Figure 5.44: Anthracite coal, the highest grade of coal. USGS. 2007. Public domain. https://commons.wikimedia.org/wiki/File:Coal_anthracite.jpg
Figure 5.45: Gyprock, a rock made of the mineral gypsum. James St. John. 2016. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Gyprock_(Castile_Formation,_Upper_Permian_Eddy_County,_New_Mexico.jpg
Figure 5.46: Sedimentary rock identification chart. Virginia Sisson. Unknown date. CC BY-NC-SA 4.0. Figure 2.13 from https://uhlibraries.pressbooks.pub/historicalgeologylab/chapter/chapter02-earthmaterials/
Figure 5.47: Horizontal strata. Matt Affolter (QFL247). 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:SEUtahStrat.JPG
Figure 5.48: Students from the University of Wooster examine beds of Ordovician limestone in central Tennessee. Wilson44691. 2007. Public domain. https://commons.wikimedia.org/wiki/File:OrdOutcropTN.JPG
Figure 5.49: Image of the classic Bouma sequence. Mikesclark. 2013. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Turbidite_from_Pigeon_Pt_Fm_at_Pescadero_Beach,_CA.jpg
Figure 5.50: Bedforms from under increasing flow velocities. US Dept. of Transportation Federal Highway Administration. 2013. Public domain. https://commons.wikimedia.org/wiki/File:Bedforms_under_various_flow_regimes.pdf
Figure 5.51: Subtle lines across this sandstone (trending from the lower left to upper right) are parting lineations. Matt Affolter (a.k.a. QFL247). 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:PartingLineation.JPG
Figure 5.52: Modern current ripple in sand from the Netherlands. Heinz-Josef Lücking. 2007. CC BY-SA 3.0 DE. https://commons.wikimedia.org/wiki/File:Rippelbildungen_am_Strand_von_Spiekeroog.JPG
Figure 5.53: A bidirectional flow creates this symmetrical wave ripple. Matt Affolter (QFL247). 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:WaveRipple.JPG
Figure 5.54: Climbing ripple deposit from India. DanHobley. 2011. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Climbing_ripples.JPG
Figure 5.55: Lithified cross-bedded dunes from the high country of Zion National Park, Utah. Dr. Igor Smolyar, NOAA/NESDIS/NODC. 2010. Public domain. https://commons.wikimedia.org/wiki/File:Cross-bedding_Of_Sandstone_Near_Mt_Carmel_Road_Zion_Canyon_Utah.jpg
Figure 5.56: Modern sand dune in Morocco. Rosino. 2005. CC BY-SA 2.0. https://en.wikipedia.org/wiki/File:Morocco_Africa_Flickr_Rosino_December_2005_84514010.jpg
Figure 5.57: Herringbone cross-bedding from the Mazomanie Formation, upper Cambrian of Minnesota. James St. John. 2015. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Herringbone_cross-stratified_quartzose_sandstones_with_trace_fossils_(Mazomanie_Formation,_Upper_Cambrian;_riverside_cliff,_western_side_of_the_St._Croix_River,_northeast_of_Lookout_Point,_Minnesota,_USA)_4_(18812079220).jpg
Figure 5.58: Hummocky-cross stratification, seen as wavy lines throughout the middle of this rock face. Matt Affolter (QFL247). 2010. CC BY-SA 3.0. https://www.wikiwand.com/en/Hummocky_cross-stratification#Media/File:HumXSec.JPG
Figure 5.59: Antidunes forming in Urdaibai, Spain. Kol35. 2011. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Antidunes_(Urdaibai_estuary).JPG
Figure 5.60: Bioturbated dolomitic siltstone from Kentucky. Jstuby. 2010. Public domain. https://en.wikipedia.org/wiki/File:Saluda_bioturbation.jpg
Figure 5.61: Lithified mudcracks from Maryland. Jstuby. 2009. Public domain. https://en.wikipedia.org/w/index.php?title=File:Mudcracks_roundtop_hill_MD.jpg
Figure 5.62: This flute cast shows a flow direction toward the upper right of the image, as seen by the bulge sticking down out of the layer above. Matt Affolter (QFL247). 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:FluteCast.JPG
Figure 5.63: Groove casts at the base of a turbidite deposit in Italy. Mikenorton. 2006. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Groove_casts.JPG
Figure 5.64: A drill core showing a load cast showing light-colored sand sticking down into dark mud. Matt Affolter. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:LoadCast.JPG
Figure 5.65: Mississippian raindrop impressions over wave ripples from Nova Scotia. Rygel, M.C. 2006. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Raindrop_impressions_mcr1.jpg
Figure 5.66: Cobbles in this conglomerate are positioned in a way that they are stacked on each other, which occurred as flow went from left to right. Verisimilus. 2008. CC BY 3.0. https://commons.wikimedia.org/wiki/File:Imbricated_fabric.jpg
Figure 5.67: This bivalve (clam) fossil was partially filled with tan sediment, partially empty. Matt Affolter. 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Geopetal.JPG
Figure 5.68: Eubrontes trace fossil from Utah, showing the geopetal direction is into the image. Wilson44691. 2008. Public domain. https://commons.wikimedia.org/wiki/File:Eubrontes01.JPG
Figure 5.69: A representation of common depositional environments. Mikenorton. 2008. CC BY-SA 3.0. https://en.wikipedia.org/wiki/File:SedimentaryEnvironment.jpg
Figure 5.70: Marine sediment thickness. Note the lack of sediment away from the continents. NOAA. 2019. Public domain. https://ngdc.noaa.gov/mgg/sedthick/
Figure 5.71: Diatomaceous earth. James St. John. 2013. CC BY 2.0. https://commons.wikimedia.org/wiki/File:Diatomite_(diatomaceous_earth)_Monterey_Formation_at_a_diatomite_quarry_just_south_of_Lompoc.jpg
Figure 5.72: Turbidites inter-deposited within submarine fans. Oggmus. 2016. CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Turbidite_formation.jpg
Figure 5.73: Contourite drift deposit imaged with seismic waves. Integrated Ocean Drilling Program. 2012. CC BY-SA 3.0. https://en.wikipedia.org/wiki/File:Contourite_sparker_seismic_elongate_drift.png
Figure 5.75: Diagram of zones of the shoreline. US government. 2012. Public domain. https://commons.wikimedia.org/wiki/File:Littoral_Zones.jpg
Figure 5.76: The rising sea levels of transgressions create onlapping sediments, regressions create offlapping. Woudloper. 2009. CC BY-SA 1.0. https://commons.wikimedia.org/wiki/File:Offlap_%26_onlap_EN.svg
Figure 5.77: Lithified heavy mineral sand (dark layers) from a beach deposit in India. Mark A. Wilson. 2008. Public domain. https://commons.wikimedia.org/wiki/File:HeavyMineralsBeachSand.jpg
Figure 5.78: General diagram of a tidal flat and associated features. Foxbat deinos. 2009. Public domain. https://commons.wikimedia.org/wiki/File:Tidal_flat_general_sketch.png
Figure 5.79: Waterpocket fold, Capitol Reef National Park, Utah. Bobak Ha’Eri. 2008. CC BY 3.0. https://commons.wikimedia.org/wiki/File:2008-0914-CapitolReef-WaterpocketFold1.jpg
Figure 5.80: A modern coral reef. Toby Hudson. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Coral_Outcrop_Flynn_Reef.jpg
Figure 5.81: The light blue reef is fringing the island of Vanatinai. NASA image by Jesse Allen and Rob Simmon, using data provided by the United States Geological Survey. 2002. Public domain. https://en.m.wikipedia.org/wiki/File:Vanatinai,_Louisiade_Archipelago.jpg
Figure 5.82: Seamounts and guyots in the North Pacific. PeterTHarris. 2015. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Distribution_of_seamounts_and_guyots_in_the_North_Pacific.pdf
Figure 5.83: Kara-Bogaz Gol lagoon, Turkmenistan. NASA. 1995. Public domain. https://commons.wikimedia.org/wiki/File:Kara-Bogaz_Gol_from_space,_September_1995.jpg
Figure 5.84: The Nile delta, in Egypt. Jacques Descloitres, MODIS Rapid Response Team, NASA/sh. 2003. Public domain. https://commons.wikimedia.org/wiki/File:Nile_River_and_delta_from_orbit.jpg
Figure 5.85: Birdfoot river-dominated delta of the Mississippi River. NASA. 2001. Public domain. https://commons.wikimedia.org/wiki/File:Mississippi_delta_from_space.jpg
Figure 5.86: Tidal delta of the Ganges River. NASA. 1994. Public domain. https://commons.wikimedia.org/wiki/File:Ganges_River_Delta,_Bangladesh,_India.jpg
Figure 5.87: The Cauto River in Cuba. Not home~commonswiki. 2007. Public domain. https://commons.wikimedia.org/wiki/File:Rio-cauto-cuba.JPG
Figure 5.88: The braided Waimakariri river in New Zealand. Greg O’Beirne. 2016. CC BY 2.5. https://www.wikiwand.com/simple/Braided_river#Media/File:Waimakariri01_gobeirne.jpg
Figure 5.89: An alluvial fan spreads out into a broad alluvial plain. Matt Affolter. 2010. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:AlluvialPlain.JPG
Figure 5.90: Oregon’s Crater Lake was formed about 7700 years ago after the eruption of Mount Mazama. Zainubrazvi. 2006. CC BY-SA 3.0. https://en.wikipedia.org/wiki/File:Crater_lake_oregon.jpg
Figure 5.91: Formation and types of dunes. NPS Natural Resources. 2016. Public domain. https://flic.kr/p/GAn1Pj
Figure 5.92: Loess Plateau in China. Till Niermann. 1987. CC BY-SA 3.0. https://en.wikipedia.org/wiki/File:Loess_landscape_china.jpg
Figure 5.93: Wide range of sediments near Athabaska Glacier, Jasper National Park, Alberta, Canada. Wing-Chi Poon. 2006. CC BY-SA 2.5. https://commons.wikimedia.org/wiki/File:Glacial_Transportation_and_Deposition.jpg
Rocks that are formed by sedimentary processes, including sediments lithifying and precipitation from solution.
An extensive, distinct, and mapped set of geologic layers.
The physical breakdown (weathering) of bedrock by processes such as pressure, ice expansion, etc.
Term for the underlying lithified rocks that make up the geologic record in an area. This term can sometimes refer to only the deeper, crystalline (non-layered) rocks.
Pieces of rock that have been weathered and possibly eroded.
Sedimentary rocks that are made of sediment, weathered pieces of bedrock.
The act of taking a solid and dissolving it into a liquid. This commonly occurs with salts and other minerals in water.
An interpretation of the rock record which describes the cause of sedimentation (i.e. ancient beach, river, swamp, etc.).
Breaking down rocks into small pieces by chemical or mechanical means.
The transport and movement of weathered sediments.
The process of turning sediment into sedimentary rock, including deposition, compaction, and cementation.
A natural substance that is typically solid, has a crystalline structure, and is typically formed by inorganic processes. Minerals are the building blocks of most rocks.
Sedimentary rocks that are precipitated, from solution.
Sedimentary rocks made of mineral grains weathered as mechanical detritus of previous rocks, e.g. sand, gravel, etc.
Two or more atoms or ions that are connected chemically.
A molecule (like water) which has a positive side and a negative side.
Forces that cause one substance to stick to another.
Forces that hold a substance together.
Stresses that pull objects apart into a larger surface area or volume; stretching forces.
A weak chemical bond which attracts hydrogen to a negative part of a molecule. Many of water's properties are due to hydrogen bonds.
The measure of the vibrational (kinetic) energy of a substance.
A chemical that can dissolve a wide range of other chemicals.
The process in which solids (like minerals) are disassociated and the ionic components are dispersed in a liquid (usually water).
The outermost chemical layer of the Earth, defined by its low density and higher concentrations of lighter elements. The crust has two types: continental, which is the thick, more ductile, and lowest density, and oceanic, which is higher density, more brittle, and thinner.
A process where water freezes inside cracks in rocks, causing expansion and mechanical weathering.
A process where plants and their roots wedge into cracks in bedrock, and widen them.
An acid that forms from carbon dioxide and water. It is a large contributor to chemical weathering.
Water breaking into ions and replacing ions in minerals; a major type of chemical weathering in silicates.
Certain metallic elements (like iron) take in oxygen, causing reactions like rust.
A type of non-eroded sediment mixed with organic matter, used by plants. Many essential elements for life, like nitrogen, are delivered to organisms via the soil.
Any downhill movement of material, caused by gravity.
A body of ice that moves downhill under its own mass.
A type of mechanical weathering in which outer layers of rock, approximately parallel to the surface, fracture off.
A type of exfoliation where homogenous rocks weather into round shapes.
Breaking down of mineral material via chemical methods, like dissolution and oxidation.
A break within a rock that has no relative movement between the sides. Caused by cooling, pressure release, tectonic forces, etc.
Root systems preserved in rocks.
Places that are under ocean water at all times.
The act of a solid coming out of solution, typically resulting from a drop in temperature or a decrease of the dissolving material.
Rounded cavities within rocks that form in various ways, including mineral growth, mainly salt.
The gases that are part of the Earth, which are mainly nitrogen and oxygen.
A positively-charged ion. In geology, this commonly includes ions of the elements Ca+2, Na+1, K+1, Fe+2,+3, Al+3, and Mg+2.
Consisting of three end members: potassium feldspar (K-spar, KAlSi3O8), plagioclase with calcium (CaAl2Si2O8, called anorthite), and plagioclase with sodium (NaAlSi3O8, called albite). Commonly blocky, with two cleavages at ~90°. Plagioclase is typically more dull white and gray, and K-spar is more vibrant white, orange, or red.
Mineral group in which the silica tetrahedra, SiO4-4, is the building block.
A negatively-charged ion. In geology, this commonly includes elements and molecules like SiO4-4, S-2, SO4-4, and O-2.
A chemical sedimentary rock that forms as water evaporates.
A chemical or biochemical rock made of mainly calcite.
A very fine grained version of silica deposited with or without microfossils.
Mineral group in which the carbonate ion, CO3-2, is the building block. This can also refer to the rocks that are made from these minerals, namely limestone and dolomite (dolostone).
CaCO3. Pure form is clear, but can take on many different colors with impurities. It is soft, fizzes in acid, and has three cleavages that are not at 90°.
Working opposite of Bowen's reaction series, it states that minerals that are formed at conditions more dissimilar to the surface are more quickly prone to chemical weathering.
The process of liquid rock solidifying into solid rock. Because liquid rock is made of many components, the process is complex as different components solidify at different temperatures.
A series of mineral formation temperatures that can explain the minerals that form in specific igneous rocks. For example, pyroxene will form with olivine and amphibole, but not quartz.
Current conditions within the atmosphere.
SiO2. Transparent, but can be any color imaginable with impurities. No cleavage, hard, and commonly forms equant masses. Perfect crystals are hexagonal prisms topped with pyramidal shapes. One of the most common minerals, and is found in many different geologic settings, including the dominant component of sand on the surface of Earth. Structure is a three-dimensional network of silica tetrahedra, connected as much as possible to each other.
Can refer to a volcanic rock with higher silica composition, or the minerals that make up those rocks, namely quartz, feldspar, and muscovite mica. Felsic rocks are lighter in color and contain more minerals that are light in color. Primary felsic rocks are rhyolite (extrusive) and granite (intrusive).
Can refer to a volcanic rock with lower silica composition, or the minerals that make up those rocks, namely olivine, pyroxene, amphibole, and biotite. Mafic rocks are darker in color and contain more minerals that are dark in color, but can contain some plagioclase feldspar. Primary mafic rocks are basalt (extrusive) and gabbro (intrusive).
(Fe,Mg)2SiO4. Typically translucent olive green and equant, with no cleavage. Common in mafic igneous rocks and in the mantle, but easily weathered in surface conditions. Structure is isolated silica tetrahedra. Known as peridot when a gem.
XY(Al,Si)2O6, in which X typically equals Na, Ca, Mg, or Fe and Y typically equals Mg, Fe, or Al. Typically black to dark green, blocky, with two cleavages at ~90°. Common in mafic igneous rocks and some metamorphic rocks. Structure is a single chain of silica tetrahedra.
Carbonate rocks which dissolve, leaving behind caverns and holes which affect the landscape.
Water that is below the surface.
A solution that has the maximum allowed dissolved component, and is unable to dissolve more.
Minerals with a luster similar to metal and contain metals, including valuable elements like lead, zinc, copper, tin, etc.
Minerals in which ions are bonded to oxygen, such as hematite (Fe2O3).
Sediment being "glued" together via mineralization, typically calcite and quartz from groundwater fluids.
The transport and movement of weathered sediments.
The living things that inhabit the Earth.
The solid, rocky parts of the Earth, including the crust, mantle, and core. Also referred to as the lithosphere.
Rocks which allow petroleum resources to collect or move.
Organic rich material found in soil.
A group of all atoms with a specific number of protons, having specific, universal, and unique properties.
Place where lava is erupted at the surface.
Specific layers within a soil profile with specific properties.
A hypothetical or real section cut through soil, showing the different layers (horizons) that exist.
Specific layers within a soil profile with specific properties.
The mineral makeup of a rock, i.e. which minerals are found within a rock.
Upper layer of soil, made mainly out of organic material.
Lower layer of the soil (B) which is a mixture of weathered bedrock, leeched materials, and organic material. Has two sublayers: the upper part, or regolith (with more organic materials), and the lower part, saprolite, which is only slightly weathered bedrock.
Loose material that is a mixture of soil components and weathered bedrock sediments.
The rocks that existed before the changes that lead to a metamorphic rock, i.e. what rock would exist if the metamorphism was reversed.
Lowest layer of the soil (C), which is mechanically weathered (not chemically weathered) bedrock.
Valuable material in the Earth, typically used for metallic mineral resources.
A highly weathered soil deposit that consists of aluminum ores.
Volcanic tephra that is less than 2 mm in diameter.
Depositional environments that are on land.
Minerals made from just a single element, bonded to itself. Examples include gold, silver, copper, and diamond, which is a native version of carbon.
A rock or sediment that has good permeability and porosity, and allows water to move easily, making it possible to get water for human use.
The average diameter of a grain of sediment, ranging from small, also known as fine-grained (e.g. clay, silt) to large, also known as coarse-grained (e.g. boulder).
The range of sediment sizes within a sediment or sediment within sedimentary rocks. Well sorted means the sediment has the same sizes, poorly sorted means many different sizes are present.
Sediment gathering together and collecting, typically in a topographic low point.
Sediment being squeezed together into a coherent mass.
Changes in sedimentary rocks due to increased (but low when compared to metamorphism) temperatures and pressures. This can include deposition of new minerals (e.g. limestone converting to dolomite) or dissolution of existing minerals.
Rocks and minerals that change within the Earth are called metamorphic, changed by heat and pressure. Metamorphism is the name of the process.
Place where two plates slide past each other, creating strike slip faults.
Empty space in a geologic material, either within sediments, or within rocks. Can be filled by air, water, or hydrocarbons.
Any evidence of ancient life.
A sequence of layers in which the sediment changes linearly in size, either getting coarser or finer.
Deposition and erosion tied to glacier movement.
A channelled body of water.
Detached, free-falling rocks from very steep slopes.
How smooth or rough the edges are within a sediment.
The ease or difficulty in scratching a mineral, measured by the qualitative Mohs hardness scale, which ranges from soft talc (#1 on the scale) to hard diamond (#10 on the scale).
A rock that contains material which can be turned into petroleum resources. Organic-rich muds form good source rocks.
The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust. Continental crust is defined as having higher concentrations of very light elements like K, Na, and Ca, and is the lowest density rocky layer of Earth. Its average composition is similar to granite.
Pieces of mudcracks that are incorporated into a sedimentary rock.
Metamorphic rock with a strong foliation but no visible minerals, derived from mudstones or shales.
Igneous rock cooling, and thus forming, outside of the Earth, i.e. on the surface.
General name of a mafic rock that is extrusive. Generally has a black groundmass color.
The study of the components of a rock, mainly sedimentary rocks, and the information that can be obtained by understanding the origin of the components.
The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.
An arrangement of many continental masses collided together into one larger mass. According to the Wilson Cycle, this occurs every half billion years or so.
A rock primarily made of sand.
ZrSiO4. Relatively chemically inert with a hardness of 8.5. Common accessory mineral in igneous and metamorphic rocks, as well as detrital sediments. Uranium can substitute for zirconium, making zircon a valuable mineral in radiometric dating.
General term for the fine-grained, not discernible part of a rock. In igneous rocks, this is the part of the rock that is not phenocrysts, and can help in determining the composition of extrusive rocks. In sedimentary rocks, it typically refers to the fine-grained components, namely mud. In metamorphic rocks, it is usually referring to material between porphyroblasts or a low-grade rock with only microscopic mineralization.
A sedimentary rock with rounded, larger (≥2 mm) clasts.
A sandstone rich in feldspar.
A sandstone with a significant mud component OR a sandstone with a significant lithic fragment component.
A rock made of primarily mud, i.e. particles smaller than sand (≤0.064 mm).
A very fine-grained rock with very thin layering (fissile).
A rock made of primarily silt.
A rock made primarily of clay.
Easily split along bedding planes, a characteristic of shale.
Chemical sedimentary rocks that have a biologic component to their origin. Many limestones are biochemical.
An atom or molecule that has a charge (positive or negative) due to the loss or gain of electrons.
Former swamp-derived (plant) material that is part of the rock record.
A dark liquid fossil fuel derived from petroleum.
Gaseous fossil fuel derived from petroleum, mostly made of methane.
An evaporite mineral, CaSo4•2H2O. Has one cleavage, hardness of 2. Typically clear or white.
Also known as rock salt, or table salt. 3 cleavages at 90°, cubic crystal habit. Typically clear or white, hardness of 3.
Porous variety of carbonate that form in relatively unheated water, sometimes as towers and spires.
Porous, concentric, or layered variety of carbonate that forms with often heated water in springs and/or caves.
A separation of light (felsic) and dark (mafic) minerals in higher grade metamorphic rocks like gneiss.
A sedimentary rock that formed long ago as free oxygen changed the solubility of iron, causing layers of iron rich and iron-poor sediments to form in thin layers, or bands.
Liquid rock within the Earth.
Spheres of calcite that form in saline waters with slight wave agitation. Ooid refers to the sphere, oolite the rock with the spheres.
A topographic high found away from the beach in deeper water, but still on the continental shelf. Typically, these are formed in tropical areas by organisms such as corals.
Adjective for a rock filled with fossils, most commonly with limestones.
Limestone made of shell fragments cemented together.
A limestone made of coccolithophore shells, a type of single-celled algae.
Limestone made of primarily fine-grained calcite mud. Microscopic fossils are commonly present.
Relatively flat ocean floor, which accumulates very fine grained detrital and chemical sediments.
Discernible layers of rock, typically from a sedimentary rock.
A liquid fossil fuel derived from shallow marine rocks (also known as crude oil).
Arrangement of minerals within a rock.
Idea championed by James Hutton that the present is the key to the past, meaning the physical laws and processes that existed and operated in the past still exist and operate today.
A specific layer of rock with identifiable properties.
The study of rock layers and their relationships to each other within a specific area.
Thin (less than 1 cm) beds of rock.
Predictable sequence of fining upward sediments, caused by turbidity flows.
Turbidite is the rock that forms from a turbidity flow, a relatively coarse and dense sediment transported to the abyssal plain.
The part of the coastline which is below any wave base action.
A qualitative measure of the speed of a fluid flow, with different amounts of flow corresponding to different sedimentary structures, called bedforms. Typically, it is split into upper and lower flow regimes, with upper being a more rapid flow.
A large pile of sediment, deposited perpendicular to flow. Internal bedding in dunes dips toward flow direction (i.e. cross bedding). Formed in the upper part of the lower flow regime.
A specific type of sedimentary structure (ripples, plane beds, etc.) linked to a specific flow regime.
Subtle ridges formed in the upper flow regime on top of plane beds in the direction of flow.
Ridges of sediment that form perpendicular to flow in the lower part of the lower flow regime.
A specific layer of rock formed by flowing fluid, either in the lowest part of the lower flow regime or lower part of the upper flow regime.
A sedimentary structure that has inclined layers within an overall layer. Forms commonly in dunes, larger in eolian dunes.
Dunes that form from many different wind directions.
Dunes that are much longer than wide, forming from wind that varies in two opposite directions.
An interconnected set of parts that combine and make up a whole.
Bottommost part of a wave.
A special type of cross bedding that forms when strong storms produce mounds and divots of cross-bedded sand in deeper water.
Similar to dunes, in that they are ridges of sand that form perpendicular to flow, but internally, the sediments dip up stream. Forms in the upper part of the upper flow regime.
A measure of a plane's (maximum) angle with respect to horizontal, where a perfectly horizontal plane has a dip of zero and a vertical plane has a dip of 90°.
Sedimentary layering disturbed by movement of organisms.
Polygonal cracking that occurs with shrinking clays. Indicative of mud submerged underwater and then exposed to air.
A piece of a rock that is caught up inside of another rock.
Wide and flat area of land covered by ocean water during high tide, but exposed to air by low tide.
A series of sedimentary structures formed on the base of a flow, eroding into underlying sediment. Examples include scour marks, flute casts, groove casts, and tool marks.
Material filling in a cavity left by a organism that has dissolved away.
A strain that occurs in a substance in which the item changes shape due to a stress.
Small circular pits formed by raindrops impacting soft sediments.
Stacked cobbles in the direction of flow.
Rock spire that is offshore and a remnant of a rock layer.
Depositional environments that are associated with running water.
A feature in a rock that allows the observer to determine which direction was up in the past.
A sedimentary structure that forms in the lower flow regime, where ridges of sediment form perpendicular to flow direction, but within the ridges, sediment layers and dips toward flow direction. Found in ripples and dunes. Can be tabular, sinuous, or trough shaped.
Evidence of biologic activity that is preserved in the fossil record, but it not the organism itself. Examples include footprints and burrows. Ichnology is the study of trace fossils.
A fossil with a wide geographic reach but short geologic time span used to match rock layers to a specific time period.
Liquid rock on the surface of the Earth.
Flat area around a river channel that is filled with water during flooding events.
Broad cone of coarse sediment deposited from a submarine flow or turbidity flow.
The deep, flat part of the ocean. Also known as the ocean floor.
Also known as the CCD, it is the point in the depths of the ocean where calcite start to dissolve, leaving only siliceous ooze behind.
Canyon carved into a continental shelf.
Submerged part of the continental mass, with a gentle slope.
Steep part of an ocean basin that is the transition between the continental mass and the ocean floor.
Part of the coastal depositional environment, near the tidal zone but below. Lower shoreface is the part of the coastline which is only disturbed by storm waves, upper shoreface is disturbed by typical, daily wave action.
A net movement that occurs as waves intersect the shoreline at non-perpendicular angles.
The part of the coastline which is directly related to water-land interaction, specifically the tidal zone and the range of wave base.
The entire area which is related to land-sea interactions.
The study of changes in the rock record caused by changing sea level over time.
Sea level rise over time.
Sea level fall over time.
The beach (shoreline) zone, where waves are crashing.
Interior body of ocean water, at least partially cut off from the main ocean water.
A mechanical process which takes ore and separates it from gangue material.
Initiation point of an earthquake or fault movement.
Ridges of sand, made from former beach sediments, that form parallel to the shoreline.
An eroded island. Since wave and weather action does not extend deep into the ocean, the root of the island is preserved as a seamount. Reefs can grow around seamounts.
Rising stationary magma, forming a succession of volcanism. This is reflected as islands on oceanic plates, and volcanic mountains or craters on land.
The act of the land surface down-warping, typically referred to when discussing sedimentation or with rapid groundwater removal.
Lagoon with brackish water, typically with abundant biologic factors.
Movements of water (rising and falling) due to the gravity of the moon and sun. This is most often seen in marine settings.
Place where rivers enter a large body of water, forming a triangular shape as the river deposits sediment and switches course.
Slope of a stream channel.
Deposition that has to do with rivers.
Low-gradient channel where rivers sweep across broad flood plains.
Channel type with many switching channels, common with large sediment volumes.
A down-warped feature in the crust.
Term for the extensional tectonic province that extends from California’s Sierra Nevada Mountains in the west, to Utah’s Wasatch Mountains to the east, to southern Oregon and Idaho to the north, to northern Mexico to the south. Known as a wide rift, each graben (basin) is bounded by horsts (ranges).
A dry lake bed in a desert valley.
Deposition with wind-blown sediment.
Deposition in and around lakes.
Hole left behind after a large volume of material erupts out of a volcano. This depression is often turned into a valley or lake after the eruption is over.
Abandoned meanders that are cut off from the main channel.
Deposition in swamps.
The measure of degrees north or south from the equator, which has a latitude of 0 degrees. The Earth's north and south poles have latitudes of 90 degrees north and south, respectively.
Wind-blown silt, mainly formed from glacial processes.
A sedimentary rock containing two distinct grain sizes, typically cobbles (or larger) mixed with mud.
General term for very poorly sorted sediment that is of glacial origin.
Large sediment (e.g. boulder) carried and then dropped by a glacier.
A specific set of features that are tied together in an interpretive group. Facies can be based on mineralogy, biologic factors, fossils, rock types, etc.
A unit of the geologic time scale; smaller than an era, larger than an epoch. We are currently in the Quaternary period.
Matching rocks of similar ages, types, etc.
The first period of the Paleozoic, 541 million years ago-485 million years ago.