Exam 3 - Sedimentary Rocks Flashcards
weathering
Weathering is the gradual destruction of rock under surface conditions. Weathering may involve physical processes (called mechanical weathering) or chemical activity (called chemical weathering). Biological activity can also result in weathering that can be construed as mechanical, chemical, or both
Weathering produces sediments, erosion moves sediments.
Weathered materials are subjected to gravitation forces pulling them downhill and are transported by forces of erosion associated with flowing water, ice, or wind.
erosion
Erosion involves the mechanical processes of wearing or grinding away materials on a landscape by the action of wind, flowing water, or glacial ice (under the influence of gravity).
This includes materials exposed on the land, below the oceans, or under glaciers
sediments
Sediments are solid fragments of inorganic or organic material that come from the weathering and erosion of rock
Sediments can be eroded and deposited. Erosion involves the mechanical processes of wearing or grinding away materials on a landscape by the action of wind, flowing water, or glacial ice (under the influence of gravity)
soil
made up of sediments and organic matter, and forms from the processes associated with weathering and erosion
can weathering occur on rocks that are not exposed on the surface of the earth’s?
Weathering processes can begin long before rocks are exposed at the surface. This is true in most places on the earth surface where rocky outcrops (bedrock) is not exposed
mechanical weathering
Mechanical weathering involves all processes that collectively break rocks into smaller pieces
Mechanical weathering includes all forms of mass wasting—a general name for processes by which soil and rock move downslope under the force of gravity
Mass wasting, a form of mechanical weathering, includes sudden events such as rock falls, landslides and avalanches—to long-lasting processes including slow movements of massive slumps or the slow creep of material down hillsides. These processes break “big pieces of rocks into smaller pieces.”
chemical weathering
Chemical weathering involves the breakdown (decomposition, decay, and dissolution) of rock by chemical means. Water is the most important agent of chemical weathering
dissolution
the action or process of dissolving or being dissolved, moving soluble components of materials into solution
leaching
the process of dissolving and removing the soluble constituents of soil or rock near the land’s surface
facts about chemical and mechanical weathering
In most surface and near surface settings, mechanical and chemical weathering are taking place simultaneously
Weathering is enhanced in environments where repeated wetting and drying periods take place. The chemical breakdown of rocks is most rapid where warm and humid climatic conditions persist. Mechanical weathering processes dominate in cold settings where daily heating and cooling, and freezing and thawing cycles occur frequently in winter months. Forest fires can have similar heating and cooling effects on breaking rocks on the surface
lithogenous sediments
Lithogenous sediments form through the processes of weathering and erosion of materials exposed on land and along coastlines
Lithogenous sediments consist of solid fragments of inorganic or organic material that come from the weathering of rock and soil erosion, and are carried and deposited by wind, water, or ice.
biogenus sediment
Biogenous sediments are composed of the remains of living organisms, including microscopic phytoplankton (plants) and microscopic zooplankton (animals), terrestrial and aquatic plants, shells of invertebrates, and vertebrate material (teeth, bone), and associated organic residues. Coal, oil, and gas are derived from biogenous sediments.
fate of soluble components of rocks
As rocks weather, they loose their soluble elemental components, they dissolve in groundwater and surface runoff and are carried away, eventually reaching the ocean, or as in the Great Basin region, end up being concentrated as salts on dry lake beds (or brine in basins such as Mono Lake (CA) or the Great Salt Lake (Utah). Over billions of years, rivers and streams, and groundwater flowing into the oceans have contributed to the saltiness of seawater. Salt in seawater is concentrated by the evaporation of water back into the atmosphere
sedimentary rock
Sedimentary rock is rock that has formed through the deposition and consolidation and solidification of sediment, especially sediment transported by fluids—including water (rivers, lakes, and oceans), ice (glaciers), and wind
how do sediments become sedimentary rocks?
Sediments can become lithified into sedimentary rocks once they’ve been deposited in a stable setting where burial, compaction, and cementation can take place. The processes, collectively called lithification (or diagenesis), typically takes place slowly over time but rates depend on many factors including the chemistry of the sediments and groundwater passing through the sediment, and how quickly or deeply burial takes place
where do sedimentary rocks occur?
Sedimentary rocks are exposed throughout the world’s continents, covering about half of the exposed land on the earth surface. This sedimentary cover blanketing continental areas was originally deposited mostly in coastal environments, in shallow seas flooding shallow continental basins, on continental shelves and in ocean basins along the margins of continents. These ancient sedimentary deposits are well exposed in mountainous regions
The mile-thick sequence of sedimentary rock formations exposed by erosion in the Grand Canyon is an exceptional example of the sedimentary cover preserved on the North American continent
hydrogenous sediments
Hydrogenous sediments are sediments directly precipitated from water. Examples include rocks called evaporites formed by the evaporation of salt bearing water (seawater or briny freshwater)
Salt (NaCl) and Gypsum (CaSO4) are Manganese nodules form on the ocean bed (mostly in the deep Pacific) from the slow precipitation of metal oxides in the absence of other kinds of sediments
cosmogenous sediments
Cosmogenous sediments originated from outer space. Scientists have used satellites to estimate how much material enters the earth’s atmosphere, with current estimates from satellite data suggesting about 100 to 300 tons (mostly cosmic dust) hits earth each day. This is just a tiny fraction of the sediments generated on earth each day.
clastic sediment
The word clastic is also commonly used to describe sediments or sedimentary rocks composed of fragments (or detritus) derived from older rocks
non-clastic sediments
The term non-clastic refers to sediments or sedimentary rocks composed of materials produced by biological activity (skeletal material, respiration, and excretion) and sediments precipitated from water (the later are also called chemical sedimentary rocks). Biogenous and hydrogenous sediments described above are non-clastic sediments
clastic sedimentary rocks
Clastic Sedimentary Rocks are rocks composed of grains of mineral and rock fragments derived from erosion of other rocks. Three general groups are coarse-grained, sand-size grained, and fine-grained (mudrocks)
gravel
Gravel is rock particles that have been moved by moving water. Gravel usually consists of a mix of the more durable and most abundant rock types in the sediment source areas (Figure 9-7). Gravel deposits typically occur along stream valleys close to mountainous source areas and along rocky coastlines with high wave action
conglomerate
Conglomerate is a sedimentary rock composed of cemented gravel. It consists of rounded to sub-angular fragments (larger than 2 mm in diameter) set in a fine-grained matrix of sand or silt, and commonly cemented by calcium carbonate, iron oxide, silica, or hardened clay; the consolidated equivalent to gravel
sand
Sand goes through degrees of refinement at it moves away from source areas. Sand deposits near mountain ranges may be enriched in feldspars
Volcanic regions may produce sand enriched in dark minerals. “Mature” sand that has traveled long distances in streams, blown by wind, or worked by waves will be enriched in quartz and individual grains will be very well rounded and well sorted (see below). Large sand deposit accumulate along stream valleys, on beaches, barrier islands, and offshore bars, and in dune fields in coastal areas and in desert environments
mud
Mud is a general term lumping together sediments consisting of a mix of clay, silt, and may contain sand. Mud is usually an unsorted mix of fine grain materials. Mud accumulates in quiet water settings separated from where coarser materials have settled out elsewhere
mudstone
Mudstone is a fine-grained sedimentary rock formed from the compaction and cementation (lithification) of muddy sediments rich in silt (but may include percentages of fine sand and clay)
shale
Shale is a soft, finely stratified sedimentary rock that formed from consolidated mud rich in clay minerals and can be split easily into fragile plates, such as along bedding plains (Figure 9-18). Shale forms from the compaction of sediment dominated by clays.
bioaccumulation
Bioaccumulation is the buildup of organic remains, such as deposits associated with coral reefs, peat bogs, shell or bone beds, and algae and planktonic ooze.
planktonic ooze
Planktonic ooze is slimy mud sediment on the bottom of an ocean or lakebed formed from the accumulation of skeletal and organic remains of microscopic organisms
lime mud
Lime mud is sediment composed of calcium carbonate (CaCO3) derived from the skeletal remains of shelled organisms, coral, and calcareous algae and plankton. Large amounts of lime mud is created by waves battering reefs and material being chewed up and excreted by reef-living organisms
limestone
sedimentary rock consisting predominantly of calcium carbonate (CaCO3) derived from the skeletal remains of marine microorganisms, including shells and coral) and eroded and transported sediments associated with reef environments in shallow, warm tropical marine waters
siliceous non-clastic sedimentary rocks
Chert is a hard, dense sedimentary rock, consisting chiefly of interlocking microscopic crystals of quartz and may contain opal. It has a conchoidal fracture and may occur in a variety of colors. Most chert forms from recrystallization of siliceous microplankton remains
carbonaceous sedimentary rocks
Organic matter is susceptible to breaking down when exposed to oxygen, so organic material (remains of plants and animals) tend not to survive for long when exposed to the air, but the organic residues can survive when buried, and separated from oxygen in air or dissolved in groundwater
Peat is an accumulation of partially decayed vegetation matter that has a brown, soil-like character typically found in of boggy, acid ground or swampy settings. With lithification peat will become coal
Organic remains that are rich in fats, oils, and lipids can with exposure to heat over time break down and separate from their source sediments and become deposits of petroleum (oil, natural gas, and tar)
evaporite
An evaporite is a rock composed of salt minerals left behind by the evaporation of salty water.
depositional environments
Sediments will erode anywhere where forces associated with currents are strong enough to dislodge and move sediment particles. The “heavier” (both larger and/or denser) the particle, the more energy it take to move. Water is perhaps the primary mover of materials on earth. Wind typical can only move small particles of dust-to-sand-sized particles. Water can move particles of any practically any size if the current is strong enough. Moving glacier ice (though limited to mountainous regions and high latitude regions during Ice Ages) can move materials including house-sized blocks of rock. In general, as a fluid speeds up materials will erode. As the fluid slows down materials will settle out and be deposited. Over time, sediments will accumulate and possibly become buried, becoming permanently deposited until possibly exposed to surface erosion at some later period in geologic time. Places where sediments accumulated are called depositional environments. Depositional environments occur in many different geologic settings on land and under water
sedimentary depositional environment
A sedimentary depositional environment includes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment. The characteristics of ancient sedimentary depositional environments are often preserved in sedimentary rocks
energy in depositional environments
Sedimentary deposits may preserve aspects of the overall energy conditions of an environmental setting. High energy environments include locations where water is flowing (streams or waves are crashing) but may be locations where coarse sediments (gravel and sand) may selectively settle out, but currents winnow out and remove the finer and lighter materials (silt, clay, organic particles) which will be carried away and deposited in a possibly distant low energy environment
high energy depositional environments
High-energy depositional environments (coarse-grain sediments dominate). Examples include: stream and river channels, beaches, dunes, offshore bars (above wave base)submarine channels and canyons where strong ocean currents persist. Weather (climate) and wave energy are variable factors in high-energy environmental settings. Sediments are constantly being deposited or eroded in these settings
low energy depositional environments
Low-energy depositional environments (fine grained sediments dominate): Examples include: river flood plains, swamps, lakes, lagoons, marshes, and offshore below wave base. Slow-moving currents prevent coarse-grained sediment from migrating into in low-energy depositional environments. Fine materials can be carried long distances before they can settle out in the absence of waves and currents
lamination and bedding
Sediments are deposited in layers ranging from paper-thin sheets to massive beds tens to hundreds of feet thick! A laminae (or lamination) is a layer of sediment or sedimentary rock layer only a small fraction of an inch (less than a centimeter) in thickness
ripple marks
a series of small ridges produced in sand by water currents or by wind
cross bedding
inclined sedimentary structures in a horizontal unit of rock. These tilted structures are deposits from bedforms such as ripples and dunes, and they indicate that the depositional environment contained a flowing fluid (typically, water or wind)
desiccation cracks
mudcracks; an irregular surface fracture pattern formed by shrinkage of clay, silt, or mud under the drying effects of atmospheric conditions at the surface
graded bedding
bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Large fragments tend to settle out fastest from a slowing turbulent flow
turbidity flows
a turbid, dense current of sediments in suspension moving along downslope and along the bottom of a ocean or lake. As turbidity flows slow down, they drop their coarse sediment fractions first, and finer and finer sediments as the currents diminish, resulting in graded bedding
fossil
is a remnant or trace of an organism of a some earlier geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth’s crust
Fossilization involves all the processes that turn plant or animal remains to stone
Not all sedimentary rocks preserve fossils. Most animal and plant remains are destroyed by a variety of processes before they can be preserved. However, some “non fossil” evidence is commonly preserved, called “trace fossils
