Chapter 6 Flashcards
Sedimentary Rocks
Arkose
A type of sandstone containing abundant feldspar, indicating minimal weathering and quick burial after deposition.
Bed
A single layer of sediment or sedimentary rock with a distinct boundary, often from changes in deposition conditions.
Biochemical Sedimentary Rock
Rock formed from the accumulation of organic material, typically from shells or skeletons of organisms, such as limestone.
Breccia
A clastic sedimentary rock composed of large, angular fragments cemented together, indicating deposition close to the source of the fragments.
Cementation
The process where minerals precipitate from water and fill the spaces between sediment grains, binding them into solid rock.
Chemical Sedimentary Rock
Rock formed by the precipitation of minerals from water solutions, such as evaporites and travertine.
Clastic Sedimentary Rock
Rock composed of fragments (clasts) of pre-existing rocks, bound together by natural cement.
Clast
Individual grain or fragment within a clastic sedimentary rock.
Coal
An organic sedimentary rock formed primarily from plant material, buried, compressed, and lithified over millions of years.
Compaction
The process of sediments being pressed together under the weight of overlying material, reducing pore space.
Conglomerate
A clastic sedimentary rock consisting of rounded, gravel-sized particles, indicating water transport and some distance from the source.
Cross Bed
Slanted layers within a bed of sediment, formed by wind or water currents, indicating a direction of flow.
Delta
A landform at the mouth of a river where sediment is deposited as water flow slows, forming layers of sedimentary material.
Deposition
The settling and accumulation of sediment, often after transportation by water, wind, or ice.
Depositional Environment
The specific location or setting where sediment accumulates, such as rivers, lakes, or deserts, affecting sediment characteristics.
Detritus
Loose fragments or particles derived from weathering of pre-existing rocks.
Diagenesis
All physical, chemical, and biological processes that transform sediment into sedimentary rock, occurring after deposition.
Dolostone
A carbonate rock composed primarily of dolomite, typically formed by alteration of limestone.
Erosion
The removal and transport of rock or sediment by natural forces like water, wind, or ice.
Geologic Map
A map showing the distribution, nature, and age relationships of rock formations at Earth’s surface.
Graded Bed
A sedimentary layer with a vertical change in particle size, typically coarser at the bottom, indicating settling from a turbidity current.
Evaporite
A type of chemical sedimentary rock formed by precipitation of minerals from evaporating water, such as gypsum or halite.
Limestone
A biochemical or chemical sedimentary rock composed primarily of calcite, often formed in marine environments from shells or coral.
Lithification
The transformation of loose sediment into solid rock through compaction and cementation
Mudstone
A fine-grained clastic rock composed of silt and clay particles, lacking distinct layering.
Organic Sedimentary Rock
Rock formed from the accumulation of organic material, like coal, typically derived from plant remains.
Regression
A geological process where sea level falls, exposing previously submerged areas and shifting depositional environments seaward.
Ripple Mark
Small ridges formed on a sediment surface by water or wind flow, often preserved in sedimentary rock.
Sandstone
A clastic sedimentary rock composed primarily of sand-sized particles, often formed in environments like rivers or beaches.
Sedimentary Basin
A low-lying area where sediment accumulates over time, often resulting from subsidence.
Sedimentary Rock
Rock formed from the accumulation and lithification of sediment, or from precipitation from solution.
Sedimentary Structure
Features within sedimentary rocks, such as bedding, ripple marks, or cross-bedding, formed during or shortly after deposition.
Shale
A fine-grained, clastic sedimentary rock composed mostly of clay, with thin, parallel layers that split easily.
Siltstone
A fine-grained clastic sedimentary rock composed mostly of silt-sized particles, intermediate between sandstone and shale.
Sorting
The degree to which sediment grains are uniform in size, indicating transport distance and energy of the depositional environment.
Strata
Layers of sedimentary rock that differ from one another in composition, grain size, or other characteristics.
Stratigraphic Formation
A recognizable, mappable unit of rock with distinct characteristics, representing a specific depositional environment.
Subsidence
The gradual sinking of an area of Earth’s crust, often leading to sediment accumulation in sedimentary basins.
Transgression
A process where sea level rises, flooding previously dry land and shifting depositional environments landward.
Travertine
A chemical sedimentary rock formed from calcium carbonate, often found near hot springs or limestone caves.
Turbidity Current
A fast-moving, sediment-laden current that flows down a slope underwater, depositing graded beds as it slows.
Describe how a clastic sedimentary rock forms from its unweathered parent rock
Clastic sedimentary rocks form through weathering and erosion of parent rock, transporting the sediment, deposition in a basin, compaction of layers, and cementation where minerals precipitate and bind grains together.
Explain how biochemical sedimentary rocks form.
Biochemical sedimentary rocks form from the accumulation of material from living organisms, such as shells or skeletons, which then compact and lithify into rock like limestone.
How do grain size and shape, sorting, sphericity, and angularity change as sediments move downstream?
As sediments move downstream, grain size decreases, shape becomes rounder, sorting improves (grains become more similar in size), and sphericity increases due to continued abrasion and transport.
Describe the two different kinds of chert. How are they similar? How are they different?
Biochemical chert forms from silica-rich remains of marine organisms, while chemical chert forms from silica precipitation in groundwater. Both are composed of microcrystalline quartz, but they form under different conditions and sources of silica.
Do all chemical sedimentary rocks have the same composition? What conditions produce evaporites?
No, chemical sedimentary rocks vary in composition depending on the minerals that precipitate from solution. Evaporites form in arid environments where water evaporation concentrates dissolved minerals, causing them to crystallize.
How does dolostone differ from limestone, and how does dolostone form?
Dolostone contains the mineral dolomite rather than calcite, as found in limestone. It forms when magnesium-rich water alters limestone, converting calcite to dolomite.
What are cross beds, and how do they form? How can you read the current direction from cross beds?
Cross beds are slanted layers within a horizontal bed, forming from wind or water moving sediment in a particular direction. The slope of the cross beds indicates the flow direction.
Describe how a turbidity current forms and moves. How does it produce graded bedding?
A turbidity current is a fast, sediment-laden underwater flow triggered by slope failure, which slows down and deposits material as it moves, creating graded bedding with coarser sediment settling first.
Compare deposits of an alluvial fan with those of a deep-marine deposit.
Alluvial fan deposits are coarse, poorly sorted, and angular, forming near mountains, while deep-marine deposits are fine-grained, well-sorted, and often layered, reflecting gradual sedimentation on the ocean floor.
Why don’t sediments accumulate everywhere? What types of tectonic conditions are required to create basins?
Sediments need low-lying areas to accumulate, which form in tectonic settings like rift zones, foreland basins, or passive margins where the crust subsides, creating space for sediment deposition.
How is it possible for sandstone derived from sediment deposited in a beach environment to comprise a formation that blankets a broad region?
Shifting sea levels during transgression can spread beach sand over vast areas, creating a widespread sandstone layer as part of a larger sedimentary formation.
