Chapter 5 (part 1) Flashcards
The Sedimentary Archives
The forces controlling deformation or structural behavior of a large area of the Earth’s crust over a long period of time are called:
Tectonics
Tectonics influences the grain size and thickness of ____ deposits.
Sedimentary
Recent uplift of the source area leads to rapid erosion of ____-Grained sediment
Coarse
____ in the depositional basin leads to the accumulation of great thicknesses of sediment.
Subsidence
____ is the stable interior of a continent; undisturbed by mountain-building events since the Precambrian.
Craton
The large areas of exposed crystalline rock are called:
Shields
Ancient crystalline rocks covered by flat-lying or gently warped sedimentary rocks are called:
Platforms
The ____ belts are the elongated regions bordering the craton which have been deformed by compression since the Precambrian.
Orogenic belts
<em>(Mountain belts)</em>
A ____ Environment describes all of the physical, chemical, biological and geographic conditions under which sediments are deposited.
Depositional
____ is the flooded edge of the continent. Flooding occurred when the glaciers melted about 10,000 years ago.
<em>Relatively flat (slope
Shallow water (less than 200 m deep)<br></br> May be up to 300 km wide (averages 80 km wide)<br></br> Exposed to waves, tides, and currents<br></br> Covered by sand, silt, and clay<br></br> Larger sedimentary grains are deposited closer to shore.<br></br> Locally cut by submarine canyons (eroded by rivers during Ice Age low sea level stand)<br></br> Coral reefs and carbonate sediments may accumulate in tropical areas</em>
Continental Shelf
____ is the steeper slope at edge of the continent.
<em>Located seaward of the continental shelf<br></br> Boundary between continental and oceanic crust<br></br> May be about 20 km wide<br></br> Deeper water<br></br> More steeply inclined (3 - 6o)<br></br> Rapid sediment transport down the slope by dense, muddy turbidity currents<br></br> Passes seaward into the continental rise</em>
Continental Slope
____ is at the base of the continental slope.
<em>More gradual slope<br></br> May be hundreds of km wide<br></br> Water depths of 1400 to 3200 m<br></br> Submarine fans form off submarine canyons<br></br> Turbidity currents transport sediment downslope from continental shelf (turbidites)<br></br> Passes seaward into the abyssal plain</em>
Continental Rise
____ is the deep ocean floor.
<em>Nearly flat<br></br> Water depths of 3 to 5 km + (2 - 3 miles +)<br></br> Covered by very fine-grained sediment and shells of microscopic organisms:<br></br> Clay, Volcanic ash, Foraminifera (calcareous), Radiolarians (siliceous), Diatoms (siliceous)</em>
Abyssal Plain
____ are fan-shaped accumulations of sediment formed where a river flows into a standing body of water, such as a lake or the sea; and it builds seaward <em>(or progrades)</em> as sediment is deposited at the river mouth.
Deltas
____ are bodies of water on the landward side of barrier islands protected from the pounding of the ocean waves by barrier islands. It contains finer sediment than the beaches (usually silt and clay) & are also present behind reefs, or in the center of atolls.
Lagoons
____ are:
• Nearly flat, low relief areas that border lagoons, shorelines, and estuaries
• Periodically flooded and exposed by tides <em>(usually twice each day)</em>
• May be cut by meandering tidal channels
• d. May be marshy, muddy, sandy or mixed sediment types <em>(terrigenous or carbonate)</em>
• Laminations and ripples are common
• Sediments are intensely burrowed
• Stromatolites may be present <em>(if conditions are appropriate)</em>
Tidal Flats
____ are:
• Mouth of a river drowned by the sea
• Brackish water<em> (mixture of fresh and salt)</em>
• May trap large volumes of sediment
• Sand, silt, and clay may be deposited <em>depending on energy level</em>
• Many estuaries formed due to sea level rise <em>as glaciers melted at end of last Ice Age</em>
• Some formed due to tectonic subsidence <em>allowing sea water to migrate upstream</em>
Estuaries
____ Environments are:
• Braided and meandering river and stream systems
• River channels, bars, levees, and floodplains are subenvironments
• Channel deposits are coarse, rounded gravel, and sand.
• Bars are sand or gravel.
• Levees are fine sand or silt.
• Floodplains are covered by silt and clay.
Fluvial
____ are:
• Fan-shaped deposits at base of mountains.
• Most common in arid and semi-arid regions with rapid erosion.
• Sediment is coarse, poorly- sorted gravel and sand.
Alluvial Fans
____ Environments are:
• May be large or small
• May be shallow or deep
• Filled with terrigenous, carbonate, or evaporitic sediments
• Sediments are typically fine grained but may be coarse near the edges
• Fine sediment and organic matter settling in some lakes produced laminated oil shales
• Playa lakes are shallow, temporary lakes that form in arid regions<em> They periodically dry up as a result of evaporation</em>
Lacustrine
<em>(Lakes)</em>
____ Environments are:
• Sediment is eroded, transported, and deposited by ice<em> (glaciers)</em>
• Glacial deposits called till contain large volumes of unsorted mixtures of boulders, gravel, sand and clay
Glacial
____ Environments are:
• Wind is the agent of sediment transport and deposition
• Dominated by sand and silt
• Common in many desert regions
Eolian
These Colors in sedimentary rocks generally indicates the presence of organic carbon and/or iron:
Black & Dark Gray
Organic carbon in sedimentary requires ____ environmental conditions.
Anoxic
The color found in sedimentary rocks indicates the presence of iron oxides is:
Red
This coloration in sedimentary rocks indicates the presence of iron, but in a reduced <em>(rather than an oxidized) </em>state:
Green & Gray
____ Iron generally occurs in oxygen-deficient environments.
Ferrous
<em>(Fe+2)</em>
The size, shape, sorting, and arrangement of grains in a sedimentary rock is called:
Texture
Sedimentary grains are categorized according to size using the ____ Scale.
Wentworth
The distribution of grain sizes in a rock is called:
Sorting
When all of the grains are the same size, the rock is ____ Sorted.
Well
When there is a mixture of grain sizes, such as sand and clay, or gravel and sand, the rock is ____ Sorted.
Poorly
____ Shape is described in terms of rounding of grain edges and sphericity. <em>(equal dimensions, or how close it is to a sphere).</em>
Grain
The shape of ____ is important in naming the coarser-grained sedimentary rocks.
Clasts
These types of rocks have rounded clasts:
Conglomerates
This type of rock has particles that are angular:
Breccia
This feature results from abrasion against other particles and grain impact during transport:
Rounding
Very well rounded sand grains suggest that a sand may have been ____ from older sandstones.
Recycled
The most obvious feature of sedimentary rocks is:
Stratification
This type of Bedding results when a sediment-laden current (such as a turbidity current) begins to slow down:
Graded
An arrangement of beds or laminations in which one set of layers is inclined relative to the others is called ____-Bedding.
Cross
Undulations of the sediment surface produced as wind or water moves across sand are called ____ Marks.
Ripple
____ Cracks describe a polygonal pattern of cracks produced on the surface of mud as it dries.
Mud
Depressions or erosional features formed as a current flows across a bed of sand are called ____ Marks.
Scour
Sandstone classification is based on the ____ of the grains.
Composition
Intense weathering and long transport produce sandstone dominated by:
Quartz
Sandstones with abundant feldspars, and ferromagnesian minerals indicate relatively little ____ & Transport.
Weathering
____ Sandstone is:
• Long time in the depositional basin
• Tectonically stable setting
• Shallow-water environments
Quartz
____ is:
• Short time in the depositional basin
• Rapid erosion
• Arid climate
• Tectonic activity
Arkose
____ is:
• Tectonically active source area & basin
• Rapid erosion
• Mud
Graywacke
____ Sandstone is:
• Deltaic coastal plains
• Nearshore marine environments
• Swamps or marshes
Lithic
Most carbonate rocks form in the ____ ____ environment.
Shallow Marine
Most ____ are the direct or indirect result of biologic activity.
Limestones
Much lime mud forms from the disintegration of ____ ____
Calcareous Algae
<em>(Halimeda and Penicillus)</em>
Tiny spheres composed of concentrically laminated calcium carbonate, forming in warm shallow water with constant wave agitation are called:
Ooids
____ is:
• A calcium-magnesium carbonate mineral <em> CaMg(CO3)2</em>
• Makes up sedimentary rock dolostone
• Forms when magnesium in sea water replaces calcium in calcium carbonate in a limestone
• Only forms in a few areas of the world where intense evaporation of seawater concentrates the magnesium.
Dolomite
____ has two definitions:
• A grain size term
• A layered silicate mineral which behaves plastically when wet and hardens upon drying or firing
Clay
____ Minerals are complex hydrous aluminosilicates with atoms arranged in layered or sheet structures.
Clay
The Weathering product of feldspars are:
Kaolinites
May contain magnesium, calcium, and/or sodium ions and swell when wet:
Smectites
The major clay mineral in ancient shales is:
Illites
A very fine-grained rock composed of clay, mud, silt, and is also fissile:
Shale
____ is:
• A very fine-grained rock composed of tiny<em> (less than 1/256 mm) </em>clay minerals, mica, and quartz
• Individual grains are too small to see
• Feels smooth to the touch <em>(not gritty)</em>
• Not fissile <em>it breaks irregularly</em>
Claystone
____ is:
• A mixture of silt and clay
• A Rock
Mudstone
A ____ Unit is:
• A body of sedimentary, extrusive igneous, metasedimentary, or metavolcanic rock
• Distinguished on the basis of texture, color, composition, etc. and stratigraphic position.
Lithostratigraphic
The smallest lithostratigraphic rock unit is the:
Bed
____ are:
• Lithologically homogeneous
• Distinct and different from rock units above and below
• Traceable from exposure to exposure, and of sufficient thickness to be mappable
• Named for a geographic locality where well exposed
Formations
Subdivisions within formations are called:
Members
A set of similar or related formations is called a:
Group
Every depositional environment puts a distinctive imprint on the sediment, making a particular:
Facies
A sea level rise is called a:
Transgression
When finer-grained <em>(deeper water)</em> facies overlie coarser-grained <em>(shallower water)</em> facies this is sometimes called an ____ Sequence.
Onlap
A sea level drop is called a:
Regression
When coarser-grained (shallower water) facies overlie finer-grained (deeper water) facies this is sometimes called an ____ Sequence.
Offlap
Sedimentation during a regression produces an ____ Sequence.
Offlap
The branch of geology that deals with the correlation of rock units from one area to another is known as:
Stratigraphy
This type of correlation works by Matching up rock units on the basis of lithology and stratigraphic position:
Lithostratigraphic
This type of correlation works by Matching up rock units on the basis of fossils they contain:
Biostratigraphic
This type of correlation works by Matching up rock units on the basis of age equivalence, as determined by radioactive dating methods or fossils:
Chronostratigraphic
Most abrupt contacts are called ____ Planes, resulting from sudden minor changes in depositional conditions.
Bedding
This type of Cross-Section is used to correlate geologic columns from different locations to show how rock units change in thickness, lithology, and fossil content in a given area:
Stratigraphic
This type of Cross-section is used to show the timing of tilting, folding, and faulting of rock units with the tops and bottoms of rock units plotted by elevation to ensure that the folds and faults are depicted clearly.
Structural
This type of Map shows the distribution of various layers and types of rocks in an area using symbols to indicate structural features<em> (folds, faults, etc.)</em> and formation names:
Geologic
This type of Map is Interpretive and depicts the geography of an area at some time in the past:
Paleogeographic
This type of Map shows the thickness of formations or other units in an area:
Isopach
This type of Map shows the distribution of lithofacies that existed at a given time over an area:
Lithofacies
