Marshak Chapter Six

what is travertine (chemical limestone)?

- it is a rock composed of crystalline calcium carbonate (CaCO3) that precipitates directly from groundwater that has seeped out at the ground surface either in hot or cold-water springs, or on the walls of caves

What are glacial environments?

-Because ice is solid, it can move sediment of any size. -As the glacier moves, it carries along all the sediment that falls on its surface or gets plucked from the ground at its base or sides -When the ice melts away, the sediment that had been in or on the ice accumulates as glacial till. -Till is unsorted and unstratified-it contains clasts raining from clay size to boulder size mixed together

What are the ways that sedimentary rocks form?

-By the cementing together of loose clasts (fragments or grains) that had been produced by physical or chemical weathering of pre-existing rock; -By the growth of mounds of shells; -By the cementing together of shells and shell fragments; -By the accumulation and subsequent alteration of organic matter derived from living organisms; -Or by the precipitation of minerals directly from surface-water solutions

What are two types of organic sedimentary rocks?

-Coal and oil shale -what do they provide? fuel for modern industry

How do particles settle in the turbidity current?

-Downslope, the turbidity current slows, and the sediment that it carried starts to settle out. -Larger grains sink faster through a fluid than do finer grains, so the coarsest sediment settles out first. -Progressively finer grains accumulate on top, with the finest sediment (clay) settling out last. -This process forms a graded bed, meaning a layer of sediment in which grain size varies from coarse at the bottom to fine at the top. -A deposit from a turbidity current is a turbidite

How does coal form?

-Forms when plant remains have been buried deeply enough and long enough for the material to become compacted and to lose significant amounts of volatiles (hydrogen, water, CO2, and ammonia). -As the volatile seeps away, the concentration of carbon increases

What are organic sedimentary rocks?

-In some environments, the organic debris settled along with other sediment and is eventually buried. -When lithified, organic-rich sediment becomes this type of rock

What is coal?

-It is a black, combustible rock containing between 40 and 90 percent carbon. -The remainder consists of clay and quartz

What is the connection between sediment and sedimentary structures?

-Many clastic sediments accumulate in moving fluids (wind, rivers, or waves). -Sedimentary Structures develop at the interface between the sediment and the fluid. -These structures, called bedforms, develop at a given location and reflect such factors as the velocity of the flow and the size of the clasts

What is biochemical limestone?

-Numerous organisms have evolved the ability to extract dissolved ions from seawater to make solid shells. -When the organisms die, the solid material in their shells survives. -This material, when lithified, comprises biochemical sedimentary rock.

What are river environments?

-Rivers transport gravel, sand, silt, and mud. The coarser sediment tumbles along the bed in the rivers challen and collects in cross-bedded, rippled layers while the finer sediments drifts along, suspended in the water. This fine sediment settles out along the banks of the river, or on the floodplain -On the floodplain, mud layers dry out between floods, so they develop mud cracks. River sediments lithify to form rippled sandstone, siltstone, and shale. -Typically, coarser sediments occur in elongate bands, relicts of river channels. -Layers of fine-grained floodplains deposits surround the relict of channels, so in cross section, the channel has a lens-like shape.

What are terrestrial (non marine depositional) environments?

-These develop inland, far enough from the shoreline that they are not affected by ocean tired and waves -Terrestrial sediments, or non marine sediments, accumulate either on dry land or under and adjacent to freshwater.

What are passive-margin basins?

-They are underlain by stretched lithosphere, the remnants of a rift whose evolution successfully led to the formation of a mid-ocean ridge and subsequent growth of a new ocean basin. -these basins form because subsidence of stretched lithosphere continues long after lifting stops. -They fill both with sediment carried to the sea by rivers, and with carbonate rocks formed in coastal reefs. -Passive-margin basins include some of the thickest accumulations of sediment on earth

How is chert formed?

-This formed from the shells of silica-secreting plankton that accumulated on the seafloor. -Gradually, after burial, the shells dissolved, forming a silica-rich gel -Chert then formed when the gel solidified

Sediment in alluvial fans may...

-accumulate close to the source, so it will not have undergone much chemical weathering -Alluvial-fan sediments become breccia, conglomerate, and arkose.

What are marine delta deposits?

-after following the river downstream for a long distance, we reach its mouth, where it emptied into the sea. -Here, the river water stops flowing, so sediment settles out to build a delta of sediment out into the sea. -They include swaps, channels, floodplains, and submarine slopes.

what is angularity and sphericity?

-angularity indicates the degrees to which clasts have smooth surfaces, or have sharp corners and edges. -Sphericity refers to how closely the shape of a clast resembles a sphere

what is dolostone?

-another carbonate rock, dolostone, differs from limestone in that it contains the mineral dolomite (CaMg[CO3]2), which contains equal amounts of calcium and magnesium. -Where does the magnesium come from? Most dolostone forms by a chemical reaction between solid calcite and magnesium-bearing groundwater. -This change may take place beneath lagoons along a shore soon after the limestone formed, or a long time after, after the limestone has been buried deeply

The deposition of graded bedding by turbidity currents:

-as the turbidity current slows, larger grains settle first, followed by progressively finer grains -As the process repeats, a succession of graded beds accumulates

What are some types of biochemical sedimentary rocks?

-biochemical limestone -biochemical chert

What characteristics are most useful when classifying clastic sedimentary rocks?

-clast size -clast composition -angularity and sphericity -sorting -character of cement

What are the four types of sedimentary rocks?

-clastic -biochemical -organic -and chemical

What is oil shale?

-contains not only clay but also between 15 and 75 percent organic materials in a form called kerogen. -The kerogen in oil shale comes from the fats and proteins that made up the living part of plankton or algae. -If the tiny organisms settle in an environment where they do not immediately rot away or get eaten, they mix with the clay minerals in mud. -When the mud gets buried and lithified, to form shale, the organic material transforms into kerogen. -The presence of organic material colors oil shale black.

Why does bedding form?

-from the accumulation of sediment by...changes in the climate, water depth, current velocity, or the sediment source control the type of sediment deposited at a location at a given time

What are examples of terrestrial environements?

-glacial environments -mountain stream environments -alluvial fan environments -desert environments -river environments -lake environments

What is transportation?

-gravity, wind, water, or ice can carry sediment. -Solid ice can transport sediment of any size -Very fast-moving, turbulent water can transport coarse fragments (cobbles and boulders), as well as finer ones; -Moderately fast-moving water can carry only sand and gravel; -Slow-moving water carries only finer-grained sediments, such as silt and clay. -Strong winds can move sand and dust, but gentle breezes carry only dust

what are mud cracks?

-if a mud layer dried up after deposition, it cracks into roughly hexagonal plates that typically curl up at their edges. -they are the openings between the plates

What are shallow-water carbonate environments

-in shallow-marine settings, where relatively little sand and mud enter the water, warm, cleearm nutrient-rich water can host an abundance of organisms with carbonate shells, which eventually become carbonate sediment -Beaches collect sand composed of shell fragments; lagoons are sites where carbonate mud accumulates; and reefs consist of coral and coral bears -Shallow-water carbonate environments transform into various kinds of limestone

What are lake environments?

-in temperate climates, where water remains at the surface throughout the year, lakes form. In the offshore portions of a lake, the deeper water is relatively quiet, and clay can settle out to form mud on the lake bed. When lithified, such laucustrine mud turns into shale

What is fossiliferous limestone?

-it consistents of visible fossil shells or fragments

when does salt precipitation occur?

-it happens when saltwater becomes supersaturated, meaning that it can't keep all the dissolved ions that it contains in solution. -This situation happens because evaporation removes water from a water body faster than the rate at which new water enters. - This process takes place in desert lakes and along the margins of restricted seas -The specific type of salt minerals comprising an evaporite depends on the amount of evaporation

what is sorting?

-it indicates the proportion of clasts in a rock that are the same size, whereas poorly sorted sediment contains a mixture of clast sizes

What is chert?

-it is a biochemical sedimentary rock. -This bedded chert developed on the deep seafloor by the deposition of plankton that secrete silica shells

What type of a rock is sandstone?

-it is a clastic sedimentary rock -it feels gritty with small grains of quartz sand grains cemented together -It consists of loose classes that have been stuck together to form a solid mass -The clasts, or grains, can consist of individual minerals (such as grains of quartz or flakes of clay) or of chunks of rock (such as pebbles of granite)

what is oil?

-it is an organic sedimentary rock. -It is deposited in layers (beds), just like other kids of sedimentary rocks

What is petrified wood?

-it is chert that forms when silica-rich sediment, such as ash from a volcanic eruption, buries trees. -The silica dissolves in groundwater and then later precipitates as microcrystalline quartz within wood, gradually replacing the wood's cellulose. -The chert deposit retina the shape of the woods cells and the growth rings within it

What is biochemical chert?

-it is made from cryptocrystalline quartz consisting of quartz grains that are too small to be seen without the extreme magnification of an electron microscope.

What is limestone?

-it is rock that breaks into chunky blocks. -It doesn't look like a pile of shell fragments. -This is because processes change the texture of the rock over time after it has been buried deeply

what is deposition?

-it is the process by which sediment settles out of the transporting medium. -Sediment settles out of wind or moving water when these fluids slow down, because as the velocity decreases, the fluids no longer have the ability to carry sediment. -Sediment carried by ice accumulates when the ice melts

What is lithification? general idea

-it is when sediment hardens into a rock -it is an aspect of a broader phenomenon called diagenesis

What is a dune?

-it looks like a ripple, but only much larger

What is the concept of weathering?

-it showed how it attacks solid rock to break it down into ions and loose sediment grains

What is the character of cement?

-not all clastic sedimentary rocks contain the same kind of cement. -In some, the cement consists predominantly of quartz, whereas in others, it consists predominantly of calcite.

What is chalk?

-plankton shells

What is clast composition?

-refers to the makeup of clasts in sedimentary rock. -Clasts may be composed of rock fragments or individual mineral grains. -Sand typically consists mostly of quartz grains

What are deep-marine deposits?

-sailing far offshore. Along the transition between coastal regions and the deep ocean, turbidity currents deposit graded beds. -In the deep-ocean realm, only fine clay and plankton provide a source for sediment. The clay eventually settled out onto the deep seafloor, forming deposits of finely laminated mudstones, and plankton shells settled to form chalk (from calcite shells) or chert (from silica shells). -Consequently, deposits of mudstone, chalk, or bedded chert indicate a deep-marine origin

How does biochemical limestone form?

-seacreature calcium carbonate shells crystalline as calcite or argonate. -When the organisms die, the shells remain and may accumulate

What does the diagram of G.K. Gilbert show?

-small lakeshore deltas contain three components: topset beds composed of gravel, forest beds of gravel and sand, and silty bottomset beds. -(gravel collects in nearly horizontal topset beds. Gravel and sand collect in sloping forest beds. Finer sediment collects in horizontal bottomset beds.)

What are marine environments?

-start at the high-tide line and extend offshore, to include the deep seafloor. -The type of sediment deposited at a given location depends on the climate, water depth, and whether or not clastic grains are available

The composition of the clasts depends on the...

-the composition of rock from which they were derived and on the degree of chemical weathering that the clasts have undergone. -Therefore, the types of clasts that accumulate in a sedimentary deposit varies with location.

What happens during transgression and regression?

-the positions of depositional environments migrate, so the depositional environment at a given location changes over time. -These processes acting over time can lead to the formation of broad blankets of sediment.

What are desert environments?

-these are very dry climates where few plants can grow and the ground surface lies exposed. -Strong winds can move dust and sand. -The dust gets carried away and the resulting well-sorted sand can accumulate into dunes. -Thus, thick layers of well-sorted sandstone, in which we can find large cross beds, are relics of desert and-dune environments

what are intracontinental basins?

-these develop in the interiors of continents, initially because of subsidence over a rift. -They continue to subside in pulses, even hundreds of millions of years after they formed

What are rift basins?

-these form in continental rifts, regions where the lithosphere is stretching horizontally, and therefore thins vertically. -As the rift grows, slip on faults drops blocks of crust down, producing low areas-narrow basins bordered by elongate mountains ridges. -These basins fill with terrestrial sediment. -In desserts, overlapping alluvial fans line the margins of the basins.

What are foreland basins?

-these form on the continental side of a mountain belt because the forces produced during convergence or collision push large slices of rock up faults and onto the surface of the continent. -The weight of these slices pushes down the surface of the continent, producing a wedge-shaped depression adjacent to the mountain range that fills with sediment eroded from the range -Fluvial and deltaic strata accumulate in foreland basins

What are beds?

-they are layers of sedimentary rocks -they occur in the upper part of the crust, and form a cover that buries the underlying basement of igneous and/or metamorphic rock

What are ripple marks?

-they are relatively small (generally no more than a few centimeters high) elongated ridges that form on a bed surface at right angles to the direction of current flow

what are evaporites?

-they are the products of saltwater evaporation

what is chemically precipitated chert?

-this forms when microscopic quartz crystals gradually replaced calcite crystals within a body of limestone was deposited

What are shallow-marine clastic deposits?

-this is offshore. In deeper water, where wave energy does not stir the seafloor, fine sediment can accumulate. It is only a few meters deep. -Clastic sediments that accumulate in this environment tend to be fine-grained, well-sorted, well-rounded silt, and they are inhibited by a great variety of organisms like mollusks and worms. -If you see beds of siltstone and mudstone containing marine fossils, you may be looking at shallow-marine clastic deposits

What are coastal beach sands?

-this is the coast. -Oceanic currents transport sand along the coastline. -The sand washes back and forth in the surf, so it becomes well sorted (waves winnow out silt and mud) and well rounded, and because of the back and forth movement of ocean water over the sand, the sand surface may become rippled. -If you find well-sorted, medium grained sandstone, perhaps with ripple marks, you may be looking at the remnants of a beach environment

What are Alluvial fan environments?

-this is the mountain front, where the fast-moving stream emptied onto a plain. - In arid regions, where there is not enough water for the stream to flow continuously, the stream deposits its load of sediment near the mountain front, producing a wedge-shaped arpon of gravel and sand called an alluvial fan.

What is lithification?

-this is the transformation of loose clasts into solid rock -step a) compaction: when the weight of overburden squeezes air or water out from between grains, so the grains can fit together more tightly -step b) cementation: minerals (commonly quartz or calcite) precipitate from groundwater and fill the remaining spaces between clasts, to form a cement that binds grains together

What is clast size?

-this refers to the diameter of fragments or grains making up a rock -The names used for clast size, listed in order from coarsest to finest, are: boulder, cobble, pebble, sand, silt, and mud

What are mountain stream environments?

-turbulent streams rush downslope in steep-sided valleys. -This fast-moving water has the power to carry large clasts. -During floods, boulders and cobbles can tumble down the streambed. -Where slopes decrease and water flow slows, the larger clasts settle out to form gravel and boulder beds, while the stream carries finer sediments like sand and mud farther downstream. -Sedimentary deposits of a mountain stream include breccia and conglomerate

What is micrite?

-very fine carbonate mud

What are the steps to the production of clastic sedimentary rocks?

-weathering -erosion -transportation -deposition -lithification

what causes Travertine (chemical limestone) precipitation?

-when the groundwater degasses, meaning that some of the carbon dioxide that had been dissolved in the groundwater bubbles out solution, for removal of carbon dioxide encourages the precipitation of carbonate -Precipitation also occurs when water evaporates, thereby increasing the concentration of carbonate

What is a bed?

A single layer of sediment or sedimentary rock with a recognizable top and bottom

How does a small delta form?

At the mouths of streams that empty into lakes, small delta may form. A delta is a wedge of sediment that accumulates where moving water enters standing water

What are layers of sedimentary rocks called?

Beds

What does the size, angularity, and sphericity and sorting of clasts depend on?

It depends on the transporting medium (water, ice, or wind) that carries the clasts and, in the case of water or wind, on both the velocity of the medium and the distance of transport.

what is sedimentary structure?

It describes the layering of sedimentary rocks, surface features on layers formed during deposition, and the arrangement of grains within layers

What is a sedimentary rock?

It is a rock that forms at or near the surface of the earth in many ways

What are strata?

Several beds together

What did rescuers find at Scott's last campsite?

They found Edward Wilson's rock specimens, some of which contained fossils of Glossopteris, the fossil whose distribution alfred wegener would use as evidence of continental drift

What do some sea creatures (clams, oysters, and snails) share in a common characteristic?

They make solid shells of calcium carbonate (CaCO3)

What are sedimentary basins?

Thick accumulations of sediment form only in special regions where the surface of the earth's lithosphere sinks, providing space in which sediment can collect

What is cross bedding?

a pattern of alternating beds of sediment that often form as wind and water deposit the sediments.

What is a stratigraphic formation?

a sequence of strata that is distinctive enough to be traced as a unit across a fairly large region

Sediment deposited in an alluvial fan, close to its source, can be feldspar rich. Lithification of this sediment yields...

arkose

what are scour marks?

as currents flow over a sediment surface, they may erode small troughs, called scour marks, parallel to the current flow

How are sedimentary rocks divided?

based on their mode of origin

Lithification of an accumulation of angular clasts yields...

breccia

What is weathering?

clasts form by disintegration of bedrock into separate grains due to physical and chemical weathering

Layers of river gravel lithify into...

conglomerate

What is used to identify a depositional environment?

grain size, composition, sorting, sedimentary structures, and fossils

When 80 percent of the water evaporates, ____ forms;

gypsum

When 90 percent of the water evaporates, ____ precipitates

halite

Sedimentary structures provide clues that:

help geologists understand the depositional environment in which sediments accumulated

How does carbonate rocks (limestone) form?

if shells are buried and preserved, these shells become limestone

What is diagensis?

is used for all the physical, chemical, and biological processes that transform sediment into sedimentary rock and that alter characteristics of sedimentary rock after the rock has formed -Once sediment has been deposited, it undergoes various changes, known as diagnesis, in response to pressure and to interaction with groundwater.

What is Transgression?

it is when relative sea level rises and the shoreline migrates inland

What is regression?

it is when the relative sea level falls and the coast migrates seaward

What is subsidence?

it refers to the process by which the surface of the lithosphere sinks, and the term sedimentary basin for the sediment-filled depression

Layers of beach or dune sand lithify into...

sandstone

Layers of mud, exposed beneath marsh grass, lithify to form...

shale

what is a bedding plane?

the boundary between two beds

What is a delta?

the mouth of the river

What is turbidity current?

the moving submarine sediment suspension

What are clastic sedimentary rocks and how do they form?

these rocks are formed from cemented-together clasts, solid fragments and grains broken off of pre-existing rocks

what are organic sedimentary rocks?

these rocks are made up of minerals that reciprocate directly from water solutions

What are biochemical sedimentary rocks?

these rocks consist of shells

What are chemical sedimentary rocks?

they consist of rock formed primarily by the precipitation of minerals from water solutions

what is erosion?

this refers to the combination of processes that separate rock or regolith (surface debris) from its substrate. Erosion involves abrasion, falling, plucking, scouring, and dissolution, and can be caused by moving air, water, or ice

The ability of a medium to carry sediment depends on the mediums...

viscosity and velocity