Chapter 7

Biochemical Chert

Made from Cyrptocrystalline quartz, that is the resultant of plankton like radiolaria and diatoms. These shell compose of Si)2. The ooze on the sea floor. Red chert is jasper

Coastal and Marine Sedimentary Environments

Marine Environments start at high-tide line and extend offshore, to include the deep ocean floor. The temperature and clarity determines the species of organisms that can live in the water, and the availability of clasts and the degree to which wave mtion moves water affects the size of the clasts that accumulate.

Intracontinental Basins

Develop in the interiors of continets, orginally of subsidence over a rift. May continue to subside in pulses even hundred of millions of years after they first formed Illinois and Michigan (has up to 7km of sediment) At times, extensive swamps formed along the shoreline in these basins. Plant matter buried to form coal

Biochemical Limestone

Diversely formed from coral, alagae, clams, oysters, snails, and lmapshells. All of these organisms form calcium carbonate (CaCO3) - either as calcite or aragonite.

Desert Environments

Dry Climate makes it unsuitable for plants to grown, and so the ground surface is exposed. Strong winds can move dust and sand. The sand accumulates into large dunes.

Terrestrial (Nonmarine) Sedimentary Environments

Environments that develop inland, far away from the ocean shoreline that they are not affected by ocean tides and waves. Settle on dry land or under and adjacent to freshwater streams, glaciers, and lakes

Seawater

Evaporites - 80% Halite, 13% Gypsum

Chemical Sedimentary Rock : Evaporties - Product of Saltwater Evaporation

Ex. Bonneville Salt Flats of Utah, formed from the evaporation of an ancient salt lake. For thick deposits of salt to form, large volumes of water must evaporate. . Occurs when plate tectonic movement temporarily cut off arms of the sea. or during a continental rift, when seawater first begings to spill into the rift valley

Sedimentary Rocks

A rock that forms at or near the fsurface of Earth in one of several ways

Clastic Sedimentary Rocks: Production

5 steps 1. Weathering - Grains that form clastic rocks come from the disintegrationg of pre existing bed rock into separate grains from phsycial or chemical weathering. The dissovled ions that eventually participate as new minerals hold the grians together in sedimentary rocks are also a product of weathering 2. Erosing - One formed, grians proudced by weathering do not stay in place forever. Erosion refers to the combination of processes that separate clasts from their orginal substrate. Dossolution of outcrop faces in water, producing dissolved ions, is also a kind of erosion 3. Transportation - Clasts and dissolved ions can be carried away in a "Transport Medium" (Wind, Water, Ice) The ability of the medium to carry sediment depends of viscosity and velocity. 4. Deposition - The transporting medium does not carry the sediment forever as it will undergo deposition. This is the proccess of by which a sediment falls out of the medium. 5. Lithification - The transformation of loose sediment into solid rock. 2 steps Compaction: Burried Sediment is pressed closely together from the pressure generated from the overlying material which squeezes out the air and water trapped inbetween the clasts. Cementation: (Quartz or Calcite) precipitate from groundwater and fill spaces between clasts. The resulting cement acts like glue and holds grains together.

Stratigraphic formation

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

Bed

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

How do Beddings form?

Changes in climate, water depth, curent velocity or the sediment source control the type of sediment deposited at a location at a given time.

Alluvial -Fan Environments

Arid Regions, not enough water for the stream to flow continuously, the stream deposits its load of sediment near the mountain front. Creating an alluvial fan.. Thus becoming breccia and arkose overtime

Micrite

Carbonate, consisting only of very fine carbonate mud

Fossiliferous Limestone

Carbonite, containing visible fossil shells or shell fragments

Classifying Clastic Sedimentary Rocks

Clast Size : The diameter of the grains making up the clastic sedminetary rock. Clast Composition : Not all clasts contain the same mineral or rock fragments. This refers to the makeup of clasts in Sedimentary rocks. Angularity and Sphericity: Angularity indicates the degree to which clasts hae smooth or angular corners and edges. SSphericity, in contrast, refers to the degree to which a clast is equidimensional, or resembles the shape of a sphere. Sorting: The degree to which the clasts in a rock are all the same size. Well sorted sediment consists entirely of sediment of the same size Sedimentary Maturity: Degree to which a sediment has evolved from being just a crushed up version of its source rock to being a well sorted and well rounded group of clasts consisting only of the minerals that are most resistant to weathering. Character of Cement: No all clastic sedminertary rocks have the same kind of cement. Quartz vs Calcite

Lake Environments

Climates where water remians at surface year round. Quiet water cannot move coarse sediment, only fine clay makes it out into the center of the lake, where it settles to form mud on the lake bed. Consist of finely laminated shale

River Environments

Climates with a flowing stream has several distinctive depositional environments. Sandstone, Shale, siltstone

Chalk

Consisting of plankton shells

OilShale

Contains not only clay but also between 15-30% organic material in a form called Kerogen. Kerogen- comes from the fats and proteins tha tamde up the living part of plankton or algae.

Passive Margin Basins

Form along the edges of continents that are not plate boundaries. The remnants of a rift whose evolution successfully led to the information of a mid ocean ridge. Form because thermal sudsidence of streched lithosphere continues long after rifting ceases and sea floor spreading begins. Sediment carried to the sea by river or coastal reefs. Thickness of 15 to 20 km

Rift Basins

Form from continental rifts, regions of the lithosphere that have been stretched.

Foreland Basins

Form on the continent 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 on the surface of the lithosphere, producing wedge shaped depression adjacent to the mountain range that fills with sediment eroded from the range. Fluvial and deltaic strata accumulate in foreland basins

Classes of Sedimentary Rock

Geologist have divided into 4 mour classes, Based on their mode of origin 1. Clastic Sedimentary Rock - Consists of cemented together clast, solid fragments and grains broken off of pre exisitng rocks 2. Biochemical Sedimentary Rock - Consist of shell grown by organisms 3. Organic Sedimentary Rock - Consists of carbon- rich relicts of cellular material from plants or other organisms 4. - Chemical Sedimentary Rock - Comes from minerals that precipitated directly from surface water solutions.

Marine Delta Deposits

Host many different sedimentary environments, including swamps, channels, floodplains, and submarine slopes. Caused from changing sea levels

Glacial Environments

Ice is a solid, it can move sediment of any size. Gathers all this sediment, and then leaves it as glacial till when melted.

Shallow Marine Clastic Deposits

In deeper water, where wave energy does not stir the sea floor, finer sediments cn accumulate. The water here is only meters to a few tens of meters deep. Clastic Sediment in this area is fine grained, wll sorted, and well rounded. Mollusks, gastropods, and worms live in the area.

Graded Bed

Larger grains sink faster through a flud than do finer grains, so the coarsest sediments settles out first. Progressively finer grains accumulate on top, with the finest sediment (clay) settling out last.

Sandstone

Layers of beach or dune lithify into Sandstone

Conglomerate

Layers of river gravel lithify into conglomerate When the river water slows, pebbles and cobbles stop moving and form a mound, or a bar, of gravel

Diagenesis

Lithification is an apsect of a broader phenomenon. Diagenesis is the term for all physical, chemical, and biological processes that transform sediment into sedimentary rock Occurs between temps of 150-300

Breccia

Lithification of an accumulation of angular clasts yields Breccia Large blocks of rock tumble off a cliff and slam into other blocks already at the bottom.

Delta

Located at the mouth of the river, Settling of silt and mud

Dune

Looks like a ripple, only it's large. May be tens of centimeters to several meters high Wind formed dunes in the desert may be tens of meters to over 100 meters high

Bed-Surface Markings

Mud Cracks - mud layer dries up after deposition, it cracks into roughly hexagonal plates that curl up at their edges. Scour Marks - Current flow over a sediment surface, they may erode small troughs parallel to the current flow. Can be buried and preserves Fossils - Fossils are relicts of past life. Some fossils are shell imprints, footprints, or feeding traces on a bedding surface

Tavertine (Chemical Limestone)

Not like most limestone which is biochemical, consist of calcium carbonate (CaCO3) that precipitate directly from groundwater that has seeped out at the grund surface either in or or cold water spring or on the wall of caves. Microbes can accelerate the process of precipitiation. @ springs it forms terraces and mounds that are meter or hundred of meters thic. @ Caves it builds up to form complex growth called speleothems Tufa - type of tavertine that has abundant large pores

Dolostone

Not pure calcite. Differs from limestone because it contains the mineral dolomite. Formed from a solid calcite and a magnesium bearing ground water.

Deep Marine Deposits

Only fine clay and plankton provide a source for sediment. Forming mudstone, and plankton shells to form chalk. Deposits of mudstone, chalk or bedded chert indicate a deep marine origin.

Chemically Precipitated Chert

Outcrops of limestone that contain nodules(small,rounded lumps or lenses) of a black chert. Used as arrowheads and scrapers The chert nodules grew when microscopic quartz crystals gradually precipitatd and replaced calcite crystals within a bed of limestone. Forms petrified wood,

Organic Sedimentary Rock

Oxygen poor quiet water in swamps, lagoons or lakes, the debris settles along with other sediments and gets buried/preserved. Chemical Reaction that transforms it into Organic Sedimentary Rock, organic chemicals can burn to produce energy/ Coal and Oil Shale

Bedforms

Ripple marks and Dunes.

Chemical Sedimentary Rock

Rock formed primarily by the precipitaition of minerals directly out of water solutions. Usually has a chrystlline structure, new crystals grow thru the expense of the old ones (Recrystilization) Crystals can be coarse or to small to see

Turbidity Current

Sediment falling down a submarine slope mixes with water to create a murky, turbulent cloud. The cloud is denser than clear water and thus flows downslopelike an underwater avalanche. Turbidite - the deposits of a turbidity current.

Strata

Several beds together

Adjectives for Sed Rocks

Siliceous rocks - contains mostly quartz Agrillicaeous rocks - contian mostly clay minerals, Carbonate rocks - mostly calcite and or dolomite

Floodplains

Silt and Clay may accumulate in flat areas bordering streams, called flood plains, Become submerged during floods

Silt & Mud

Silt when lithified becomes siltstone Mud when lithified becomes shale or mudstone

Bedding plane

The boundary between the two beds

Main Bedding

The boundary between two successive layers

Depositional Environment

The conditions in which the sediment was deposited distinguishable by grain size, clast composition, soritng, bed surface marks, cross bedding, and fossils to identify a depositional environment.

Cross Bedding

The growth of both Ripples marks and Dunes

Bedding

The overall arrangement of sediment into a sequence of beds

Subsidence

The process by which this sinking takes place and the term. Lithosphere sinking

Layer or Beds of Sedimentary Rock

They are like the pages of a book, recording tales of ancient events and ancient environments. Occur only in the upper part of the crust, and form a cover that buries the underlying "basement" of igneousand or metamorhpic rock

Mountain Stream Environments

Turbulent streams rush downslope in steep-sided valleys. Has the ability to carry large clasts, during floods boulders and cobbles can tumble down the stream bed. The largest clast begin to settle out, and only sand and mud continue.

Shallow Water Carbonate Environments

Very little sand and mud allows the water, warm , clear, nutrient rich can hst an abundance of organisms with carbonate shells, which becomes carbonate sediment. Reef/lagoons Transform into various kinds of Limestones

Coastal Beach Sands

Waves winnow out mud and silt, and the back and forth current creates ripples in the sand. Well- sorted, medium grained sandstone could be the remnants of a beach environment

Regression

When the sea level falls, the coast migrates seaward. The record of a regression will not be well preserved because as sea level drops areas that had been sites of deposition become exposed to erosion. Depositional Sequence : A succession of strata deposited during a cycle of transgression and regression

Bioturbation

Worms, clams, and other creatures chrun sediment and may leave behind burrows. This disrupts the perseverance of the bed

Coal

black, combustible rock containing between 40-90% carbon, the remainder is clay and quartz Macerals - typicaly 85% carbon and 15% oxygen, nitrogen, and hydrogen Forms from plant remains

Wacke

poorly sorted sedimentary rock, consists of sand grains and lithic fragments suspended in a matrix of mud

Transgression

relative Sea level rises, the shoreline migrates inland. terrestrial sediments are progressively buried by coastal sediments, and coastal sediments are buried by deeper water sediment.

Ripple Marks

relatively small (Ginerally no more than a few centimeters high) elongated ridges that form on a bed surface at right angles to the direction of current flow. If the current always flow in the same direction, the ripple marks will appear asymmetric. Along the shore, ripple marks appear to be symmetric from the back and forth current.

Glacial Till

the debris left behind as Glaciers melt

Sedimentary Basin

the resulting sediment filled depression. Different kinds of sedimentary basins

Agate

type of chert, precipitiates in concentric rings inside open hollows in a rock.

Diamicton

very poorly sorted sediment that contains clasts of all sizes. Contains cobbles or boulders surrounded by a matrix of sand, silt, and clay. Rock made from Diamicton is Diamictite Formed from the lithification of debris flow (Mud mixed with larger clasts), both on land and underwater