Geol 102 Exam 2

Clastic sedimentary rocks

Rocks formed from the lithification of transported sediments, classified by grain size.

Biochemical sedimentary rocks

Rocks formed through the precipitation of materials in solution or lithification of organic material.

Well-sorted grains

Grains that imply consistent energy conditions, often found in environments like beaches or sand dunes.

Poorly sorted grains

Grains that imply inconsistent energy conditions, typically found in environments like glaciers or landslides.

Bedding

Depositional layering in sedimentary rocks that can indicate various environmental conditions.

Laminations

Bedding layers that are less than 1cm thick, indicating fine sediment deposition.

Graded beds

Bedding where grain size gets smaller as you move up the layer.

Cross bedding

Inclined bedding surfaces indicating sediment transport by wind or water.

Imbrication

The preferred orientation of clasts indicating the direction of sediment transport.

Ripple marks

Physical features formed by the movement of wind or water, including symmetrical wave-formed and asymmetrical current ripple marks.

Fluvial environment

Related to rivers and streams, characterized by features like point bars and current ripples.

Glacial outwash

Sediment deposited by glacial meltwaters, often creating braided streams.

Dropstones

Rocks that fall to the bottom of a glacial lake from melting ice.

Varves

Layered sediments found in glacial lakes, indicating seasonal deposition.

Transitional environments

Areas like deltas and tidal flats where sedimentary characteristics change between aquatic and terrestrial.

Reefs

Biologically active areas typically composed of fossiliferous limestone.

Deep ocean deposits

Characterized by fine sediments like micrite, found in deep ocean environments.

Bedding

depositional laying in sedimentary rocks

laminations

bedding that is less than 1cm thick

graded bedding

grain size gets smaller as you move up

cross bedding

inclined bedding surfaces, tangent on the bottom

tabular cross bedding

very horizontal cross-bedded units, essentially flat at an angle; planar basal contacts

trough cross bedding

curved contacts, end at a point, common in stream channels

imbrication

preferred orientation of clasts

ripple marks

formed by movement of wind or water

wave formed ripple marks

symmetrical due to oscillating currents

current ripple marks

asymmetric due to current flowing in one direction

mud cracks

clay shrinks when dry, indicating wet/dry climate

trace fossils

tracks or burrows

carbonates

made of calcite; micrite, fossiliferous limestone, coquina

evaporites

form when water evaporates in bay or lake, rock gypsum and salt

diatomite

exoskeletons made of silica

fluvial or meandering streams

point bars that make trough beds and current ripples

glacial outwash

creates braided streams carrying sand and gravel

Glacial lakes

dropstones are rocks that fall to the bottom of the lake

glacial lakes

varves which are laminated mud deposits

moraines

till, poorly sorted sediment dropped by ice

playa lakes

evaporite deposits and mudcracks

transitional environments

delta = ripples and crossbeds, tidal flats = alternating cross beds, swamp, beach/barrier islands

continental shelf

submerged continent, has underwater avalances that deposit mud and sand (graded bedding)

reefs

fossiliferous limestone

deep ocean

micrite