Geology lesson 5

A horizon

layer of soil; particles mixed with humus; area where soluble chemicals are leached from

abyssal plain

the vast flat ocean floor

aeolian

deposits of windblown sediments

alluvial

deposited by the intermittent flow of water

B horizon

layer of soil; particles mixed with humus; chemicals removed from the upper layers and collected here

bedding planes

the planes that separate the layers in sedimentary and some volcanic rocks

biochemical sedimentary rocks

sedimentary rock formed when minerals precipitate out of an aqueous solution as a result of biological processes

bioturbation

disruption of bedding layers as a result of organisms burrowing through soft sediment

breccia

clastic sedimentary rock composed of large angular grains in a finer matrix of sediment

C horizon

layer of soil; slightly weathered parent material

cementation

process of gluing sediment grains together

chalk

biochemical sedimentary rock composed of high concentrations of shells from a microorganism

chemical sedimentary rocks

sedimentary rocks formed from precipitated materials

chemical weathering

weathering processes that cause a change in composition

chert

inorganic chemical sedimentary rock formed as silica precipitates from water

clastic sedimentary rocks

sedimentary rocks formed as sediment is collected, compacted and cemented together

claystone

clastic sedimentary rock made of clay

compaction

process of squeezing air out of a sediment layer due the weight of overlying materials

conglomerate

clastic sedimentary rock composed of large rounded grains in a finer matrix of sediment

coquina

biochemical sedimentary rock composed of loosely-cemented shells and shell fragments

delta

deposit of sand and other fine materials that form as sediment drops out where rivers enter lakes or oceans

diagenisis

process associated with sedimentary rock formation where sediments are slightly chemically altered by heat and pressure

dissolution

a reaction that dissolves minerals in bedrock and leaves the ions in solution

erosion

a mechanical process, usually driven by water, gravity, wind, or ice that removes sediment from the place of weathering

evaporites

group of inorganic sedimentary rocks formed from salts

fissile

property of rock resulting in it splitting into thin layers

fluvial

of a river

fossiliferous limestone

biochemical sedimentary rock with many visible fossils

frost wedging

rock breaking apart as water in cracks freezes and expands

graded bedding

a sequence of increasingly coarse- or fine-grained sediment layers

imbrication

a stack of large and usually flat clasts—cobbles, gravels, mud chips, etc.—that are aligned in the direction of fluid flow

inorganic sedimentary rock

sedimentary rock formed when minerals precipitate out of an aqueous solution

lagoon

small body of seawater located inland from the shore or isolated by another geographic feature, such as a reef or barrier island

limestone

sedimentary rock composed of calcite; comes in numerous forms with varying names

lithification

process of compaction and cementation of particles resulting in the formation of a rock

littoral zone

the beach

lacustrine

lake systems and deposits

mechanical weathering

weathering processes that cause a reduction in grainsize

mudcracks

cracks in clay-rich sediment formed as the material is submerged underwater and later dries out

mudstone

clastic sedimentary rock made of mud (silt and clay)

O horizon

layer of soil; top layer of organic material

organic sedimentary rocks

sedimentary rocks made of lithified organic material

oxidation

chemical reaction that causes rust in metallic iron; occurs geologically when iron atoms in a mineral bond with oxygen

paleocurrents

or currents found in the geologic past

pressure expansion

the process by which a sudden pressure drop causes the rock to rapidly expand and crack

provenance

the consideration of the source of the sediment or sedimentary rock

R horizon

layer of soil; unweathered, parent material

raindrop impressions

small pits or bumps found in soft sediment

reef

any topographically-elevated feature on the continental shelf, located oceanward of and separate from the beach

ripples

ridges or undulations in the a sediment or sedimentary rock layer

root wedging

rock breaking apart as roots grow into cracks

rounding

property of sediment grains describing how angular or smooth their edges are

sandstone

clastic sedimentary rock made of sand

seamount

the base of an ocean island left standing underwater after the upper part is eroded away by waves

sediment

pieces of minerals or rock created through weathering that is transported

shale

clastic sedimentary rock made of mud (silt and clay); fissile

siltstone

clastic sedimentary rock made of silt

soil

combination of air, water, minerals, and organic matter that is made when weathering breaks down rock or sediment and creates weathering products in place

soil horizons

distinct layers of soil

sorting

property of a sediment describing the range of grain sizes

tidal flats

sedimentary environments that are regularly flooded and drained by ocean tides

turbidite deposits

coarse materials deposited just offshore under ocean water; occurs as sediment is disturbed creating dense slurries that flush down the underwater canyons and deposit in areas that generally only have fine sediment

travertine

inorganic chemical sedimentary rock formed by the chemical precipitation of calcite into bands