Chapter 7 - Sediments and Sedimentary Rocks Flashcards
Stratification
Arrangement of sediment in distinct layers (layering of rocks) (strata)
Bedding
Layered arrangement of strata in a body of sediment or sedimentary rock
Bed
individual layer - distinguished by differences in thickness or character
Bedding plane
top or bottom surface of a bed
Clastic Sediment
loose, fragmental detritus produced by mechanical breakdown of older rocks
Clast
an individual particle of clastic sediment
Poortly Sorted
Wide particles size range
Well Sorted
Narrow size range (same size particles)
non-sorted sediment
different sizes arranged chaotically - without obvious order
rhythmic layering - Varves
paired lighter (nonorganic) and darker (organic) colored lake sediments
cross bedding
beds inclined with respect to thicker stratum in which they occur (created from sand dunes)
graded bedding
particles grade upward from coarser to finer (created from streams)
Mineral composition
most coarse clastic sediments consist of those mineral grains and rock fragments least susceptible to chemical/physical breakdown (quartz is common)
Chemical Sediment
formed by precipitation of minerals from solution in water
Biogenic Sediment
composed mainly of fossils (remains of plants and animals)
Bioclastic sediment
composed largely of fossil fragments
Deep-sea ooze
Accumulation of microscopic marine organisms on sea floor
Sedimentary Facies
any sediment that can be distinguished from a contemporary sediment that formed in different depositional environment
Facies
The character of a rock expressed by its formation, composition, and fossil content
Lithification
process whereby unconsolidated sediment is converted into rock (e.g. sand into sandstone)
Diagenesis
all changes that occur after deposition and during and after lithification
Compaction
weight of sediment reduces pore spaces and forces out water - fine grain rocks (e.g. mudrocks)
Cementation
dissolved substances precipitate from water in pores - course grain rocks (e.g. sand and gravel into stone)
Recrystallization
less stable minerals may recrystallize to more stable forms
Chemical alteration
if oxygen is present organic remains conveted to CO2 and Water. if oxygen is absent organic matter transforms into mostly carbon (e.g. plants turn into coal)
Clastic Sedimentary Rocks
classified on basis of predominant particle size
Sole marks
collective term for features preserved on bedding surfaces
ripple marks
preserved in sand that was moved by wind, streams, or waves
mud cracks
polygonal markings caused by shrinking and cracking of drying mud
trace fossils
footprints and trails of animals
raindrop impressions
small indents left from raindrops
color
may indicate if sediment was deposited in reducing (black) or oxidizing (red) environment
