Sedimentary Rocks Flashcards
____% of the land being sedimentary rocks
75%
Deposition or sedimentation occurs when
particles settle out or dissolved minerals precipitate
Burial occurs when
layers of sediment accumulate and compact previous layers
As a river carrying sediments enters the ocean, the coarser material (sand) is deposited ___
first
As a river carrying sediments enters the ocean, the finer material (silts and clays) is deposited ___
last (into deeper waters)
Clastic sedimentary rocks
products of the mechanical weathering of pre-existing rocks and are transported by gravity, water, ice or wind to accumulate as sediments in streams, lakes, oceans, soils or deserts
Chemical sedimentary rocks
do not form from themechanical break-up and transport of grains. Instead, they derive from the precipitation of minerals from supersaturated solutions
Examples of chemical sedimentary rocks
limestone (composed of calcite)
chert (composed of silica)
iron formations (composed of Fe oxides)
evaporites (gypsum and halite)
Biological sedimentary rocks
formed biologically from the shells of plankton
Examples of biological sedimentary rocks
diatoms and foraminifera
Sorting
the tendency for variations in current velocity to segregate sediments according to size (larger sand particles being deposited first)
Well-sorted sediments have been subject to ____ water or wind action
prolonged ( a lot)
Poorly-sorted sediments are either ____ from their source or deposited by ____
not far from their source (not far removed)
glaciers
The more round sand is, the ____ it has been transported
longer
The longer the transport process the more ____ the particles are subject to, making the rocks ____ and ____
abrasion, smaller, rounder
Sedimentary structures
sediment is deposited in horizontal layers called beds. in a sequence called strata. The sediment sinks and becomes thicker, with the oldest sediment at the bottom
Cross bedding
Changing the orientation of grains, consisting of bedding material deposited by wind or water and inclined at angles
Areas where cross-bedding occurs
steeper slopes of sand dunes and sandbars in rivers under the sea
Ripples
very small dunes of sand or silt whose long dimensions are at right angles to the wave direction
Graded bedding is deposited by
dense muddy turbidity currents
each layer in a graded bed progress from ___ grained to ___ grains
fine
coarse
turbidites
accumulations of many fine grained-beds
Bioturbated Structures
Bedding in sediments that are broken down due to the burrowing activity of animals (can be seen as cylindrical tubes the represent burros excavated by worms, clams, shrimp, etc).
Process of forming sediment
sediments are buried, compacted, and lithified at earth’s crust
