Sediment and Sedimentary Rocks
Hydrocarbons are formed largely from the ____.
remains of microscopic organisms
The most common and effective agent for transporting sediment is ____.
running water
Marine regression occurs when ____.
sea level falls with respect to a continent
A major characteristic of graded bedding is that the rock layers ____.
show an upward decrease in grain size
When geologists trace a layer of sediment or sedimentary rock laterally, the layers change in composition, texture, or both. These changes result from the ____.
simultaneous operation of different processes in adjacent depositional environments
Fossils are common because ____.
so many billions of organisms lived during the past
Wave-formed ripple marks ____.
tend to have symmetrical profiles
Geologists use ____ and their knowledge of present-day depositional processes to make determinations about a rock's depositional environment.
the principle of uniformitarianism
Graded bedding forms when ____.
turbidity currents deposit coarse and then fine sediments
Oil shales are ____.
useful for the kerogen that can be extracted
A sedimentary rock in which all the grains are about the same size can be characterized as ____.
well-sorted
The Navajo Sandstone is a wind-blown sand deposit with large cross-beds. How would the sand of these ancient sedimentary rocks be characterized?
well-sorted
All deposited sediments will eventually form sedimentary rocks.
False
Large fossils are more useful for environmental interpretations than are microfossils.
False
Placer deposits are surface accumulations resulting from the mixing of materials as they are transported.
False
Sedimentary rocks are rarely encountered on Earth without digging.
False
Texture and geometry are usually sufficient to determine the depositional environment of a sedimentary rock.
False
Conglomerate is common, but sedimentary breccia is not. Why?
The gravel becomes rounded very quickly during transport.
A vertical sequence of transgressive and regressive facies records the rise and fall of sea level.
True
Microscopic crystals of silica form a hard rock called chert, which can be shaped to form sharp cutting edges.
True
Most limestone is of biochemical origin.
True
Siltstone, mudstone, and claystone are all types of mudrock.
True
Tar sand is a type of sandstone in which viscous, asphalt-like hydrocarbons fill the pore spaces.
True
Sedimentary structures ____.
are features that form as a result of physical or biological processes operating in a depositional environment
The most common chemical sedimentary rocks are ____.
carbonate
Detrital sedimentary rocks can undergo lithification by ____.
cementation
Lithification of sand and gravel requires both compaction and ____.
cementation
One reason that sedimentary rocks are important in deciphering Earth history is that they ____.
contain fossils that are rare or absent in other types of rocks
Calcium carbonate readily dissolves in water that ____.
contains a small amount of carbonic acid
A rock composed almost entirely of fragmented seashells is called ____.
coquina
Chemical sedimentary rocks can have a clastic texture or an interlocking grain texture called ____.
crystalline
Marine transgressions are created when ____.
deposition occurs during a time when sea level rises and the shoreline moves inland
Detrital sedimentary rocks are ____.
derived from parent material and usually classified by the size of their constituent particles
Sediments are classified as ____ and ____.
detrital; chemical
Rock salt and rock gypsum are both examples of ____.
evaporites
Historically, most coal mined in the United States has been ____.
from the Appalachian region
Poorly-sorted sediment has ____.
great size variation
Anthracite coal ____.
is actually a metamorphic type rock
Most gravel ____.
is made up of rock fragments
Carnotite ____.
is the source of most of the uranium used in nuclear reactors in North America