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