Page 278 - (DK) The Ultimate Visual Dictionary 2nd Ed.

GEOLOGY, GEOGRAPHY, AND METEOROLOGY

Sedimentary rocks EXAMPLES OF UNCONFORMITIES

Early beds tilted Later beds
and eroded horizontal
SEDIMENTARY ROCKS ARE FORMED BY THE ACCUMULATION and consolidation
of sediments (see pp. 266-267). There are three main types of sedimentary
rock. Clastic sedimentary rocks, such as breccia or sandstone, are formed
from other rocks that have been broken down into fragments by weathering
(see pp. 282-283), which have then been transported and deposited elsewhere.
Organic sedimentary rocks—for example, coal (see pp. 280-281)—are derived ANGULAR UNCONFORMITY
from plant and animal remains. Chemical sedimentary rocks are formed by No bedding in Later beds
early rocks horizontal
chemical processes. For example, rock salt
is formed when salt dissolved in water is
deposited as the water evaporates.
Sedimentary rocks are laid down in layers,
called beds or strata. Each new layer is laid
down horizontally over older ones. There NONCONFORMITY
are usually some gaps in the sequence, Early beds Later beds
folded and horizontal
called unconformities. These represent
eroded
periods in which no new sediments were
being laid down, or when earlier
THE GRAND CANYON, USA sedimentary layers were raised
above sea level and eroded away.
DISCONFORMITY
SEDIMENTARY LAYERS OF THE GRAND CANYON REGION
Wasatch formation Dakota
sandstone Carmel Pink Bryce Zion
Kaiparowits Tropic formation Cliffs Canyon Canyon Gray
formation formation Cliffs Sevier White Pipe
fault Cliffs Spring
Wahweap
sandstone

Temple Cap Navajo Kayenta Moenave Chinle Shinarump Moenkopi Kaibab Toroweap Coconino Hermit
sandstone sandstone formation formation formation member formation limestone formation sandstone shale

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