Page 188 - Laboratory Manual in Physical Geology

Quartz grains (translucent gray)

0 1 2 3 cm
K-feldspar grains (orange)
FIGURE 6.11 Photograph of hand sample X (actual size).

Refer to the first row of the Activity 6.7 worksheet to see the example of how this rock’s composition, texture, and origin were described.

ACTIVITY be transported, so they are in situ (formed where they are
found). Body fossils, even those of hard shells, are worn
6.10 “Reading” Earth History away quickly if transported, so they are generally in situ
as well.
from a Sequence of Strata
| Sedimentary structures are things like layers of sediment
THINK What can sedimentary rocks tell Sedimentary Structures
About It us about Earth’s history and past and fossil burrows in the layers. They are structures made
environments and ecosystems?
of the sediment as it accumulated or after it accumulated
( FIGURE 6.12 ). Some are the result of physical processes, and

OBJECTIVE Infer Earth history by “reading” others are the result of the activities of plants or animals.
(interpreting) a sequence of strata, from bottom
to top.
Stratigraphic Sequences
PROCEDURES As sediments accumulate, they cover up the sediments that
1. Before you begin , read about Stratigraphic were already deposited at an earlier (older) time. Environ-
Sequences below. Also, this is what you ments also change through time, as layers of sediment
will need :
accumulate. Therefore, at any particular location, bodies of
___ Activity 6.10 Worksheet (p. 186 ) and pencil sediment have accumulated in different times and environ-
2. Then follow your instructor’s directions for ments. These bodies of sediment then changed into rock
completing the worksheets. units, which have different textures, compositions, and
sedimentary structures.

Sedimentary Processes, Rocks, and Environments ■ 167