Geology Reference
In-Depth Information
Figure 6.16 Rounding and Sorting in Sediments
a Beginning students mistake rounding to
mean ball-shaped or spherical. These three
stones are all rounded, but only the one at
the upper left is spherical.
b Deposit of moderately sorted gravel. The
largest particle is about 5 cm across.
c Angular, poorly sorted gravel. Note the
quarter for scale.
Glacial
environment
Stream
environment
Lake
Beach
Sand
dunes
Delta
Tidal
flat
Alluvial
fan
Lagoon
Continental
shelf
Submarine
fan
Deep
marine
environment
Barrier
island
Figure 6.17 Depositional Environment Continental environments are shown in red type. The
environments along the shoreline, shown in blue type, are transitional between continental and
marine. The others, shown in black type, are marine environments.
transport, deposition, and lithifi cation. We now turn to the
types of sedimentary rocks and how they are classifi ed. The
two broad classes or types of sedimentary rocks are detrital
and chemical , although the latter has a subcategory known as
biochemical (Table 6.2).
they are composed of particles or fragments known as clasts.
The several varieties of detrital rocks are classifi ed by the size
of their constituent particles, although composition is used
to modify some rock names.
Both conglomerate and sedimentary breccia are composed
of gravel-sized particles (Figure 6.18 and
Figure 6.19a, b);
but conglomerate has rounded gravel, whereas sedimentary
breccia has angular gravel. Conglomerate is common, but
sedimentary breccia is rare because gravel becomes rounded
very quickly during transport. Thus, if you encounter
sedimentary breccia, you can conclude that its angular
Detrital Sedimentary Rocks
Detrital sedimentary rocks are made up of solid particles
such as sand and gravel derived from parent material. All
detrital sedimentary rocks have a clastic texture , meaning
 
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