Page 11 - Practical Petroleum Geology, 2nd Edition

PRACTICAL PETROLEUM GEOLOGY Sedimentation

Petroleum Extension-The University of Texas at Austin

In this chapter:

• The means by which sedimentary rock is formed 2
• The transport and deposition of sedimentary particles
• Lithification and classification of sedimentary rocks Sedimentation

• The principles of stratigraphy

Because nearly all of the world’s supply of petroleum is found in sedimen-
tary rock, it is the most interesting type of rock for petroleum geologists.
To understand the correlation between petroleum and sedimentary rock,
we must learn more about sedimentation—in other words, how sedimentary
particles are formed, transported, deposited, and transformed into the great
sheets of rock that cover most of the world’s land area.

The process by which sedimentary rock is formed can perhaps best be ORIGINS OF
demonstrated by examining its smallest unit—the sedimentary particle. As SEDIMENTARY
does the rock as a whole, the individual particle embodies the history of PARTICLES
both its source material and the changes it undergoes on the Earth’s surface.

Sediments are classified primarily by grain size (table 2.1). Gravel, sand, Clastics
and silt particles can be of a variety of minerals—quartz and feldspar are
common—while clay particles are microscopic platelets of various hydrous
aluminum silicates. Gravel, sand, and silt are mostly noncohesive; that is, they
do not stick together. Clay, on the other hand, is very cohesive; its particles
are attracted to one another by minute electrical charges and adsorb water
readily, causing clay to swell.

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