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Correlating Rocks With Microfossils Sometimes, in certain areas, the well samples that are returned to the surface from the drill bit do not consist of various alternating beds of shale, limestone and sandstone. The offshore Texas Gulf Coast is one of these places. Instead of rocks that are fairly easy for the Petroleum Geologist to identify, the well may drill through thousands and thousands of feet of rocks that are made up only of shale. This makes it very hard for the PG to tell what exactly what rock layers are being drilled, since most shale looks like most other shale. But, the PG has an answer for this. In these difficult
areas, the rocks are identified by the tiny A PG that studies microfossils through a microscope is doing very specialized work. This type of geologist is called a micropalentologist (my-crow pale-lee-on-tall-o-jist). If a PG finds a certain microfossil in a rock layer (call it "Fossil A") that is 9,000 feet deep, and then finds the exact same microfossil in another well at a depth of only 8,000 feet, he may decide that the rocks containing Fossil A in each well are the same layer. He may then name these rocks the "Fosssil A Layer". Other PG's can then use pictures of Fossil A to identify
The drawings of microfossils on this page like planularia and textularia are expanded many times! These tiny fossils would fit on the head of a pin!
More Microfossils Clockwise from top left: ostracode, planktic foraminifer, diatom, benthic foraminifer, and pollen grain. (From USGS Sound Waves, Jan/Feb 2009)
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Copyright © 1996-2010 by D. Smith. All rights reserved. This site is protected by copyright. Do not copy materials from this site.
This site is maintained as a public and educational service. Thank you for visiting. The author assumes no liability for any incidental, consequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this material, the author assumes no responsibility for omissions or errors. R05172009:2200
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"microfossils" they contain. These
microfossils are the skeletons of the tiny animals 
or
plants that have lived in the ocean for
millions of years. Eventually, they died, and were buried in the shale on the ocean floor. The
animals changed and evolved through time, and PG's have learned how to identify rock layers by
looking
at the types of microfossils contained in them. This kind of work is always done
with a microscope
the
Fossil A Layer in their own wells. If enough PG's learn to
recognize Fossil A, it becomes an important tool to identify certain rocks, and PG's can
talk with each other about the Fossil A Zone....and other PG's will know what they are talking about.
