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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 608

Last Page: 608

Title: Morphologic Evolution of Cambrian Algal Mounds, Texas, with Changing Depositional Environment: ABSTRACT

Author(s): H. S. Chafetz

Article Type: Meeting abstract


Algal mounds within the Morgan Creek Limestone (Upper Cambrian) of central Texas, exhibit an overall change in morphology with height in the section. This "evolutionary" trend is associated with a change in depositional environment. The modification in algal-mound morphology is believed to be a response of the algal communities to change in the level of water turbulence and water depth.

The earliest forms are discrete club-shaped mounds exhibiting a relatively simple, highly arched, non-branching, concentric structure. They are up to 1.5 ft thick and 2 ft in diameter. They are succeeded by larger mounds, 0.75-3 ft thick and 1-5 ft in diameter, with a complex, digitate internal structure. Near the top of the Morgan Creek Limestone are the largest algal mounds, biconvex lenses up to 5 ft thick and 25 ft in diameter. The overlying strata contain some flat, algal-laminated structures.

This evolution in mound form, a decrease in height-to-width ratio and from simple to complex internal structure, is associated with a decrease in water turbulence and a shift from shallow marine to intertidal to supratidal site of deposition. This environmental response demonstrates that changes of mound morphology can be useful in interpreting depositional environments.

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Copyright 1997 American Association of Petroleum Geologists