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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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