Marine Science Faculty Publications

Test Surface Degradation in Archaias Angulatus

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Archaias angulatus (Fichtel and Moll) is the dominant larger foraminifer of Caribbean backreef systems. We undertook experimental and field studies to determine if taphonomic processes altering Archaias tests are indicative of depositional environment. Dissolution of tests under experimental conditions revealed the following sequence of events: 1) partial removal of the outer tile-roof layer composed of elongate calcite crystals; 2) etching of the inner-wall layer composed of randomly oriented calcite needles; 3) coalescing of pseudopores; 4) creation of flat, etched surfaces; 5) exposure of the interior walls of pseudopores (inverted pseudopores); 6) collapse of inverted pseudopores; and 7) complete loss of the outer test wall exposing underlying septa and chamberlets. Abrasion of tests by carbonate sediments under experimental conditions produced pitted surfaces and impact depressions. In field samples, tests from low energy, organic-rich sediments of Largo Sound are characterized by dissolution, whereas tests from shallow, open-shelf sites are characterized by abrasion. Breakage of the test periphery does not indicate environment of deposition because it can result from physical, chemical or biological processes.

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Journal of Foraminiferal Research, v. 18, issue 3, p. 187-202