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Information Loss in the Transition from Life to Death Assemblages of Foraminifera in Back Reef Environments, Key Largo, Florida

Ronald E. Martin and Ramil C. Wright
Journal of Paleontology
Vol. 62, No. 3 (May, 1988), pp. 399-410
Published by: Paleontological Society
Stable URL: http://www.jstor.org/stable/1305415
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Information Loss in the Transition from Life to Death Assemblages of Foraminifera in Back Reef Environments, Key Largo, Florida
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Abstract

Despite numerous distributional studies of foraminifera in modern shallow-water carbonate environments, information loss and taphonomic bias in the transition from life to death assemblages of foraminifera in these environments have not previously been examined in detail. Surface sediment and vegetation samples were collected along six nearshore traverses and one traverse across the back reef lagoon off Key Largo, Florida. Living foraminifera are found in abundance on algae and the marine angiosperm, Thalassia testudinum, while foraminifera in sediment assemblages are represented primarily by empty tests. Q-mode cluster analysis of living assemblages on Thalassia delineates inshore (depth 0.4-2.7 m) and offshore (3.0-9.0 m) back reef biofacies. Calcareous imperforate (suborder Miliolina) species thrive in quiet waters of the inshore biofacies, in which biotic interactions appear to be the prime factor in determining small-scale species distributions of living foraminifera. Fragile species are most susceptible to test destruction, and, therefore, sediment assemblages are dominated by more robust forms (e.g., Archaias angulatus, Valvulina oviedoiana, thick-walled species of Quinqueloculina). Water turbulence primarily determines species composition of living populations of the offshore biofacies. These assemblages are dominated by the calcareous perforate (suborder Rotaliina) species Planorbulina acervalis and Rosalina bahamaensis. These species resist transport by encrusting Thalassia blades and having a test which fits flush with grass blades, respectively. However, sediment assemblages of the offshore biofacies are also dominated by typical inshore, robust species (Archaias angulatus, thick-walled miliolids). Thus, inshore and offshore biofacies are not readily differentiated by Q-mode cluster analysis of sediment assemblages. Robust species are wide ranging and often abundant in sediment because of differential preservation and time-averaging of sediment assemblages. The resultant taphonomic bias may interfere with paleoecologic interpretations concerning intensity of water energy and distance from shore.

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