Experimental analysis of abrasion and dissolution resistance of modern reef-dwelling Foraminifera: Implications for the preservation of biogenic carbonate

Document Type

Article

Journal/Book Title/Conference

Palaios

Volume

7

Publication Date

1992

First Page

244

Last Page

276

Abstract

Fringing coral reefs at Discovery Bay, Jamaica, exhibit a pronounced depth-related gradient in water turbulence and associated physicochemical taphonomic factors (abrasion, dissolution), and thus provide ideal settings for investigating the influence of taphonomic processes on the formation of fossil assemblages. Foraminifera are prominent constituents of bioclastic sediments at Discovery Bay, and exhibit a high diversity of test sizes, shapes, wall compositions, architectures, and microstructures which may potentially affect their post-mortem behavior. We have developed a taphofacies model for Jamaican north coast fringing reefs and associated environments that has allowed us to generate hypotheses about the formation of foraminiferal sediment assemblages. Herein, we test the taphofacies model via laboratory and field experiments coupled with previous analyses of foraminiferal sediment assemblages. Based on laboratory and field investigations, dissolution and abrasion acting together are much more effective taphonomic agents than either agent acting alone. Most species tested are, however, resistant to both agents (acting alone or synergistically), although test surfaces may be severely altered (e.g., Amphistegina gibbosa). Only the most fragile species were totally destroyed (e.g., Planorbulina acervalis). Foraminiferal preservation in carbonate sediments may, in some cases, mimic that of condensed intervals of siliciclastic environments, in which shell-rich layers create an environment favorable to their preservation by buffering pore waters of the surface mixed layer against dissolution. Conversely, carbonate and shell-poor terrigenous regimes are predicted to differ in the intensity of physicochemical processes affecting incipient fossil assemblages. Given that carbonate and terrigenous sedimentary regimes also differ in the continuity and rate of sedimentation, shelfal carbonate and shell-poor siliciclastic regimes may differ fundamentally in the taphonomic constraints they place on our interpretation of the paleoecology, biostratigraphy, and evolution of ancient microorganisms. Relative rates of test destruction in carbonate and terrigenous sediments may hold important implications for carbonate budgets and the global carbon cycle.

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