Wetland Microfossil Taphonomy and Holocene Sea-Level Fluctuations

Bradley E. Hoge

Taphonomic signals can be applied to sediment records to determine small scale sea-level fluctuations because freshwater flooding in wetlands produces different taphonomic signals than salt water encroachment or periods of normal accretion. No single microtaxonomic group occurs nor is preserved in all depositional environments, however. By choosing taxonomic groups that are distributed across overlapping ecological gradients but with contrasting taphonomic histories, the record of fine scale sea-level fluctuations can be ascertained.

Foraminiferal assemblages can delineate salt to brackish water marsh environments, but are absent in fresh water marsh sediments. Arcellaceans are present in fresh marsh sediments, but are found sporadically in death assemblages. Ostracode death assemblages are preserved only under standing wager and so are inconsistent in tidal marsh sediments. Diatoms occur in all marsh types, but thanatocoenoses become too similar for each type to significantly indicate the different biocoenoses.

Fluctuations in sea-level are indicated for the past 3.3 Ky by an interpretation of these taphonomic signals from the Holocene record of the Galveston Bay system in Texas. These fluctuations are consistent across core transects with contrasting hydrologic and sedimentalogic dynamics, indicating that the records are reliable. Further interpretation of these results indicates that any pattern seen within these fluctuations may be due to statistical averaging rather than cyclic events, however.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995