Taphonomy of foraminifera and bioturbation in marshes: Implications for reconstructing paleoenvironments and resolving Holocene sea-level records.

摘要

This dissertation investigates the effects of foraminiferal preservation and bioturbation on the construction of Holocene sea-level curves. Marsh foraminifera were collected seasonally for two years from low-, intermediate-, and high-marsh subenvironments from Bombay Hook National Wildlife Refuge (BHNWR), Smyrna, Delaware. Surficial and infaunal sampling (1–3 cm, 10 cm, 20 cm, 30 cm, 40 cm, 50 cm, and 60 cm) produced over 28,000 samples dominated by five species: Trochammina inflata, Jadammina macrescens , Arenoparrella mexicana, Miliammina fusca , and Pseudothurammina limnetis.; The BHNWR foraminiferal populations differ from New England marshes in several important ways: First, a larger fraction of the population lives infaunally in BHNWR, which has implications for selective preservation. Second, the subenvironmental distribution of foraminifera is different in BHNWR. Unlike in New England, BHNWR does not appear to exhibit a strong correlation between elevation and foraminiferal species. Nevertheless, with a proper local analog, compiled over numerous seasons, an accurate paleo-sea-level record was recovered from the BHNWR low marsh.; This dissertation also investigated the use of natural and artificial tracers to measure the rate and magnitude of mixing in salt marshes. Natural tracers (foraminifera) from washover fans on Folly Island, South Carolina, were used to estimate mixing rates in marsh subenvironments. These results were compared to the results of an artificial tracer (glass-bead) study from Folly Island, South Carolina and Bombay Hook National Wildlife Refuge, Delaware.; The effects of bioturbation increase from high to low marsh and through time. These trends are apparent in Folly Island, South Carolina (using both natural and artificial tracers) and in BHNWR. Despite this variable mixing, the bioturbation rates were on the order of those calculated for deep-sea sediments suggesting that salt-marshes may be an ideal place to recover short-term temporal signals.