A modern distribution of foraminifera to reconstruct environmental change offshore Galveston Bay, Texas

Abstract

Sand is an important resource for coastal engineering. In Texas, many offshore sand deposits are found buried in Holocene fluvial sediments or estuarine environments like tidal channels or bayhead, flood, and ebb tide deltas. Exploring for these resources requires a comprehensive understanding of the depositional system in which they are buried. The distribution of benthic foraminifera can be used to reconstruct the paleoenvironment of sand-bearing Holocene estuary deposits. The Gulf of Mexico foraminifera have long been tied to specific environments, and facies in which one genera of benthic foraminifera is most abundant (i.e., the predominance facies) represent a promising technique to reconstruct paleoenvironment in Holocene cores. Although predominance facies have been well documented in Galveston Bay, to date, there are no equivalent records directly offshore for comparison, leaving the inner shelf assemblage unconstrained. Additionally, no direct comparisons have been made between ancient estuary assemblages and the modern living assemblages in Galveston Bay. To address this knowledge gap, this project examines the environmental evolution of the Trinity River estuary using benthic foraminifera and core data. The foraminifera trends offshore Galveston Bay show a greater diversity compared to estuary samples, which is likely driven by increased salinity on the inner shelf compared to Galveston Bay. The increased diversity of inner shelf assemblages compared to those of the bay can be used for recognizing offshore assemblages as distinct from estuarine samples in core data. Additionally, the comparison of living and Holocene estuary populations shows ancient samples with much higher dominance of Elphidium than is observed in the modern bay. This non-analogue population suggests environmental conditions (likely salinity) in the Holocene Trinity River estuary varied significantly from modern conditions implying a recent environmental change in the bay.