FORAMINIFERAL AND SEDIMENTOLOGICAL INTERPRETATION OF HOLOCENE CLIMATE CHANGE IN BAFFIN BAY, TEXAS

Baffin Bay, Texas is an incised valley cut from 120-20 ka during the most recent Quaternary sea-level fall. With subsequent flooding, the valley was partly filled with mixed siliciclastic/carbonate sediments that provide an 8 ky record of environmental change. A previous study of sedimentary and seismic facies in the bay allowed for the recognition of four different stratigraphic surfaces which have been placed within a chronostratigraphic framework using carbon dates. Although the first order control on the facies architecture of Baffin Bay is sea-level rise, climate change appears to have also significantly influenced sedimentary character. The objective of this study is to use foraminifers to establish an independent record of change to test whether some of the variations in sedimentology are due to climatic fluctuations. To accomplish this goal, foraminifers were sampled at intervals from a 14.4 m long dated core. Results of the foraminiferal analysis were then compared with the sedimentological study to determine changes in foraminiferal assemblages coincide with probable climate changes indicated by sedimentary datasets. Three different foraminiferal communities are clearly defined by multiple discriminate analysis, which was used to compare sections of the core according to proportions of species present. Separations between these communities correspond to two of the flooding surfaces observed in the core, one at about 8.0 ka and the other at 5.5 ka. At the 8.0 ka flooding surface, caused by rapid sea-level rise associated with the draining of proglacial Lake Agassiz, the foraminiferal assemblage shifts from that of a deltaic environment to an open bay environment. Faunal changes across the 5.5 ka flooding surface, including lower abundance and species numbers, support the sedimentological interpretation that this surface is attributed to a shift in climate and restriction of the bay by the formation of Padre Island. To conclude, foraminiferal analysis corroborates sedimentological analysis, with assemblages corresponding to the different sedimentary facies and parasequences observed in the core.