MARINE OSTRACODES FROM THE LATEST PLEISTOCENE OF CENTRAL MAINE: EVIDENCE FOR PALEOSALINITY AND PALEOBATHYMETRY IN THE WANING PHASES OF MARINE EMERGENCE

Samples were taken from each of four diffusely fossiliferous pockets within the upper 6.5 m of shelly marine Presumpscot Formation silts in an abandoned gravel pit in Norridgewock, Maine, at approximately 44^o43.1'N, 69^o48.9'W. Separate small samples were taken for ostracode and foraminiferal analyses, and large bulk samples were collected for molluscan faunal study and radiocarbon age determination. Though results from the ¹⁴C samples are pending, past experience indicates they will likely yield ages of 12,300-12,500 ¹⁴C years b.p. This presents initial results of the study of the marine ostracodes. Four to seven species of ostracodes were identified in each of the samples. The most abundant species was Heterocyprideis sorbyana, comprising 40-80% of the total fauna in each sample, while remaining fauna included Cytheropteron spp. (particularly juveniles), Finmarchinella spp., and Cytheromorpha sp. A (of Mcdougall et al.). The high abundance and consistent distribution of Heterocyprideis sorbyana throughout the samples, as well as the presence of Cytheromorpha sp A. in at least one of the samples, are consistent with shallow-water near-shore depositional environments. However, the presence of Cytheropteron spp. and Finmarchinella spp. indicate instead a marine environment of inner to middle neritic water depths, with fairly stable temperature-salinity conditions. Collectively, this suggests an estuarine environment, exhibiting seasonally reduced salinity conditions and frigid to sub-frigid water temperatures. The abundance of juvenile Cytheropteron is consistent, because sudden freshwater influx in warmer months would reduce salinities such that it was no longer suitable for their survival. On the other hand, the euryhaline, eurythermal, and eurytopo Heterocyprideis sorbyana would have tolerated these seasonal changes, consistent with the abundance of mature specimens seen in all samples. The presence of Finmarchinella curvicosta may mark the onset of a return to modern conditions following deglaciation, as the influence of glacial meltwater influx gradually decreased and salinities, temperatures and depths fluctuated less on a seasonal basis.