The Holocene San Francisco Bay and adjacent ocean-shelf foraminiferal fauna have been divided into five principal biofacies: brackish-water nearshore mudflat, marsh, normal bay, open bay, and open ocean. The open-ocean biofacies probably is restricted to the area outside the Golden Gate; at some localities individual specimens were found to occur within the open bay, but they were thought to have been current transported. By analogy, these biofacies provided the basis necessary for recognizing Pleistocene paleoenvironments in two bay cores.

Cold-water, open-ocean influence existed at the onset of Pleistocene deposition within the bay, reaching inland as far as the east side of Yerba Buena Island (core 88), and at times as far southeast as the Oakland Estuary (core 484). The degree of periodic open-ocean influence, both in its geographic extent and its duration, was far greater than anticipated. Fluctuations ranging from open-ocean to marsh conditions persisted throughout the Pleistocene and correlate with Pleistocene and Holocene periods of glacial and interglacial eustatic sea-level changes. No faunal evidence was found to indicate the existence of Pleistocene nearshore mudflat biofacies. This may have been indicative of either lack of preservation or rapidly changing environments. The core samples contained five specie not found within the Holocene bay: Bulimina marginata, Elphidium albiumbilicatum, Lagena filicosta, Oolina melo, and Globigerina quinqueloba.

End_of_Article - Last_Page 1702------------