Dynamic Systems modeling suggests that complex coastal dinoflagellate biosystems can be modeled using environmental parameters such as temperature, salinity, and bulk nutrient levels. The former Salisbury Embayment of northern Virginia and Maryland is modeled here, using STELLA I and FORTRAN models based on physical oceanography and temperature, salinity, and nutrient conditions of the modern Yellow Sea. In these models, dinoflagellate assemblages are predicted based on environmental conditions associated with depth. Cluster analyses of fossil dinoflagellate frequency data from Tertiary Pamunky Group (Aquia and Nanjemoy Formations) of the Salisbury Embayment produce 17 discrete groupings. Samples within the Salisbury fossil cluster groups are statistically similar (via ANOVA analysis), but not the same. Therefore they represent paleocommunity types rather than paleocommunities. Although individual sinofiagellate species recur in similar environmental settings, the paleocommunity types do not appear to repeat. In the past, such associations have been used as depth indicators. It is suggested here that they relate to estuarine, nearshore, and offshore coastal regions because of the temperature, salinity, and nutrient conditions of each. In the modern Yellow Sea, nearshore and offshore regions are separated by discrete lateral fronts in some areas, and by gradational regions of mixing in others. Both types of water mass boundaries are modeled in this study. Results suggest that evidences that discrete water mass boundaries might have occurred between some fossil dinoflagellate associations. Circulation patterns of the Salisbury Embayment may have been roughly similar to those of the modern Yellow Sea. / Master of Science