| Extensive and closely spaced cores (204) were analyzed to find detailed facies (and their subgroups: microfacies and nannofacies) and paleoenvironments in the subsurface sediments along the Delaware Bay estuarine coast and Atlantic Ocean coast of Delaware. To determine detailed facies and paleoenvironments, several composite methods were employed: traditional lithological analysis, botanical analysis, macro- and micro-fossil identification, grain size analysis, organic and inorganic content, water content, mineral composition, particulate plant, and radionuclide methods ({dollar}sp{lcub}14{rcub}{dollar}C dating, {dollar}sp{lcub}210{rcub}{dollar}Pb, and {dollar}sp{lcub}137{rcub}{dollar}Cs methods).; Twenty-two sedimentary microfacies were identified in the surface and subsurface sediments of the study area. Most of the lower section of the Holocene intercalated with fluvial microfacies or brackish tidal flat/tidal stream microfacies. After tides encroached upon the nontidal freshwater marshes and swamps (which are non-transgressive sequences), several events of transgression and regression were recorded in the Holocene stratigraphic section. Finally, saline paleoenvironments predominated at the top section of subsurface sediments. Within sub-microfacies, three subgroups of salt marsh microfacies were identified: high salt marsh sub-microfacies, middle salt marsh sub-microfacies, and low salt marsh sub-microfacies. High salt marsh sub-microfacies contains two nannofacies: Spartina patens nannofacies and Distichlis spicata nannofacies. The major controlling factors of these paleoenvironmental changes were local relative sea-level fluctuations, sediment supply, the configuration of the pre-Holocene surface, fluvial activity, groundwater influence, climatic change, sediment compaction, tectonics, isostasy, and biological competition.; Most of the forty-four transects showed multiple transgressions and regressions. The maximum numbers of transgression and regression were ten, but mostly ranged from two to six. Three transects apparently contained no evidence of multiple events of transgression and regression, but this is related to the elevation of the pre-Holocene surface and the distance from the coasts. Further investigation might find the specific time intervals with more {dollar}sp{lcub}14{rcub}{dollar}C dates in order to understand the details of these records and local relative sea-level fluctuations. |
