CORRELATING GEOLOGIC UNITS AND A DISCUSSION OF CHALLENGING STRATIGRAPHIC RELATIONSHIPS IN NORTHEAST FLORIDA

What Florida lacks in topographic relief it makes up for with its unassuming complex coastal, marine, and karst geology. Florida’s diverse geomorphology yields insight into the near surface and surficial geology. In the deeper subsurface, Florida’s crystalline basement rocks provide a glimpse of its deep-seated architecture. The Florida Platform includes the entire emergent portion of the state and extends offshore into the Atlantic and Gulf of Mexico, is variably thick, and developed atop this crystalline basement. Its spatial distribution and unit thicknesses are due in part to both inherent basin structure/architecture and subsequent depositional and erosional features and cycles. The result is a multitude of both positive and negative features and their associated basin stratigraphy that developed over the course of more than 100 my (Late Jurassic-late Oligocene). This complex, primarily subsurface stratigraphy is blanketed by equally complex and variably thick package(s) of Oligocene-Holocene mixed carbonate and siliciclastic units that characterize the surficial geology. Florida’s subsurface geology is interpreted primarily through borehole samples and geophysical surveys. Adding to the complexity of understanding the geology, Florida’s formations are comprised of lithologies that are largely non-conducive to traditional dating techniques based on 1) their mineralogy, 2) having experienced repeated transgressive and regressive events, and 3) their presumed depositional age.

In this session we highlight two correlation issues in NE Florida, the factors contributing to these issues, and present representative samples of these units to display and discuss. These include 1) interpreting the middle Miocene Hawthorn Group units (Statenville Formation, Coosawhatchie Formation, Charlton Member, and undifferentiated Hawthorn Group), and 2) the Pliocene and younger surficial sands (Tertiary-Quaternary undifferentiated sediments, Trail Ridge sands, Cypresshead Formation, Quaternary undifferentiated sediments). With respect to younger sediments, we find difficulty in reconciling and correlating units previously defined on a regional scale using relict shorelines, terraces, and escarpments guided by modern elevations