Mineral resource assessments for the continental shelf of Georgia as a part of the Continental Margins Studies Program: Seismic interpretation of the phosphatic Miocene-age Hawthorne Group

Abstract

Phosphate-bearing strata have long been recognized in the shallow continental shelf of the Southeastern Atlantic, including off the coast of Georgia. Prior to the Continental Margins Studies Program, these strata were poorly defined, both geographically and stratigraphically. The strata of interest are believed to be a part of the Miocene Hawthorne Group, which serves as the confining unit for the Floridan Aquifer System. This aquifer system is the major source of fresh water for coastal Georgia, South Carolina and Florida. In the event that economic phosphate deposits are found to occur, it will be imperative to define the relationship of these phosphate deposits to the aquifer. The Middle Miocene strata can easily be distinguished in seismic profiles. Characteristic continuous, strongly banded, parallel reflectors can be traced throughout the study area. The general trend of the Middle Miocene strata is a southward thickening and increasing depth. The Tybee Phosphorite Member is approximately 10 m thick in Chatham County, Georgia. Lack of lithologic information precludes a delineation of its extent and thickness seaward, but evidence does support its presence on the inner shelf.