Date of Award
Open Access Thesis
Earth and Ocean Sciences
James H. Knapp
Reanalysis of published seismic and well data from the South Georgia Embayment provides important new constraints on the geologic structure and evolution of the Eastern North American margin. A lower Paleozoic stratigraphic section (Silurian to Devonian) sampled in offshore wells drilled in the late 1970’s, can be correlated continuously along the entire ~250 km N-S length of the BA-3 profile acquired in 1989. Other than gentle warping and minor fault offsets, this Paleozoic section is essentially undeformed, precluding both Paleozoic contractional deformation associated with Appalachian orogeny, or subsequent Mesozoic extensional deformation and magmatism associated with continental rifting and formation of the Central Atlantic. Accordingly, crustal properties generating the Brunswick Magnetic Anomaly (BMA) in the central portion of the profile were most likely imparted during Proterozoic tectonic and magmatic processes, and the BMA is an inherited feature of the Gondwanan continental crust pre-dating the basal Paleozoic unconformity. Similar “layered basement” was previously identified on numerous other seismic reflection profiles on the continental margin, implying (1) the Suwanee and Brunswick/Charleston terranes were part of Gondwana, and acted as a coherent and stable block of continental crust throughout the Phanerozoic evolution of southeastern North America, and (2) the Alleghanian suture must sit north of these occurrences, and most likely coincides with the boundary on the magnetic map defined by Higgins and Zietz (1983). Paleozoic collisional tectonics were subsequently followed by extensional processes during the Mesozoic. The southern central Atlantic Ocean along the east coast of North America is commonly associated with a large volcanic province, referred to as the Central Atlantic Magmatic Province (CAMP) emplaced during this time of extension. A prominent seismic reflection, known as the J-Horizon, underlies this entire region and has been historically correlated to a sedimentary basalt contact. However, the J-Horizon has been reevaluated onshore as a contact between Coastal Plain sediments and the base of the coastal plain, regardless of the presence of basalt. This study reevaluates the character and origin of the J-Horizon beneath the Carolina Trough and Blake Plateau Basin in order to reevaluate the extent of a continental flood basalt associated with CAMP. Offshore wells have been identified near the distribution of “J” that penetrate basement rock, none of which encounter Jurassic basalt; however, no wells have been directly drilled in this proposed region. From correlating well and seismic data throughout the region, analysis suggests that, as with the onshore, the J Horizon represents a boundary between overlying Coastal Plain sedimentary rocks, and underlying Mesozoic rift basin and Paleozoic basement rocks. These data indicate that CAMP is not as aerially widespread as previously estimated in the Southeastern United States. This new interpretation removes the strongest line of evidence connecting the central Southern Atlantic Ocean to open 200 Ma and consequently removes evidence suggesting the opening of the central Atlantic Ocean of North America was diachronus.
Pollack, A. C.(2014). Tectonic Studies of the Atlantic Margin in the Southeastern United States. (Master's thesis). Retrieved from https://scholarcommons.sc.edu/etd/2871