Late Mesozoic Carbonate Banks and Reefs Along U.S. Atlantic Margin: ABSTRACT

Abstract

A paleoshelf-edge complex of Late Jurassic and Early Cretaceous age rocks observed in seismic profile off the United States east coast probably represents a group of carbonate banks and/or reefs. The paleoshelf-edge lies 10 to 15 km seaward of the present shelf edge in Georges Bank, 20 to 30 km in the Baltimore Canyon trough, 30 to 150 km in the Carolina trough, and 150 to 300 km in the Blake Plateau basin. Refraction studies of the margin observed velocities of about 5 km/sec at depths of 2 to 3 km beneath the outer continental shelf and upper continental slope that correspond to the top of this paleoshelf-edge complex. Drilling results from COST wells in Georges Bank basin and in Baltimore Canyon trough indicate that a carbonate-evaporite depositional regime was dominant behind the paleoshelf-edge during the Jurassic. Lower Cretaceous algal reef debris has been sampled in Heezen Canyon (Georges Bank slope). DSDP Site 390 also drilled back-reef carbonates of Early Cretaceous age along the seaward edge of the Blake Plateau, and recent submersible dives have recovered Albian-Aptian rudist reefal materials along the Blake Escarpment. While strong evidence exists for carbonate bank and algal reef deposits all along the paleoshelf edge, the evidence for rudist reefs is presently restricted to the Blake Plateau basin. Erosional retreat of the ancient shelf edge, especially in the Blake Plateau basin, resulted in the removal and breaching of the Lower Cretaceous-Jurassic carbonate bank or reef margin at some locations. End_of_Article - Last_Page 575------------