Abstract

This paper is an abbreviated geologic atlas providing a framework within which petroleum exploration of the Atlantic margin of the United States can be placed in context with the other North Atlantic borderlands. Twelve maps illustrate the gross tectonic and lithostratigraphic relationships of the various borderlands as the Atlantic Ocean evolved to its present configuration.

Three maps of Paleozoic time depict the terminal phases of the closing predecessor ocean, Iapetus, and the resulting supercontinent, Pangaea. Several wrench fault lineations related to the Paleozoic collisional events are reflected as transform offsets in Mesozoic seafloor spreading.

Six maps illustrate the initiation of rifting, rupture, and seafloor spreading as well as the highly variable lithostratigraphy in Mesozoic time. During the initial phases of rifting the topographic gradient of the continental surface was away from the peripheral rift valleys. Evaporite deposition was often associated with these restricted rift valley seaways. Continued marginal subsidence and increased marine circulation resulted in a shift to carbonate deposition. Seafloor spreading moved the original rift margin locale progressively farther into the plate interior while subsidence redirected drainage toward the rift margin and clastic sedimentation became dominant.

Only two maps are used to illustrate Tertiary time when the United States Atlantic borderland was nearing isostatic equilibrium and much Tertiary sediment was moved downslope to the continental rise prism and abyssal plain.

A single map of Quaternary time is included to depict the present boundaries of the plates related to the present day North Atlantic Ocean.