Comparison of Tertiary Depositional Sequences, Age of Bounding Unconformities, and Coastal Onlap Patterns in Baltimore Canyon Trough, Offshore New Jersey, and Main Pass, Offshore Alabama

S. M. Greenlee

Interpretation of high-quality seismic reflection profiles tied to well bores has delineated the Tertiary geologic history of the Baltimore Canyon Trough and the Main Pass area. During the Tertiary both areas subsided slowly, were in comparable paleogeographic position, and were the focus of primarily siliciclastic, progradational sedimentation. Because these areas are so similar geologically and have extensive seismic, log, and paleontologic data, they provide a unique opportunity to compare the character, timing, and extent of depositional sequences found on two different portions of the North American continental margin.

The Cretaceous-Tertiary boundary is characterized by an erosional unconformity which is downlapped by overlying Paleocene clinoforms. This downlap surface is interpreted to be a result of the rapid rise in sea level in the late Maastrichtian and early Paleocene. Both areas remained in deep water throughout the Paleocene and Eocene and record second-order (5-10 m.y.) eustatic cycles. Following a major basinward shift of coastal onlap in the Oligocene, thick progradational deltaic wedges are found within the study areas which record the effects of third-order (~ 1 m.y.) eustatic cycles. These depositional sequences may be grouped into second-order eustatic cycles recognized by major downward shifts in coastal onlap in the Oligocene, lower Miocene, and at the end of the middle Miocene.

Landward and basinward shifts in coastal onlap patterns show a high degree of similarity among the study areas and with the global coastal onlap chart. A departure in the middle Miocene is attributed to differing subsidence histories of the two margins.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.