Depositional Sequences of Upper Continental Rise Seaward of Baltimore Canyon Trough

J. S. Schlee, Karl Hinz

Five major depositional sequences were mapped in a 2,350 line-km survey of the United States continental rise seaward of the northern Baltimore Canyon Trough. The sequences, which range in age from Jurassic(?) to Quaternary, record a gradual sedimentary buildup of fine-grained onlapping and slope-front fill, which was deposited seaward of a conspicuous platform and formed a broad wedge up to 5 km thick (Jurassic?).

During the Cretaceous, the slope-rise transition became much gentler, and sequences are more blanketlike as the declivity seaward of the platform was smoothed and filled in by fine-grained clastic sediments and thin, bedded limestones. The main constructional phase for the continental rise was during the Cenozoic when a thick (< 0.1-2.4 km) wedge built seaward of the shelf edge in response to a major fluctuation in sea level and erosion of the gentle ancestral continental slope.

The Cenozoic rise section can be subdivided into two main sequences separated by a conspicuous unconformity (A_u). The lower sequence is mostly a blanket of Paleogene hemipelagic ooze and claystone, 0.2-0.8 km thick. The sequence above the unconformity is a complex association of Neogene slump deposits, turbidites, hemipelagic clays, and channel fill that thickens seaward to 2.2 km under the middle continental rise. The final phase of rise construction was caused by widespread fluctuations in coastal onlap. These regressions resulted in deltaic outbuilding on the shelf, extensive Pleistocene erosion of the slope landward, and the accumulation of a broad sedimentary apron on the rise.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.