The geologic age of the first marine sediments deposited in the North Atlantic basin is of basic importance in reconstructing the basin's early geologic history. Thus, although the oldest dated marine sediments penetrated on the U.S. North Atlantic margin by DSDP wells are of Callovian age (Blake-Bahama basin), both the Georges Bank and Baltimore Canyon basins include much older Jurassic strata of Bajocian-Bathonian age, as well as an Upper Triassic section. Microplankton provide the basis for a Mesozoic biostratigraphic framework of three basins where drilling has occurred on the U.S. Atlantic outer continental shelf. Studies of closely sampled subsea sections from multiple wells drilled on the Georges Bank basin, the Baltimore Canyon Trough, and the Southeast Georgia em ayment, make dating possible by standard age and subage equivalents ranging from Middle Jurassic (Bajocian) to Maestrichtian (Late Cretaceous). This age sequence is documented by dinoflagellate range tops recorded in the offshore Canadian Grand Banks and Scotian Shelf, as well as by reference to ammonite-controlled type localities in northwestern Europe. The age of this sequence is supported from the Callovian to the top of the Maestrichtian by calcareous nannofossils. Additional biostratigraphic markers include a few benthonic and planktonic foraminifers and spores and pollen of age-guide value. The post-Middle Jurassic section in the Baltimore Canyon Trough averages over twice the thickness of the equivalent section in the Georges Bank basin, so that the base of the Middle Jurassic mar ne section has not been penetrated in the Mid-Atlantic. Georges Bank also has an Upper Triassic section.

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