QUANTITATIVE BIOSTRATIGRAPHIC ANALYSIS OF MIDDLE CRETACEOUS SEQUENCES IN BALTIMORE CANYON TROUGH, OFFSHORE MID ATLANTIC U.S. MARGIN

The use of biostratigraphic data is critical to improving the resolution of mappable units in offshore oil and gas reservoirs. Gradstein and Agterberg’s RAnking and SCaling method of quantitative biostratigraphy uses statistical, probabilistic techniques to constrain microfossil zones. Inconstancies in the biostratigraphic record, such as incomplete sampling and variation in the distribution of taxa, are minimized through the calculation of crossover frequencies and interevent distances. We applied the RASC method to Cretaceous wells from the Baltimore Canyon Trough offshore of the Mid-Atlantic U.S. Here, 132 nannofossil and planktonic foraminifera events spanning 24 wells were used to define assemblage and interval zones, as well as major paleoenvironmental changes in the Dawson Canyon, Logan Canyon, and Missisagua Formations. The proposed biozones are as follows: Zone Dcx (Rotalipora cushmani Zone, Upper Cenomanian), Zone LC1a (Planomalina buxtorfi zone, Lower Cenomanian), Zone LC1b (Podorhabdus albianus zone, Upper Albian), Zone LC2 (Conusphaera mexicana zone, Lower Albian), Zone LC3 (Cyclagelosphaera margereli zone, Aptian). Further, four large breaks in scaling were identified, and are thought to indicate major changes in sequence stratigraphy, including stratigraphic gaps and/or paleoenvironmental changes. These biozones are supported by the presence of six strong seismic reflectors that can be traced across the basin. Together, these seismic and biostratigraphic interpretations can be used to evaluate reservoir continuity, which helps assess the viability of the basin for its newly designated purpose as an offshore carbon storage reservoir.