Memorial University of Newfoundland, Earth Sciences Department, Canada

Ocean Drilling Program (ODP) Site 1276 was drilled in 4549 meters water depth in the Newfoundland Basin approximately 360 km east of Hibernia Field, off Canada. It records the post-rift burial of irregular basement topography. Below a cased, uncored depth of 800 meters, 933 m of lower Oligocene to uppermost Aptian(?)-lower Albian sedimentary rocks were cored ( approximately 85% recovery). Drilling terminated in diabase sills coincident with a prominent seismic reflector (U) previously hypothesized to correlate with the Avalon Unconformity. The stratigraphy at Site 1276 is similar to that drilled on the conjugate Iberian margin. Background hemipelagic mudrocks and interbedded coarser gravity-flow deposits form the bulk of the succession at Site 1276. They include debris flows, turbidites, and muddy viscous gravity-flow deposits that range in composition from siliciclastic sandstones and mudrocks to carbonate grainstones and marlstones. Most gravity-flow deposits contain significant biogenic carbonate, whereas most of the interbedded hemipelagic sediments are non-calcareous, reflecting deposition below the carbonate compensation depth. The Albian-Cenomanian section is characterized by moderately enriched total organic carbon (TOC) content (max. of approximately 10% TOC), low hydrogen indices (HI < 100), C/N ratios averaging approximately 20, and a positive correlation between C/N and TOC, suggesting a strong influence of terrestrially derived organic matter. Finely laminated, discrete organic-rich "black shales" with higher TOC are present. Two such intervals may correspond with Oceanic Anoxic Events 1b and 2; they have HI > 150, characteristic of marine organic matter and have S (sub 2) up to 25 mgHC/g, indicating that they originally had petroleum-generating potential.