Comparing Mesozoic and Cenozoic Mixed Carbonate-Siliciclastic Systems From A Single Basin During Greenhouse and Icehouse Times; What Role Does Climate Play?

Coffey, Brian P.¹, Richard Sunde², J. Fred Read³ (1) Simon Fraser University, Chapel Hill, NC (2) Simon Fraser University, Burnaby, BC (3) Virginia Tech, Blacksburg, VA

Regional lithology-based sequence stratigraphic frameworks constructed across the subsurface of the Albemarle basin of eastern North Carolina (USA) from Jurassic, Cretaceous, and Paleogene time intervals reveal striking similarities within each of these passive margin shelf successions. Studied units were deposited over a broad temporal range at very different paleolatitudinal positions and global climatic regimes.

Previous interpretation of the Paleogene depositional facies successions concluded that deposition was heavily influenced by paleolatitudinal position (subtropical to warm-temperate), coupled with the major global transition from greenhouse to icehouse conditions. However, examination of more deeply buried Lower Cretaceous mixed carbonate-siliciclastic strata from the same basin reveals carbonate lithofacies that closely resemble late Paleogene updip shelf facies and stacking patterns consisting of admixed quartz sands/silts and mollusk-foraminifera dominated skeletal carbonate sands. Deep shelf marls also are comparable. Preliminary analyses suggest that facies similarities also exist into the underlying Upper Jurassic interval.

These observations suggest that while eustasy and climate strongly influence thickness and stacking patterns, the paleogeographic position of the shelf as a promontory exposed to open ocean wave energy and currents plays a major role in facies development through time. This shelf position subjected the waters of the basin to repeated pulses of ocean-derived elevated nutrient levels, similar to the modern palimpsest Carolina shelf. These observations further suggest that boundary currents (cool, proto-Labrador and warm, ancestral Gulf Stream) may have existed and mixed in this study area during Mesozoic times, albeit with lower intensities than observed in late Paleogene-Neogene icehouse conditions.