ABSTRACT

Part of the Upper Cretaceous Blufftown Formation in Alabama consists of thin shelfal parasequences composed of high-energy storm event beds and intercalated fine-grained, inner-shelf sediments. In a nearshore-to-shelf direction, individual correlative storm event beds display a lateral gradation from (1) a distal lower-shoreface sandy conglomerate containing abundant Exogyra valves, to (2) an inner-shelf graded coquinoid sandstone, and ultimately to (3) a shelf hummocky cross-stratified silty sandstone. Individual storm event beds have lateral continuity over many miles. These storm event beds are interpreted to have been deposited initially from low-slope turbidity currents produced by cyclic loading of shoreface sands by powerful storm waves, and subsequent modification by deep-acting storm waves. The shelf parasequences occur in the high-stand systems tracts of two depositional sequences within the Blufftown Formation. Estimated average periodicity for the sandy event beds is consistent with obliquity-induced climatic cycles of approximately 41 ka duration.