ABSTRACT The Cretaceous-Paleocene (K/P) boundary intervals are rarely preserved in successions of shallow-water limestones. Here, we describe a shallow rocky shore on the active orogenic wedge of the eastern Alps (Austria) fringed by a carbonate platform that was largely cannibalized by erosion. We compared this succession with similar nearshore environments globally, as well as the deep sea, to gain a better understanding of the environmental response to the K/P boundary transition. In the eastern Alps, Cretaceous and Paleocene lithofacies across the K/P boundary transition are separated by a hardground that formed during subaerial exposure and that terminates Upper Maastrichtian limestone with planktic foraminiferal assemblages deposited at neritic depth during zone CF3 (ca. 66.500 Ma). Above the hardground, there are beachrocks with early Danian zone P1a(1) assemblages, which indicate the hardground spans about ~600 k.y. of nondeposition and/or erosion. During the early Danian, the marine transgressive fringe fluctuated between “shoreface to emersion” environments, depositing limestones rich in bryozoans, rhynchonellids, coralline algae, and rare planktic foraminifera along with abraded, bored, and/or encrusted clasts eroded from older rocks. Repeated short subaerial exposure is marked by vadose diagenesis and hardgrounds, including an ~1.5 m.y. interval between magnetochrons C29n to C28n and planktic foraminiferal zones P1b to P1c(2). Comparison with platform carbonate sequences from Croatia, Oman, Madagascar, Belize, and Guatemala, as well as nearshore siliciclastic environments of southern Tunisia, Texas, and Argentina, across the K/P boundary transition revealed surprisingly similar deposition and erosion patterns, with the latter correlative with sea-level falls and repeated subaerial exposure forming hardgrounds. Comparison with deep-sea depositional patterns revealed coeval but shorter intervals of erosion. This pattern shows a uniform response to the K/P boundary transition linked to climate and sea-level changes, whether in shallow nearshore or deep-sea environments, with climate change tied to Deccan volcanism in magnetochrons C29r-C29n.

ABSTRACT Mississippian depositional systems in the subsurface of Oklahoma consist of a mix of carbonates and siliciclastic rocks that were variously interpreted as deposited on a regional shelf, ramp, or distally steepened ramp. These varied interpretations resulted in significantly different models for associated facies types and distribution, including potential reservoir types and the distribution of these units that may occur in the subsurface. Fundamental differences in the facies types and distribution of a shelf and shelf margin system versus a ramp or distally steepened ramp include the varying regional distribution for high- and low-energy facies, reef facies, and downslope mass transport deposits. Recent work in both the subsurface of Oklahoma, as well as local outcrops in Arkansas and Missouri, indicates that the facies were deposited on a distally steepened ramp due to the lateral facies distribution and the vertical facies successions identified throughout the system. The presence and characteristics associated with debris flows as described in this study, especially when defined within the context of a sequence stratigraphic hierarchy, supports the interpretation of a distally steepened ramp conceptual model and provides insight into similar mass transport deposits that may occur in the subsurface.