Paleobiologic Effects of the Late Cretaceous Wetumpka Marine Impact, a 7.6-km-Diameter Impact Structure, Gulf Coastal Plain, USA

摘要: The 7.6-km-diameter Wetumpka impact structure in Alabama, USA, formed by a bolide within the shallow epicontinental Gulf of Mexico, during Late Cretaceous (late Santonian to early Campanian). Water depths for epicenter this event are estimated have been 30 100 m, and feature probably ∼ 25 km local barrier-island shoreline. All indications that would locally devastating event. For example, infra-red flash-burn radius extended shore area substantial seismic waves followed strong atmospheric blast wave reached shoreline tropical forest very shortly after impact. Further, discontinuous ejecta beyond other effects such as tsunami run-up into shore-area well. lower crater-filling unit contains an impactentombed fossil record: there is considerably more lignite (fragments finely divided material) some breccias sands than existed any target strata. This implies comminuted wood from coeval, forests was swept up returning marine-water washback-surgeback -- or air-borne winds thus became incorporated deep parts crater fill. Wetumpka’s fill also includes mixed trace body fossils slumped materials blocks displaying relic sedimentary facies units. Since impact, rim structure, mainly composed crystalline basement rocks, appears enduring subaerial feature. Rim height estimates indicate (comprised today remnant 270° arc elevated schists gneisses) subaerially exposed Deep soil development (saprolitization) characterizes most higher elevations rim, attesting long-term exposure since Cretaceous. We theorize limited terrestrial ecosystem could at upon floor well interval between end fall-back sedimentation subsequent late-stage collapse; however only intra-crater paleosol atop remains evidence possible period stasis. Late-stage collapse resulted catastrophic across area.