Stratigraphy and paleoenvironments of early postimpact deposits at the USGS-NASA langley corehole, chesapeake bay impact crater

摘要: The USGS-NASA Langley corehole was drilled into the Chesapeake Bay impact crater in Hampton, Va. We used whole and split cores, seismic-reflection surveys (multichannel single channel), downhole geophysical logs (spontaneous potential gamma ray), micropaleontology (planktonic benthic foraminifera bolboformids), stable-isotope records (δ 18 O, δ 13 C) to interpret lithic, biotic, paleoenviron-mental, properties contained in, or represented by, late synimpact early postimpact deposits (fallout layer, dead zone, Chickahominy Formation) overlying Exmore breccia core. initial deposit core (resting above a fallout layer) is barren of indigenous foraminifera, which represents an interval hostile sea-floor paleoenvironments; length between less than 1,000 years 8,000 years. Full recovery foraminiferal community rapid once amenable conditions were reestablished at beginning time. Planktonic bolboformids show that biochronozones P15 5 P16-P17 Eocene are by Formation corehole. These same previously documented from inside Kiptopeke sites. foraminferal assemblages encompassed biozone (Cibicidoides pippeni Zone), 126 calcareous agglutinated species Cibicidoides Zone can be divided five subbiozones (Bathysiphon, Bulimina jacksonensis, Lagenoglandulina virginiana, Uvigerina dumblei, Bolivina tectiformis Subzones). most abundant stratigraphically persistent assemblage indicate paleodepth about 300 meters (∼1,000 feet) for sea floor, exhibited oxygen deprivation high flux rates organic carbon. At corehole, spontaneous-potential gamma-ray curves allow recognition four lithic subunits, correlate approximately with those similarly distinguished three other intracrater coreholes (North, Bayside, Kiptopeke). Lithically, differs its equivalents coreholes, however, having greater permeability volume glauconite near base formation. paleoclimate, as expressed O record characterized negative excursions (interpreted represent pulses atmospheric warmth). A significant excursion C upper part consistent net global decrease carbon burial. isotopic successions have been recorded well many locations around globe. isotope provides evidence impacts may exerted long-term influence on climate changes, culminated well-known Oligocene mass extinction event.