Abstract It is hypothesized that submarine transport of sediments down a continental slope induces physical disintegration of pristine (non-broken) foraminiferal shells, and thus mass transport deposits should include a significant percentage of fragmented shells. To validate this hypothesis, we studied two gravity-cores from the eastern Mediterranean continental slope, offshore Israel: AM113 sampled within a landslide lobe at 848 m water depth, and AM015 located away from a landslide at 1080 m. At least one interval, c. 0.5 m thick, of heterogeneous sediments (i.e. debrite) was identified within each core. The timing of these debrites, based on biostratigraphy, oxygen isotopes and total organic carbon data, predates sapropel S1 in both cores and is contemporaneous (AM113) or slightly predates (AM015) the most recent deglaciation. We found a noticeable increase in the fragmentation of benthic and planktic foraminiferal shells through the last deglaciation and up to the base of S1. This strongly fragmented sequence is located in the debrite of AM113 but overlays the debrite of AM015. Accordingly, we suggest two possible mechanisms for the increased fragmentation of foraminiferal shells in both cores: sediment transport and turbulence related to submarine mass-transport events, or geochemical changes in the lower water column properties at the transition from MIS-2 to the Holocene.

Abstract Integrated biostratigraphy, sedimentology, and stable isotopes of 11 outcrops and wells along the Brazos River of Falls County, Texas, U.S.A., reveal the stratigraphic separation and sequential depositional history of the Chicxulub impact, followed by the sandstone complex and associated sea-level fall, which in turn was followed by the Cretaceous–Tertiary boundary (KTB). The KTB was identified up to 1 m above the sandstone complex based on three global standard criteria: the mass extinction in planktic foraminifera, evolution of first Danian species, and negative δ 13 C shift. No Ir anomaly is associated with the KTB or the Chicxulub impact ejecta layers. Upper Maastrichtian sediment deposition occurred in a middle-shelf environment that shallowed to inner-shelf depth at the time of deposition of the sandstone complex. At this time, Brazos sections show distinct shallowing from inner-neritic in the north to infra-neritic and lagoonal at Cottonmouth Creek, with further shallowing to intertidal swamp or marsh conditions in the Darting Minnow Creek area to the south. The sandstone complex is the most prominent feature of the Brazos sections. At the base of this unit are reworked Chicxulub impact spherules and lithified clasts with impact spherules and mud cracks that bear witness to erosion of an older primary spherule deposit. This primary Chicxulub impact ejecta layer was discovered between 45 and 60 cm below the sandstone complex in a 3 cm thick yellow clay altered impact glass layer. The sandstone complex, the reworked impact spherules, the spherule-rich clasts, and the yellow clay layer all clearly predate the KTB.

Abstract Investigation of late Maastrichtian faunal and environmental changes in three subsurface wells spanning over 3 km along the Brazos River, Texas, reveals similar minimum-diversity high-stress assemblages associated with shallow shelf conditions. Upper Maastrichtian sediments recovered span planktic foraminiferal (CF) zones CF1 to CF4 in well Mullinax-1 to the north and well KT3 at Cottonmouth Creek, and zones CF1-CF2 in Mullinax-3 at Darting Minnow Creek. Biotic stress conditions are demonstrated by the minimum species richness, near exclusion of larger specialized species, dwarfing, and dominance of small generalist taxa. Faunal assemblages dominated by alternating abundances of the disaster opportunist Guembelitria cretacea (Cushman) (particularly in zones CF4 and CF2-CF1) and heterohelicid species [e.g., Heterohelix globulosa (Ehrenberg), H. planata (Cushman), Paraspiroplecta navarroensis (Loeblich)]. Other small surface and subsurface mixed-layer dwellers are rare to common (e.g., hedbergellids, globigerinellids, pseudoguembelinids). The coincidence of Guembelitria blooms with lithological changes and oxygen and carbon stable isotope excursions may represent discrete episodes of freshwater runoff related to short-term pulses of the latest Maastrichtian (zone CF1-CF2) global climate warming. Climate warming ended in the upper part of zone CF1 with the return to a cooler climate, lower sea level, and the formation of incised valleys in a coastal–lagoonal environment. With the subsequent early transgression, incised valleys were infilled by a sandstone complex with reworked impact spherules, as well as lithified clasts with impact spherules up to 80 cm below the KT boundary. In this environment the shallow inner-neritic setting superimposed by changes in sea level and climate is the most probable cause for the observed conditions of high biotic stress preceding the KTB in the Brazos area.