Kyte, Frank T. (1999): Cretaceous-Tertiary impact ejecta; distribution, composition, and implications for impact and extinction mechanisms. Geological Society of America (GSA), Boulder, CO, United States, In: Anonymous, Geological Society of America, 1999 annual meeting, 31 (7), 240, georefid:2001-015169

Ejecta from the Chicxulub impact was deposited at the K/T boundary. Three depositional units have been described: a thick, proximal ejecta blanket extending a few hundred km from the crater, a regional tektite-bearing layer derived from melted target materials that extends up to 7000 km from the impact, and an Ir-rich global layer. The global layer is 2-3 mm thick when well preserved, is composed primarily of crystallized spherules (Smit, 1999, estimates 20,000 spherules per square cm) and has peak concentrations of Ir and shocked quartz. At least two types of spherules occur in the global deposit. One with Ca-rich augite (preserved only at DSDP Site 577) is probably mostly target material. The other contains altered silicates and a relict, high-temperature, Ni-rich magnesioferrite. These spherules are Ir-rich and probably contain a large fraction of projectile material. Components of the global layer have an asymmetric distribution, an observation significant to unraveling the effects of the impact. The size and abundance of shocked quartz decreases with distance from the impact site and there appears to be considerably more of this component in the Pacific than at European sites equally distant from Chicxulub. Also, while skeletal or dendritic habits are common for mangesioferrite grains from European sites, this phase occurs as an irregular myrmekytic intergrowth with Ni-rich magnesiowustite in Pacific spherules. Apparently Pacific spherules formed under hotter, more oxidizing conditions than those at European sites. A mechanism commonly invoked to explain these asymmetries is an impact trajectory coming from the east, possibly at a low angle with the most early ejecta transported westward, potentially leading to severe devastation over North America. This is generally consistent with one interpretation of asymmetry of the Chicxulub structure. Since most of the global ejecta was sub-mm spheroidal debris, the amount of globally dispersed fine-grained dust may have been orders-of magnitude less than originally hypothesized by Alvarez et al. in their global darkness scenario. However, heating of the atmosphere by the infalling ejecta likely ignited global wildfires, an alternative mechanism for darkening. Elemental carbon and soot from these wildfires may have higher concentrations than shocked quartz in the global ejecta layer.
West: -117.0000 East: 75.0000 North: 71.0000 South: 14.3000
West: NaN East: NaN North: NaN South: NaN
West: NaN East: NaN North: NaN South: NaN
West: NaN East: NaN North: NaN South: NaN
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