In order to better define the late Eocene clinopyroxene-bearing (cpx) spherule layer and to determine how the ejecta vary with distance from the presumed source crater (Popigai), we searched for the layer at 23 additional sites. We identified the layer at six (maybe seven) of these sites: Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) Holes 592, 699A, 703A, 709C, 786A, 1090B, and probably 738B. The cpx spherule layer occurs in magnetochron 16n.1n, which indicates an age of ca. 35.4 ± 0.1 Ma for the layer. We found the highest abundance of cpx spherules and associated microtektites in Hole 709C in the northwest Indian Ocean, and we found coesite and shocked quartz in the cpx spherule layer at this site. We also found coesite in the cpx spherule layer at Site 216 in the northeast Indian Ocean. This is the first time that coesite has been found in the cpx spherule layer, and it provides additional support for the impact origin of this layer. In addition, the discovery of coesite and shocked quartz grains (with planar deformation features [PDFs]) supports the conclusion that the pancake-shaped clay spherules associated with quartz grains exhibiting PDFs are diagenetically altered cpx spherules. An Ir anomaly was found associated with the cpx spherule layer at all four of the new sites (699A, 709C, 738B, 1090B) for which we obtained Ir data. The geometric mean of the Ir fluence for the 12 sites with Ir data is 5.7 ng/cm 2 , which is ~10% of the fluence estimated for the Cretaceous-Tertiary boundary. Based on the geographic distribution of the 23 sites now known to contain the cpx spherule layer, and 12 sites where we have good chronostratigraphy but the cpx spherule layer is apparently absent, we propose that the cpx spherule strewn field may have a ray-like distribution pattern. Within one of the rays, the abundance of spherules decreases and the percent microtektites increases with distance from Popigai. Shocked quartz and coesite have been found only in this ray at the two sites that are closest to Popigai. At several sites in the Southern Ocean, an increase in δ 18 O in the bulk carbonate occurs immediately above the cpx spherule layer. This increase may indicate a drop in temperature coincident with the impact that produced the cpx spherule layer.

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Sediments containing components produced by accretionary events should contain sufficient geochemical evidence to constrain several of the variables involved in modeling the environmental consequences of such events. We consider the geochemical record expected for 3 modes of accretion: accretion from an interstellar cloud, non-impacting accretion of weak materials subjected to tidal and atmospheric disruption, and the impact of dense asteroidal or cometary materials. To constrain an accretionary event, it is important to determine: 1) the siderophile abundance patterns; 2) the duration of the event; 3) the geographic extent of the anomaly; 4) the physical nature of the extraterrestrial materials and their siderophile concentrations; and 5) the source of the terrestrial component. In attempting to constrain the Cretaceous-Tertiary and the Antarctic Basin late-Pliocene events we find that the necessary evidence is only partially available. It seems clear that the Cretaceous-Tertiary event generated fallout on a worldwide basis, and that its duration was ⩽1 ka, but other features are not yet well defined. The siderophile pattern is generally chondritic, but variations from site to site (and even sample to sample) indicate differing geochemical fractionations during deposition and make it impossible to associate the projectile with a specific group of meteorites. Future studies of unusually well-preserved basal layers at Caravaca and DSDP 465A may improve the precision with which the siderophile patterns are determined. Magnesium concentrations and isotopic studies argue against a mantle ejecta component in the boundary layer, and thus against the oceanic impact of a dense projectile.