In 1995, an expedition on board the research vessel FS Polarstern explored the impact site of the Eltanin asteroid in the Southern Ocean, the only known asteroid impact into a deep ocean basin. Analyses of the geological record of the impact region place the event in the late Pliocene (approximately 2.15 Myr) and constrain the size of the asteroid to be >1 km. The explosive force inferred for this event places it at the threshold of impacts believed to have global consequences, and its study should therefore provide a baseline for the reconstruction and modelling of similar events, which are common on geological timescales.

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The Cretaceous/Tertiary (K/T) boundary Ir anomaly has been identified in deep-sea clays at three new localities in the North Pacific: Ocean Drilling Program Site 886 near the Chinook Trough (44°41.4'N, 168°14.4'W), ODP Site 803 on the Ontong-Java Plateau (2°26.0'N, 160°32.5'E), and Deep Sea Drilling Project Site 576 in the western North Pacific (32°21.4'N, 164°16.5'E). At each of these sites, the K/T boundary is characterized by a large Ir anomaly, coincident with minor enrichments of Cr and abundant shocked quartz and magnesioferrite spinel. Spheroidal material has also been observed in K/T boundary sediments at ODP Site 886 and DSDP Site 576. The magnitude of the Ir anomaly is comparable to that observed at other marine sites around the world, with estimated net fluences of 52, 140, 130, and 90 ng Ir cm" 2 in Holes 886C, 803D, 576, and 576B, respectively. At Sites 803 and 576, some biostratigraphic control was available from poorly preserved nannofossils and ichthyoliths, respectively. At Site 886, it was necessary to survey Ir concentrations across a 18.1-meter-thick unit of clay (54.3 to 72.4 mbsf) known to record sedimentation from 80 to 10 Ma.

Quantitative analyses of the size distribution and abundance of shocked quartz (quartz with planar deformation features [PDFs]) were performed on CretaceousTertiary (K/T) boundary sediments from seven localites in thePacific basin: LL44-GPC3; DSDP (Deep Sea Drilling Project) Sites 465, 576, 577, and 596; and ODP (Ocean Drilling Project) Sites 803 and 886. Quartz with PDFs was found at each site.On average, 63% of the quartz grains in Pacific K/T sediments with diameters >30 µm have PDFs. The fluences of quartz with PDFs are relatively uniform across the Pacific; estimates for the abundances of shocked grains >30 µm in diameter range from ~1,000 to 2,000 grains/cm 2 . One exception is ODP site 886, where we estimate a fluence of 13,800 grains/cm 2 . Ten PDF-bearing quartz grains larger than 200 µm were recovered, including one with a maximum diameter of 320 µm. These largest grains were all from the sites nearest North America: DSDP 465, ODP 886 and LL44-GPC3. This may reflect proximity of these sites to Chicxulub.Comparison to other globally distributed sites is difficult. We conclude that shocked quartz in the Pacific is on average significantly smaller and about an order of magnitude less abundant (in mass/cm 2 ) than that deposited in North America. Maximum grain sizes of shocked quartz in the North Pacific appear to be larger than at sites in Europe, although these sites were similar distances from Chicxulub at 66 Ma.