28. IDENTIFICATION AND CHARACTERIZATION OF THE CRETACEOUS/TERTIARY BOUNDARY AT ODP SITES 886 AND 803 AND DSDP SITE 5761

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.