Abstract:
ODP Site 1049 recovered a complete Cretaceous-Tertiary (K/T) boundary. From bottom to top: 1) Slumped A. mayaroensis Zone ooze. 2) A 17 cm thick graded layer consisting of green spherules. The spherule layer contains also Maastrichtian foraminifers and is presumably re-deposited. A few lime-clasts occur, similar to non-melted limestone ejecta clasts from the Gulf of Mexico. 3) A 1 mm thick diagenetic orange layer with small spherules, capping the green spherule layer 4) A 3 cm thick bioturbated dark ooze of P0 Zone age, grading into 5) A light gray ooze with abundant "G"fringa, "G"eugubina, "G"minutula, of P1a Zone age. Burrows filled with this ooze extend downwards into the underlying dark marl. Iridium analyses of 1049b show an increase in Ir concentration from <0.06 ppb at the base of the spherule layer towards about 1 ppb in the top of the ejecta layer. The orange layer(3) represents a minimum in the Ir distribution (0.3 ppb). In the basal Tertiary dark ooze (4) Ir concentrations decrease from 1.3 ppb to <0.05 ppb within 3 cm. This Ir-profile is consistent with ejecta layers of the Western Interior, the Gulf coast and Beloc. The K/T ejecta layers at ODP site 1049 show a little disturbed sequence of impact ejecta and biotic events at the K/T boundary, in contrast to the ejecta layers in the Gulf of Mexico that are disturbed by tsunami's. The strong foraminiferal changes at the K/T boundary are strictly coincident with the emplacement of the ejecta layer, and do not postdate the ejecta layer. Hole 1053 contains an expanded highly siliceous sequence across the North American and Pacific tektite and microkrystite strewn fields. The foraminiferal changes and microprobe analyses of the ejecta layers are compared with the K/T boundary events.