Stratigraphy around the Cretaceous-Paleogene boundary in sediment cores from the Lord Howe Rise, Southwest Pacific

During Deep Sea Drilling Project (DSDP) Leg 21, Cenozoic and latest Cretaceous sediments were recovered at Site 208 on the Lord Howe Rise, Southwest Pacific. We provide new biostratigraphic, magnetostratigraphic and chemostratigraphic data from Site 208 to constrain the stratigraphy around the Cretaceous-Paleogene (K-Pg) boundary and to determine the depth of the K-Pg boundary more precisely. Biostratigraphic data from calcareous nannofossils indicate a nearcontinuous succession of sediments from the mid-Maastrichtian (Late Cretaceous) to lowermost Thanetian (Paleocene) at depths of 540-590 m below seafloor (mbsf). The biostratigraphic data suggest that the K-Pg boundary corresponds to a siliceous claystone at the base of an interval of silicified sediments (576.0-576.8 mbsf). Carbonate carbon isotopic composition (delta C-13(carb)) reveals a negative shift across this interval, which is consistent with global patterns of 6 13 C across the K-Pg boundary. Osmium concentration and Os isotopic composition (Os-187/Os-188) can also be used to identify the K-Pg boundary interval, as it is marked by a peak in Os concentration and a drop in Os-187/Os-188 values to 0.12-0.15, both of which are the result of the Chicxulub impact event. Our Os-187/Os-188 data show trends similar to those of coeval global seawater with the lowest value of 0.12-0.16 in the siliceous claystone (576.8 mbsf). However, the concentration of Os is low (<80 pg g(-1)) in this sample, which suggests that this siliceous claystone was deposited around the K-Pg boundary but may not include the boundary itself. Although the sedimentary record across the K-Pg interval at Site 208 may not be completely continuous, it nevertheless captures a time interval that is close to the Chicxulub impact event.

Automated summary

New biostratigraphic, magnetostratigraphic, and chemostratigraphic data from Site 208 provide a better understanding of the stratigraphy and depth of the Cretaceous-Paleogene (K-Pg) boundary. The sedimentary record at this site captures a time interval close to the Chicxulub impact event, although it may not be completely continuous.