Description: Bulk rock composition analysis was conducted by X-Ray Fluorescence spectrometry (WD-XRF) using AXIOS Plus (Panalytical) at University of Oldenburg on shipboard residual sample powders analyzed by ICP-AES [Huber et al., 2019]. Borate glass beads were prepared from the sample powder using di-lithium tetraborate as a flux (700 mg sample, 4.2 g flux). Calibration of the XRF instrument is based on 52 international reference samples and in-house standards. Precision was determined from the pooled standard deviation of several duplicates and is better than 3% for major elements and better than 5% for trace elements when concentration levels are above the limit of quantitation. Accuracy was checked by analyzing international and in-house reference samples that are not included in the calibration and was better than 7% for all elements above the limit of quantitation. Results between XRF and ICP-AES analysis are generally in excellent agreement, except for elements affected by incomplete dissolution in borate digestion, especially Cr, and low-abundance elements like Rb and Nb that were not measured well by ICP-AES.

Description: Basalt sills cored in lowermost Berriasian sediments on Shatsky Rise in the northwest Pacific yield a mean 40Ar-39Ar incremental heating age of 144.6+/-0.8 Ma, providing a minimum estimate on the age of the Jurassic-Cretaceous boundary. The largest part of the rise was emplaced at rates similar to those of several continental flood basalts. The rise formed at an oceanic triple junction, and the sills, as well as lavas from two dredge sites, exhibit an ocean ridge-type Nd-Pb-Sr isotope signature. This signature is provisionally consistent with either a perisphere or meteorite-impact model, but is not predicted by the plume-head model of plateau formation. However, no model can yet be rejected, given the very sparse sampling of Shatsky Rise.

Description: We present initial isotopic ratios of lead for Early Cretaceous (Barremian-Aptian) sections from Shatsky Rise (Pacific) and Gorgo a Cerbara (Italy). Our Pb isotopic data track an interval representing Oceanic Anoxic Event (OAE)-1a, which is characterized by quasi-global deposition of organic carbon-rich black shale. Pb isotopic compositions of sediments from Shatsky Rise decrease at the end of Barremian time, from radiogenic continental values to unradiogenic values, and subsequently remained less radiogenic until the end of early Aptian time. We explain the isotopic shift by a significant increase in supply rate of unradiogenic Pb, most likely due to massive volcanism. In contrast, the Pb isotopic compositions from the Italian section, which was situated at the western end of Tethys, are mostly identical to those of upper continental crust, showing no significant change in supply rate of unradiogenic Pb. The discrepancy between two sites is attributed to quiescent deep-submarine eruptions of Pacific large igneous provinces (LIPs) such as the Ontong Java Plateau (OJP), which severely limited dispersion of Pb-carrying particles out of the Pacific Ocean. Published Os isotopic data from the Italian section indicate two episodes of massive eruptions of OJP or contemporaneous Manihiki and Hikurangi plateaus starting from earliest Aptian time, slightly later than that indicated by the sedimentary Pb isotopic record from Shatsky Rise. Differences in isotopic variations between Pb and Os likely reflect differences in their chemical behaviors in the oceans, i.e., Pb isotopic compositions would have varied in response to local or regional changes in sediment provenances, whereas large-scale changes in Os inputs are required to explain variations in seawater Os isotopic compositions. Our Pb isotopic data, together with the published Os isotopic record, provide new evidence for the eruptive history of OJP together with contemporaneous Pacific plateaus and its environmental consequences, starting from end-Barremian time and extending through early Aptian time.