Carbonate minerals, uranium and thorium concentration and U-Th ages of sediments from ODP Leg 166 sites

We have performed U-Th isotope analyses on pure aragonite samples from the upper sections of Leg 166 cores to assign each aragonite-rich sediment package to the correct sea-level highstand. The uppermost sediment package from each of the four sites investigated (Sites 1003, 1005, 1006, and 1007) yielded a Holocene U-Th age. Sediment packages from deeper in the cores have suffered diagenesis. This diagenesis consists of significant U loss (up to 40%) in the site nearest the platform (Site 1005), slight U gain in sites further from the platform, and continuous loss of pure 234U caused by alpha recoil at all sites. The difference in diagenesis between the sites can be explained by the different fluid-flow histories they have experienced. Site 1005 is sufficiently close to the platform to have probably experienced a change in flow direction whenever the banks have flooded or become exposed. Other sites have probably experienced continuous flow into the sediment. Although diagenesis prevents assignment of accurate ages, it is sufficiently systematic that it can be corrected for and each aragonite-rich package assigned to a unique highstand interval. Site 1005 has sediment packages from highstands associated with marine isotope Stages 1, 5, 7, 9, and 11. Site 1006 is similar, except that the Stage 7 highstand is missing, at least in Hole 1006A. Site 1003 has sediment only from Stage 1 and 11 highstands within the U-Th age range. And Site 1007 has sediment only from the stage 1 highstand. This information will allow the construction of better age models for these sites. No high-aragonite sediments are seen for Stage 3 or Substages 5a and 5c. Unless rather unusual erosion has occurred, this indicates that the banks did not flood during these periods. If true, this would require the sea level for Substages 5a and 5c to have remained at least ~10 m lower than today.

Carbonate content and d13C record of a Jordan Cretaceous outcrop (Section GM3 (Ghawr Al Mazar (Ghor al Mazrar))

An evaluation of the global synchronicity and duration of "3rd-order" sea-level fluctuations during the Cretaceous greenhouse has been hampered by poor constraints on potential climatic and tectonic drivers, and limitations of geochronology and chronostratigraphic correlation. To provide insight into the nature of such sea-level fluctuations, here we present a new Late Cretaceous record from the Jordanian Levant Platform, comprising a detailed physical-, bio-, chemo- and sequence stratigraphy. Carbonate content of these strata reflects overall sequence stratigraphic development, and demonstrates a dramatic 3rd-order-scale cycle that is also apparent in the d°C record. Updated radioisotopic constraints and astrochronologic testing provide support for the inference of an ~1 million year long sea-level oscillation associated with this 3rd-order cycle, which likely reflects a long-period obliquity (1.2 Myr) control on eustasy and stratigraphic sequence development, linked to the global carbon cycle. The observation of cyclic sea-level fluctuations on this time scale suggests sustained global modulation of continental fresh-water-storage. The hypothesized link between astronomical forcing and sea-level forms a baseline approach in the global correlation of sequence boundaries.