Abstract
Magnetic susceptibility (MS) measurements of marine rocks provide an underutilized but powerful high-resolution tool in stratigraphy. In ideal circumstances and when combined with other stratigraphic techniques, the method can yield resolution to 10,000 years or less. This paper applies the MS method to solving a Cretaceous global correlation problem. Because of the active global processes that drove significant evolutionary changes during this time, the Upper Cretaceous is important in Earth history. However, correlations among geological sequences are difficult, in part because Earth's magnetic polarity was essentially non-varying from the Aptian to the Santonian. Here we present high-resolution correlations for Upper Cretaceous marine sedimentary successions spanning all or part of the Santonian Stage from the Western Interior Seaway (U.S.A.) and the Western Sinai Peninsula (Egypt). To do this we have integrated the results of magnetic susceptibility (MS) measurements of unoriented samples from lithified marine rocks (in outcrop and from core) and biostratigraphic data sets from these sequences. In this study a MS zonation for the Santonian Stage has been developed and graphic comparison has been used for correlation. In the main, correlation between the U.S. and Egyptian sequences is excellent. Third order T/R cycles (>100 kyr) observed in this high-resolution data set for the Santonian Stage indicate significant similarities between the U.S. and Egyptian sections and allow correlation among sequences. We interpret these correlations to result from cyclicities caused by climate-controlled continental erosion and deposition of detrital components, mainly clay, in the marine realm. Second-order cycles (>1 Myr) are also observed in these data sets but show distinctive differences between the U.S. and Egyptian sequences. We interpret these second-order differences to result from local synsedimentary tectonic controls on sediment erosion and deposition. Also observed are two distinct, short-term MS marker events that can be correlated globally.