Miocene evolution of carbonate sedimentation at the Ceara Rise: a multivariate data/proxy approach

Abstract

Synthetic records of percent CaCO 3 , carbonate mass accumulation, and noncarbonate (terrigenous) mass accumulation are developed for late Neogene portions of Ceara Rise Sites 925-929. Shipboard measurements of natural gamma emissions and magnetic susceptibility, collected at 3-to 10-cm intervals at each site, are combined with equally high resolution measurements of digital color reßectance to estimate lithologic variations over the whole sequence. Where magnetic susceptibility and natural gamma were measured in adjacent holes, the between-hole meters composite depth (mcd) scale was reÞned so that all data from a given site could be combined. A linear regression model is developed that predicts percent CaCO 3 from high-resolution measurements of stacked natural gamma emissions, stacked magnetic susceptibility, and digital color reßectance. Over 1300 measurements of percent CaCO 3 were made to develop a robust regression equation for each site. An orbitally calibrated chronology for Sites 925-929 relates all data to a common temporal framework. Carbonate and noncarbonate (terrigenous) mass accumulation rates are estimated from 5 to 14 Ma at Sites 925-929. These data are in turn used to evaluate variations in the lysocline from the Miocene to Holocene as a function of depth and time. Over the depth transect, CaCO 3 ßuxes during the Miocene undergo signiÞcant changes, most likely owing to development and intensiÞcation of North Atlantic Deep Water during the late Miocene. Terrigenous ßuxes show a long-term trend of increasing accumulation in response to Andean uplift and late Miocene development of the Amazon drainage into the Atlantic Ocean.