Abstract:
Paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid-Cretaceous are important for a better understanding of the Earth's climate system operating in an exceptionally warm mode. Here we applied an organic geochemical proxy (TEX (sub 86) ) on organic matter-rich Albian-Santonian sediments, recovered from Ocean Drilling Program Leg 207 Sites 1258 and 1259 on Demerara Rise, to reconstruct sea surface temperatures (SSTs) in the western equatorial Atlantic. Preceded by a stepwise Cenomanian warming trend ( approximately 31-35 degrees C), the onset of the Cretaceous thermal maximum coincided here with the Cenomanian-Turonian boundary event. Once established, this extreme warm climate regime, characterized by averaged tropical SSTs close to 35 degrees C, lasted up to the Turonian-Coniacian transition. Two pronounced cooler intervals ( approximately 2-3 degrees C) interrupt this otherwise remarkably stable record, providing the first delta (super 18) O independent evidence for middle Turonian cooling that previously has been attributed to glacioeustatic sea-level lowering. Coniacian SSTs decline stepwise, reaching a minimum in the Santonian ( approximately 32-33 degrees C), where cooling is most pronounced, presumably concomitant with the first progressive opening of a deep-water passage through the equatorial Atlantic gateway.