Provenance constraints on the Cretaceous-Paleocene erosional history of the Guiana Shield as determined from the geochemistry of clay-size fraction of sediments from the Arapaima-1 well (Guyana-Suriname basin)

摘要

Recent studies have emphasized the role of the Equatorial Atlantic Ocean opening on the drainage reorganization and erosion of the West African and northeastern Brazilian cratons during the Cretaceous. However, such studies are lacking regarding the Guiana Shield. To fill this gap, we determined the provenance of sediments deposited in the Suriname-Guyana basin during the Cretaceous-Paleocene based on the total organic carbon (TOC) content, delta C-13(TOC), major and trace element concentrations, and Sr-Nd isotopic data of nineteen clay-size fraction samples from one industrial well (Arapaima-1). Overall, the absence of correlation between the TOC content, delta C-13(TOC) and provenance proxies as well as the lack of Ce anomaly indicate that marine authigenesis, reducing conditions, and weathering have not markedly affected the trace element ratios (Eu/Eu*, Cr/Th, Th/Sc) and Sr-Nd isotopic compositions used as provenance proxies. Three samples (Early Cretaceous, Cenomanian and Late Campanian) have radiogenic epsilon(Nd(0)) values > - 2.2. The Early Cretaceous sample may have been sourced by Precambrian or Mesozoic mafic rocks of the Guiana Shield or contemporaneous basic volcanic rocks. The Cenomanian sample is likely to have been sourced by basic volcanic rocks of the Caribbean Large Igneous Province or the Takutu rift whereas the Late Campanian sample may have recorded more acid volcanism in the Takutu Rift. The other samples have an overall Guiana cratonic provenance with variable contributions of the Paleoproterozoic and Mesoproterozoic terranes and Jurassic or Precambrian mafic dykes. Increases in Sr-87/Sr-86 ratios and trace element ratios characteristic of more differentiated sources suggest an increasing contribution from the inner part of the Guiana Shield after the Coniacian. Because of the possible presence of active volcanism during the deposition of analyzed samples, post rift mantle upwelling under the equatorial margin is the favored mechanism to explain the increasing erosion of the Guiana Shield inner parts.