Evolution of the Suriname coastal environment and implications for the arrival of Amazon River sediment in the Guianas

The coastline of the Guianas is characterized by mudflats formed by Amazon River sediments. However, the timing of onset of these mudflats and associated mangrove vegetation (dominated by Rhizophoraceae) is yet unknown. In this study we investigate the history of the Suriname coastal environment and vegetation. We analyzed cuttings samples from the nearshore Powisi-01 well and determined the palynological and geochemical composition of these sediments. We identified two main palynological zones and six subzones, the latter representing biome changes throughout the Cenozoic. Between samples 600–610 to 690–700 m below sea level (mbsl), diagnostic palynomorphs of Late Paleocene to earliest Eocene age occur, including abundant palms and other angiosperms. A peak of Apectodinium spp. dinoflagellate cysts from samples 600–610 to 610–620 mbsl signals the Paleocene-Eocene Thermal Maximum (PETM), the first formal documentation of this hyperthermal along the Equatorial Atlantic Margin. A barren section follows, that is overlain by Early Miocene (samples 270–280 to 490–500 mbsl), and Middle/Late Miocene to Pleistocene sediments (samples 190–200 to 260–270 mbsl). The Miocene record is dominated by Rhizophoraceae mangrove pollen, preceding the arrival of Amazon River muds. Throughout the section palynological diversity is high and pointing at a tropical lowland flora in the hinterland. The Sm Nd isotopic composition further indicate that sediments are mainly of cratonic provenance, with the top c. <190–200 mbsl (Plio-Pleistocene) of the section presenting a mixed sediment signal of Andean/Amazon, Orinoco, and Amazon craton-derived sediments. Regional literature suggests a Late Miocene arrival of (Andean) sediments at the Guiana coastline. However, further study is needed to pinpoint the precise onset of Amazon River influence along the Suriname coastline.