NEW ARTICLE PUBLISHED

Water-mass evolution in the Cretaceous Western Interior Seaway of North America and equatorial Atlantic

James S. Eldrett, Paul Dodsworth, Steven C. Bergman, Milly Wright and Daniel Minisini

Abstract. The Late Cretaceous Epoch was characterized by major  global  perturbations  in  the  carbon  cycle,  the  most prominent  occurring  near  the  Cenomanian–Turonian (CT) transition  marked  by  Oceanic  Anoxic  Event  2  (OAE-2) at  94.9–93.7 Ma.  The  Cretaceous  Western  Interior  Seaway (KWIS) was one of several epicontinental seas in which a complex water-mass evolution was recorded in widespread sedimentary  successions.  This  contribution  integrates  new data on the main components of organic matter, geochemistry, and stable isotopes along a north–south transect from the  KWIS  to  the  equatorial  western  Atlantic  and  Southern Ocean. In particular, cored sedimentary rocks from the Eagle Ford Group of west Texas (∼90–98 Ma) demonstrate subtle  temporal  and  spatial  variations  in  palaeoenvironmental conditions  and  provide  an  important  geographic  constraint for interpreting water-mass evolution. High-latitude (boreal–austral),  equatorial  Atlantic  Tethyan  and  locally  sourced Western Interior Seaway water masses are distinguished by distinct palynological assemblages and geochemical signatures.  The  northward  migration  of  an  equatorial  Atlantic Tethyan  water  mass  into  the  KWIS  occurred  during  the early–middle  Cenomanian  (98–95 Ma)  followed  by  a  major re-organization during the latest Cenomanian–Turonian (95–94 Ma) as a full connection with a northerly boreal water  mass  was  established  during  peak  transgression.  This oceanographic change promoted de-stratification of the water column and improved oxygenation throughout the KWIS and as far south as the Demerara Rise off Suriname. In addition, the recorded decline in redox-sensitive trace metals during the onset of OAE-2 likely reflects a genuine oxygenation event related to open water-mass exchange and may have been complicated by variable contribution of organic matter from different sources (e.g. refractory/terrigenous material), requiring further investigation.

Clim. Past, 13, 855–878, 2017
https://doi.org/10.5194/cp-13-855-2017