Abstract
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.
Highlights
The Late Cretaceous Epoch was characterized by sustained global warming, emplacement of several large igneous provinces (LIPs), global extinctions, global sea-level highstands leading to several epicontinental seaways, and major global perturbations in the carbon cycle termed oceanic anoxic events (OAEs), the most prominent occurring at the Cenomanian–Turonian transition, and termed Oceanic Anoxic Event 2 (OAE-2) (Schlanger and Jenkins, 1976)
It has been proposed that ocean circulation in the KWIS was restricted during the Cenomanian, promoting anoxia due to a sill in the southern gateway (i.e.Texas/Mexico) and that late Cenomanian sea level rise (Greenhorn cyclothem of Kauffman, 1977, 1984) was sufficient to reach a critical sill depth allowing a breach of the southern end of the seaway, and the rapid incursion of warm, normal saline Tethyan waters (Arthur and Sageman, 2005)
Two of these carbon isotope excursion (CIE) have specific relevance for this contribution: (i) the ∼ 2 ‰ positive δ13Corg excursion in Iona-1 (143.73–139.27 m) and Innes (76.88–74.63 m) that corresponds with the Middle Cenomanian Event (MCE) and (ii) the Cenomanian–Turonian CIE that is clearly expressed with a positive CIE of up to 4 ‰ occurring in Iona1 (112.45–92.73 m), Innes-1 (55.74–42.51 m) and well “X” (1639.9 m – the top is not recorded because it is above the cored interval)
Summary
The Late Cretaceous Epoch was characterized by sustained global warming, emplacement of several large igneous provinces (LIPs), global extinctions, global sea-level highstands leading to several epicontinental seaways, and major global perturbations in the carbon cycle termed oceanic anoxic events (OAEs), the most prominent occurring at the Cenomanian–Turonian transition, and termed OAE-2 (Schlanger and Jenkins, 1976). This event is globally recognized by a positive carbon isotope excursion (CIE) reflecting the widespread sequestration of 12C-enriched organic matter in marine sediments under global anoxic conditions (see Jenkyns, 2010, and references therein). Previous publications have characterized the inflow of Tethyan waters at this time by the (i) improved environmental conditions as indicated by the sharp increase in abundance and diversity of foraminiferal/molluscan and ammonite assemblages reaching far north into the KWIS (McNeil and Caldwell, 1981; Kauffman, 1984, 1985; Eicher and Diner, 1985; Elder, 1985; Leckie et al, 1998; Caldwell et al, 1993; Kauffman and Caldwell, 1993, Elderbak and Leckie, 2016) and (ii) the lithologic transition from organic-rich mudrocks to a highly bioturbated limestone dominated facies (Corbett et al, 2014; Lowery et al, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
