The Late Cretaceous Western Interior Seaway as a model for oxygenation change in epicontinental restricted basins

Abstract

Deoxygenation is a critical problem facing the ocean as the world warms, and has the potential to effect coastal upwelling zones, shelf areas influenced by high runoff and nutrification, and restricted and semi-restricted basins. The mechanisms that drive deoxygenation in these diverse environments are still not fully understood, in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean. Here, we address this problem of scale by studying deoxygenation in the geologic past. We summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the Cretaceous Western Interior Sea (WIS) of North America over ~13 myr (Cenomanian-Campanian), spanning two major sea level cycles. The WIS was prone to major changes in dissolved oxygen content throughout its long history, sometimes directly antiphase to trends in the global ocean. Presented as maps, our data show that bottom water oxygen within the WIS was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction. Areas flooded by cool Boreal (northern-sourced) waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway, which were flooded by warmer Tethyan (southern-sourced) waters. Beyond east-west differences explained by water mass, the entire seaway was better oxygenated during periods of transgression, and more poorly oxygenated to anoxic during periods of peak transgression/highstand and regression. We suggest that this pattern was due to the formation and downwelling of Western Interior Intermediate Water by the mixing of Tethyan and Boreal waters. During transgressions, an increasing volume of these watermasses entered the 3 seaway, mixed, and downwelled well-oxygenated surface water to the seafloor. During late transgression/highstand, partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor, but continued downwelling prevented anoxia. During the subsequent regression, a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia. As a model for other semi-restricted basins, the trends observed in the WIS show that local changes in relative sea level, mixing, and circulation are critical in controlling oceanic deoxygenation in these environments, in clear contrast to continental margins impinged by oxygen minimum zones, like the contemporaneous Demerara Rise in the southern Caribbean. Although the WIS is larger than most semi-restricted basins, it is characterized by quasi-estuarine circulation driving the interaction of normal marine and brackish watermasses, and thus serves a model for similar shallow epicontinental basins of any size. Understanding how these processes vary in different environments is key to predicting susceptibility of regional water ...

Exploring the Impact of Cenomanian Paleogeography and Marine Gateways on Oceanic Oxygen

“…Seven sites document anoxic conditions before OAE2. They are located in the Southern Central Atlantic and in the Gulf of Mexico (Figure 10; Kuypers et al., 2002; Lowery, Cunningham, et al., 2017; Lowery, Leckie, et al., 2017; Owens et al., 2012; Perez‐Infante et al., 1996; van Helmond, Ruvalcaba Baroni, et al., 2014; Westermann et al., 2014). In particular, previous studies suggested that the anoxic area surrounding the Equatorial Atlantic Gateway was driven by the estuarine circulation established between the Pacific and Central Atlantic (Topper et al., 2011; Trabucho Alexandre et al., 2010) but our results demonstrate that this anoxic area is stable even in the ShallowCAS simulation despite the disappearance of the estuarine circulation.…”

Age constraint for the Moreno Hill Formation (Zuni Basin) by CA-TIMS and LA-ICP-MS detrital zircon geochronology

“…The once delta plain shifted to a distal floodplain with the continued development of the fluvial complex and adjacent floodplain fines preserved in slightly more arid climatic conditions ( Roybal, 1982 ; Campbell, 1984 ; Hoffman, 1996 ; this study). In a broader context, with the newly interpreted MDAs for the Moreno Hill, emplacement of sediment into the depo-center would have initiated during the latest phase of the Greenhorn continuing through the Frontier-Ferron regression (Mancos Seaway) ( Kauffman, 1984 , Blakey, 2014 ; Lowery et al, 2018 , Fig. 4, p. 14; Miall & Catuneanu, 2019 ; and references therein).…”

Quantifying successional change and ecological similarity among Cretaceous and modern cold-seep faunas

“…WIS marine faunas are generally more depauperate than other Cretaceous faunas due to the basin's restricted circulation, brackish surface waters, dysoxic benthos, and episodic connection between the northern and southern regions, which would restrict dispersal (Jeletzky 1970; Hay et al 1993; Lowery et al 2018). An even smaller pool of species with the physiological tolerances necessary to colonize Black Hills seep habitats would have been present in the WIS; for example, tolerance of sulfide is important for colonization of shallow seeps (Dando 2010).…”

“…In addition to stress from seep-fluid composition, the restricted circulation and low-oxygen conditions common in the WIS could be an additional stressor leading to more homogeneous assemblages (Jeletzky 1970; Wright 1987; Hay et al 1993; Lowery et al 2018). Well-developed oxygen minimum zones in the modern ocean tend to homogenize faunal assemblages (Levin et al 2000a); thus the low-heterogeneity of the Black Hills seeps may instead reflect lower-oxygen conditions during their formation.…”