The impact of global climate events on local ecosystems can vary spatially. Understanding this heterogeneity can illuminate which environments will be most impacted and the proximal drivers of ecosystem responses. Cenomanian-Turonian marine deposits of the Western Interior Seaway (WIS) record paleoceanographic changes associated with transgression and the onset of Oceanic Anoxic Event 2 (OAE2). They provide an ideal setting to study basinwide paleoecological responses during a global perturbation. Here, we integrate benthic foraminiferal assemblages from before, during, and after OAE2 via multivariate ordination analysis to examine spatial patterns in faunal responses across the western United States on a common scale and to interrogate a previously defined faunal marker used for basin-wide correlation, the Benthonic Zone (BZ). We identify oxygenation and organic matter quality as primary and secondary controls of variation across the 10 stratigraphic records and use this variation to infer paleoenvironmental changes. Stratigraphic trends reveal, in contrast to previous studies, deoxygenation at the onset of OAE2. They also reveal temporal patterns in oxygenation and productivity consistent with the gradual northward migration of a southern water mass into the WIS. This spatial heterogeneity hinders the use of the BZ in biostratigraphy because assemblages change in response to diachronous environmental change, and thus timing of the BZ with respect to OAE2 is not consistent across the basin. Our study demonstrates that regional processes can overshadow ecosystem responses to global events and underscores the importance of considering how changes in the position of water masses impact the expression of global biogeochemical perturbations.

Main data file: Proportional abundances for this study were obtained from Elderbak et al 2014, Lowery et al. 2014, and Bryant et al. 2021. Additional data from Eicher and Worstell (1970) was manually digitized, and some data were converted from original categorical abundances (Abundant, Common, Rare) to estimated proportional abundances based upon the category the taxa were assigned to by the original authors and the number of taxa in each category in each sample. See Bryant and Belanger (associated publication) for details of this data conversion. All data sets were taxonomically standardized and proportional abundances were normalized to 100% before multivariate analysis. Each species was also assigned a morphotype (see Bryant and Belanger for details of the assignments) in order to perform the morphotype-level multivariate analysis.

Supplementary materials included: three supplementary figures and six supplementary tables. 

The file is .csv and can be opened and edited with Microsoft Excel and can be processed in R studio.

Supplementary figures 1–3 are included in one .pdf file. Supplementary tables 1, 3, 4, and 6 are included in one .pdf file, while supplementary tables 2 and 5 are in individual tabs of one .xlsx file.