Abstract
Understanding how regional ecosystems respond to sea‐level and environmental perturbations is a main challenge in palaeoecology. Here we use quantitative abundance estimates, integrated within a sequence stratigraphic and environmental framework, to reconstruct benthic community changes through the 13 myr history of the Jurassic Sundance Seaway in the western United States. Sundance Seaway communities are notable for their low richness and high dominance relative to most areas globally in the Jurassic, and this probably reflects steep temperature and salinity gradients along the 2000 km length of the Seaway that hindered colonization of species from the open ocean. Ordination of samples shows a main turnover event at the Middle–Upper Jurassic transition, which coincided with a shift from carbonate to siliciclastic depositional systems in the Seaway, probably initiated by northward drift from subtropical latitudes to more humid temperate latitudes, and possibly global cooling. Turnover was not uniform across the onshore–offshore gradient, but was higher in offshore environments. The higher resilience of onshore communities to third‐order sea‐level fluctuations and to the change from a carbonate to a siliciclastic system was driven by a few abundant eurytopic species that persisted from the opening to the closing of the Seaway. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species. Such increased onshore stability in community composition contrasts with the well‐documented onshore increase in taxonomic turnover rates, and this study underscores how ecological analyses of relative abundance may contrast with taxonomically based analyses. We also demonstrate the importance of a stratigraphic palaeobiological approach to reconstructing the links between environmental and faunal gradients, and how their evolution through time produces local stratigraphic changes in community composition.
Highlights
T H E deep-time fossil record can be used to understand the ecological and evolutionary responses of species to changes in their environment, and provides an important tool for identifying those factors that might impart resilience in the face of environmental change (Willis et al 2010)
Understanding the link between biotic turnover and environmental change remains a challenge in palaeoecology, because much environmental change has a minimal effect on turnover (e.g. Morris et al 1995), whereas some environmental change appears to trigger marked turnover, suggesting possible threshold effects (e.g. Hesselbo et al 2007; Zhang et al 2009; Finnegan et al 2012; Danise et al 2013, 2015)
We present a species-level study of marine benthic community response to sea-level and climate change from the Middle–Upper Jurassic Sundance Seaway of the western United States
Summary
T H E deep-time fossil record can be used to understand the ecological and evolutionary responses of species to changes in their environment, and provides an important tool for identifying those factors that might impart resilience in the face of environmental change (Willis et al 2010). Developed within marine deposits of the Jurassic Sundance Seaway are eight third-order, unconformity-bounded, depositional sequences, collectively representing approximately 13 myr (Pipiringos 1968; Pipiringos & O’Sullivan 1978; Brenner & Peterson 1994; McMullen et al 2014; Clement & Holland 2016). Superimposed on these cyclical changes in sea level is a transition from subtropical arid climates into progressively more humid conditions (Boucot et al 2013), resulting in part from the northward migration of the North American plate (Johnson 1992). These environmental and climatic changes make the Sundance Seaway an ideal site to investigate the linkage between environmental change and turnover
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