Harnessing stratigraphic bias at the section scale: conodont diversity in the Homerian (Silurian) of the Midland Platform, England

Abstract

Fossil abundance and diversity in geological successions are subject to bias arising from shifting depositional and diagenetic environments, resulting in variable rates of fossil accumulation and preservation. In simulations, this bias can be constrained based on sequence-stratigraphic architecture. Nonetheless, a practical quantitative method of incorporating the contribution of sequence-stratigraphic architecture in community palaeoecology and diversity analyses derived from individual successions is missing. As a model of faunal turnover affected by the stratigraphic bias, we use the 'Mulde event', a postulated mid-Silurian interval of elevated conodont turnover, which coincides with global eustatic sea-level changes and which has been based on regionally constrained observations. We test whether conodont turnover is highest at the boundary corresponding to the 'event' and post-'event' interval against the alternative that conodont turnover reflects habitat tracking and peaks at facies shifts. Based on the previously documented, parasequence-level stratigraphic framework of sections in the northern and central part of the Midland Platform, the relative controls of sequence-stratigraphic architecture, time and depositional environment over conodont distribution are evaluated using permutational multivariate analysis of variance. The depositional environment controls the largest part of variability in conodont assemblage composition, whereas the postulated 'Mulde event', or genuine temporal change in conodont diversity, cannot be detected. Depending on the binning of the stratigraphic succession, contrasting diversity and turnover patterns can be produced. The simple approach proposed here, emulating partitioning of b diversity into spatial and temporal components, may help to constrain the stratigraphic bias, even at the scale of an individual section.

Biodiversity patterns across the Late Paleozoic Ice Age

“…Changes in faunal diversity as a response to transgression and regression are likely idiosyncratic, as there are numerous additional factors that need to be taken into account when considering the habitat and geographic distribution of fauna (e.g., shape of the coast, steepness of the shelf, direction of sea-level change or topography; Holland, 2012). The pattern of turnover is possibly a stratigraphic artifact and might not necessarily reflect true turnover driven by sea-level change alone (e.g., Dunhill at al., 2014;Jarochowska et al, 2018), but it is accompanied by a complex combination of factors that complicate interpretation (compare Holland, 2012). In contrast to our results, Stanley and Powell (2003) found turnover rates to be low until the Sakmarian.…”

Revision of thelodonts, acanthodians, conodonts, and the depositional environments in the Burgen outlier (Ludlow, Silurian) of Gotland, Sweden

“…novoexcavatus, are reported exclusively from Gotland, where they co-occur in the same samples starting from the upper Eke Formation. Silurian collections in Estonia (Männik, 2010) and our (Jarochowska et al, 2018) observations from the Silurian of England indicate that 'Ou. ex.…”

Reconstructing Depositional Rates and Their Effect on Paleoenvironmental Proxies: The Case of the Lau Carbon Isotope Excursion in Gotland, Sweden

“…Therefore, local sedimentological processes such as winnowing or changes in provenance can be excluded as driving the observed trend. The onshore-offshore gradient is the main factor differentiating multiple environmental parameters at the basin scale, including the distribution of organisms (Jarochowska et al, 2018;Scarponi & Kowalewski, 2004;Tomašových, 2006), the composition and variability of sediment composition (Coimbra et al, 2015), and Th concentration (Adams & Weaver, 1958;Doveton, 1994;Ehrenberg & Svånå, 2001). It is also manifest as the driving force behind the composition and abundance of palynomorph assemblages in the Silurian carbonate platforms (Mullins et al, 2004;Stricanne et al, 2004Stricanne et al, , 2006.…”

“…On the other hand, sedimentary and sequence‐stratigraphic indicators often provide insights into relative changes in the depositional rate at high resolution, for example, flooding surfaces at parasequence bases or firmgrounds. Changes in depositional rates within a given basin or facies model are often highly predictable and vary systematically together with the position within the depositional sequence (Brett, 1995; Holland, 2000; Jarochowska et al, 2018; Ray & Thomas, 2007).…”