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

Abstract

Variations in depositional rates affect the temporal depositional resolutions of proxies used for paleoenvironmental reconstructions; for example, condensation can make reconstructed environmental changes appear very abrupt. This is commonly addressed by transforming proxy data using age models, but this approach is limited to situations where numerical ages are available or can be reliably inferred by correlation. Here we propose a new solution, in which relative age models are constructed based on proxies for depositional rates. As a case study, we use the onset of the late Silurian Lau Carbon Isotope Excursion (LCIE) in Gotland, Sweden. The studied succession is a gradual record of shallowing upward in a tropical, neritic carbonate platform. As proxies for depositional rates we tested thorium concentration, carbonate content, and the concentration of pelagic palynomorphs. These three proxies were used to create relative age models using the previously published DAIME model. We applied these models to transform the δ13Ccarb values as well as concentrations of selected redox‐sensitive elements. The three relative age models yielded qualitatively similar results. In our case study, variations in depositional rates resulted in peaks of redox proxies appearing up to 76% higher when taken at face value, compared to when accounting for these rates. In the most extreme cases, our corrections resulted in a reversal in the stratigraphic trend of elemental concentrations. This approach can be applied and developed across depositional setting and types of paleoenvironmental proxies. It provides a flexible tool for developing quantitative models to improve our understanding of the stratigraphic record.

Inferring time averaging and hiatus durations in the stratigraphic record of high‐frequency depositional sequences

“…Hiatuses and condensed intervals can be qualitatively detected in the stratigraphic record based on ichnological, cyclostratigraphic and geochemical signals (Moore et al ., 1978; Amorosi, 1995; Pemberton et al ., 2004; Caron et al ., 2005; Andrieu et al ., 2018; Kemp et al ., 2018; Amorosi & Sammartino, 2018; Weedon et al ., 2018; Jarochowska et al ., 2020). Nonetheless, hiatus durations are difficult to determine in pre‐Holocene successions (Hillgärtner, 1998; Meyers & Sageman, 2004; Catuneanu, 2019a,b; Davies et al ., 2019; Holbrook & Miall, 2020; Brigaud et al ., 2021).…”

Identification of the mode of evolution in incomplete carbonate successions

“…They also offer the possibility to evaluate the robustness of identifications of the mode of evolution and estimates of its parameters under different simulated age-depth models. Finally, sedimentological information may aliment age-depth models (Hohmann 2021a; Jarochowska et al 2020). The proliferation of ever better stratigraphic forward models (e.g.…”

Incorporating Information on Varying Sedimentation Rates Into Paleontological Analyses

“…Absolute ages at given stratigraphic heights in a section provide limits on the maximum duration of deposition and hiatuses as well as on the volume of deposition. However, even in the absence of absolute ages, the effects of varying sediment accumulation rates can be approximated quantitatively and compared using an auxiliary relative age model ranging from 0 (lowest part of the section) to 1 (highest part of the section), an approach that has been successfully applied to a Silurian carbonate platform (Jarochowska et al 2020). Both approaches can be refined using sequence stratigraphic interpretations to inform about relative changes in sediment accumulation rates, characterizing intervals with higher or lower sediment accumulation rates, identifying gradients of sediment accumulation rates, and putting constraints of the duration and location of hiatuses (Galloway and Williams 1991;Amorosi et al 2020).…”