Investigating the preservation of orbital forcing in peritidal carbonates

Abstract

Metre-scale cycles in ancient peritidal carbonate facies have long been thought to represent the product of shallow water carbonate accumulation under orbitally controlled sea-level oscillations. The theory remains somewhat controversial, however, and a contrasting view is that these cycles are the product of intrinsic, and perhaps random, processes. Owing to this debate, it is important to understand the conditions that do, or do not, favour the preservation of orbital forcing, and the precise stratigraphic expression of that forcing. In this work, a one-dimensional forward model of carbonate accumulation is used to test the ability of orbitally paced sea-level changes to reconstruct cyclicities and cycle stacking patterns observed in greenhouse peritidal carbonate successions. Importantly, the modelling specifically tests insolation-based sea-level curves that probably best reflect the pattern and amplitude of sea-level change in the absence of large-scale glacioeustasy. This study found that such sea-level histories can generate precession and eccentricity water depth/facies cycles in models, as well as eccentricity-modulated cycles in precession cycle thicknesses (bundles). Nevertheless, preservation of orbital forcing is highly sensitive to carbonate production rates and amplitudes of sea-level change, and the conditions best suited to preserving orbital cycles in facies/water depth are different to those best suited to preserving eccentricity-scale bundling. In addition, it can be demonstrated that the preservation of orbital forcing is commonly associated with both stratigraphic incompleteness (missing cycles) and complex cycle thickness distributions (for example, exponential), with corresponding implications for the use of peritidal carbonate successions to build accurate astronomical timescales.

The limited link between accommodation space, sediment thickness, and inner platform facies distribution (Holocene–Pleistocene, Bahamas)

“…For ancient carbonate platforms, similar observations were made suggesting that infill of accommodation space was a more random process, e.g., the Maiella platform margin (Central Italy; Eberli, 2013), the Latemar limestone platform (northern Italy; Kemp, Manen, Pollitt, & Burgess, 2016), and the Cambrian and Ordovician peritidal sequences exposed throughout the south-central Appalachians (Wilkinson, Diedrich, & Drummond, 1996). In these studies, unpredictable variations were found as variable or incomplete cycle thickness, variable cycle frequency, and absence of a shallowing-upward trend within the cycle (Eberli, 2013;Kemp et al, 2016;Wilkinson et al, 1996). Other uncertainties relate to the partial erosion of sediment infilling accommodation space during sea-level fall as well as facies-dependent variations in sediment compaction (Strasser, Pittet, Hillgärtner, & Pasquier, 1999).…”

“…Studies of the GBB as a modern example show that the Holocene sediment infill of the available accommodation space is a recent feature west of Andros Island (Maloof & Grotzinger, 2012) and the major part of the platform has remained unfilled (Bergman et al, 2010;Boss & Rasmussen, 1995). For ancient carbonate platforms, similar observations were made suggesting that infill of accommodation space was a more random process, e.g., the Maiella platform margin (Central Italy; Eberli, 2013), the Latemar limestone platform (northern Italy; Kemp, Manen, Pollitt, & Burgess, 2016), and the Cambrian and Ordovician peritidal sequences exposed throughout the south-central Appalachians (Wilkinson, Diedrich, & Drummond, 1996). In these studies, unpredictable variations were found as variable or incomplete cycle thickness, variable cycle frequency, and absence of a shallowing-upward trend within the cycle (Eberli, 2013;Kemp et al, 2016;Wilkinson et al, 1996).…”

“…Other studies (Drummond & Wilkinson, 1993;Strasser et al, 1999;Wilkinson et al, 1997) showed that the assumption might be correct only when the cycle top is intertidal and erosion is absent, and when the sediment column has been decompacted. Often shallow-water carbonate sequences contain incomplete or missing cycles (Eberli, 2013;Kemp et al, 2016;Strasser, 2015). Many ancient carbonate platforms showed an exponential thickness frequency distribution (Drummond & Wilkinson, 1993;Wilkinson et al, 1997) disproving the occurrence of any periodic process within such cycles.…”

Metre‐scale cycles in shallow water carbonate successions: Milankovitch and stochastic origins

“…This is modelled as a stochastic process to match the findings of Blanchon & Blakeway () (Fig. A) who determined a modal lag time of ca 1 to 2 kyr, with a distribution skewed towards shorter (<1 kyr) durations (see also Kemp et al ., ). Once initiated, accumulation is modelled as either positive (aggradational) or negative (erosional) at each time step.…”

“…Figure A illustrates the model, which is based largely on that presented in Kemp et al . () (MATLAB model code is available in Appendix ). In detail, when the platform is submerged, accumulation can occur, but it is subject to a lag time that reflects patchy (re)colonization of the platform surface by carbonate producers (Tipper, ).…”