FORWARD MODELING δ13CCARB CHEMOSTRATIGRAPHIES ACROSS CARBONATE PLATFORMS

Across a carbonate platform, aliasing and distortion of a primary δ¹³C_carb signal can arise from numerous syn-depositional processes, including local change in accommodation and heterogeneous geographic distribution of lithofacies, and post-depositional processes, such as diagenesis and stratigraphic sampling (Myrow and Grotzinger, 2000; Dyer et al., 2018). Nevertheless, local δ¹³C_carb records routinely correlate across and between depositional settings. To explore the relative importance of these processes in dictating a local δ¹³C_carb signal and the correlation of these signals across space, we adapted a numerical forward model of 3-D carbonate deposition (CarboCAT; Burgess, 2013) to include δ¹³C_carb chemostratigraphy. CarboCAT employs a cellular automata modeling approach to model accommodation (parameterizing eustatic sea level and subsidence) and sediment accumulation (by tuning carbonate production rates and down-dip sediment transport). We present a variety of scenarios for two platform morphologies—a homoclinal ramp and flat-top platform—that isolate the role of carbonate production, carbonate transport, basin subsidence, and eustasy in dictating a local δ¹³C_carb signal. The simplest scenarios neglect carbonate transport and explore how different parameterizations of the three depth-dependent carbonate production factories embedded in CarboCAT (proxies for lithofacies) fill accommodation over time. Subsequent scenarios add complexity by introducing sediment transport; time-dependent changes in accommodation through constant/differential subsidence or sinusoidal, multi-period sea level fluctuations; and, finally, combinations thereof. We alter δ¹³C_carb values in cells adjacent to subaerial exposure surfaces to mimic diagenesis. Reference model parameterizations allow us to vary individual syn- or post-depositional processes to isolate their impact on intrabasinal δ¹³C_carb correlation (e.g, across ramp or platform in a strike or dip direction). Comparison of model δ¹³C_carb signals between the two platform morphologies probe the feasibility of interbasinal correlation (e.g, the δ¹³C_carb record of the same geographic cell for the ramp versus platform model). We employ an algorithm to assess the alignment of modeled δ¹³C_carb signals (Hay et al., 2019).