Forward Stratigraphic Modeling Experiment to Evaluate the Sensitivity of Passive Margin Stratigraphy to Variations in Sea Level, Sediment Supply, and Subsidence

In a numerical modeling experiment, we demonstrate that variations in sea level and thermally- and flexurally-driven subsidence produce unique signatures in passive continental margin stratigraphy. Having produced a 10 Myr synthetic stratigraphic section using a set of known parameters within a forward stratigraphic model, that model output was recursively fit using a Bayesian optimization algorithm to test: 1) if the output of the model applied with assigned parameters could be accurately reconstructed; 2) if the parameters used to create the original model output could be recovered; and 3) the sensitivity of the model output to given model parameters and the attendant physical processes. The original synthetic stratigraphic section was produced with imposed cyclical sea-level variations of 40 m and 30 m with 2.4 Myr and 10 Myr periods, respectively. Sediment was also supplied cyclically, in 2.4 Myr and 10 Myr cycles with amplitudes of 30 and 80 tons/100 kyr, respectively, varying from a mean of 232 tons/100 kyr. Parameter values were sampled to fit the model using a Markov chain Monte Carlo algorithm, resulting in a ±5 m (1σ) variation between the experimental output and the original. Sea level varied by ±7 m (1σ) within the posterior distribution of parameters. As a result, both the 10 Myr and 2.4 Myr sea-level cycles could be extracted from the original output. The tolerated variation in sediment supply was approximately ±38 tons/100 kyr (1σ) and, as a result, only the larger long-term supply variations could be accurately recovered in refitting the model. The variation in thermal, flexural, and total subsidence across those parameter sets is less than ±10 m (1σ). The original section experienced 150 m of total subsidence at the depocenter. Individual parameters defining the numerical representation of these processes (e.g. elastic thickness of the crust) varied more widely. The results suggest that large-scale processes (e.g., sea level and subsidence) leave a distinct imprint on continental margin stratigraphy. Moreover, we conclude that sea-level change produces a defined effect on the geometries of stratigraphic architecture on passive continental margins, and that techniques applied for the purpose of delineating sea-level variation from continental margin strata have a well-founded conceptual basis.