The influence of variable progradation to aggradation ratio and facies partitioning on the development of syndepositional deformation in steep-walled carbonate platforms

One of the remaining questions in carbonate geology and reservoir studies is the origin of steep-walled carbonate platform margins and the role of gravity versus other structural processes in controlling the distribution of fracture networks and failure surfaces. This study is an attempt to document the role of gravity, interacting with stratigraphic architecture in controlling fracture patterns and margin collapse. We employ finite-discrete element models to illustrate that progradation/aggradation (P/A) ratio and facies tract partitioning in steep-walled carbonate platforms affects the development, distribution, and intensity of syndepositional deformation. All models are under the influence of only gravitational loading, where pore pressure is held constant. We utilize a modified Mohr-Coulomb constitutive law with a Rankine Rotating crack tensile corner to capture both tensile and shear brittle failure. Our results illustrate that P/A ratio affects the distribution and intensity of discrete fractures that form in steep-walled carbonate platforms. Our results suggest that deformation is more extensive in a progradational carbonate platform, where shelf edge angles are greatest and the clinoform is thickest. Alternatively, aggradational carbonate platforms experience localized deformation in front of the antecedent shelf edge where the clinoform is thickest and steepest. The introduction of mechanical heterogeneity associated with facies tract partitioning affects the intensity of fracturing in both progradational and aggradational models, with the greatest number of fractures developing in reef facies in both scenarios. Development of brittle deformation under the sole application of gravity and lack of seaward lithostatic confinement is consistent with the syndepositional nature of deformation in these settings. This work illustrates the interplay between carbonate platform geometry, facies distribution, and the resulting syndepositional deformation.