Investigating the effect of sediment loading on the growth of a shale-cored anticline using finite element modelling: an example from the South Caspian Basin

• Published in: Geomechanics and geophysics for geo-energy and geo-resources. Vol. 10; no. 1; pp. 1 - 20
• Main Authors: Procter, Andrew, Roberts, Daniel T., Lonergan, Lidia, Dee, Stephen J.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2024; Springer Nature B.V; Springer
• Subjects: 2023; Anticlines; Atlanta; Correspondence; Density; Elastoplasticity; Energy; Engineering; Environmental Science and Engineering; Finite element method; Finite element modelling; Folding; Foundations; Geoengineering; Geomechanics; Geophysics/Geodesy; Geotechnical Engineering & Applied Earth Sciences; Growth rate; Hydraulics; Kinematics; Load distribution; Morphology; Overburden; Plane strain; Sediment; Sediment load; Sediment loading; Sediment transport; Sedimentary rocks; Sedimentation; Sedimentation & deposition; Sedimentation rates; Sediments; Selected Contributions from the 57th US Rock Mechanics/Geomechanics Symposium; Shale; Shale tectonics; Shales; South Caspian Basin; Tectonics; Viscosity; Sediment loading; Geomechanics; Finite element modelling; South Caspian Basin; Shale tectonics; Folding
• ISSN: 2363-8419; 2363-8427
• DOI: 10.1007/s40948-024-00898-z

Large-scale folding of sedimentary rock is generally considered to be a response to horizontal tectonic shortening. We test an alternative hypothesis where we propose that in basins with high sedimentation rates where folds are cored by mechanically weak mobile shale, fold growth can be amplified by the gravitational loading of the weak underlying shale. We use two-dimensional plane-strain, finite element code to investigate the mechanics of growth of a shale-cored fold in the South Caspian Sea Basin, where c.10 km of sediment was deposited in the last 6 My. The overburden and syn-kinematic sediments are modelled as poro-elastoplastic materials using a modified Cam-Clay critical state model and the mobile shale is modelled as visco-plastic Herschell-Bulkley material, representative of conditions at critical state. The results show that the atypical geometries of the fold strata can be explained by the application of horizontal shortening and simultaneous sediment loading of the visco-plastic layer. The viscosity of the shale determines whether differential loading will cause fold growth and its density controls the magnitude of fold amplification, with a lower density causing greater fold amplification. Results demonstrate that the magnitude of shale inflation is controlled by complex interaction of the relative amounts of shortening and sedimentation rate. Article Highlights Growth histories of mobile shale cored folds in the South Caspian Basin are influenced by the density and viscosity of the mobile shale. The interaction of sedimentation rate, mobile shale thickness and amount of tectonic shortening control the fold morphology. Sediment loading and the distribution of the sediment load across the shale cored folds control fold growth rate and morphology.