Tectonic subsidence patterns in the multi-stage extension systems: Insights from quantitative backstripping analysis and modelling of the margins of Dahra and Beda Platforms, Sirt Basin, Libya

Abstract

Quantitative analysis of tectonic subsidence patterns of 13 wells from the margins of Dahra and Beda Platforms provides new insights into the development of two major fault blocks in a tectonically active region of the western Sirt Basin. Backstripped subsidence curves and tectonic subsidence rates reveal four different tectonic stages (I–IV) from the Late Cretaceous to Middle Eocene. Continental rifting was initiated during the Cenomanian-Turonian period. Model curves predict maximum crustal stretching factor is 1.11 for this stage. From Campanian to Maastrichtian an exponentially decaying subsidence behaviour is described in the backstripped curves, indicating a stage of thermal sagging associated with the widespread distribution of Maastrichtian shallow-marine sediments according to a regional transect that crosses the margins of both platforms. Rapid short-term subsidence alterations from thermally driven long-term sagging, were recognised during the Palaeocene. The stretching factors for this third stage are about 1.3 for the southeastern margin of the Dahra Platform and >1.21 for the Amin High. The termination of subsidence during the Eocene is defined as a thermal subsidence stage. The stretching factor possibly decreased to an average 1.18 on both platforms. However, well data indicate that the Middle Eocene sediments exposed along the margins of Dahra and Beda Platforms, indicating that the sedimentary rocks of the post-Eocene succession, were whether not deposited or were mostly removed by erosion in the study area, due to a subsequent regional phase of differential uplift during the Oligocene-Miocene. This uplift phase is clearly distinguished on the tectonic subsidence curve from the Middle Maradah Trough.