2D flexural backstripping of extensional basins; the need for a sideways glance

Abstract

Backstripping is a technique employed to analyse the subsidence history of extensional basins, and involves the progressive removal of sediment loads, incorporating the isostatic and sediment decompaction responses to this unloading. The results of backstripping calculations using 1D models employing local (Airy) isostasy and 2D models employing "flexural" isostasy are compared for three cross-sections of the North Sea rift basin. Backstripping is commonly used to estimate stretching factor (beta ) across extensional basins. At structural highs 1D Airy backstripping will overestimate beta by comparison with predictions from 2D flexural backstripping, because Airy isostasy fails to acknowledge the effects of lateral differential loading. Predictions of beta from 2D flexural backstripping are closer to those derived from forward modelling. 1D Airy backstripping also produces unrealistic internal deformation of individual fault-blocks and overestimates beta when the pre-rift sequence is not fully decompacted. The palaeobathymetric data required by 1D Airy backstripping are often inaccurate, which yields misleading results. 2D flexural backstripping has been formulated as reverse post-rift modelling, which is used to produce sequential (isostatically balanced) palinspastic post-rift cross-sections. These are calibrated using only high-quality palaeobathymetric data, allowing 2D flexural backstripping to be used to predict palaeobathymetry away from the calibration points.