Sediment deformation structures and the palaeotectonic analysis of sedimentary basins, with a case-study from the Carboniferous of northern England

TLDR

Syn‑sedimentary faulting from earthquakes >5 generates soft‑sediment intrafolial deformation, which can be autokinetic or allokinetic, with large dewatering pipes and recumbent‑folded cross‑stratification typically allokinetic. The study aims to define and map an Allokinetic Deformation Number across lithofacies in a sedimentary basin. The authors map the Allokinetic Deformation Number and integrate it with lithofacies thickening, stacking, and rollover deformation data to outline the basin’s palaeotectonic evolution. Large dewatering pipes and recumbent‑folded cross‑stratification are predominantly allokinetic, and the methodology applied to the Northumberland Basin yields encouraging results.

Abstract

Summary There is a close link between syn-sedimentary faulting caused by earthquakes of magnitude >5 and accompanying ‘soft’ sediment intrafolial deformation in active neotectonic settings. Certain of these intrafolial structures may also be produced by purely sedimentary processes and are termed ‘autokinetic’. Those caused by earthquake-induced stresses are termed ‘allokinetic’. Although certain structures may be caused by either mechanism, it appears that large amplitude dewatering pipes and recumbent-folded cross stratification are likely to be predominantly allokinetic in origin. These structures may be used to define the Allokinetic Deformation Number which can be systematically mapped out in particular lithofacies over outcrops in a sedimentary basin. Results of this mapping are then combined with data on lithofacies thickening and stacking (tectonically-controlled architecture), hangingwall rollover deformation etc., to establish an interdisciplinary outline of palaeotectonic evolution. This methodology of palaeotectonics is tested in the suspected extensional terrain of the Northumberland Basin with encouraging results.