3D seismic analysis of the geometry and development of a deep water fold and thrust belt

Higgins, Simon Mark 2007. 3D seismic analysis of the geometry and development of a deep water fold and thrust belt. PhD Thesis, Cardiff University.

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Abstract

This thesis uses industry 3D seismic to investigate the nature and distribution of strain in a deep water fold and thrust belt and describes the complex fault plane and stratal geometries that result from fold and thrust linkage. The principal aim is to gain a better understanding of the structural architecture and evolution of toe-of-slope compressional settings. To this end, the project represents a logical series of arguments involving the study of individual structures and fold and fault pairs, to considering a fold belt as a whole. The outer thrust belt of the Niger Delta is observed to comprise of synthetic and antithetic faults that interact and link along strike. A preliminary geometric classification is proposed for antithetic thrust fault linkage zones based on observations of fault surface and stratal geometries. The relationship between fault interaction and fold characteristics is also investigated. The connectivity of stratigraphic horizons across fault surfaces and through transfer zones is shown to vary with the type of linkage and with depth. Conclusions drawn on the along strike variability of fault network density, orientation and vertical extent are shown to have significant application to modelling of fluid flow. The concept of numerous and geometrically distinct thrust fault linkages forming through-going folds is developed through the investigation of a single isolated fold that comprises a number of linking forethrusts and backthrusts. This case study, involving the quantification of the development of this relatively simple structure, allows conclusions to be drawn on fold growth that are later applied to a more complex and closely spaced fold belt. The internal structural geometry of faults and stratigraphic horizons within the single fold are described though detailed three-dimensional mapping. The analysis of the distribution of fault and fold strain, both on individual thrusts within the fold and for the structure as a whole, suggest efficient displacement transfer between numerous linking faults that accommodated shortening as a coherent unit. In addition to this, variations in the magnitude of fault heave are compensated by complementary trends in fold strain. A study of syn-kinematic units demonstrates that the single structural culmination present today was initially made up of a number of folds with local structural highs. Major thrust surfaces within the fold are also interpreted to be the product of the along strike linkage and amalgamation of initially distinct faults. These observations made on the isolated fold are applied to a complex, closely spaced fold belt. The relative timing of individual faults and folds agree with established models of a progressive foreland propagating sequence of thrust faults but also display out-of-sequence events. Findings demonstrate a significant period of synchronous development between all structures in the fold belt. Aggregation of fault and fold shortening profiles indicate that displacement transfer occurs along strike and also in a dip-parallel direction between within the fold belt. Bulk shortening is thus conserved along strike within the syn-kinematic units and low lateral heave gradients suggest efficient displacement transfer between all constituent structures. The evidence presented here shows that all elements of a fold belt can be kinematically linked during growth. Irregularities in the distribution of deformation in pre-kinematic units corroborate findings that the folds are the product of along strike linkage of discrete segments, in a similar manner to that documented in extensional systems.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QE Geology
ISBN:	9781303213496
Date of First Compliant Deposit:	30 March 2016
Last Modified:	31 Jan 2020 07:34
URI:	https://orca.cardiff.ac.uk/id/eprint/54746

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