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Title: Sedimentology of Jurassic syn-rift resedimented carbonate sandbodies
Author: Abbots, Frances Vivien
ISNI:       0000 0001 3388 826X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 1989
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This thesis discusses the sedimentology of three contrasting Jurassic carbonate sand turbidite systems from Southern Europe: the Cutri Formation (Bathonian) of Mallorca; the Vajont Limestone (Bajocian-Callovian) of northern Italy; and the Peniche sequence (Toarcian-Aalenian) of the Brenha Formation of western Portugal. These sandbodies all formed in syn-rift extensional settings which imposed a primary morpho-tectonic control on both the source platform and depositional basin morphology. The three sandbodies in question display varying geometries and architectures and are discussed in terms of the palaeogeographic, tectonic and eustatic controls that governed their individual development; as well as being used to test the recently developed apron model against that of the submarine fan. In this context oolitic carbonate aprons associated with palaeowindward and palaeoleeward platform margins have been distinguished. The Cutri Formation is interpreted as a oolitic base-of-slope apron, that displays a minor single syn-rift thinning upward megacycle (retrogradational) trend indicative of subsidence out-pacing sedimentation. The apron correlates with a eustatic sea-level drawdown and was characterised by infrequently laterally correlatable, oolitic turbidite units separated by hemipelagic interbeds. This sandbody is relatively sand-poor in nature, and is interpreted as being sourced from a palaeowindward platform margin. The Vajont Limestone is re-interpreted as an aggraded oolitic apron from its original interpretation as a sub-marine fan. The apron is composed of stacked oolitic grainstone turbidites and is locally up to 800m thick. It is interpreted as being sourced from a stable `keep up' palaeoleeward platform margin, where dominant off-bank sand transport led to development of line-sourced oolitic turbidites, which were actively aggraded by on-going basin subsidence. Statistics were used to demonstrate a random turbidite sequence which enhances the apron interpretation. The Peniche sequence is reconfirmed as a carbonate-siliciclastic fan, its facies development conforming to a siliciclastic sand-rich fan model. Statistical analysis indicates a non-random (cyclic) turbidite sequence, thereby enhancing the fan interpretation. The fan occurs as a localised development within fine-grained basinal facies and correlates stratigraphically with a eustatic sea-level drawdown. Interpreted as being sourced from a palaeoleeward margin, the sequence progradates from outer fan lobes to a thick, multi-storey braided channel complex. These syn-rift resedimented carbonate sandbodies have the potential to be stratigraphically associated with basinal source rocks and therefore may be viewed as prospective hydrocarbon reservoir facies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geology