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Title: Palaeoenvironment studies in the Miocene (Libya, Australia)
Author: Doust, Harry
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 1968
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The environments of deposition and geological history of lower and middle Miocene rocks belonging to the Marada group have been considered. The rocks, cropping out in east-west trending escarpments in the area of the Zelten oilfield in central Cyrenaica, Libya, are flat lying and consist of rapid alternations of various lithelogical types. The basis of the study has been a detailed examination of the fossils and bioturtation from an ecological point of view. The fossils have been grouped into biofacies, 20 of which have been recognised, while the bioturbation has been both described and grouped into 10 ichno - fades. The environments represented by the rocks have been deduced from their internal structures and fossil content. Two phases of deposition have been recognised: (i) An earlier elastic phase, comprising fluviatile sands and shales together with intertidal and subtidal oalcareous sands, shales and interlaminated beds, found in the lower parts of the southern and western sections. The fluviatile sediments contain a rich biota of vertebrates and silicified wood indicating a tropical savannah climate, while the intertidal sediments are characterised by heavy bioturbation by Ophiamorpha Lundgren and Caegichnus nom.nov. amongst others. This phase is thought to be late Aquitanian and early Burdigalian. (ii) A later phase of carbonate deposition, thought to be Burdigalian and Helvetian characterises the upper parts of the northern an eastern sections. It comprises richly fossiliferous shallow water lime stones and estuarine calcareous sandstones and shales. The former were deposited in water depths of 0 - 50 metres and were nearly always affected by influxes of brackish water, only rarely being wholly eh-motorised by fully marine genera such as Echinolampas, Idmonea and Licgta. In most units large numbers of euryhaline genera like Crassostrea and Placenta are present, and they also characterise the estuarine calcareous sands and shales.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available