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Title: Palaeoenvironmental studies in mid-Tertiary carbonates of SW Sicily
Author: Crawford, Robin
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1984
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Upper Oligocene limestones up to c. 50 m thick form disconnected outcrops within a 20 km radius of Sciacca in southwest Sicily. Two facies are present: foraminiferal grainstone-packstones (dominatedby large benthonic foraminifera, particularly Lepidocyclines), and rhodolithic algal packstone-wackestones (in which eight species of coralline red algae are present). Petrology, fauna and flora indicate deposition in cool oxygenated waters of normal marine salinity at depths of 80-250 m in tropical subtropical latitudes; the two facies representing differences in local water depth and turbulence. Rare feldspars within the limestones are diagenetic, with a variable sodic oligoclase - calcic anorthoclase composition related to localised synchronous glauconitisation. The limestones rest disconformably on Cretaceous/Eocene carbonates, locally burrowed by paradoxioa. A basal conglomerate contains both locally derived limestone cobbles and allochthonous phosphatised Eocene pebbles. All phosphate occurs as francolite re-placing limestone. Features of major, trace and Rare Earth elements clearly differentiate these phosphates from Lower Miocene phosphorites of both southeast Sicily and the Maltese islands, which have a very similar geochemistry. Lower Miocene limestones form similar outcrops generally to the north of the Upper Oligocene limestones and comprise a glauconitic limestone facies and a sandy limestone facies. Glauconite occurs as ubiquitous pellets, its geochemistry indicating formation by a gradational alteration of calcium carbonate. Petrology indicates deposition of the sediments in an outer shelf environment. Field relations of the two facies indicate that the Western Sicily Bridge (auot,) was a positive structural feature from basal Miocene times, acting as a barrier to the arenaceous Numidian Flysch facies derived from the west-southwest. Porosity of the Oligocene - Miocene limestones has been greatly reduced by compaction and by phases of both early submarine and latesubaerial diagenesis. Southward thrusting and associated folding post Lower Miocene times have slightly transported the sequences from their original (Saccense) carbonate platform and (Sicani) basin environments.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Sedimentary Geology