Holmes, Ian Frederick (1980) Geochemistry and mineralogy of the Bembridge and Hampstead beds (oligocene), Isle of Wight. PhD thesis, University of Sheffield.
Abstract
Samples were collected from exposures of the Bembridge and
Hamstead Beds in Whitecliff Bay, Hamstead Cliff and Bouldnor
Cliff. Samples representative of various depositional environments
were analysed for twenty-six major and trace elements.
Mineralogical investigation by X-ray diffraction included
quantification of the clay minerals, calcite and quartz.
Attempts to utilise geochemical indicators of palaeosalinity
proved fruitless. Pyrite occurs in association with the two
marine transgressions, suggesting that the source of sulphur was
from solution. Alteration of pyrite to goethite and gypsum
occured during Pleistocene weathering of the Corbula Beds and the
movement of ions in solution associated with this affected the
original exchangeable cation contents. An increase in zirconium
content was found in samples deposited in high energy
environments, although exceptions to this occur. The Oligocene
sediments are enriched in lead, compared to average shales, due
to lead fixation in clay minerals formed from the Cornubian
granites. Aragonite occurs only in samples from the Bembridge
Oyster Bed, in other samples only low-magnesium calcite was
identified. The calcite in the Oligocene samples is poor in
substituent trace elements.
The clay mineralogy is an illite/smectite/kaolinite
assemblage, with traces of chlorite. The clay minerals are of a
dominantly detrital origin, from Mesozoic and Tertiary sediments
which lay to the north-west. The Lower Bembridge Beds in
Whitecliff Bay show evidence for derivation from a kaolinite-poor,
north-easterly source. There is evidence that transformation of
smectite into illite and illite-smectite occurred, possibly
following periods of more intense weathering in the hinterland.
Two samples show evidence for the neoformation of smectite. One
contains nontronite formed in a palaeosol, the other contains a
smectite which is thought to have been formed from volcanic
material. No variation in clay mineralogy was observed between
marine and non-marine samples.
Metadata
Keywords: | Geology |
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Awarding institution: | University of Sheffield |
Academic unit: | Department of Geology |
Identification Number/EthosID: | uk.bl.ethos.258117 |
Depositing User: | EThOS Import Sheffield |
Date Deposited: | 12 Apr 2016 14:04 |
Last Modified: | 12 Apr 2016 14:04 |
Open Archives Initiative ID (OAI ID): | oai:etheses.whiterose.ac.uk:10196 |
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