Mathematical investigation of variation in the petrographical and chemical composition of the Chatburn limestone (Lower Carboniferous) of the Ribblesdale lowland

Petridou-Penna, Vassiliki (1977) Mathematical investigation of variation in the petrographical and chemical composition of the Chatburn limestone (Lower Carboniferous) of the Ribblesdale lowland. University of Southampton, Doctoral Thesis.

Abstract

The Chatburn Limestone of Lower Carboniferous age (late CourceyanChadian stages), an alternating sequence of flat bedded limestones and shales, has been examined at outcrop and, in the laboratory, bythin section petrography (including staining techniques), X-ray dffraction, X-ray fluorescence and by wet chemical analysis. All the results obtained have been subjected to computer scrutiny.Petrographical study of the rocks from twenty-eight measured outcrops has revealed the presence of major grain associations in the bioclasts. At Clitheroe there were two major associations: crinoid-ostracodbrachiopod and algae-foraminifera, whereas at Skipton the one dominant association was crinoid-ostracod-brachiopod-algae-foraminifera plus corals and bryozoa. Minor grain associations - of non-bioclastic components - also occurred. These associations are thought to represent the different parts of the reef environment from where these sediments were derived. Diagenetic.alteration occurs in all the limestones, but fails to obliterate the primary components. The two major bioclast associations were reflected in both mineral composition, where the crinoid-ostracod-brachiopod association showed consistently higher dolomite and silica concentration, and chemical composition, where the crinoid-ostracod-brachiopod association showed higher Si02, T102, A1203, Fe203, K20, S, Mn, Rb concentrations and the algae-foraminifera association showed higher CaO, C02, Ce, Sr concentrations.Statistical investigation of the two major outcrops of the Chatburn Limestone, at Clitheroe and Skipton, involved time-trend analysis, crosscorrelation and cross-association analyses, and Fourier analysis of both bed thickness variation and the geochemical data. Previously published computer programs were used in all cases, modified wherenecessary to suit the data. The investigation showed a consistent correlation between the upper part of the Skipton section and the base of the Clitheroe section. This confirms the recent revisionof the biostratigraphy (Ramsbottom, 1976). The bed-thickness of the shales, but not of the limestones, shows cyclicity, which is also present in those elements associated with clays.Turbidity currents are thought to have deposited the sediments of the Chatburn Limestone. This process required a steeply graded submarine canyon to Fenorate the currents, which built a submarine .fan in deep water (c.1000 m.) at the canyon mouth. The proximal part of the fan should have been channelled and small outcrops between Clitheroe and Skipton seem to show this channel-environment. The submarine canyon was probably located along; the South Craven Fault and the sediment was generated as the Martin Limestone of the Furness area.

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