Inter Relationships Between Sedimentary Facies, Diagenesis and Fluid Flow in the Garvock Group, Lower Old Red Sandstone, Scotland, U.K

Kennedy, Deborah A (1989) Inter Relationships Between Sedimentary Facies, Diagenesis and Fluid Flow in the Garvock Group, Lower Old Red Sandstone, Scotland, U.K. MSc(R) thesis, University of Glasgow.

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Sedimentary facies may be distinguished not only by their morphology and grain size but also by different diagenetic histories. In sand bodies which constitute hydrocarbon reservoirs, it is therefore of some interest to attempt to recognise and delineate these different diagenetic zones. A single sand bar within the fluvial succession of the Garvock Group Lower Devonian, was chosen for study, since this would aid in understanding the controls on the distribution of good reservoir characteristics to be found in association with fluvial sediments. The Crossgates sediments showed a range of diagenetic zones which may reflect the diagenetic pathways defined by depositional environment, sand body geometry, and porosity / permeability anisotropy. The intrusion of a quartz tholeiite dyke during the Late Carboniferous has led to local hydrothermal overprints on the diagenetic history. Porosity / permeabilty anisotropy within the Crossgates sequence can be closely correlated to the sedimentary facies observed within the sand bar. This porosity / permeability anisotropy has had a profound effect on the diagenesis of the Crossgates sequence. Original differences in porosity and framework mineralogy have resulted in different diagenetic histories for different sedimetary facies. Within the sequence the upper regions of the bar were originally the finest-grained and more clay-rich, here porosity and permeability were poorer and fluid circulation more restricted, this has resulted in diagenetic effects being less marked. This contrasts with other locations where porosity and permeability may have been high and only subsequently reduced by compaction and diagenesis. The diagenetic history can be briefly summarised as follows: Grain coating haematie and mixed layer clays are initially developed. Subsequent pore-filling kaolinite and associated minor quartz are prominent in the silty-grade facies. Calcite and contemporaneous anatase are pervasive, and partly replacive of earlier cements and detrital silicates, but are predominantly pore-filling. Pore-bridging fibrous illite is then developed and this is the final diagenetic event prior to dyke induced hydrothermal alteration. This hydrothermal alteration results in the devolpment of chlorite in sediments adjacent to the dyke, and the re-mobilisation of earlier carbonate cements. Stable isotopic data indicate temperatures of precipitation for the carbonate of between 35 to 50

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Keywords: Geology, Sedimentary geology
Date of Award: 1989
Depositing User: Enlighten Team
Unique ID: glathesis:1989-77917
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:48
Last Modified: 30 Jan 2020 15:48

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