St Andrews Research Repository

St Andrews University Home
View Item 
  •   St Andrews Research Repository
  • Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)
  • Geography & Geosciences (Previous name for currents schools of Earth & Environmental Sciences and ...)
  • Geography & Geosciences Theses
  • View Item
  •   St Andrews Research Repository
  • Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)
  • Geography & Geosciences (Previous name for currents schools of Earth & Environmental Sciences and ...)
  • Geography & Geosciences Theses
  • View Item
  •   St Andrews Research Repository
  • Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)
  • Geography & Geosciences (Previous name for currents schools of Earth & Environmental Sciences and ...)
  • Geography & Geosciences Theses
  • View Item
  • Login
JavaScript is disabled for your browser. Some features of this site may not work without it.

The Karoo Supergroup (Triassic-Jurassic), Seychelles : sedimentology, provenance and diagenesis of a terrestrial succession and comparisons with marginal sediments from Elk Point group (Devonian), Alberta, Canada

Thumbnail
View/Open
KhannaMohitPhDThesis.pdf (21.77Mb)
Date
07/1992
Author
Khanna, Mohit
Supervisor
Walton, E. K. (Ewart Kendall)
Funder
Overseas Research Award by the Committee of Vice-Chancellors and Principals of the Universities in U.K.;
Sir Ernest Cassel Memorial Trust
Metadata
Show full item record
Altmetrics Handle Statistics
Abstract
The offshore Karoo Supergroup (+2 km thick) of the Seychelles has been divided into five members based mainly on sandstone/mudstone development as revealed by wireline logs and lithological samples. The four lower members are characterized by thick sandstones with minor mudstones and the lowest member distinguished by the presence of occasional bands of lignite; the topmost member has thick mudstones as well as thick sandstones. Members 2 and 3, and 4 and 5 form two upward-fining megacycles in which members 2 and 4 have coarser-grained pebbly, sandstones while the sandstones of 3 and 5 are medium and fine-grained. The sediments are fluvial in origin, possibly braid plain except for the uppermost member which may have formed under a meandering system. Paleogeographic reconstruction invokes a source area in north-east Madagascar shedding debris eastwards towards the Seychelles which at that time (pre-mid-Jurassic) lay between Madagascar to the west, and India to the east. Burial curves are presented from considerations of sediment thickness and texture, structure, including the positions of unconformities and diagenesis as an aid in assessing oil potential. With possible source rocks in overlying marine sediments, hydrocarbon generation may have occurred in late Mesozoic and early Tertiary. Migration could possibly have taken place into fault-juxtaposed Karoo sandstones. For comparative purposes petrographic features of samples from the Elk Point Group Alberta, Canada were studied. This Devonian sequence comprises marginal and marine sediments including carbonates and evaporites, but the sandstones studied come from marginal deltaic deposits. Sandstones studied are remarkably similar in both original composition and diagenetic history. Primary mineralogy was determined by similar source areas - predominantly granitic with minor metamorphic and volcanic components. Despite being deposited in different sedimentary environments both groups show extensive diagenesis involving dissolution of feldspars and lithoclasts, precipitation of quartz, and a second phase of dissolution of feldspar, lithoclasts and quartz. Kaolinite is the dominating clay in the sandstones of Karoo Supergroup up to depths of 10,000 ft, while illite prevails over other clays in the sequence between 10,000-12,500 ft. Illite and chlorite are present in the Elk Point Group: kaolinite is absent. The last stage of cementation in Elk Point sandstones was anhydrite precipitation during Cretaceous times. Precipitation of authigenic cements ended with the formation of carbonates in Karoo sandstones. Cementation, especially by quartz appears to have considerably reduced porosity in many places in both the successions. In both the study areas early diagenesis was controlled by meteoric waters while burial and marine influence are responsible for later diagenetic episodes. The presence of illite and chlorite against kaolinite in the Elk Point Group is due to greater depths of burial than Karoo sandstones. Presence of evaporitic environments lead to the formation of anhydrite in the sandstones of Elk Point Group, while feldspar overgrowths are formed as a result of retention of pore-fluids due to the formation of a closed system controlled by marine flooding surfaces.
Type
Thesis, PhD Doctor of Philosophy
Collections
  • Geography & Geosciences Theses
URI
http://hdl.handle.net/10023/15472

Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.

Advanced Search

Browse

All of RepositoryCommunities & CollectionsBy Issue DateNamesTitlesSubjectsClassificationTypeFunderThis CollectionBy Issue DateNamesTitlesSubjectsClassificationTypeFunder

My Account

Login

Open Access

To find out how you can benefit from open access to research, see our library web pages and Open Access blog. For open access help contact: openaccess@st-andrews.ac.uk.

Accessibility

Read our Accessibility statement.

How to submit research papers

The full text of research papers can be submitted to the repository via Pure, the University's research information system. For help see our guide: How to deposit in Pure.

Electronic thesis deposit

Help with deposit.

Repository help

For repository help contact: Digital-Repository@st-andrews.ac.uk.

Give Feedback

Cookie policy

This site may use cookies. Please see Terms and Conditions.

Usage statistics

COUNTER-compliant statistics on downloads from the repository are available from the IRUS-UK Service. Contact us for information.

© University of St Andrews Library

University of St Andrews is a charity registered in Scotland, No SC013532.

  • Facebook
  • Twitter