Sedimentary models for coal formation in the Klip River coalfield.
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Date
1988
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Abstract
The primary objective of this study was to establish sedimentary models for
peat formation in the southern part of the Klip River coalfield during Ecca
(Permian) times and to assess palaeoenvironmental controls on coal seam
behaviour and distribution. In order to achieve this approximately 2 400
borehole logs and 25 field sections were collected.
The coal-bearing Vryheid Formation records early to late Permian
fluvio-deltaic sedimentation within the northeastern main Karoo basin. Three
informal lithostratigraphic subdivisions, based on the investigations of
Blignaut and Furter (1940, 1952), are proposed: the Lower zone, Coal zone and
Upper zone.
An examination of the structural framework and history of the northeastern
Karoo basin reveals that the southern and western boundaries of the Klip River
coalfield are defined by zones of rapid basement subsidence : the Tugela and
Oannhauser Troughs respectively. There is some doubt as to the locality of the
source area to the rivers emptying into the Ecca sea. Ryan (1967) postulated
the "Eastern Highlands" situated off the present southeast African coast, but
it is contended that the Swaziland area, situated no more than 200 to 300 km to
the northeast of the Klip River coalfield, constituted a more plausible source
area.
The Lower zone represents sedimentation along a westerly to southeasterly
prograding coastline dominated by high-constructive lobate or braid deltas, but
also showing significant influence by wave processes. The Coal zone, which
varies in thickness from 35 to 60 m, represents a major phase of coastal
progradation and braided-river deposition on extensive alluvial plains.
Significant coal seams formed only during periods of fluvial inactivity, the
duration of which was dependent on source-area processes.
Coal seam geometry and behaviour in the Klip River coalfield were not
influenced by the depositional environments of associated clastic sediments.
The following factors were found to have of profound influence in determining
the extent, distribution and rate of peat accumulation:
1. Platform stability and temporal and spatial variations therein.
2. The absence or presence of penecontemporaneous clastic sedimentation.
3. Duration of periods of peat formation.
4. Lithology and topographic expression of clastic sediments underlying
peat-forming swamps.
The peat-forming phase of the Vryheid Formation was terminated by an
extensive transgression brought about by an eustatic rise in basin water-level
and/or an increased rate of platform subsidence.
Description
Thesis (Ph.D.)-University of Natal, 1988.
Keywords
Coal--Geology--KwaZulu-Natal., Sedimentation and deposition--KwaZulu-Natal., Geology--KwaZulu-Natal., Theses--Geology.