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AAPG Bulletin, V.
Ground truthing chemostratigraphic correlations in fluvial systems
1Chemostrat Ltd., Unit 1, Ravenscroft Court, Buttington Cross Enterprise Park, Welshpool, Powys SY21 8SL, United Kingdom; [email protected]
2University of Manchester, School of Earth, Atmospheric and Environmental Sciences, United Kingdom; Present address: Chemostat Australia Pty, Unit 12, 33 Delawney Street, Balcatta, WA 6021, Australia; [email protected]
3Chevron Energy Technology Company, 250 St Georges Terrace, Perth, Western 6000, Australia; [email protected]
4UniCIPR, Centre for Integrated Petroleum Research, Allégaten 41, N-5077 Bergen, Norway; [email protected]
5Chemostrat Inc., 750 Bering, Suite 550, Houston, Texas 77057; [email protected]
6University of Manchester, School of Earth, Atmospheric and Environmental Sciences, United Kingdom; [email protected]
Changes in elemental chemistry have been used to define stratigraphic correlations between wellbores in petroleum basins. Few publications, however, relate defined chemical stratigraphy to physical correlations, and none have been found that do so in fluvial systems. Here, chemostratigraphy is applied to Permian fluvial sediments within the Beaufort Group of the Karoo Basin in South Africa, and a correlation between three logged sections is defined. This correlation is tested against physically determined chronostratigraphic correlations achieved using Heli-LIDAR data to provide a high-resolution correlation between two sections 7 km (4.4 mi) apart, and mapping of strata using Google Earth to produce a correlation between sections 25.5 km (15.8 mi) apart.
The chemostratigraphic characterization that is defined using data from fine-grained lithologies resulted in the recognition of eight chemostratigraphic packages, with thicknesses between 50 and 250 m (164 and 820 ft) over a stratigraphic interval of approximately 900 m (2953 ft). Two distinctive changes in geochemical composition of the coarser lithologies (fluvial channel belts) were seen over this interval. In the two sections that are 7 km (4.4 mi) apart, higher resolution subdivision of chemostratigraphic packages was achieved to produce four correlative geochemical units (30–60 m [98–197 ft] in thickness) that provide a high-resolution correlation.
The chemostratigraphic and chronostratigraphic correlations are in close agreement in both the 7-km- (4.4-mi) and the 25.5-km- (15.8 mi) spaced sections. The thickness of the study interval and spacing of sections is analogous to published chemostratigraphy studies on subsurface sequences; thereby, ground truthing the use of chemostratigraphy for correlation in subsurface fluvial systems that are, to some degree, analogous to the Beaufort Group sediments of this paper.
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