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Claus Diessel1,
Ronald Boyd1,
Jennifer Wadsworth1,
Gareth Chalmers1
(1) The University of Newcastle, Callaghan, Australia
Abstract: The Identification of Accommodation Trends in Coal Seams
Lithotype-based strip samples covering the full thickness of paralic coal seams were analysed microscopically for components indicating trends in accommodation / peat-accumulation ratios at the time of deposition. It was found that accommodation cycles can be identified by a combination of detrital minerals and key macerals, supplemented by isometamorphic telovitrinite reflectance and fluorescence variations.
The results of the study enabled definition of five new stratigraphic surfaces in terrestrial rocks. On account of its widespread occurrence, we expect one of these surfaces, the Accommodation Reversal Surface (ARS), to acquire a high degree of significance in onshore sequence stratigraphy. This surface results from cyclic shifts between balanced and unbalanced accommodation / peat-accumulation ratios that follow the vertical pattern A-B-C-B-A, whereby the reversal surface coincides with the symmetry plane located in C.
We found a Non-marine Flooding Surface (NFS), to overly a shallowing-upward succession following an abrupt reversal from decreasing to increasing accommodation. Because of the hydrological connection between sea level and groundwater table in paralic coal measures, this usually hiatal surface correlates seaward with a marine-flooding surface.
A Give-up Transgressive Surface (GUTS) marks the non-hiatal end of peat accumulation following a gradual increase in accommodation, whereas a Terrestrialisation Surface (TeS) is positioned at the non-hiatal contact of the lower portion of a coal seam with its floor sediments. It results from a decrease in water depth and accommodation.
Finally, a Paludification Surface (PaS) marks the beginning of peat accumulation on a previously dry and often hiatal surface due to increasing accommodation.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana