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Applying the ratio matching method in the correlation of sedimentary sequences and individual beds in a coal-bearing unit. Advantages and limitations of the technique

Abstract:

Conventional techniques employed in the correlation of sedimentary sequences or single beds make use of non-diagnostic parameters, such as lithological and palaentological features, or simply field criteria. More sophisticated tools are provided by compositional data. Particularly useful is the geochemical matrix derived from the trace element analysis as "fingerprint", e.g. in the correlation of coal beds, or Chemostratigraphy. Trace elements exhibit several advantages for correlation purposes, but their management requires specific statistical methods. A procedure pointed out in the literature is the Ratio Matching Method, successfully utilized in the determination of effluents in a lake, as like in the pbkp_rediction of sand grains movement in a shoreline. In this work, the Ratio Matching Method was assayed as a statistical aid searching for genetic relationships in two case studies: A) correlating a sedimentary sequence outcropping in three localities of Falcón State (northern Venezuela) separated 4-10 km between them, using all lithologies in the stratigraphic unit; and b) in the correlation of coal-bearing sequences using only geochemical data from coals. A simple macro from MICROSOFT EXCEL® software was required for nearly all calculations. Correlation with Ratio Matching numerical method was possible between coal beds only for short distances (<20 km); the utility of the tool decreases as long as the geographical distance between localities increases, and the confidence is low. On the other hand, Ratio Matching is a powerful tool for the correlation of sedimentary sequences using all lithologies present, where the pool of data is higher, with the aid of stratigraphic criteria for a stronger validity in the assigned correlations. Criteria taken in the sampling procedure have a little effect on the results.