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ABSTRACT

Cyclic characteristics of the Bochumer coal measures have been studied statistically using first-order embedded Markov chain analysis on data from thirty-two boreholes. Separate tally matrices which were made for the Lower, Middle and Upper units by summing the tally matrices for all the boreholes, were used to produce various transition probability matrices, which were then subjected to the chi-square test. Results strongly suggest that the Bochumer succession was deposited by a Markovian mechanism, and that the sequence represents cyclic sedimentation.

The preferential upward transition path for lithologic changes that can be derived in the total area and in individual logs is: coal\rightarrow shale\rightarrowsiltstone\rightarrowsandstone\rightarrowsiltstone\rightarrowrooty bed\rightarrowcoal. Among the noteworthy features are a two-way transition between siltstone and sandstone, which implies frequent interbedding of the two lithologies, and the transition, up out of siltstone to rooty beds. There are, however, minor variations, locally, either by way of subsidiary transitions or in the extent to which the above transitions can be followed. When tested for stationarity through time and space, the Markov chain analysis yields results which show the upward sequence of lithologic states (facies) to be stationary at individual localities, but non-stationary when the entire data are tested for the whole area. The relationship of the number of coal-bearing cycles to total thickness of strata and average thickness of coal-cycles is examined using linear regression. Significant positive relationships are present between the number of cycles and total thickness, and significant negative correlations occur between the number of cycles and their average thickness.

The results of the study have been used to infer sedimentological evolution of the succession and sediment cyclicity. Environmentally, the Bochumer cycles fit suitably into the concept of deltaic cycles.