Cyclic characteristics of coal‐bearing sediments in the Bochumer Formation (Westphal A 2) Ruhrgebiet, Germany

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.

Cyclic Sedimentation of the Barakar Formation, Singrauli Coalfield, India: Statistical Assessment from Borehole Logs

“…This leads to the rejection of the null hypothesis (H 0 ) that the correlation ber of cycles present. This direct relationship suggests th coefficients are not significantly different from zero and acceptance of the alternative hypothesis (H 1 ) that the the Singrauli coalfield was controlled by autocyclic process, which operated within the depositional basin rather Table 6) exists between total thickness of strata (net subsidence) and average thickness of sedimentary cycles (Figure 6), which matches well with the findings of Casshyap [5], Hota and Das [9], Hota [10] and Johnson and Cook [12]. Such relationship implies inconsistent relation between the factors, which determine the total thickness of strata (net subsidence), and those which control coal formation (peat accumulation).…”

“…This is in conformity with the findings of Casshyap [5], Hota and Sahoo [8] and Hota and Das [9], Duff [11], Johnson and Cook [12], Read and Dean [13], Hota and Pandya [24]. Thicker the succession i.e.…”

“…According to Udden [19] a cycle commences at the base of coal seam whereas Weller [20] gave a formation status to each cycle with sandstone at the base and coal seam at the top. Read and Dean [21] suggested the minimum thickness of a cycle to be 0.3 m while Casshyap [5] put it 1 m. In the present work, the sequence of strata of more than 1 m thickness with basal coarse member (conglomerate or sandstone) and terminating with a coal seam has been considered to constitute a cycle. For simplicity of analysis and to avoid the risk of error [4,5], the lithologies observed in the surficial study were condensed into five facies states on the basis of lithology and texture as observed in the borehole records.…”

“…n probability (p ij ) random probability (r ij ) and difference (d ij ) matrices using the following equations proposed by Miall, Casshyap and Tewari et al [4,5,23]. …”

“…Statistical methods like Markov chain and entropy analyses reveal the cyclic arrangement of lithofacies and their degree of ordering [1][2][3]. These methods have been extensively used for analysis of coal measure cyclothems as well as alluvial, deltaic and marine successions of different geological ages throughout the globe [4][5][6][7][8][9][10]. Quantitative relationship between net subsidence and sedimentary cycles reveals the cause of cyclic sedimentation [5,[11][12][13][14].…”