Markov Chain Analysis of the Shallow Marine lBhuj Sandstone of Early Cretaceous Age, Kachchh Basin, India

Cyclic characteristics of lithofacies of the shallow marine Bhuj Sandstone were studied statistically, using embedded Markov chain analysis and the concept of entropy. Data came from thirteen measured sections. The upward transmissions from one sedimentary lithofacies to another are plotted on a 5×5 matrix and a transition tree is constructed. Results strongly suggest that the Bhuj Sandstone was influenced by a Markovian mechanism and accumulating in well-defined depositional environments; the vertical distribution of lithofacies was controlled by a number of natural processes. The preferential upward transition path of lithologic and depositional envitonment changes are as follows: Carbonaceous siltstone/shale (A) (Coastallagoon) → Coarse-grained cross bedded Sandstone (8) (Estuarine channel) → interbedded sandstone siltstone (C) (Tidal flat-tidal channel) → silty sandstone (D) (Sandflat - shoal) → Bioturbated sandstone (E) (Shelf Sheet sand) → Carbonaceous siltstone/shale (A) (Coastal lagoon).

This sequence is an asymmetrical cycle. It can be identified into a progradational event (lithofacies A-D) and a transgressive event (lithofacies E). The statistical results concur with the sedimentological evidence for depositional environments.

Entropy plots of the E^(pre) and E^(post) values of each lithological state correspond to the type A-4 category (Hattori, 1976), signifying lower and upper truncated asymmetrical cycles. The values of E (system) fall just on the boundary of the area allocated for the neritic environment. The area occupied by the Bhuj Sandstone evidently represents the domain of deposits of a coastal complex of estuary, lagoon and tidal flat environments, deposits for which Hattori had no data base.