A modified stochastic approach to detect differences between sedimentary histories: Case study from the Roztoka-Mokrzeszów Graben (SW Poland)

Discrete stochastic processes are shown as tools for recognizing basin-scale differences between sedimentary histories available as borehole records. It is assumed that the vertical arrangement of lithologies within a borehole corresponds to a sample path of an unknown stochastic process. This allows one to seek its properties by means of statistical methods and, if these are detected, to compare probabilistic results obtained for different boreholes drilled within a basin. Sedimentary histories are assumed to differ if they exhibit different statistical properties. In this article, (1) dependence/independence in the succession of lithologies and (2) the existence of the Markov property within the vertical arrangement of lithologies are used to compare histories of sedimentation at different sites. For sparse borehole data we propose to apply Monte Carlo simulation under the null hypothesis of quasi-independence. This approach is applied to detect differences between sedimentary histories recorded in Neogene deposits from two sites within the Roztoka-Mokrzeszów Graben (SW Poland). Using statistical methods we conclude that sedimentation in the Mokrzeszów borehole exhibited dependence. On the other hand, no dependent structure has been revealed in the adjacent Szymanów borehole. We interpret these results as the evidence for existence of two minor subsidence areas within the regional subsiding structure of the Roztoka-Mokrzeszów Graben, each characterized by its own specific sedimentary history.