Organic-matter vitrinite reflectance variability in the Outer Carpathians, Poland: relationship to tectonic evolution

Abstract

Random vitrinite reflectance of allochthonous plant material varies throughout all the flysch sedimentary units of the Outer Western Carpathians. The vitrinite reflectance of coalified phytogenic matter is variable even within the same lithostratigraphic unit. There is no clear relationship between random vitrinite reflectance and stratigraphy (age of particular strata) within surface samples. The typical pattern of increasing random reflectance with depth in boreholes is unsettled by R_r^o “jumps” which occur within folds and overthrusts. However, this study revealed a trend of increasing random vitrinite reflectance from north to south in the area of the Magura Unit. A compressional regime involving phases of uplift and burial, varying from place to place in the flysch basin, was the main factor influencing coalification. The initial maturity of organic matter transported to the marine environment was a secondary factor. A degree of coalification had occurred in the flysch sediments prior to the main stage of fold-and-thrust movements associated with the phase of maximum tectonic subsidence at the end of the Eocene. It is generally assumed that coalified plant material dispersed in sedimentary rocks experienced the same physical and chemical changes as those in larger accumulations of coal. Coalification of phytogenic material coeval with flysch in the Outer Carpathians corresponds to the interval from sub-bituminous to low-medium-rank bituminous coal.