Abstract
The paper presents the latest state of knowledge on clastic sedimentary rocks from the Carboniferous complex in the SW part of the Polish Lowlands, studied to help determine their potential prospectivity for the occurrence of oil and/or gas deposits. Rocks were analyzed with respect to the petrographic-mineralogical characteristics of the Carboniferous deposits, their diagenesis, determinations of pressure-temperature conditions of mineral formation and the hydrocarbon occurrence. Analyses were carried out on samples from four selected boreholes in the Fore-Sudetic Monocline. After microscopic analysis of rocks and minerals in thin sections, the following techniques were used: luminescence analysis (UV, blue light), microthermometric analysis of fluid inclusions in double-sided polished wafers, cathodoluminescence analysis, electron scanning microscope studies, XRD analyses, stable isotopic analyses (carbon, oxygen) on calcite and dolomite-ankerite and Raman spectra of fluid inclusions. Orthochemical components, such as carbonates and authigenic quartz, that form cements or fill the veins cutting the sample material have been studied. Fluid inclusion data in quartz and carbonates result in homogenization temperatures of 74–233 °C. The Raman analysis gives temperature estimations for the organic matter of about 164 °C and 197 °C, depending on the borehole, which points to a low coalification degree. The post-sedimentary processes of compaction, cementation and diagenetic dissolution under eo- and meso-diagenetic conditions to temperatures of over 160 °C influenced the present character of the deposits. P-T conditions of brines and methane trapping have been estimated to be ~850–920 bars and 185–210 °C (vein calcite) and ~1140 bars and 220 °C (Fe-dolomite/ankerite). Therefore, locally, temperatures might have been higher (>200 °C), which may be a symptom of local regional metamorphism of a very low degree.
Highlights
Carboniferous deposits in the Fore-Sudetic Monocline have been under study since the 70s of the 20th century
The Carboniferous sediments are represented by sandstones, mudstones and claystones
Lithoclasts are partly replaced by carbonates and hematite, being argilitized and chloritized
Summary
Carboniferous deposits in the Fore-Sudetic Monocline have been under study since the 70s of the 20th century. The Carboniferous clastic deposits in the Wielkopolska-Silesian zone, mainly in the Wielkoposka area [9], are Mississippian and Pennsylvanian in age. They were penetrated by over a dozen boreholes (Figure 1). These deposits have been again the object of interest of research projects [10,11].
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