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Mineralogical characteristics of the heterolithic formations from the Carpathian Foredeep Miocene sediments, south-eastern Poland

Przelaskowska Anna, Zagórska Urszula, Urbaniec Andrzej, Łykowska Grażyna, Klaja Jolanta, Grela Jacek, Kędracka Katarzyna

Geology, Geophysics and Environment

2022

Vol. 48, no. 3

219--242

Heterolithic complexes from the Carpathian Foredeep are a subject of growing attention as many natural gas accumulations of industrial importance have been discovered in such formations during the last decades. The aim of the presented work was to determine lithotypes of different lithology and mineralogical composition in the heterolithic sequences. Individual lithotypes were distinguished of macroscopic observations of cores, X-ray diffraction analysis (XRD) and X-ray fluorescence method (XRF). Preliminary distinction between the lithotypes was based on macroscopic observations of the core samples. Correlation plots between the contents of particular minerals (XRD analyses) and corresponding elements (XRF analyses) were used for verification of the lithotypes distinguished based on macroscopic observations. Swelling properties of the investigated rocks were determined using the cation exchange capacity (CEC) values. The following lithotypes were identified: medium- to fine-grained sandstones, fine- to very fine-grained sandstones, clayey sandstones, sand-dominated heteroliths, heteroliths with approx. equal proportions of sandstones and mudstones, mud-dominated heteroliths, mudstones, clayey shales. Such division provides a basis for precise petrophysical characterization of the analyzed profiles, that is assignment of particular petrophysical parameters values to individual lithotypes. More reliable petrophysical parameters in the geophysical interpretation of heterolithic sequences allow for a more precise determination of zones characterized by good reservoir parameters.

Sedimentology and ichnology of Neogene Coastal Swamp deposits in the Niger Delta Basin, Nigeria

Ezeh S. C., Mode W. A., Ozumba B. M., Yelwa N. A.

Geologos

2016

Vol. 22, No. 3

191--200

Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mudstones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamma ray logs, described sedimentological cores showing sedimentary features and ichnological characteristics; these were integrated to define the depositional settings. Some portions from one of the well sections reveal a blocky gamma ray well log signature instead of a coarsening-upward trend that characterises a shoreface setting while in other wells the signatures for heteroliths at some sections are bell blocky in shaped rather than serrated. Besides, heteroliths and mudstones within the proximal facies and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on sedimentology and ichnology of cores from these facies was used to correct these inconsistencies. It follows that depositional environment interpretation (especially in multifarious depositional environments such as the Niger Delta) should ideally be made together with other raw data for accuracy and those based solely on well log signatures should be treated with caution.

Sedimentary environments of the Middle Jurassic epicontinental deposits from the central part of the Polish Basin (Kuiavian Region)

Feldman-Olszewska A.

Volumina Jurassica

2006

Vol. 4, no. 1

86-86

The Polish Basin was the eastern part of the Jurassic European epicontinental basin. The zone of maximum thickness of the Middle Jurassic deposits runs along the so called Mid-Polish Trough which extends from the West Pomerania (NW) to the Holy Cross Mountains (SE), generally along the Teisseyre-Tornquist Zone. The complete litological profile of the Middle Jurassic deposits exceeds 1100 m in the depocentre of the Mid-Polish Trough (in the Kuiavian Region). Sediments are represented by sandstones, mudstones, heteroliths and claystones with intercalations of siderites, dolomites and coquina beds. Subordinately, crinoidal limestones, arenaceous limestones, gaizes and oolitic ironstones occur. Sedimentological studies were based on investigation of cores from ten deep boreholes. Nineteen lithofacies were distinguished: black shales, massive mudstones, bioturbated mudstones, lenticular bedded mudstones, heteroliths, wavy bedded sandstones, flaser bedded sandstones, sandstones with clay drapes, structureless sandstones (massive and bioturbated), parallel bedded sandstones, cross bedded sandstones, HCS (hummocky cross stratification) cross bedded sandstones, ripple bedded sandstones, herringbone cross bedded sandstones, chamosite sandstones, calcareous sandstones and arenaceous limestones, crinoidal limestones, conglomerates, condensed bed. Additionally, 15 ichnogenera of trace fossils: Asterosoma isp., Bergaueria isp., Chondrites isp., Diplocraterion isp., Gyrochorte isp., Lockeia isp., Ophiomorpha isp., Palaeophycus isp., Planolites isp., Rosselia isp., Skolithos isp., (?)Spongeliomorpha isp., Teichichnus isp., Terebellina isp. and Thalassinoides isp. were recognized in the Middle Jurassic deposits of Kuiavian Region. They point to sedimentation in the transition zone - foreshore environments. Based on the geochemical and palaeoecological investigations, four biofacies connected with different oxygenation of the bottom waters during sedimentation of the black shales have been proposed. The Upper Aalenian - Lower Bajocian deposits represent clayey sedimentation which occurred in dysoxic to anoxic environment. On the other hand, the Upper Bajocian - Lower Bathonian deposits represent dysoxic to oxic conditions. Sedimentation of the Middle Jurassic deposits in the central part of the Polish Basin took place in the shallow epicontinental sea, in environment spanning offshore to foreshore zones of a shallow siliciclastic shelf. Precise sedimentological studies point that the Middle Jurassic succession can be divided into 8 transgressive-regressive cycles. The oldest (Lower Aalenian) one begins with estuarine/foreshore sediments, sharply covered with offshore black shale facies. The Upper Aalenian, Bajocian and Lower Bathonian cycles are built of the transgressive offshore black shales and progradational regressive successions composed of mudstones and heteroliths and topped by shallow or middle shoreface sandstones. The Middle and Upper Bathonian cycles begin with transition zone sediments or lower shoreface deposits. The uppermost part of these cycles are built of sandstones and limestones representing the upper shoreface, foreshore and lagoon environments. The transgressive part of the last (Callovian) cycle is documented by carbonate-siliciclastic shoreface deposits which pass upwards into limestones of the Upper Jurassic. At the boundary between the Middle and the Upper Jurassic a condensed bed occurs.