Analiza basenów sedymentacyjnych jako strategia badawcza

Abstract

Analiza basenów jest strategią geologicznych badań regionalnych intensywnie rozwijaną w ostatnich kilkunastu latach. Celem badań jest na ogół określenie perspektyw surowcowych, w tym szczególnie ropo- i gazonośności, a skala badań nawiązuje do szerokiego kontekstu naturalnych jednostek geodynamicznych. Istotą analizy basenów jest integracja różnych dziedzin i metod badawczych w celu wszechstronnego odtworzenia historii geologicznej basenu, a na jej tle - regionalizacji i przebiegu procesów złożotwórczych. Wiele cech predestynuje omawianą analizę do wykorzystania przez krajową służbę geologiczną jako podstawowej strategii badań regionalnych.

SEDIMENTARY BASIN ANALYSIS AS A RESEARCH STRATEGY

Basin analysis is an integrated strategy or regional geological studies that has been developing extensively since the seventies. A driving force for its development is provided by the needs of a petroleum industry with its comprehensive concept of "petroleum play" embracing generation, migration and accumulation of hydrocarbons.

Generally, the aim of the studies is thus defined in terms of determining prospects of oil and gas occurance, but also towards prospecting for coal, salts and sediment-hosted metal deposits. On the other hand, versatility of a basin analysis guarantees an increase in general geological knowledge of the studied area. The latter achievement can be initially defined as an additional or even main goal of the research. In turn, the scale of research involves natural geodynamic entities, i.e. fragments of the Earth's crust with a common subsidence history taking place within a common tectonic framework. Such an approach results from the assumption that understanding of an origin and distribution of local geological phenomena, mineral deposits included, is possible only within the broad contex of an entire sedimentary basin with its tectonical background (Figs 1 and 4). Basin analysis is characterized by a high degree or integration of different fields and methods of study, this reflecting a complex relationships between different factors influencing basinal evolution (Fig. 2). Storage and processing of a multitude of various data neccessitates utilization of appropriate computer techniques (Fig. 3).

A complete cycle of a basin analysis embraces studies conduced simultaneously in several basic fields. Tectonic studies are aimed towards restoring structural controls on an evolution of a basin, from its birth through sedimentary fill stage to eventual deformation and uplift. The aim of stratigraphic/sedimentological studies is to reconstruct a depositional architecture, i.e. a primary basinal fill as a logical and thus predictable pattern of three-dimensional mutually related sediment bodies. Burial history takes place within a basin being filled with sediments, and against the background of changing thermal and hydrological regimes. The studies involve above all restoring a sequence of diagenetic processes and episodes, and a reconstruction of thermal history. Paleohydrological studies are directed towards interpretation of regional flow patterns (Fig. 5) as well as chemical composition of basinal fluids. One of the final results of a basin analysis is a reconstruction of a subsidence development in time and space. The geohistory analysis of a subsidence integrates many analytical procedures i.a. decompaction technique, and paleobathymetrical analysis (Figs 6 and 7). Backstrtpping is a quantitative method of subsidence analysis in order to discriminate between isostatic and tectonic components. It involves assumptions regarding, i.a. magnitude of eustatic sea-level changes and rheologic behaviour of the crust underlying a basin.

Several characteristic of a modem basin analysis predestine it for introducing in the Polish Geological Survey as a leading strategy of regional studies. The introduction of the analysis should however take into account particular features of a geological structure in Poland as well as certain "historical" and organization problems.