Warstwy krośnieńskie w profilu Osławy

Abstract

Na podstawie 14 otworów wykonanych na fałdach Mokrego, Czaszyna i Tarnawy - Wielopola odkryto nowe akumulacje ropy poniżej znanych horyzontów produktywnych (Mokre, Tarnawa - Wielopole). Mimo znacznych głębokości otworów, nie osiągnięto spągu warstw krośnieńskich, co ze względu na monotonię ich wykształcenia utrudniało ogromnie korelację. Dla uzyskania dodatkowych materiałów dla korelacji wykonano bardzo szczegółowe obserwacje profilu Ostawy na długości 24,5 km. Zróżnicowanie litologiczne pozwoliło na rozpoziomowanie i korelację wydzielonych kompleksów. Zrezygnowano z wykorzystania dla korelacji łupków jasielskich, gdyż w badanym profilu występują one tylko w dwóch punktach. Z rozważań tektonicznych wynika, że nawiercenie głębszych poziomów fliszu jest tu niemożliwe.THE KROSNO BEDS IN THE OSŁAWA RIVER SECTION In the years 1948-1955, the Oil Industry carried out search for oil and gas in area where the Osława River cuts through three folds building the central synclinorium of the Carpathians: Mokre (Rajskie), Czaszyn and Tarnawa - Wielopole folds. Of 14 drillings made there, one (T-W 12) has reached depth of 3081 m, not penetrating the Krosno Beds. The search resulted in discovery of new accumulations of oil in the Tarnawa - Wielopole and Mokre folds, situated beneath the exploited ones. Correlation of rocks of the Krosno Beds in the three above mentioned elements appeared, however, fairly troublesome. That is why the present author decided to carry out studies along the Osława River section at distance of 24.5 km (in the scale 1: 10,000), aimed at reconstruction of their development and gathering new data which would make possible the correlation. The studies were extended northwards to comprise the Zagórz and Sanok - Uherce elements and, therefore, to make possible compilation of transversal section through the synclinorium, from Korzuszne in the south to Zasław in the north. The map (Fig. 1) shows the results of the studies, the cross-section (Fig. 2) - deep structure reconstructed also on the basis of borehole data, and litho logical columns (Fig. 3) - correlation of the strata. The area discussed here was studied by Z. Opolski, J. Wdowiarz, F. Szymakowska and A. Ślączka. In the course of studies on the Osława River section, the author paid much attention to clearly marked changes in lithology of the Krosno Beds, assuming that their extent is wider than hitherto assumed. At the same time, the Jasło Shales were looked for as a time-stable horizon. Taking into account lithological premises, four horizons were differentiated throughout the area except for the Sanok - Uherce fold, the profile of which differs from the established succession. Much attention was also paid to directions of transportation of clastic material to the Krosno basin. South-western limb of the Sanok - Uherce fold displays rock of the Krosno Beds with real thickness of about 2100 m, developed in strongly sandy facies. The Jasło Shales occur there about 650 m above the base of the sequence. Measurements of orientation of current marks show that material building this sequence was mainly coming from the north-west. In the Tarnawa - Wielopole fold, the: profile of the Krosno Beds is known to the depth of 3081 m (Fig. 2) and their actual thickness is estimated at about 2950 m. The author differentiated here 3 members. Lower member, at least 1150 m thick, is characterized by very monotonous development and predominance of sandstones over gray shales. Sandstones are here usually fine-grained, thick-to medium or, sometimes. thin-bedded, and with rich assemblage of sedimentary structures and fairly common graded bedding. Middle member consists of alternating packets of thick·bedded and shaly sand-stones, with marked predominance of the former, and its thickness is estimated at 1300 m. Upper member, recorded along south-western part of the fold, is characterized by overhelming predominance of gray, marly shales over thin-bedded fine-grained sandstones. It is about 500 m thick. Moreover, a member mixed in character was differentiated at the boundary of the middle and upper ones. Occasionally found hieroglyphs indicate transportation of clastic material for exposed part of the sequence from the north-west. The section of the Krosno Beds in the Czaszyn fold is mainly known from the studies in the Osława River section and, in the case of its lower part, boreholes Czaszyn 1 and 2. Here were differentiated 3 members. Lower member, building a core part of this fold, primarily comprises thick-bedded sand-stones and its known thickness is of the order of 500 m. In middle member, 1400 m thick, the share of thick-bedded sandstones is over 95%, and in the upper, 500 m thick, the share of shales is close to 85%. Moreover, a series mixed in character and about 400 m in thickness was differentiated between the latter two members. In that series. shales are accompanied by packets of thick-bedded sandstones. Six current marks, four of which are certain, indicate transportation of clastic material for the thick-bedded sand-stones from the south, and for rocks of the shaly series - from the north-west. Similarly as in the above case, the development of the Krosno Beds building the Mokre fold was analysed on the basis of data concerning its south-western limb. The available data show the possibility to differentiate at least four members. First of these members, at least 350 m thick, is mixed in character, with gray-black. noncalcareous shales at the base. The second member corresponds to the Otryt sand-stones, i.e. ridge-forming from morphological point of view, in its setting and development. Its thickness is estimated at 730 m. The series is characterized by marked predominance of thick-bedded hard sand-stones with intercalations of beds mixed in character. Current marks oriented from the south and south-west were found in its lower part, and fragments of redeposited shales - on upper surface of some layers. The third member is mixed in character, and the fourth, 1200 m thick, consists of gray marly shales and generally thin-bedded sandstones. The latter is overlain by a 150 m packet of thick-bedded (1 - 2 m thick) sandstones known from outcrops at Korzuszne. The Jasło Shales are only known from northern limb of this fold in the Osława River section. A limited distribution and hard to precise position of the Jasło Shales in the studied section made it necessary to base correlation of the Krosno Beds in this. part of the synclinorium on lithological criteria, supplemented with results of analysis of direction of transportation of clastic material. This made it possible to differentiate (Fig. 3): lower horizon, mixed or with predominance of sandstones. middle one, with overhelming predominance of thick-bedded sandstones, a mixed horizon at the top of the latter and, finally, upper horizon. usually displays marked predominance of shales. Clastic material for the middle horizon was coming from the south or similar directions, and for the other ones - mainly from the north-west. The, Sanok - Uherce fold displays specific development of the Krosno Beds sequence. In the Osława River section, the central synclinorium (with the exception of its innermost part) consists of five tectonic elements. Geological cross-section best depicting their structure is that also comprising frontal uplift of Lower Cretaceous rocks. Such section makes possible better understanding of structure of the Silesian Unit as the synclinorium represents a depressed part of that unit. This uplift is thrusted over the Skole Unit. The Sanok - Uhercc fault displays structure of the chimney type, built of rocks of the Krosno Beds only. In the section, it is separated from the next, Zagórz fold, the smallest in dimensions. by a deep syncline. The third, Tarnawa - Wielopole fold. 2.5 km wide, is asymmetrical, which is expressed by south-western limb almost four times wider than the north-eastern. The Czaszyn fold has a form of a slice 4350 m wide. Its core part, built of rocks of the lowermost member of the Krosno beds only, appeared refolded and overthrown to north-east. South-western limb is isoclinally dipping to SW and the north-eastern - reduced to some hundred meters and presumably turned up at some depth. The fifth Mokre (Rajskie) fold is almost 5.5 km wide. Its core part is built of refolded rocks of lower member of the Krosno Beds, and syncline separating the folds appears deeply drawn beneath the southern fold. South-western limb isoclinaIly dips to SW and the north-eastern - strongly reduced, almost vertical at the surface and presumably turned up at some depth.