Rozwój utworów jurajskich na Przedgórzu Karpat w rejonie Dąbrowy Tarnowskiej-Szczucina
Abstract
The Upper Jurassic sediments in the Foreland of the Polish Carpathians (Sandomierz Basin)
This paper is concerned with the Upper Jurassic carbonate rocks in the central part of the Carpathian Foreland (Southern Poland). The study area (Fig. 1) is a foreland basin of low relief which is defined geographically as the Sandomierz Basin. The Jurassic rocks are here burried by thick Tertiary and Cretaceous sediments and are nowhere exposed at the surface. Accordingly, all informations concerning the Jurassic of the study area are based upon investigations of drill cores and electric logs. The presence of the Jurassic rooks in the Sandomierz Basin has already been mentioned by several authors (see references) but no comprehensive account of these rocks is available. This paper is primarily concerned with the Upper Jurassic carbonates and aims to present the results of lithologieal, sedimontological and paleoecological investigations. An attempt is also made to divide the Upper Jurassic carbonates into formations and to discuss the sedimentary and paleogeographic conditions attending the deposition of these formations. To begin our discussion let us recall some major features of the study area. Like elsewhere in the Carpathian Foreland, the Jurassic rocks are faulted but, except of broad undulations, they are nearly flat-lying and dip gently towards the Carpathians. The Jurassic rocks rest unconformably upon slightly tilted and eroded Triassic sediments and/or upon more strongly disturbed Paleozoic rocks. The deposition .of the marine Jurassic sediments began here during the Upper Bathonian and, except of temporary break during the Lower Callovian, continued till the end of Jurassic time. The deposition went on coneomittantly with subsidence is that the Jurassic sequence attains a considerable thickness of 1100 m (Fig. 5). The Jurassic rocks are separated from the overlying Cretaceous and Tertiary sediments by ancient erosional surfaces of regional extent. As already indicated the Jurassic rocks have been warped into a series of broad folds and planed off before the Cretaceous and later during Lower Tertiary time. Consequently, the planation surface beneath the Miocene sediments exhibits the Oxfordian rocks on the top of truncated anticlines and the Kimmeridgian rocks in syndines (Figs. 7, 8). We know from drilling that the Jurassic strata slope at very low angle to the south and south-east. Such gradual dip, although complicated by faulting, is well displayed in the location off the pre-Miocene planation surface. While to the north, in the vicinity of Szczucin—Solec the planation surface lies approximately at the sea level, it is located 900 m below that level further south in the vicinity of Dąbrowa Tarnowska (Fig. 7). Beneath the marginal parts of the Carpathian thrusts, the surface in question is already submerged down to a few kilometers. Still further to the south the Jurassic rocks can no longer be reached by drilling and disappear for good. Like elsewhere in the Carpathian Foreland, the Jurassic strata in the study area are dismembered by numerous dislocations into fault blocks. The faults trending NW—SE and NE—SW are believed to have been formed late in Miocene time (during the Lower Sarmatian), but some of them are reactivated older faults. Associated with these faults are fractures some
This paper is concerned with the Upper Jurassic carbonate rocks in the central part of the Carpathian Foreland (Southern Poland). The study area (Fig. 1) is a foreland basin of low relief which is defined geographically as the Sandomierz Basin. The Jurassic rocks are here burried by thick Tertiary and Cretaceous sediments and are nowhere exposed at the surface. Accordingly, all informations concerning the Jurassic of the study area are based upon investigations of drill cores and electric logs. The presence of the Jurassic rooks in the Sandomierz Basin has already been mentioned by several authors (see references) but no comprehensive account of these rocks is available. This paper is primarily concerned with the Upper Jurassic carbonates and aims to present the results of lithologieal, sedimontological and paleoecological investigations. An attempt is also made to divide the Upper Jurassic carbonates into formations and to discuss the sedimentary and paleogeographic conditions attending the deposition of these formations. To begin our discussion let us recall some major features of the study area. Like elsewhere in the Carpathian Foreland, the Jurassic rocks are faulted but, except of broad undulations, they are nearly flat-lying and dip gently towards the Carpathians. The Jurassic rocks rest unconformably upon slightly tilted and eroded Triassic sediments and/or upon more strongly disturbed Paleozoic rocks. The deposition .of the marine Jurassic sediments began here during the Upper Bathonian and, except of temporary break during the Lower Callovian, continued till the end of Jurassic time. The deposition went on coneomittantly with subsidence is that the Jurassic sequence attains a considerable thickness of 1100 m (Fig. 5). The Jurassic rocks are separated from the overlying Cretaceous and Tertiary sediments by ancient erosional surfaces of regional extent. As already indicated the Jurassic rocks have been warped into a series of broad folds and planed off before the Cretaceous and later during Lower Tertiary time. Consequently, the planation surface beneath the Miocene sediments exhibits the Oxfordian rocks on the top of truncated anticlines and the Kimmeridgian rocks in syndines (Figs. 7, 8). We know from drilling that the Jurassic strata slope at very low angle to the south and south-east. Such gradual dip, although complicated by faulting, is well displayed in the location off the pre-Miocene planation surface. While to the north, in the vicinity of Szczucin—Solec the planation surface lies approximately at the sea level, it is located 900 m below that level further south in the vicinity of Dąbrowa Tarnowska (Fig. 7). Beneath the marginal parts of the Carpathian thrusts, the surface in question is already submerged down to a few kilometers. Still further to the south the Jurassic rocks can no longer be reached by drilling and disappear for good. Like elsewhere in the Carpathian Foreland, the Jurassic strata in the study area are dismembered by numerous dislocations into fault blocks. The faults trending NW—SE and NE—SW are believed to have been formed late in Miocene time (during the Lower Sarmatian), but some of them are reactivated older faults. Associated with these faults are fractures some