Analiza facjalna naj wyższego triasu i liasu Wyżyny Krakowsko-Wieluńskiej oraz perspektywy występowania surowców ilastych
Abstract
FACIAL ANALYSIS OF THE UPPERMOST TRIASSIC AND THE LIASSIC OF THE CRACOW-WIELUŃ UPLAND AND PROSPECTES FOR OCCURRENCE OF CLAY DEPOSITS
Summary
Several new boreholes from the Cracow-Wieluń height allowed to recognize the paleoenvironmental characteristics of the uppermost Triassic and Liassic terrigenous deposits. Uppermost Triassic is represented mostly by fluvial/lacustrine red-beds, except of a thin intercalati9n of marginal-marine sediments in Praszka and Przystajń boreholes and some grey mudstones in the uppermost several meters of the profile. Uppermost Triassic sedimentation took place on a widespread fluvial plain with dominance of seasonal lakes and braided river systems. Caliche profiles with pisoids and dessication cracks are common and plant roots do occur. Some alluvial fan intercalations have been found. Periods of a more humid climate are indicated by more "compete" fining-upward cycles with levess, crevasses and abundant plant remains, which indicate meandering-river systems. The several top meters of Triassic profile are represented by clays and mudstones with siderite sphaerulites. This grey facies was forming probably during the whole Lower Liassic time (when the climate was humid) as a weathered cover of the red Triassic deposits.
The Lower Liassic is absent, probably because of erosion. Pleinsbachian deposits rest always with an erosional contact on the underlaying rocks and are represented by fluvial sediments, which form fining-upward cycles. These cycles represent mostly meandering channels interfingering with fluvial plain and lacustrine facies. In the Praszka borehole one may observe an intercalation of brackish-mar 'n e facies, which is builded up of mostly heterolithic and muddy sediments with burrows, plant remains and fauna of Cardiinidae. Those sediments were deposited as coarsening-upward cycles of deltaic systems filling up shallow brackish embayments and lagoons. Some lacustrine/swampy equivalents of these deposits occur in Bolesławiec section and some more marine facies were found south-east of the area studied. This marine intercalation is absent in Przystajń and Wręczyca boreholes, where intensive fluvial sedimentation was dominating for the Pliensbachian time.
Overlaying Lower Toarcian is developed in characteristic greenish muddy-heterolithic facies deposited in a very extensive brackish-marine reservoir. The lower transgressive boundary of Lower Toarcian constitutes an excellent correlative horizon. The character of transgressive deposits depends on the type of underlaying Pliensbachian fluvial facies - above the sandy deposits one may find some meters of nearshore sandstones, while above the muddy fluvial plain or lacustrine deposits only muds or lenticularly-bedded heterolithes are present. A vast majority of Lower Toarcian is builded up of heterolithic/muddy deposits. Feeding burrows are common and some Diplocraterion structures mark the most marine conditions in this basin. Upper part of the Lower Toarcian show regressive tendencies, the brackish-marine reservoir was gradually replaced by extensive marshes. These marshes are consequently covered by fluvial deposits, which represent Upper Toarcian. Overlyaing Middle Jurassic is developed again in marine or brackish marine facies. The sequence of mixed continental-marginal marine-marine environments is probably caused by eustatic oscillations. The best prospects of finding of clay mineral resources (of which kaolinite is the most important) are connected with Liassic fluvial plains and lacustrine facies and with palaeoweathering cover above the Uppermost Triassic.
Summary
Several new boreholes from the Cracow-Wieluń height allowed to recognize the paleoenvironmental characteristics of the uppermost Triassic and Liassic terrigenous deposits. Uppermost Triassic is represented mostly by fluvial/lacustrine red-beds, except of a thin intercalati9n of marginal-marine sediments in Praszka and Przystajń boreholes and some grey mudstones in the uppermost several meters of the profile. Uppermost Triassic sedimentation took place on a widespread fluvial plain with dominance of seasonal lakes and braided river systems. Caliche profiles with pisoids and dessication cracks are common and plant roots do occur. Some alluvial fan intercalations have been found. Periods of a more humid climate are indicated by more "compete" fining-upward cycles with levess, crevasses and abundant plant remains, which indicate meandering-river systems. The several top meters of Triassic profile are represented by clays and mudstones with siderite sphaerulites. This grey facies was forming probably during the whole Lower Liassic time (when the climate was humid) as a weathered cover of the red Triassic deposits.
The Lower Liassic is absent, probably because of erosion. Pleinsbachian deposits rest always with an erosional contact on the underlaying rocks and are represented by fluvial sediments, which form fining-upward cycles. These cycles represent mostly meandering channels interfingering with fluvial plain and lacustrine facies. In the Praszka borehole one may observe an intercalation of brackish-mar 'n e facies, which is builded up of mostly heterolithic and muddy sediments with burrows, plant remains and fauna of Cardiinidae. Those sediments were deposited as coarsening-upward cycles of deltaic systems filling up shallow brackish embayments and lagoons. Some lacustrine/swampy equivalents of these deposits occur in Bolesławiec section and some more marine facies were found south-east of the area studied. This marine intercalation is absent in Przystajń and Wręczyca boreholes, where intensive fluvial sedimentation was dominating for the Pliensbachian time.
Overlaying Lower Toarcian is developed in characteristic greenish muddy-heterolithic facies deposited in a very extensive brackish-marine reservoir. The lower transgressive boundary of Lower Toarcian constitutes an excellent correlative horizon. The character of transgressive deposits depends on the type of underlaying Pliensbachian fluvial facies - above the sandy deposits one may find some meters of nearshore sandstones, while above the muddy fluvial plain or lacustrine deposits only muds or lenticularly-bedded heterolithes are present. A vast majority of Lower Toarcian is builded up of heterolithic/muddy deposits. Feeding burrows are common and some Diplocraterion structures mark the most marine conditions in this basin. Upper part of the Lower Toarcian show regressive tendencies, the brackish-marine reservoir was gradually replaced by extensive marshes. These marshes are consequently covered by fluvial deposits, which represent Upper Toarcian. Overlyaing Middle Jurassic is developed again in marine or brackish marine facies. The sequence of mixed continental-marginal marine-marine environments is probably caused by eustatic oscillations. The best prospects of finding of clay mineral resources (of which kaolinite is the most important) are connected with Liassic fluvial plains and lacustrine facies and with palaeoweathering cover above the Uppermost Triassic.