Abstract:Terminal Triassic environmental changes are characterized by an integrated study of lithology, litho-and cyclostratigraphy, paleontology, mineralogy, geochemistry and rock magnetism in the Tatra Mts. The Carpathian Keuper sequence was deposited in an arid environment with only seasonal rivers, temporal lakes and swamps with scarce vegetation. Combination of a wide range of 18 O values (-0.7 to + 2.7) with negative 13 C values documents dolomite precipitation either from brackish or hypersaline lake water, or its derivation from pore water comparably to the Recent Coorong B-dolostone. Negative 13 C values indicate microbial C productivity. Rhaetian transgressive deposits with restricted Rhaetavicula fauna accumulated in nearshore swamps and lagoons. Associations of foraminifers, bivalves and sharks in the Zliechov Basin were controlled by physical factors. Bivalve mollusc biostromes were repetitively destroyed by storms, and temporary firm bottoms were colonized by oysters and burrowers. Subsequent black shale deposition recorded input of eolian dust. Bottom colonization by pachyodont bivalves, brachiopod and corals started much later, during highstand conditions. Facies evolution also revealed by geochemical data, C and O isotope curves reflect eustatic and climatic changes and help reconstruct the evolution of Rhaetian marine carbonate ramp. The Fatra Formation consists of 100 kyr eccentricity and 40 kyr obliquity cycles; much finer rhythmicity may record monsoonlike climatic fluctuations. Fluvial and eolian events were indicated by analysis of grain size and content of clastic quartz, concentrations of foraminiferal (Agathammina) tests in thin laminae indicates marine ingression events. Magnetic susceptibility (MS) variations reflect the distribution of authigenic and detrital constituents in the sequence. Increasing trend of MS correlates with the regressive Carpathian Keuper sequence and culminates within the bottom part of the Fatra Formation. Decreasing trend of MS is observed upwards the transgressive deposits of the Fatra Formation.
1 Jagiellonian Uni ver sity, In sti tute of Geo log i cal Sci ences, Oleandry 2a, 30-063, Kraków, Po land Wójcik-Tabol, P., 2015. Depositional re dox con di tions of the Grybów Suc ces sion (Oligocene, Pol ish Carpathians) in the light of pet ro log i cal and geo chem i cal in di ces. Geo log i cal Quar terly, 59 (4): 603-614, doi: 10.7306/gq.1240 This study de tails the pe trol ogy and chem is try of the Oligocene suc ces sion of the Grybów Nappe in its stratotype-lo cal ity in the Grybów tec tonic win dow (Pol ish Carpathians). The sec tion stud ied is com posed of the Sub-Grybów Beds, the Grybów Marl For ma tion (GMF), and the Cergowa Beds, rep re sent ing the mid dle to up per part of the Oligocene suc ces sion. The rocks stud ied con sist of quartz, cal cite, Na-plagioclase, mus co vite and clay min er als (illite-smectite with 25-30% of smectite and kaolinite). Ad di tion ally, he ma tite oc curs in the GMF and chlorite in the Cergowa Beds, re spec tively. The macerals as semblage of the GMF is dom i nated by landplant-de rived com pounds of liptinite, as so ci ated with mi nor amounts of vitrinite rep resent ing type II kerogen. The to tal or ganic car bon (TOC) con tent is be tween 0.45 and 6.16 wt.%. The d 13 C org val ues of the GMF vary be tween -27.1 and -27.9‰. The val ues of both car bon and ox y gen iso to pic ra tios of car bon ates range for d 13 C from -1.1 to -4.3‰ VPDB, and for O from -1.5 to -4.8‰ VPDB. The con cen tra tions of Co, U, Ni, As, and Mo are higher in the GMF than in the ad ja cent strata and pos i tively cor re late with TOC and S. Val ues of the TOC/S and V/V+Ni ra tios are 0.7 to 3.5 and 0.67 to 0.78, re spec tively, and in di cate anoxic con di tions. The ra tios of U/Th and V/Cr (0.3-2.2, 1.18-3.18, re spectively) sug gest the change of oxic con di tions to re duc ing con di tions oc curred dur ing the GMF de po si tion. This change could have been pre ceded by a plank ton bloom, ini ti ated by a nu tri ent-rich fresh wa ter in flow that is in ferred from the de crease of the d 13 C carb val ues and the ter res trial de tri tus sup ply. Ther mal al ter ation of the Grybów Suc ces sion is con cluded on the ba sis of smectite illitisation and low d18 O val ues.
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