Abstract
AbstractAlthough the Mesozoic rocks of the Transdanubian Range have been the subject of a multitude of different studies, mineralogical research is largely underrepresented. The clay mineralogy of Lower Jurassic (especially the Pliensbachian and Toarcian) strata was broadly investigated earlier; however, systematic high-resolution clay mineralogical studies remain scarce. Here we present a mineralogical study focusing on the Upper Pliensbachian strata of the Lókút-Hosszúárok section, located near the Eplény Manganese Ore Field. We identified dioctahedral smectite, randomly interstratified illite/smectite, illite as 10 Å phyllosilicate, quartz and cristobalite. Based on our new results we propose that the smectite was formed by aging of Mg or Fe hydroxide-silica precipitates. The smectite and cristobalite were presumably formed from the siliceous tests of radiolarians, whose abundance was controlled by a local upwelling system. The occurrence of Pliensbachian smectite in the Lókút outcrop shows similarities with the Úrkút smectites known from both Pliensbachian and Toarcian strata, which implies that similar processes controlled the sedimentation during the Pliensbachian as well as during the black (gray) shale-hosted ore accumulation in the Eplény and Úrkút basins.
Highlights
Jurassic sedimentary strata of the Transdanubian Range are dominated by carbonates and have been the broader focus of scientific research
The smectite and cristobalite were presumably formed from the siliceous tests of radiolarians, whose abundance was controlled by a local upwelling system
We investigated the occurrence of smectite in the Pliensbachian limestone at the LokutHosszuarok outcrop, because of its proximity to the Epleny manganese deposit
Summary
Jurassic sedimentary strata of the Transdanubian Range are dominated by carbonates and have been the broader focus of scientific research. From a mineralogical aspect, beside the carbonate minerals, only a few studies have been devoted to accessory minerals; investigation of clay minerals has been scarce. An exception is the comprehensive study of Viczian (1995) who carried out a large-scale clay mineral investigation in the entire Transdanubian Range but only at a low stratigraphic resolution. Clay mineralogy is remarkably suitable for reconstruction of depositional environments, because the formation of the different clay minerals is well-defined, and such information will complement and enhance our previous knowledge from other studies. We investigated the occurrence of clay minerals within the Pliensbachian strata, with a special focus on the occurrence of smectite
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