Magnetic susceptibility and selected geochemical–mineralogical data as proxies for Early to Middle Frasnian (Late Devonian) carbonate depositional settings in the Holy Cross Mountains, southern Poland

Abstract

The magnetic susceptibility (MS) and other petromagnetic features of Early to Middle Frasnian carbonates from the Holy Cross Mountains (southern Poland) were studied. They were correlated with the Eovariscan tectonic activity and palaeoenvironmental changes. The MS logs were compared with the available geochemical and mineralogical data. A substantial paramagnetic contribution to the MS of the Frasnian carbonates is evidenced by a poor correlation of this parameter with the isothermal remanent magnetization values, and by a decrease of MS values at low temperatures. An estimation of paramagnetic input indicates the dominance of this contribution to the magnetic susceptibility in 60% of studied samples. The MS low widely documented in samples through the Palmatolepis punctata Zone is particularly due to limited input of paramagnetic mineral particles into the basin where also amounts of larger detrital grains of quartz, hematite and goethite were significantly reduced. This depression corresponds well to anomalously high carbon isotope ( δ 13C) values for carbonates. Nevertheless, a transient MS rise across the E-MF boundary, linked with an increase in detrital quartz content, suggests together that both the initiation and termination phases of the punctata Event indeed coincided with increased terrigenous (?eolian) input from uplifted lands. The MS high identified in the lower part of the Palmatolepis hassi Zone coincides with higher content of detrital quartz, hematite and goethite, being accompanied by low δ 13C values. In spite of similar MS stratigraphic signatures in other basins, the increased detrital input of proximal provenance is likely connected with the first Variscan tectonic events that spread over the region and subsequently led to gradual closing of the Saxothuringian ocean segments with basement uplift in the area of the Mid-German Crystalline High.