Palaeoenvironmental context of the Famennian red pelagic limestones in the Křtiny quarry (Czechia). In: Ondřej Bábek, Stanislava Vodrážková: 35th IAS Meeting of Sedimentology Virtual Meeting Prague, Czech Republic, 21–25 June 2021. Book of Abstracts, p. 110.
|Year of publication||2021|
|MU Faculty or unit|
|Description||This contribution is focused on the grey to red Famennian Křtiny Limestone that are exposed in the Marble Quarry (49°17'35.943"N; 16°44'5.806"E) at the Křtiny village in Czech Republic. In this study, we employed analysis of trace elements (ICP-MS, ED-XRF) and microfacies in order to determine the palaeoenvironmental conditions in the time of the deposition of the red sedimentary intervals. The studied interval ranges from the marginifera to ultimus conodont zones. First, thinner level of reddish to pinkish nodular limestones occur in marginifera/trachytera conodont zones interval, and second, thicker red level occurs in expansa to ultimus conodont zones interval. Both intervals are separated by grey limestones. The grey limestones are getting gradually darker with culmination just before the second red interval. Microfacies analysis shows that the section is mostly composed of bioturbated radiolarian and ostracod wackestones to lime mudstones with occasional packstone levels and breccia, deposited in the upper carbonate slope setting. Dark gray interval that is preceding the second red interval shows increased values of the redox proxy U/Th. These values indicate fluctuating dysoxic to anoxic conditions. Simultaneously, increased productivity is recorded by rising P and TOC content in the dark grey interval. Conodont assemblages revealed manca/expansa age and, therefore, this interval is tentatively correlated with the global hypoxic Dasberg Crisis (following high-resolution conodont biostratigraphy studies must evidence the correlation). U/Th values in the subsequent red interval are ten times lower and reflects oxic environment. Detrital proxies Ti/Al and Zr/Al show steady conditions of clastic input for most of the section, without significant changes in grain size or provenance. K/Al reveals systematically higher values in the red intervals and as such it can display more intense physical weathering which might indicate an affinity towards cooler climate. Positive ?13Ccarb excursion (3 ‰) has been previously documented from the second red interval and probably records increase in carbon burial during shift from dark grey to red facies. Change from the Famennian dark grey limestones, deposited in times of increased productivity and reducing condition, to predominantly reddish limestones of cooler climate is similar e.g. to change from the Cenomanian black shales of the OAE1 to the oceanic red beds, or to occurrence of the Lower Devonian red pelagic limestones deposited in times of switching between mesotrophic and cooler oligothrophic marine conditions. This work was financially supported by the Czech Science Foundation (grant number GA19-17435S).|