Wojciech Kozłowski

Late Neoproterozoic to Early Palaeozoic palaoegeography of the Holy Cross Mountains (Central Europe): an integrated approach

Study of geochemistry, examination of isotope ages of detrital minerals, palaeomagnetic analysis, and a study of the trilobites were performed to provide constraints on the palaeogeographical position of the Holy Cross Mountains in Late Ediacaran–Early Palaeozoic time. The geochemical results indicate an active continental margin or continental island arc provenance of the Ediacaran sediments. Sediments from a passive continental margin were deposited here during the Cambrian and Ordovician. The palaeomagnetic pole isolated from Cambrian rocks of the Małopolska region of the Holy Cross Mountains corresponds to the Cambrian segment of the Baltic apparent polar wander path. Isotope age estimations indicate that Cambrian sediments of the Małopolska region contain detritus not only from a latest Neoproterozoic source but also from sources with ages of c. 0.8–0.9 Ga, 1.5 Ga and 1.8 Ga. The Małopolska, Brunosilesia, Dobrugea and Moesia terranes, which originally developed near the present southern edge of Baltica and were partly involved in the Cadomian orogen, were dextrally relocated along its Trans-European Suture Zone margin. The first stage of this movement took place as early as latest Ediacaran time, while Baltica rotated anticlockwise. Anticlockwise rotation of Baltica at the Cambrian–Ordovician boundary implies further dextral movement of the Małopolska block.

An unusual microbial-rostroconch assemblage from the Mulde Event (Homerian, middle Silurian) in Podolia, Western Ukraine

The Homerian (middle Silurian) Mulde Event is an extinction event affecting hemipelagic organisms associated with a positive stable carbon isotope excursion, and an increased proliferation of microbial deposits. The Event is recorded in the Bagovytsya section (Podolia, Ukraine), representing a carbonate ramp setting in the East European Craton, and recording the δ13Ccarb excursion with values reaching +5.17%. The associated facies include oncolitic beds, mud-mounds and thrombolitic buildups dominated by cyanobacteria and microproblematica with proposed bacterial affinities. The associated faunal assemblage includes a high proportion of rostroconchs and abundant gastropods and trilobites. The co-occurrence of grazing organisms and microbial sediments suggests that the microbial preservation was not caused by decreased grazing rates.

Anomalous massive water-column carbonate precipitation (whitings) as another factor linking Silurian oceanic events

Abstract The geological record of the mid-Homerian Mulde event in the deep-water settings of the East European Platform is characterized by a profound graptolite extinction event and a low amplitude positive δ13C excursion. It is also associated with a negative natural gamma excursion occurring in a monotonous shaly succession, visible on well logs and traceable across the entire basin. Nevertheless, its origin has not been clarified yet. We present new data on the geophysical and microfacies record across the stratigraphic interval of this event in northern Poland. The present paper tests a hypothesis that the anomalies are related to the appearance of syngenetic and/or detrital carbonates at the onset of this Silurian event. New data reveal that both: (1) natural gamma radiation and magnetic susceptibility negative anomalies and (2) facies changes manifested in the increased carbonate content and ingression of ‘varve-like’ laminated calcisiltite containing large amounts of ‘sparoids’ (interpreted as carbonate suspensoids) occur simultaneously in the middle Homerian. Despite different palaeogeographic situations of the basin in the Wenlock and Ludlow due to the progressive collision of Baltica with Avalonia and the evolution of Caledonian foredeep, the geophysical and facies record of the Mulde Event is strikingly similar to that of the Ludfordian Lau Event record from the same basin. This leads to the conclusion that carbonate hypersaturation, resulting in the mass appearance of water-column carbonate precipitates (whitings) played a significant role during both Mulde and Lau events and represents palaeoceanographic phenomena rather than single case local anomalies.