THREE TYPES OF REEFS IN THE ŠTRAMBERK LIMESTONE DEVELOPED AT THE JURASSIC/CRETACEOUS TRANSITION (CARPATHIANS, CZECH REPUBLIC)

Abstract

The locality Štramberk near Ostrava in Moravia (Czech Republic) is one of the most renowned paleontological sites. The Štramberk Limestone is known for its reefal facies with numerous corals and other fossils, but in fact, these limestones include various facies deposited at the Jurassic/

Cretaceous transition on the Štramberk Carbonate Platform and its slope (Eliáš and Eliášová 1984;

Kołodziej et al. 2023). These limestones occur as olistoliths and large blocks embedded in the

Cretaceous flysch of the Outer Carpathians.

The Štramberk Limestone contains the world's most diversified coral assemblages (c. 115 species of 50 genera) in the reefs developed at the Jurassic/Cretaceous transition (Tithonian-

Berriasian). They were described in 1897 by Maria Ogilvie and later in numerous papers by Helena

Eliášová (see Eliáš and Eliášová 1984; Kołodziej et al. 2023). Corals occur in the coral-microbial boundstones. Besides microbialites, photophile microencrusters (e.g., "Lithocodium-Bacinella") are common. During our studies, we found that in addition to the coral microbial boundstones, there are also boundstones which can be attributed to the microencruster-microbial-cement reefs and sponge-microbial reefs (Kołodziej et al. 2023).

Late Jurassic-earliest Cretaceous reefs with a microencruster-microbial-cement framework and with rare (microsolenids) or without corals and without photophile microencrusters were distinguished for the first time by Schlagintweit and Gawlick in 2008 in the Alps. In the Štramberk

Limestone, they were recognized by Hoffmann et al. (2017). Such reefs are known only from the

Tethyan domain where they were developed in a deeper environment, in a high-energy, upper fore-reef slope setting.

Sponge-microbial reefs were common in the Late Jurassic on the northern margin of the Tethys, but are poorly known from the Tethyan domain and never described before from the Štramberk

Limestone. Recent studies in the new, lowest level of the huge Kotouč quarry in Štramberk revealed olistoliths of sponge-microbial boundstones with rare corals (Kołodziej et al. 2023). Further studies will aim to determine the age of these boundstones to reveal whether they were formed before the development of a shallow-water carbonate platform or are coeval with coral reefs but developed in a deeper environment. In contrast to the northern Tethyan margin (European epicontinental seas; e.g., Wierzbowski and Stolarski 2023) mesophotic coral reefs dominated by platy microsolenids were not recognized in the Štramberk Limestone.