Microencruster-microbial framework and synsedimentary cements in the Štramberk Limestone (Carpathians, Czech Republic): Insights into reef zonation

Abstract

The Štramberk Limestone (Tithonian-lower Berriasian) was developed on a northerly located, isolated intra-Tethyan carbonate platform. It is composed of various facies that can be observed in olistoliths and blocks embedded in the Cretaceous flysch of the Outer Carpathians in Moravia (Czech Republic). Corals, microbialites, microencrusters and synsedimentary cements contributed on various scales to the reef framework. The importance of corals and some microencrusters to the formation of the Štramberk reef complex is well recognized, while other components received less attention in previous studies. Two end members of boundstone types are described from the Kotouč Quarry, near Štramberk. Boundstone type A is dominated by phaceloid (branching-type) corals, encrusted by microbialites and microencrusters, in particular photophile species ("Lithocodium-Bacinella", Koskinobullina socialis Cherchi et Schroeder, Iberopora bodeuri Granier et Berthou). Boundstone type B is composed of microencrusters, microbialites and synsedimentary isopachous fibrous cements, while corals are absent or subordinate. Microencrusters [Crescentiella morronensis (Crescenti), Labes atramentosa Eliášová, Perturbatacrusta leini Schlagintweit et Gawlick, Radiomura cautica Senowbari-Daryan et Schäfer, thin encrusting calcified sponges] are main biotic components of the microencruster-cement boundstone. Some identified microencrusters are known only or mostly from intra-Tethyan carbonate platforms. Except for C. morronensis, other common microencrusters in the coral-microbial boundstone (type A) are rare in the microencruster-cement boundstone (type B). The depositional setting of boundstone type A corresponds to a low-energy environment of an inner platform. Boundstone type B, until now not recognized in the Štramberk Limestone, was developed in a high-energy, upper fore-reef slope environment. Other important facies in the Kotouč Quarry are reef-derived breccias: matrix-supported breccia and clast-supported breccia with radiaxial-fibrous cement (showing some similarities to Triassic "evinosponges" cement), interpreted as being dominantly synsedimentary (pre-burial). The preliminary studies by the present authors, supported by observations under cathodoluminescence, highlight the significance of synsedimentary cementation for the formation of a boundstone framework (type B) and the stabilization of fore-reef, slope deposits.

Crescentiella-microbial-cement microframeworks in the Upper Jurassic reefs of the Crimean Peninsula

“…The North Tethys/Atlantic reefs that developed on extensive ramp-type platforms can be assigned to three broad compositional types: (1) coraldominated, (2) siliceous sponge-dominated, and (3) microbialite-dominated (e.g., Leinfelder et al 2002). In contrast hereto, the isolated reefs growing at the margins of intra-Tethyan platforms were dominated mostly by mixed, coralscalcified sponges (including stromatoporoids and chaetetids) facies (e.g., Turnšek et al 1981;Leinfelder et al 2002Leinfelder et al , 2005Vlahović et al 2005;Ivanova et al 2008;Rusciadelli et al 2011;Della Porta et al 2013;Hoffmann et al 2017). Their characteristic lateral assemblages allow the zonation of these reef complexes, corresponding to fore-reef, reef crest, and flat to back-reef environments.…”

“…These reefs are regarded as close analogues to the Late Jurassic reefs found in the Shatsky Ridge (Afanasenkov et al 2005;Guo et al 2011). The Ai-Petri Massif is a spectacular example of the Late Kimmeridgian-Tithonian reef complex Olszewska 2006, 2007) resembling the Štramberk-type reefs well known from the Pontides, Moesia, Southern Carpathian, Polish and Czech Outer Carpathian, Southern Crimea and the Northern Caucasus Mts (e.g., Matyszkiewicz and Słomka 2004;Bucur and Săsăran 2005;Ivanova et al 2008;Guo et al 2011;Piskunov et al 2012;Pleş et al 2013;Kaya and Altiner 2015;Kołodziej 2015;Strzeboński et al 2017;Hoffmann et al 2017;Vincent et al 2018). The main part of the Late Jurassic successions from the Crimean Mts.…”

“…In recent papers dealing with both the Tethyan northern shelf and the intra-Tethyan platforms, still-growing attention is paid to the presence and the role of a wide spectrum of socalled "microencrusters" (e.g., Crescentiella, bacinellid fabrics, Thaumatoporella, Radiomura, Lithocodium, Iberopora, etc., e.g., Schmid 1996;Leinfelder et al 1996;Ivanova et al 2008;Pleş et al 2013Pleş et al , 2017Kaya and Altiner 2015;Hoffmann et al 2017) in the formation of reef frameworks. Apart from microbial crusts, these microencrusters were important components of coral and sponge reefs as secondary reefbuilders.…”

“…Sometimes they form microbial-microencruster boundstones with a significant content of early cements. Late Jurassic to earliest Cretaceous microbial-microencrustercement-boundstones (microframeworks) assigned to outer margin-upper slope depositional settings have been reported from various intra-Tethyan (mostly southern Tethyan) platform carbonates: Austria (Schlagintweit and Gawlick 2008, Plassen Limestone), Bulgaria, Czech Republic and Poland (Ivanova et al 2008;Hoffmann et al 2017, Štramberk-type Limestone), Romania (Pleş et al 2013(Pleş et al , 2017, Italy (Rusciadelli et al 2011, e.g., Table 1, Ellipsactinia Limestone), Turkey (Kaya and Altiner 2015) and Japan (Shiraishi and Kano 2004;Ohga et al 2013, Torinosu Limestone). For a paleogeographic sketch displaying these occurrences in the western part of the Tethys see Fig.…”

The oldest stage of the Outer Carpathian evolution in the light of Oxfordian–Kimmeridgian exotic clast studies (southern Poland)

“…The oncoid-intraclast-Crescentiella limestones (FT 2) dominated by various coated grains, bioclasts and intraclasts with numerous Crescentiella are commonly observed in many parts of Upper Jurassic, open marine, shallow-water platforms (above the storm wave base i.e., around 40-60 m depth) of the Tethyan Realm in the Central Europe (e.g., Leinfelder et al 1996;Krajewski and Olszewska 2006;Matyszkiewicz et al 2006Matyszkiewicz et al , 2012Schlagintweit and Gawlick 2008;Hoffmann et al 2017;Pleş et al 2017;Krajewski and Schlagintweit 2018; and references therein). On the northern Tethyan shelf area, such associations are common in a mid-ramp setting (e.g., Leinfelder et al 1996;Senowbari-Daryan et al 2008;Krajewski et al 2016Olchowy et al 2019).…”