Microencruster-microbial-cement framework of the Upper Jurassic reef developed on the slope of the intra-Tethyan carbonate platform (Bulgaria) Bogusław Kołodziej a, *, Daria Ivanova b a Institute of Geological Sciences, Jagiellonian University, ul. Gronostajowa 3a, 30-387 Kraków, Poland b Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria A R T I C L E I N F O Article history: Received 2 July 2020 Received in revised form 18 October 2020 Accepted 20 October 2020 Available online xxx Keywords: Reefs Microencrusters Syndepositional cements Microbialites Moesian Platform Jurassic A B S T R A C T The carbonate succession in the Lyalintsi section of the western Moesian Platform (western Bulgaria) displays a shallowing-upward trend. Growth of the Tithonian–Valanginian coral biostromes and low- relief bioherms was preceded by Oxfordian–Kimmeridgian sedimentation of fine-grained peloidal- bioclastic limestones and Saccocoma-bearing limestones on the homoclinal ramp and the carbonate platform slope. In the late Kimmeridgian, boundstones with very rare corals, but with easily recognisable biohermal morphology, were developed. The main components of this reef are encrusting micro- organisms, microbial crusts and synsedimentary cements. Microencrusters Labes atramentosa, Crescent- iella morronensis, Perturbatacrusta leini and Radiomura cautica, as well as thin crusts of calcified sponges (sclerosponges), are the main biotic components. Corals (almost exclusively microsolenids) are sparse, whereas photophilic microencrusters (e.g., “Lithocodium–Bacinella”), are absent, although they are common in the overlying shallow-water part of the Lyalintsi sequence. Microbialites and synsedimentary cements provided additional support for the reef framework. The framework, especially the biotic components, and the reefal facies position within the sedimentary succession, implies that the high- energy upper slope of the carbonate platform was the depositional setting of the microencruster- microbial-cement reef studied. Encrusting microorganisms, except for C. morronensis and sponges, are only known from the intra-Tethyan platforms. This study supports conclusion of studies of coeval Alpine reefs that the presence of the microencruster-microbial-cement framework provides insight into the palaeobathymetry, palaeogeography and tectonic configuration of the intra-Tethyan carbonate platforms. © 2020 The Geologists' Association. Published by Elsevier Ltd. All rights reserved. 1. Introduction Corals and sponges were the main reef framework builders during the Late Jurassic. They were commonly associated with microbial communities, which alone can form microbialite reefs (Leinfelder et al., 2002). Based on studies in the Northern Calcareous Alps (Austria), Schlagintweit and Gawlick (2008) distinguished “microencruster frameworks with variable amounts of cement" and "cement-supported microencruster boundstones". It seems that reefs composed of non-photophilic microencrusters, microbialites and synsedimentary cement crusts can be consid- ered as an independent Jurassic reef type. In contrast to Permian and Triassic reefs, Jurassic reefs displaying such frameworks have not been recognised until the work of Schlagintweit and Gawlick (2008). More recently, other Upper Jurassic–Lower Cretaceous reefs with sparse corals but distinctive microencruster-microbial- cement frameworks, were described (Hoffmann et al., 2017, and Hoffmann et al. (under review); Krajewski and Schlagintweit, 2018; Pleş et al., 2019, Pleş et al. (in press)). The encrusting microorganisms identified in these reefs are mainly reported from the carbonate platforms of the Tethyan domain (Schlagintweit and Gawlick, 2008, 2009, 2011; Pleş et al., 2013, 2019; Pleş and Schlagintweit, 2014; Chatalov et al., 2015; Ivanova et al., 2015; Kaya and Altıner, 2015; Kołodziej et al., 2015; Hoffmann et al., 2017 and Hoffmann et al. (under review)). Schlagintweit and Gawlick (2008) assigned the microencruster-cement reef to the platform margin-slope transition (fore-reef slope environment), but the depositional setting of other coeval, similar reefs was rarely well constrained. * Corresponding author. E-mail addresses: boguslaw.kolodziej@uj.edu.pl (B. Kołodziej), dariaiv@geology.bas.bg (D. Ivanova). https://doi.org/10.1016/j.pgeola.2020.10.007 0016-7878/© 2020 The Geologists' Association. Published by Elsevier Ltd. All rights reserved. Proceedings of the Geologists’ Association xxx (xxxx) xxx–xxx G Model PGEOLA-873; No. of Pages 12 Please cite this article as: B. Kołodziej and D. Ivanova, Microencruster-microbial-cement framework of the Upper Jurassic reef developed on the slope of the intra-Tethyan carbonate platform (Bulgaria), Proc. Geol. Assoc., https://doi.org/10.1016/j.pgeola.2020.10.007 Contents lists available at ScienceDirect Proceedings of the Geologists’ Association journal homepa ge: www.elsev ier.com/locate /pgeola