Development of coral–sponge–microbialite reefs in a coated grain-dominated carbonate ramp (Upper Jurassic, eastern Sardinia, Italy)

Abstract

The Late Jurassic is a peak time of diversification of reefs with corals, stromatoporoids, calcareous and siliceous sponges, and microbialites during the Phanerozoic. This study focuses on the Callovian–Kimmeridgian carbonate succession of eastern Sardinia, deposited at tropical latitudes on the European passive margin that recorded from the late Oxfordian the evolution from a coated grain-dominated to a reef-bearing carbonate ramp. The coated grain-dominated carbonate ramp (phase 1; Callovian–middle Oxfordian) includes inner ramp ooidal shoals and peloidal packstone in the middle-to-outer ramp. The overlying reef-bearing ramp (phase 2; late Oxfordian–late Kimmeridgian) is characterized by three types (1–3) of bioconstructions. The distribution of these build-ups along the middle-to-outer ramp depositional profile reflects bathymetric parameters, related to the interplay of water energy and light penetration. Type 1 build-ups developed in the proximal middle ramp and consist of 45 m thick, 100 m wide, coral-stromatoporoid boundstone associated with coral–stromatoporoid rudstone–grainstone. Type 2 build-ups, colonizing deeper environments in the middle ramp, are lens-shaped coral–calcareous sponge–diceratid boundstone including stromatoporoids and chaetetid sponges, 1–2 m thick and 3–4 m wide, associated with bioclastic packstone–grainstone. Type 3 lens-shaped calcareous and siliceous sponge–coral–microbialite boundstone build-ups (1 m thick and a few metres wide) formed in lower energy, distal middle-to-outer ramp settings. The evolution of the eastern Sardinian carbonate ramp reflects the Oxfordian–Kimmeridgian spread of the coral–sponge-microbialite reefs along the Tethyan European passive margin.

Reply to Comment by John J.G. Reijmer on ‘Understanding carbonate factories through palaeoecological and sedimentological signals – Tribute to Luis Pomar’ by Brandano et al. (2022), Sedimentology, 69, 5–23

“…2 The same type of approach allowed documentation of the migration of the scleractinians upward in the water column from the mesophotic into the euphotic zone, when the first modern type of reefs appeared and developed in shallow and highly agitated waters above the chlorocline (Pomar, 2001b(Pomar, , 2020Pomar & Hallock, 2007Pomar et al, 2017). This upward shift was coeval with: (i) the onset and evolution of a thermocline 10 to 5 Ma, induced by a sharp 4 to 6°C increase of the thermal gradient (Nikolaev et al, 1998); (ii) the diversification of Symbiodinium dinoflagellates (Pochon et al, 2006); (iii) a sharp negative carbon isotope excursion (Zachos et al, 2001); (iv) a climate switch, from humid to arid, in the Western Mediterranean (Calvo et al, 1993); and (v) a sharp climate change at 8.8 to 8.5 Ma with the establishment of a truly dry season in central Iberia around 8.5 Ma (Van Dam, 1997, 2006Van Dam & Weltje, 1999).…”

“…), LBF and diverse heterozoan biota (Mateu‐Vicens et al ., 2012; Morsilli et al ., 2012; Pomar et al ., 2014; Shabafrooz et al ., 2014). During the Cretaceous, corals thrived with rudist bivalves (Skelton et al ., 1997; Johnson & Kauffman, 2001; Pomar et al ., 2005), and during the Jurassic with microbes and stromatoporoids (Leinfelder et al ., 2002; San Miguel et al ., 2013; Nembrini et al ., 2020). Thus, the use of obligatory autotrophic components such as red and green algae is the best approach for the definition of light‐based bathymetric zones, and this seems to be valid for the Cenozoic, most of the Mesozoic and even the late Palaeozoic (e.g.…”

A lost carbonate platform deciphered from clasts embedded in flysch: Štramberk-type limestones, Polish Outer Carpathians

“…The Štramberk Limestone rarely features in discussions on the intra-Tethyan carbonate platforms (Leinfelder et al, 2002(Leinfelder et al, , 2005Rusciadelli et al, 2011). Recently, in a paper on the Upper Jurassic reefs of Sardinia (passive margin of the Alpine Tethys) the Štramberk Limestone were not included among examples of Upper Jurassic reefs, even though there were references to ten papers on other Tethyan platforms (Nembrini et al, 2021). Hoffmann et al (2017) discussed the biotic and sedimentary characteristics that the Štramberk Limestone shares with the Late Jurassic platforms of the Tethyan realm.…”

“…The limestones in the Carpathians of the Czech Republic and Poland deserve attention, because they are relatively rare examples of carbonate platforms, especially reefs, developed in the Tithonian and earliest Cretaceous. They are known mostly from the area of the earlier Tethyan domain (e.g., Steiger and Wurm, 1980;Eliáš and Eliášová, 1984;Morsilli and Bosellini, 1997;Krajewski, 2008;Schlagintweit and Gawlick, 2008;Rusciadelli et al, 2011;Ohga et al, 2013;Pleş et al, 2013Pleş et al, , 2019Chatalov et al, 2015;Kaya and Altıner, 2015;Hoffmann et al, 2017;Atasoy et al, 2018;Ricci et al, 2018a, b;Mircescu et al, 2019;Nembrini et al, 2021;and Leinfelder et al, 2002 for more references), in contrast to the Oxfordian-Kimmeridgian reefs of the Tethyan shelf (Leinfelder et al, 2002). The Oxfordian and Kimmeridgian were times of strong coral reef development (Insalaco et al, 1997;Leinfelder et al, 2002).…”