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Pavel Kabanov, Paleontological Institute RAS (Russian Federation)
Simon Beavington-Penney, BG Energy Holdings Limited (United Kingdom)
Giovanna Della Porta, Cardiff University (United Kingdom)
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The time span between the Frasnian/Famennian demise of stromatoporoid buildups and the latest Carboniferous recovery of reef-building association records minimal ability of carbonate-producing ecosystems to build reef crests. In Late Visean-lower Moscovian, a specific type of seismic-scale (>100 m high) platform slope bioconstructions developed in Paleotethys and adjacent basins, which is recorded by the Late Visean-Bashkirian bioherms of Bolshoi Karatau, Bashkirian-lowermost Moscovian of the westernmost Paleotethys (Asturias, N Spain), and some Late Visean-Serpukhovian carbonate platforms in the Pricaspian Depression. These bioconstructions are distinct by (1) facing the high-rising carbonate platforms in rapid subsidence settings; 2) carbonate slope accretion lacking a raised rim at the margin; (3) upper slopes with volumetrically prevalent microbial micrites and/or cementstones (recrystallized aragonitic and radiaxial) with relatively small contribution by skeletal biota, primarily fenestellid bryozoans and upright algae (Donezella/Praedonezella and Beresellaceae).
A thick Serphukhovian boundstone section is discovered in the Iriklinskoe Quarry (southern East Uralian basin). The lower 65-70 m of the section consists of Gigantoproductus - rich pale gray bioclastic packstones, grainstones and rudstones. In the middle of this unit, appearance of fenestellid-supported radiaxial cementstone lenses mark commencement of bioconstruction. The boundstone part of the section is at least 290 m thick and consists of radiaxial to recrystallized-aragonitic ("botryoidal") cemenstones with subsequent algal and bryozoan growth. The continuity of the buildup is interrupted by thin (<2m thick) bioclastic beds that grade up to cementstone framestones. The upper 140 m are composed of tight aragonite spar - dominated cementstones with few packstone and grainstone lenses. The top of the buildup is not exposed. The Iriklinskoe boundstone section is interpreted as an aggrading upper slope of a high-rising platform. It is different from the Sierra del Cuera platform (Asturias) in more important cementstone facies, fewer microbial micrites, and aggrading stacking pattern. The Iriklinskoe outcrop extends knowledge on the variability of thick Visean-Moscovian platform-slope boundstones previously limited to Asturias and Bolshoi Karatau observations.
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