Global, regional and local controls on the development of a Triassic carbonate ramp system, Western Balkanides, Bulgaria

Abstract

The Early to Late Triassic development of a carbonate ramp system in the subtropical belt of the NW Tethys was controlled by the interplay of several global and regional factors: geotectonic setting (slow continuous subsidence on a passive continental margin), antecedent topography (low-gradient relief inherited from preceding depositional regime), climate and oceanography (warm and dry climatic conditions, storm influence), relative sea-level changes (Olenekian to Anisian eustatic rise, middle Anisian to early Carnian sea-level fall), lack of frame-builders (favouring the maintenance of ramp morphology), and carbonate production (abundant formation of lime mud, non-skeletal grains and marine cements, development of diverse biota controlled by biological evolution and environmental conditions). Elevated palaeorelief affected the ramp initialization on a local scale, while autogenic processes largely controlled the formation of peritidal cyclicity during the early stage of ramp retrogradation. Probably fault-driven differential subsidence caused a local distal steepening of the ramp profile in middle–late Anisian time. The generally favourable conditions promoted long-term maintenance of homoclinal ramp morphology and accumulation of carbonate sediments having great maximum thickness (~500 m). Shutdown of the carbonate factory and demise of the ramp system in the early Carnian resulted from relative sea-level fall and subsequent emergence. After a period of subaerial exposure with minor karstification, the deposition of continental quartz arenites suggests the possible effect of the Carnian Pluvial Episode.

Facies and evolution of the carbonate factory during the Permian–Triassic crisis in South Tibet, China

“…Subsidence rates during the Early Triassic are estimated to have been slow ( ca 18 m per m.a.) (Liu & Einsele, ); the low, uniform subsidence rates of passive continental margins favour the formation of homoclinal carbonate ramps (Chatalov, , ). This is because passive continental margins provide a flat base for carbonate accumulation and hinders detrital input (Chatalov, ).…”

“…(Liu & Einsele, ); the low, uniform subsidence rates of passive continental margins favour the formation of homoclinal carbonate ramps (Chatalov, , ). This is because passive continental margins provide a flat base for carbonate accumulation and hinders detrital input (Chatalov, ). Sections from South Tibet contain low amounts of detrital grains, including quartz, mica and feldspar, indicating a low detritus input from the landmass.…”

Early Triassic oceanic red beds coupled with deep sea oxidation in South Tethys

“…Cortoids, in association with thick-shelled bivalves floating in a micritic matrix, are interpreted as rapidly-emplaced proximal tempestite (e.g., Chatalov, 2016).…”

Origin of fabric-selective dolomitization recognizable in the field: two case studies from Anisian carbonate rocks in the western Balkanides

“…Biostratigraphic and sedimentological studies indicate that marine deposition occurred from the late Olenekian or early Anisian to the early Carnian (Tronkov, 1968(Tronkov, , 1973Ajdanlijsky et al, 2018; see also Chatalov, 2017b) on a homoclinal carbonate ramp with local distal steepening, which evolved in the subtropical belt on the north-western shelf area of the Tethys Ocean (Čatalov, 1988;Chatalov, 2013aChatalov, , 2018. Two main stages of the ramp development (retrogradational and progradational) produced two genetic units (transgressive and regressive) that are separated by a maximum flooding zone, i.e., Terebratula Beds (Chatalov, 2013a(Chatalov, , 2018. Subtidal, intertidal and supratidal facies were formed in several depositional environments of three ramp zones: inner ramp, mid-ramp, and outer ramp (Chatalov, 2013a(Chatalov, , 2018Chatalov et al, 2015).…”

“…Two main stages of the ramp development (retrogradational and progradational) produced two genetic units (transgressive and regressive) that are separated by a maximum flooding zone, i.e., Terebratula Beds (Chatalov, 2013a(Chatalov, , 2018. Subtidal, intertidal and supratidal facies were formed in several depositional environments of three ramp zones: inner ramp, mid-ramp, and outer ramp (Chatalov, 2013a(Chatalov, , 2018Chatalov et al, 2015). Various environmental constraints of the ramp depositional system and controlling factors on its development have been recognized and thoroughly discussed (Chatalov, 2013a(Chatalov, , 2018.…”