Genetically different organogenic buildups in isotope values δ 13С and δ 18О

Abstract

The isotopic composition of carbon and oxygen of 165 samples of carbonate rocks of genetically different organogenic structures: the Upper Ordovician Bol'shaya Kos'yu reef, the Upper Devonian Shar'yu microbial mound, the Kozhym skeletal mound, the Upper Miocene Kazantip bioherm complex and deep-water organogenic-carbonate structures of the north of the Mid-Atlantic Ridge was studied. The reef and microbial mound are characterized by δ 13СPDB values within the limits close to normal-sedimentary marine carbonates (–0.33—3.13 ‰) and (0.8—3.0 ‰), but with significant variations in δ 18ОSMOW — (22.24—30.0 ‰) and (20.4—26.3 ‰), respectively. The most isotopically-heavy carbon composition (5.1—7.3 ‰) in combination with varying δ 18ОSMOWvalues (22.4— 30.0 ‰) is characteristic of limestones and brachiopods of the skeletal mound. Fluctuations of δ 13СPDB and δ 18ОSMOW values in carbonate rocks of the Kazantip bioherm complex are the most expressive (–2.76—7.17 ‰) and (24.20—33.1 ‰), respectively. Deepwater organogenic structures from the bottom of the axial zone with active volcanism, in contrast to others, showed stable δ 13СPDB values (–0.98—0.83 ‰) within the area of normal-sedimentary marine carbonates, whereas for oxygen the values are istopic-heavy (32.27—39.75 ‰). As a result, the specificity of the development of the objects under study, established by lithological-paleoecological and chemical-physical methods, found its substantiation in isotopic values, paleosalinity and paleotemperatures caused by paleogeographic and climatic conditions.