Dolocretes in the uppermost Famennian to Mississippian siliciclastic deposits /Dolokreedid Lati Devoni Skervelise kihistu ranirikastes purdkivimites

• Published in: Estonian journal of earth sciences 2023-06, Vol.72 (2), p.211
• Main Authors: Pipira, Daiga, Keipane, Lauma, Stinkulis, Girts, Vircava, Ilze, Martma, Tonu
• Format: Article
• Language: English
• Subjects: Analysis; Carbonates; Fossils; Geomorphology; Sedimentary structures
• ISSN: 1736-4728
• DOI: 10.3176/earth.2023.86

Siliciclastic deposits and dolostones of the Skervelis Formation in southwestern Latvia were studied in outcrops, polished slabs, thin sections, and by geochemical methods, including stable isotope analyses. Siliciclastic fluvial deposits alternate with soils and carbonates. As the soil processes became dominant, up to 6 m thick dolocretes formed, but they still preserve remnant sedimentary structures and textures. The strong role of soil processes is indicated by the presence of ooids and pisoids together with fine laminar layers, chert and phosphatic inclusions, rhizoids, and stable isotope values. Peculiar vertical clay-dolomite structures, up to 1.7 m long, are root structures or their combination with Vertisol-like soil development. The extensive development of soil processes and formation of the vertical structures was stimulated by seasonally wet monsoon climate. The scarcity of fossils in the studied deposits does not allow their age to be determined precisely, but probably the thick dolocrete unit in the upper part of the studied succession formed during the end-Devonian glaciation and the period of related sea regression. Edela-Latis asuva Skervelise kihistu ranirikkaid purdkivimeid ja dolomiite uuriti paljandites, poleeritud/lihvitud palade ja ohikute abil ning geokeemiliste meetoditega, sealhulgas stabiilsete isotoopide analuusiga. Vooluveelised rani purdsetete kuhjed vaheldusid korduvalt mulla moodustumise ja karbonaatide settimisega. Kui mulla protsessid muutusid domineerivaks, moodustusid kuni 6 m paksused dolokreedid, sailitades siiski ka algseid struktuure ja tekstuure. Mullaprotsesside olulist rolli naitab ooidide ja pisoidide olemasolu koos ohukeste vahekihikeste, ranikivide, fosfaatsete suletiste ja risoididega ning stabiilsete isotoopide vaartused. Omaparased kuni 1,7 m pikkused vertikaalsed savi-dolomiidi struktuurid on juure struktuurid voi nende kombinatsioon vertisoli-sarnase mulla arenguga. Mullaprotsesside laialdast levikut ja vertikaalsete struktuuride moodustumist soodustas hooajaliselt niiske mussoonkliima. Fossiilide vahesus uuritud setetes ei voimalda vanust tapselt maarata, kuid toenaoliselt moodustus uuritud labiloike ulemises osas olev paks dolokreetide kiht Devoni lopuperioodil toimunud jaatumise ja sellega seotud mere regressiooni ajal.