Palaeotemperature reconstruction based on oxygen stable isotopic trends from the Ordovician-Silurian brachiopods of Baltoscandia
Date
2024-11-01
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Abstract
Vanaaegkonna kliimamuutused on viimasel kahel aastakümnel olnud teadusuuringute teravdatud tähelepanu all. Baltoskandiat peetakse selliste uuringute jaoks ideaalseks piirkonnaks, kus selleaegsed settekivimid on vaid väheste settimisjärgsete muutustega. Väitekiri keskendub minevikus aset leidnud keskkonna- ja kliimamuutuste uurimisele Baltoskandia paleobasseinis, kasutades Ordoviitsiumi ja Siluri käsijalgsete kojamaterjali stabiilsete hapnikuisotoopide suhet, mis võimaldab interpreteerida paleotemperatuuri trende uuritavas piirkonnas. Vaatamata absoluutse temperatuuri hinnangute võimalikele ebatäpsustele näitavad tulemused, et käsijalgsete kojamaterjali isotoopkoosseis on üldjoontes kasutatav kliimamuutuste interpreteerimisel. Uuring tuvastas, et Ordoviitsiumi ja Siluri ajastu olulisemad stabiilse süsiniku suhtarvu (δ¹³C) kõvera globaalse levikuga ekskursioonid, sealhulgas Kesk-Darriwili isotoopekskursioon (MDICE), Hirnanti isotoopekskursioon (HICE) ja Irevikeni sündmus, kajastuvad ka käsijalgsete kojamaterjali koostise muutustes. Biokaltsiidi hapnikuisotoopide suhte muutused kajastavad üldist jahenemistrendi Vara-Ordoviitsiumi lõpust ja läbi Kesk-Ordoviitsiumi, kusjuures ookeanivee pinnalähedane temperatuur langes ligikaudu 8 °C võrra. See jahtumine peegeldas tõenäoliselt pigem globaalseid kliimatrende kui kohalikke keskkonnamuutusi. Pärast suhteliselt sooja perioodi Katy eal leidis Hirnanti jäätumise tõttu aset märkimisväärne globaalne jahenemine, millele järgnes taas soojenemine Siluri ajastu algul. Tulemused näitavad, et vaatamata Baltica mandri laamtektoonilisele triivile troopiliste laiuskraadide suunas kontrollis merekeskkonnas aset leidnud regionaalseid muutusi peamiselt globaalne temperatuurilangus. Baltoskandia käsijalgsete δ¹⁸O muutuste alusel tehtud järeldused on heas kooskõlas teiste kontinentide andmetega ja käsijalgsetes salvestunud keskkonnaindikaatoreid saab seega pidada Vanaaegkonna paleokliima uurimisel usaldusväärse info allikaiks.
Over the last two decades, extensive research has focused on climate fluctuations during the Ordovician-Silurian period. Baltoscandia is considered an ideal region for such studies due to well-preserved Palaeozoic sediments and minimal post-depositional alteration. The current study is focusing on the environmental and climatic changes reflected in the Ordovician-Silurian Baltoscandian Palaeobasin, using the stable oxygen isotopic data from the brachiopod shell calcite as a proxy for paleoclimate, providing a comprehensive record of palaeotemperature trends in this region. Despite certain limitations in absolute temperature precision, the results show that brachiopod isotope data can be used for interpretation of climatic trends. The study identifies that more significant global δ¹³C excursions in the Ordovician-Silurian periods, including the Mid-Darriwilian Carbon Isotope Excursion (MDICE), the Hirnantian Isotope Carbon Excursion (HICE) and Ireviken Event, are also reflected in the brachiopod shell composition. The oxygen isotope data from brachiopods shows an overall trend of cooling from the Early to Middle Ordovician, with a significant temperature decrease of about 8 °C. This cooling likely reflects global climate trends rather than local environmental disturbances. Following a relatively warm late Katian age, a significant global cooling occurred during the Hirnantian glaciation, with a subsequent rise of temperatures during the early Silurian. The study also highlights that, despite the plate tectonic drift of Baltica towards tropical latitudes, the regional palaeoenvironmental changes were primarily influenced by the global climatic shifts towards cooler climate. The δ¹⁸O values from brachiopods of the Baltoscandian region are consistent with those from other continents. Brachiopods are therefore considered a reliable proxy for understanding palaeoclimate during the Ordovician-Silurian periods.
Over the last two decades, extensive research has focused on climate fluctuations during the Ordovician-Silurian period. Baltoscandia is considered an ideal region for such studies due to well-preserved Palaeozoic sediments and minimal post-depositional alteration. The current study is focusing on the environmental and climatic changes reflected in the Ordovician-Silurian Baltoscandian Palaeobasin, using the stable oxygen isotopic data from the brachiopod shell calcite as a proxy for paleoclimate, providing a comprehensive record of palaeotemperature trends in this region. Despite certain limitations in absolute temperature precision, the results show that brachiopod isotope data can be used for interpretation of climatic trends. The study identifies that more significant global δ¹³C excursions in the Ordovician-Silurian periods, including the Mid-Darriwilian Carbon Isotope Excursion (MDICE), the Hirnantian Isotope Carbon Excursion (HICE) and Ireviken Event, are also reflected in the brachiopod shell composition. The oxygen isotope data from brachiopods shows an overall trend of cooling from the Early to Middle Ordovician, with a significant temperature decrease of about 8 °C. This cooling likely reflects global climate trends rather than local environmental disturbances. Following a relatively warm late Katian age, a significant global cooling occurred during the Hirnantian glaciation, with a subsequent rise of temperatures during the early Silurian. The study also highlights that, despite the plate tectonic drift of Baltica towards tropical latitudes, the regional palaeoenvironmental changes were primarily influenced by the global climatic shifts towards cooler climate. The δ¹⁸O values from brachiopods of the Baltoscandian region are consistent with those from other continents. Brachiopods are therefore considered a reliable proxy for understanding palaeoclimate during the Ordovician-Silurian periods.
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