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New 40Ar/39Ar radiometric ages of lamproites indicate latest Tortonian marine restriction of the Fortuna Basin, Eastern Betics, southern Spain Lamproite的新40Ar/39Ar辐射年龄表明西班牙南部Betics东部Fortuna盆地的最新托托期海洋限制

Evolving Earth Pub Date : 2023-06-14 DOI: 10.1016/j.eve.2023.100001

Luis Gibert , Alan Deino , Ariana Carrazana , David Cruset , Elisabet Playà , Jordi Ibáñez-Insa , Domingo Gimeno , Javier García-Veigas , Maria Lería , Victoriano Pineda

{"title":"New 40Ar/39Ar radiometric ages of lamproites indicate latest Tortonian marine restriction of the Fortuna Basin, Eastern Betics, southern Spain","authors":"Luis Gibert , Alan Deino , Ariana Carrazana , David Cruset , Elisabet Playà , Jordi Ibáñez-Insa , Domingo Gimeno , Javier García-Veigas , Maria Lería , Victoriano Pineda","doi":"10.1016/j.eve.2023.100001","DOIUrl":"https://doi.org/10.1016/j.eve.2023.100001","url":null,"abstract":"<div><p>Exposures of lamproitic volcanic rocks have been used to constrain the age of the evaporitic basin-fill in the Fortuna Basin of southern Spain. K/Ar dates initially suggested a Messinian age assignment for these deposits; however, subsequent <sup>40</sup>Ar/<sup>39</sup>Ar dates indicated a Tortonian age, implying the early onset of evaporite formation in the eastern Betic Cordillera, in an event termed the “Tortonian Salinity Crisis”. In this paper, we critically review the published chronology of the key igneous outcrops and provide new <sup>40</sup>Ar/<sup>39</sup>Ar ages, which show that the Cabezos Negros lamproites lie close to the Tortonian-Messinian boundary (c. 7.25 Ma). We also provide new paleomagnetic measurements from each of the three lamproitic outcrops (Cabezos Negros, Derramadores, and El Tale), which demonstrate normal magnetic polarity coincident with episodes of volcanic and subvolcanic activity. The presence of peperites and pillow structures indicate that volcanism at Cabezos Negros was coeval with deposition of the lower part of Rambla Salada Gypsum Member. Therefore, the normal polarity identified in this unit should be equivalent to the normal polarity on the Cabezos Negros lamproites. These results indicate that the initial marine restriction and evaporitic deposition of Fortuna Basin occurred more than a million years before the Messinian Salinity Crisis.</p></div>","PeriodicalId":100516,"journal":{"name":"Evolving Earth","volume":"1 ","pages":"Article 100001"},"PeriodicalIF":0.0,"publicationDate":"2023-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50203452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Analysis of the environmental impacts affecting Cambrian reef building and carbonate settings during the Miaolingian and Furongian epochs: A hypothesis for consideration 庙岭期和芙蓉期影响寒武系造礁和碳酸盐岩环境的环境影响分析：一个值得考虑的假设

Evolving Earth Pub Date : 2023-06-08 DOI: 10.1016/j.eve.2023.100002

David R. Cordie

{"title":"Analysis of the environmental impacts affecting Cambrian reef building and carbonate settings during the Miaolingian and Furongian epochs: A hypothesis for consideration","authors":"David R. Cordie","doi":"10.1016/j.eve.2023.100002","DOIUrl":"https://doi.org/10.1016/j.eve.2023.100002","url":null,"abstract":"<div><p>The Miaolingian and Furongian epochs of the Cambrian period have been identified as a time of limited metazoan reef development. The aim of this paper is to improve understanding of the biological and geochemical conditions that affected reefs during this interval, and to propose a hypothesis for understanding why metazoan reef development was inhibited. To address these issues, a global dataset of fossil occurrences (N = 25,307) spanning Cambrian Stage 4 to the early Ordovician (Tremadocian) was extracted from the Paleobiology Database, Paleoreef Database, and a review of the primary literature. Findings show that the proportion of reefs constructed by metazoans fell from 40% in the Wuliuan age to 0% in the Drumian age, with reefs being overwhelmingly dominated by microbial ecosystems through the remainder of the Cambrian. The proportion of skeletal material constructed from carbonate fell from 85% in the Wuliuan age to 63% in the Drumian age across all the fossil occurrence data, before recovering. These findings suggest that environmental conditions may have not been favorable to carbonate organisms, but this does not fully explain the prolonged reduction of metazoans within reefs throughout this interval. A hypothesis proposed here is that Miaolingian to Furongian metazoan reef abundances were low because of two factors: (1) shallow water anoxia – and other factors such as elevated temperatures and ocean acidification – caused the extinction of metazoan reef builders in the late-early Cambrian and (2) deep water anoxia and marine regression, resulted in a loss of habitat. These inhibiting conditions were not necessarily concurrent but are inferred to have collectively suppressed the growth of metazoan reefs until the Early Ordovician when more shelf space for new reef development occurred. This hypothesis provides a first step in exploration of these conditions during the middle and late Cambrian and for reef development in general.</p></div>","PeriodicalId":100516,"journal":{"name":"Evolving Earth","volume":"1 ","pages":"Article 100002"},"PeriodicalIF":0.0,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50203546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

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