{"title":"波罗的海奥陶纪和志留纪腕足动物碳和氧稳定同位素趋势:对古环境和古温度变化的影响","authors":"Bilal Gul, Leho Ainsaar, Tánu Meidla","doi":"10.7306/gq.1742","DOIUrl":null,"url":null,"abstract":"<p>Oxygen isotope palaeotemperature studies of Paleozoic limestones are based mainly on brachiopod shell material which is resistant to diagenesis and generally precipitated in oxygen isotopic equilibrium with ambient sea water. Here we present brachiopod C and O stable isotopic data from the Baltoscandian Ordovician-Silurian succession, and evaluate palaeotemperature and palaeoenvironmental variability during deposition of the Estonian Shelf facies. As the region has not been influenced significantly by tectonic events or deep burial diagenesis, the carbonate rocks and fossils are well-preserved in most of the locations studied. δ<sup>18</sup>O values for the Ordovician and Silurian carbonates and brachiopods range between ~–7 and 0‰. High δ<sup>18</sup>O values, locally accompanied by higher δ<sup>13</sup>O values, correspond to cooling if the isotope signal reflects the original oxygen isotopic composition in sea water and vice versa. Several Ordovician-Silurian δ<sup>13</sup>O<sub>brac</sub> excursions identified on the Estonian Shelf reflect global palaeoenvironmental history and events, being synchronous with previously documented excursions in the bulk carbonate stable isotopic curves. Combining the published and new d13Cbrac and δ<sup>13O<sub>brac</sub></sup> data allows us to address chemostratigraphic correlation of the interval from Lower Ordovician (Floian) up to the topmost Silurian (Přídolí). The δ<sup>18O<sub>brac</sub></sup> data corroborate warmer temperatures during Early Ordovician (Floian-Dapingian) and a cooling trend into the Mid-Ordovician documented by previous studies in different palaeobasins. The Hirnatian isotopic carbon excursion (HICE) episode reveals the minimum temperature in this interval and the post-HICE data suggest a rising temperature trend. Another temperature minimum is evident in the strata reflecting the Ireviken Event (Sheinwoodian). Our study shows that brachiopod d18O values from the Ordovician-Silurian carbonates may tentatively be interpreted as reflecting major temperature trends</p><p> </p>","PeriodicalId":12587,"journal":{"name":"Geological Quarterly","volume":"90 1","pages":""},"PeriodicalIF":0.9000,"publicationDate":"2024-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Baltoscandian Ordovician and Silurian brachiopod carbon and oxygen stable isotope trends: implications for palaeoenvironmental and palaeotemperature changes\",\"authors\":\"Bilal Gul, Leho Ainsaar, Tánu Meidla\",\"doi\":\"10.7306/gq.1742\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>Oxygen isotope palaeotemperature studies of Paleozoic limestones are based mainly on brachiopod shell material which is resistant to diagenesis and generally precipitated in oxygen isotopic equilibrium with ambient sea water. Here we present brachiopod C and O stable isotopic data from the Baltoscandian Ordovician-Silurian succession, and evaluate palaeotemperature and palaeoenvironmental variability during deposition of the Estonian Shelf facies. As the region has not been influenced significantly by tectonic events or deep burial diagenesis, the carbonate rocks and fossils are well-preserved in most of the locations studied. δ<sup>18</sup>O values for the Ordovician and Silurian carbonates and brachiopods range between ~–7 and 0‰. High δ<sup>18</sup>O values, locally accompanied by higher δ<sup>13</sup>O values, correspond to cooling if the isotope signal reflects the original oxygen isotopic composition in sea water and vice versa. Several Ordovician-Silurian δ<sup>13</sup>O<sub>brac</sub> excursions identified on the Estonian Shelf reflect global palaeoenvironmental history and events, being synchronous with previously documented excursions in the bulk carbonate stable isotopic curves. Combining the published and new d13Cbrac and δ<sup>13O<sub>brac</sub></sup> data allows us to address chemostratigraphic correlation of the interval from Lower Ordovician (Floian) up to the topmost Silurian (Přídolí). The δ<sup>18O<sub>brac</sub></sup> data corroborate warmer temperatures during Early Ordovician (Floian-Dapingian) and a cooling trend into the Mid-Ordovician documented by previous studies in different palaeobasins. The Hirnatian isotopic carbon excursion (HICE) episode reveals the minimum temperature in this interval and the post-HICE data suggest a rising temperature trend. Another temperature minimum is evident in the strata reflecting the Ireviken Event (Sheinwoodian). 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引用次数: 0
摘要
古生代石灰岩的氧同位素古温度研究主要基于腕足类贝壳材料,这种材料耐成岩作用,通常在与环境海水氧同位素平衡的状态下沉淀。在这里,我们展示了来自波罗的海奥陶纪-志留纪演替的腕足类 C 和 O 稳定同位素数据,并评估了爱沙尼亚大陆架岩层沉积过程中的古温度和古环境变化。由于该地区没有受到构造事件或深埋成岩作用的明显影响,因此所研究的大多数地点的碳酸盐岩和化石都保存完好。奥陶纪和志留纪碳酸盐岩和腕足动物的δ18O值介于~-7和0‰之间。如果同位素信号反映的是海水中原始的氧同位素组成,那么高δ18O值(局部伴有较高的δ13O值)与冷却相对应,反之亦然。在爱沙尼亚大陆架发现的几处奥陶纪-志留纪δ13Obrac偏移反映了全球古环境历史和事件,与之前记录的大量碳酸盐稳定同位素曲线的偏移是同步的。结合已公布的和新的 d13Cbrac 和 δ13Obrac 数据,我们可以解决从下奥陶纪(弗洛亚)到最上志留纪(普里多利)之间的化合地层相关性问题。δ18Obrac数据证实了早奥陶世(弗洛纪-大平纪)的温度较高,以及之前不同古盆地研究中记录的进入中奥陶世的降温趋势。希纳特世同位素碳偏移(HICE)事件揭示了这一时期的最低气温,HICE 之后的数据则表明气温呈上升趋势。另一个温度最低点出现在反映伊雷维肯事件(Sheinwoodian)的地层中。我们的研究表明,奥陶纪-志留纪碳酸盐岩中的腕足类 d18O 值可初步解释为反映了主要的温度趋势
Baltoscandian Ordovician and Silurian brachiopod carbon and oxygen stable isotope trends: implications for palaeoenvironmental and palaeotemperature changes
Oxygen isotope palaeotemperature studies of Paleozoic limestones are based mainly on brachiopod shell material which is resistant to diagenesis and generally precipitated in oxygen isotopic equilibrium with ambient sea water. Here we present brachiopod C and O stable isotopic data from the Baltoscandian Ordovician-Silurian succession, and evaluate palaeotemperature and palaeoenvironmental variability during deposition of the Estonian Shelf facies. As the region has not been influenced significantly by tectonic events or deep burial diagenesis, the carbonate rocks and fossils are well-preserved in most of the locations studied. δ18O values for the Ordovician and Silurian carbonates and brachiopods range between ~–7 and 0‰. High δ18O values, locally accompanied by higher δ13O values, correspond to cooling if the isotope signal reflects the original oxygen isotopic composition in sea water and vice versa. Several Ordovician-Silurian δ13Obrac excursions identified on the Estonian Shelf reflect global palaeoenvironmental history and events, being synchronous with previously documented excursions in the bulk carbonate stable isotopic curves. Combining the published and new d13Cbrac and δ13Obrac data allows us to address chemostratigraphic correlation of the interval from Lower Ordovician (Floian) up to the topmost Silurian (Přídolí). The δ18Obrac data corroborate warmer temperatures during Early Ordovician (Floian-Dapingian) and a cooling trend into the Mid-Ordovician documented by previous studies in different palaeobasins. The Hirnatian isotopic carbon excursion (HICE) episode reveals the minimum temperature in this interval and the post-HICE data suggest a rising temperature trend. Another temperature minimum is evident in the strata reflecting the Ireviken Event (Sheinwoodian). Our study shows that brachiopod d18O values from the Ordovician-Silurian carbonates may tentatively be interpreted as reflecting major temperature trends
期刊介绍:
The policy of the Geological Quarterly is to publish significant contributions of information and geological insight relevant to an international readership. The journal has been issued since 1957 at the Polish Geological Institute - National Research Institute and, at present, is the leading Earth sciences journal in Poland. All aspects of Earth and related sciences, and universal and broad regional rather than locally oriented topics are covered.
The journal is intended to be an international forum for the exchange of information and ideas, particularly on important geological topics of Central Europe.