Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic
Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic
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DOI：
10.1029/2011pa002160
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发表时间：
2011-12
期刊：
影响因子：
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通讯作者：
C. Korte;S. Hesselbo
中科院分区：
文献类型：
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作者：
C. Korte;S. Hesselbo
在中生代的大部分记录中，关于同位素代表环境变化和层序地层沉积层序的全球意义的争论一直没有定论。本文以英国克利夫兰盆地浅海演替中的海洋底栖动物、内底栖软体动物和腕足动物为研究对象，给出了早侏罗世部分时期的碳氧同位素和元素记录。无脊椎动物的同位素记录补充了来自化石木材的碳同位素数据，这些数据对大气中的碳进行了采样。新的数据阐明了两个主要的全球碳同位素事件，Sinemurian-Pliensbachian边界的负偏移~ 2‰，以及晚Pliensbachian的正偏移~ 2‰。Sinemurian-Pliensbachian边界事件与稍年轻的Toarcian Oceanic缺氧事件相似，其特征是沉积相对深水的富有机质页岩。而晚普林恩巴氏地层则以浅海沉积为特征。氧同位素数据表明，这两个事件都发生了局部降温。然而，由于克利夫兰盆地Sinemurian-Pliensbachian边界具有较深的水条件，因此温度下降可能具有局部意义；相比之下，凉爽的晚普林恩巴氏浅层海底与先前关于部分冰窖条件的推断一致。大尺度、长期和小尺度、短周期的同位素旋回都与层序地层学先前记录的相对海平面变化相一致。同位素事件和海平面周期反映了具有全球意义的过程，支持早侏罗世在1 ~ 10 Ma的时间尺度上发生从冰窖到温室和超级温室条件的周期波动的观点。
[1] For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ∼2‰ at the Sinemurian–Pliensbachian boundary, and a positive excursion of ∼2‰ in the Late Pliensbachian. The Sinemurian–Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic-rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian–Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large-scale, long-term and small-scale, short-duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma.