The Pliensbachian-Toarcian (Pl-To) boundary was marked by an extinction event in marine organisms, and localised ocean anoxia – resulting in the deposition of black shales. Negative isotopic excursions in bulk organic carbon in many of these black shales, are widely believed to indicate that a global carbon cycle disruption accompanied this extinction event. The Pl-To preceded a period of more intense global carbon cycle disruption that occurred during the Toarcian Oceanic Anoxic Event (T-OAE) by around a million years. It is evident from targeted carbon isotopic analyses of marine and terrestrial organic matter that simultaneous disruptions to the marine and terrestrial carbon cycles occurred during the T-OAE. However, it remains a matter of debate whether the main source of carbon emissions was a climate-sensitive methane reservoir, or volcanic processes. No records of terrestrial carbon cycle disruption exist for the latest Pliensbachian, and so the causal mechanisms behind localised anoxia in this stage of the Lower Jurassic are poorly constrained. We present a record of concomitant isotopic depletion in short and long-chain n-alkanes derived from a thin black shale (the Lower Sulphur Band – LSB) deposited during the latest Pliensbachian (located in Yorkshire, UK). A key argument is that simultaneous isotopic depletions in these different compound classes implies the presence of a brief global hyperthermal event in the latest Pliensbachian, with a timescale too short to have been captured by previous analyses of the Yorkshire section. We discuss the relevance of our data to the stratigraphic record of the Lower Jurassic sediments of Yorkshire, highlighting, in particular, the need for better constraint on the ammonite biostratigraphy of the study section. We further argue that the brief climate disruption that occurred in the latest Pliensbachian made the shallow marine environment vulnerable to the development of more widespread marine anoxia, during the succeeding Toarcian stage.

中文翻译：

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海洋和陆地碳库同时同位素耗尽证明了普林斯巴赫纪（下侏罗世）期间全球碳循环的破坏


普林斯巴赫阶-托阿尔阶 (Pl-To) 边界的标志是海洋生物灭绝事件和局部海洋缺氧，导致黑色页岩沉积。人们普遍认为，许多黑色页岩中大量有机碳的负同位素偏移表明，全球碳循环中断伴随着这一灭绝事件。 PI-To 事件发生在托阿尔纪海洋缺氧事件 (T-OAE) 期间发生的更严重的全球碳循环破坏时期大约一百万年。对海洋和陆地有机质的针对性碳同位素分析表明，在 T-OAE 期间，海洋和陆地碳循环同时发生了破坏。然而，碳排放的主要来源是气候敏感的甲烷库还是火山过程仍然存在争议。普林斯巴赫纪末期没有陆地碳循环破坏的记录，因此下侏罗世这一阶段局部缺氧背后的因果机制很少受到限制。我们提出了源自普林斯巴赫纪末期（位于英国约克郡）沉积的薄黑色页岩（下硫带 - LSB）的短链和长链正构烷烃伴随同位素消耗的记录。一个关键的论点是，这些不同化合物类别中同时发生的同位素耗尽意味着在最新的普林斯巴赫阶中存在短暂的全球高温事件，其时间尺度太短，无法通过之前对约克郡剖面的分析来捕获。我们讨论了我们的数据与约克郡下侏罗统沉积物地层记录的相关性，特别强调需要更好地限制研究部分的菊石生物地层。 我们进一步认为，普林斯巴赫纪末发生的短暂气候破坏使得浅海环境在随后的托阿尔纪阶段容易受到更广泛的海洋缺氧的影响。