Organic geochemistry, stable isotopes, and facies analysis of the Early Aptian OAE-New records from Spain (Western Tethys)
Organic geochemistry, stable isotopes, and facies analysis of the Early Aptian OAE-New records from Spain (Western Tethys)
复制标题
DOI：
10.1016/j.palaeo.2012.09.033
复制
发表时间：
2012-12
期刊：
影响因子：
--
通讯作者：
M. L. Quijano;J. M. Castro;R. Pancost;G. A. Gea;M. Najarro;R. Aguado;I. Rosales;J. Martín‑Chivelet
中科院分区：
文献类型：
--
作者：
M. L. Quijano;J. M. Castro;R. Pancost;G. A. Gea;M. Najarro;R. Aguado;I. Rosales;J. Martín‑Chivelet
早阿普第阶海洋缺氧事件（OAE 1a）是一个时间间隔，其特征是海洋沉积物中有机碳积累增加，显著的沉积和生物变化，以及碳同位素突然漂移，表明与全球碳循环扰动有关的重大古环境变化。在这里，我们提出了四个部分的研究记录OAE 1a（早Aptian）在西班牙，这是位于两个广泛的盆地，分别位于南部和北部的伊比利亚：南伊比利亚古陆（Carbonero、La Frontera和Cau剖面）和巴斯克-坎塔布里亚盆地（Puentenansa部分），它们代表了从浅海到深海的沉积环境（远端斜坡-Cau-和淹没平台-Puentenansa-）到远洋环境（Carbonero，La Frontera）。对四个剖面的生物标志化合物组成、碳同位素剖面、生物地层资料和相分析进行了对比和综合。碳同位素曲线都呈现出明显的负偏移，然后是正偏移。整合的C-同位素曲线与生物地层学数据已被用来相关的研究部分，并初步确定以前提出的八个部分从阿尔卑斯山域，随后确定在全球范围内的部分。四类主要化合物存在于所有部分：正烷烃、类异戊二烯、藿烷和甾烷。正构烷烃和无环类异戊二烯（植烷和姥鲛烷）在大多数样品中占主导地位。Hopane由一系列C27至C35组分代表，由于热成熟度的差异，各部分之间的特定异构体有所不同。甾烷以C27、C28和C29异构体的形式出现，而二甾烷仅出现在热成熟度最高的部分（Carbonero）。其他感兴趣的化合物包括伽马蜡烷和甲藻甾烷。热成熟度的差异似乎是一阶控制不同的生物标志物组合之间的研究部分。卡尔博内罗段是热成熟的，而附近的拉弗龙特拉和卡乌段是不成熟的。普恩特南萨有中间值。有机物质来自一系列陆地、海洋和细菌来源。C29甾烷异构体在所有部分的优势表明高等植物的强大的贡献。伽马蜡烷的存在表明水柱分层，和高C29/C30藿烷的比例表明在水/沉积物界面缺氧，分别。沉积学分析也表明沉积过程中的缺氧条件，但强烈和持久的水柱缺氧的证据是模棱两可的。剖面的对比表明，富有机相的沉积在远洋环境中开始较早，在浅海环境中开始较晚，这可能与在OAE 1a的发育过程中，有机质积累和保存的有利条件从深海沃茨扩展到较浅的台地环境有关。
The Early Aptian Oceanic Anoxic Event (OAE1a) is a time interval characterized by increased organic carbon accumulation in marine sediments, notable sedimentary and biotic changes, and abrupt carbon-isotope excursions indicative of significant major palaeoenvironmental changes linked to a perturbation in the global carbon cycle. Here we present the study of four sections recording the OAE1a (Early Aptian) in Spain, which are located in two broad basins respectively located in the South and the North of Iberia: the Southern Iberian Palaeomargin (Carbonero, La Frontera and Cau sections) and the Basque–Cantabrian Basin (Puentenansa section), which represent depositional settings ranging from shallow marine (distal ramp -Cau- and drowned platform -Puentenansa-) to pelagic environments (Carbonero, La Frontera). Biomarker compositions, C-isotope profiles, biostratigraphic data and facies analysis from the four sections are correlated and integrated. The C-isotope curves all present a clear negative excursion followed by a positive shift. The integration of the C-isotope curves with the biostratigraphic data has been used to correlate the studied sections and to tentatively identify the eight segments formerly proposed from the Alpine domain, and subsequently identified in sections worldwide. Four main groups of compounds are present in all sections: n-alkanes, isoprenoids, hopanes and steranes. n-Alkanes and acyclic isoprenoids (pristane and phytane) are dominant in most samples. The hopanes are represented by a range of C27to C35components, with the specific isomers varying amongst the sections due to differences in thermal maturity. Steranes occur as a range of C27, C28and C29isomers, whereas diasteranes only occur in the most thermally mature section (Carbonero). Other compounds of interest include gammacerane and dinosterane. Differences in thermal maturity appear to be the first order control on different biomarker assemblages amongst the studied sections. The Carbonero section is thermally mature, whereas the nearby La Frontera and Cau sections are immature. Puentenansa has intermediate values. Organic matter is derived from a range of terrestrial, marine and bacterial sources. The dominance of the C29sterane isomers in all sections suggests a strong contribution from higher plants. The presence of gammacerane indicates water column stratification, and high C29/C30hopane ratios suggest anoxia at the water/sediment interface, respectively. Sedimentologic analysis also suggests anoxic conditions during sedimentation, but evidence for strong and persistent water column anoxia is equivocal. The correlation of the sections reveals that sedimentation of organic-rich facies started earlier in pelagic and later in the shallow marine settings, which can be related to an expansion of the favorable conditions for organic matter accumulation and preservation from deep marine waters to shallower platform environments during the development of OAE1a.