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首页> 外文期刊>Arabian journal of geosciences >Integrated biostratigraphy and geochemistry of the lower Cretaceous Radiolarian Flood Zone of the base of the Garau Formation, northwest of Zagros Mountains, Iran
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Integrated biostratigraphy and geochemistry of the lower Cretaceous Radiolarian Flood Zone of the base of the Garau Formation, northwest of Zagros Mountains, Iran

机译：伊朗扎格罗斯山脉西北部加劳组底部低白垩纪放射虫洪水带的综合生物地层和地球化学

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The lower Garau Formation known as the Radiolaria Flood Zone (RFZ) is investigated for reconstructing palaeoceanography and controlling factors that resulted in the organic matter and radiolarian rich beds. A stratigraphic section named Tang-e-Haft located to the northwest of Zagros range with a thickness of 320 m mainly composed of argillaceous limestone, and limestone is used for this study. The RFZ is dated late Berriasian to earliest Aptian via using nannofossils, foraminifera, and palynology integrated. Semi-quantitative study of different microfossil groups and biofacies analaysis demonstrates deposition of this member in an intermediate depth under dys- to anaerobic marine condition with a shallowing upward trend. Richness of radiolarians with prevailed spumellaria assemblage and high organic matter content revealed presence of high palaeoproductivity during time of deposition. This productivity was induced by paleocurrents and upwelling systems. Values of total organic carbon (TOC), gamma ray, and amount of amorphous organic matter (AOM) in palynology slides in the lower parts of the section show a peak that indicates that palaeoproductivity was more intense in the lowermost part. Dominance of the radiolarians and consequently the RFZ unit ended up in the early Aptian. This time is coincided with Leupoldina cabri bloom and Oceanic Anoxic Event 1a (OAE1a). This event resulted in an extinction and significant reduction among radiolarians. Depopulation of radiolarians made new habitats for other organisms that planktonic foraminifera with elongated chambers were the first group to benefit the situation.
机译：为了重建古海洋学和控制导致有机质和放射l虫床层丰富的因素，研究了名为“放射虫洪泛区”（RFZ）的下部Garau组。本研究使用了位于Zagros山脉西北部的地层剖面Tang-e-Haft，厚度为320 m，主要由泥质灰岩和石灰岩组成。通过使用纳米化石，有孔虫和综合孢粉学，RFZ的年代定于贝里亚斯晚期至最早的Aptian。对不同微化石群和生物相分析的半定量研究表明，该构件在从厌氧到厌氧的海洋条件下，处于中等深度的沉积，并具有逐渐上升的趋势。放射虫具有丰富的孢粉组合和高有机质含量，这表明其沉积过程中存在高古生产力。这种生产力是由古流和上升流系统引起的。该部分下部的孢粉切片中的总有机碳（TOC），γ射线和无定形有机物（AOM）的值显示一个峰值，表明最下部的古生产力更高。放射虫的主导地位以及RFZ部队最终在Aptian早期结束。这次恰逢Leupoldina cabri绽放和海洋缺氧事件1a（OAE1a）。该事件导致了放射虫的灭绝并大大减少。放射虫种群的减少为其他生物创造了新的栖息地，带有拉长腔室的浮游有孔虫是第一个使这种情况受益的生物。

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