巴基斯坦北部前寒武系-寒武系剖面碳、氧同位素曲线

在新元古代及其向寒武纪的过渡时期，全球碳循环和大气二氧化碳浓度经历了极端扰动。这些波动在全球许多地区该时期沉积的碳酸盐碳同位素中得以记录。其中一些较为显著的同位素变化既可以用于全球地层对比、划定特定地层边界或年代地层界线，还能借其分析古环境条件和碳循环动态。在科考调查中，对巴基斯坦西喜马拉雅山脉Hazara盆地Pind-Khankhel（34°7'8.59"N 72°55'46.69"E）、Neelor（34°05'49.7"N 73°00'05.8"E）、Tanakki（34°06'08.3"N 73°10'59.3"E）以及Salhad（34°07'24.5"N 73°11'37.8"E）剖面的Kakul组、Abbottabad组以及Hazira组开展了较为全面的碳同位素分析，发现三个显著的负碳同位素偏移，可对比到三个同期全球典型的碳循环扰动，分别为：Kakul组底部的CANCE负漂移（δ¹³C值达到-5‰）、Abbottabad组Sirban段下部相当于中埃迪卡拉世晚期的Shuram/DOUNCE负偏移（δ¹³C值达到-9‰），以及Sirban段上部的寒武纪底部负偏移（BACE，δ¹³C值达到-5‰）。
该研究为约束和重建Hazara盆地新元古代晚期至寒武纪早期地层序列的年代地层框架提供了关键依据。首先，马里诺冰期（Marinoan）后的盖帽碳酸岩及其中的CANCE碳同位素偏移的发现，有助于在Kakul组底部确定成冰纪与埃迪卡拉纪的边界。随后，结合Abbottabad组中部碳同位素曲线的模式与Shuram/DOUNCE负漂移的存在以及该组上部BACE负漂移的出现，可以将该段地层时代限定为埃迪卡拉纪末期至寒武纪早期。该碳同位素曲线再结合新的生物地层学进展，可以较为精确地将埃迪卡拉纪-寒武纪边界限定于Abbottabad组Sirban段的上部。根据上述对比得出的新地层框架显著区别于之前将Abbottabad组及其下覆的Kakul组均归为寒武纪早期的假设。
总体而言，上述新发现增进了我们对巴基斯坦北部西喜马拉雅地区新元古代晚期至寒武纪早期地层学、环境扰动和碳循环动态的理解。

During the Neoproterozoic and its transition to the Cambrian, the global carbon cycle and atmospheric CO₂ concentrations experienced extreme perturbations. These fluctuations are recorded in carbonate carbon isotopes from sediments deposited in this interval across many global regions. Some prominent isotopic shifts can be used for global stratigraphic correlation, delimitation of specific stratigraphic or chronostratigraphic boundaries, as well as analysis of paleoenvironmental conditions and carbon cycle dynamics. Through geological field surveys, comprehensive carbon isotope analyses were conducted on the Kakul, Abbottabad, and Hazira formations in the Pind-Khankhel (34°7'8.59"N 72°55'46.69"E), Neelor (34°05'49.7"N 73°00'05.8"E), Tanakki (34°06'08.3"N 73°10'59.3"E), and Salhad (34°07'24.5"N 73°11'37.8"E) sections of the Hazara Basin in the western Himalayas, Pakistan. Three prominent negative carbon isotope excursions were identified, which can be correlated to three coeval global typical carbon cycle perturbations: the CANCE negative shift at the base of the Kakul Formation (with δ¹³C values reaching -5‰), the Shuram/DOUNCE negative shift equivalent to the late Middle Ediacaran in the lower Sirban Member of the Abbottabad Formation (with δ¹³C values reaching -9‰), and the basal Cambrian negative shift (BACE) in the upper Sirban Member (with δ¹³C values reaching -5‰).

This study provides critical evidence for constraining and reconstructing the chronostratigraphic framework of the late Neoproterozoic to Early Cambrian stratigraphic sequence in the Hazara Basin. First, the discovery of cap carbonates postdating the Marinoan glaciation and the CANCE carbon isotope excursion within them helps define the Cryogenian-Ediacaran boundary at the base of the Kakul Formation. Subsequently, combining the carbon isotope curve pattern in the middle part of the Abbottabad Formation, the presence of the Shuram/DOUNCE negative shift, and the occurrence of the BACE negative shift in the upper part of this formation, the age of this stratigraphic interval can be constrained to the latest Ediacaran to Early Cambrian. Combined with new biostratigraphic advances, this carbon isotope curve can precisely restrict the Ediacaran-Cambrian boundary to the upper part of the Sirban Member of the Abbottabad Formation. The new stratigraphic framework derived from the above correlations differs significantly from the previous hypothesis that both the Abbottabad Formation and its underlying Kakul Formation were assigned to the Early Cambrian.

Overall, these new findings advance our understanding of the stratigraphy, environmental perturbations, and carbon cycle dynamics of the late Neoproterozoic to Early Cambrian intervals in the western Himalayan region of northern Pakistan.

搜集汇总

背景与挑战

背景概述

该数据集总结了巴基斯坦北部Hazara盆地前寒武系-寒武系剖面的碳同位素曲线，揭示了三个全球性负碳同位素偏移（CANCE、Shuram/DOUNCE、BACE），用于地层年代对比和古环境重建。这些数据帮助确定了关键地层边界（如埃迪卡拉纪-寒武纪边界），修正了区域地层框架，增进了对新元古代晚期至寒武纪早期碳循环动态和古环境扰动的理解。