巴西paran盆地下二叠统含煤里约热内卢Bonito组野火发生的多代理证据

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
M.M. Bicca , W. Kalkreuth , T.F. Silva , M. Guerra-Sommer , I. Degani-Schmidt , C.M. Felix , D.R. Boardman , P.A. Souza
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引用次数: 0

摘要

来自巴西南部的煤被保存在帕拉南盆地的下二叠世冰期后里约热内卢Bonito组中。以往对坎迪奥塔煤田的研究表明,Banco Louco和S9煤层具有明显的惰性矿物聚集。为了了解这些异常惰质岩聚集的原因,本研究分析了来自candota coal Superior (CCS)、Banco Louco (BL)、S9和上覆S8煤层(异常后)顶部的异常富惰质层和下伏碳质粉砂岩的煤样。利用有机岩石学、扫描电镜、孢粉学和生物标志物(PAH)技术对样品进行了分析。结果表明,古沼泽中惰质组以交替小旋回的方式富集,各煤层顶部均有普遍富集的惰质组(云母组、半云母组和惰质组)。大炭在所有煤层中以烧焦的木材、叶片碎片和一个生殖结构的形式存在。富贫质层段的峰值出现在S9煤层,微炭主要分布在细粒沉积物中,呈全黑色,表明该层段受野火事件影响较大。惯性反射率测量表明,地面和地面火灾事件占主导地位,很少发生树冠火灾。有机质的燃烧也以3-5环多环芳烃为主,局部出现6环多环芳烃(包括冠烯)。泥炭地植物区系主要由喜湿石松类和丝松类组成,次要成分以喜湿石松类、中湿石松类和中湿针叶树类为代表。植被组成的频繁振荡可能与气候变化和相关环境条件有关,从亲湿型到中亲湿型再到中亲湿型,表明植被组成适应环境/气候变化,这主要表现在产花粉菌群向BL层顶部的变化及其在异常区间顶部的上覆层中的扩张。在S9煤层中部,全暗的孢岩和植物碎屑,加上6环多环芳烃等高丰度的热生生物标志物,表明在干燥、变暖时期,泥炭地富惰质层的峰值与显著的火灾事件有关,这有助于改变泥炭地的古生态模式。阿塞利亚时代(约298 Ma)坎迪奥塔煤田的古野火是巴西南部泥炭形成环境中最古老的野火记录,与冈瓦纳西部晚古生代冰期结束时的一个变暖期同期。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Multiproxy-based evidence of wildfire occurrence in the Lower Permian coal-bearing Rio Bonito Formation, Paraná Basin, Brazil
Coals from southern Brazil are preserved in the Lower Permian postglacial Rio Bonito Formation of the Paraná Basin. Previous studies on the Candiota Coalfield have shown intervals with significant accumulations of inertinite macerals in the Banco Louco and S9 coal seams. Aiming to understand the causes of these anomalous inertinite accumulations, this study analyzed coal samples from the anomalous inertinite-rich interval and underlying carbonaceous siltites from the top of the Candiota Coal Superior (CCS), Banco Louco (BL), S9, and overlying S8 seams (post-anomalous) obtained from two borehole cores. The samples were analyzed using organic petrology, SEM, palynology, and biomarker (PAH) techniques. The results indicate that inertinite macerals accumulated in the paleoswamp in alternating small cycles, with general inertinite enrichment (fusinite, semifusinite, and inertodetrinite) towards the top of each coal seam analyzed. Macrocharcoal was present in all coal seams as charred wood, leaf fragments, and one reproductive structure. The peak of the inertinite-rich interval occurs at the S9 seam with the dominance of microcharcoal dispersed in fine-grained sediments and completely black palynomorphs, suggesting a significant wildfire event affecting the interval. Inertinite reflectance measurements indicated the predominance of ground and surface fire events with the rare occurrence of crown fires. Combustion of organic matter is also marked by the dominant presence of 3–5 ring PAHs and local occurrence of 6-ring PAHs (including coronene). The peatland flora was mainly composed of hygrophilous lycopsids and filicopsids, with subordinate elements represented by sphenopsids, mesophilous glossopterids, and meso-xerophilous conifers. The frequent oscillations in the vegetation composition were potentially related to climate changes and related environmental conditions, varying from hygrophilous to meso-hygrophilous and mesophilous, indicating that the vegetation composition adapted to environmental/climate changes as recognized by the alteration in the pollen-spore-producing flora towards the top of BL seam and their expansion in the overlying seams at the top of the anomalous interval. In the middle of the S9 seam, the completely dark palynomorphs and phytoclasts, plus a high abundance of pyrogenic biomarkers including 6-ring PAHs, point to significant fire events linked to the peak of the inertinite-rich interval during drier, warming intervals, which contributed to modifying the paleoecological patterns of the peatland. The paleo-wildfires of the Asselian age (ca. 298 Ma) Candiota Coalfield are the oldest record of wildfires in peat-forming environments of southern Brazil, being coeval with a warming period at the end of the Late Paleozoic Ice Age in Western Gondwana.
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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