Birbal Sahni Institute of Palaeosciences, 53 University Road, Lucknow, 226007, UP, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
Environ Geochem Health. 2023 Oct;45(10):6923-6953. doi: 10.1007/s10653-023-01517-8. Epub 2023 Mar 8.
Early Permian floral diversity and palaeodepositional environment of the Lower Permian Rajhara sequence of Damodar Basin have been studied based on mega-, microfossil and geochemical proxies. Even though Gondwana sediments are generally considered as fluvio-lacustrine deposits, recent studies indicate marine inundations with patchy records. Here in the present study, an attempt has been made to address the changeover from fluviatile to shallow marine conditions and also to address the palaeodepositional aspects. Luxuriant vegetation during deposition of the Lower Barakar Formation generated thick coal seams. The macroplant fossil assemblage shows Glossopteridales, Cordaitales and Equisetales comprising one palynoassemblage with the dominance of bisaccate pollen grains having glossopterid affinities. However, Lycopsids are absent in the megafloral record and are represented in megaspore assemblage. The present floral assemblage led to envisage the presence of dense forest with swampy conditions and prevalence of warm and humid climate during the deposition of Barakar sediments. Correlation with the coeval Indian assemblages and those from other Gondwanan continents also supports an Artinskian age and reveals a stronger affinity with flora of Africa than that of South America. Biomarker analysis reveals low pristane/phytane values (0.30-0.84), noticeable absence of hopanoid triterpenoids and long-chain n-alkanes that is attributed to the obliteration of organic compounds and subsequent alteration of composition due to thermal effect. The high chemical index of alteration, A-CN-K plot and PIA also suggest severe denudation under a warm/humid climate. The V/AlO and PO/AlO indicated freshwater-near-shore conditions. However, signature of possible marine influence is identified from Th/U and Sr/Ba ratios resulted from the eustatic fluctuations during Permian.
本研究基于宏化石、微化石和地球化学指标，对印度达莫德尔盆地下二叠统拉贾哈拉地层的早二叠世植物多样性和古沉积环境进行了研究。尽管冈瓦纳沉积物通常被认为是河流-湖泊沉积物，但最近的研究表明存在间歇性的海水淹没，记录较为零散。本研究试图探讨从河流到浅海环境的转变，并探讨古沉积方面的问题。下巴拉卡尔组沉积时期，繁茂的植被生成了厚厚的煤层。宏观植物化石组合显示，舌羊齿目、科达目和楔叶木目包括一个以双囊花粉为主的孢粉组合，具有舌羊齿目亲缘关系。然而，在大型植物化石记录中没有出现石松类植物，而在大孢子组合中有所代表。目前的植物组合表明，在巴拉卡尔沉积物沉积期间，存在茂密的森林，伴有沼泽环境，气候温暖潮湿。与同期印度组合以及来自其他冈瓦纳大陆的组合的对比也支持了阿丁斯克时代，并显示出与非洲植物群的亲缘关系比与南美洲的亲缘关系更强。生物标志物分析表明，姥鲛烷/植烷值较低（0.30-0.84），明显缺乏藿烷三萜类化合物和长链正构烷烃，这归因于有机化合物的破坏和随后因热效应而导致的组成变化。高化学蚀变指数、A-CN-K 图和 PIA 也表明在温暖/潮湿气候下遭受了严重的剥蚀。V/AlO 和 PO/AlO 表明为淡水-近岸条件。然而，可能的海洋影响的特征是通过在二叠纪期间的海平面波动从 Th/U 和 Sr/Ba 比值中识别出来的。
