Abstract

The sandstone-shale-coal succession of the Barakar Formation (early Permian) of the Raniganj Basin, India hosts low-diversity ichnoassemblages, containing ichnogenera Arenicolites, Chondrites, Diplocraterion, Monocraterion, Ophiomorpha, Palaeophycus, Planolites, Skolithos, Taenidium, and Thalassinoides, produced by shallow marine infaunal invertebrates. Sedimentary facies architecture depicts a transgressive, fluvio-tidal (with a minor wave) interactive estuarine depositional setting. The fluvial deposits, lying beyond the zone of tidal encroachments, record absence of trace fossils, which is attributed to a low colonization window caused by high fluvial discharge and frequent channel migrations. Tidal interactions with high fluvial discharge led to bay-head deltas in the inner-middle estuary with the dominance of suspension-feeding and deposit-feeding ichnotaxa in coarser- and finer-dominated sediments, respectively, suggesting a mixed Skolithos–Cruziana ichnofacies. Increasing tidal influence with very less fluvial input allowed opportunistic colonizers and deposit feeders of the Cruziana ichnofacies to flourish in the central estuarine setting. Intermittent low-oxygenated restricted conditions marked by the chemosymbiotic ichnoassemblages of the Zoophycos ichnofacies indicate very low energy conditions. The outer estuary with increasing wave dominance is inhabited by suspension-feeding, domicile ichnotaxa of Skolithos ichnofacies, frequently mixed with the ichnotaxa of the Cruziana ichnofacies. The recurrent juxtaposition and lateral distribution of the Seilacherian marginal marine ichnofacies is attributed to complex sediment–organism interaction patterns in response to prevalent energy conditions, sediment discharge and substrate conditions in different zones of the fluvio-tidal estuarine setting. The integrated sedimentological-ichnological model signifies marine transgressions that affected the palaeogeography of the Permian continental Gondwanaland.

Research Highlights

• Sedimentological–ichnological analysis signifies marine encroachment in Barakar Formation in peninsular India.

• Ichnoassemblages point to complex pattern of sediment–organism interactions with gross energy distribution.

• Sustained marine transgression event within the continental Gondwanaland during early Permian is visualized.

中文翻译：

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印度Raniganj盆地二叠纪早期潮红-海洋Barakar组的鱼鳞生物类群的古地理意义

摘要

在拉尼甘杰盆地Barakar组（早二叠世），印度主机低多样性ichnoassemblages，含ichnogenera的砂岩页岩煤继承Arenicolites，球粒陨石，Diplocraterion，Monocraterion，Ophiomorpha，Palaeophycus，Planolites，Skolithos，Taenidium，并Thalassinoides由浅海无脊椎动物无脊椎动物产生。沉积相结构描绘了海侵，潮汐（带小波浪）交互式河口沉积环境。潮汐侵蚀带以外的河流沉积物记录到没有痕迹化石，这归因于大量河流排放和频繁的河道迁移造成的低定殖窗口。潮汐与高流量排放的相互作用导致中-内河口形成湾头三角洲，分别在较粗和较细的沉积物中分别以悬浮饲料和沉积物饲料鱼类为主导，这表明斯科里索斯-克鲁斯金鱼混杂。潮汐影响的增加以及河流投入的减少，使克鲁兹亚氏鱼的机会定居者和沉积物饲养者在河口中部繁荣发展。Zoophycos鱼眼相的化学共生鱼眼组合的间歇性低氧限制条件表明能量条件很低。波浪主导优势的外河口被悬浮饲养的Skolithos鱼类生境的栖栖鱼类栖居，经常与Cruziana鱼类生栖鱼类混合在一起。Seilacherian边缘海洋鱼类相的反复并置和侧向分布归因于潮汐河口环境不同区域对普遍的能量条件，沉积物排放和底物条件的响应，造成了复杂的沉积物-生物相互作用模式。

研究重点

• 沉积学-流变学分析表明印度半岛巴拉卡尔组海侵。

• 形态组合指出了沉积物与生物相互作用与总能量分布的复杂模式。

• 可以看到二叠纪初期冈瓦纳大陆内部持续的海侵事件。