Marine deposits in the Neogene Siwalik succession have been documented from the Tista valley, Bhutan and Kameng river sections of the Eastern Himalaya. This study was designed to investigate possible marine influence further east. During this investigation, it was revealed that the current classification and description of the stratigraphic units were inadequate to describe the variations present in this succession fully. In place of the existing three-fold classification, a four-fold lithostratigraphic classification of the Siwalik Group in the Arunachal Himalaya has been proposed by adding a new Siji Formation. This newly proposed formation is completely different from the underlying sand-dominated Subansiri or overlying conglomerate-dominated Kimin formations. Nearly 1000 m thick succession of the Siji Formation is characterised by of alternating tabular sheet like beds of grey mudstone, siltstone and sandstone with uncommon thin conglomerate beds. On the basis of the four-fold classification, the Siwalik rocks of the Arunachal Himalaya have been mapped over a strike length of ∼230 km, demonstrating the lateral continuity of the individual formations and the large-scale deformational features affecting the rocks. Three lithologs prepared show the distinctive lithological characters and overall paleocurrent pattern of these formations. The lithological, sedimentological and ichnological features of the Dafla and Siji formations provide evidence for marine influence in the study area. The proposed new lithostratigraphic subdivisions are expected to facilitate regional correlation and evidence of marine sedimentation which will throw new light on the basin analysis of the Siwalik Group in the Eastern Himalayan.

从新喜马拉雅山脉的提斯塔河谷，不丹和卡缅河河段记录了新近纪西瓦里克继承的海相沉积物。这项研究的目的是调查东海岸可能的海洋影响。在这项调查期间，发现目前的地层单位分类和描述不足以充分描述这一演替中存在的变化。代替现有的三重分类法，已经通过增加新的西吉组建议了阿鲁纳恰尔喜马拉雅山的西瓦利克组的四重岩相地层学分类。这个新提议的地层与下面的以砂为主的苏南西里或上覆的以砾岩为主的基民地层完全不同。寺集组近1000 m厚的岩层特征为板状薄片交替排列，如灰色泥岩，粉砂岩和砂岩层，还有罕见的薄砾岩层。在四重分类的基础上，对阿鲁纳恰尔喜马拉雅山的西瓦利克岩进行了测绘，其走向长度约为230 km，表明了单个地层的横向连续性和影响岩石的大规模变形特征。制备的三个岩石学资料显示了这些地层的独特岩性特征和整体古流型。达夫拉（Dafla）和西吉（Siji）地层的岩性，沉积学和岩石学特征为研究区域的海洋影响提供了证据。