Neogene sediments of the Andaman and Nicobar Islands in northern Indian Ocean, specifically the lower Miocene (Burdigalian) to lower Pliocene (Zanclean) sequences, were analysed for calcareous nannofossils that yielded well-preserved and diverse assemblages. The majority of samples contained stratigraphic marker taxa that allowed us to identify successions within the Burdigalian-Langhian (uppermost lower Miocene to lowermost middle Miocene) on the Havelock Island, Tortonian (upper Miocene) on the Neil Island and Zanclean (lower Pliocene) on the Car Nicobar Island. The nannofossil assemblages of uppermost lower Miocene to lowermost middle Miocene sediments reflect strong preference for warm tropical climate and nutricline condition i.e., depth dependent high variation of nutrient content. The presence of relatively unusual assemblage compositions, especially the presence of abundant sphenoliths and small reticulofenestrids, in conjunction with rare discoasters and alongside common diatoms, are indicative of high-productivity surface waters and probably upwelling conditions in the late Miocene. In the Tortonian (upper Miocene), low abundance of discoasters and high abundance of small reticulofenestrids (<3 μm) indicate eutrophic condition. The high-productivity surface-water environments can be linked with the intensification of the Indian Summer Monsoon. Well-preserved calcareous nannofossils have been also been recovered from the Zanclean (lower Pliocene) sediments on Car Nicobar Island. During the Zanclean warm water condition prevailed and from marginal to deep water setting i.e., transgressive event was recognised in the northern Indian Ocean.

分析了印度洋北部安达曼和尼科巴群岛的新近纪沉积物，特别是中新世 (Burdigalian) 到上新世 (Zanclean) 序列的下部，分析了钙质纳米化石，这些纳米化石产生了保存完好的多样化组合。大多数样品包含地层标记分类群，使我们能够确定哈夫洛克岛的布尔迪加阶 - 朗吉阶（最下中新世至最下中中新世）、尼尔岛的托托阶（上中新世）和 Zanclean（上新世下）的序列。汽车尼科巴岛。下中新世最上层到中中新世最下层沉积物的纳米化石组合反映了对温暖热带气候和营养条件的强烈偏好，即深度依赖于营养含量的高度变化。相对不寻常的组合组合的存在，尤其是存在丰富的酚石和小型网状花甲藻，再加上罕见的飞碟和常见的硅藻，表明地表水的生产力很高，并且可能是中新世晚期的上涌条件。在 Tortonian（上中新世），低丰度的 discoasters 和高丰度的小网状丝虫 (<3 μm) 表明富营养化条件。高生产力的地表水环境可能与印度夏季风的加剧有关。从 Car Nicobar 岛上的 Zanclean（下上新世）沉积物中也发现了保存完好的钙质纳米化石。在赞克利温水条件盛行期间，从边缘到深水环境，即在北印度洋发现海侵事件。