Abstract

The rise of the Himalayas governed the Indian Summer Monsoon in Karewa basin during Plio-Pleistocene. A palynological study is presented to delineate the climate-vegetation relationship using an 8.5-m thick fluvio-lacustrine sequence of the Hirpur Formation (2.4–2.1 Ma). Our results suggest that the sediment sequence is mainly comprised of two units, namely, Unit 1 and Unit 2. Unit 1 shows the dominance of sub-tropical to broad-leaf temperate vegetation when mean annual temperature (MAT) was ~17°C and mean annual precipitation (MAP) was 1025 mm. The subsequent increase in sand followed by a thin lignite layer with Trapa megafossil (fruits) demarcates fluvial adjustments, suggesting a low altitude fluvio-lacustrine ecosystem. Conversely, Unit 2 shows a decline in rainforest pollen with a steady increase in conifers. The abrupt dominance of diatom species Tetracyclus lacustris and related species with MAT and MAP reducing to 10°C and 770 mm reveal a colder climate with the lacustrine ecosystem. This change of tropical to cool temperate vegetation could be attributed to the altitudinal rise of the Pir Panjal Mountains and consequent obstruction of the south-west monsoon, which resulted in lower precipitation and temperature during ~2.4–2.1 Ma. Hence, the relic tropical flora of Palaeogene/Neogene transformed to Himalayan temperate flora sometime ~2.1 Ma.

Highlights

• Climate–vegetation relationship is established through a palynological record.

• Unit 1 comprises subtropical to broad-leaf temperate vegetation with warmer mean annual temperature and higher mean annual precipitation.

• Unit 2 comprises colder diatom species and is following cooler mean annual temperature and lower mean annual precipitation.

• A shift of tropical to cool temperate vegetation is related to the rise of the Pir Panjal Mountains, obstructing monsoon.

中文翻译：

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气候对克什米尔喜马拉雅山构造活跃的卡累瓦盆地植被演变的影响

摘要

喜马拉雅山脉的兴起在上新世时期统治了卡累瓦盆地的印度夏季风。提出了一项古生物学研究，以利用Hirpur地层（2.4-2.1 Ma）厚8.5 m的河流-湖相层序来描述气候与植被的关系。我们的结果表明，沉积物序列主要由两个单元组成，即单元1和单元2。单元1显示了当年平均温度（MAT）为〜17°C时，亚热带对阔叶温带植被的优势。年平均降水量（MAP）为1025 mm。随后的沙子增加，接着是带有Trapa的薄褐煤层巨型化石（水果）对河流的调整进行了划分，表明低海拔的河流湖泊生态系统。相反，第2单元显示雨林花粉减少，针叶树稳定增加。硅藻物种Tetracyclus lacustris和相关物种的突然优势（MAT和MAP降低至10°C和770 mm）揭示了湖生态系统的气候较冷。热带到凉爽的温带植被的这种变化可能归因于Pir Panjal山的海拔高度上升以及西南季风的阻塞，这导致〜2.4–2.1 Ma期间的降水和温度降低。因此，古近纪/新近纪的遗迹热带植物区系在约〜2.1 Ma的时间内转变为喜马拉雅温带植物区系。

强调

• 气候与植被的关系是通过古生物学记录建立的。

• 第1单元包括亚热带至阔叶温带植被，年平均气温较高，年平均降水量较高。

• 第2单元包含较冷的硅藻物种，并且遵循较低的年平均温度和较低的年平均降水量。

• 热带向凉爽的温带植被的转移与Pir Panjal山的崛起有关，阻碍了季风。