Palynomorph assemblages from the Fenghuoshan Group, southern Qinghai, China: their age and palaeoenvironmental significance

Abstract

The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditions are not conducive to their preservation. As a result, there has been a long-term disagreement among geologists about its age. Despite a few lists of fossil names in individual publications, no detailed research on the palaeontology, including palynology, has been reported previously. In this study, we recovered many pollen grains and spores from two samples that were collected on the northern slope of Fenghuo Mountain. They indicate an age no younger than Maastrichtian for the upper part of the Fenghuoshan Group. It is considered likely that the entire Fenghuoshan Group represents deposition between the late Early Cretaceous (possibly Albian) and the Maastrichtian. The palynoflora consists mainly of angiosperm pollen, gymnosperm pollen and fern and bryophyte spores being subordinate. Pollen grains referable to the Ephedrales and the Taxaceae–Cupressaceae groups dominate the assemblage, implying a warm, arid climate and subtropical forest–shrub vegetation at the time of deposition.

摘要

风火山群为青藏高原北部羌塘、可可西里地区的一套红层, 因沉积环境及岩性等因素, 其化石发现非常稀少, 关于其时代存在各种不同看法,影响了青藏高原地质过程的正确重建。本次从青海省南部风火山北坡该群上部层位的2 块样品中发现了丰富的孢粉化石, 其时代可以明确地限定为晚白垩世晚期即?晚 Campanian 至 Maastrichtian。 结合前人的化石记录, 推测整个风火山群的沉积时代可能为早白垩世晚期 (?Albian) 至 Maastrichtian。 当前风火山群孢粉植物群以被子植物花粉为主, 裸子植物花粉和蕨类、苔藓类孢子次之, 且麻黄类和与杉科、柏科有关的花粉在组合中含量突出, 指示当时的气候温暖、干旱, 是一种亚热带森林-灌丛植被景观。