Discovery of paleogene palynological assemblages from the Wanbaogou Group-complex in western part of the Eastern Kunlun orogenic belt and its geological significance

Abstract

The Wanbaogou Group-complex is a suit of mélange aggregation of the Eastern Kunlun orogenic belt, which is divided into two parts, i.e. the exotic blocks and the matrix strata. Based on stromatolite fossils yielded in the exotic blocks, the age of this group-complex was once defined to the Precambrian. Recently, two Paleogene palynological assemblages have been found in samples from the matrix strata of the Upper Part in this group-complex by the authors: in ascending order, the Alnipollenites-Quercoidites assemblage of Late Eocene and the Caryapollenites-Pinuspollenites assemblage of Early Oligocene. Those results show that the matrix strata of this mélange were mainly formed in Paleogene, and the event causing mixture should be a Himalayan Movement Phase. This paper is designed to provide some detailed evidence for determining the age of the matrix strata in this group-complex based upon study at the Kunlunqiao Section, which would be of important geological significance for further understanding this group-complex as a suit of mélange aggregation and establishing or improving the stratigraphic framework of the studied region. The new finding will certainly benefit from now on the investigation on geotectonic and sedimentary evolution of Eastern Kunlun.

Palynological evidence sheds new light on the age of the Liuqu Conglomerates in Tibet and its geological significance

“…This assemblage contains a number of Abiespollenites that did not appear until Oligocene in the lower Ganchaigou Formation of the Qaidam basin in China [45]. We also found sporadic Tsugaepollenites, which only appeared sporadically in the Oligocene and commonly until the Miocene [32,45,48]. Thus, we assign the Liuqu Conglomerates to the Oligocene.…”

“…Unique geomorphologic feature may have appeared during Oligocene, resulting in the differences between the above-mentioned palynological assemblages and the palynological assemblage of Liuqu Conglomerates. The paleovegetation and paleoclimate of the Liuqu Conglomerates closely resemble the Oligocene paleovegetation and paleoclimate of the Qinghai-Tibet Plateau and its surrounding areas, such as the lower Ganchaigou Formation in the Qaidam basin of Qinghai Province [45], the lower Lunpola Group in the Lunpola basin of northern Tibet [56], and the Wanbaogou Group in the western part of the Eastern Kunlun orogenic belt [48]. The palynological assemblage of lower Ganchaigou Formation in the Qaidam basin is dominated by angiosperm pollens such as Quercoidites, Meliaceoidites and Betulaceae type pollens, conifer saccate pollens account for more than 27.97% of the total number, and Piceapollis is about 13.67% of the total number; Tsugaepollenites and Abiespollenites begin to appear; Ephedripites occurs in relative abundance, about 13.81%; and Herbaceous pollens do not form dominant representations [45].…”

“…The palynological assemblage of lower Ganchaigou Formation in the Qaidam basin is dominated by angiosperm pollens such as Quercoidites, Meliaceoidites and Betulaceae type pollens, conifer saccate pollens account for more than 27.97% of the total number, and Piceapollis is about 13.67% of the total number; Tsugaepollenites and Abiespollenites begin to appear; Ephedripites occurs in relative abundance, about 13.81%; and Herbaceous pollens do not form dominant representations [45]. The palynological assemblage of Wanbaogou Group in the western part of the Eastern Kunlun orogenic belt is dominated by angiosperm pollens (about 68%), followed by gymnosperm pollens (about 26%) and pteridophyta spores (about 6%); the broad-leaved deciduous plant pollens dominated the angiosperm pollens by a large percentage of Caryapollenites (12%) and followed by Ulmipollenites, Betulaceoipollenites and Momipites; the gymnosperm pollens consist mainly of conifer pollens (about 20%) and Ephedripites (about 7%) [48]. The above mentioned two palynological assemblages have a high representation of Ephedripites, indicating that the climates of the two areas are relatively drier than this area during that time.…”