Paleovegetation and paleoclimate in the Baise Basin during Oligocene

Abstract

To reconstruct the palaeovegetation and palaeoclimate in the Baise Basin during the Oligocene, in this work, we analyzed sporopollen fossils from the Fuping Formation in this region. Thirty-four genera sporopollen fossils are found and divided into two assemblages: (Ⅰ) Abietineaepollenites-Quercoidites-Polypodiaceaesporites Assemblage and (Ⅱ) Abietineaepollenites-Pinuspollenites-Pediastrum Assemblage. The age of assemblage Ⅰ and Ⅱ are mid-Rupelian to Oligocene, and late-Rupelian to early-Chattian to Oligocene, respectively. The paleovegetation changed from conifer-broad leaf forest with fern vegetation growing at the bottom to coniferous forest. Through the study of the characteristics of the palynological assemblages, assemblage Ⅰ represents a subtropical humid climate condition with relatively high humidity, while assemblage Ⅱ represents a humid climate condition in the subtropical zone. The coexistence approach of the nearest living relatives of the palynomorphs shows that during the period of the mid-Rupelian to the early Chattian of the Oligocene, the mean annual precipitation (MAP) was 797.5-1 293.7 mm, and the mean annual temperature (MAT) was 11.3-22.6℃ in the Baise Basin. The characteristics of this basin were a northern subtropical climate during the mid-Rupelian to the early Chattian. However, the present Baise Basin is located in the southern subtropics(MAT: 22.0℃, MAP: 1 070.5 mm). The difference between the Oligocene and today may be related to the "right-rotation" of the Asian Plate caused by the collision between the Cenozoic Indian Plate and the Asian Plate.

Keywords

• baise basin
• oligocene
• sporopollen assemblage
• paleoclimate
• coexistence approach