Synchronous Sedimentation in Gonjo Basin, Southeast Tibet in Response to India‐Asia Collision Constrained by Magnetostratigraphy

Abstract

The India-Asia collision has been the object of vigorous debate for decades, with ages of the start ranging from Late Cretaceous to Oligocene. Sedimentary records preserved in both near-field and far-field settings provide critical evidence concerning the age and mechanism of the collision. Gonjo Basin, one of a series of fault-controlled basins developed along the eastern margin of Tibetan Plateau, contains well-exposed sedimentary successions, providing great potential for understanding depositional, tectonic-geomorphological and climatic history associated with India-Asia collision and plateau uplift. Lithofacies analysis reveals that the sequences consist of sandstone, mudstone and conglomerate, formed in fluvial-lacustrine systems. High-resolution magnetostratigraphy, constrained by U-Pb dating of zircon from a volcaniclastic layer which has been found in the central Gonjo Basin for the first time, indicates that sedimentation started at 69 Ma and continued in this locality until 50 Ma. Anisotropy of magnetic susceptibility (AMS) interpretation based on the age framework reveals a post-depositional compression after 50 Ma, responding simultaneously to the early uplift of southeast Tibetan Plateau driven by India-Asia collision. XIAO ET AL.

Paleogene Sedimentary Records of the Paleo‐Jinshajiang (Upper Yangtze) in the Jianchuan Basin, Yunnan, SW China

“…These data also indicate that the basin experienced ∼10° counter‐clockwise rotation at 69–67 Ma and ∼30° clockwise rotation at 52–48 Ma, followed by another ∼30° clockwise rotation sometime after 41 Ma. However, recent research using high‐resolution magnetostratigraphy, constrained by zircon U‐Pb dating from volcaniclastic layers shows that sedimentation in the center of the Gonjo Basin started at 69 Ma and continued until 50 Ma (Xiao et al., 2021). Although the exact sedimentary age of the Gonjo Basin is still under debate, the depositional age of the Gonjo Basin coincides with the time of the proposed paleo‐Jinshajiang, but whether it formed part of the paleo‐river system needs further work to verify.…”

Eccentricity Forcing of the Hydrological Cycle in East Asia During the Early Eocene Climatic Optimum (EECO)

“…The NNW‐SSE orientated Gonjo Basin (Figure 1), has a ∼260 km length, ∼2–16 km width and present‐day mean elevation of ∼4 km (Xiao et al., 2021). The fill of the Gonjo Basin forms an asymmetrical syncline controlled by thrust faults, with thicker sediments in the west compared to the east of the syncline (Li et al., 2020; Xiao et al., 2021; Xiong et al., 2020). The basin is filled with late Cretaceous to early Eocene fluvio‐lacustrine sediments (>2,500 m thickness) (Studnicki‐Gizbert et al., 2008; Xiao et al., 2021).…”

Middle Eocene Paleoenvironmental Reconstruction in the Gonjo Basin, Eastern Tibetan Plateau: Evidence From Palynological and Evaporite Records

“…A magnetostratigraphic study in the central part of the basin revealed that the ages of the continuous sequences of the Gonjo and Ranmugou formations ranged from ~69 Ma to 41.5 Ma, of which the Ranmugou Formation is ~65.2 Ma to 41.5 Ma (Li et al, 2020) (Figure 2). Xiao et al (2021) indicated that the Gonjo and Ranmugou formations are 69 to 50 Ma in the central Gonjo Basin, and the Ranmugou Formation was assigned an age ranging between 63.5 Ma and 50 Ma. They believed that the magnetostratigraphic results of Li et al (2020) were inaccurate due to their isotopic age deriving from other sections.…”

“…Sparse sporomorphs fossils indicate a wide age range of Paleocene to Oligocene (BGMRT, 1993;Studnicki-Gizbert et al, 2008). The magnetostratigraphy and volcanic U-Pb studies limited the age from 50 to 40 Ma (Xiong et al, 2020) or from 43.4 to 41.5 Ma (Li et al, 2020) or from 54 to 50 Ma (Xiao et al, 2021) for the upper Ranmugou Formation. The palynoflora assemblages in the Youzha section discussed below give an age of middle Eocene, which is congruent with the isotopic ages in the Qudeng section (Xiong et al, 2020).…”

“…The Gonjo Basin, located on the eastern part of the Central Watershed Mountain, hosts a thick, successive Paleocene-Eocene sedimentary record (Studnicki-Gizbert et al, 2008). The accurate age constraints based on magnetostratigraphy and radioactive isotopes (Li et al, 2020;Xiao et al, 2021) of uplift history (Xiong et al, 2020) make the ~2,000 m sedimentary sequences in the Gonjo Basin perfect for conducting Eocene paleoclimatic and paleovegetation reconstruction, although the age of the Ranmugou Formation is still controversial. Palynological studies are a useful tool for constraining the age and reconstructing the vegetation, paleoclimate, and paleoecological evolution of a region (Hoorn et al, 2012;Miao et al, 2016;Tang et al, 2020).…”