Abstract
The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ18O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time.
Highlights
The Tibetan Plateau is widely considered to be the result of shortening related to convergence both preceding and post-dating the initial collision between the Indian and Eurasia plates at 65–50 Ma1–3
A detailed summary of 121 geological maps (1:250000) of the Tibetan Plateau area, and they estimated that the average palaeoelevation in central Tibet was ~500 m at ca. 34 Ma
Foraminifera fossils mainly occur in marine strata, they are distributed in Late Quaternary strata located hundreds of kilometres away from current shorelines associated with marine transgressions[26,27]
Summary
The Tibetan Plateau is widely considered to be the result of shortening related to convergence both preceding and post-dating the initial collision between the Indian and Eurasia plates at 65–50 Ma1–3. Arguing for an Eocene “proto-Tibetan Plateau”, Kapp et al.[8] suggested that the collision between the Lhasa terrane and the Qiangtang terrane resulted in crustal shortening of the Lhasa terrane that may have raised southern Tibet to an elevation of 3–4 km during the Cretaceous, prior to India-Asia collision This inference of a high proto-Tibetan plateau prior to India-Asia collision is reinforced by paleoelevation reconstructions of the Linzhou Basin, which suggest that the Gandese magmatic arc region in the southern Lhasa terrane attained an elevation of ~4500 m by the time of India-Asia collision[9]. 34 Ma. Based on conflicting evidence for high paleoelevations from sparse stable isotope studies and low paleoevelations from fossil, stratigraphic, and thermochronology/thermal modelling studies, it remains unclear whether the Lhasa terrane was at a high elevation at and following the collision of the Indian and Eurasian plates. We provide age information for these deposits, based on magnetostratigraphy with additional age constraints from fossils and zircon U-Pb dates
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