Early Cretaceous stratigraphy and SHRIMP U-Pb age constrain the Valanginian–Hauterivian boundary in southern Tibet

Abstract

Wan, X., Scott, R., Chen, W., Gao, L. & Zhang, Y. 2011: Early Cretaceous stratigraphy and SHRIMP U‐Pb age constrain the Valanginian–Hauterivian boundary in southern Tibet. Lethaia, Vol. 44, pp. 231–244. The Late Jurassic to the Early Cretaceous marine strata are extensively distributed in southern Tibet. In Gyangze, the strata are divided into the Weimei and Jiabula formations. In Nagarze, they are divided into the Weimei and Sangxiu formations. Previous work has reported diverse ammonite species of Haplophylloceras and Himalayites in the Weimei Formation, and a few species of Spiticeras in the lower Jiabula and Sangxiu formations. The present study has found the bivalve Inoceramus and nannofossil assemblages in the lower Jiabula and Sangxiu formations. The nannofossil assemblage of Nannoconus steimannii steinmannii, N. steinmannii minor and Watznaueria barnesae indicates Berriasian age, and the Calcicalathina oblongata–Speetonia colligata assemblage is Valanginian in age. Numerical ages for the Jiabula and Jiabula‐goukou sections in Gyangze have been interpolated by comparing the fossil ranges with ages calibrated in other sections. The correlation experiment plots fossil ranges in the two sections to the CRET1 Database. The estimated rate of sediment accumulation of the lower Sangxiu Formation is 22.6 m/myr. The Jurassic–Cretaceous (J/K) boundary is at the bottom of the Jiabula Formation in Gyangze, and the base of the Sangxiu Formation in Nagarze. The boundary is marked by the appearance of the ammonite Spiticeras and the nannofossil assemblage of Nannoconus st. steinmannii–N. st. minor–Watznaueria barnesae. The radiometric age in Tibet is the first to be integrated with upper Valanginian fossils. The volcanic rocks of the upper Sangxiu Formation are dated at 136 ± 3.0 Ma deduced from zircon SHRIMP age of rhyolite. By consideration of the rate of sediment accumulation of the underlying sedimentary deposits, the J/K boundary in the Gyangze–Nagarze area is approximately 145 Ma as suggested by the newly issued International Stratigraphic Chart, and the Valanginian/Hauterivian boundary lies between 134 Ma and 136 Ma. □ Biostratigraphy, graphic plot, Jurassic/Cretaceous boundary, nannofossil, SHRIMP U‐Pb age, Southern Tibet, Valanginian/Hauterivian boundary.

Paleomagnetic and Geochronological Results From the Zhela and Weimei Formations Lava Flows of the Eastern Tethyan Himalaya: New Insights Into the Breakup of Eastern Gondwana

“…lava flows in the Luozha area are consistent with the ages of the Sangxiu Fm. in the adjacent areas, such as Luozha (~135–124 Ma; Ma et al, ), Gyangze (~136 Ma; Wan et al, ), and southeastern Yamdrok Tso (~133 Ma; Zhu et al, ). In addition, our new LA‐ICP‐MS zircon U‐Pb analyses, combined with SHRIMP zircon U‐Pb analyses (Hou, ; Shi et al, ), indicate that the Lakang Fm.…”

“…Zircon U‐Pb dating indicates that the Sangxiu Fm. volcanic rocks erupted during ~136–124 Ma (Ma et al, ; Wan et al, ; Zhu et al, 2009, , 2005). Notably, the Weimei and Zhela Fms.…”

Filling the gap: new precise Early Cretaceous radioisotopic ages from the Andes

“…Wan et al (2011) studied Lower Cretaceous strata exposed in southern Tibet in order to identify the Jurassic/Cretaceous (J/K) boundary using calcareous nannofossil assemblages and to constrain the age of Valanginian nannofossils with U–Pb SHRIMP zircon dating. Based on a single date from a rhyolite, they proposed that the numerical age of the Valanginian⁄Hauterivian boundary should be no older than 136±3.0 Ma and, by considering sedimentary accumulation rates in the studied sections, the J⁄K boundary was estimated to be 145 Ma.…”

Searching for a non-marine Jurassic/Cretaceous boundary in northeastern China

“…Although Chinese scientists previously proposed several J/K boundary ages, such as 124 Ma , 125 Ma (Chen et al, 2005), 130 Ma , 135-137 Ma (Hao et al, 1982), recent research on the marine J/K transition sequences in the Gyangze-Nagarze areas of southern Tibet indicates that the base of Hauterivian is not older than 136 3 Ma (Wan et al, 2011), and 140-142 Ma SIMS zircon U-Pb ages for the mid-Berriasian supported the 145 Ma for the J/K boundary age proposed by Gradstein et al (2012). Thus, the potential J/K boundary should be lower than the Yixian Formation, i.e.…”