The disappearance of a Late Jurassic remnant sea in the southern Qiangtang Block (Shamuluo Formation, Najiangco area): Implications for the tectonic uplift of central Tibet

Abstract

Located between the Bangong-Nujiang suture zone and the Qiangtang Block in central Tibet, the Najiangco area (~5 km to the north of Nima-Selingco) contains an Upper Jurassic-Lower Cretaceous sedimentary succession deposited during a period of marine regression. The youngest marine sedimentary unit in the Najiangco area is the Upper Jurassic Shamuluo Formation, which consists of sandstone, limestone, siltstone, and shale. Sedimentary facies analysis shows that tidal flat and subtidal lagoonal facies characterized the northern margin of the basin, while delta front and prodelta facies dominated the middle part, and carbonate shoal and patch reef facies prevailed along the southern margin. Provenance analysis, including petrographic modal analysis of sandstones and U-Pb dating of detrital zircons, shows that a recycled orogen in the central Qiangtang to the north of Najiangco area was the source of the sandstones in the Shamuluo Formation. Biostratigraphy and U-Pb zircon dating of a porphyritic granitoid dike (150.8 ± 1.9 Ma) indicate that the Shamuluo Formation was deposited during the Late Jurassic (Oxfordian to Kimmeridgian). During Middle Jurassic time, the southern Qiangtang Basin was dominated by shallow-marine environments. Later, during the Late Jurassic (Oxfordian to Kimmeridgian), the shallow-marine facies retreated to the southern margin of the basin. Combined with regional paleogeographic data from central Tibet, two 2 / 38 stages of southward retreat of the Qiangtang remnant sea, and three stages of topographic uplift of the Qiangtang Block can be recognized during late Middle Jurassic to Early Cretaceous time.

Reconciling Orogenic Drivers for the Evolution of the Bangong‐Nujiang Tethys During Middle‐Late Jurassic

“…Similar events have also been recognized in the forearc regions of the Rutog-Gerze arc-trench system (Figures 8c and 9) including rapid deposition of Gamulong conglomerates in a trench environment at approximately 166 Ma with poor Table S5, as well as from Zhu et al (2016), Zhang et al (2017), Zhong, Hu, et al (2017), C. , and A. Ma, Hu, et al (2018).…”

“…Three lines of evidence imply that uplift and erosion of the arc is the cause of this sediment influx. First, paleogeographic reconstruction implies that the eastern SQ lay within a shallow-marine environment, whereas the eastern BNS, where the Daru Tso arc developed, lay in a deep-marine environment during Early-Middle Jurassic (~183-163 Ma et al, 2017;A. Ma, Hu, et al, 2018).…”

“…The uplift of Daru Tso arc is coeval with angular unconformities in the retro-arc regions (Figures 8a and 9) between the Shamuluo formation and underlying Dongqiao-Amdo mélange belt (at approximately 164 Wang et al, 2013) and between Biluoco and underlying Buqu formations (at approximately 166 Ma), based on fossil and detrital zircon ages (Ma et al, 2017;A. Ma, Hu, et al, 2018).…”

Internal Drainage Has Sustained Low‐Relief Tibetan Landscapes Since the Early Miocene

“…n = counted grains. (c) Histograms show the distribution of gravel grain sizes from conglomerate (from measured sections of the Lunpola Basin, see (a) and Figure S1 for the counting locations) and modern riverbeds (see Figure 1b for counting sites (Chapman & Kapp, 2017;Fan et al, 2016;Gehrels et al, 2011, and references therein;Guynn et al, 2012;Huang et al, 2017;Lai et al, 2017;Li et al, 2014;Ma et al, 2017;Ma, Hu, et al, 2018;Meng et al, 2018;Pullen et al, 2008Pullen et al, , 2011Sun et al, 2015;Zhang et al, 2017;Zhang et al, 2011;Zhu et al, 2011). Qt = total quartz; F = total feldspar; L = total lithic grains; CB = continental block; RO = recycled orogen; MA = magmatic arc.…”

Reply to Comment by W.‐Y. Chen et al. on “Sedimentary and Tectonic Evolution of the Southern Qiangtang Basin: Implications for the Lhasa–Qiangtang Collision Timing”

“…In the Bangong‐Nujiang suture zone, the Mugagangri Group mélange is overlain by the shallow‐marine limestones and sandstones of the Shamuluo Formation, which were deposited during Late Jurassic time (ca. 163–152 Ma), as constrained by coral and foraminifera biostratigraphy and the U–Pb zircon age of porphyritic granitoid intrusions (Ma et al, ). The J–K turbidite unit (as young as ~125 Ma) mentioned by the Comment was reported further south in the southern Nima basin by Kapp et al ().…”