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High-Precision U-Pb Age Constraints on the Permian Floral Turnovers

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High-Precision U-Pb Age Constraints on the Permian Floral Turnovers https://doi.org/10.1130/G48051.1 Manuscript received 20 June 2020 Revised manuscript received 13 November 2020 Manuscript accepted 13 December 2020 © 2021 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 5 February 2021 High-precision U-Pb age constraints on the Permian floral turnovers, paleoclimate change, and tectonics of the North China block Qiong Wu1, Jahandar Ramezani2, Hua Zhang3,4*, Jun Wang3,4, Fangui Zeng5, Yichun Zhang3,4, Feng Liu3,4, Jun Chen6, Yaofeng Cai3,4, Zhangshuai Hou1, Chao Liu5, Wan Yang7, Charles M. Henderson8 and Shu-zhong Shen1,4,9* 1 State Key Laboratory for Mineral Deposits Research and School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China 2 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 3 State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China 4 Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210023, China 5 Department of Earth Science & Engineering, Taiyuan University of Technology, Taiyuan 030024, China 6 State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China 7 Geology and Geophysics Program, Missouri University of Science and Technology, Rolla, Missouri 65409, USA 8 Department of Geoscience, University of Calgary, Calgary, AB T2N 1N4, Canada 9 Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research and Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China ABSTRACT INTRODUCTION The Permian marine-terrestrial system of the North China block provides an excep- The North China block occupied northerly tional window into the evolution of northern temperate ecosystems during the critical tropical to subtropical paleolatitudes (Boucot transition from icehouse to greenhouse following the late Paleozoic ice age (LPIA). Despite et al., 2013), marginal to the Paleo-Asian Ocean many studies on its rich hydrocarbon reserves and climate-sensitive fossil flora, uncertain (PAO), during the critical Cisuralian (298.9– temporal constraints and correlations have hampered a thorough understanding of the 273.0) transitions from an icehouse to a green- records of geologic, biologic, and climatic change from the North China block. We present house world (Fig. 1). The late Carboniferous to a new chronostratigraphy based on high-precision U-Pb chemical abrasion–isotope dilu- Permian marine and marginal-marine to terres- tion–thermal ionization mass spectrometry (CA-ID-TIMS) geochronology of tuffs from a trial sequences in North China preserve highly near-complete latest Carboniferous–Permian succession in North China. The results indicate diverse and abundant plant fossils in addition to that the predominance of continental red beds, climate aridification, and the disappear- their significant economic hydrocarbon resources ance of coals and characteristic tropical flora were well under way during the Cisuralian (Yang et al., 2005; Wang, 2010; Liu et al., 2015). (Early Permian) in the North China block, significantly earlier than previously thought. A These characteristics provide a unique opportu- nearly 20 m.y. hiatus spanning the early Kungurian to the mid-Guadalupian (or later) is nity to investigate the interactions among ter- revealed in the northern North China block to have close temporal and spatial associations restrial biotic evolution, regional tectonics, and with the closure and/or subduction of the Paleo-Asian Ocean and its related tectonic con- global climate change during a critical period of vergence. This long hiatus was concomitant with the prominent loss of the highly diverse geologic history. However, poor constraints on and abundant Cathaysian floras and the widespread invasion of the monotonous Angaran age and correlation have hampered a deep under- floras under arid climate conditions in the North China block. Similarities in the floral standing of those events in the North China block. and climate shift histories between Euramerica and North China suggest that aside from In the absence of diagnostic marine fossils from the regional tectonic controls and continental movement, extensive volcanism during the key intervals, stratigraphic correlation within and Cisuralian may have played a major role in the global warming and aridification in the beyond North China has relied on uncalibrated aftermath of the LPIA. palynostratigraphy and phytostratigraphy (Wang, 2010; Liu et al., 2015) and magnetostratigraphy (Embleton et al., 1996). Detrital zircon geochro- nology by U-Pb in situ analyses from Permian *E-mails: [email protected]; [email protected] volcaniclastic sandstones (e.g., Zhu et al., 2014; CITATION: Wu, Q., et al., 2021, High-precision U-Pb age constraints on the Permian floral turnovers, paleoclimate change, and tectonics of the North China block: Geology, v. 49, p. 677–681, https://doi.org/10.1130/G48051.1 Geological Society of America | GEOLOGY | Volume 49 | Number 6 | www.gsapubs.org 677 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/49/6/677/5323271/g48051.1.pdf by guest on 02 October 2021 A B Figure 1. Location of study area. (A) Reconstruction of Cisuralian paleogeography (Boucot et al., 2013) showing the study area and major volcanic provinces. PAO—Paleo-Asian Ocean; P—Panjal Traps; S—Skagerrak-Centered large igneous province (LIP); T—Tarim LIP. (B) Loca- tions of study sections in Shanxi Province, North China. Yang et al., 2017) generally lacked the necessary 2015). Carboniferous–Permian basin evolution METHODS AND RESULTS precision or stratigraphic range to place reliable in North China was largely controlled by con- We collected 11 bentonitic tuff and tuffaceous constraints on depositional ages. vergent tectonics during the closure of the PAO mudstone samples from the Palougou, Qiaotou, We report high-precision U-Pb zircon geo- along the northern margin of the North China and Sigou sections in Shanxi Province, northern chronology by the chemical abrasion–isotope block (Zhu et al., 2014). North China (Fig. 1), for U-Pb geochronology dilution–thermal ionization mass spectrometry The age and regional correlation of the Pen- by the CA-ID-TIMS method. These samples en- (CA-ID-TIMS) method focused on bentonitic chi and Taiyuan Formations have been well compass the middle Taiyuan to basal Sunjiagou tuffs from the Permian succession in North Chi- constrained by fusuline and conodont fossils Formations. The weighted mean 206Pb/238U dates na. The results necessitate fundamental revisions from their marine strata (see the Supplemental of the analyzed zircons along with a Bayesian to the traditional Permian terrestrial deposition- Material1) as well as new U-Pb CA-ID-TIMS interpolation algorithm are used to construct a al history and chronostratigraphy of the North geochronology from the subsurface of southeast- statistically robust chronostratigraphic frame- China block and provide a new timeline and ern North China (Yang et al., 2020). However, work for the Permian succession of North China, important insights for the history of continen- the correlation of the Permian succession above from which the ages of lithostratigraphic bound- tal collision, floral turnovers, and paleoclimate the Taiyuan Formation has long been a subject of aries, floral changes, and climate proxies can be change as recorded in the North China block. debate. The Shansi and Lower Shihhotse Forma- extrapolated. Detailed descriptions of the stratig- tions were roughly assigned to the Cisuralian, the raphy, tuff samples, U-Pb analytical procedures, STRATIGRAPHY AND GEOLOGIC Upper Shihhotse Formation to the Guadalupian data reduction, age interpretation, reliability, and SETTING (273.0–259.5 Ma), and the Sunjiagou Formation Bayesian modeling are provided in the Supple- Paleozoic epicontinental deposition in the to the Lopingian (259.5–251.9 Ma) in the classic mental Material. The U-Pb geochronological North China block was interrupted by a long peri- area of Shanxi Province in North China, based on results are summarized in Table 1. od of craton-wide non-deposition and/or erosion fossil plant and palynological analyses (Wang, from the Late Ordovician to late Carboniferous 2010; Liu et al., 2015). DISCUSSION (Yang et al., 2005). A late Carboniferous marine Limited tuff zircon geochronology by in A set of five new weighted mean 206Pb/238U transgression led to the deposition of the Pen- situ techniques previously resulted in U-Pb dates from bentonites of the Palougou section chi Formation, overlain by the Carboniferous– age estimates of 293.0 ± 2.5 Ma for the Shansi forms the basis of a Bayesian age-stratigraphic Permian Taiyuan Formation, in shallow-marine Formation (Yang et al., 2014), 290.1 ± 5.8 Ma model, which for the first time provides a near- and tidal-flat environments. The latter consists for a northerly correlative of the Taiyuan and/ complete temporal calibration for the Permian of alternating marine limestone and shale along or Shansi Formations (Cope et al., 2005), and system of North China (Fig. 2; Fig. S5 in the with extensive coal seams that transition upward 296 ± 4 Ma for a presumed correlative unit of Supplemental Material). The Carboniferous- into lagoonal-swamp and shoreline deposits.
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