GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 123-12
Presentation Time: 9:00 AM-6:30 PM


ZHANG, Tianran1, MYROW, Paul M.2, CHEN, Jitao3, FIKE, David A.4, MCKENZIE, N. Ryan5, LI, Wenjie3 and TIAN, Xiaoxu3, (1)Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, (2)Department of Geology, Colorado College, Colorado Springs, CO 80903, (3)CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China, (4)Earth and Planetary Sciences, Washington University in St. Louis, One Brookings Drive, Campus Box 1169, St Louis, MO 63130, (5)Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong

Mesoproterozoic rocks of the western margin of the North China Block have received little attention despite the presence of exceptional exposures of carbonate strata that record a surprisingly low level of deformation relative to most rocks of this age worldwide. We reconstruct the early tectonic and depositional history of the western part of the North China Block through a detailed sedimentological, geochronological, chemostratigraphic, and paleoenvironment analysis for the Huangqikou and Wangquankou formations in the northern Helan Mountains. Red beds and overlying white quartz arenite of the Huangqikou Formation represents terrestrial and shallow marine deposits, respectively, with the former representing alluvial fan to fluvial environments, possibly in a rift setting. Overlying stromatolite-bearing dolostone of the Wangquankou Formation records shallow marine deposits of a transgressive systems tract with numerous m-scale parasequences. Stromatolitic beds record various morphologies, including common planar, domal, columnar forms, as well as unique sharp-peaked forms. δ13C data from the Wangquankou Formation average ~0‰ and show approximately ±1‰ variations with δ18O data ranging from -6 to -10‰. Potential chemostratigraphic correlations with other Mesoproterozoic sections are difficult to establish due to a lack of precise age constraints, but show significant short-term variability that hold great potential for regional correlation to other sections in the North China Block. Four detrital zircon U–Pb age spectra from the Mesoproterozoic strata and one from overlying Cambrian rocks all contain 1760–1820 Ma and 2400–2510 Ma peaks. Along with published data, these suggest no significant changes in provenance in this region from the Mesoproterozoic to Middle Ordovician.