The Guttenberg δ13C excursion (GICE) and paleoclimate change recorded in the early Late Ordovician carbonate succession of the Ordos Basin, Northern Chinas

Abstract

The well-known Guttenberg isotopic carbon excursion (GICE) is a global palaeoceanographic event in the early Katian, Late Ordovician. Here, based on analysis of the carbon oxygen isotopes and K-bentonite characteristics, we documented the evidence of the GICE from the Upper Ordovician carbonate succession in the Ordos Basin, Northern China. The results revealed a positive δ13C excursion occurred in the Jinsushan Formation. Based on SHRIMP U-Pb dating of the K-bentonites and biostratigraphic constraints, the carbon isotope excursion of X1 (in Xilingggou section) and Z1 (in Zhaolaoyu section) identified in the area can be regarded as local expressions of the GICE. It is the first time that the GICE was identified in the Ordos Basin. Compared with the GICE profiles from the Dolly Ridge, North America and the Mehikoorma Drill Core from Europe, the X1 profile exhibits a similar feature with a positive δ13C excursion of 2.11‰. While the Z1 profile shows a two-peaks curve with a positive shift up to 5.61‰, representing one of the largest shifts in δ13C for the GICE so far. Considering that the X1 and Z1 profiles started immediately above the K-bentonites, and the GICE in North America and Europe were also in close association with marked bentonites, we argued that the carbon cycle perturbation depicted by the GICE and its equivalents were genetically related to increased volcanic eruptions in the early Late Ordovician, which may have led to a climate cooling and enhanced organic burial, thus resulted in the positive δ13C excursion.