Positive carbon isotope excursions: global correlation and genesis in the Middle–Upper Ordovician in the northern Tarim Basin, Northwest China

Ming-Xia Luo,Zhi-Li Zhang,Peng Luo,Cun-Ge Liu,Yong-Li Liu,Li-Xin Qi,Xiao-Ming Shao

doi:10.1007/s12182-016-0096-3

Abstract

Stable carbon isotope ratio (δ13Ccarb) analysis has been widely applied to the study of the inter-continental or global marine carbonate correlation. Large-scale Cambrian–Ordovician carbonate platforms were developed in the Tarim Basin. But research on fluctuation characteristics and global correlation of δ13Ccarb is still weak. Based on conodont biostratigraphy and whole-rock δ13Ccarb data in the Tahe oil–gas field of the northern Tarim Basin, the global correlation and genesis of positive carbon isotope excursions in the Darriwilian—Early Katian was examined. Three positive excursions were identified in the Tahe oil–gas field including the middle Darriwilian carbon isotope excursion (MDICE), the Guttenberg carbon isotope excursion (GICE), and a positive excursion within the Pygodus anserinus conodont zone which is named the Early Sandbian carbon isotope excursion (ESICE) in this paper. Furthermore, these positive excursions had no direct relation with sea level fluctuations. MDICE and GICE could be globally correlated. The Middle–Upper Ordovician Saergan Formation source rocks of the Kalpin outcrops were in accordance with the geological time of MDICE and ESICE. GICE had close relationship with the source rock of the Lianglitag Formation in the basin. Massive organic carbon burial was an important factor controlling the genesis of these positive excursions.

Highlights

The stable carbon isotope ratio in dissolved inorganic carbon (d13Ccarb) reflects the initial isotope composition in the original seawater (Saltzman 2005; Ainsaar et al 2010; Munnecke et al 2011)
According to research on Ordovician sequence stratigraphy in the Tahe oil–gas field and Tarim Basin and our results shown in Fig. 2 (Deng et al 2007; Wu et al 2012; Liu et al 2012), the positive excursion A occurred in the Highstand System Tract (HST) of the Yijianfang Formation, the positive excursion B in the transgressive system tract (TST) of the Qiaerbak Formation, and the positive excursion C in the HST of the Qiaerbak Formation and the TST of the Lianglitag Formation, which indicated that three positive excursions had no direct relationships with sea level fluctuation, and could be correlated regionally or globally
According to outcrop and drilling data from the Tarim Basin, Ordovician source rocks consist of the Middle– Lower Ordovician Heituwa Formation in the Manjiaer Depression (Fig. 1a), the Middle–Upper Ordovician Saergan Formation in the Kalpin outcrop and the Upper Ordovician Lianglitag Formation in the basin (Wang 2000; Zhang et al 2006; Gao et al 2007; Zhao et al 2008)

Summary

Introduction

The stable carbon isotope ratio in dissolved inorganic carbon (d13Ccarb) reflects the initial isotope composition in the original seawater (Saltzman 2005; Ainsaar et al 2010; Munnecke et al 2011). Paleoceanographic environment change results in the death of many organisms and the burial of 12C in them, which can enrich the 13C in the sea water and increase the d13Ccarb values of carbonate rocks (Sial et al 2013). D13Ccarb had been widely used in studies of regional or global correlation on marine carbonate strata and paleoceanographic environment (Zhang et al 2010a; Ainsaar et al 2010; Fan et al 2011). Three short-lived d13Ccarb-positive excursions have been globally identified in the Ordovician (Zhang et al 2010a; Sial et al 2013), including the middle Darriwilian carbon isotope excursion (MDICE), Early Katian Guttenberg carbon isotope excursion (GICE), and

Methods

Results

Conclusion