Carbonate Concretions from the Gaoyuzhuang Formation (ca. 1.6 Ga) of the North China Platform: Implication for a Methane-Rich Mesoproterozoic Ocean

摘要

The Gaoyuzhuang Formation (ca. 1.6 Ga) consists of up to 1 500 m thick, light gray to dark dolomite and limestone that are widespread in the North China platform. Abundant biological and sedimentary structures have been reported from this unit, including stromatolites of varying shapes from the lower part (the Guandi Member), macro-algal fossils from the lower middle part (the Sangshu'an Member) and enigmatic molar-tooth structures (MTs) from the upper middle part (the Zhangjiayu Member). The MTs in particular have attracted considerable attention, although their origin remains debated.