EDIACARAN OCEAN PH AND CONTINENTAL WEATHERING: A MULTI-PROXY COMPARISON BETWEEN KAZAKHSTAN, CHINA AND NAMIBIA

The study of ancient ocean pH and weathering conditions is essential to understand the ocean geochemical evolution and ocean-continent-atmosphere interaction of the past. It also allows reconstruction of habitable marine environments and nutrient availabilities in the ocean. To compare ocean pH conditions and quantify continental weathering between different paleo-continents and time intervals, we present a multi-proxy isotope (δ¹¹B, δ^44/40Ca and ⁸⁷Sr/⁸⁶Sr) approach on Ediacaran cap carbonates and carbonates of the Ediacaran-Cambrian transition. In detail, we evaluate the local, regional and global significance of these parameters at the Yangtze Platform (South China), the Malyi Karatau Range (Kazakhstan) and the Congo craton (Namibia).

Cap carbonates deposited in the immediate aftermath of the Marinoan glaciation record a global-scale ocean acidification event together with distinct changes in continental weathering rates and regimes caused by elevated atmospheric CO₂ levels. A similar transient ocean acidification and enhanced weathering situation seems to be present at the Precambrian-Cambrian (PCC) transition. However, both the duration of the ocean acidification as well as the weathering rates differ notably between Kazakhstan and South China. In contrast to the Marinoan aftermath, the cause of the environmental change at the PCC transition seems to be related to changes in the ocean redox state and bioproductivity leading to anoxic conditions instead of relevant fluctuations in atmospheric pCO₂.