Abstract
The indirect detection of cryptotephra in black shales has become a key aspect of stratigraphic age, stratigraphic correlation, environmental variation, climate change, and organic matter enrichment in relation to volcanic eruptions. Common proxies for volcanic ash in sediments include the ratios of Hg to total organic carbon (TOC) and total sulfur (TS). Recent studies have shown that volcanic eruptions can lead to an increase in organic matter, but whether the relationship between elements found in volcanic ash and TOC can be used as an additional proxy to detect cryptotephra within lacustrine sediments has yet to be tested. In this study, black shales from the Chang 73 Member of the Triassic Yanchang Formation in the Ordos Basin of North China were collected for petrological and geochemical analysis. Petrological analysis revealed small amounts of zircon, cryptotephra, and fibrous apatite in the black shales. Geochemical analysis revealed that Zr in the shales originated mainly from zircon deposited directly from volcanic eruptions and that the Zr/Al ratio is positively correlated with TOC. Thus, the positive correlation between Zr/Al and TOC is a reliable proxy for cryptotephra in black shales.-
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