MULTIPLE PROXIES OF ANCIENT CLIMATE AND SEA-LEVEL CHANGE: A PERMIAN-TRIASSIC TRANSITION EXAMPLE

Multiple proxies of climate and sea-level change enhance confidence in the detection of glacio- eustatic oscillations in sedimentary sequences. To decipher the relationship of climate and sea-level change, we study eleven high-resolution proxies measured on two sections from South China, which were deposited in the Tethys region during the Permian-Triassic transition interval. The proxies are spectral gamma ray (gamma-ray intensity, and potassium, uranium, and thorium content), calcium content from X-ray fluorescence, rock color series (L*, a* and b*), magnetic susceptibility (MS), water depth, and bed thickness.

Potassium and thorium content, as well as MS, are proxies for detrital input from terrestrial sources to the marine environment. Uranium content indicates the presence of organic material and uranium-rich minerals such as feldspar and clay. Gamma ray intensity is the composite response of potassium, thorium and uranium. L* quantifies sediment lightness and reflects carbonate content, and is supported by calcium content; a* quantifies red-green chromatic balance and the relative balance between Fe³⁺ and Fe²⁺ dominated compounds. Both uranium and a* indicate the redox condition of seawater. b* quantifies the yellow-blue chromatic balance of the sediment. Although it is not clearly identified with a specific geological process, b* anti-correlates strongly with L*, which suggests a link to non-carbonate sediment. The thicknesses of individual limestone and mudstone beds are connected with water depth and accommodation space.

Cyclostratigraphic study of these proxies reveals evidence for astronomical forcing of terrestrial weathering, detrital input, productivity, redox and sea-level.