Paleoclimate proxies for cyclostratigraphy: Comparative analysis using a Lower Triassic marine section in South China

Multiple proxies for paleoclimatic and paleoenvironmental change within sedimentary sequences have been developed; but understanding their relationships and their relative strengths or weaknesses are required to access a wealth of untapped paleoclimate information. We propose two main criteria for multiple proxy datasets to estimate their individual signal-to-noise levels and to decipher the relationship between multiple proxies. First, for proxies affected by similar processes, then their time-dependent changes should be similar. Second, a paleoclimate proxy that is more sensitive to an external forcing, such as astronomical forcing, is more useful than those that do not have such a response. We introduce two methods to evaluate these criteria: (1) hierarchical cluster analysis (HCA) probes the relationships among multiple proxies based on similarities of their oscillation patterns, and (2) power decomposition analysis (PDA) tests proxy sensitivity to external climate forcing. We evaluate 16 high-resolution paleoclimate proxies in detail for their applications in paleoclimatology from the marine Lower Triassic Daye Formation at the Daxiakou section in the Three Gorges region of South China, which has carbonate-claystone cycles deposited on an outer ramp. The proxies are spectral gamma ray (gamma ray intensity, potassium, uranium, thorium, thorium/uranium and thorium/potassium), rock color lightness (L*), redness (a*) and yellowness (b*), magnetic susceptibility (measured in both laboratory and outcrop), anhysteretic remanent magnetization (ARM), lithologic rank, simplified lithologic rank and non-carbonate fraction, carbonate thickness and couplet thickness. Hierarchical cluster analysis (HCA) gathers these proxies into groups likely affected by the same process. The ARM and thorium/uranium proxies seem to reflect the hinterland-weathering process during the Early Triassic. Gamma-ray, potassium, uranium, thorium, magnetic susceptibility and non-carbonate fraction proxies refer to terrestrial input. The L*, a* and lithologic rank proxies indicate the productivity, the redox state and the relative sea level, respectively at this section. This case study contributes to the understanding of the sensitivity of these types of proxies within marine strata for deep-time paleoclimate and astronomical-tuned time scales.