CYCLOSTRATIGRAPHY OF THE MIDDLE EDIACARAN UPPER JIBALAH GROUP, EASTERN ARABIAN SHIELD, SAUDI ARABIA

During the Ediacaran Period (ca. 635–541 Ma), Earth experienced a series of important geological, biological and climatic events that irreversibly changed the nature of the surface environment and biological evolution. An accurate and precise geological time scale is required to properly reconstruct the changes to the Earth system during this formative interval in Earth’s history. Small, isolated sedimentary basins of middle Ediacaran age occur widely across the eastern Arabian Shield. The Jibalah Group, which fills these basins in the eastern part of the Arabian Shield, was previously been dated to between 620 Ma and 560 Ma. The Antaq basin is one of the largest and best exposed of the Jibalah basins, and previous studies have identified textured organic surfaces and putative Ediacaran fossils in the Muraykhah Formation of the upper Jibalah Group. The Muraykhah Formation here comprises a series of >50 regular and striking, 1–10 m-scale, mainly siltstone-sandstone cycles, interpreted to be deposited in a marginal marine environment. Silicified volcanic tuffs occurred throughout the Muraykhah Formation present an opportunity for new high-resolution U-Pb zircon ages. These dates anchor an astrochronological analysis of the Muraykhah cycles, which was performed on grayscale logs generated from high-resolution satellite imagery. Multi-taper method (MTM) spectral analysis of grayscale data through the logged lower Murraykhah Formation of the Antaq basin reveals 12-13 predominant ~20 m sedimentary cycles that correspond to 405-ka long eccentricity cycles, along with ~4.9 m wavelength corresponding to the short eccentricity cycle. The MTM spectral analysis results of the 405-ka-tuned grayscale series indicate the existence of significant cycles at the ~1-Ma, 405-ka, 125-ka, 100-ka, 85-ka, and 76-ka frequencies. Combining these results with new, precise U-Pb zircon ages for this succession will anchor a poorly calibrated interval of the middle Ediacaran Period and facilitate future global correlation.