Cyclostratigraphy of the Cryogenian Fiq Formation, Oman and its implications for the age of the Marinoan glaciation

Abstract

Cyclostratigraphy is a powerful tool in chronostratigraphic studies, and has shown its potential in Precambrian time. The Cryogenian Period is one of the most dynamic and intriguing intervals in Earth history and it is a witness to the most extreme climate changes on the planet, known as two Snowball Earth events. However, a robust chronostratigraphic framework is still lacking especially for the younger Marinoan Snowball Earth event, hampering the stratigraphic correlation and comparison among geographically separated records, as well as the understanding of the initiation and termination of this global-scale glaciation. The Cryogenian Fiq Formation in Oman is thought to be Marinoan-equivalent. The duration of the nonglacial units in the Fiq Formation could provide a conservative age constraint on the previously not well-determined onset age of the Marinoan glaciation. In this work, a cyclostratigraphic study has been conducted on three drill cores of the Fiq Formation. The multi-taper method (MTM) spectral analysis, the correlation coefficient (COCO), and the evolutionary correlation coefficient (eCOCO) analyses were performed on the high-resolution gamma-ray (GR) data from the three cores. A hierarchy of Milankovitch cycles (eccentricities, obliquities, and precessions) has been identified, which was used to estimate the optimal sedimentary accumulate rates and the duration of the Fiq Formation in each core. Based on the cyclostratigraphic results, the time scale of the Fiq Formation is at least ~6 Myr. Integrating the radiometric ages and the cyclostratigraphic data from other continents, the onset age of the Marinoan glaciation is suggested to be 650–641 Ma. This new result helps improve the chronostratigraphic framework for the Cryogenian Period and also provides critical temporal constraints for the geological and numerical models that explore the possible mechanisms for the Snowball Earth events.