Microbial mat, organic-wall microfossils and geochemistry of the Ediacaran inter-diamictite black sediments in NW China: A short-lived habitable benthic, oxic and photic “ice-free oases”

Abstract

The Ediacaran glaciation has garnered considerable attention for its potential biological impact because it witnesses the birth of complex animals. Many researchers question whether large-scale regional or even global glaciations, represent critical barriers to the evolution of macroscopic animals. So how did complex animals survive during a major glaciation? One possible explanation is the existence of isolated shallower refugia or ice-free oases. However, the sedimentary evolution of such ice-free oases and how they could support the survival of complex life forms are not yet fully understood. This study focuses on the inter-diamictite black sediments in the Ediacaran Talisayi Formation of NW China (Yili block), which may represent a habitable ice-free oasis during the Gaskiers glaciation. The sedimentary facies and geochemical analyses indicate that these deposits were formed in oxygenated and photic shallow glacier lake environments with highly developed microbial mat substrates, it was formed during a short-lived partial deglaciation with enhanced weathering. And diverse organic-wall microfossils were found within the inter-diamictite black sediments. Furthermore, based on the growth habits of modern microbial algal mats, a paleontological clock can be established to estimate the duration of partial deglaciation, which may have lasted only for thousands of years. The ice-free oasis formed during this period could potentially harbor complex ecosystems, providing valuable ecological and temporal windows for the evolution of complex animals.