PROLIFERATION OF MISS-RELATED MICROBIAL MATS FOLLOWING THE END-PERMIAN MASS EXTINCTION: EVIDENCE FROM THE LOWER TRIASSIC OF THE YIYANG AREA, NORTH CHINA

Microbially induced sedimentary structures (MISSs) are common in siliciclastic shallow marine settings following the end-Permian mass extinction, but have been rarely reported in terrestrial ecosystems. Here, we present six types of well-preserved MISSs from the upper Sunjiagou Formation and lower Liujiagou Formation of Induan (Early Triassic) age in the Yiyang area, Henan Province, North China. These MISSs include: polygonal sand cracks, worm-like structures, wrinkle structures, sponge pore fabrics, gas domes, and leveled ripple marks. Microanalysis shows that these MISSs are characterized by thin clayey laminae and filamentous mica grains arranged parallel to bedding plane as well as oriented matrix supported quartz grains, which are all indicative of biogenic origin. Facies analysis suggests that the MISS-hosting sediments were deposited in a fluvial sedimentary system during the Early Triassic, including lake delta, riverbeds/point bars and flood plain paleoenvironments. Abundant MISSs from Yiyang indicate that microbes also proliferated in terrestrial ecosystems in the subsequent aftermath of the Permian–Triassic Great Dying, like they behaved in marine ecosystems. No reliable body or trace fossils have been discovered directly from the beds hosting MISSs. However, in contrast, the Olenekian Heshanggou Formation are highly bioturbated and yield abundant burrows, but lack MISSs. Therefore, microbial blooms, together with scarcity of metazoan fossils or burrows, may reflect environmental stress and devastation of terrestrial ecosystems immediately after the severe Permian–Triassic crisis.