Upper Lower Triassic stromatolite from Anhui, South China: Geobiologic features and paleoenvironmental implications

摘要: Abstract Widespread stromatolites and other microbialite deposits characterize Lower Triassic marine successions worldwide. This study documents a stromatolite deposit, 1.1 m thick, from the upper Spathian (Lower Triassic) of Susong area, South China. The comprises distinct laminated domes in basal part columns at part. Dark laminae are loosely spaced interlayered with thicker light colored laminae. Diffusive dark composed peloidal micrite that grade locally into microclotted structures, yield copies bacteria clump-like coccoid-like spheroid aggregates. former characterized by cloudy, nuclei rimmed coarse-grained, euhedral sparry calcite crystals, while latter comprised solid crystal coated rather thin envelopes. resemble structures observed present-day travertine. Both spheroids surrounded coarse-grained suggesting similar accretion mechanism. spherical therefore could be crucial stromatolite. laminated/microclotted interpreted as result variation timing lithification relative to decay microbes. Micro-analysis also unravels common occurrence authigenic micro-quartz crystals association Fe-bearing illite clay minerals columns. Their coalescing nature each other, together associated pyrite grains, strongly support formation microbial reduction an smectite precursor sulfate reducing bacteria. A comparison its counterparts strata Dajiang, China reveals many similarities microstructures, harsh, euxinic–anoxic environment resulting bloom most likely extended latest