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Keywords:

  • algal mound;
  • algal colonization;
  • palaeoecology;
  • Moscovian;
  • Late Carboniferous;
  • Tarim Basin;
  • NW China

A Beresella-dominated algal mound and its internal construction from Paojianggou, southwestern Tarim Basin, NW China are studied for the first time. This algal mound was constructed during the early–middle late Moscovian and its age is constrained by fusulinids of the Fusulina kamensis and F. quasicylindrica zones of middle Pennsylvanian age. The mound substrate beds are composed of crinoid and brachiopod grainstones. Crinoid bank and brachiopod-dominated skeletal shoals indicate a high-energy environment and produced a local topographic high on which the mound grew. Komia bafflestone of the foremound facies further increased the relief of the crinoid bank on the seafloor. The lower part of the mound framework is dominated by Shamovella–Archaeolithoporella boundstone, while the main (upper) mound framework consists predominantly of Beresella boundstone. Grainstone–packstone characterizes the windward mound flank facies. The mound capping facies include a lower skeletal packstone–wackestone and an upper lagoon facies marlstone and black shale. Various algal colonies performed different roles in the formation of the mound. Komia colonies were the mound constructors that baffled higher energy currents and entrapped fine sediment. Archaeolithoporella, Shamovella and possibly microbes (cyanobacteria) acted as the binders to stabilize mud and fine-grained sediment. Beresella colonies were the major framework constructors whose network entrapped the mud to build the mound.

The growth of the Paojianggou mound in the Tarim Basin has undergone three major algal colonization stages: Komia baffling, laminar Archaeolithoporella and Shamovella encrusting and binding, and Beresella binding and stabilizing. The Paojianggou mound developed in a protected lagoonal position behind the shoals and grew during a short rise in sea level followed by a long-period sea-level fall. Its demise was caused by terrigenous siliciclastic input due to regional tectonic uplifting in the Tarim Basin during the latest Moscovian time. Copyright © 2012 John Wiley & Sons, Ltd.