Formation and evolution of an Early Cambrian foreland basin in the northwest Yangtze Block, South China

The Ediacaran to Cambrian in the northwest Yangtze Block has long been considered to be formed in a passive margin. The Ediacaran is dominated by thick carbonate rocks, whereas the Lower Cambrian comprises a thick clastic succession. The transition from carbonate to clastic record, and the provenance and tectonic setting of the clastic succession are poorly understood. Stratigraphic correlation shows a distinct stratigraphic absence from the Lower Cambrian to Devonian in the Bikou terrane. A regional seismic profile presents a wedge geometry of the Lower Cambrian from NW to SE. Outcrops reveal an overall coarsening-upwards succession of the Lower Cambrian. The petrographic analysis of clastic rocks presents an immature feature implying a proximal source. Paleocurrent measurements of clastic rocks point to dominant SE-vergent orientations. The age spectra of detrital zircons imply that they were derived from Early Cambrian continental arcs and older continental crust. Geological, geophysical, and geochemical evidence indicates that an Early Cambrian foreland basin was formed in the northwest Yangtze Block. This foreland basin appears to have been strongly influenced by an orogenic loading northwestward. We propose that this orogenic event can be named as the Motianling orogeny, the origin of which may be related to subduction of the Proto-Tethys ocean beneath the northwest Yangtze Block.
 
 Supplementary material:
 Supplementary tables A-D and petrological description of detrital zircons are available at
 https://doi.org/10.6084/m9.figshare.c.6332980
