This field excursion will show you the superbly-exposed Precambrian to lower Paleozoic depositional sequence in the western margin of the North China Block. The succession consists of Paleoproterozoic gneiss, Mesoproterozoic siliciclastic facies, Cambrian mixed siliciclastic and carbonate facies, and Ordovician platform and slope carbonates (and siliciclastics), separated by remarkable unconformities, respectively. We will emphasize the lower Paleozoic strata and will see a large variety of textbook-level sedimentary structures and facies overall. Further, the lower Paleozoic record a significant stratigraphic hiatus (Furongian-Lower Ordovician), the timing and magnitude of which are similar to those of the northern Indian continental margin of the Himalaya, suggesting a linkage between northwest China Block and northern Indian, and potentially influenced by same orogeny. On the other hand, the Middle Ordovician records an abrupt facies change from platform carbonates (Zhuozishan Formation) to slope carbonates and overlying shale (the Kelimoli Formation, with spectacular, and sometimes unique, slumping structures and mass transport deposits), which implies a passive to foreland basin tectonic transition, and associated platform foundering and steepening of the slope. The field excursion will walk us through from several aspects of sedimentology, from classical field sedimentary features to basinal evolution, refreshing and enhancing principles of sedimentology grained from textbooks.

The SBG section in the Subaigou valley (photo taken in 2014 by Jitao Chen)
 

Imbricated bed and highly folded beds in the XLF section  (Li, Chen* et al., Sedimentology, 2022)