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Loess of China,regardless of its age,exhibits similarity in the surface texture of siltquartz grains,all of them having conchoidal fractures,flat cleavage planes(or plates),andmechanical cracks,and having been re-worked by silica precipitation and chemical dissolution.Silica precipitation,different-degree chemical etching and dissolution are commonly found onthese grains,indicating that they would be separated from source rocks,such as granites,gneisses,etc.;or they may have been subjected to relatively long weathering in-situ beforetransported to loess-accumulating areas,or they probably underwent diagenesis when broughtinto the sedimentation system,followed by weathering and erosion and then transported toloess-accumulating areas.It is evident from the relationship between loess of China,desertsand Gobis,and loessic composition and its regional distribution that Mesozoic-Cenozoic landdetrital sediments widely spread in the Ordos and Alashan regions are the principal sourceof loessie material in China.
Loess of China, regardless of its age, exhibits similarity in the surface texture of siltquartz grains, all of them having conchoidal fractures, flat cleavage planes (or plates), and mechanical cracks, and having been re-worked by silica precipitation and chemical dissolution. Silica precipitation, different-degree chemical etching and dissolution are commonly found on the grains, indicating that they would be separated from source rocks, such as granites, gneisses, etc.; or they may have been to to relatively long weathering in-situ before transports to loess-accumulating areas, or they probably underwent diagenesis when broughtinto the sedimentation system, followed by weathering and erosion and then transported toloess-accumulating areas. It is evident from the relationship between loess of China, deserts and Gobis, and loessic composition and its regional distribution that Mesozoic-Cenozoic land detrital sediments widely spread in the Ordos and Alashan regions are the principal sourceof loessie material in China.