Periglacial Process and Pleistocene Environment in Northern China
GUO, XUDONG, and LIU DONGSHENG, Academia Sinica, Beijing, China, and YAN FUHUA, State Seismological Bureau, Beijing, China
In the present time, five kinds of periglacial phenomena have been defined: Ice wedges, periglacial involutions, congelifolds, congeliturbations, and loess dunes. From the stratigraphical and geochronological data, the periglacial process is divided into six stages. (1) Guanting periglacial stage, characterized by the congeliturbative deposits that have developed in early Pleistocene Guanting loess-like formation. Paleomagnetic dating gives 2.43 Ma B.P. (2) Yanchi periglacial stage, characterized by the congelifold that has developed in middle Pleistocene Yanchi Lishi loess formation. Paleomagnetic dating gives 0.50 Ma B.P. (3) Zhaitang periglacial stage (II), characterized by the periglacial involutions that have developed in lower middle Pleistocene Lishi loess formation. Paleomagne ic dating gives 0.30 Ma B.P. (4) Zhaitang periglacial stage (I), characterized by the ice (soil) wedge that has developed in upper-middle Pleistocene Lishi loess formation. Paleomagnetic dating gives 0.20 Ma B.P. (5) Qiansangyu periglacial stage (11), characterized by the ice (sand) wedges that has developed in late Pleistocene Malan loess formation. Paleomagnetic dating gives 0.13 Ma B.P. (6) Qiansangyu periglacial stage (I), characterized by the ice (soil) wedge that has developed in late Pleistocene Malan loess-like formation. Thermoluminescent dating gives 0.018 Ma B.P.
Spore-pollen composition analysis shows that the savanna steppe environment prevailed in northern China during Pleistocene periglacial periods. These fossilized periglacial phenomena indicate a rather arid and windy periglacial environment with a mean annual temperature estimated some 12 degrees - 15 degrees C colder than that in the present. About 0.50-0.018 Ma B.P., the southern boundary of permafrost extended to the latitudes 38 degrees - 32 degrees N. The depth of permafrost is about -3 m to -20 m or more during Pleistocene periglacial periods.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)