Paleo-environmental study on the growth of magnetotactic bacteria and precipitation of magnetosomes in Chinese loess-paleosol sequences

405 samples were collected from L-5-S-5-L-6 in consideration of obvious var iations in susceptibility of the geological sections, which are section Xif eng in Gansu Province and section Duanjiapo in Shaanxi Province for study o f magnetotactic bacteria (MB) and magnetosomes (MS) in Chinese loess-paleos ol sequences. MB in each sample were observed by TEM after being cultured u nder 8-18 degrees C, room temperature (RT), 25 degrees C, 26 degrees C and 30 degrees C conditions. In general, MB are distributed widely in loess-pal eosol sequences, fewer in loess layers with predomination of vibriod in sha pe. However, there are more MB in paleosol layers with morphological variet ies such as reddish, vibriod and occasionally approximately coccus. The mag netosomes (MS) in MB of paleosol are usually arranged in chains along the c ells. It was also found that MB growth and MS formation are associated with the environment in which MB live. it can be inferred from the distribution s of MB and MS that the paleoclimates fluctuated during the formation of lo ess-paleosol sequences in the Chinese Loess Plateau. The climate became gra dually warmer but displayed more frequent fluctuations from the northwest t o the southeast of the Plateau.