In this study, grain-size of 507 bulk samples from the QA-I Mioceneloess-soil sequence at Qinan were analyzed, and the grain-size features are compared with those oftypical Quaternary loess and soil samples, represent...In this study, grain-size of 507 bulk samples from the QA-I Mioceneloess-soil sequence at Qinan were analyzed, and the grain-size features are compared with those oftypical Quaternary loess and soil samples, representative lacustrine and fluvial samples. Theresults indicate that the grain-size distribution pattern of the Miocene loess is essentiallysimilar to that of Quaternary loess, but greatly differs from the lacustrine and fluvial sediments.Loess layers are regularly coarser than soil layers, indicating cyclical climate changes. Mediangrain-size along the 253.1 m sequence varies from 6 to 13 μm and the 】 63 μm fraction representsonly 5.3% in maximum, 0.9% in average. Long-term grain-size variations are consistent with the loessaccumulation rate at Qinan and with the eolian mass accumulation rate in the North Pacific. Thesefeatures firmly indicate an eolian origin of the studied sequence, and also reveal a coeval changesbetween the long-term changes of eolian grain-size and continental aridity in the dust sourceregions.展开更多
The distal extremity of a rhinocerotid humerus from the upper part of the Dingqing Formation at the Lunbori locality in Baingoin County,northern Tibet,is the first mammalian fossil found in Cenozoic deposits of the Lu...The distal extremity of a rhinocerotid humerus from the upper part of the Dingqing Formation at the Lunbori locality in Baingoin County,northern Tibet,is the first mammalian fossil found in Cenozoic deposits of the Lunpola Basin.The medial condyle of the distal trochlea of the humerus specimen from Lunbori gradually contracts from medially to laterally.The margin of the medial surface of the medial condyle is not prominent,the well-developed medial epicondyle strongly extends posteriorly,and is divided from the articular facet of the medial condyle by a groove;all of which are characteristic for the Rhinocerotidae.The medial condyle is wide at the bottom and narrow at the top.The medial collateral ligament fossa is relatively shallow,and the medial collateral ligament tubercle is very weak.The medial part of the upper margin of the medial condyle smoothly connects to the bony surface above,but there is no clear boundary between them.All of these characteristics are identical with those of Plesiaceratherium.These comparisons imply that the Lunbori specimen is closest to Plesiaceratherium gracile in the Shanwang Fauna from Linqu,Shandong Province,in size and morphology.Thus,its age is suggested to be the late Early Miocene(Shanwangian Age),about 18-16 Ma.Discovery of the rhinocerotid fossil suggests that the upper part of the Dingqing Formation deposited in the Neogene.While adjusting to paleo-temperatures of the Early Miocene,a paleo-ecosystem reconstruction indicates that the paleo-elevation was close to 3000 m in the Lunpola Basin during this time.展开更多
基金This work was supported by the Chinese Academy of Sciences(Grant No.KZCX3-SW-139)the National Natural Science Foundation of China(Grant Nos.40231001 and 40272088)the'973'Project(Grant No.2004CB720203).
文摘In this study, grain-size of 507 bulk samples from the QA-I Mioceneloess-soil sequence at Qinan were analyzed, and the grain-size features are compared with those oftypical Quaternary loess and soil samples, representative lacustrine and fluvial samples. Theresults indicate that the grain-size distribution pattern of the Miocene loess is essentiallysimilar to that of Quaternary loess, but greatly differs from the lacustrine and fluvial sediments.Loess layers are regularly coarser than soil layers, indicating cyclical climate changes. Mediangrain-size along the 253.1 m sequence varies from 6 to 13 μm and the 】 63 μm fraction representsonly 5.3% in maximum, 0.9% in average. Long-term grain-size variations are consistent with the loessaccumulation rate at Qinan and with the eolian mass accumulation rate in the North Pacific. Thesefeatures firmly indicate an eolian origin of the studied sequence, and also reveal a coeval changesbetween the long-term changes of eolian grain-size and continental aridity in the dust sourceregions.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-Q09)the National Basic Research Program of China (2012CB821906)the National Natural Science Foundation of China (40730210)
文摘The distal extremity of a rhinocerotid humerus from the upper part of the Dingqing Formation at the Lunbori locality in Baingoin County,northern Tibet,is the first mammalian fossil found in Cenozoic deposits of the Lunpola Basin.The medial condyle of the distal trochlea of the humerus specimen from Lunbori gradually contracts from medially to laterally.The margin of the medial surface of the medial condyle is not prominent,the well-developed medial epicondyle strongly extends posteriorly,and is divided from the articular facet of the medial condyle by a groove;all of which are characteristic for the Rhinocerotidae.The medial condyle is wide at the bottom and narrow at the top.The medial collateral ligament fossa is relatively shallow,and the medial collateral ligament tubercle is very weak.The medial part of the upper margin of the medial condyle smoothly connects to the bony surface above,but there is no clear boundary between them.All of these characteristics are identical with those of Plesiaceratherium.These comparisons imply that the Lunbori specimen is closest to Plesiaceratherium gracile in the Shanwang Fauna from Linqu,Shandong Province,in size and morphology.Thus,its age is suggested to be the late Early Miocene(Shanwangian Age),about 18-16 Ma.Discovery of the rhinocerotid fossil suggests that the upper part of the Dingqing Formation deposited in the Neogene.While adjusting to paleo-temperatures of the Early Miocene,a paleo-ecosystem reconstruction indicates that the paleo-elevation was close to 3000 m in the Lunpola Basin during this time.
