| Datong Volcanic Group is located in Datong basin which is in the northern of the Shan(xi)Shaanxi(xi)graben system.During the Quaternary period,the Datong volcano erupted several times.Since the beginning of 1930,Many scholars have conducted research work about the Datong volcano and Datong basin.They want to know it's tectonic background,volcano magmatic type,chemical composition,volcano dynamics mechanism and activities.Finally,they own many research achievements.Due to the difficulties of collecting sampling and the factors of the volcano activities many times,the current result about the volcano's age data unable to form the effective ratio,also does not reflect the feature of the historical period about Datong volcano activity.So the problem of Datong volcano activity is a controversial topic..The result of field investigation show that the volcanic clastic layer buried in the lacustrine sedimentary facies and Loess-paleosol facies.At the foot of the volcanic cone are covered with a plurality of pyroclastic layers.At the foot of the volcanic slope,there are many sets of pyroclastic layers with different dip angles.The dip angle of the pyroclastic layer at the bottom is larger than that of the upper clastic layer.Lacustrine sediment and loess-paleosol deposits have been found in the continuation of multilayer gray matter suspected volcano sedimentary layer material thin black.These sedimentary phenomena show that Datong volcano has many active periods in geological history.The lacustrine deposits and loess-paleosol deposits in the region have recorded the information of volcanic activity at the same time.In order to obtain more detailed information about volcanic activity from the sedimentary layer and establish the framework of the sedimentary profile?to determine the sedimentary age of the volcanic material deposited in the sedimentary profile.In this paper,a detailed description of the physical form and the high precision sampling of the lacustrine sedimentary facies and the loess-paleosol sedimentary layer affected by the volcanic activities are carried out.In this paper,we selected Chen Zhuang profile as the typical lake sediments section,and the black mountain section as the typical section of Loess deposition.In the field investigation,we found that there are obvious records of volcanic activity in the profiles.The laboratory analysis shows that there are many layers in the two sections which are affected by the regional volcanic activity.Four layers of sedimentary layers shown the magnetic susceptibility,Ti content,Fe content and composition of average particle size were outlier in synchronous abnormal lacustrine sedimentary profile.In loess-paleosol sedimentary section in three layers of magnetic susceptibility,Ti content or Fe content becomes large synchronous shown it is abnormal sedimentary horizon.Those phenomenon of the increase of these anomalies indicates that the sedimentary environment is affected by the regional environmental change.In Datong Basin,the regional sedimentary environment change caused by volcanic activity.Using the paleomagnetic dating and loess-paleosol dating results established the date framework about the different sedimentary profile,determined the lacustrine sedimentary depositional age of four volcano sedimentary layers in laminated material are: over 0.90 Ma B.P.,about 0.51 MaB.P.,about 0.32 MaB.P.and 0.09 Ma B.P.;The depositional age of three volcano sedimentary layer material in the loess-paleosol sediments were about 0.32 MaB.P.,0.19 Ma B.P.and 0.09 MaB.P.Comparison those dating results,wo found that the Datong volcano sedimentary layer in the presence of a total of five active period... |
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