The Seismogenic Structure of the 2010 Suining Ms 5.0 Earthquake and its Geometry,Kinematics and Dynamics Analysis

In January 2010, the Suining Ms5.0 earthquake occurred in central Sichuan Basin, with the epicenter in Moxi-Longnvsi structural belt and a focal depth of 10 km. Based on structural interpretations of seismic profiles in this area, we recognized a regional detachment fault located at a depth of 9-10 km in the Presinian basement of the Suining area, transferring its slipping from NW to SE orientation. This detachment fault slipped from NW to SE, and underwent several shears and bends, which caused the basement to be rolled in and the overlaying strata fold deformation. It formed a fault-bend fold in the Moxi area with an approximate slip of 4 km. Correspondingly, the formation of the Moxi anticline is related to the detachment fault. With the earthquake＇s epicenter on the ramp of the detachment fault, there is a new point of view that the Suining earthquake was caused by re-activation of this basement detachment fault. Since the Late Jurassic period, under the influence of regional tectonic stress, the detachment fault transfered its slip from the Longmen Mountains （LMS） thrust belt to the hinterland of the Sichuan Basin, and finally to the piedmont zone of southwest Huayingshan （HYS）, which indicates that HYS might be the final front area of the LMS thrust belt.

Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau:Its Paleoclimatic Implications

Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.

Detection and indication of 1,3,4-C27-29 triol in the sediment of northern South China Sea

After the detection of the 1,20,21-C29 long-chain triol in some sediments and freshwater pteridophytes, in this study a new homologous long-chain triol, 1,3,4-C27-29, is detected for the first time in the Site4B core sediment in the northern South China Sea. The hydroxyl location and length of the carbon chain of this newly discovered triol differ from those of 1,20,21-C29 triol. The test results of its molecular distribution and individual carbon isotope reveal that 1,3,4-C29triol has a good correlation with n-C26-30 even carbon-numbered long-chain fatty alcohols, with R2 （n=68） values of 0.905, 0.929 and 0.903, respectively, and its carbon isotope composition, at -32.3%o_1.9%o, is similar to that of rt-C26.30, at -29.13%o^0.87%o, -32.98%o^1.28%o, and -32.98%o^1.28%o. 1,3,4-C29 triol from the Site4B core sediment and terrigenous long-chain fatty alcohol （n-C26.34） show highly consistent distribution trends in the entire section; thus, the former could serve as a proxy indicator of the terrigenous input. Considering that the 1,20,21-C29 triol in previous research belongs to Azolla, which are fresh water pteridophytes, the 1,3,4-C27-29 triol identified in this study might have similar biogenetic derivation. Thus, determination of its biogenic area and growing environment could provide potential organic geochemical evidence supporting the terrigenous input and source in the northern South China Sea.