Abstract:
ODP Site 1144 (20 degrees 3.18'N,117 degrees 25.14'E, water depth 2037 m) is located on the northern margin of the South China Sea. The core was sampled continuously through the microtektite layer every 1-2 cm. Many microtektites were collected from sediment samples at depths of 386.17-386.27 mcd. More than 969 microtektites and 1 543 fragments scatter across a 10 cm interval were recovered from ODP Site 1144. The number of microtektites per square cm was estimated to be at least 7100/cm (super 2) , and approximately 61% of the microtektites are fragments. All microtektites are transparent to translucent and are entirely glassy. The color varies from dark brown to pale yellow. They are mostly spherical and oval in shape and have a great deal bubbles in these glassy spheres. The composition of these microtektites falls well within the range defined for Australasian ones and agrees with the normal microtektites. The Oxides diagrams show that there is a negative relationship between Al (sub 2) O (sub 3) , TiO (sub 2) , FeO, MgO and SiO (sub 2) . The result show original materials of microtektites must the terrestrial. Based on the geographic variation in the concentration and percentage fragments of Australasian microtektites, the source crater is probably further to the northeast and more close proximity of South China than previously predicted. These new occurrences suggest that the size of the crater is estimated to be 50-140 km.