On the basis of the analysis of the sub-bottom profile gathered from the north part of Okinawa trough in 1994 and 2000, large area of oblique bedding delta depositions and buried-channels were found in the area near t...On the basis of the analysis of the sub-bottom profile gathered from the north part of Okinawa trough in 1994 and 2000, large area of oblique bedding delta depositions and buried-channels were found in the area near the continental break, which provides the new evidence for the existence of large rivers from the mainland of China entering Okinawa trough during the last period of Late Pleistocene.The sub-bottom profile data show that two sets of the strata characterized by large scale and low angle foreset reflection beddings, appearing as delta deposition, were found in the neritic strata of continental break in the west side of the north part of Okinawa Trough. The existence of large scale of foreset oblique bedding is one of the most important symbols indicating the existence of delta. An erosion surface exits between the two layers of the delta depositions. In the profile these delta sand bodies can reach more than 10 km in length and 30～70 m in thickness. The water depth there is 110～200 m at present, being deep in the north and shallow in the south. The width of the buried channel ranges from several kilometers to over 10 km in general. The discovery of such a large scale of estuarine deposit structure in the survey area has a great significance. Delta deposition lies in two areas. The one in the south is small with the area of 7500km2 and the one in the north is bigger with the area of tens of thousand square kilometers. The main part of the delta body lies in the side of continental shelf near break, with forepart acrossing the break and reaching the upper part of the continental slope.Several of buried channel sections with obvious characteristics of incision and filling reflection configuration were discovered in the area to the west of and in the paleo-deltas distribution area, which reaches more than 10km wide in the profiles, with the incision depth up to 20m. Most of these channels lie in the west or northwest of the delta deposition area, forming an integrated river deposition system. This phenomenon proves that the delta sand bodies came from big rivers of China. The filling of the channels happened in the postglacial trangressive epoch.In the most prosperous period of Wurm Glacial Stage,sea level had descended about 130～150m. Corresponding to the seabed geomorphology here, the fore part of the paleo-delta is just at the location of the ancient coastline. The fore part just lay in the location of the ancient coastline where the depth was about 150m. Buried paleo-delta discussed in this paper was likely formed during that period.According to the dimension of the delta, it can be concluded that the river forming the delta was very big; According to the location, it can be deduced that they were likely the Changjiang River or the Yellow River.展开更多
文摘On the basis of the analysis of the sub-bottom profile gathered from the north part of Okinawa trough in 1994 and 2000, large area of oblique bedding delta depositions and buried-channels were found in the area near the continental break, which provides the new evidence for the existence of large rivers from the mainland of China entering Okinawa trough during the last period of Late Pleistocene.The sub-bottom profile data show that two sets of the strata characterized by large scale and low angle foreset reflection beddings, appearing as delta deposition, were found in the neritic strata of continental break in the west side of the north part of Okinawa Trough. The existence of large scale of foreset oblique bedding is one of the most important symbols indicating the existence of delta. An erosion surface exits between the two layers of the delta depositions. In the profile these delta sand bodies can reach more than 10 km in length and 30～70 m in thickness. The water depth there is 110～200 m at present, being deep in the north and shallow in the south. The width of the buried channel ranges from several kilometers to over 10 km in general. The discovery of such a large scale of estuarine deposit structure in the survey area has a great significance. Delta deposition lies in two areas. The one in the south is small with the area of 7500km2 and the one in the north is bigger with the area of tens of thousand square kilometers. The main part of the delta body lies in the side of continental shelf near break, with forepart acrossing the break and reaching the upper part of the continental slope.Several of buried channel sections with obvious characteristics of incision and filling reflection configuration were discovered in the area to the west of and in the paleo-deltas distribution area, which reaches more than 10km wide in the profiles, with the incision depth up to 20m. Most of these channels lie in the west or northwest of the delta deposition area, forming an integrated river deposition system. This phenomenon proves that the delta sand bodies came from big rivers of China. The filling of the channels happened in the postglacial trangressive epoch.In the most prosperous period of Wurm Glacial Stage,sea level had descended about 130～150m. Corresponding to the seabed geomorphology here, the fore part of the paleo-delta is just at the location of the ancient coastline. The fore part just lay in the location of the ancient coastline where the depth was about 150m. Buried paleo-delta discussed in this paper was likely formed during that period.According to the dimension of the delta, it can be concluded that the river forming the delta was very big; According to the location, it can be deduced that they were likely the Changjiang River or the Yellow River.
