鄂尔多斯盆地上三叠统延长组长4＋5油层组中的古地震记录

Paleo-seismic records of Chang 4+5 oil-bearing intervals of the Upper Triassic Yanchang Formation in Ordos Basin

鄂尔多斯盆地上三叠统延长组长4+5油层组湖泊三角洲前缘沉积中同生变形构造十分发育。通过对岩心观察及各种资料的综合分析,认为砂球、砂枕、球—枕构造、微断层递变层、微裂缝、液化卷曲变形等同生变形构造主要是由震积液化作用形成的。震积作用沉积可分为A、B、C、D、E等5个单元,分别组合形成ABCD型、BCD型或CD型、AB型、BCE型或BE型、BEBE型5种沉积序列类型,其中BCD型(CD型)和AB型最为发育。通过对古构造的分析,认为晚三叠世鄂尔多斯盆地拗陷中心的北西向基底"活化"及北西、北东向同生正断层的活动是导致该区古地震形成的主要原因。

Syndepositional deformation structures were well developed in the lacustrine delta front deposits of Chang 4 ＋ 5 oil-bearing intervals of the Upper Triassic Yanchang Formation in the Ordos Basin. It is concluded that these structures, such as sand balls, sand pillows, ball-pillows, graded micro-faults, micro-fissures, liquefied convolute deformation beddings were mainly produced by seismic liquefaction. According to seismite sedimentary characteristics, seismic sedimentary process can be divided into A, B, C, D and E units, which are respectively associated into five sedimentary sequence types, namely as type ABCD, BCD or CD, AB, BCE or BE and BEBE, of which types BCD （CD） and AB are the most dominant types. Through analyses of the palaeo-tectonics, it indicates that the paleo-seismic activities are mainly formed due to the activation of the northwest-trending basement and the activities of the northwest-trending and northeast-trending growth normal faults in the depression center during the Late Triassic in the Ordos Basin.