南极利文斯顿岛上三叠统Miers Bluff组及其与相当地层对比

南极南设得兰群岛利文斯顿岛 Miers Bluff组 (MBF)是一套岩层倒转、强烈变形、浅变质的浊流沉积地层 ,主要由砂岩、泥岩、粉砂岩及含砾砂岩组成 ,具有很好的韵律层 ,形成鲍玛序列 ,通常被认为属于近海底扇浊流沉积 ,并当作中新生代火山岩的基底。最近发现的孢粉化石指明其时代属晚三叠世 ,从而解决了久来时代的疑问(石炭—三叠纪 ,二叠—三叠纪 ,或前侏罗纪 )。分布在南极半岛格雷厄姆地的特里尼蒂半岛群、南奥克尼群岛的杂砂岩—页岩组、智利南部乔诺斯群岛乔诺斯变质杂岩的 Potranca组以及新西兰惠灵顿的 Torlesse杂岩应是时代相当、岩性及沉积环境相似的岩层。三叠纪末受太平洋板块俯冲影响 ,这一浊流地层褶皱、变形、隆升 ,具有相同的构造风格 ,是冈瓦纳古陆在侏罗纪早期开始裂解前夕一次构造事件的重要佐证

Upper Triassic Miers Bluff Formation of the Livingston Island,Antarctica and its Stratigraphical Correlations with Adjacent Areas

The Miers Bluff Formation (MBF), cropping out at Hurd Peninsula on Livingston Island, consists mainly of greywacks, mudstones, siltstones and pebbly mudstones, attaining a thickness of about 3000 m. The strongly deformed and low graded metasedimentary sequences are interpreted to be turbidite deposits of submarine fan. It is composed of, in ascending order, the Johnsons Dock Member, the Napier Peak Member and possibly the Moores Peak breccias. The age of the formation is poorly constrained ranging from late Paleozoic to early Mesozoic due to lack of identifiable fossils. Plant microfossils have been found from the MBF, including a total of about 45 species (forma) referred to 37 genera of miospores. The sporadic occurrence of Aratrisporites and Classopollis as well as the absence of bisaccate striatiti indicates that the age of the MBF should not be older than Noirian and possibly ranges from Norian to Rhaetian. Abundant organic matter including rich wood fragments (tracheids) in the MBF appears to show that the sedimentary site was not far apart from the land. The luxuriant parentflora with diverse pteridophytes seems to indicate a warm and humid climate. The MBF may be synchronous with those turbidite sequences represented by such formations as the Hope Bay, the Paradise Harbour and the Cape Legoupil of the Antarctic Peninsula and the Greywake Shale of South Orkney Islands, the Portranca Formation in Chile as well as the upper Torlesse Complex in New Zealand. All of these might have been contemporaneously deposited under similar tectonic style just prior to the break up of Gondwana in earlier Jurassic times.