【Title】THE DISCOVERY AND GEOLOGICAL SIGNIFICANCE OF PEBBLY MUDSTONE IN THE MIERS BLUFF FORMATION IN LIVINGSTON ISLAND, WEST ANTARCTICA
【摘要】西南极南设得兰群岛利文斯顿岛赫德半岛中分布的一套主要由复理石相岩石组成的低级变质沉积岩（迈尔斯陡崖组）被认为是中－ 新生代火山岩的基底（晚古生代－ 早中生代？）。以前含砾泥岩在迈尔斯陡崖组局部地点曾有零星报道，但详细的地质填图确认此地有四层含砾泥岩分布。研究表明，这些含砾泥岩可能是水下碎屑流沉积，其生成环境可能是海底扇中扇的水道。对比在南极半岛所发现有大量的含砾泥岩，则进一步表明利文斯顿岛早期地质特征可与南极半岛相比，两者在中－ 新生代岩浆弧形成之前处于相同的构造环境。
【Abstract】Livingston Island constains several distinctive sedimentary and volcanic sequences, which document the history and evolution of an important part of the South Shetland Islands magmatic arc. The sedimentary sequence is named the Miers Bluff Formation (MBF) and is interpreted as turbidite since the first geological study on South Shetland Islands. It base and top are not exposed, but a thickness of more than 3000m has been suggested and seems plausible. The turbidite is overlain by Mid-Cretaceous volcanic rocks and intruded by Eocene tonalites. The Miers Bluff Formation and its correlatives, including Trinity Peninsula Group(TPG) in Graham Land, Antarctic Peninsula and Greywacke-Shale Formation (GSF) in South Orkney Islands, display the same lithology and tectonic style, share a common provenance and possibly the same age, but the age is poorly constrained Late Carboniferous-Early Triassic. The pebbly mudstone is common in the TPG, but is scarce in MBF outcrops. In the 1997-1998 year field exploration, four pebbly mudstone layers are distinguished near the Spanish Antarctic Base-“Juan Carles I” Station in Hurd Peninsula, Livingston Island. These layers of pebbly mudstone are massive and no-traction flow structure, and usually over ten meters thick and contain great amount of igneous,sedimentary and metamorphic pebbles. In general, grained size is 4-7 cm, the largest pebble is up to 85 cm, but the bigger pebbles(>50cm) are sparse and are preserved near upper surface in common. Their sorting is bad but their psephicity is well-rounded. These layers of pebbly mudstone are sharply contact with thickened sandstones, they are common in the MBF. The pebbly mudstone is the typical rock of debris flow, may belongs to sediments in the mouth of canyon, the channel of and upper and middle fan of submarine fan and the boundary between the deep sea basin and steep slope. Meanwhile, the depositional environment of MBF is the upper and lower of mid-fan of submarine fan. Hence, the depositonal environment of pebbly mudstone may be the channel of mid fan of submarine fan. MBF has the same tectonic setting, therefore, as the TPG, may be the same history of sedimentary and metamorphism as TPG, too, and Livingston Island contacts with Antarctic Peninsula before the formation of Mesozoic-Cenozoic magmatic arc.