湘东南桂阳莲塘上泥盆系风暴岩特征及其古地理、古气候意义

The Upper Devonian Tempestites from Liantang,Guiyang,Southeastern Hunan Province and Its Palaeogeographic and Palaeoclimatic Significance

湖南省桂阳县莲塘镇石龙村上泥盆统锡矿山组以台地相灰岩、白云质灰岩、灰质白云岩为主。该组下部发育典型的风暴岩沉积。风暴沉积标志包括:渠铸型、竹叶状砾屑放射状组构、丘状或洼状交错层理、平行层理、递变层理、块状层理。风暴岩包括4种岩相类型:A-具块状层理的"竹叶状"砾屑灰岩(底部为冲刷侵蚀面或冲刷渠),B-具递变层理的砾屑灰岩,C-具丘状、洼状交错层理的砂屑灰岩,D-具均质或水平层理的泥状灰岩。它们组成4种典型的风暴沉积序列:A—D序列、A—C—D序列、B—C—D序列、B—D序列。湘东南上泥盆统风暴岩的首次发现表明晚泥盆世该区位于低纬度的风暴作用带,它对认识泥盆纪的古气候具有重要意义。

The Upper Devonian Xikuangshan Formation in Shilong, Liantang, Guiyang county, southeastern Hunan Province consists of limestones, dolomites, dolomitized limestones and lime dolomites of platform facies, in which typical tempestites develop. The criteria of storm deposits conclude bottom gutter casts, radial fabric of ＂wormkalk＂ calclrudite, hummocky or swaley cross bedding, parallel bedding, massive bedding and graded bedding. The tempestites consist of 4 types of lithofacies： A-＂ wormkalk＂ calclrudite with massive bedding and bottom gutter casts. B- ＂wormkalk＂ calclrudite with graded bedding. C-calcarenite with hummocky or swaley cross-bedding and parallel bedding. D- mudstone with homogeneous or horizontal bedding. These lithofacies constitute 4 types of depositional succession： A-D succession, A-C-D succession, B-C-D succession and B-D succession. The storm deposits indicate that southeastern Hunan locate in platform to shelf of low latitude zone（5° -20°） in the Late Devonian. The discovery of the storm deposits has important significance for the interpretation of the palaeoclimate of Devonian.