新疆西准噶尔洪古勒楞组与泥盆系-石炭系界线新知

New knowledge on the Hongguleleng Formation and Devonian-Carboniferous boundary in western Junggar,Xinjiang

通过对西准噶尔地区洪古勒楞组多条剖面的综合研究,提出洪古勒楞组与上覆黑山头组以钙质碎屑岩的消失、暗色细火山碎屑岩的出现为界,其顶界为一套近岸浅水沉积的碎屑岩(含舌形贝的钙质粉砂岩、凝灰质砂岩、细砾岩或含介壳的砂砾岩),称之为"杨庄砂岩",该界线在多条剖面上易于识别和对比。在洪古勒楞组上部和黑山头组下部发现三叶虫9属(亚属)14种:Omegops sp.,Pudoproetus sp.,Linguaphillipsia?sp.,Belgibole sp.,B.abruptirhachis,Philliboloides sp.,Winterbergia(W.)sp.,W.(Eowinterbergia)sp.,Weberiphillipsia sp.,Conophillipsia sp.1,C.sp.2,C.sp.3,C.paucicostata,C.morganensis。根据三叶虫生物地层学研究,认为西准噶尔地区存在泥盆系-石炭系界线,界线位置在Omegops的消失层位和Belgibole-Conophillipsia组合带的首现层位之间,该界线与洪古勒楞组和黑山头组之间的界线基本一致。洪古勒楞组顶部的"杨庄砂岩"是泥盆纪末期海平面下降事件在西准噶尔火山岛弧背景下的沉积产物,也是泥盆纪-石炭纪之交Hangenberg事件在西准噶尔地区的体现。

Based on a comprehensive research on several sections of the Hongguleleng Formation in western Junggar, the boundary between the Hongguleleng and Heishantou Formations was proposed at the disappearance of calcareous clastic rocks and the appearance of dark fine-grained volcanoclastic rocks. The uppermost part of the Hongguleleng Formation is a suite of clastic rocks(calcareous siltstones with ‘Lingula’, tuffaceous sandstones, granule conglomerates, or sandy conglomerates with shellsdeposited in the backshore environment, and is named the "Yangzhuang Sandstone". The boundary between the two formations can be easily identified and correlated in many stratal sections. Nine genera(or subgenera) and 14 species of trilobites were collected from the upper part of the Hongguleleng Formation and the lower part of the Heishantou Formationincluding Omegopssp. Pudoproetussp. Linguaphillipsia sp. Belgibole sp. B.abruptirhachis Philliboloides sp., Winterbergia(W.)sp., W.(Eowinterbergia) sp., Weberiphillipsia sp., Conophillipsia sp.1, C.sp.2, C. sp.3, C. paucicostata, and C. morganensis. According to the biostratigraphy of trilobitesthe Devonian-Carboniferous boundary was established in western Junggar and is placed between the disappearance level of Omegops and the appearance level of the Belgibole-Conophillpsia assemblage zone. The Devonian-Carboniferous boundary is in accordance with the boundary between the Hongguleleng and Heishantou Formations. The "Yangzhuang Sandstone" resulted from a sea-level fall event that happened at the end of Devonian in the island-arc context, and is also the embodiment of the Hangenberg event during the Devonian-Carboniferous transition in western Junggar.