秦岭核桃坝石炭系深水相遗迹化石,沉积环境和古地理分析

研究剖面位于陕西凤县核桃坝，构造上属秦岭造山带的商丹缝合带。核桃坝剖面下部为浅海陆棚相粉砂岩、泥灰岩和灰岩；中、上部以重力流沉积为主。在中部浊积岩中产遗迹化石：Ｎｅｒｅｉｔｅｓ ｆｅｎｇｘｉａｎｅｎｓｉｓ ｉｃｈｎｏｓｐ．ｎｏｖ．，Ａｃａｎｔｈｏｒｈａｐｈｅ ｃｆ． Ａ． ｉｎｃｅｒｔａ Ｋｓｉａｚｋｉｅｗｉｃｚ，Ｃｈｏｎｄｒｉｔｅｓ ｉｃｈｎｏｓｐ．，Ｐｌａｎｏｌｉｔｅｓ ｉｃｈｎｏｓｐ．等。其

CARBONIFEROUS DEEP-WATER TRACE FOSSILS, SEDIMENTARY ENVIRONMENTS AND PALEOGEOGRAPHY AT HETAOBA IN THE QINLING MOUNTAINS

Situated at Hetaoba of Fengxian County, Shaanxi Province, the studied section tectonically belongs to the Shangdan suture zone of the Qinling orogen. The lower part of the Hetaoba section consists dominantly of siltstone, marl and limestone of neritic shelf fades; while its middle and upper parts are composed mainly of gravity flow deposits. The turbidites in the middle yield trace fossils:Nereites fengxianensis ichnosp. nov. , Acanthorhaphe cf. , A. incerta Ksiazkiewicz, Planolites ichnosp. and Chondrites ichnosp. Of these, Chondrites, which is small in size and scanty in quantity, occurs in greyish black silty mudstone, representing a foreset trace fossil assemblage and displaying dysaerobic or anaerobic conditions. Other trace fossils all occur on the surface of moderately thick-bedded sandstone, representing the Nereites facies of the backset trace fossil assemblage. There were formed in an abyssal fan environment. Sedimentary and pa- . leontological evidence indicates that before the middle Late Carboniferous the bottom of deposition was gentle and that the waters were relatively shallow and well connected with seawaters in other areas of South Qinling. Later, owing to the influence of extension, the landform in the Hetaoba area became progressively steep and the waters became deep, thus receiving deposits of turbidity current and mass-gravity transport.