doi:10.16186/j.cnki.1673-9787.2020.2.4

Received:2019/06/15

Revised:2019/08/02

Published:2020/03/15

The Origin of calcareous concretions in the upper part of the Sunjiagou formation ofUpper Permian in Yiyang area，western Henan province and its indicatingsignificance to paleoclimate

ZHENG Deshun, QI Shuaishuai, YANG Wentao, WANG Yanpeng, LI Yu

Institute of Resources and Environment， Henan Polytechnic University ，Jiaozuo 454000 ， Henan， China

Abstract:As one of the important records in the sedimentary strata， calcareous concretions contain abundant paleoclimate informations. In this paper， the calcareous concretions in the upper part of the upper Permian Sunjiagou formation in the Yiyang area of western Henan were selected as the research object， and their characteristics and causes were studied by petrology and geochemistry to recover the coeval paleoclimate. The results showed that ： （1 ） Calcareous concretions in the upper member of the Sunjiagou formation could be divided into two types according to different petrological characteristics. The type I concretions distributed at the bottom and top were mainly purplish red， grayish yellow mass and ginger knot. The origin of type I concretions were formed by CaCO§ saturated precipitation， dissolution and metasomatism during the late diagenesis. The type II concretions were mainly khaki ellipsoid， which had concentric texture and obvious boundary with surrounding strata in the middle and upper parts. The origin of type I concretions were due to the continuous precipitation of carbonate after saturation and affection by cementation nucleation， which continuously grew from core to outside. （2） The variable characteristics of carbon and oxygen isotopes， paleosalinity “ Z value" ，" S value“ of the type I concretions indicated that the upper strata was closed brackish water-saltwater lacustrine deposits. The paleoclimate features were mainly hot-arid and semi-arid. （ 3 ） The occurrence of calcareous concretions in the upper member of the Sunjiagou formation from the Yiyang area indicated that the paleoclimate changed from warm and humid to hot and arid during the late Permian. This study was of important significance to reveal the change of terrestrial paleoclimate at the end of the Permian.

Key words:Late Permian;Sunjiagou Formation;calcareous concretion;paleoclimate;Yiyang areawestern

豫西宜阳地区上二叠统孙家沟组上段_省略_质结核成因及其对古气候的指示意义_郑德顺.pdf