福建泰宁世界地质公园丹霞红层研究

福建省泰宁世界地质公园以典型的年青期丹霞地貌为其地质特色,丹霞地貌由晚白垩世沙县组和崇安组红层构成。考察确认在金湖风洞一带的崇安组红层底部含较厚的流纹质火山岩夹层,这在福建全省境内是唯一的,从而为确定丹霞红层的准确时代提供了可能。研究表明,崇安组底部的火山岩由两次流纹质岩浆爆发性喷发形成,测得其锆石LAICP-MSU-Pb法年龄为98.52±0.96Ma,说明丹霞红层主体的形成时代为早、晚白垩世之交,而非以往认为的晚白垩世中—晚期,因此对华南丹霞红层的形成时代及其地质背景应重新审视,这一新认识对国内其他以丹霞地貌为特色的地质公园也同样有参考价值。

RED BEDS OF DANXIA LANDFORM IN THE TAINING GEOPARK,FUJIAN PROVINCE

The Taining Geopark in Fujian is characterized by young Danxia landform consisting of red beds of the Cretaceous Shaxian Formation and Chongan Formation.A thick volcanic interbed occurs in the lower Chongan Formation in the Fengdong area near the Jinhu Lake.This is the only volcanic interbed in the Chongan Formation in Fujian Province and provides an opportunity to determine the accurate age of the Danxia red beds.The volcanic interbed was formed in two episodes of rhyolitic eruptions , and gives a zircon LA ICP-MS U-Pb age of 98.52±0.96Ma.Thus , the Danxia red beds of the Taining Geopark were deposited at the transition between the Early and Late Cretaceous , rather than in the middle-late stage of the Late Cretaceous as proposed previously.The age and geological setting of Danxia red beds in South China need to be reconsidered.The new data from Fujian Province are also valuable in the study of other Chinese geoparks of Danxia landform.