四川盆地川西北地区首次发现下白垩统七曲寺组脊椎动物化石组合及其古环境意义

摘要:四川盆地川西北地区下白垩统七曲寺组长期缺乏脊椎动物化石佐证,时代归属、地层划分及古环境演化争议突出。本研究实测绵阳市8条剖面(总长65.4 km),于七曲寺组第5段(K₁q⁵)至第7段(K₁q⁷)首次发现69件脊椎动物化石组合,含泰坦龙类(蜥脚类)、异特龙超科(兽脚类,驰龙科可能性不排除)、辐鳍鱼类、龟鳖类等,伴生双壳类19枚、介形类36枚(核心组合Rhinocypris—Pinnocypridea—Darwinula)及8类遗迹化石(含Skolithos、Scoyenia等)。结合介形类标准化石与多学科分析,将七曲寺组时代精准限定为早白垩世巴雷姆阶—阿普特阶(125—110 Ma),修正了部分研究的时代模糊判定。沉积相分析表明,该组为“辫状河—曲流河—滨湖”多相沉积,古环境呈温暖湿润向半干旱过渡的间歇性干旱特征,发育古土壤与事件性洪水沉积记录,修正了白垩纪红层“单一干旱”的传统认知;同时证实原剑阁组与七曲寺组为“同期异相”,解决了区域地层辨识度低的争议,填补了东亚四川盆地早白垩世脊椎动物化石组合的区域记录空白,为东亚陆相生物群多样性演化提供了关键线索。 Abstract (English) The Lower Cretaceous Qiqu Temple Formation in the northwestern Sichuan Basin has long lacked vertebrate fossil evidence, leading to prominent controversies regarding its age assignment, stratigraphic subdivision, and paleoenvironmental evolution. In this study, 8 sections (total length 65.4 km) in Mianyang City were measured, and 69 vertebrate fossil specimens were discovered for the first time from the 5th (K₁q⁵) to 7th (K₁q⁷) members of the Qiqu Temple Formation. The assemblage includes titanosauriforms (sauropods), allosauroids (theropods, with dromaeosaurid affinities not excluded), actinopterygians, and testudines, associated with 19 bivalve specimens, 36 ostracod specimens (with the core assemblage Rhinocypris—Pinnocypridea—Darwinula), and 8 types of trace fossils (including Skolithos and Scoyenia). Combined with ostracod index fossils and multidisciplinary analyses, the age of the Qiqu Temple Formation is precisely constrained to the Early Cretaceous Barremian–Aptian (125–110 Ma), correcting the ambiguous age determinations of some previous studies. Sedimentary facies analysis indicates that the formation represents a multi-phase sedimentary system of "braided river–meandering river–littoral lake," with paleoenvironmental conditions characterized by intermittent aridity transitioning from warm and humid to semi-arid, evidenced by paleosol development and episodic flood deposits. This revises the traditional view of the Cretaceous red beds as representing a "single arid" environment. Furthermore, this study confirms that the original Jiange Formation and the Qiqu Temple Formation are "contemporaneous heterofacies," resolving the controversy of low regional stratigraphic distinguishability. It fills the regional gap in Early Cretaceous vertebrate fossil assemblages from the Sichuan Basin in East Asia, providing key clues for the evolutionary diversity of East Asian continental biotas.