Oxfordian (Jurassic) mayaitid (ammonite) dispersal in the Tibetan Himalaya as the first signal of the establishment of the Indo-Austrai subrealm

New fossil collections in the Lanongla area, Tibetan Himalaya enables the establishment of the Upper Jurassic ammonoidsuccession. Middle Oxfordian ammonite-fauna is characterized by endemic epimayaittds with a marine deepening event, suggesling a high stand of sea Ievel in the Tibetan Himalaya. Distribution of mayaitids around the Eastern Gondwana can be regarded as the first signal of the Indo-AustraI Subrealm that was progressively established during the Late Jurassic and Early Cretaceous times.     

Oxfordian (Jurassic) mayaitid (ammonite) dispersal in the Tibetan Himalaya as the first signal of the establishment of the Indo-Austral subrealm

New fossil collections in the Lanongla area, Tibetan Himalaya enables the establishment of the Upper Jurassic ammonoid succession. Middle Oxfordian ammonite-fauna is characterized by endemic epimayaitids with a marine deepening event, suggesting a high stand of sea level in the Tibetan Himalaya. Distribution of mayaitids around the Eastern Gondwana can be regarded as the first signal of the Indo-Austral Subrealm that was progressively established during the Late Jurassic and Early Cretaceous times.     

恰什古伊地区碳氧同位素地层学分析

土库曼斯坦恰什古伊地区有效储集层为卡洛夫-牛津阶碳酸盐岩,该段GR 变化小,旋回分析困难,导致
有利储层预测难。利用该区Cha–21 井所取岩芯中采集的41 个样品测定的碳氧同位素,结合区域沉积演化分析资
料,探讨了卡洛夫-牛津阶储层段沉积时的海平面变化。结果表明,氧同位素的原始信息已被成岩作用破坏,而碳
同位素基本保持了原始特征,因此碳同位素可用于同位素地层研究和古环境分析;据此计算出盐度指数变化范围为
128.25～136.63,明显大于海水和淡水的分界标准,反映成岩流体具有较高盐度海源水性质;由δ13C 的变化所确定的研
究区的海平面变化曲线与卡洛夫-牛津阶全球海平面变化曲线吻合,印证了该区储层地质年代定为卡洛夫-牛津期
是准确的;依据海平面变化曲线,将卡洛夫-牛津阶主力储层段分为3 个沉积旋回5 个演化阶段。该成果填补了该区
碳氧同位素地层研究的空白,对深化盆地沉积演化规律的认识及预测储层有利区块具有重要意义。