晚白垩世介形类壳体稳定同位素尝试——以松科1井南孔样品为例

Attempt to the Late Cretaceous Ostracod Carapace Stable Isotope Measurement——Case Study on the SK1 Drill Cores

白垩纪中期的全球温室气候引发的迅速同位素波动具有全球的同期性,可作为地质历史中气候变化的替代指标。在诸多陆相沉积体系中,湖泊沉积记录保存了相对连续的古气候信息,是恢复陆相高分辨率古环境和古气候演变的有利依据。松辽盆地为大型白垩纪沉积盆地,对其研究可以提供大陆内部的古气候信息。对白垩纪稳定同位素的研究常采用全岩样品的分析手段。然而,陆相湖盆同位素组成复杂,全岩样品难免受多种因素的干扰。尝试利用松科1井连续的介形类壳体为材料获取原生碳酸盐,为稳定同位素的高精度古气候恢复提供有效指标。尝试的首要工作是仔细开展采样分析、化石壳体挑选和受成岩影响样品的排除的每一步骤。在实体显微镜下精心剥离出纯净的化石壳体,然后对纯净壳体、含充填物壳体和围岩3种样品进行抽样对比,印证实验所用的介形类化石样品的可靠性,明确化石材料受成岩作用影响微弱。测试结果显示,松科1井介形类壳体碳氧同位素保存了长期连续的气候历史记录,深入研究能为中国甚至东亚白垩纪同期陆相研究提供稳定同位素标准序列。

Rapid isotopic variation affected by Late Cretaceous green-house is of globe implication,and can be used as proxy of climate change in the Earth＇s history.In continental sedimentary system,relatively continuous paleoclimate signal is recorded in lacustrine sediments.It is an ideal record to recover high-resolution paleoenvironment and paleoclimate changes.The Songliao lacustrine basin is a large Cretaceous sedimentary basin.A coring program,the＂Cretaceous Continental Scientific Drilling Programme of China（SK1）＂,was initiated to the study of Cretaceous climate change.Under this programme,an ambitious effort is now underway to develop an oxygen and carbon isotopic record for a nearly complete Cretaceous lacustrine section in the Songliao basin to reveal paleoclimate change in inner-continental area.Bulk samples were normally used to the Cretaceous stable isotope analysis.The compositions of terrestrial stable isotopes are complicated and can be affected by various factors.The present authors attempt to select ostracod carapaces as analytical materials.As a result,ostracods were handpicked from samples collected from drill cores.After removing them from rock matrix,the ostracod carapaces,matrix and filling materials were then visually examined for possible secondary calcite,such as sparry calcite,respectively.The result indicates that ostracod carapaces are avoided from secondary calcite and /or diagenesis.They are reliable materials for the isotopic study.Specifically,we demonstrate that the carbon and oxygen isotopes recorded in the ostracod carapaces of the Songliao basin seemingly track the corresponding contemporaneous isotopic records during Late Cretaceous.The isotopic curves will be the criterion of terrestrial isotopic succession in China after detailed study.