苏北盆地高邮凹陷古近系戴南组一段元素地球化学特征及其地质意义

Geochemical Characteristics of the 1st Member of Paleogene Dainan Formation in Gaoyou Depression of the North Jiangsu Basin, and Its Geological Significance

苏北盆地高邮凹陷所经历的风化作用以物理风化为主,化学风化程度很弱。其中南部陡坡带的大部分地区所经历化学风化程度相对北部缓坡带较强,说明古气候条件更为温暖潮湿;北部缓坡带及黄珏、邵伯地区所经历的物理风化作用相对较强且差异较大,说明曾经历较强的构造运动。研究区源岩主要为长英质物质和再旋回沉积物质,受中基性物质的影响较小。高邮凹陷边缘及吴堡低凸起附近地区戴一段下部地层具有下伏阜宁组地层的海相地化特征,因此研究区物源中可能有较多部分来自基底母岩被剥蚀和再旋回沉积的产物。地化数据反映研究区构造背景为安第斯型活动大陆边缘,由于地史及动力学机制的差异,其构造背景有别于东太平洋典型的安第斯型活动大陆边缘,可反映我国东部大陆边缘特殊的地体构造特征。

The type of weathering experienced in Gaoyou depression of North Jiangsu basin was mainly physical weathering. In the depression, the degree of chemical weathering suffered in the majority of the southern step-fault zone was more intensive and the paleoclimate was relatively warmer and damper than those in the northern counterpart. On the contrast, in the northern slope zone, including Huangjue and Shaobo area, the provenance underwent strong weathering or severe tectonic movement for having caused rapid denudation and fast sedimentation in the depression. Mother rocks in Gaoyou depression are mainly felsic rocks and recycling sedimentary deposits, containing little intermediate-basic magmatic source rocks. In strata of the 1st Member of Dainan Formation, the margin of Gaoyou depression and its neighbouring Wubao salient contained marine features that are similar to the underlying Funing Formation. Hence, we deduce that the majority of source rocks in studied area come from denuded original basement and recycling sedimentary deposits. Geochemical data display that the tectonic setting of studied area is included in the Andean-type continental margin. We deem that this tectonic setting of North Jiangsu basin reflects a special tectonics of East China and is differed to the typical Andean active continental margin of the eastern Pacific Ocean, for the big divergence between these two regions no matter in geologic history or in dynamic mechanism.