西天山伊犁地块北缘早石炭世硅化木的发现及其意义

在西天山伊犁地块北缘琼阿希河谷中首次发现硅化木,对硅化木的基本特征进行了描述。根据地层中腕足、珊瑚化石的鉴定结果,将地层的时代定为早石炭世维宪期,因此该硅化木的产出层位为下石炭统阿克沙克组。硅化木产于阿克沙克组底部黑色薄层状泥岩、粉砂岩中,这套岩性组合形成于扇三角洲前缘水下分流间湾。伊犁地块北缘阿克沙克组底部扇三角洲沉积环境的确定和硅化木化石的发现说明:研究区早石炭世维宪期不是一套连续的海相沉积,而是陆相—海陆过渡相沉积,研究区所处的地理位置距离古陆地不远。这一发现对于重新认识伊犁地块早石炭世古地理和古构造格局具有重要意义。

The discovery of silicified wood in the Early Carboniferous strata on the northern margin of Yili block, West Tianshan, and its significance

Recently silicified wood was discovered for the first time in Qiong Axi valley on the northern margin of Yili block, West Tianshan, and its basic characteristics are described in this paper. The identification of brachiopods and corals reveals that the strata are of the Early Carboniferous Visean stage, and hence the strata that produced silicified wood should be the Lower Carboniferous Akeshake Formation. Silicified wood was found in the black thin-bedded mudstone and siltstone formed in the subaqueous interdistributary estuary of the delta front. The determination of fan delta facies and the discovery of silicified wood show that the study area was characterized by a continental or transitional facies sedimentation instead of a continuous marine facies sedimentation during the Early Carboniferous Visean stage. It is also proved that the ancient geographical position of the study area was not far from the old land. This new discovery is of great significance for re-understanding Early Carboniferous paleogeography and paleotectonic framework of Yili block.