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.