LATE JURASSIC PETRIFIED FORESTS IN XINJIANG, CHINA: INVESTIGATIONS OF ANATOMY, TAPHONOMY AND PALEOCLIMATE

The Junggar Basin in Xinjiang, northwest China contains various petrified forests, which are mainly distributed in the Jiangjunmiao area of northern Qitai County. The petrified trees are preserved in the lower part of the Upper Jurassic Shishugou Group of the fluvial deposit containing abundant silicified tree stumps and logs, showing variations in log size and thicknesses of the well preserved growth rings. An investigation is being carried out in order to carefully study the wood anatomy to determine if the trees predominately represent one species or various species. We hope to determine the systematic relationships for each fossil log. Preliminary investigation shows that, at least four fossil conifer genera can be identified including Araucaryoxylon, Cupressinoxylon, Protopiceoxylon and Xenoxylon. The taphonomy of the deposition of these fossil logs and tree stumps, and the ecology of the ancient forests in which they grew, are being investigated using multiple approaches, such as sedimentlogy, field mapping of the fossil stumps and logs, wood growth in relationship to habit analysis and the identification of the fossil wood types in relation to their positions with in the sediments. In addition, the relationship between fossil logs and wood rotting fungi as well as possible animal interactions are being considered in this investigation. The annual growth ring analysis of the various fossil wood indicates that seasonal climate variations (mega-monsoonal climate) existed during the early Late Jurassic of the Junggar Basin. This result coincides with the histological evidence of dinosaur (sauropods) bones which are preserved in association with the fossil forest, that show growth cycles. These dinosaur bone growth cycles probably reflect the seasonal nature of the early Late Jurassic climate in the Junggar Basin.