辽西义县下白垩统沙海组木化石新材料*

辽西地区下白垩统沙海组是我国北方地区重要的白垩纪木化石产出层位,其产出的木化石数量丰富、类型多样.尽管前人开展了部分研究,但目前对沙海组木化石植物群组成特征的认识仍相对薄弱.本文报道了辽西义县上石洞沟地区沙海组产出的木化石新材料,共鉴定出2属3种,分别为:Phyllocladoxylon cf.eboracense(Holden)Kr?usel、Xenoxylon conchylianum Fliche 及 X.watarianum Nishida and Nishida.此发现丰富了对沙海组木化石多样性特征的认识,为揭示辽西地区早白垩世晚期的森林组成特征提供了新的化石证据.本文总结了辽西地区早白垩世木化石的多样性特征,从木化石的角度推断辽西地区在早白垩世中晚期森林植被面貌可能发生了一定程度的更替.此外,本文对比了辽西地区侏罗纪及白垩纪异木属木化石种级多样性,认为该属在辽西地区晚中生代一直是优势类群,但种级组成上差异明显.

New record of petrified wood from the Lower Cretaceous Shahai Formation in Yixian of western Liaoning, Northeast China

The western Liaoning region is known as one of the most significant fossil wood localities in China with diverse and abundant Cretaceous petrified woods. The Early Cretaceous petrified wood bearing horizons, including the Yixian, Jiufotang, Shahai and Fuxin formations, are relatively continuous. Among them, the most abundant wood fossils are found from the Shahai Formation. Though some studies have been carried out previously, the composition of the fossil wood flora of the Shahai Formation remains poorly understood. In this paper, we report some well-preserved fossil woods from the Shahai Formation in Shidonggou village of Yixian County, Liaoning Province. Three species referable to two genera are identified, i.e., Phyllocladoxylon cf. eboracense (Holden) Kr?usel, Xenoxylon conchylianum Fliche and X. watarianum Nishida and Nishida. Among them, Phyllocladoxylon cf. eboracense is anatomically characterized by having distinct growth rings, uniseriate distant radial pits, and one large oopore per cross-field. Xenoxylon watarianum is featured by the presence of distinct growth rings, typical xenoxylean radial pitting, window-like cross-field pits, and a low ray height of 1?10 (mostly 2?5) cells. Then for X. conchylianum, it also bears xenoxylean radial pitting and window-like cross-field pits, but with a higher ray height of 1?21 (mostly 3?10) cells. The current new finding contributes to further understanding of the fossil wood diversity of the Shahai Formation and provides new fossil evidence for revealing the forest composition in western Liaoning during the late Early Cretaceous. The diversity of the Early Cretaceous wood fossils in western Liaoning are summarized. From the perspective of the wood fossils, it is inferred that the forest vegetation may have undergone some degree of changes during the transition of the middle to late Early Cretaceous in western Liaoning. In addition, this paper analyzes the species-level diversity of the Jurassic and Cretaceous Xenoxylon in western Liaoning area, and proposes that this genus was a dominant group all through the late Mesozoic. However, there is a difference in species-level composition between the Jurassic and Cretaceous intervals.