New Records Of Petrified Wood From The Lower Cretaceous Shahai Formation In Yixian Of Western Liaoning,NE China

Petrified wood plays an important role in revealing the composition and evolution of the plant kingdom in geological past.The in-depth study of wood fossils can not only enrich the understanding of the floral diversity of the geological history,but also provide evidences for understanding the palaeoclimate,palaeoenvironment and palaeoecological characteristics of its survival period.The Lower Cretaceous Shahai Formation in western Liaoning is one of the most important horizons for fossil wood in northern China,and it yields a variety of gymnosperm wood fossils.However,fossil woods from the Shahai Formation were just sporadically studied and poorly understood.In this paper,a systematic study is carried out on the fossil wood remains from the Shahai Formation in Yixian County,western Liaoning Province,NE China.A total of six species of five genera of fossil coniferous wood were described and identified,including 1 species of 1 genus of Podocarpaceae(Phyllocladoxylon cf.eboracense(Holden)Kr?usel,1919),1 species of 1 genus of Pinaceae(Keteleerioxylon yixianense sp.nov),2 species referred to 2 genera of Cupressaceae(Cupressinoxylon sp.and Taxodioxylon sp.),and 2 species of the form gneus Xenoxylon(i.e.,X.watarianum Nishida & Nishida,1986 and X.conchylianum Fliche,1910).The discovery of the above-mentioned new materials brings the total number of reported wood fossils from the Shahai Formation in this area to 13 species of 9genera,which further enriches our understanding of the diversity of wood fossils from the Shahai Formation.This paper summarizes and analyzes the fossil diversity of the Late Mesozoic Xenoxylon species in western Liaoning.The results show that although Xenoxylon has abundant fossil records in both the Jurassic and Early Cretaceous in the western Liaoning,the Xenoxylon of the two time intervals shows significant differences in the species-level composition.This paper systematically analyses the temporal and spatial distribution characteristics of the Early Cretaceous wood in the western Liaoning area,and preliminarily discusses the composition and succession characteristics of the early Cretaceous forest plants in the western Liaoning.In addition,using the principle of dendrochronology,the statistical analysis of series of parameters which are of palaeoclimatic implications,including the early/late wood ratio(E/L),annual sensitivity(AS)and mean sensitivity(MS),were carried out.The results show that the paleoenvironment in which fossil woods grew at that time had obvious seasonal changes.It is worth noting that some of the fossil wood remains of the Shahai Formation studied herein have typical wood decay characteristics,which are very similar to those of the modern white pocket rot caused by white rotting fungi.The new discovery represent the first Cretaceous record of such kind of wood rot in China,and provides key evidence for understanding the decay characteristics of wood in the Cretaceous.