Mesozoic fossil wood of Kiên Giang Province, southwestern Vietnam

摘要

New fossil wood from the youngest Mesozoic continental red beds referred to as the "Grès supérieurs" (or "Upper Indosinias") of the Phú Qu?c and Th? Chau Islands (Kiên Giang Province, southwestern Vietnam) is described. The fossil wood samples belong to Agathoxylon saravanensis (Serra) Philippe et al., and Protophyllocladoxylon xalucense sp. nov. Moreover, Cycadeanoxylon pteridospermoides, originally discovered in the Pleistocene terrace "+40 m" of the Mekong River, was also found in the Th? Chau Island. These species, in addition to Brachyoxylon orientale (Serra) Philippe and Prototaxoxylon asiaticum Serra already known from this region, complete our understanding of the arborescent diversity. The discovery of A. saravanensis and B. orientale and associated angiospermous pollen grains in the Th? Chau Islands suggests an Early Cretaceous age for the "Upper Sandstones" of southern Vietnam. Thanks to the reappraisal of thin sections of several holotypes and a literature review, we propose a synthetc table summarizing the Mesozoic southeastern Asiatic species of Protophyllocladoxylon and Agathoxylon. Numerous degradations of the wood structures are associated with the presence of wood-decay fungi, which can be used to infer their attack strategies on wood. Tylosis was also noticed in Protophyllocladoxylon. Finally, some climatic and ecological characteristics are inferred from the observation of the fossil woods as well as from published palynological analyses.