First record of Brachyoxylon wood from Upper Jurassic of Sichuan Basin, Southwest China and its paleoenvironmental significance

Abstract

Diverse and abundant foliage fossils are well known and well documented from the Upper Triassic to the Lower and Middle Jurassic of the Sichuan Basin in Southwest China. Yet, the fossil record of Upper Jurassic plants in this region is sparse. Decades ago, hundreds of fossil wood specimens were unearthed from the Upper Jurassic in the central part of the Sichuan Basin, offering important insights into the region’s past terrestrial ecosystems and paleoclimate. Despite their significance, systematic studies of these fossils have been limited. Here, we describe the anatomy of a fossil wood specimen from the Upper Jurassic Penglaizhen Formation in Shehong City, Sichuan Province. The specimen displays key Brachyoxylon features, including mixed radial tracheid pitting in conjunction with araucarioid cross-field pitting. This is the first record of the coniferous wood Brachyoxylon in the central Sichuan Basin. Paleoclimatic evidence from associated leaves, pollen, and sediments, suggests that these trees thrived under generally warm and semi-arid to arid conditions, likely in riparian and lacustrine environments with local water abundance, as indicated by the growth rings with narrow latewood bands.