Quaternary petrified trunks from Kamphaeng Phet, Thailand: Implications for past climate and preservation

Petrified trunks in Mueang Kamphaeng Phet District, upper Central Thailand, were unearthed in Quaternary deposits on the western rim of the Ping River. The sediments consist mainly of semi-consolidated gravel, sand, silt, and clay, indicating that the woods were transported by the ancient Ping River. Macroscopic features revealed that preservation of these fossils (e.g., intercellular spaces, iron oxides, quartz crystals, colors, and weathering conditions) shared many similarities to some petrified trunks in Tak Province. We investigated both large (approx. 0.50–0.7 m wide, at least 10–20 meters long) and small fragments of fossils for both wood anatomical features and mineralogy. Diffuse porosity with indistinct growth rings and wide vessels at low densities suggest a tropical lowland forest paleoenvironment. Parenchyma patterns are aliform to confluent, banded, and diffuse-in aggregate. At least four distinct types of wood were recognized from this site. Among them, three wood types originate from legume trees (Fabaceae), while the fourth is from a eudicotyledonous tree. Two of the three legumes show closest resemblance to a tall (canopy emergent) legume tree, Koompassia cf. malaccensis Maingay ex Benth. and one resembles the legume Koompassia cf. malaccensis or cf. Pahudioxylon bankurensis Chowdhury, Ghosh, et Kazmi. The other legume-like wood shows banded parenchyma. Petrified wood from Kamphaeng Phet is correlative with other Quaternary paleofloras found in Northern Thailand in both preservation and taxa. The past climate, as inferred according to the Köppen-Geiger classification, was possibly similar to modern-day tropical rainforests (Af) in southern Thailand, Malaysia, and Indonesia in contrast to the modern vegetation in Mueang District, Kamphaeng Phet that is a mixed deciduous and dry dipterocarp forest where the modern climate in the area is tropical wet and dry (Aw).