The Sung-Len Bac Mountain Section is one of the best section to study stratigraphy and paleontology of the Middle-Upper Devonian, Lower Carboniferous to Middle Permian sediments in North-central Vietnam, including formations in the ascending order: The Dong Tho Formation (D2-3 dt) is composed of silstone and quartz sandstone, 250m thick containing fish Bothiolepis sp, brachiopod? Holynetes caurongensis, tentaculite Homoctenus sp, plant Lepidodendropsis sp. of the Late Givetian-Early Frasnian. The Xom Nha Formation is composed of stylolitic limestone, 20m thick containing conodonts of the Palmatolepis glabra Zone of the Famennian age. The La Khe Formation is composed of silstone, shale, sandstone, cherty limestone bearing abundant crinoids, brachiopods, ammonoids, trilobites, plants of the Viséan age. The Muong Long Formation is composed of thick-bedded limestone over 1000m thick, containig foraminifers Millerella, Eostafella, Quydatella, Fusulinella, Obsoletes, Triticites, Schwagerina, Robustoschwagerina, Misellina, Neoschwagerina; and brachiopod Phricodothyris asiatica of the Carboniferous-Middle Permian age. An abundant fossil assemblage of plants Archaeocalamites sp., Sigillaria sp., Lepidodendron sp. associated with brachiopods Plicatifera sp., Chonetes sp., Lingula sp.; bivalve Mytilarca sp.; ammonoids Sulcogirtyoceras cf. limatum, Neoglyphioceras sp.; trilobites Linguaphillipsia cf. subconical, Phillipsia propiqua of nearshore facies has been found in the upper part of the La Khe Formation by the Hanoi Fossil Museum in 2022.