et al. - สืบค้น แบบ ไล่ เรียง - กรมทรัพยากรธรณี

RevisedLithostratigraphy of the Kaeng Krachan GroupBy Pol ChaodumrongBureau of Geological Survey, Department of Mineral ResourcesABSTRACTLithostratigraphy of the Kaeng Krachan Group is revised here, due to controversial ontheir unit names, ages and their depositional environments, including to conform guideline of theInternational Commission on Stratigraphy. As a result, 18 of the Kaeng Krachan sections and 2sections from the underlying strata, from Kanchanaburi southward through peninsular Thailand,have been investigated in detail for their lithostratigraphy, paleontology and sedimentology.Reviews of all previous work are included. The revised Kaeng Krachan Group ranging in agefrom Asselian to Kungurian and consists of 5 formations, which are in ascending order the LaemMai Phai, Spillway, Ko He, Khao Phra and Khao Chao Formations. However, the SpillwayFormation occurs locally. Nine clastic lithofacies have been designated. The lower part of theAsselian to Kungurian Kaeng Krachan Group was deposited by gravity flow sediments, possiblyin submarine fan environment, in outer shelf and basin plain areas under glaciomarine conditionsas indicated by abundant Cruziana ichnofacies and rare dropstones. The upper part wasshallow marine with occasional storm deposits.The Kaeng Krachan Group is overlain conformably by carbonate sequence of the RatburiGroup. These two distinctive megasequences crop out widely from Malaysia, through peninsularThailand, Myanmar, West Yunnan, to Lhasa. A Late Carboniferous hiatus is proposed for theShan-Thai terrane. Neither Late Carboniferous fossils nor the relationship of the Kaeng KrachanGroup with underlying strata have been observed which probably indicates a Late Carboniferouserosional phase. The Shan-Thai terrane rifted from Gondwana not later than the Early Permian.Evidences from paleocurrent directions, provenance of clasts, and grain size distribution, allsuggest a roughly eastward (modern-day) paleoflow direction. These also imply that the riftedbasin was a half graben in which the escarpment on the Gondwana side. Keywords: Kaeng Krachan Group, Laem Mai Phai Formation, Spillway Formation, Ko He Formation, Khao Phra Formation, Khao Chao Formation, Late Carboniferous hiatus, Shan-Thai terrane