The Frasnian-Famennian (F-F) boundary occurs within the Upper Devonian Xom Nha Formation in Quang Binh Province, Central Vietnam. The stratotype section of the Xom Nha Formation (bed numbers Xo 1-39) comprises carbonates, and is divided into Unit I (Xo 1-13) mainly composed of whitish-gray bioclastic grainstone and wackestone, Unit II (Xo 14-28) dominated by bioclastic packstone and wackestone, and Unit III (Xo 29-39) characterized by weakly parallel laminated gray to dark gray lime-mudstone. Units I-III commonly contain well-preserved conodonts and ostracods. Some horizons of Unit II yield brachiopods, ammonoids, nautiloids, bivalves, tentaculitoids, crinoids and acritarchs. Age diagnostic conodont species of the Frasnian Palmatolepis linguiformis is commonly obtained from the upper part of Unit II. Unit III yields Pa. delicatula that is characteristic of the lowermost Famennian Pa. triangularis conodont Biozone. Two positive carbon isotope excursions are recognized, the lower excursion peaking in Unit I whilst the upper excursion peaks just below the local Frasnian-Famennian boundary (bed number Xo 28). Based on the biostratigraphy, these excursions equate to the Lower and Upper Kellwasser events. In the upper part of Unit II (Pa. linguiformis Biozone, bed numbers Xo 16-23), relatively diverse marine assemblages are recognized, indicating a temporal recovery of ecosystem after the Lower Kellwasser Event. By contrast, the diversity of lowermost Famennian marine organisms decreased markedly after the Upper Kellwasser event.

The Upper Cretaceous Himenoura Group and the Eocene Shiratake Formation of the Miroku Group distributed in the Amakusa Islands, Kumamoto Prefecture, are known as having oil showing and oil smell since long ago, and, therefore, these strata are inferred to have petroleum potential. So, in order to evaluate source rock potential of mudrocks from the Himenoura Group, a geological survey and organic geochemical analyses by Rock-Eval pyrolysis were carried out on the Himenoura mudrocks distributed around Kojima, Himedo Town, Kami-Amakusa City, Kumamoto Prefecture.

The Middle Member of the Santonian Hinoshima Formation of the Himenoura Group is distributed in the study area, and it is composed mainly of massive dark-gray mudstone with some thin layers of very fine-grained sandstone and tuff. The mudrocks have TOC (Total Organic Carbon) ranging from 0.65 to 1.10 wt%. The values of Rock Eval S₁ (the amount of free hydrocarbon), S₂ (the amount of pyrolysis hydrocarbon) and S₃ (the amount of pyrolytic carbon dioxide) are 0.02-0.13 mg_HC/g_Rock, 0.12-0.36 mg_HC/g_Rock, and 0.12-0.63 mg_CO2/g_Rock, respectively. Further, Tmax ranges from 460 to 534°C, indicating that these rocks are at the stage of postmature. The above facts that the substantial amount of the organic matter still remain in the Himenoura mudrocks in spite of at the already postmatured stage at present suggest that those rocks had the high potential of petroleum productivity primalily, and that the hydrocarbon which were produced at the early burial stage had already spilled out or moved to some reservoir rocks.