Abstract The Silurian-Devonian (mid-Paleozoic), a time of periodic, exceptional sea level highstands, vast epicontinental sea lanes, and global greenhouse climates well above Holocene norms, also identifies ihe ma ximal extent of Phanerozoic metazoan reef development and the acme of coral and sponge reef biodiversity Two peaks are identified for reef distribution, a mid-Silurian (Wenlock) maximum and a Mid- to Late Devonian (Eifel-Givet-middle Frasne) maximum, with reefs spread to latitudes as high as 45 lo 60 degrees, and major barrier-platform tropical reef belts stretched over more than 2000 km. Reef abundance broadly matched patterns of rise and fall in generic biodiversity for (he major cneiazoan reef builders (corals and stromatoporoids) and algae during this 80 million year episode. The mid-Paleosoic reef community originated in the Late Ordovician, taking over from the Cambro-Ordovician mud mound-dominated reef spectrum. It was only modestly affected by the glaciation-induced end-Ordovician(Hirnantian) mass extinction events Late Devonian reef extinction losses were initiated al the Givetian-Frasnian boundary by major declines in coral, stromatoporoid, and brachiopod bentliic components Reefs then experienced a second global expansion in the middle Frasnian, but with reduced faunal diversity. Catastrophic reef declines began in the late Frasnian rhenana conodont Zone and continued through the final lingurformis Zone, with events probably lasting ca.l Myr.Thecorat-stromatopofoid reef community was eliminated worldwide, with surviving patch reefs and reefalrnud mounds in ihe Famennian constructed by consortia of catcimicrobes, lifhisrid sponges, green and red algae, and foraminiferans. The surviving Famennian corals were primarily solitary, deep-water forms that played no major reef role. The last stramatoporoids died out within the Strunian praesuicata Zone, at the Devonian -Carboniferous boundary Widespread organic-rich carbonates of Civetian through Famennian age, normally taken as indicative of anoxia, do not show any correlation with local or global reef declines The Frasnian-Famennian extinction events foi reefs and reef faunas appear to have been second only to the end-Permian reef losses in terms of severity Metazoan reef extinction in the Late Devonian best parallels evidence for Famennian glaciarions, loss of reef accommodation space assealevels fell, 3nd increasing oxygenation of the atmosphere via the evolution of the first pteridophyte rainforests, forcing the terminal Famennian icehouse phases

Abstract The surface geology of NE Thailand consists almost entirely of Jurassic to Mid-Cretaceous Khorat Group red-beds. During the last 30 years, however, hydrocarbon exploration has resulted in 40 deep wells being drilled through the Khorat Group cover into an extensive system of Late Triassic (Kuchinarai Group) and Mid–Carboniferous to earliest Late Permian (Saraburi Group) basins. The sedimentary fill of these basins has proved to be similar to the Upper Carboniferous–Triassic strata which crop out to the west and SW in the Loei–Phetchabun Fold Belt (Fig. 9.1 ). In addition, an extensive grid of two-dimensional (2D) seismic lines covers almost the entire region (Fig. 9.2 ) and can be used to map out the basin systems containing the Saraburi and Kuchinarai Groups. Most of the seismic and well data have been released by Thailand’s Department of Mineral Fuels and, wherever possible, reference is made only to these open-file reports. The reader should bear in mind that a large part of the geological history presented in this chapter is a synthesis of work that was conducted by many different oil company and government geologists. However, much of this work has never been published and is only recorded in company reports (often without the names of the authors). Consequently, proper reference cannot be made to many of the geologists who conducted this pioneering work. At the present day the so-called Khorat Plateau is in reality a relatively flat plain, generally 150-200 m above sea level, rimmed by low mountains and a