Advanced analysis of basins along the Vietnamese margin and the greater region: Central Vietnam's Neogene carbonate platform development

For close to 20 years, Vietnamese geology and hydrocarbon prospectivity have been studied by the ENRECA research team (VPI/Petrovietnam & GEUS). During the course of this study, on- and offshore basins from the Hanoi Trough in the north to the Malay-Tho Chu basin in the south have been analysed. The research carried out includes amongst others tectonic, depositional, petrographic, geochemical, provenance and uplift analysis. In this paper, the ENRECA-work is exemplified by a study of Neogene carbonate growth along the central Vietnamese margin.
Miocene carbonate platforms cover a large part of the Central Vietnam’s East Vietnam Sea margin. Early carbonate deposition took place on two regional platforms separated by a narrow depression developed along the trace of the East Vietnam Boundary Fault Zone. West of the East Vietnam Boundary Fault Zone, the Tuy Hoa Carbonate Platform fringes the continental margin between Da Nang and Nha Trang. Here, platform growth initiated during the Early Miocene and continued until Middle Miocene time when regional uplift led to subaerial exposure, termination of platform growth and karstification. East of the fault zone, the Tri Ton Carbonate Platform was also initiated during the Early Miocene. Carbonate growth thrived during Early and part of Middle Miocene time and a thick, clean Lower and Middle Miocene carbonate succession covers the Tri Ton Horst and the Quy Nhon ridge. During the Middle Miocene, partial drowning resulted in the splitup of the Tri Ton Carbonate Platform. Repeated partial drowning events throughout the Middle and Late Miocene resulted in westwards retreat of platform growth and eventual platform drowning and termination of carbonate deposition. Modern carbonate growth continues on isolated platforms hosting the Paracel Islands farther seawards. The onset of widespread carbonate deposition largely reflects the Early Miocene transgression of the area linked with early post-rift subsidence and the opening of the East Vietnam Sea. The mid-Neogene shift in carbonate deposition is interpreted as a consequence of regional uplift and denudation of central and south Indochina starting during Middle Miocene time when the Tuy Hoa Carbonate Platform became subaerially exposed. Stressed carbonate growth conditions on the Tri Ton Carbonate Platform probably resulted from increased inorganic nutrient input derived from the uplifted mainland, possibly enhanced by deteriorated climatic conditions and rapid sea-level fluctuations promoting platform drowning.