The Hoanh Bo Trough‐a landward keyhole to the syn‐rift Late <scp>Eocene–Early</scp> Oligocene terrestrial succession of the northern Song Hong Basin (onshore north‐east Vietnam)

Located on the northern Vietnam onshore/offshore transition, Hoanh Bo Trough is an excellently exposed terrestrial Palaeogene sedimentary sequence that may be treated as analogue for regional interpretations of and structural evolution Song Hong Basin. The lies to north Basin west Beibuwan Basin, origin which are linked with South China Sea rifting. Field archival well sedimentological observations were made throughout succession Trough, samples collected palynological, petrographical, geochemical analysis. Based coexistence particular lithofacies, proximal alluvial fan, distal fluvial plain channels, and/or lake margin, lacustrine facies associations distinguished. Palynological analyses suggest infill Late Eocene–Early Oligocene age was deposited in a very warm tropical/subtropical climate. In turn, results demonstrate deposits have intermediate chemical maturity probably reworked from older rock sources. Moreover, it suggested combine Dong Ho Tieu Giao formations synonymize them Formation. pattern, age, climatic conditions, align rift initiation, development, termination tectonic system tracts. could landward keyhole offshore basins: instance, Kien An