ARCHITECTURE OF MARINE RIFT-BASIN SUCCESSIONS

Marine rift basins represent a continuum ranging from mixed nonmarine/ marine through shallow marine to deep marine, or from partly emergent through partly submergent to completely submergent basin types. These rift basin types have strongly variable synrift sedimentary architectu res because of temporal changes in relative sea level, accommodation c reation, and sediment supply throughout the rift cycle. Accommodation changes are controlled mainly by local basin-floor rotation, basin-wid e background subsidence, and, to a lesser degree, by eustatic changes. Sediment supply determines how much of the accommodation is filled an d in what manner, and is controlled by the distance to the main hinter land areas, and the size and sediment-yield potential of any local fau lt-block source area. Marine siliciclastic synrift successions, whethe r dominantly shallow or deep marine in nature, are classified in terms of sediment supply as overfilled, balanced, underfilled, and starved. Sediment-overfilled and sediment-balanced infill types are characteri zed by a threefold sandstone-mudstone-sandstone synrift sediment-infil l motif; the sediment-underfilled type is represented by a two-fold co nglomerate-sandstone-mudstone motif; and the sediment-starved ts pe co mmonly is represented by a one-fold mudstone motif. The sequential dev elopment, Linked depositional systems, and stratigraphic signatures of the early synrift, the rift climax, and the late synrift to early pos trift stages vary significantly between these rift basin infill types, as do the tectonic significance (timing of initiation and duration) o f stratal surfaces, such as foot wall unconformities, nondepositional hiatuses, and marine condensed sections. The construction of the fourf old rift basin infill classification scheme provides a first basis and a strong tool for predicting the distribution and geometry of synrift reservoir and source rock types, despite the inherent variability of the marine synrift infills.