Sedimentary architecture during Carboniferous rift initiation — the arid Billefjorden Trough, Svalbard

Analysis of the sedimentary architecture of the early Billefjorden Trough, an exceptionally well exposed Carboniferous half-graben located in Svalbard, Arctic Norway, allows detailed reconstruction of fault development and basin geometry. Sedimentary facies distribution reveals facies variability in an early syn-rift fill, when an array of meso-scale intra basinal faults segmented the basin into rotated blocks with differential subsidence. Growth of these faults into larger systems impacted the distribution of accommodation space and the drainage pattern expressed in fluvial and deltaic sandstone-dominated units. An axially back stepping character of the early syn-rift facies associations (Stages 1–3) is reflected in aggrading homogenous facies types of continental depositional Stage 1, which evolved into back-stepping facies belts of deltaic to nearshore depositional environment, Stages 2 and 3, due to the opening of a connection to the sea. The drainage pattern and accommodation distribution in the early syn-rift deposits reflect a relatively symmetrical basin that predates a later prominent half-graben configuration of the basin.