Accretionary, forced regressive shoreface sands of the Holocene-Recent Skagen Odde spit complex, Denmark - a possible outcrop analogue to fault-attached shoreface sandstone reservoirs

Spit systems are often important components of Recent deltas and coastal plains, where waves redistribute fluvial-derived sediments and they show large variations in terms of size, volume and grain size. However, spit systems are likely to form along any wave-influenced coastline and may form where faulted terrains of poorly to moderately lithified rocks are exposed to wave erosion. In such areas large spit systems are likely to be formed down-current from fault escarpments, along fault crests and on fault ramps, but appear to have been overlooked in the geological record. The Holocene-Recent Skagen Odde spit complex has developed within the last 8000 years and is still growing. The most important factors that have governed its growth are well-known, including climate, sea-level changes, palaeo-relief, free fetch, tidal range, progradation and sediment transport rates. The spit system has developed down-current from a steep slope comparable to a fault escarpment. It shows a triangular form with sides of 30-40 km and it contains 5-10 km³ of sand. The main part of the spit system consists of five sedimentary units that constitute a shallowing-upward shoreface succession: (lower) storm sand; bar-trough sand; beach sand; peat and (upper) modern aeolian sand. The succession was formed during a forced regression as uplift outpaced eustatic rise. As the average basin-floor gradient has been steeper than the shoreline trajectory, the accommodation increased during basinward progradation of the spit system, and the resulting succession represents an accretionary, forced regression. The spit-system model may serve as an analogue to ancient fault-related shoreface sandstones without associated fluvial or deltaic deposits.