Coarse‐grained, marine, sub‐wave base, high‐angle clinoform sets: A little‐known outcrop facies illustrated by Jurassic examples from East Greenland

Abstract

AbstractOutcrops of coarse‐grained, high‐angle clinoform sets are mainly thought to represent Gilbert‐type deltas. Superficially similar clinoform sets may, however, form in marine, sub‐wave base settings. They are interpreted to have formed as a result of storms where downwelling, seaward‐directed currents transported sand from the coastal area and shoreface across the shelf in suspension or as bedload to be deposited as clinothems. An additional transport of sand took place by strong coast‐parallel currents. The clinoform sets appear to be associated with rift events, the creation of accommodation space and an increasing supply of coarse‐grained sediment. A major protracted rift phase was initiated in East Greenland in Middle Jurassic times and intensified through the Late Jurassic to reach a climax close to the Jurassic–Cretaceous boundary. Rifting caused uplift of borderlands, creation of accommodation space and development of shallow marine shelves passing offshore into submarine slopes and deeper basinal areas. Each rift event was accompanied by the formation of clinoform sets prograding seawards towards the east and southeast away from the cratonic coastline in water depths below the wave base. The clinoform sets are interpreted as typical motifs for rift events in the relatively shallow epeiric Jurassic seaway between East Greenland and Norway. Outcrops of such sets represent a little‐known, commonly misinterpreted sedimentary system and may serve as motifs for rifting in shallow marine areas elsewhere in the geological record. Similar sets have been recorded in outcrop from the Mediterranean, and elsewhere and are probably more common than hitherto realized.