ATTRIBUTES OF A CRETACEOUS STORM BED FROM SPITSBERGEN, NORWAY

A distinctive 15-50 cm thick horizon occurs at a consistent stratigraphic position within the Aptian, Carolinefjellet Fm. of Spitsbergen. 4 of the localities studied are along a 28 km stretch on the S side of Adventdalen, while the 5th is at Festningen, 45 km to the W. The bed displays basal scour, and is typically normally graded with basal grits or conglomerates. Upper and/or middle portions show well developed planar lamination, and at Festningen, climbing ripples indicate offshore transport. Fragments of molluscs (especially scaphopods), forams, echinoderm plates and spines, and plant fragments are common. Clasts include a great variety of fine-grained carbonate hardgrounds, concretions (including glendonites), altered basaltic and chert lithics, and quartz and plagioclase grains. Carbonate cements found selectively on the underside of large clasts and in sheet cracks are interpreted as an early authigenic phase formed in pockets caused by decay. Overall, these traits are consistent with deposition by a storm-surge-related, return flow current in deep enough water that subsequent reworking by storm waves did not occur. Due to storm 'sampling' and quick burial the bed is particularly rich in paleo-environmental information. Stratigraphically, the bed occurs in the transition between the shallow marine, sand dominated Dalkjegla Member, which is dominated by wave reworking, and the overlying, finer-grained, deeper water Innkjegla Member, and the contact can be interpreted as a parasequence flooding boundary. It is usually a singular horizon, although at one locality, two beds occur in close stratigraphic proximity. The highest such storm bed makes a convenient and meaningful marker to define the top of the Dalkjegla Member, which is otherwise described as transitional. In the Aptian, Spitsbergen was at paleolatitudes in excess of 60 degrees. The glendonites and a high content of plagioclase in the sands are consistent with a high-latitude, colder climate. However, abundant plant fragments indicate significant terrestrial plant biomass in the source to the NW. Oscillation ripple marks and longshore drift indicates the prevailing Aptian wind directions were generally out of the ENE, consistent with generation by a polar high.