Jurassic biota and biofacies in erratics from the Sortland area, Vesterålen, northern Norway
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- Artikler 
Erratic blocks occurring on the shore at Sortland, northern Norway, consists of fine-to coarse-grained siliclastics, in places conglomeratic, which exhibit signs of large-scale cross-bedding or, less commonly, are bioturbated. The blocks contain either abundant plant debris (which indicate fluvial environments or at least a strong terrestrial influence) or shells and shell debris of a variety of marine benthic organisms. Most common are bivalves, followed by serpulids, gastropods, brachipods and echinoid spines. Belemnites constitute the only nektic element. The benthic fauna occurs scattered, as shell pavements, or in small lenes. Altogether 39 taxa were identified, and one of them (Lopatinia (Paralopatinia) sortlandensis sp. nov) is new. The remaining taxa are typical elements of boreal faunas elsewhere (e.g., East Greenland, northern Russia) and suggest av Volgian age of most, if not all, of the boulders with shelly remains at Sortland. This age is supported by 87Sr\/86Sr isotope ratios of oyster shells. The benthic fauna is grouped into eight assemblages, nearly all of them exhibiting signs of reworking and\/or transport. Together with their sediments they form characteristic biofacies. These represent environments ranging from shallow-water, high-energy, nearshore areas above the fair-weather wave-base to offshore, quieter environments. Most likely, deposition took place in a fault-controlled coastal area, on tilted fault blocks, and thus mirrors the situation on the opposite (western) margin of the Arctic Seaway in the Late Jurassic.