Palaeoenvironmental significance of trace fossils from the shallow marine Lower Jurassic Neill Klinter Formation, East Greenland

Abstract

The shallow marine deposits of the Lower Jurassic Neill Klinter Formation of East Greenland contain a diverse assemblage of well-preserved trace fossils. Thirty-four ichnotaxa are distributed among 11 different ichnocoenoses, characterized by Diplocraterion habichi, Diplocraterion parallelum, Arenicolites isp. 1, Arenicolites isp. 2, Cochlichnus, Curvolithos, Taenidium, Ophiomorpha, Rhizocorallium, Phoebichnus and Planolites. The ichnocoenoses are interpreted in the light of their trophic and ethological properties and show a strong correlation with the sedimentary environments. Their distribution reflects changes in factors controlled by water depth and bottom water oxygenation. Evidence fo opportunitic recolonization following major environmental changes has also been preserved. The Diplocraterion paralellum ichnocoenosis occurs typically in foreshore and shoreface environments as well as tidal sandwave field environments on the inner shelf. Together with Diplocraterion habichi ichnocoenosis it also characterizes transgressive surfaces where they form omission suites. The Cochlichnus ichnocoenosis has the highest diversity and is characteristic of tidally-influenced rippled inner shelf environments. The Phoebichnus ichnocoenosis occurs in oxygen-limited shelf environments that were exploited thoroughly by a population of opportunistic organisms. The Curvolithos ichnoceonosis occurs in the distal portion of subaqueous fan delta environments and in open shelf settings and the Arenicolites isp. 2 ichnocoenoesis in the proximal portion of subaqueous fan delta environments. The Planolites, Rhizocorallium, Taenidium, Ophiomorpha and Arenicolites isp. 1 ichonocoenoses are characteristic of storm-dominated shelf environments. The ichnocoenoses of the Neill Klinter Formation are taxonomically identical, or nearly so, to the trace fossil assemblages of other marine Jurassic and Lower Cretaceous sandstones of East Greenland. They often occur in similar lithofacies, which underlines their use in palaeoenvironmental interpretations.