Triassic to Early Jurassic climatic evolution in East Greenland: mudstone and sandstone archives of the past

The Jameson Land Basin lies between 70º and 72ºN in East Greenland. However, during the Early Triassic Central East Greenland was located around 30ºN, in the Northern arid belt, and reached a latitude of about 60ºN by the Late Jurassic. This northward drift through different climatic zones had a major influence on mudstone and sandstone composition throughout the Triassic and Jurassic.

The Jameson Land Basin is aligned north-south and is about 280 km long and 80 km wide. The Triassic fill comprises an initial marine turbidite succession (Wordie Creek Formation) which shallows up into coarse clastics of continental origin. These continental clastics consist of alluvial sediments at their base (Pingo Dal Formation) which are, in turn, overlain by a succession of fine-grained, evaporate-rich playa/lacustrine sediments (Gipsdalen Formation) followed by a succession of red mudstones with subordinate sandstones deposited in lacustrine and fluvial environments (Fleming Fjord Formation). The uppermost Triassic grades into dark organic rich, and in places coaly, mudstones and buff coarse-grained sandstones of lacustrine origin which belong to the Kap Stewart Group and occur across the Triassic-Jurassic boundary. The lower to middle Jurassic succession comprises the marine Neill Klinter Group.

Clay mineralogy analyses highlight significant variations in the kaolinite/illite ratio, from both mudstone and sandstone samples, through the Triassic-Jurassic. This observed variation is consistent with sedimentological evidence for a trend towards more humid condition through the Late Triassic to Early Jurassic as well as for a significant pluvial period during the mid Carnian. Furthermore, petrography data show a similar trend in compositional maturity through the succession. Significant stratigraphic variations in provenance have also been recognised through the Triassic, using heavy mineral analysis.

Understanding the impact of variations in climate, and changes in provenance, on sandstone maturity is key for hydrocarbon reservoir prediction in adjacent basins.