Triassic to Early Jurassic climatic trends recorded inthe Jameson Land Basin, East Greenland: clay mineralogy, petrography and heavy mineralogy

During the Early Triassic the Jameson Land Basin (Central East Greenland) was located around 30 degrees N, in the Northern arid belt, but by the Early Jurassic was positioned at a latitude of approximately 50 degrees N. This study examines the record of this transition through a largely continental succession using clay mineralogy, sedimentology, petrography and heavy mineralogy. The Jameson Land Basin is aligned north-south and is 280km long and 80km wide. Following an Early Triassic marine phase the basin was filled by predominantly continental sediments. The Early-to-Late Triassic succession comprises coarse alluvial clastics (Pingo Dal Formation) overlain by a succession of fine-grained evaporite-rich playa/lacustrine sediments (Gipsdalen Formation), indicative of arid climatic conditions. The overlying buff, dolomitic and then red lacustrine mudstones with subordinate sandstones (Fleming Fjord Formation) record reduced aridity. The uppermost Triassic grades into dark organic-rich, and in places coaly, mudstones and buff coarse-grained sandstones of lacustrine origin that belong to the Kap Stewart Group, which spans the Triassic-Jurassic boundary, and appear to record more humid climatic conditions. Clay mineralogy analyses highlight significant variations in the kaolinite/illite ratio, from both mudstone and sandstone samples, through the Triassic and into the earliest Jurassic. Complementary heavy mineral analyses demonstrate that the variations recognised in clay mineralogy and sandstone maturity through the Triassic-Early Jurassic succession are not a product of major provenance change or the effect of significant diagenetic alteration. The observed variations are consistent with sedimentological evidence for a long-term trend towards more humid conditions through the Late Triassic to Early Jurassic, and the suggestion of a significant pluvial episode in the mid-Carnian.