Paleoproterozoic and Mesoproterozoic sedimentary and volcanic successions in the northern parts of the East Greenland Caledonian orogen and its foreland

The crystalline basement within the northern parts of the Caledonian orogen, and in the adjacent foreland, is overlain by a several-kilometer-thick succession of sedimentary and volcanic rocks, the Paleoproterozoic- Mesoproterozoic Independence Fjord Group and the Mesoproterozoic Zig-Zag Dal Basalt Formation. The lowermost strata of the Independence Fjord Group, composed of quartzitic and feldspathic sandstones and conglomerates with interbedded volcanic rocks, occur within the Caledonian orogen and are strongly deformed. These strata were deposited around 1740 Ma ago, and they were associated with a period of rifting that succeeded a long sequence of Paleoproterozoic orogenic events. Similar sandstones, interbedded with siltstone units but without volcanic rocks, are widespread in the Caledonian foreland, where they are virtually undeformed. These foreland deposits were laid down in a continental sag basin under semiarid conditions. Sedimentary structures indicate a largely fluvial origin, with intermittent eolian transport. The siltstones were deposited in extensive shallow lakes. Desiccated bedding surfaces show that these periodically dried out. The sandstones of the Independence Fjord Group are cut by a multitude of doleritic sheets and dikes, the ca. 1380 Ma Midsommersø Dolerites, and more silicic intrusions, most of which show evidence of hydrothermal alteration and variable contamination with components derived from the crystalline basement and the sandstones. Some intrusions consist almost entirely of crustally derived material. The Zig-Zag Dal Basalt Formation conformably overlies the Independence Fjord Group. Compositional similarities suggest a genetic relationship with the Midsommersø Dolerites, but the basalts appear to be less crustally contaminated. The basalts were deposited within a basin that underwent subsidence during and after volcanic activity. The Zig-Zag Dal Basalt Formation is unconformably overlain by Neoproterozoic sedimentary successions. The unconformity represents a stratigraphic hiatus of some 500 m.y., for which no information is available from North Greenland.