A record of dust deposition in northern, mid-latitude Pangaea during peak icehouse conditions of the late Paleozoic ice age

The Wordiekammen Formation, a carbonate ramp on Spitsbergen developed on the Northern Pangaean margin in Moscovian (Carboniferous) through Sakmarian (Permian) time at a paleolatitude of 30–35° N. The study site on the Nordfjorden High was isolated from any source of fluvio-deltaic input, such that detrital material that occurs in this system experienced eolian transport, thus forming a proxy for atmospheric dust loading. We analyzed two intervals, of Moscovian (10 m) and Asselian (27 m) age, at 20 cm resolution, and identified five mid-ramp subtidal facies organized in upwardly shallowing, high-frequency sequences 3–5 m thick. High-frequency sequence boundaries commonly exhibit signs of subaerial exposure (e.g., Microcodium) developed atop subtidal facies, recording glacioeustatic falls (glacial phases), although the Moscovian section has a severe karst overprint attributable to prolonged exposure on a paleohigh. Samples were processed to isolate the silicate-mineral fraction (SMF), which includes both detrital silicate material and authigenic silica mostly in the form of (fine-sand-size) doubly terminated quartz crystals. Detrital cores in these crystals, together with other evidence, indicate recrystallization from fine-grained (silt- and clay-size) dust. Analysis of the dust record demonstrates that the Asselian (peak icehouse) had a significantly higher atmospheric dust load than the Moscovian (moderate icehouse). In the Asselian interval, dust input varies commensurate with glacial–interglacial cyclicity. Highest dust contents correspond to transgressive facies immediately above sequence boundaries, indicating peak atmospheric dust loading at lowstand to incipient interglacial times. Provenance data from detrital-zircon and whole-rock geochemistry indicate two distinct source regions for the dust. Dust from the Moscovian and lower Asselian intervals reflects a continental island-arc signature consistent with sourcing from the basement of northeast Greenland. Dust from the upper Asselian interval is more consistent with recycling from Devonian and Carboniferous strata of the east Greenland Caledonides, likely deflated from fluvial systems draining this orogenic system, indicating an expansion of regions of eolian deflation.