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Abstract

El’gygytgyn is a 18 km diameter, 3.6 Ma old impact crater in NE Siberia. International Continental Scientific Drilling Program—El’gygytgyn hole 1C was drilled on the frozen crater lake, 2.3 km from the crater center to a final depth of 517 m below the lake floor. Petrographic and geochemical analyses of 26 drill core samples, three impact melt rocks from the surface, and seven glass spherules from surface deposits outside the crater are used to characterize the impactite inventory at El’gygytgyn. The bottom 98 m of hole 1C intersected monomict brecciated, unshocked, rhyolitic ignimbrite with minor intercalations of polymict breccia and mafic inclusions. These lithologies are overlain by 89 m of polymict breccia whose components occasionally exhibit scarce, low-degree shock metamorphic features. This unit is succeeded by 10 m of suevite that contains about 1 vol% glassy impact melt shards <1 cm in size and a low amount of shock metamorphosed lithic clasts. The suevite is capped by a reworked fallout deposit that constitutes a transition over 4 m into lacustrine sedimentation. A higher abundance of shock metamorphosed lithic clasts, and glass spherules, some with Ni-rich spinel and admixture of an ultramafic component, characterize this unit. We tentatively interpret this impactite section as allochthonous breccia in the vicinity of El’gygytgyn’s central ring uplift. The geochemical compositions of seven glass spherules from terrace deposits 2 km outside the crater and eight spherules from the reworked fallout deposit in hole 1C show far greater variability than the composition of impact melt shards and impact melt rocks. Some of these spherules also show strong enrichments in siderophile elements.