Origin, timing and paleogeographic implications of Paleogene karst bauxites in the northern Transdanubian range, Hungary

Abstract

Paleogene karst bauxites in the northeastern Transdanubian Range and their cover sequences provide valuable sedimentary archives, despite their weathered nature and vague paleontological records. U–Pb detrital zircon geochronology combined with heavy mineral analysis indicates ‘local’ Alpine aeolian and fluvial sources and ‘distant’ aeolian sources connected to the Bohemian Massif. Records of episodic Paleogene volcanic eruptions related to igneous complexes of the Adamello and probably also the Bergell, Recsk and Balkan Peninsula, are reflected by euhedral zircon crystals. Their U–Pb geochronology supplies age constraints for the phases of subaerial exposure of the karstic surface and the accumulation of bauxitic protoliths and helps to improve the existing stratigraphic records and to define stages of denudation in the northeastern Transdanubian Range. Distinct phases of subaerial exposure and accumulation of the bauxite's protoliths are identified as ca. 42, 35 and 31 Ma; alternating with episodes of subsidence, represented by siliciclastic and carbonatic sequences at ca. 38, 32 and 31 Ma. Besides Paleogene volcanism, zircon dating also revealed contributions from the Middle Triassic tuffs of the Transdanubian Range. Garnet, epidote, kyanite, staurolite, and xenotime/monazite crystals suggest fluvial drainage of diverse metamorphic units of the Austroalpine basement from the Eastern- and Southern Alps, which also supplied most of the pre-Mesozoic zircons. However, the unexpectedly high proportion of Variscan ages in the bauxites most likely relate to igneous rocks of the Bohemian Massif, thus suggesting additional long-distance aeolian sources. The new data allow for detailed reconstructions of the Paleogene evolution and palaeogeography of the northeastern Transdanubian range.