Constraining the timing, kinematics and cyclicity of Mississippian-Early Pennsylvanian glaciations in the Paraná Basin, Brazil

Abstract

Abstract Ice-contact deposits emplaced by Late Paleozoic Ice Age (LPIA) glaciers are rarely exposed due to a low degree of preservation and their capping by thick glaciomarine deglaciation sequences. In this paper, we present new data on glacial cyclicity, relative age constraints and paleoice flow interpretations for an ice-contact succession of the lowermost Itarare Group in eastern Parana Basin (Brazil). The 80\u202fm-thick ice-contact complex rests over the Itarare Group basal unconformity and comprises four stacked informal stratigraphic units regarded as the depositional/deformational record of three ice lobes advance/retreat cycles. Glacial cycle 1 comprises a sheet of massive diamictite resting on striated pavements carved on Devonian sandstones and topped by grooved/fluted surfaces, which indicate subglacial emplacement from a northward flowing ice lobe. The glacial cycle 2 succession was deposited in a proglacial to ice-marginal marine setting and subsequently deformed due to minor ice margin fluctuations of a westward/southwestward flowing grounded ice lobe. Glacial cycle 3 is interpreted as a thick overridden push moraine composed of grounding-line fan deposits capped by a subglacial diamictite emplaced by grounded ice advancing northwestward. A middle Visean-early Serpukhovian palynomorph assemblage was recorded in cycle two deposits, representing the oldest late Paleozoic glacial rocks in the Parana Basin. The ice-contact complex elucidates multiple waxing and waning phases of the Windhoek Ice Sheet onto the eastern margin of the Parana Basin during the Mississippian-Early Pennsylvanian, demonstrating that ice sheets of the early stages of the LPIA were also present in the Brazilian-African domain of southwestern Gondwana.