Interaction of basin-margin faults and tidal currents on nearshore sedimentary architecture and composition: a case study from the Early Miocene of northern Hungary

Abstract

The Darnó Conglomerate and the Pétervására Sandstone with conglomeratic intercalations, both cropping out in northern Hungary, were formed along the eastern margin of the shallow Early Miocene sea within the Carpathian arc. Ophiolite-derived clastic components in both formations indicate a close genetic relationship with each other and with the activity of the basin-margin Darnó Fault, which seems to correspond with the coeval shoreline. The Darnó Conglomerate was part of a small fault-controlled fan-delta supplying coarse clastics into the sea where the Pétervására Sandstone deposited. The conglomerates occur as small lobes interbedded within a field of tidally-driven sand waves. The coarse-grained clastics, which were admixed to the main material of the sandstone, have been derived from Triassic-Jurassic ophiolite-related series (Meliata nappes) east of the Darnó Fault. The composition of the lobes indicates that they were formed as small spit-like platforms attached to the fan-deltas of the Darnó Conglomerate. As base level rose spits became drowned and their sediment was washed into the basin and reworked by the strong northward-directed tidal currents into elongated lobes ‘mimicking’ sand waves. A reduction in the amount of the less resistant pebble components of ophiolite-related origin and a relative enrichment of the resistant components towards the west indicate that pebbles had partly been transported in the offshore direction. The increasing rate of accumulation of ophiolite-derived heavy minerals and pebbles along the northern part of the coast indirectly suggests a contemporaneous left-lateral displacement along the basin-margin Darnó Fault.