Seismic stratigraphic analyses and studies of core samples from three wells indicate that infilling of the Pannonian basin of Hungary resulted primarily from deltaic sedimentation from the northwest, north, and northeast. Infilling of the basin involved a single cycle of sedimentation which probably began in Sarmatian or earliest Pannonian time when water depths in the basin were > 1,000 m. The subsequent history of the basin, during Pannonian and Quaternary time, reflects continuously shoaling waters. This shoaling resulted from sediment input rates that were generally higher than basin subsidence rates.

In general, two stages of delta construction can be recognized. In an early stage of construction, turbidite-fronted, deep water deltas were built in water depths as deep as 800-900 m. During this early constructional stage, subsidence rates and associated sediment input rates were high, and upbuilding and southward progradation of large deltaic sediment wedges filled subbasins near the source areas, overwhelmed local basement highs, and spilled sediments into subbasins in the southern part of Hungary. During a later stage of construction, prograding shallow water deltas were built in water depths of 200-400 m, and topographically low areas in the southern part of Hungary were filled by sediments discharged from river systems that advanced about 100 km southward across strata deposite during the initial stages of construction.

Seismic evidence indicates that in some areas of the Pannonian basin, the sedimentary rocks representing the two stages of delta construction are separated by a depositional unit which possibly represents a destructive phase. This unit may have been deposited during a short-lived transgressive phase or, perhaps, it was deposited following a period of accelerated lake shoaling.

The youngest and final stage of deposition is represented by delta plain facies; depositional environments varied from shallow lake, fluvial, and marsh to terrestrial soils. This unit is inferred to represent more widespread lake conditions coupled with continued shoaling and eventual disappearance of the Pannonian lake. During this period of sediment deposition, basin subsidence rates and associated sediment input rates were probably lower, and the sediment input rate is inferred to have kept pace generally with the basin subsidence rate.

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