Depositional Environments of Lacustrine-Deltaic Sediments, Southeast Hungary

R. Lawrence Phillips, Istvan Berczi, Robert E. Mattick, Janos Rumpler

More than 6,000 m of Neogene lacustrine, deltaic, and fluvial sediments fill the Mako-Hodmezovasahely graben in southeast Hungary. Studies of geophysical profiles, well logs, and cores define the facies and basin-fill processes. Five facies are recognized and include in ascending order (1) basal facies (392 m of interbedded marls and graded beds of sandstone and conglomerate), (2) deep basin facies (1,165 m of laminated calcareous to silty marls), (3) prodelta facies (1,035 m of parallel beds of marl and graded sandstone changing vertically to inclined and deformed strata), (4) delta-front facies (733 m of inclined strata of marl and sandstone containing abundant soft-sediment deformation features), and (5) delta-plain facies (2,500 m of horizontal bedded marl, sandstone, lignite, and red beds).

The five facies record the filling of a deep stratified lacustrine basin. A euxinic environment dominated the basal three facies. Marl and turbidite deposition characterized the initial depositional stage of fill (basal facies). Deposition of marl continued (deep basin facies) with increasing fine-grain clastic sediment input into the basin. The clastic sediment content rapidly increased with deposition of sandy turbidites and slump deposits (prodelta facies). The prograding delta (delta-front facies) represents sedimentation dominated by turbidity currents, grain flows, and slumping of the slope deposits. The final stage of deposition (delta-plain facies) contains environments ranging from shallow lake, marsh, and fluvial to terrestrial.

Identification of the depositional environments and facies will aid in locating possible depositional petroleum traps, define possible petroleum migration pathways, document the facies where petroleum has accumulated (delta-front and delta-plain), and record the history of lacustrine basin fill.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.