Facies and Depositional Environments of Miocene Sedimentary Rocks

Abstract

The area of the Békés basin began to subside in early Badenian time during the late Styrian orogenic phase. The initial phase of subsidence and transgression of the Paratethys Sea is marked by conglomerate and/or breccia that is present almost everywhere where Miocene deposits occur. The Miocene sequence is 0-275 m thick, where penetrated by wells in the Békés basin; however, in the deepest parts of the basin the sequence is inferred to be more than 1000 m thick based on interpretation of seismic data.

During the Badenian, the region was covered by a shallow, well-oxygenated, warm sea of normal salinity. Numerous, small islands, that exist now as buried basement highs, were fringed by Lithothamnium algal flats. Along the shorelines of the Badenian sea, dominantly coarse, sandy sediments, and in littoral zones, sandstones and carbonates were deposited. Shelf and offshore areas are represented by complex interfingering lithofacies, ranging from bioclastic limestones that make up the fabric of submarine plateaus, to dark-colored, turbiditic marls and shales in the deepest parts of the basin.

In early Badenian time an almost continuous transgression of marine waters took place; whereas, in the late Badenian almost continuous regression of the sea followed. The Sarmatian epoch started with a new transgression in the southern part of the basin, while in the northern part regression continued, indicating a tilting of the basin. From the beginning of Sarmatian time, the area became isolated from the Paratethys Sea, the salinity of the water gradually decreased, and an endemic fauna characterized by euryhaline living organisms developed in an anoxic environment.

Sarmatian sedimentation took place in a basin whose extent was smaller than its Badenian equivalent, as indicated by the deposition of lower Pannonian sediments on lower Badenian rocks, especially in the northern part of the Békés basin. In the deepest parts of the basin, however, sedimentation may have been continuous from middle Miocene through Pliocene time with the lower Pannonian section being highly condensed as a result of little or no deposition.