Abstract The late Miocene-early Pliocene Lake Pannon was a large, long-lived, brackish lake that occupied the Pannonian Basin system in Central Europe. Traditionally, the stratigraphic subdivision of its several-kilometer-thick sediment pile has been based on fossils of endemic mollusks. For a long time, however, stratigraphers were misled by the unconventional architecture of the lacustrine-deltaic sequence. Due to progradation, the increasingly younger sediment packages have been deposited horizontally next to each other instead of forming a purely vertical succession. This pattern was fully recognized recently by seismic exploration of the basin. Newly interpreted biostratigraphy using anagenetically evolving mollusk lineages (in the littoral and sublittoral facies) and dinoflagellate algae (in the sublittoral and profundal facies) is consistent with this progradation model. The regional Lake Pannon stratigraphy is tentatively correlated with the geologic time scale through mammal stratigraphy, magnetostratigraphy, and radio-metric age measurements. This correlation suggests that temporal resolution of the biozones is on the order of 1 m.y.

Abstract The Algyo field is currently one of the largest oil- and gas-producing fields in the Pannonian Basin, Central Europe. Located in the southern part of Hungary, it was discovered in 1965, and it has produced 31 million t of oil and 70 billion m 3 (2.47 tcf) of gas. Today, it provides more than half of Hungary's oil production and also holds the largest reserves. The areal extent of the field is about 80 km 2 (31 mi 2 ), and it comprises several dozens of sandstone reservoir beds with 5-30 m (16-100 ft) of gross thickness each. The reservoir sands as well as the probable source rocks were deposited in Lake Pannon and in adjacent deltaic and fluvial environments during the late Miocene and earliest Pliocene. Lake Pannon was a huge, long-lived, brackish lake, similar to the modern Caspian Sea. The hydrocarbon traps formed in a compaction anticline above a northwest–southeast-trending metamorphic core complex. A recently shot three-dimensional seismic survey was a milestone for further development and opened new ways for exploration effort, including the use of direct hydrocarbon indicators, to find additional satellite fields in the vicinity of this significant field. Complex interpretation of all available data and using sequence stratigraphy and its chronostratigraphical framework have been tremendously improving our understanding of the mechanisms controlling the reservoir characteristics, facies development, and the oil- and gas-trapping mechanism. Copyright ©2006. The American Association of Petroleum Geologists. DOI:10.1306/985629M841463