Abstract: On the Thermal Regime of the Transylvanian Basin, Romania

Constantin Cranganu, David Deming

The Transylvanian basin, located in central Romania, is a Neogene depression superimposed on the Cretaceous nappe system of the Romanian

Carpathians. This intramountain basin experienced rapid Neogene subsidence and molasse sedimentation. The Middle Miocene to Pliocene molasse deposits overlie a folded basement covered with Late Cretaceous-Paleogene rocks. The structure of the Transylvanian basin is complicated by extensive basement faulting; the different structural elements are similar to major tectonic styles found in the neighboring Carpathian mountains.

The sedimentary cover of the Transylvanian basin has a maximum depth of (approx.) 6500 m in the central part. The Transylvanian basin contains the main gas reserves of Romania and is one of the most important gas producing areas of continental Europe. More than 60 gas fields have been producing since 1902.

Average heat flow in the Transylvanian basin is (approx.) 45-50 mW/sq m, relatively low compared to geological surrounding units (83-110 mW/sq m in neo-volcanic chain of the Eastern Carpathians, approx. 80 mW/sq m in Apuseni Mountains and 85-100 mW/sq m in the eastern part of the Pannonian basin) (Veliciu and Demetrescu, 1979).

Relatively low heat flow in the Transylvanian basin may be explained by one or more of the following hypotheses:

1. Rapid sedimentation during the main phases of the Transylvanian basin subsidence (in Badenian, 17-13.3 m.y., total thickness: approx. 1432 m, sedimentation rate: approx. 387 m/m.y.; in Buglovian, 13.3-12.6 m.y., total thickness: approx. 514 m, sedimentation rate: approx. 735 m/m.y.; in Sarmatian, 12.6-11.0 m.y., total thickness: approx. 904 m, sedimentation rate: approx. 565 m/m.y.) (Cranganu, 1985, 1986, 1987);

2. A descending convection current in the mantle related to the possible formation of a mantle diapir below the Pannonian basin;

3. A fluid flow pattern conveying heat from the center of the basin toward its borders (which are much hotter).

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994