The Neogene Transylvanian Basin (TB), enclosed between the eastern and southern Carpathians
and the Apuseni Mountains in Romania, is a significant natural gas province with a
long production history. In order to improve the (bio) stratigraphic resolution, correlations
and dating in the several 100-m-thick upper Miocene (Pannonian) succession of the
basin, the largest and most fossiliferous outcrop at Gusterita (northeastern part
of Sibiu) was investigated and set as a reference section for the Congeria banatica
zone in the entire TB. Grey, laminated and massive silty marl, deposited in the deep-water
environment of Lake Pannon, was exposed in the similar to 55-m-high outcrop. The uppermost
25 m of the section was sampled in high resolution (sampling per metres) for macro-
and microfossils, including palynology; for authigenic Be-10/Be-9 dating and for magnetostratigraphy;
in addition, macrofossils and samples for authigenic Be-10/Be-9 isotopic measurements
were collected from the lower part of the section as well. The studied sedimentary
record belongs to the profundal C banatica mollusc assemblage zone. The upper 25 m
can be correlated to the Hemicytheria tenuistriata and Propontoniella candeo ostracod
biozones, the uppermost part of the Spiniferites oblongus, the entire Pontiadinium
pecsvaradense and the lowermost part of the Spiniferites hennersdorfensis organic-walled
microplankton zones. All samples contained endemic Pannonian calcareous nannofossils,
representing the Noelaerhabdus bozinovicae zone. Nine samples were analysed for authigenic
Be-10/Be-9 isotopic measurements. The calculated age data of six samples provided
a weighted mean value of 10.42 +/- 0.39 Ma. However, three samples within the section
exhibited higher isotopic ratios and yielded younger apparent ages. A nearly twofold
change in the initial Be-10/Be-9 ratio is a possible reason for the higher measured
isotopic ratios of these samples. Magnetostratigraphic samples showed normal polarity
for the entire upper part of the outcrop and can be correlated with the C5n.2n polarity
chron (11.056-9.984 Ma, ATNTS2012), which is in agreement with the biostratigraphic
data. Based on these newly obtained data and correlation of the biozones with other
parts of the Pannonian Basin System, the Guterita section represents the similar to
11.0-10.5 Ma interval, and it is a key section for correlation of mollusc, ostracod,
dinoflagellate and calcareous nannoplankton biostratigraphic records within this time
interval.
