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Multi-disciplinary research
at the Pestera cu Oase
Stefan Milota at the time of discovery of the Oase 2 face
Researches carried out under the framework of the CLIMKARST Project - "Rapid climate oscillations recorded in karst deposits from Romania as revealed by isotopic and paleomagnetic proxies" - CEEX Grant 627/2005
The site

Pestera cu Oase is one of the most important caves studied through the CLIMKARST Project. Researches to the site have begun as early as 2003, following the discovery of the remains of the oldest Homo sapiens in Europe (Trinkaus et al., 2003; Rougier et al., 2007; Zilhao et al., 2007), within a multidisciplinary international team. The team was lead by prof. Erik Trinkaus (Washington University of St. Louis), Joao Zilhao (now at Bristol University, UK) and Silviu Constantin ("Emil Racovita" Institute of Speleology) and benefited from various funding agencies (NSF, Leaky and Wenner Gren Foundation, ANCS Romania, etc.).

The name "Pestera cu Oase" designates the upper (inactive) level of an extensive karst system located in the Aninei Mountains which includes several other inactive caves, a multi-level network of active (river) and temporarily flooded passages as well as several hundreds meters of underwater passages which are exclusively accessible through cave-diving.
progressing through the Oase underground stream
The accces

Pestera cu Oase is an absolutely pristine site. This is due to a combination of: (i) extremely difficult access to the actual site, (ii) protective measures and (iii) protective atitude of all those involved in excavation. To clearly describe the situation, digging at Oase involves a dangerous cave-diving through a 5 m-deep sump, climbing of a 17 m-high shaft, crawling through a narrow squeeze and commuting people, gear, bones and sediments back and forth along this route. The passage is protected by a gate and the number of persons involved in excavation was always kept to a minimum. As in all cases of such pristine sites, protection is as high as possible and the media coverage was kept to a minimum.
ready to dive
climbing the shaft
stratigraphy of the excavation on the Ramp of Ancestors
The deposit

Pestera cu Oase is one of the inactive sectors of this system where the topography has allowed the accumulation of a massive deposit of fossil remains. Among these, the most important are those of
Ursus spelaeus (~5,000 bone remains excavated from less than 6 cbm during 3 field campaigns) making up ~94% of the total excavated bones. To these other fossil animals are added such as Crocuta crocuta spelaea (cave hyena), herbivorous such as Cervus sp. and Capra ibex, small carnivores (Canis lupus, Vulpes sp.) and rodents.

The excavated remains are found within the sector known as 'the Ramp of Ancestors' where the Oase 1 and Oase 2 human mandible and skull where found at the surface or close to it. Beneath the surface, a first ('Level 1'), deposit was found consisting of bones and fine sediments which indicate a low-energy hydraulic regime and a second ('Level 2'), high-energy, depositional layer consisting of a bone jumble mixed with coarse pebbles and cobbles and older speleothems in a sandy matrix. To these we may add speleothem deposits consisting of altered calcite ('paleo-calcite') which are indicative for a much older evolutionary stage of the cave, as well as a massive sediments deposit (mostly clays, but also a cave-breccia including small bones fragments). All these deposits were analysed during our researches.
Investigations at the Pestera cu Oase

(1) Radiometric datings of the fossil remains from the 3 levels identified during the excavations, either directly (radiocarbon) or indirectly (U-series datings on flowstone and stalagmites from stratigraphically-significant positions);
(2) Datings of speleothems from the 3 passages investigated in order to establish the evolution of cave system, the genesis of the accumulation of sediments and fossil remains;
(3) Magnetic and sedimentologic study of some stratigraphic sequences bearing paleoclimatic and paleoenvironmental significance;
(4) Isotopic study of fossil remains of mammals aiming to the reconstruction of paleodiets.

All these have completed the routine investigative activities which included surface and underground surveys, systematic excavations, paleontologic measurements, diagnosis and research, etc.
during the excavation on the Ramp of Ancestors
Digging the 9 m exploration trench in the sediments from the Shaft
Detail of the exploratory trench within the sediments in the Shafts. Labels designate samples for sedimentological and magnetical analyses.
One of the tens of cave bear skulls
Ibex horns with stalagmites grewn on them
Main results

(1) Sedimentological and stratigraphical analysis of the deposit of fossil remains from the Ramp of Ancestors (see map below) have proven that this formed following two rapid (torrential) episodes during MIS 3, about 42 ka ago. Direct datings of speleothems interbedded within the deposit have allowed both the calibration and crosschecking of radiocarbon ages as well as estimating the timing of this climate oscillation to a maximum of several hundreds years.
Map of the Pestera cu Oase, the position of fossil remains and location of sampling points.
(2) Since the collagen levels of the human remains was to low to provide reliable replicate radiocarbon dates, U-series dating of the speleothems interbeded within the bonebed was a crucial element to confirm the age of ~40.5 ka for Oase 1, the oldest Homo sapiens in Europe (Rougier et al.; Zilhao et al., 2007) (see the section through stalagmite PPL6);

(3) the study of the magnetic properties along a 9 m-long profile along the Shaft, calibrated by using U-series datings of a stalagmite and ESR datings of fossil remains from the sediments have offered a first record of climate and hydrological variations between ~16.5 ka and ~120 ka (see below);

Section through stalagmite PPL6. The base is formed of a rolled fragment of an older stal embedded within Level 2. The sediments and bones within the new and old stals belong to Level 1.
The magnetic profile along the sediments in the Shaft
(4) the paleontologic (Quiles et al., 2006) and stable isotope study of the fossil remains of Ursus spelaeus, correlated with radiocarbon datings and ancient DNA (Stiller et al., 2006; Richards et al., 2008) indicate a surprising diet of these large mammals. As opposed to cave bears from Western and Central Europe, the specimens from Pestera cu Oase show abnormal d15N/d13C values, typical for omnivorous and carnivorous mammals (see below).
The abnormally high values of d15N for cave bears, close to those recorded from wolves indicate a more carnivorous or mixed diet
The researches carried out at the Pestera cu Oase revealed an exceptionally valuable site for the paleoclimate and paleoenvironment during (at least) the last 50,000 years. Climate oscillations recorded during MIS3 may be correlated at regional (Constantin et al., 2007) and european scale (Genty et al., 2003) (see also the figure below). In spite of the limited extension of our excavation (only 5-10% of the volume of the actual deposit), Pestera cu Oase is, to the best of our knowldege, the best-documented fossil site for Ursus spelaeus in Europe.

The research as the Pestera cu Oase is ongoing and will further focus on taphonomy issues, the possible relationship humans-cave bears-hyaenas and paleoenvironmental significances.
the timing of deposition of sediment layers at the Ramp constrained by PPL6 U-series datings and radiocarbon dates of fossil remains and correlated with MIS3 known oscillations
References

Quilès, J., Petrea, C., Moldovan, O., Zilhao, J., Rodrigo, R., Rougier, H., Constantin, S., Milota, S., Gherase, M., Sarcina, L., and Trinkaus, E. (2006).
Cave bears (Ursus spelaeus) from the Pestera cu Oase (Banat, Romania): Paleobiology and taphonomy. C.R. Palevol 5, 927-934.

Richards, M. P., Pacher, M., Stiller, M., Quilès, J., Hofreiter, M., Constantin, S., Zilhão, J., and Trinkaus, E. (2008).
Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Pestera cu Oase, Romania. Proc. Nat. Acad. Sci. USA 105, 600-604.

Rougier, H., Milota, S., Rodrigo, R., Gherase, M., Sarcina, L., Moldovan, O., Zilhao, J., Constantin, S., Franciscus, R. G., Zollikofer, C. P. E., Ponce de Leon, M., and Trinkaus, E. (2007).
Pestera cu Oase 2 and the cranial morphology of early modern Europeans. Proc. Nat. Acad. Sci. USA 104, 1165-1170.

Stiller, M., Hofreiter, M., Trinkaus, E., Zilhao, J., Constantin, S., Quilès, J., and Richards, M. P. (2006). Ancient DNA and stable isotopes from cave bears of Pestera cu Oase, Romania. Preliminary results. In "12th Intl. Cave Bear Symposium." Aridea, Greece, abstract book, p. 27.

Trinkaus, E., Moldovan, O., Milota, S., Bîlgar, A., Sarcina, L., Athreya, S., Bailey, S. E., Rodrigo, R., Mircea, G., Higham, T., Bronk Ramsey, C., and van der Plicht, J. (2003). An early modern human from the Pestera cu Oase, Romania. Proc. Nat, Acad. Sci. USA 100, 11231-11236.

Zilhao, J., Trinkaus, E., Constantin, S., Milota, S., Gherase, M., Sarcina, L., Danciu, A., Rougier, H., Quilès, J., and Rodrigo, R. (2007).
The Pestera cu Oase people: Europe's earliest modern humans. In "Rethinking the Human Revolution." (P. Mellars, K. Boyle, O. Bar-Yosef, and C. Stringer, Eds.) McDonald Institute for Archaeological Research, Cambridge, pp. 249-262.
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