U/TH DATING AND OPEN SYSTEM BEHAVIOR: IMPLICATIONS FOR TRAVERTINES BASED

Reliable dating is essential in order to put palaeoclimatological, palaeoenvironmental and archeological information from continental carbonates in the correct time frame. This study evaluates U/Th dating of travertines based on two case studies, i.e., in the Ballik (Denizli, SW Turkey) and Sutto (N Hungary) areas. Previous petrographic, mineralogical and elemental characterization of the travertines enabled sampling of, purely calcitic, micrite or spar dominant, zones that are non-, or solely weak, cathodoluminescent. Despite adapted sampling and detrital thorium corrections, U/Th ages of the Ballik and the Sato travertines are inconsistent with their stratigraphic position. Based on the observation of wavy extinction affecting micritic fabrics and ghost structures, the studied travertines behaved as an open system for uranium after deposition through recrystallisation. Their U/Th ages, consequently, can only be considered as minimum ages. The Ballik travertines precipitated earlier than 0.55-1.31 Ma ago, when late-stage cementation along fractures and in cavities took place, and form the oldest travertines deposited in the Denizli basin. The formation of the Sato travertine area started at the earliest around 2.5 Ma with precipitation of the Cukor travertine. With some short interruptions, active travertine formation in the area took place maximally until 120 ka. The decreasing ages of the Sutto travertines towards the Danube, prove the complex nature of travertines both during deposition as well as during diagenesis, which leads to anomalies with regard to the law of superposition.The diagenetic susceptibility of continental carbonate deposits poses problems in terms of accurate and precise dating. U/Th dating of the intrinsically heterogeneous fabrics of travertines and tufa, as presently applied, should be ceased. Travertines and tufa up to similar to 100 ka might be the exception due to the limited extent of recrystallisation. Sparite cements and veins can be dated more accurately but, even with multiple samples from the same study site and inclusion of coeval samples, give only minimum ages for the whole deposits. To better constrain the time frame of the whole bodies, results from independent dating methods and from the surrounding deposits are necessary. In addition, it is important to keep in mind that the open-system behavior of continental carbonates has implications for diagenetic, palaeoenvironmental and palaeoclimatological studies based on geochemical proxies.C1 [Claes, Hannes; Torok, Agnes; Soete, Jeroen; Mohammadi, Zahra; Vassilieva, Elvira; Hamaekers, Helen; Marques Erthal, Marcelle; Aratman, Cihan; Swennen, Rudy] Katholieke Univ Leuven, Dept Earth & Environm Sci, Geodynam & Geofluids Res Grp, BE-3001 Heverlee, Belgium.[Claes, Hannes] Rhein Westfal TH Aachen, Clay & Interface Mineral CIM, Bunsenstr 8, DE-52072 Aachen, Germany.[Torok, Agnes; Mindszenty, Andrea] Eotvos Lorand Univ, Inst Geog & Earth Sci, Dept Phys & Appl Geol, Pazmany P Setany 1-c, HU-1117 Budapest, Hungary.[Soete, Jeroen] Katholieke Univ Leuven, Dept Mat Engn, Nondestruct Testing Res Grp, BE-3001 Heverlee, Belgium.[Hamaekers, Helen] SCR Sibelco Nv, Dept Geol, De Zate 1, BE-2480 Dessel, Belgium.[Marques Erthal, Marcelle] Petrobras Res Ctr, Av Horacio de Macedo Cidade Univ 950, BR-21941915 Rio De Janeiro, RJ, Brazil.[Aratman, Cihan; Ozkul, Mehmet] Pamukkale Univ, Dept Geol Engn, Kinikli Campus, TR-20070 Denizli, Turkey.[Cheng, Hai; Edwards, R. Lawrence] Univ Minnesota, Dept Earth Sci, Minneapolis, MN 55455 USA.[Cheng, Hai] Xi An Jiao Tong Univ, Inst Global Environm Change, Xian 710049, Peoples R China.[Shen, Chuan-Chou] Natl Taiwan Univ, Dept Geosci, High Precis Mass Spectrometry & Environm Change L, Taipei 10617, Taiwan.[Shen, Chuan-Chou] Natl Taiwan Univ, Res Ctr Future Earth, Taipei 10617, Taiwan.[Shen, Chuan-Chou] Natl Taiwan Univ, Global Change Res Ctr, Taipei 10617, Taiwan.[Kele, Sandor] Hungarian Acad Sci, Inst Geol & Geochem Res, Res Ctr Astron & Earth Sci, Budaorsi Ut 45, HU-1112 Budapest, Hungary