The Porhanyó-Quarry's N E - S W section (Fig. 3) exposes the freshwater limestone in 100 m length and in 15 m thickness. The bedrock of the limestone is Pannonian sand and clay. Numerous carbonate vents, cones, tetaratas and cascades can be disting-uished in the section and out of the section, next to the Oreg-lake (Fig. 4). During field investigations connections between the carbonate vents and the other morpho-logical forms more revealed. The vents are often intergrowned along the setion and in some cases they are morphologically similar to the cascade forms.
Algal and other phytoclastic and phytohermal grainstone, boundstone and float-stone are considered to be the dominant microfacies of Tata travertines (Fig. 5). The 15 m thick lacustrine travertine can be divided to six units (Fig. 3). Unit 1 (14.7-12.4 m) consists of massive, thickbedded phytoclastic travertine with some gastropods, and covered by a sharp discontinuity surface, parallel to the bedding. Unit 2 (12.4-11,8 m) comprises the archaeological "culture layer" and is build up by a 30-40 cm thick pal-aesoil horizon at the bottom. This sandy clay is rich in bones, in Palaeolithic human tools, artefacts and show fragments of charcoal. The palaeosoil horizon is covered by siliciclastic fluvial channel deposits with a N-S direction that could have deposited from a rapidly flowing water. A new discontinuity surface separates the next unit, a bedded phytoclastic and gastropods bearing travertines (Unit 3 11.8-4.5 m) from the
"culture layer". Unit 3 is built up from 20-60 cm thick, layered limestone that contains bones ordered in a N-S direction together with gastropods and plants. Unit 4 is a soft, laminated, phytoclastic travertine terminated by a new discontinuity surface, which covers the vents and cones. Unit 4 is covered by a loose clastic travertine-bear-ing horizon of Unit 5 (2.5-1,0 m), which is imbedded in fluvial-eolian sand, Eolian sand of Unit 6 (1,0-0.0 m) terminates the section.
K O R M O S 1912.; V É R T E S 1964.; D O B O S I 2003, 205-214.
D O B O S I 2003, 205-214.
V É G H V I C Z I Á N 1964, 129131.; V É R T E S 1964.; K R E T Z O I V É R T E S 1964, 251256.; R U S Z K I -C Z A Y - R Ü D R I G E R 2003.
In the T a t a freshwater limestone (and also in the Budakalász freshwater lime-stone),11 Characea algae a n d Ostracods occur1 2 indicating shallow-lake environment.
The vertebrata fauna of the T a t a freshwater limestone was described by Kormos and Kretzoi1 3 while at Budakalász Jánossy1 4 a n d at the BudaVárhegy M o t t l a n d K r o -lopp et al.15 made similar investigations. D u r i n g the initial period of the lake evolu-tion the climate was w a r m and humid, b u t later it changed gradually to a cold, con-tinental desert at the termination of the lake evolution,16 Krolopp and Korpás1 7 also have drawn a similar conclusion by studying the Buda-Vár-hegy freshwater lime-stone. Using modern analogies and studying the fossil flora, Pavletic18 postulated a temperate (20-25 °C) deposition environment for the T a t a travertine.
Sampling and analytical methods
Eighteen samples were collected from one vertical section for pétrographie evalua-tion (Fig. 3). Addievalua-tionally we sampled the most typical carbonate formes (7 samples.;
Fig. 6), Eight samples were taken from one undetermined form (Fig. 7) which can be either carbonate vent or cascade.
Pétrographie a n d microfacies analyses on thin sections were performed at the H u n g a r i a n Academy of Sciences, Institute for Geochemical Research. Detailed X R D studies were conducted on bulk samples and on insoluble residue collected in the vertical section a n d on samples collected from the palaeosoil horizon. T h e analy-ses a n d the interpretation of the results was performed by P. Kovács-Pálffy a n d I.
Baráth ( M A F I ) . T h e dissolution of the limestones was made with acetic acid (30%) at the Geological Institute of H u n g a r y by I. Partényi and F. Hózer. T h e detailed description of the m e t h o d is given in the paper of Kovács-Pálffy and Földvári.19
Paleomagnetic measurements from one vertical section (including samples from the palaeosoil horizon) were also used to determine the timing of travertine forma-tion. T h e analyses a n d the interpretation of the results was performed by M , Lan-tos at the Geological Institute of Hungary. T h e detailed description of the m e t h o d is given in the paper of Lantos.2 0
11 KELE et al, 2003,161 - 175.
12 D I E B E L - P I E T Z E N I U K 1990,145-162.
13 KORMOS 1912,; KRETZOI 1964,105-126.
14 JÁNOSSY 1961, 63-74.
15 M O T T L 1943, 285-292.; KROLOPP et al. 1976,17-78.
16 KRETZOI 1964,105-126.; KORPÁS et al. 2003, 81-105.
17 KROLOPP 1961,146.; KROLOPP et al. 1976,17-78.; KORPÁS et al. 2003, 81-105.; 2004.
18 PAVLETIC 1964, 47-49.
19 KOVÁCS-PÁLFFY-FÖLDVÁRI 2004.
20 LANTOS et al, 2004, 227-236.
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Mineralogy of the Tata travertine
Stable isotope studies have been used to characterize the genesis of travertines since the 1950s.21 Systematic mineralogical a n d stable isotope analyses on H u n g a r i a n travertine occurrences have not been carried out yet. T h e first mineralogical a n d stable isotope geochemical studies were made by Rózsavölgyi, Mihályi-Lányi a n d Opauszky on the T a t a freshwater limestone.2 2
O n the base of X R D analyses the samples collected along the vertical section of the P o r h a n y ó - Q u a r r y are composed of pure, magnesium-free calcite (94-98%). Inso
luble residues of samples collected from units 1-4 contain a few siliciclastic grains (0.53%) whereas unit 5 contains more quartz grains (2.29%). T h e palaeosoil of the cul
ture-layer (2n d unit) contains a small a m o u n t (4%) of dolomite Q u a r t z , feldspar a n d rare muscovite represent the scarce extraclast. X R D measurements on insoluble resi
dues indicate the presence of quartz, plagioclase, K-feldspar, muscovite, illite, chlo
rite, montmorillonite. Additional traces of kaolinite, amfibole, magnetite, maghemite, hematite, goethite, gyps and pyrite were detected. X R D analyses on the palaeosoil horizon indicated the presence of quartz, calcite, dolomite, muscovite, chlorite, pla
gioclase a n d K-feldspar as well as traces of montmorillonite, illite a n d traces of amfi
bole, hematite, pyrite and gypsum. T h e fluvial eolian sand units (5t h and 6t h units) show extremely high values of detrial minerals.
Chronology of the Tata travertine
Age determinations performed so far on the T a t a limestone were based on radiogenic (14C, T h / U , ESR) methods, paleontology, archaeology and paleomagnetic measure
ments. T h e I 4C measurements was performed by de Vries a n d de W a a r d2 3 in t h e culture-layer yielding 33,6 ± 1,1 ky a n d 55 ± 2,5 ky above the culture-layer. T h / U age determinations on travertine localities at Tata, D u n a a l m á s , Vértesszőlős a n d Buda-Var-hegy travertines2 4 resulted in an estimated age of 100 ky.25 O n the basis of palae-ontological data, the formation of travertine complex took place at the end of the last interglacial, and the fauna belongs to t h e Subalyuk biozone.2 6 Archaeological stud
ies2 7 suggested Middle palaeolithic (~ioo ky) age for the travertine, while the indefi
nite radiometric methods resulted in ages ranging between 33,6 to 10 Ky.
21 CRAIG 1953, 53-92.
2 2 RÓZSAVÖLGYI 1964, 31-36.; MIHÁLYI-LÁNYI 1964, 37-42.; OPAUSZKY et al. 1964,19-29.
23 V R I E S - W A A R D 1964, 35-36.
2 4 PÉCSI 1973, 109-119.; H E N N I N G et al. 1983.; S C H E U E R - S C H W E I T Z E R 1988, 131.; OSMOND 1990, 545.; OAKLEY 1990, 543544.; CHERDINTSEVKAZACHEWSKI 1990, 547.; S C H W A R Z -LATHAM 1990, 549-552.
25 SCHWARZ-SKOFLEK 1982, 590-591.
26 KRETZOI I964, IO5-I26.; JÁNOSSY I979, 207.
27 VERTES et al. 1964.; DOBOSI 2003, 205-214.
Systematic paleomagnetic sampling and magnetostratigraphic studies2 8 of t h e Buda-Vár-hegy, Budakalász, Vértesszőlős, Tata, Les-hegy, D u n a a l m á s a n d S ü t t ő travertine occurences led to the conclusion that two main periods of travertine for
mation occured (Fig. 8). The older one belongs to the Matuyama-chron around the C2 anomaly (Dunaalmás, Süttő, Les-hegy). The younger one may have occured in the Matuyama-Brunhes, starting at about the Jaramillo chron and ending at t h e reverse anomaly in t h e middle of the Brunhes chron (Buda-Vár-hegy, Budakalász, Vértes
szőlős, Tata). A systematic palaeomagnetic log of the T a t a travertine has given an uniform normal polarity record for the entire travertine section (Fig. 3), including the
"culture layer" (Fig. 9). It seems plausible to correlate this normal polarity record with certain parts of the Brunhes.2 9
Carbonate vents, terraces, cascades
The horizontal units of the P o r h a n y ó - Q u a r r y are often interrupted by carbonate vents, cones a n d other morphological forms which were formed due to t h e former intensive spring activity. The microscopic photos of samples taken from t h e centre of the carbonate vents show clastic q u a r t z grains cemented in the freshwater limestone (Fig. 10). These grains derived from t h e Pannonian siliciclastic bedrock a n d come to the surface with the discharging springwater and cemented in the carbonates precipi
tating simultaneously (Fig. 11). The clastic fabric is characteristic to t h e centre of the carbonate vents and the size and frequency of the quartz grains decrease with increas
ing distance from the spring orifice. T h e presence of clastic grains indicate t h e inten
sity and the discharge of the ancient spring activity. The vents are spatially connected to each other, to the cascades and to t h e tetaratas. The different faciès (vent, cascade, pond) migrated during the evolution of t h e travertine complex due to changes in morphology a n d flow direction.
Conclusions
The travertine of the P o r h a n y ó - Q u a r r y of T a t a can be divided to six horizontal units.
T h e travertines can be sedimentologically classified as algal a n d other phytoclas-tic a n d phytohermal grainstone, boundstone and floatstone microfacies types. The lake in which the travertine was deposited was fed by thermal springs discharging on a siliciclastic floodplain or delta system. Three main lacustrine phases of the lake evolution can be distinguished (Fig. 12). Travertine formation was interrupted first by a palaeosoil formation and flooding event, followed by a fluvial-eolian event and
2 8 LANTOS et al. 2000.; KORPÁS et al. 2003, 81-105.
2 9 L A N T O S et al. 2004, 227-236.
38