European Geologist Journal 48
The Geological Garden at Tata (Hungary): A geosite of outstanding scientific and geo-educational significance
by István Szente1, Erzsébet Harman-Tóth2 and Tamás G. Weiszburg1
1 ELTE Geological Garden, Pázmány P. s. 1/c, H-1117 Budapest, Hungary
2 Eötvös Museum of Natural History, Pázmány P. s. 1/c, H-1117 Budapest, Hungary
Contact: szente@ludens.elte.hu
Abstract
The Geological Garden is a nature conservation area located in Tata, about 70 km to the west of Budapest. It has been established as an open-air geological museum where a succession of Mesozoic sedimentary rocks characteristic of the Alpine-Carpathian region is excellently exposed in abandoned quarries and cleaned rock surfaces. Several formations widely distributed in the Transdanubian Range of Hungary were studied here in detail, and type-sections of three of them have been designated on Kálvária Hill. In addition to geological values, the area houses Copper Age chert mines as well as a collection of mountain-building rocks of Hungary. Due to its scientific value and educational potential, the Geological Garden is one of the most important Hungarian geosites.
Introduction
Quarries and other man-made exposures are of paramount importance to geological research and geoeducation. This statement applies especially to inland areas of moderate topographic relief, where quarries often provide the only access to geology (Prosser, in press). The territory of Hungary, dominated by lowland areas, is characterised by geologically young, i.e. Neogene and Quaternary, soft surface sediments. Largely due to quarrying, however, the country is relatively rich in scientifically significant geosites representing earlier periods of the history of Earth.
The Mesozoic succession of the Transdanubian Range is particularly noteworthy in this respect. It has been built of rocks representing typical sedimentary facies of the Alpine-Carpathian region and as a rule was not affected by considerable post-depositional deformations. Thus, original layering and the stratigraphic successionshave been well preserved. A large number of geosites have become known as a result of quarrying. Exploitation has come to an end at most places and the abandoned quarries, if not refilled, now form spectacular landscapes at some places.
Abandoned quarries usually receive less attention than underground mines in terms of their protection (Storemyr, 2006). In Hungary, on the contrary, they are highly valued and well represented among protected geosites. Most of them are, however, scattered and far from roads and settlements. An exception to this rule is the town of Tata around 70 km to the west of Budapest, where a well exposed succession of Mesozoic sedimentary rocks can be studied in easily accessible and safe abandoned quarries and cleaned rock surfaces of Kálvária Hill (Calvary Hill, if translated), a fault-bounded horst, the area of which is now largely occupied by an open-air museum called Geological Garden and managed by Eötvös Loránd University (Figure 1).
Figure 1: Location of the Tata Geological Garden.
A brief history of the Tata Geological Garden
The history of the geological and archaeological research of Kálvária Hill as well as its geology is reviewed in detail in Szente et al. (in press). Dominated by soft Cainozoic surface sediments, Tata and its environs are relatively poor in natural building stones. Thus, beds of variegated Triassic, Jurassic and Cretaceous limestones cropping out at Kálvária Hill aroused interest long ago and were extensively quarried for centuries. Robert Townson, an English traveller who visited Tata in 1793, was the first to document the abundant occurrence of red limestone (Townson, 1797). Scientific study of the Mesozoic formations began in the 1850s with the work of Austrian and Hungarian geologists and led to the identification of the Upper Triassic Dachstein Limestone, Lower Jurassic red ammonitic limestone and Lower Cretaceous crinoidal limestone. Observations were made mostly in three quarries, called “Whitestone”, “Redstone” and “Bluestone”, operating at those times.
A new chapter in the study of Kálvária Hill began in the mid-1950s when József Fülöp (1928–1994) started working on it. Fülöp, who played a major role in geology in Hungary for about three decades, had the opportunity to clean large rock surfaces in order to study Middle and Upper Jurassic rocks that had never been quarried, as they were unsuitable for building. Due to the scientific value of these exposures, a section of Kálvária Hill was declared to be a nature conservation area in 1958. Quarrying came to an end in the seventies and since 1976 the area has been developing as an open-air geological museum, founded by the Hungarian Geological Institute.It has been managed since 1994 by Eötvös Loránd University (ELTE). The extent of the protected area, now called at full length “ELTE Tata Geological Garden – Nature Conservation Area and Open-Air Geological Museum”, has increased to 3.5 ha. Due to a grant of EUR 175,300 received by the Eötvös University from the European Union, a large-scale cleaning project was carried out in 2015. As a result of it, the Geological Garden now functions as an appealing place for research, teaching,public outreach and recreation.
Geological values of Kálvária Hill
The favourable exposure conditions made possible a very detailed study of the Mesozoic succession of Kálvária Hill, resulting in the comprehensive monograph by Fülöp (1976). An approximately 50 m thick suite of beds divided into nine formations is exposed at Kálvária Hill (Figure 2), displaying intermediate facies characteristics between the successions of the Bakony and Gerecse Mountains.
Figure 2: Stratigraphic column of the Mesozoic cropping out at Kálvária Hill. (Abbreviations: Oxford.–Kimm. = Oxfordian–Kimmeridgian; Se. = Series; L. = Lower; M. = Middle; U. = Upper; Sy. = Systems; Cret. = Cretaceous) (after Haas & Hámor, 2001).
The oldest rock cropping out is Upper Triassic Dachstein Limestone; it is well exposed in the “Whitestone Quarry” located outside the Geological Garden (Figure 3).
Figure 3: “Whitestone Quarry” exposing predominantly lagoonal Dachstein Limestone overlain by deeper-water pink Lower Jurassic Pisznice Limestone Formation.
The cyclic succession of the Dachstein Limestone, formed in peritidal to shallowinternal platform lagoon environments, is visible in the “Whitestone Quarry” section. Limestone beds of lagoonal origin are prevalent and contain abundant megalodontid bivalves, usually preserved in life position. Other spectacular phenomena include submarine fissure infillings, often called neptunian dykes. The fissures penetrate both Dachstein Limestone and the lowermost Jurassic beds and reach 30 cm in width at some places. They are filled by pink or red mudstone commonly containing clasts of the host rock (Figure 4).
Figure 4: Lower Jurassic fissure infilling in Upper Triassic Dachstein Limestone.
The boundary between Triassic and Jurassic beds is a flat surface truncating megalodontid bivalves at some places. The Dachstein Limestone is overlain conformably by pink then red Jurassic limestone beds assigned to the Pisznice and Törökbükk Formations, corresponding to the “red marble” of the older literature. This pure carbonate succession, Hettangian to Pliensbachian in age, is magnificently exposed in the large quarry wall (former “Redstone Quarry”) of the Geological Garden (Figure 5).
Figure 5: “Redstone Quarry” exposing an undisturbed Upper Triassic to Lower Jurassic (Pliensbachian) limestone succession. A segment of the wall appearing as an oblique darker band in the photograph was not cleaned in 2015 in order to display the original state of the wall as well as to study the effects of weathering and growth of vegetation.
The sharp boundary between the Upper Triassic carbonate platform deposits and the overlying deeper-water Lower Jurassic red limestone is a spectacular example of drowning unconformities and it is a characteristic feature of the Gerecse Jurassic. Fossils extracted from the lowermost beds of the Pisznice Limestone indicate a depositional depth exceeding 200 m (Pálfy et al., 2007). The red limestone succession is more than 30 m thick, while the cumulative thickness of younger Jurassic strata is less than 15 m. The fine-grained Pisznice Limestone is followed by the Törökbükk Limestone Formation, an intensively bioturbated crinoidal limestone (encrinite) of Pliensbachian age (Figure 6). Although named after a quarry located in the Gerecse Mountains, this lithostratigraphic unit was introduced by Fülöp (1976) on the basis of the Kálvária Hill quarries.
Figure 6: Bioturbated beds of the Pisznice Limestone Formation.
Due to a normal fault running almost parallel to the “Redstone Quarry” wall, Middle and Upper Jurassic as well as Lower Cretaceous beds are hardly visible in the lower yard of the Geological Garden. Fine exposures can be found, however, on the upper terrace (Figure 7).
Figure 7: Cleaned rock surface on the upper terrace of the Geological Garden exposing Jurassic–Lower Cretaceous beds dissected by normal faults. The “Oxfordian Breccia” appears in the photo as a near-horizontal light grey band at the foot of the mound covered with grass.
The older part of the Middle Jurassic series, assigned to the Tölgyhát Limestone Formation, is strikingly diverse in facies: red marly limestone containing Fe-Mn oxide nodules, crinoidal layers and beds formed by small-sized bivalve (Bositra) shells occur. The carbonate-dominated succession is followed by brown radiolarian chert beds of the Lókút Radiolarite Formation. This chert was exploited at Kálvária Hill by Copper Age peoples. In addition to the two ancient mining pits discovered in the 1960s and now visible in the exhibition building of the Geological Garden, a third one was discovered in 2015 (Biró-T. et al., 2018)
The basal member of the Upper Jurassic is a peculiar sedimentary breccia bed, known as “Oxfordian Breccia”, of 30-80 cm in thickness. Younger beds of the Upper Jurassic as well as the lowermost Cretaceous are developed in a thin succession of pelagic limestones. Ammonite pavements visible on some bedding planes of the Kimmeridgian Pálihálás Limestone are highlights of the Geological Garden (Figure 8).
Figure 8: Ammonite in the Upper Jurassic Pálihálás Limestone.
The Jurassic/Cretaceous boundary can be drawn within the Szentivánhegy Limestone representing Tithonian, Berriasian and partly Valanginian Stages. This latter lithostratigraphic unit was named after a medieval settlement (Szentivánhegy) once located on Kálvária Hill, at the time called Szentiván Hill.
The present-day area of the Transdanubian Range was deformed during an early phase of the Alpine orogeny in the late Early Cretaceous. This resulted in the interruption of the more or less continuous marine sedimentation that began in the Early Triassic and lasted for more than 110 million years. On Kálvária Hill, approximately 20 million years are not recorded in rocks. Sedimentation resumed around 115 million years ago and led to the deposition of the Late Aptian Tata Limestone –another formation whose type locality is Kálvária Hill – that overlies the eroded surface of tilted Upper Jurassic limestone beds (Figure 9).
Figure 9: Uneven surface of Upper Jurassic limestone overlain by well bedded Lower Cretaceous Tata Limestone in the former “Bluestone Quarry”. Earlier researchers interpreted this exposure as a “fossilised rocky coast”.
Tata Limestone is the youngest known example of the vanished facies called “regional encrinite”. The term is used to denote crinoidal limestone successions of considerable thickness and lateral extent. This unit is widespread along the Transdanubian Range, from the town of Sümeg (located near the western margin of the range) to Tata, but is completely lacking from the Gerecse Mountains. Cretaceous rocks younger than Tata Limestone are not exposed on Kálvária Hill.
The Geological Garden as a place for geoeducation
As in most European countries, geology does not appear as an independent discipline in secondary school curricula in Hungary and is taught within the subject of geography. The proportion of time allotted to geography has been drastically reduced in the last decades if the total number of lessons is considered. It is therefore of vital importance to utilise the educational opportunity provided by features of geological heritage. Abandoned quarries often serve as valuable resources for education (e.g. Macadam & Shail, 2002).The Geological Garden provides an inspiring environment for teaching. In the last ten years more than 5,000 students have learned geology there. Primary and secondary school students living in Tata or enrolled in schools located in the area, as well as ELTE students and employees, may visit the Geological Garden free of charge.In addition to outdoor geology lessons held on a more or less regular basis, the Geological Garden often serves as a locale for outreach events attended by a wider audience. The “Day of Geotopes”, organized jointly each October with the Kuny Domokos Museum of Tata, has proved to be especially popular.
Because it is located in the vicinity of Budapest, the Geological Garden is usually the site of the first full-day field trip of freshman undergraduate geology students of ELTE. Exposures of Kálvária Hill offer a good opportunity to study different rocks and a wide range of geological phenomena. In addition to local rocks, the area houses more than 40 boulders representing the most important mountain-forming rocks of Hungary. The collection, unequalled elsewhere in Hungary, is exhibited in the lower yard and is profited during field trips (Figure 10).
Figure 10: Boulders of the Oligocene Csatka Conglomerate in the “Mountain-forming rocks of Hungary” collection exhibited in the lower yard of the Geological Garden.
Conclusion
According to Brilha (2018), geological heritage is materialised by exceptional elements of geological diversity, and typically elements of high value are considered as exceptional. The Geological Garden at Tata houses a number of geodiversity elements of high scientific value, including type sections of three lithostratigraphic units. Due to the favourable conditions, the area also has a high educational value and provides visitors with an opportunity – unique in Hungary – to study a spectacular succession of Mesozoic marine sedimentary rocks, as well as visit prehistoric chert mines and a collection of mountain-building rocks of Hungary, in easily accessible abandoned quarries and other exposures concentrated in a well-groomed garden environment.
References
Biró-T., K., Harman-Tóth, E., Dúzs, K. (2018) New research at Tata-Kálváriadomb, Hungary. In: Werra, H.D., Woźny, M. (eds.) Between History and Archaeology – Papers in honour of Jacek Lech. Archaeopress Publishing Ltd, Oxford, pp 49–57.
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