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Geology of Haţeg

Today Haţeg is a landlocked town within the Eastern European country of Romania but 70 million years ago during the late Cretaceous it was an island within a shallow sea that covered much of today's Southern Europe. At almost 80,000 square kilometers in size it was similar to today's Caribbean island of Hispaniola (Csiki 2005). It was formed by uplift caused by the closing of the Tethys Ocean by the collision of the African and Eurasian plates, a collision which is also responsable for mountain chains in both Southern Europe and North Africa and a process which is still occuring today as Africa pushes North. This island contains one of the most studied late Cretaceous dinosaur fauna outside of North America.

The Densus-Ciula and Sânpetru Rock Formations

Left: Figure 1. Lithological sequence of fossiliferous sites near Sânpetru, the type-locality of Nopcsa's "Sânpetru sandstone", from where most of the specimens he collected came.

The sediments that once formed the island of Haţeg have been lithified, and now form the rock formations of Densus-Ciula and Sânpetru. These date from the Maastrichtian stage of the late Cretaceous (65.5- 70.6 million years ago) and contain a wealth of fossil remains, including those of the famous dwarf dinosaurs that inspired Romanian Palaeontologist Franz Nopcsa's theory of Insular Dwarfism (also known as the [island rule]-#hyperlink to Island Rule Website#). These formations are thought to be roughly the same age (Csiki et al. 2008) and were laid down in similar environments of lakes and rivers (Therrien 2006).

Outcropping mainly in the Râul Mare and Sibisel valleys is the 2.5km thick Sânpetru formation, which historically has been divided into two members based upon a number of differences within the rock; the lower member consists of red and grey-green mudstones and pyroclastic material (Nopcsa, 1905; Grigorescu 1983; Weishampel et al. 1991) while the upper member differs by lacking the red mudstones and in the inclusion of numerous conglomerate beds (Grigorescu 1983, 1992; Weishampel et al. 1991). However there has been some question as to whether this division extends throghout the formation or just in the Sibisel Valley where historically the majority of study has occured (Therrien 2006).

The Densus-Ciula formation in the north-west of the Haţeg basin is almost 4km thick and like the Sânpetru formation is divided into members based upon recognisable differences in the rock. The rock has three members; with the lowest consisting of a volcanic/sedimentary sequence interspersed with lake deposited lime-muds (lacustrine marls), the middle of matrix-supported conglomerates, sandstones, red, brown, and green-grey mudstones and an abundance of fossils and the topmost member is distinguished by being both poor in fossils and volcanic sediments. The middle member of this formation is most famous for the numerous different fossils found within, including dinosaur bones and eggs (Grigorescu et al. 1990, Grigorescu & Csiki 2008), mollusks and plants (Antonescu et al., 1983) and a wide range of microvertebrates (Grigorescu et al. 1999), including lissamphibians (modern amphibians) and squamates (lizards and snakes) (Folie and Codrea, 2005), small theropods (Csiki and Grigorescu 1998), pterosaurs (Jianu et al. 1997; Buffetaut et al. 2002), and mammals (Grigorescu et al. 1985; Csiki and Grigorescu 2000).

Despite having a wealth of fossil remains the fossil beds of Haţeg are impoverished with respect to the number of dinosaur species present, with 13 being found in the Sânpetru Formation and 10 from the Densus-Ciula Formation, this is compared to the late Cretacean fossil faunas of North American and Asia where numbers of taxa commonly excede 30 or 40 e.g. Hell Creek Formation of South Dakota, Wyoming, and Montana; Lance and Nemegt formations of Mongolia. The European late Cretaceous dinosaurian faunas are not only all impoverished in numbers, but also in ecological types and major clades. Missing groups throughout Europe include large Tetanuran Theropods (including Tyrannosaurs), Ankylosaurids, Pachycephalosaurs, and Ceratopsians. The Haţeg faunas show closest similarities to Late Cretaceous faunas from Gosau in Austria, southern France, and Spain (Holtz et al., 2004) as well as Hungary (Ösi and Rabi,2006). Indeed this impoverishment has been a key point in the arguement to show that Haţeg was an island, as on an island there a correspondingly fewer species than in a similar sized area on the mainland.

Figure 2. Palaeogeographic map of the Mediterranean sector of Tethys during the Maastrichtian stage of the late Cretaceous, showing the location of Haţeg. Palaeolatitude revised based on Panaiotu and Panaiotu (2002).

Abbreviations: A - Apulia; AA - Austro-Alpine Domain; Ab - Alboran Block; ACP - Apennine Carbonate Platform; AM - Armorican Massif; AT - Atlas; BM - Bohemian Massif; BoT - Bosnian Trough; Cb - Calabrian Block; CfB - Carpathian Flysch Basin; CR-CAU - Crimea-Caucasus; Do - Dobrogea; HB - Hatton Bank; HK - High Karst (Dinaric Carbonate Platform); IB - Iberia; IM - Irish Massif; Ka - Kabylia; KS - Kirshehir; MC - Massif Central; ME - Menderes; MoP - Moesian Platform; NsB - North Sea Basin; PIa - Pontides Island arc; RB - Rockall Bank; RH - Rhodope Massif; RM - Rhenish Massif; Sa-Co - Sardinian-Corsican Block; SP - Serbo-Pelagonian Massif; TD - Tisia-Dacia Block (the position of "Haţeg Island" is marked by a black star); UM - Ukrainian Massif; 1, the western boundary of Tisia-Dacia, as marked by the Maramures-Szolnok Trough and the Mid-Hungarian Line.

Legend: 1, deepmarine basins (pelagic carbonates, flysch); 2, shallow-marine basins (mainly siliciclastic and carbonate shelf deposits); 3, island arc; 4, emergent land; 5, active speading ridge; 6, thrust; 7, subduction.

Source - Benton (2010)

Environment and Geography

Palaeogeographic reconstructions of Southern Europe during the Maastrichtian (see figure 2) and palaeomagnetic analyses of sedimentary deposits (Patrascu and Panaiotu 1990; Panaiotu and Panaiotu 2002) have placed Haţeg island at a latitude between 20 and 30 degrees North, which is a similar latitude to that of the islands of the Caribbean today.

Based upon the study of paleosols (fossilised soils) the climate is thought to have been sub-tropical with distinct wet- and dry-seasons (Van Itterbeeck et al. 2004), the analysis of Carbon isotopes indicate "dry woodland" conditions (Bojar et al., 2005), and oxygen isotope analysis suggests a mean annual temperature of about 20-25 °C. The rainfall estimates differ whether they are based upon the types of plant fossils found and the type of palaeosol present. The palaeosols indicate that the climate was charactorised by having seasonal precipitation of less than 1000 mm/year, with greater evapotranspiration than precipitation and a fluctuating watertable (Therrien, 2005). This differs significantly from the estimates based upon the fossil plants where mean rainfall is given as 1300-2500 mm/year (Pop and Petrescu, 1983). This difference may be explained by the ability of tropical plants to live in warm, monsoonal climates if they have access to sufficient water during the dry seasons to satisfy their metabolic needs, and so the palaeobotanical value was perhaps an overestimate (Therrien, 2005).

Haţeg - Island?

Not suprisingly the first to suggest that the rock assemblages of modern Haţeg represented a prehistoric island was the famous Franz Nopcsa (1914), however he based his argument that because the dinosaur fossls he had found were small then they must have undergone island dwarfing and so had to have lived on an island. Indeed it was not until the late 20th century that geological evidence was found to support the idea that Haţeg had been an island.

The size of Haţeg island has been debated for many years with estimates ranging 7500 to 200,000 square kilometers. The island of Haţeg would have been larger than just the Haţeg area today, as as well as the preserved depositional sediment there would undoubtably have been areas with no overall deposition. Thus more reliable estimates have put the size of the island at 80,000 square kilometers (Csiki 2005).

Modern reconstructions of the world during the late Cretaceous have built up a picture of a shattered archipelago of tropical islands covering much of what today is Southern Europe, with the rock formaions that made up the Haţeg site coming from an isolated island, separated from the mainland, indeed Palaeogeographic reconstructions such as that shown in figure 2 show that the Haţeg island would have been 200-300km away from the nearest sizable landmass in all directions. This isolation can be seen in marine sediment deposits surrounding the Haţeg site.

Literature cited

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  • Benton M. J., Csiki Z., Grigorescu D., Redelstorff R., Sander P. M., Stein K. and Weishampel D. B., 2010, Dinosaurs and the island rule: The dwarfed dinosaurs from Haţeg Island, Palaeogeography, Palaeoclimatology, Palaeoecology Article in Press
  • Bojar, A.V., Grigorescu, D., Ottner, F., Csiki, Z., 2005. Palaeoenvironmental interpretation of dinosaur- and mammal-bearing continental Maastrichtian deposits, Haţeg basin, Romania. Geological Quarterly 49, 205-222.
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  • Grigorescu, D., Csiki, Z., 2008. A new site with megaloolithid egg remains in the Maastrichtian of the Haţeg basin. Acta Palaeontologica Romaniae 6, 115-121.
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  • Van Itterbeeck, J., Sasaran, E., Codrea, V., Sasaran, L., Bultynck, P., 2004. Sedimentology of the Upper Cretaceous mammal- and dinosaur-bearing sites along the Râul Mare and Bărbat rivers, Hațeg Basin, Romania. Cretaceous Research 25, 517-530.
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Authored by Tom Baird and Richard Conium

Dicynodon Illustration courtesy of John Sibbick.
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