Pictures and Sketches illustrating El Molino Formation
Abstract:
The late Cretaceous vertebrate ichnofacies of Bolivia, Facts & Implications
Cretaceous dinosaur tracks are known in Central Bolivia since 1968. Recent work shows, that tracksites are widespread and occur in multiple layers from the Campanian to the Late Maastrichtian. The ichnofauna is associated with alluvial to deltaic as well as lacustrine settings. Several new sites with tracks of titanosaurids and theropods in the upper part of the Chaunaca Formation (Campanian) correspond to similar stratigraphic levels in the Toro-Toro Formation further north. The Late Maastrichtian sediments form part of a megatracksite that spreads from southern Peru (Vilquechico Fm) to the Central Bolivian Andes (El Molino Fm) down to the Salta province in northern Argentina (Yacoraite Fm).
The ichnofauna of the El Molino Formation has been studied in detail at the Cal Orcko locality, 5 km west of Sucre (Bolivia). The trackbearing surface is in an active cement quarry of the Fabrica Nacional de Cementos (FANCESA). It consists of a limestone wall with a shear size of 25'000 square meters literally covered by dinosaur tracks. Up to now it is the largest dinosaur tracksite known on the planet. The site has been investigated during july and august 1998. The limestone wall, where the dinosaur tracks have been observed, is steeply inclined (70 ) and could only be mapped with heavy climbing equipment.
The track assemblage occurs in the middle part of the El Molino Formation (Maastrichtian) which is thought to have been deposited in a marginal marine to brackish setting.The El Molino Formation itself has an extended fossil record, including charophytes, stromatolites, molluscs, and actinopterygians; they indicate a late Campanian to Maastrichtian age. Palynology indicates a Maastrichtian age for the second sequence of the El Molino Formation .
The trackbearing levels show episodic pedogenesis, stromatolites and tempestites and were deposited in ephemeral and perennial lakes. More than 250 trackways on seven levels have been registered. Six different types of dinosaurs are present. The most spectacular trackways are those of quadrupedal titanosaurs, herbivore animals with a size between 15 and 25m. For the first time, the presence of ankylosaurs on the South American continent can be demonstrated. Footprints of bipedal carnivorous dinosaurs are very common. They were made by animals of different size classes ranging from 1.2m up to 6 m in height. Some of those trackways show that the animals were limping; others indicate a speed of more than 30 km per hour. One trackway of a theropod dinosaur can be followed for more than 350 m and presents the longest ever recorded. The high diversity of the track assemblage clearly demonstrates, that contrary to current opinions, there was no gradual decline in terrestrial diversity towards the end of the Cretaceous and favours a drastic event at the K/T boundary.
The high diversity of the track assemblage clearly shows, that there was no gradual decline in dinosaur diversity towards the end of the Cretaceous and favours a drastic event at the K/T boundary.Literature:
- Lockley, M., Meyer, Chr.-A., The late Cretaceous vertebrate ichnofacies of Bolivia: facts and implications, VII int. symposium on mesozoic terrestrial ecosystems, 1999, Abstracts
- Hippler D., Bucher, S., Meyer,
Chr.-A. & Fügenschuh, B., Preliminary results on
the sedimentology of the Late Cretaceous El Molino
Formation (Sucre, Bolivia), Seventh Swiss Sed Meetin
1999, Abstracts
Sponsors:
Swiss National Science Foundation, Swiss Academy of Natural Sciences, Mammut Arova (Switzerland), FANCESA (Sucre, Bolivia), Leica (Switzerland), Petzl (Switzerland), Tramp Store (Switzerland), Drawin (Germany).
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