The Jurassic Treasures of Asturias by J. C. García-Ramos, L. Piñuela and J. Lire
by, J. C. García-Ramos, L. Piñuela and J. Lires
Asturias is one of the most beautiful yet least known areas of Spain, with a strong Celtic culture and traditions stretching back over thousand years. Asturias is located in the north of Spain at the coast of the Bay of Biscay. It was at the start of the Jurassic that the progressive breaking up of the supercontinent Pangea began and dinosaurs roamed the Iberian Peninsula including the province Asturias, and left there tracks in the earth.
The Jurassic landscape was very different from the landscape at the present time. Asturias was placed in Upper Jurassic times at a paleolatitude about 33 degrees N., the coast was not yet cliffed and it did not show the present west-east orientation, either. Morover, the Cantabrian Mountains and the present inland reliefs was due to Alpine Orogeny, which reached its peak about 30 million years ago, during the first half of the Tertiary Era, and it also caused the inclination that the Jurassic stata show nowadays. The Iberian Peninsula was during the Late Jurassic a large island close to the coast of Newfoundland. The most spectacular rock outcrops from the Jurassic in Asturias extend along a practically continuous segment of coast between Cape Torres (west of Gijón) and 2 km east of Ribadesella, limited in both cases by important faults which relate them to much older rocks belonging to the Paleozoic Era.
The Jurassic history of Asturias
The Jurassic landscape in Asturias underwent many changes over a long period of time that lasted 62 million years. At the outset of the Late Jurassic the landscape in Asturias underwent a drastic change which resulted in a quick uplift and emersion of the land due to the tectonic activity. This gave rise to an irregular relief, specially marked towards to the southwest. Siliceous sediments originated in this part of the region and began to deposited in the whole area. These sediments arose from the relief erosion of Paleozoic rocks which showed above the surface of the ground because of fault activity.
The material resulting from the erosion of this relief (gravel, sand, mud) was drifted by river courses to a coast which must have lain to the east of the region. This material makes up the Vega Formation nowadays. The climate exhibited certain aridity at that time, judging both by the existence of carbonate fossil soils called \"caliches\" and by the vertical arrangement of root traces, which evidences a low phreatic level. The are corresponding to present-day Sueve Range was also partially raised by faulting, and most Jurassic marine rocks accumulated in the previous stage were eroded away by natural agents.
The emersion which resulted in asudden shift from sea to continental conditions, became spectacularly displayed in the geological record due to a distinct contact between carbonate and siliceous rocks, such as that which can be observed in the Jurassic rock successions on the coastal cliffs in Huerres (Colunga), El Puntal and Santa Mera (Villaviciosa), Lastres and the beaches of Peñarrubia, La Griega, Vega and Ribadesella. This rock contact represents a \"stratigraphic gap\", because the sequence lacks many rocks, at least from the Mid-Jurassic. From this stage, where the whole land emerged as dry land, we find the first signs of dinosaurs: isolated vertebrae in the gravel beds of Jurassic rivers, together with various footprints (ichnites).
In some of the inactive river channels and certain depressions on side areas lay occasional small pools and fresh water ponds where algae and minute crustaceans (ostracods) proliferated. Nevertheless, most of these areas situated between channels remained in the open air, as a result, their sediments were oxidized, which produced the typical reddish coloration of the Vega Formation strata.
A new rise of the Jurassic sea level moving forward the northeast progressively flooded the central eastern part of the Asturian region. Here settled a low irregular coastline, with plentiful dark muds rich in organic matter and variable proportions of sand borne by small deltas. These flowed into a tideless inland sea, cut off from the open sea by a \"threshold\" or barrier which served as protection against storms at the time. Between this threshold and the coastline lay a large depression of still brackish waters, at the bottom of which a great amount of muds was laid down. The sediments which were deposited in these environments turned into the rocks that today make up the Tereñes Formation. These rocks contain high levels of dark-coloured mudstones, very rich in dense accumulation of fossil shells (gastropods and bivalves) called
\"coquinas\" or \"shelly beds\".
The final episodes of the Jurassic history of the region, which gave rise to the rocks of the Lastres Formation, were characterized by an increase in the activty of the river system, which resulted in a bigger proportion of sand supplies on the coast, due to the activity of small deltas. This caused the coast to extend even further nort-east, though its previous NW-SE orientation remained unaltered. Dinosaurs lived in those areas of dry land close to the coast, and on the coast itself, as can be inferred from the frequent findings of fossil bones and, especially, of footprints. These fossils found in Tereñes and Lastres Formations prove that the vertebrate fauna was rich and varied, including dinosaurs, crocodiles, turtles, flying reptiles (pterosaurs) and fishes.
In marshy and swampy areas of the coastal plain the vegetation was varied: from ferns to trunks over 11 meter long and about 1 meter wide. In some cases we can even notice the remains of petrified forests in which the stumps have kept their original position and preserved their roots. The woody parts of the trunks, fossillized and hydrocarbon-impregnated, have produced jet, a variety of lignite highly appreciated in jewellery which has been long exploited in Asturias, especially in the coastal area of the borough of Villaviciosa (Oles, Argüero, Quintes, Tazones, etc.)
Plain evidence of the abundance and variety of dinosaurs in Asturias in the Jurassic is provided by the numerous findings of footprints in the three formations of the Late Jurassic (Vega, Tereñes and Lastres), which crop out on the coastal cliffs in the boroughs of Villaviciosa, Colunga and Ribadesella. From analysis of the tracks found in Asturias and comparison with other known sites the following conclusions can be drawn: There is evidence of both bipeds (theropods and ornithopods) and quadrupeds (mostly sauropods) in the region. The frequent occurrence of footprints preserved as natural casts in the outcrops often allows an accurate reproduction of the anatomical features of the fore- and hindfoot of the dinosaurs which created these tracks (claws, toe pads, irregular skin texture, and so on).
Judging by the size of tracks, there were dinosaurs of very varied proportions in this region, from small ones , the size of a present day bird, to huge ones, as in the case of brachiosaurs. Some of the footprints left by sauropods, such as those found on the beach of La Griega or on the cliffs in Tereñes, are the biggest tracks known in Spain and are more among the largest in the world. The main groupings of footprints appear around former deltaic areas on the coastal plain, especially inland and on the banks of small deltaic channels next to their mouth, as well as in areas bordering marshes, swamps and lagoons situated between those channels.
Some of the footprints constitute rather long trackways, like the ones on the cliffs in Oles, those west of Tazones and Tereñes, or those in Merón and Ribadesella beaches. To sum up, this area can be said to represent the most important Jurassic site of dinosaur tracks in Spain. It is also the Spanish site with the largest number of quadrupedal dinosaur footprints (mostly sauropods). In the spring of 2003, a Jurassic Museum, spectacular tridactyl shape will be inaugurated near the La Griega beach in the village of Colunga.The name of the museum will be Museo del Jurasico de Asturias (MUJA). Dinosaur footprints have recently been designated as a Natural Monument by the Government of Asturias. Asturian formations with dinosaur footprints, along with similar sites elsewhere in the Iberian Peninsula, are also candidates for designation as UNESCO Heritage Monuments.
Isolated dinosaur bones and teeth
The Upper Jurassic strata of Asturias have provided several theropod and sauropod bony remains. These materials come from the fluvial Vega Formation and deltaic Lastres Formation, and include some vertebrae and teeth. Within Sauropoda there are some large Pes footprint of a big sauropod caudal vertebrae, a tooth of \"spoon-like\" shape (JVLH-163) that has been assigned to Camarasauridae. The best preserved specimens of the theropod teeth are JVLH-180 and JRVH- 20, both show denticles in the mesial and distal carinae; their measures are 69x27x13 mm and 45x29 mm, respectively. Another teeth (JVLH-195 and 196) have characters that suggest affinities with Dromaeosauridae. On the other hand, a great caudal vertebra (JRVH-197) documents the presence of carnivorous dinosaurs of similar or bigger size than Allosaurus,
Ceratosaurus or Megalosaurus in the Upper Jurassic of Asturias. The last discovery, not yet studied, is a large bone from the limb of a sauropod dinosaur.
Photos: J. C. García-Ramos Special thanks to Fred Bervoets who gave us the opportunity of write this article. To Daniel Sanchez, Heather Stoll and Victoria Alonso for reviewing the English text. And to Luis Alfonso Fernandez.
García-Ramos, J. C., Aramburu, C., Piñuela, L. and Lires, J. (2001). The Dinosaur Coast. Field Guide to the Jurassic of Asturias. Consejería de Educación y Cultura del Principado de Asturias, 33 p.
Martínez, R.,Garcia-Ramos, J. C., Piñuela, L., Lires, J. and Luna, M. (2001). Dinosaur remains from the Principality of Asturias, Spain. Journal of Vertebrate Paleontology, 21(3): 78A.