La Hoya de Baza, the Andalucía prehistoric spa

A scientific paper published in the journal of Quaternary Science Reviews endorses a strong hydrothermal activity in the area during the last million years

1.5 million years ago there was a lake with a permanent sheet of water that was partially fed by hot springs around 36º C

PHOTOS

The Guadix-Baza, located in the Granada highlands and surrounded by the highest peaks of the Betic Cordillera (Sierra Nevada, Sierra de Baza, Sierra de las Estancias, Sierras de la Sagra, Cazorla and Segura) is a semidesert region of unusual beauty, whose landscape recalls the last strongholds of the moorish kingdom in Andalucia. Its regions harbor a unique historical and natural heritage, giving it an international dimension to this wild region. Thus, in the Hoya de Baza depression, are found the most important archaeo-paleontological localities in the northern stream of the Mediterranean, only comparable to the legendary Rift Valley in East Africa.

Currently at several sites in the basin, located in the vicinity of the village of Orce, as Barranco León, Fuente Nueva-3 and Venta Micena are taking place systematic excavations sponsored by the Ministry of Culture of the Junta de Andalucia, in an unprecedent effort to value this heritage. These excavations have recovered the oldest fossil evidence of human presence in Western Europe, dated at one million four hundred thousand years, accurately documenting the ecological and paleoenvironmental setting of the large mammal communities where these remote villagers were inserted, developed in the environment of a large salty lake.

However, the basin holds many other surprises, as the work that has just appeared in the journal Quaternary Science Reviews, an elite review of the Quaternary research. It analyzes and documents a variety of geochemical evidence, mineralogical and stratigraphic, as the presence of celestine deposits of native sulfur, magnesium clays, stromatolites and travertine formations, pointing to the existence of a strong hydrothermal activity in the region during the last million years.

The study was led by Dr. José Manuel García Aguilar, professor at the University of Malaga, along with other scientists from the fields of Paleontology, Stratigraphy and Botany from the same center, as Drs. Antonio Flores Moya, Antonio Guerra Merchan, Paul Palmqvist Barrena and Francisco Serrano Lozano, as well as Dr. Bienvenido Martínez-Navarro, ICREA researcher at the Institut Català de Paleoecologia Humana i Evolució Social (IPHES), who is the coordinator in turn of the paleontological research project at Orce.

About this hydrotherapy, which is linked to the evolution of the basin fill, product of the erosion of the surrounding mountains and conditioned by the existence of high seismicity manifested by the presence of numerous active faults, stay today as ruins in the spas at Alicún of Torres or Zújar, or the less warm water springs of Fuencaliente in Orce and Huescar, among others.

Unusual aspects

It is precisely the discovery of such anomalies related to hydrothermal phenomena which can explain a number of unusual aspects of La Hoya de Baza in the early Pleistocene, about 1.5 million years ago, at the time the deposit of Venta Micena was formed, as the existence of a lake that held a sheet of permanent water throughout the year. The rain that falls today in the region just represents 350 millimeters per year, clearly insufficient to recharge the aquifer when it was an endorheic basin. This means that the lake would have drained seasonally, as today in the Laguna de Fuente de Piedra, current analog but in a smaller scale of Lake Baza.

In addition, the low winter temperatures would have indicated the freeze of the water surface, which would preclude the existence of certain elements of the fauna, as the giant Pleistocene hippopotamus, well documented in the  paleontological region. “Now, this megaherbivore, whose body mass is the double of that of the current specie, had a greater dependence on the liquid medium, as was only fed with the aquatic vegetation,” says Bienvenido Martínez-Navarro.

The key lies in the isotopic values ​​recovered in the fossil collagen of the fauna at Venta Micena, they indicate that a million and a half years ago, rainfall in the basin of Baza, was around 800 milliliters, much more higher than the actual. This water level, added to the hotsprings whose temperatures were around the 36 ° C, would result in the hydrological stability of the lake, necessary for the existence of the fauna with a significant subtropical character. This scenario configure what is known as a hotspot of a high biological productivity, similar to that found in the chain of lakes in East Africa, cradle of humanity.

Reference

García-Aguilar, J.M et al. “Hydrothermal activity and its paleoecological implications in the latest Miocene to Middle Pleistocene lacustrine environments of the Baza Basin (Betic Cordillera, SE Spain)”. Quaternary Science Reviews 96, 204-221 (2014)

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