CHARACTERISATION OF MATERIALS AND EVALUATION OF WATER-REPELLENT TREATMENTS FOR THE CONSERVATION OF THE NATURAL MONUMENT OF FOSSIL JELLYFISH FOOTPRINTS (CONSTANTINA, SEVILLA)

This site is located in the Sierra Morena Natural Park in Seville, designated as a World Geopark by UNESCO. It is distinguished for housing one of the most relevant records worldwide of impressions of soft-bodied organisms, interpreted as hydrozoan medusozoans. It is estimated to be 540 million years old, corresponding to the Lower Cambrian.

The uniqueness of this site lies both in its remote antiquity and in the number and size of the prints preserved. About 300 impressions have been recorded, with diameters ranging from 10 to 120 cm. During the Lower Cambrian, only one other site with medusozoan imprints is known from southeastern California (USA), where only 13 specimens have been identified, ranging in size from 3 to 21 cm in diameter. On the other hand, a site of similar age (518 million years old) is found in Qingjian, southern China. However, the medusoids from this site are fossil bodies rather than impressions, and they are barely more than 1 cm in length.

Description

The conservation project of this Fossil Site, declared a Natural Monument in 2019, has revealed the existence of up to 289 impressions. These are distributed over a surface area of approximately 20 metres long by 7.5 metres wide, forming an area of about 150 m². The surface has an average slope of 23° to the south-west and shows small ripples with straight ridges, interpreted as marks left by marine currents.

The impressions present two clearly differentiated morphotypes. The first is composed of two circular or almost circular grooves (external and internal), which may be concentric and are connected by between 25 and 40 straight and radial grooves. The second, corresponding to the area surrounded by the outer groove, is usually flat, although it may present slight convexities in specimens of subumbrellar morphology and concavities in those of exumbrellar morphology. It is common to find overlapping impressions, totally or partially, in both morphologies.

Interpretation

The outer groove is interpreted as the annular canal, while the inner groove could correspond to the manubrium. These features are identified as subumbrellar and exumbrellar impressions of ancient jellyfish with large radial halos. Its modern analogue would be the genus Aequorea, a transparent, flattened hydromedusa with a diameter of up to 30 cm.

Its history

During the early Lower Cambrian, a major sea-level change (transgressive episode) generated the formation of a very shallow sublittoral marine environment, favourable for the preservation of these impressions. The appearance of several superimposed specimens could be associated with mass stranding events.

Its importance

Thanks to its age, the large number of specimens preserved and the size of the impressions, this site is considered unique in the world. From a heritage perspective, it is not only of great palaeontological value, but also constitutes an important tourist resource.

TESELA as an analytical agent

The aim of this study was to evaluate the behaviour of 5 water-repellent treatments on the stone material from the ‘Monumento Natural de Huellas Fósiles de Medusas’ in Constantina, Seville. Likewise, a complete characterisation of this stone material has also been carried out.
of this stone material has also been carried out. For this purpose, compositional, physical, morphological and textural analyses have been carried out, as well as in-situ, hydric and durability tests that provide objective and precise data on these materials and treatments.