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Santiago Moliner Aznar Ph D. Thesis
Santiago Moliner Aznar defended the Ph. D. Thesis “Caracterización y valorización del patrimonio geológico del área de Sierra Espuña (Cordillera Bética: SE, España” on April 27th 2022.
Abstract:
The Sierra Espuña area (Murcia: SE Spain) is characterized by their great biodiversity integrated in the Intercontinental Biosphere Reserve of the Mediterranean. Although authorities are very interested in valorization and protection of biodiversity (flora and fauna), the interest in geological heritage is still much lower. So, this PH Thesis tries to show and give value to the very best sites of geologic interest recognizable in the area (Sierra Espuña and the Mula-Pliego-Gebas Depression). So, 55 sites have been proposed as suitable to be considered as geological heritage. The characterization of these sites is done through an approach of combination of recent methods practiced and published. The methodology allows the identification of general data, physical description, evaluation of scientific value (SV), the Potential Educational Use (PEU), Potential Tourism Use (PTU) and the Degradation Risk (DR). The use of the quantification methodology (Brilha, 2016) confirmed that the sites of the Regional Park of Sierra Espuña are of international relevance with a solid and objective inventory. Similarly, the results of the valorization indicate that 51 sites have high or very high scientific value, while all the sites reach high or very high didactic and touristic values. Contrarily, the degradational risk is mostly low or moderate. Only 19 sites show high or very high values. The inventoried sites are distributed over Sierra Espuña Regional Park and neighboring areas (Mula-Pliego-Gebas Depression), being located along pedestrian paths, trails, tracks and motorways. These sites present a wide variety of geological typologies such as structural geology, stratigraphy, sedimentology, paleontology, geomaterials, petrology, geomorphology, hydraulic and hydrogeology. The valuation of the selected geosites led us to their distribution and integration in 8georoutes (El Berro, with 8 sites; Las Alquerías, with 7 sites; Cumbres Espuña, with 7 sites; Valle de Malvariche, with 9 sites; Aledo-La Santa, with 5 sites; Pliego Depression, with 6 sites; Paraje de Gebas, with 7 sites; Mula, with 6 sites). Finally, some actions following the criteria of the Global Geoparks Network by UNESCO have been proposed for the better conservation of the geosites but also to contribute to education and to promote tourism. These actions would also stimulate economic activity and sustainable development in the area by attracting increasing numbers of visitors interested in the geological heritage.
Sierra Espuña Malaguide an example of geological heritage
The Cenozoic Malaguide Basin from Sierra Espuña (Internal Betic Zone, S Spain) due to the quality of outcropping, areal representation, and continuity in the sedimentation can be considered a key-basin. In the last 30 years, a large number of studies with very different methodological approaches have been done in the area. Models indicate an evolution from passive margin to wedgetop basin from Late Cretaceous to Early Miocene. Sedimentation changes from limestone platforms with scarce terrigenous inputs, during the Paleocene to Early Oligocene, to the deep basin with huge supplies of turbidite sandstones and conglomerates during the Late Oligocene to Early Miocene. The area now appears structured as an antiformal stack with evidence of synsedimentary tectonics. The Cenozoic tectono-sedimentary basin evolution is related to three phases: (1) flexural tectonics during most of the Paleogene times to create the basin; (2) fault and fold compartmentation of the basin with the creation of structural highs and subsiding areas related to blind-fault-propagation folds, deforming the basin from south to north during Late Oligocene to Early Aquitanian times; (3) thin-skin thrusting tectonics when the basin began to be eroded during the Late Aquitanian-Burdigalian. In recent times some works on the geological heritage of the area have been performed trying to diffuse different geological aspects of the sector to the general public. A review of the studies performed and the revisiting of the area allow proposing different key-outcrops to follow the tectono-sedimentary evolution of the Cenozoic basin from this area. Eight sites of geological interest have been selected (Cretaceous-Cenozoic boundary, Paleocene Mula Fm, Lower Eocene Espuña- Valdelaparra Fms, Middle Eocene Malvariche-Cánovas Fms, Lowermost Oligocene As Fm, Upper Oligocene-Lower Aquitanian Bosque Fm, Upper Oligocene-Aquitanian Río Pliego Fm, Burdigalian El Niño Fm) and an evaluation has been performed to obtain four parameters: the scientific value, the educational and touristic potential, and the degradation risk. The firsts three parameters obtained values above 50 being considered of “high” or “very high” interest (“very high” in most of the cases). The last parameter shows always values below 50 indicating a “moderate” or “low” risk of degradation. The obtained values allow us considering the tectono-sedimentary evolution of this basin worthy of being proposed as a geological heritage.
Middle Eocene carbonate platforms of the westernmost Tethys
A study of the paleoenvironmental evolution of the middle Eocene platforms recognized in the westernmost Tethys has been carried out in the well exposed middle Eocene succession from Sierra Espuña-Mula basin (Betic Cordillera, S Spain). Eight microfacies (Mf1 to Mf8) have been recognized, based mainly on fossil assemblages (principally larger benthic foraminifera), and rock texture and fabric.
The fossiliferous assemblage can be asigned to the ‘subtropical’ heterozoan association or to the low-latitude ‘foralgal facies’ , which are dominated by non-framework building, light-dependent biota such as perforate larger benthic foraminifera, coralline algae, and sometimes green algae and solitary corals. Larger benthic foraminifer assemblages, corresponding from euphotic to oligophotic conditions and the large surface showed, suggest a progressive marine ramp under essentially oligotrophic conditions. Eventually, supply of detrital sediments from the continent and/or upwelling currents increasse the nutrients of marine waters. Comparision with other Tethyan sectors allows stating that coral-reef buildups (z-corals) were widespread on shallow platforms of the central and eastern Tethys Ocean, but that these were neither of great dimensions nor dominant because of the much more dominant presence of larger benthic foraminifera. Moreover, these coral constructions were completely absents in the westernmost Tethys. The dominance of larger benthic foraminifera and the absence of z-corals in the westernmost Tethys is explained by particular paleogeographic features due to the occurrence of a narrow and deep oceanic branch (i.e., the Maghrebian Flysch Basin) connecting the Tethys with the Atlantic Ocean.
The various issues regarding the morphological characters and evolution of larger benthic foraminifera in the study area, such as sizes of tests, specific diversity and/or intraspecific variability, number of appearances and last occurrences during the middle Eocene are analyzed and compared with those appearing in other Tethyan sectors. In addition, the early to late Bartonian boundary is recognized in the study area as critical for the biological change as in other shallow-marine environments along the Tethys margins.
Compactation in sedimentary basins
Subsidence analysis is an important technique in the study of sedimentary basins but the effects of compaction must be “backstripped”. The compaction of sediments is also of importance for petroleum and water reservoir research with very important economic derivations. Most methods for calculating compaction are based on empirically derived porosity-depth relationships from a variety of known sediment types. The challenge of this paper is to apply alternative methods for calculating compaction in sedimentary basins based on: physical calculation with elastic by Steinbrenner, oedometric and change of the specific weight of the sediment methods; and use of Loadcap software.
The Triassic to Lower Miocene 3025m thick succession of Sierra Espuña (SE Spain) is used as case study for the calculations. In this succession former mineralogical studies and apatite fission-track suggested an original thickness between 4 and 6km. The validity of each one of the proposed methods is discussed, as well as, compared for the whole succession compaction but also separately for hard vs soft sediments and for thick vs thin beds.
The compaction values obtained with the alternative methods are similar to those resulting with the lower-limit curves of the porosity-depth change method. The new methods have provided values slightly higher than 4km for the whole original thickness using the geotechnical software and the change of the sediments specific weigh methods; meanwhile values below 4km for other methods. So, in our opinion, the geotechnical software and the change of the specific weight of the sediment methods are compatible with mineralogical constraints and also, the input data are usually better known and easier to determinate. Otherwise, the elastic method seems only accurate for soft sediments; meanwhile the oedometric method is highly influenced by the thickness of the considered beds.
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