Insights on the climatic evolution at the pre-Jaramillo to Jaramillo transition in Europe using mineralogical analysis of the Quibas paleontological site (Early Pleistocene, southern Iberian Peninsula)
ELIA DEL CASTILLO
Departamento de Química Agrícola, Geología y Edafología, Universidad de Murcia. Facultad de Química, Campus Espinardo, 30100 Murcia, España; email@example.com.
MARÍA ASUNCIÓN ALÍAS LINARES
Departamento de Química Agrícola, Geología y Edafología, Universidad de Murcia. Facultad de Química, Campus Espinardo, 30100 Murcia, España; firstname.lastname@example.org.
IPHES-CERCA, Institut Català de Paleoecologia Humana i Evolució Social, Zona Educacional 4, Campus Sescelades URV (Edifici W3), 43007 Tarragona, España; email@example.com.
IPHES-CERCA, Institut Català de Paleoecologia Humana i Evolució Social, Zona Educacional 4, Campus Sescelades URV (Edifici W3), 43007 Tarragona, España; firstname.lastname@example.org.
Departament de Geologia, Universitat Autònoma de Barcelona, 08193, Bellaterra, España;
ICP-CERCA, Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Edifici ICTA-ICP, Carrer de les Columnes s/n, Campus de la UAB, 08193, Cerdanyola del Vallès, Barcelona, España; email@example.com.
IPHES-CERCA, Institut Català de Paleoecologia Humana i Evolució Social, Zona Educacional 4, Campus Sescelades URV (Edifici W3), 43007 Tarragona, España; firstname.lastname@example.org.
ICREA, Institució Catalana de Recerca i Estudis Avançats, Pg. Lluís Companys 23, 08010 Barcelona, España.
Àrea de Prehistòria, Universitat Rovira i Virgili (URV), Avinguda de Catalunya 35, 43002 Tarragona, España.
The Early–Middle Pleistocene transition took place between 1.2 and 0.5 Ma (million years ago) and was characterized by a fundamental change in the Earth’s climatic cyclicity, with a strong intensification of glacial periods. At the beginning of the Middle Pleistocene, intense longer-lasting glacial cycles were established that contrasted with the short interglacial pulses and the cycle duration changed from 41,000 to 100,000 years.
In this context, the information obtained through the study of the Quibas paleontological site, located in southeastern Spain (Abanilla, Murcia; Fig. 1), represents an important contribution to the understanding of the climatic and faunal events that took place a million years ago in the Iberian southeast. With an age between 1.1 and 0.9 Ma, this site represents the only continuous sequence of terrestrial vertebrates of pre-Jaramillo to Jaramillo period in Europe. Precisely at this time, the first humans settled in the westernmost parts of the European continent.
Since its discovery in 1994, this karstic outcrop has provided fossil remains of more than 90 species of vertebrates, including large and small mammals, birds, reptiles and amphibians. The site is made up of a complex of karst galleries apparently filled with detrital materials from the Early Pleistocene. The complex is formed by two main structures (part of the same gallery): Quibas-Sima and Quibas-Cueva (Fig. 2A). Quibas-Sima comprises seven distinct detrital units (QS-1 to QS-7) (Fig. 2B). According to magnetobiostratigraphic correlations, QS-1 has an age between 1.1 and 1.07 Ma, QS-2 to QS-5 between 1.07 and 0.99 Ma (Jaramillo subchron), and QS- 6 and QS-7 between 0.99 and 0.9 Ma. It is the lowest levels (QS-1 to QS-4) that offer most remains of large and small vertebrates. In Quibas-Cueva, six different levels have been distinguished (QC-1 to QC-6). The most basal units of Quibas-Cueva are equivalent in age to QS-1 (1.1–1.07 Ma). Stratigraphic observations indicate that the highest level of Quibas-Cueva (QC-6) represents an extension of the QS-2/QS-3 level of Quibas-Sima (Fig. 2A).
In this work, the mineralogical composition of the sediments that make up the stratigraphic units of the Quibas-Sima section is studied using a spectrum of analyses with the objective of analyzing possible paleoclimatic trends.
MATERIALS AND METHODS
At the beginning of 2022, samples were collected from the Quibas deposit to carry out analysis of the mineralogical composition. A total of 14 samples were extracted from all the units of Quibas-Sima, except QS-7. Samples 8–14 were taken from the original profile (Fig. 3A), while samples 1–5 were taken from the core profile of the site (Fig. 3B), since the original QS-6 to QS-4 units were dismantled as excavations progressed in different campaigns since 2014. Samples 6 and 7 were obtained from the excavation surface, currently at units QS-3 and QS-2/3 (Fig. 3C). Each sample was subjected to different analyses to determine its mineralogical composition: X-ray diffraction analysis (XRD), electrical conductivity, ion chromatography and inductively coupled plasma optical emission spectrometry (ICP-OES) using argon plasma.
RESULTS AND DISCUSSION
The results of XRD present the mineral content of the different Quibas-Sima samples (Tab. 1). The electrical conductivity analysis allows to identify the degree of salinity contained in the studied levels (Tab. 2) with samples exceeding the value of 4 dS m-1 considered to be beginning to present a notable salt content. The results indicate that the units QS-5 Top, QS-5 Base, QS-4 Top, QS-4 Base and QS-1.1 dark have very high salinity values, so their anion and cation content was determined. The ion chromatography technique allowed us to obtain the values of chloride, nitrate and sulfate present at the selected levels. Finally, the ICP-OES technique shows the content of cations present at these levels (Tab. 3).
The electrical conductivity results indicate that QS-4 and QS-5 have a high salt content (≥ 4 dS m-1). Therefore, the samples at these units were subjected to an ion chromatography analysis and ICP-OES using argon plasma to determine the anionic and cationic content, respectively. The data showed that the most abundant anions in these samples are chloride and sulfate, while the most abundant cations are calcium and sodium. This is a clear indication of the presence of sodium chloride (halite) and calcium sulfate (gypsum). The high values of these salts in QS-4 and QS-5 indicates lower precipitation with respect to the rest of the units, which may be associated with moments of aridity. The solubility values of halite and gypsum are 360 g/L and 2.5 g/L, respectively, so the presence of these salts corroborates arid regions with warm climates and scarce precipitation. Therefore, an increase in aridity is evident from the lowest units of the Quibas-Sima section towards QS-5.
This climatic trend recorded along the Quibas-Sima sequence is also consistent with the results of the XRD, since from QS-2 to QS-4 and QS-5, an increase in carbonates is observed. In general, it is considered that carbonate layers such as caliches originate after long periods of evaporation, which is very common in periods of aridity. Precisely in the upper parts of QS-4 and in QS-5, the presence of caliche has been confirmed. In addition to the increase in salts, this increase in the concentration of carbonates along the sequence is compatible with a progressive decrease in precipitation at the time of deposition of the levels. According to these results, it can be inferred that between 1.1 and 1 Ma, a climate change occurred in the southeast of the Iberian Peninsula that had an impact on the precipitation regime (Fig. 4).
In our latitudes, the glacial episodes of the Early Pleistocene did not imply as much decrease in general temperatures as increase in aridity with the extension of open spaces. The opposite occurred during the interglacial phases, in which precipitation increased and with it the forest mass. According to the results of the mineralogical composition of the different Quibas-Sima units, there is evidence of a transition from humid interglacial conditions to arid glacial conditions. These results are consistent with those offered by the succession of small vertebrates identified in Quibas-Sima, from QS-1 to QS-4. The oldest of these units (QS-1) has provided fossils of a flying squirrel of the genus Hylopetes, a type of rodent that is currently linked to forest environments. This first unit also includes remains of the water shrew Neomys sp., an insectivore with semi-aquatic habits whose presence implies the development of stable water courses in the surroundings at the time of deposit of this stratum. Furthermore, QS-1 is correlated with QC-4/5 (Quibas-Cueva), a level recording the legless lizard Ophisaurus manchenioi, a reptile whose current relatives live in tropical and subtropical areas. Its appearance in Quibas certifies that the southeast of the Iberian Peninsula acted as the last refuge for subtropical species in Europe. The presence of these species in the oldest levels of the site indicates that forests developed under relatively humid conditions during its formation (Fig. 4).
However, Neomys sp. and Ophisaurus manchenioi disappear from QS-2, and Hylopetes sp. from QS-3. This is consistent with the supposed loss of habitat conducive to the survival of these species during the deposition of these levels. On the other hand, QS-3 and Q-S4 have presented fossils of reptiles linked to open and scrub environments, such as the Montpellier snake (Malpolon monspessulanus) and the snub-nosed viper (Vipera latastei), taxa absent in QS-1. Like the mineralogical composition, the ecological affinities of the small vertebrates of Quibas-Sima show the record of a climate change that goes from forested and humid conditions in its oldest part (QS-1) towards more arid conditions, with a greater development of open scrubland spaces towards the most recent levels (QS-2 to QS-4) (Fig. 4).
Thus, the data obtained is consistent with the beginning of a glacial phase that implied an increase in aridity and, consequently, a reduction in tree cover a million years ago in the southeast of Iberia. This environmental change that occurred at the beginning of the Jaramillo subchron (1.07–0.99 Ma) coincides with the transition from MIS-31 interglacial (1.081–1.062 Ma) to MIS-30 glacial. Hence, the Quibas site becomes a key location to understand the climatic events that occurred around a million years ago in southern Europe.
Key words: Jaramillo subchron, southern Spain, mineralogical composition, paleoclimatology, X-ray diffraction.
How to cite: Del Castillo, E., Alías Linares, M. A., Laborda-López, C., Iannicelli, C., Pal, S., Agustí, J. & Piñero, P. 2023. Insights on the climatic evolution at the pre-Jaramillo to Jaramillo transition in Europe using mineralogical analysis of the Quibas paleontological site (Early Pleistocene, southern Iberian Peninsula) [Claves de la evolución climática durante la transición pre-Jaramillo a Jaramillo en Europa a partir del análisis mineralógico del yacimiento paleontológico de Quibas (Pleistoceno Inferior, sureste ibérico)]. Spanish Journal of Palaeontology, 38, 255-264.
Received 11 September 2023, Accepted 23 October 2023, Published online 30 October 2023