Contexto estratigráfico y sedimentario de los yacimientos de grandes mamíferos del sector central de la Cuenca de Guadix (Cordillera Bética). / Pla Pueyo, Sila.

Granada, Spain : Digibug (Repositorio de la Universidad de Granada), 2009. 287 p.

Research output: ThesisDoctoral Thesis

Published

Abstract

The study area of this research is situated in the central sector of the Guadix Basin (central part of the Betic Cordillera), within the Granada province of southern Spain. It is located on the ancient contact between the two main structural realms of the Betic Cordillera which act as the main sources of sediment input in the sector: the Internal Zones (or Alboran Block; Andrieux et al., 1971) and the External Zones (corresponding to the folded and faulted South Iberian paleomargin; Vera, 2000),
This investigation concentrates on the two youngest genetic units of the continental sedimentary infill of the Guadix Basin, units V and VI (Fernández et al., 1996a; Viseras et al., 2005). In these two last units, three main drainage systems could be identified (Viseras, 1991; Fernández et al., 1996b). The Axial System flowed longitudinally through the basin, parallel to its axis, and in this part of the basin, consisted of a high sinuosity fluvial system that drained towards a shallow lake located to the northeast in the neighboring Baza Basin. The other two drainage systems of the study area (External and Internal Transverse Systems) were formed by alluvial fans feeding transversally into the axial valley (Viseras, 1991; Fernández et al., 1991a, 1991c, 1993; Viseras and Fernández, 1994, 1995).
The basin, reaching its final filling stage in the Late Pleistocene (top of Unit VI) (Fernández et al., 1996b; Soria et al., 1998, 1999) evolved into an exoreic (external drainage) depression, resulting in a deep incision of the Holocene drainage network into the sedimentary infilling of the basin (Vera, 1970b; Estévez et al., 1976; Viseras and Fernández, 1992; Calvache and Viseras, 1995, 1997; Calvache et al., 1996). This extensive erosion produced exceptional outcrop exposure with many paleontologic vertebrate sites. The most important mammal sites have been found in the central sector of the basin, within units V and VI, by the research team of the Fonelas Project (Viseras et al., 2006; Garrido, 2006; Arribas and Garrido, 2007; Pla-Pueyo et al., 2006, 2008a; Garrido and Arribas, 2008).
Research here is focused on the stratigraphic, sedimentologic and petrographic characterization of the central sector of the Guadix Basin, where most of the large-mammal sites appear. The environmental characterization of the sediments is crucial to understand the ecologic and geologic processes leading to the formation of some of the most significant mammal sites in Europe (Viseras et al., 2006; Arribas and Garrido, 2007; Garrido and Arribas, 2008). The paleontologic sites in the current study are FPB-4, FP-1, FSCC-1, FSCC-2, FSCC-3, FBP-SVY-1, M-3, M-4, M-5, M-8, M-9 and FST-1.
The stratigraphic studies were supported by the construction of a geologic map of the central sector of the Guadix Basin, together with the measurement of fifteen stratigraphic profiles, most of them measured at the important paleontologic sites. Combining their lithologic correlation with previous biostratigraphic data and new magnetostratigraphic data led to a detailed chronostratigraphic scheme showing the stratigraphic architecture of the central sector of the basin. Within this scheme, the age and the relative spatial position of the most important mammal sites are related, most of them close to the Pliocene-Pleistocene boundary. The results of the current work, in adition to the previous biochronologic data, provide an absolute age for the sites, allowing their chronologic arrangement from the oldest to the youngest one, as follows: FSSC-3 and FSCC-2 (2.5-2.4 Ma), FST-1 (from 2.5-2.4 Ma, the age of FSCC-2/FSCC-3 sites to 2.148 Ma, the starting age of the Reunion subchron), FPB-4 (from 2.128 to 2.0 Ma, reverse polarity between the Reunion subchron and FP-1 site), FP-1 and FSCC-1, the former a bit older than the later, but both around 2.0 Ma old, FBP-SVY-1 (1.9 Ma), M-8 (1.9-1.8 Ma), M-3, M-4 and M-5 (from 1.778 Ma, the top of Olduvai subchron, to 1.072 Ma, the starting age of Jaramillo subchron), and M-9 (1.5-1.4 Ma).
Moreover, the magnetostratigraphic data were a very useful tool for estimating and comparing sedimentation rates from the margin and the center of the study area. The estimates for unit V are 5.2 cm/Kyr in the center of the basin, represented by section FP-1, while in the northern margin, where the basin is limited by the External Zones, the sedimentation rate is close to 3 cm/Kyr. In unit VI, sedimentation rates are similar in the center and the margin (2.3 cm/Kyr and 2.4 cm/Kyr respectively), and therefore they are lower than those estimated for unit V. The litho-, bio- and magnetostratigraphic correlation scheme has been also helpful to establish the exact position and the age (1.778 Ma) of the surface separating units V and VI.
The sedimentologic studies dealt with the description of the architectural elements appearing within the study area. They are hierarchically described, starting from the first order elements (simple lithofacies) and ending with the sixth order elements (macrosequences affecting several basins). 39 basic lithofacies have been identified in the study area, some of them described for the first time in the basin. They combine to form fifteen second-order elements that have been grouped according to their main lithologic composition. The siliciclastic dominated elements are divided into channeled elements (gravel-sand channels, sand channels, multistorey channels, V-shaped channels and pseudotabular channeled complexes) or unchanneled elements (tabular bodies, breccia beds, flat-convex lenses, lutite-marly beds, sand-clay grey beds and sand-clay grey beds). The carbonate elements involve palustrine carbonates, calcretes and calcareous tufas. Second-order elements associations are recognized to form third order elements.
These third order elements are characterized by basic sequences representing different environments of each of the three main drainage systems (Axial System, Internal Transverse System and External Transverse System) identified for the Pliocene and Pleistocene in units V and VI. These systems were previously characterized by Viseras (1991) and Fernández et al. (1996b), for each unit (V and VI) for the whole continental filling of the basin, so in this work, a sedimentary model for the Axial System is provided just for the central sector of the basin.
Architectural elements on the fourth, fifth, and sixth orders are described together as the result of the influence on sedimentation by allogenic processes such as climate, tectonism, and base level changes.
The astronomical forcing on the sedimentation in the study area is evidenced by the cyclic arrangement of the Internal Transverse System and the Axial System. Each one of the resulting cycles corresponds to a 100 Kyr time span, indicating the influence of the orbital eccentricity variations in terms of climate.
In addition to the cyclicity identified as astronomical forcing, the petrographic features of the carbonate facies provide a proxy to the climate prevailing during sedimentation of units V and VI. The palustrine carbonate textures, together with a nearly perennial character deduced for the fluvial channels, indicate that unit V experienced an intermediate to sub-humid climate during deposition. As to temperature estimates, the morphology of tufa build-ups in unit V point to a cool to temperate climate. This agrees with the cold temperature previously estimatedfor this unit (Minwer-Barakat, 2005) from the micrommamal faunal association of some paleontologic sites located to the north of the study area. There are no clues on temperature during the deposition of unit VI, but taking into account the abundance of vertically-stacked palustrine sequences and their petrographic textures, the climate conditions would be quite similar to that affecting unit V. A lower exposure index for palustrine carbonates textures of unit VI suggest only a slightly more humid climate for this unit.
Apart from the climate, the tectonism is also an important allogenic factor that needs to be taken into account. In this sense, the sedimentation rates estimates for units V and VI in the study area, calculated for each unit in the center and the margin, show an evolution that can be interpreted as a decrease of the accommodation space rate from unit V to unit VI.
The concept of stratigraphic level (Shanley and McCabe, 1994) is used here to estimate base level changes through time. A general situation of rising base level, with punctuated moments of base level fall, is deduced for unit V from the third order sequences established for the sediments of the Axial System and the External Transverse System. A generally high base level is deduced for unit VI.
Finally, a classification of units V and VI in terms of sequence stratigraphy is proposed, starting from two pre-existing sequence-stratigraphic models for fluvio-lacustrine basins. One of these models deals with siliciclastic deposits (Martinsen et al., 1999) and the other mainly carbonate sedimentation (Alonso-Zarza, 2003). Those models are based on the interplay between the available accommodation space (A) and the sediment supply (S), using them as indicators of variations in the base level (ratio A/S). As a result, Unit V is classified as a high accommodation systems tract (HAS), while unit VI meets the requirements to be defined as a low accommodation systems tract (LAS). The contact between both units corresponds to a sequence boundary, while the mature calcretes on top of unit VI suggest long periods of subaerial exposure and lack of sedimentation.
Therefore, this work integrates the current knowledge about the siliciclastic and carbonate sedimentology of the fluvio-lacustrine and alluvial systems in the sector of the Guadix Basin containing paleontologic sites. As a result, a sequence stratigraphic context is proposed for units V and VI, for insight into the evolutionary development of continental siliciclastic and carbonate sedimentation in the Guadix Basin over the last 3.8 Ma.
Translated title of the contributionStratigraphic and sedimentary context of the large-mammal sites in the central sector of the Guadix Basin, Betic Cordillera
Original languageSpanish
QualificationPhD
Awarding Institution
  • Universidad de Granada
Supervisors/Advisors
  • Viseras, César, Supervisor, External person
  • Soria, Jesús M., Supervisor, External person
  • Arribas, Alfonso, Supervisor, External person
Thesis sponsors
  • IGME
Award date6 Jul 2009
Place of PublicationGranada, Spain
Publisher
  • Digibug (Repositorio de la Universidad de Granada)
Electronic ISBNs978-84-692-4179-0
Publication statusPublished - 2009
This open access research output is licenced under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

ID: 2692218