Pre-Messinian connectivity of the Atlantic and Mediterranean

Overview

The development of the Betic orogen reflects regional tectonics and the interplay between uplift, erosion and basin filling. In Spain, uplift of the Sierra Nevada and other blocks was accompanied by filling of inter-montane basins which were periodically inter-linked to produce direct connections between the Atlantic and Mediterranean. Rapid basin fill is associated with high rates of denudation and source areas can be determined from distinctive changes in provenance of these fills. Although the timing of basin fill can be locally constrained through both thermochronological and biostratigraphic means, the sparse nature of such data mean that the timing of infill remains uncertain in many of the key locations. Hence, debates continue regarding the sequence of tectonic events and the timing of opening and closure of inter-oceanic corridors.
Infill deposits can be found throughout the Betic orogen and surrounding basins. Particularly well-exposed deposits are found at el Chorro in the Guadalhorce Corridor. Here, van der Schee et al (2018) describe interbedded conglomerates and silts (80m), silts containing large cross-beds and rip-up clasts (190m), overlain by 120m of sands and conglomerates. Using a biostratigraphic marker, van der Schee et al conclude that this Corridor closed earlier than 7.51 Ma, in contrast to an estimate based on oxygen isotopes in foraminifera of 6.18Ma (Pérez-Asensio et al, 2012). The difference in these dates is extremely significant because of the role of closure of the links to the Atlantic in initiating the Messinian Salinity Crisis (5.97-5.33 Ma). As well as this difference in ages, different interpretations of the sedimentology of the sequence lead to debates about whether the connection had a two-way flow between the two oceans and hence about the potential for high-salinity Mediterranean water to enter the North Atlantic, with implications for circulation and the climate of NW Europe.
The different dates for the el Chorro deposits that have been obtained are important, and this project seeks to provide independent dating of sedimentation. Cosmogenic burial dating (using 26Al and 10Be in quartz; Ciampalini et al 2015) will be used to determine the onset of major episodes of sedimentation. Samples will be collected from immediately above erosional surfaces towards the base of the sequence, towards the top, and from at least one location mid-sequence. Using two isotopes with differing half-lives, the onset of burial can be determined.
Field evidence for flow directions (uni- or bi-directional) at different elevations will inform interpretation of flow directions and the nature of the connection through time. Using established relationships between bedform geometry and flow properties (depth; velocity) the nature of the sedimentary environment will be quantified in greater detail than previously. Statistical modelling of palaeocurrent data will be used to infer potential sediment sources (Owen et al 2015).
Together with the burial dating, this sedimentological information will provide a new interpretation of the sequence, rate and type of infilling processes in the Guadalhorce Corridor. The project will include formal statistical comparison of dates obtained by different methods and at different locations in the sequence to test hypotheses regarding the timing of closure and the nature of the Corridor prior to its closure.
This project therefore aims to independently constrain the timing of closure of the Guadalhorce Corridor, which linked the two oceans. The project will develop new constraints on the timing of infill, and will provide new quantitative determination of the depositional environments. Taken together, these aims will enhance understanding of the evolution of the Betic orogen, and so contribute to a wider understanding of orogenesis.

Methodology

Much of the infill at el Chorro is accessible on foot. The applied methods will include the following:
Fieldwork:
(a) Sedimentary logging: grain-size; palaeo-currents;
(b) Sampling for sediment analysis and micro-fossil biostratigraphy;
(c) Photogrammetry;
(d) Sampling for cosmogenic dating.
Laboratory techniques:
(e) SEM imaging and automated petrographic analysis (Durham);
(f) Preparation of targets for cosmogenic nuclide analysis. Measurements will be made under the guidance of Dr Derek Fabel at SUERC (Scottish Universities Environmental Research Centre);
Data analysis:
(g) Image processing and analysis (field images; SEM images);
(h) Statistical analysis.

Because the exposure is so extensive in this area, field sampling will be planned following an initial reconnaissance visit during which an overview of the site will be obtained. Initial samples from key parts of the sequence will be used to inform detailed sampling in two subsequent extended periods of fieldwork.

Project Timeline

Year 1

Training in key field and laboratory skills
Reconnaissance field visit and initial sampling (spring)
Meta-analysis of published data
Application to NERC Cosmogenic Isotope Analysis Facility (CIAF)

Year 2

Field work (2 x 4 week periods) – logging, photography, sampling
Laboratory sample preparation and SEM analysis
Conference attendance to present poster of initial data
Cosmogenic measurement and analysis

Year 3

Cosmogenic measurement and analysis (Reserve date)
Statistical analysis of all data
International Conference to present main results
Final analysis and write-up (paper submission).

Year 3.5

Continued write-up and submission (paper submission).

Training
& Skills

Specific training depends on the prior skills and experience of the student, but will include several of:
– fieldwork safety and 1st aid
– field survey using drone and dGPS
– field sedimentology (logging; sampling)
– sample preparation for SEM and SEM operation and analysis
– mineral separation
– target preparation for cosmogenic nuclide dating
– principles of cosmogenic nuclide analysis, including error modelling
– advanced spatial statistics in R
– use of Matlab, Python and/or R for data analysis and presentation

References & further reading

Ciampalini, A, Persano, C, Fabel, FD, and Firpo, M 2015 Dating Pleistocene deltaic deposits using in-situ Al-26 and Be-10 cosmogenic nuclides. Quaternary Geochronology 28, 71-9 https://doi.org/10.1016/j.quageo.2015.04.005
Owen, A, Jupp, PE, Nichols, GJ, Hartley, AJ, Weissmann, GS and Sadykova, D 2015 Statistical estimation of the position of an apex: application to the geological record. Journal of Sedimentary Research, 85, 142-152. doi:10.2110/jsr.2015.16
Pérez-Asensio, JN, Aguirre, J, Schmiedl, G and Civis, J 2012 Impact of restriction on the Atlantic-Mediterranean gateway on the Mediterranean Outflow Water and eastern Atlantic circulation during the Messinian Palaeoceanography 27, PA3222 31.
Reinhardt, LJ, Dempster, TJ, Shroder, JF and Persano, C 2007 Tectonic denudation and topographic development in the Spanish Sierra Nevada. Tectonics, 26, doi:10.1029/2006TC001954
Reinhardt, LJ, Bishop, P, Hoey, TB, Dempster, TJ and Sanderson, DCW 2007. Quantification of the transient response to base-level fall in a steep mountain catchment. Journal of Geophysical Research – Earth Surface 112, F03S05 doi:10.1029/2006JF000524
Schoorl, JM and Veldkamp, A 2003 late Cenozoic landscape development and its tectonic implications for the Guadalhorce valley near Ãlora (Southern Spain) Geomorphology 50, 43-57
van der Schee, M 2018 New age constraints on the western Betic intramontane basins: a late Tortonian closure of the Guadalhorce Corridor? Terra Nova 30, 325-32. DOI: 10.1111/ter.12347

Further Information

Applications: to apply for this PhD please use the url: https://www.gla.ac.uk/study/applyonline/?CAREER=PGR&PLAN_CODES=CF18-7316

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