Post field season blog from Martin

Tabernas Basin: Tectonics Vs. Climate

A big hello to all new & existing BSG Postgraduate members, I hope the research is going well and post-Christmas life is just grand. I have recently returned from my third field season in the Tabernas basin in SE Spain and thought I would take a little time to enlighten you all on my recent exploits!

Research Focus: Briefly summarised my research is focused on the Quaternary evolution of the Tabernas basin in SE Spain. As such the study aims to assess (qualify/quantify) the significance of external drivers (tectonics, climate) in the evolution of the basin landscape spanning back to the latest Pliocene.

Tabernas Basin: The basin itself forms just one of a series of Neogene intramontane sedimentary basins of the Almería region in SE Spain (Fig. 1). Broadly speaking the Almeria region is characterised by a series of major extant ranges (sierras) and intramontane sedimentary basins, that have formed due to north-south compressional tectonic regimes throughout the Mid-Tertiary (Sanz de Galdeano & Vera, 1992). The emergence of the region via tectonic convergence resulted in a change from marine to continental conditions and, during the Quaternary, the switch to basin inversion and rapid incision of drainages (Harvey et al., 2003).

bsg1Figure 1 – Digital Elevation extract for the Almerίa region, SE Spain. Date sourced from: Instituto Geográfico Nacional, Spain

Across the basin the vast range of geomorphological styles, as attributed to the effects of Quaternary tectonics and climatic change, has created a landscape of spectacular diversity and beauty that has even been the base for numerous movies in the recent past (e.g. A Fistful of Dollars, Indiana Jones and the Last Crusade, etc.). In the east, the basin is characterised by a series of climatically controlled coalescent alluvial fan sequences with a typically featureless topography. In contrast, the west of the basin demonstrates the significance of on-going tectonics with some 250m of post-inversion incision, forming a landscape dominated by deeply entrenched bedrock fluvial systems and badlands (Fig. 2).

bsg2newFigure 2 – Major geomorphological features of the Tabernas Basin. A: Morphological map of major Quaternary landscape units, B: Travertine Curtain at Las Salinas, C: El Cautivo Badlands

Fieldwork: So how do you assess the significance of tectonics and climate in a sedimentary basin? – Well in the case of the Tabernas basin we focus on extensive preserved landscape surfaces and isolated fluvial terraces that record both stages of tectonic uplift (creation of accommodation space/down cutting of drainages) and periods of climatic dominance. My task is to make sense of these major cut/fill style landscape levels in order to assess their interactions over a range of spatial and temporal scales across the basin (Fig.3). Ultimately unravelling the spatial complexity of the landscape surfaces requires a good degree of time in the field, with the resultant mapping of surface levels after intensive reconnaissance. Field mapping is made slightly easier with what I term- ‘Martin’s Magical Field Kit’ (might have been alone in a basin for slightly to long!). In my field kit I have all basic tools for logging/locating sections, but in addition I carry the Trimble TruPulse360- a fantastic laser sighting device that enables remote measurements of horizontal & vertical distance, slope distances, azimuth and inclination. Typically the TruPulse has a range of approx. 300m for sighting and works in most conditions, however readings can be limited by humidity or in the case of Dartmoor blanket fog! Recently I have also added the Trimble Juno unit to my ‘magical field kit’- this windows based field unit running ArcPad10 software can be utilised in the field to assess topographic levels, directly map features or take digitally referenced field photographs.

bsg3newFigure 3- Quaternary landscape levels in Rambla Buho. A: Field photograph of landscape surfaces, B: Comparison image formatted in ArcGlobe10 utilising 5m Ortho-corrected digital imagery and elevation data, soruced from Instituto Geográfico Nacional, Spain

Assessing the temporal nature of sequences across the basin is deeply rooted in the spatial relationships and interactions of units. In simplified terms I am looking to formalise relative stratigraphic levels across the basin and understand how these levels relate to each other both in terms of elevation and sedimentology. This relative stratigraphy is, hopefully – touching lots of wood, going to be supplemented by absolute dates obtained from Optically Stimulated Luminescence (OSL) dating (Fig.4). Finally the outcomes from this research will enable the qualification and quantification of extrinsic drivers upon long-term landscape evolution within the Tabernas basin (easy as that – I wish!!).

Well that is all from me for now, if you have any questions/ feedback with regard to my research or the equipment I use in the field please contact me via email or on twitter.
Take care and happy new year!!
Martin Geach

bsg4Figure 4- Field gamma-spectrometry within OSL sampling location in upper surface of terrace remnant. Note supervisor for scale- not too sure about the slight militant stance.

References:

Harvey, A. M., Foster, G., Hannam, J. & Mather, A. E. (2003) ‘The Tabernas alluvial fan and lake system, southeast Spain: applications of mineral magnetic and pedogenic iron oxide analyses towards clarifying the Quaternary sediment sequences’. Geomorphology, 50 pp 151-171.

Sanz de Galdeano, C. & Vera, J. A. (1992) ‘Stratigraphic record and palaeogeographic context of the Neogene basins in the Betic Cordillera, Spain’. Basin Research, 4 pp 21-36.

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