Free time in Fuerteventura

I'd some ideas for a project plan for the Masters module and spent a few days before and after the OUGS trip checking out possible evidence, exposures etc.
On previous trips I'd noticed fossil shells (? Pliocene) at locations quite far inland and I thought that might be the basis for a project around sea level change, and/or tsunamis. The first few free days were spent, besides reccying locations for the trip, in searching for more shells to see if there was sufficient data to work with.

Tindaya Plains

Limpet shell - Tindaya

We'd originally spotted these shells below Montana Tindaya, at a height well above any probably sea level rise at e.g. the end of the last glacial, but the gentle slope down to the west coast might allow a tsunami to spread this far. A tsunami could be triggered by a landslide on a neighbouring island, Tenerife or Gran Canaria for example, and could pick up shells and wash them inland.

Ventral view of Tindaya limpet

We found more of these shells in the original locality (in the centre of the first image), often cemented into the caliche/calcrete surface deposits, and with caliche deposits on them.
 

There were also gastropods with knobbed ornament on the shells and again these were often cemented into the caliche and had surface coatings of caliche. There were also bivalve shells, e.g. mussels, which are more fragile and many shells were fragmented.

Moving away from the original area we searched thoroughly for more but, disappointingly, found none. It seems possible that the shells are kitchen midden deposits from prehistoric settlement on Tindaya's lower slopes.

On another day, further south, we explored the area to the east of Tuineje which is flat, and caliche covered, surrounded by flows from prehistoric cinder cone eruptions.
This flat-lying area is covered with sandy material, with the buff colour characteristic of caliche.

The flat Tuineje Plains

Lava flows at the edge of the flat plains, and a cinder cone in the distance

Clasts cemented by caliche

We parked by the edge of the lava flow and had a good look around for shells but found none. We did notice though that pebbles of (older) caliche were cemented by younger caliche!

The only shell we found

Eventually we did find a single limpet shell but felt this was insufficient evidence that the area had been flooded by the sea, even though it did have the appearance of an, at least ephemeral, lake bed.

What I finally ended up with:

Introduction

Thick layers of caliche (calcrete crust) are widespread on Fuerteventura and Lanzarote, the easternmost, closest to the African mainland, and most arid of the Canary Islands. This is highly unusual on oceanic volcanic islands composed of mafic/ultramafic igneous rocks, where there is only sparse carbonate sediment as a source for calcium and magnesium carbonates. Caliches are important to the islands, contributing chemical elements to soils. Caliche source(s) may be finite or continuing; they may be climate (wind and/or temperature) or sea level dependent. Materials can be fingerprinted, and sources identified, using metal isotope ratios as well as major, trace and REE analysis. If material availability has varied significantly over the islands’ 20 Ma history, it is likely also to vary in future, with implications for retaining present soil, vital to the island’s agriculture, and for replacing or augmenting this soil.

Research question

This study will use metal isotope ratios to assess past and present sources of supply of carbonate and associated materials to caliche on Fuerteventura and Lanzarote, Canary Islands.

Null hypothesis: There has been no change over time of the source of carbonate material supplied to Fuerteventura and Lanzarote, Canary Islands.