Bedrock Quest: Reflections on Fieldwork in the Azuero Peninsula

Delicate and intricate, the complexity of ecology and climate in the tropics presents a challenge for any scientist wishing to study more closely patterns of the naturaleza. Especially for geologists, accessing the bedrock, the layer of rock that forms the base of the land–underlying all soil and bodies of water–, is especially tricky. Hot and humid weather year round in tropical latitudes makes for incredible biological productivity, and happy microbes break down rocks into soils at a startling pace. Thus, to find exposures of rock outcrops that were fresh enough to determine the lithology, or composition, required a bit of effort.

A group of students from the University of the Andes examining an outcrop of basalt in Rio Verdadero.

A group of students from the University of the Andes discuss the orientation and lithology of an outcrop of basalt in Rio Verdadero. Plant growth in the rock’s cracks (fractures and faults) highlights patterns in the orientations of such features. Noting the primary direction and orientation of fractures can give information about regional stresses and tectonic changes.

In Azuero especially, it was difficult to see any bedrock beneath thick layers of red- iron rich tropical soils. The majority of land in the past 60 years has been deforested, and pasture land stretches for miles. Thus, to access the rocks, the majority of our time was spent in rivers, where water carved into the bedrock below.

Tiny sparkling grains of a blue-green metamorphic mineral (most likely epidote) that forms when volcanic basalts are hydrothermally altered. Notice the thin orange layer (perhaps microbial) on the surface, which shows weathering or breakdown of the rock ('meteorizado' in spanish). Oftentimes it requires a rock hammer to break open the rock and see past this superficial rind.

Tiny sparkling grains of a blue-green metamorphic mineral (most likely epidote) that forms when volcanic basalts are hydrothermally altered. Notice the thin orange layer (perhaps microbial) on the surface, which shows weathering or breakdown of the rock (‘meteorizado’ in spanish). Oftentimes it requires a rock hammer to break open the rock and see past this superficial rind.

And so, our group of geologists embarked on a quest to find bedrock exposures in the countryside of rural Panama. Pictured in the foreground PCP-PIRE intern Paris Morgan.

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Together with a group of twenty-plus students from the University of the Andes, de Bogota, Colombia, the Summer 2015 PCP-PIRE intern team shared in a three week mission to map the bedrock geology of western Panama.

A half-day’s drive from the Panama Canal Zone, the Azuero peninsula is comprised of rocks much older than those encountered in the Canal. Our goal was to learn more about the tectonic history of the region, to better inform our understanding of the ‘how’ and ‘why’ of the closure of the Isthmus of Panama.  To do this, we spent each day hiking through rivers and along beaches to access outcrops (‘afloramientos’ in spanish), where we would diligently document (in colored pencils on topographic maps) the rock types we encountered, their orientation and extent. By compiling bits of color day after day, it was possible to draw connections between similar rock types and infer (or, quite literally ‘color-in’) the bedrock geologic map of the south-western portion of the peninsula. Increíble!

Paleontologist Jorge Moreno-Bernal, field leader PCP-PIRE.

Paleontologist Jorge Moreno-Bernal, field leader PCP-PIRE.

Trekking through the rural countryside of Panama, the pursuit of a geologic field mapper is to learn the layout of the land…by foot. This caterpillar and paleontologist both captured in the view, caught moving at a slightly different pace.

 

July 2015. By Gina Roberti, PCP-PIRE Intern.

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