The flood with unexpected consequences (it fossilized plants!)
West of Comodoro Rivadavia, a prosperous but mostly unattractive town devoted to the petroleum business, is the village of Sarmiento. Most of Patagonia is a desert with low-growing bushes and long vistas. Between C. Rivadavia and Sarmiento, one is reminded of Texas, with oil wells (here referred to as penguinos – penguins!) on a relatively featureless landscape (affectionately referred to as vast by Texans!). There are oases in this desert. Places like Sarmiento are located in broad river valleys that flow mostly from west to east, from the cordillera (the Andes) to the sea. These valleys benefit from additional water and are green, agriculturally-productive areas. We are staying at Estancia Labrador (estancia=ranch) that has sheep, horses, and cherry orchards. They sell honey and sweet products such as alfajores, an Argentinian specialty whose main ingredient is dulce de leche. It’s a great place to sample the estancia culture as well as delicious homemade food.
The main attraction for this trip is the Bosque Petrificado, a protected area with rangers to provide information and keep visitors from slipping hunks of petrified wood into their pockets (it’s very tempting, as my husband Jay can tell you!). The landscape has a badlands-like appearance. Although they are 65 million years old, the sediments are not well consolidated and they erode into soft mound shapes. Adding to the allure of the place is the multiple colors of the sedimentary layers, shown in the photo below.
In the time when these sediments were deposited (near the Meozoic-Cenozoic boundary when the dinosaurs went extinct) this area was located on a broad coastal plain with estuaries and marshes. Landward of the coast were forests with palm trees and other tropical plants. One day a large flood carried vast amounts of plant material, including tree trunks up to a meter in diameter and many meters long, into the coastal zone where they were quickly buried by sediments, thus preserving them from rotting, the fate of most plant material. After burial, silica-rich fluids, apparently provided by volcanic activity in the region, flowed through the porous sand and turned the wood into rock made of quartz. Most of the tree trunks are surrounded by a thin veneer of sand that is also cemented with silica. In the photo below, there is a log sticking out of the sediment within which it was deposited; most of the fossil plants are no longer in their original positions but are located on the landscape where they have collected as the softer sediment around them has eroded away.
Unlike the petrified forest you may have seen in Arizona, this event preserved even the smallest splinter, as well as seeds. A sign from along the path explains how this occurred.
Another photo may give a sense of how real these tree pieces appear – I found myself continually checking the pieces to make sure they were really rock and not wood, because the smallest details of the wood have been preserved.
Our weather yesterday was not ideal, as we had wind that nearly blew us away, and we were hoping for sun to better show the brilliant sediment colors. But we were not disappointed with the petrified forest. (Note: to the south there is another petrified forest that was buried and silicified as a result of a volcanic eruption.) Another benefit of the outing was some cultural education. Our driver brought with her several friends and, in true Argentinian style, it quickly turned into a moving party. Below you can see Anita drinking her first mate, as we received instructions on proper form when invited to partake of this ubiquitous national beverage.