I was always amazed by fossils. The fact that somebody left the footprint several millions years ago and we discovered it nowadays is astonishing. Usually popular movies present the discovery of fossils as something trivial: “Look, there are several bones which are easily assembled into the beautiful dinosaur.” I guess that the procedure is not as simple.
In this blog I am focused on salt lakes. About a month ago I found nice paper co-authored by Ricardo Melchor and his Argentinean colleagues. The paper is both has relevance to salt lakes and perfectly demonstrates how scientists attempt to decode ancient footprints.
The paper is about flamingo footprints which were imprinted into the Argentinean clay 20-30 million years ago. Those who ever observed the flock of flamingo which feed on the shore of a lake can imagine how difficult will be to find footprints after several million years (one year ago I visited Argentina and cannot imagine how they can remain for one month).
Imaging that you are standing near the 30-m thick rock which consists of sedimentary facies (actually if you are not geologist you have no idea what does it mean “sedimentary facies”). This rock is a part of well known for geologists Vinchina Formation – a 5100 m thick red bed succession composed of sandstones and mudstones, which represents different styles of fluvial sedimentation. Radiometry suggests that the Vinchina ages from Late Oligocene to Early Miocene.
You know that these rocks are pretty old and many years ago there were valleys and a lot of flowing water in the area. You propose that millions of years ago a lot of shorebirds walked through the mud searching the food. And you start looking for the footprints. To verify what you found it will be wise to compare the fossil bird-like footprints with the footprints which are typical for the today birds. Well, you are going to the field to observe modern shorebirds – the footprints, the behavior, the pattern of the pond sediments trampled by shorebirds.
Finally when you collect hundreds of obscure fossil images, compare them with modern footprints and combine it with your expertise and imagination you are making conclusions:
- First of all that the trace-fossil is dominated by the bird footprints and arthropod furrows. It is also logical to suggest that arthropod fossils may correspond to those left by the organisms that the birds were searching in the lake mud.
- The strong similarity between the footprints of modern Chilean flamingos and footprints found in the fossils suggested that the track maker of the Late Oligocene–Early Miocene footprints was a member of Palaelodidae or Phoenicopteridae.
- Finally palaeonvironmental and palaeoecological observations allows to conclude that the sedimentary environment of the trace-fossil bearing succession was the wave-dominated littoral zone of a shallow but permanent saline or alkaline lake.
I really appreciate this type of research: from ancient footprints to the hypothesis on the existence of the saline lake 20-30 millions years ago. I hope that 30 millions years will pass and there will be somebody on the planet Earth to find and decode our footprints.
Melchor, R., Cardonatto, M., & Visconti, G. (2012). Palaeonvironmental and palaeoecological significance of flamingo-like footprints in shallow-lacustrine rocks: An example from the Oligocene–Miocene Vinchina Formation, Argentina Palaeogeography, Palaeoclimatology, Palaeoecology, 315-316, 181-198 DOI: 10.1016/j.palaeo.2011.12.005