Ostracod faunas from the Late Mississippian–Early Pennsylvanian, Calingasta–Uspallata Basin, central west Argentina: new records from glacial–postglacial successions
by: María José Salas, Andrea Fabiana Sterren and Gabriela Adriana Cisterna
Summarized by: Max Schwartzman; a senior geology major at Binghamton University. He is exploring various geology fields before going for his master’s degree in graduate school, and is considering possibly going further for a Ph.D. as well. When not studying geology, he is often playing games, trying to learn new things, or watching shows with his friends or family.
Data utilized: The authors and researchers of the original article acquired most of their fossil data through collected field samples in basins in Argentina from the Callingasta-Upallata Basin across four different locations. A majority of these collected samples and gathered data were fossils of ostracods; two-shelled critters most closely related to modern day shrimp, most of which resemble a ‘D’. These fossils that were collected were either fully preserved shells, or more commonly, molds of the species themselves which were imprinted into the sediment of the basins. These samples and collected data were then compared against data sets collected in a number of other previous analyses on these fossils by other researchers of the topic. In addition to these data sets, the researchers summarized findings from other authors regarding the study of the ostracod species from the Carboniferous–Permian Periods in Texas, USA (359–299 million years ago)
Hypothesis/Objective: The objective of the study was to perform a more in-depth exploration of ostracods from glacial periods during Earth’s history in order to construct a better record of both the time and place these ostracods existed, as well as uncover the taxonomic diversity of the group.
Methods: Data was collected from mudstone intervals and dropstones collected between 2005 – 2020. The material that the ostracods were preserved in was poorly preserved, with some external molds (when a fossil leaves their imprint behind in the rock without the fossil itself)showing more details of the valve features; to accurately collect these molds, the ostracods were prepared using a tool called a vibro-tool and fine needles for best accuracy, to clean off any extra sediment obscuring fossil details. The science team then used rubber latex to create a 3D replica of the imprint to better see the details. All of these samples were recorded and photographed.
Results: The location of these fossils and the basins in which they were deposited tie into the glacial events in Southwest Gondwana, part of a former supercontinent that was made up of South America, Antarctica, and parts of Africa, much of which was centered around the south pole. The deposits these fossils were found in were found either below or between diamictites, a type of rock created by glaciers as they are moving. Using the location of these deposits, scientists were able to track how expansive the glaciers were, how their locations changed, and how long it took for each deposit to be left behind. Along with the glacial data, eight species of ostracods, some already known to science and some new, were identified from the collected data. Figure 1 shows many of the ostracod samples and molds that were uncovered in the areas that were being investigated, with many of them displaying similar characteristics to one another, with differing species also having similar characteristics with one another. For example, one new species was identified: this new species was identified by a lump between where they curve. Two species were found outside of Bolivian geologic deposits for the first time, and two others were documented for the first time in South American geologic deposits.
Importance of Study: This study is particularly important as it indicates the range of ostracods outside of where they were first documented. The Southern Gondwana glacier itself, due to its massive size, indicates colder climates globally. Using this knowledge, we can infer how organisms like ostracods lived in these colder conditions and how their ranges expanded or contracted along with the glaciations.
Broader implications: The ostracods are helpful in the study of both paleoclimate and paleobiology, and gives a better understanding between how life evolves through global climate changes, such as through the Southern Gondwana glacier.