Abstract:Pyroclastic sediments provide an unusual and favorable medium for the recording, burial, and preservation of tetrapod tracks and other traces. Twenty-two tracksites were reviewed for the purpose of determining how these deposits contribute to track formation, burial, and preservation. These include Jurassic sites in Argentina and Mexico, Cretaceous sites in Korea, Miocene sites in Mexico and the United States, Pliocene sites in Tanzania, Pleistocene sites in Mexico, Korea, and Italy, and Holocene sites in Mexi… Show more
“…Additional examples of modern human footprints in a pyroclastic substrate were examined at the Acahualinca site, in Nicaragua where multiple trackways were preserved in lithified deposits of a phreatic eruption of Masaya volcano ca. 2.1 ka (Houck et al, 2009;Schmincke et al, 2009). These later two examples, in particular, provide a natural experiment to contrast early hominin footprints with modern human footprints, both laid down in a substrate of very similar consistency (Mastin et al, 1999).…”
“…Additional examples of modern human footprints in a pyroclastic substrate were examined at the Acahualinca site, in Nicaragua where multiple trackways were preserved in lithified deposits of a phreatic eruption of Masaya volcano ca. 2.1 ka (Houck et al, 2009;Schmincke et al, 2009). These later two examples, in particular, provide a natural experiment to contrast early hominin footprints with modern human footprints, both laid down in a substrate of very similar consistency (Mastin et al, 1999).…”
“…The second explanation is that the trackmakers did not normally frequent environments where bird tracks were typically preserved. The third is that the volcanic ash provided a temporary substrate on which well preserved tracks could be preserved (Houck et al, 2009). It is possible that combinations of these three factors combined to influence the distributions we see.…”
Section: Paleoenvironmental Interpretation Of Track Bedsmentioning
We explore developments in tephra science that consider more than chronology, using case studies of morphological transformations of tephra deposits. Volcanic processes and prevailing weather conditions determine the distribution of tephra deposits immediately after an eruption, but as these freshly fallen tephra become part of the stratigraphic record, the thickness, morphology and definition of the layers they form changes, reflecting the interplay of the tephra, climate, Earth surface processes, topography and vegetation structure, plus direct or indirect modification caused by people and animals. Once part of the stratigraphic record, there can be further diagnostic changes to the morphology of tephra layers, such as the creation of over folds by cryoturbation. Thus, tephra layers may contain proxy evidence of both past surface environments and subsurface processes. Transformations of tephra deposits can complicate the reconstruction of past volcanic processes and make the application of classical tephrochronology as pioneered by Thorarinsson (Sigurður Þórarinsson in Icelandic) challenging. However, as Thorarinsson also noted, novel sources of environmental data can exist within transformed tephra sequences that include the spread or removal of tephra, variations in layer thickness and internal structures, the nature of contact surfaces and the orientation of layers.
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