Plio-Pleistocene volcanism of Lower Bed I, Olduvai Gorge, Tanzania: transportation mechanisms, volcaniclastic sedimentation and ecological significance
Zusammenfassung der Projektergebnisse
Consideration of single-grain geochemical composition of volcaniclastic sandstones allows for higher stratigraphic resolution than possible solely using Marker Tuff tephrostratigraphy and has been identified as a helpful tool to improve correlations of mixed pyroclastic/epiclastic deposits through the definition of "geochemical zones". This method has been applied to Bed I strata at paleoanthropologically important sites of the Olduvai Gorge "junction area" and to a much larger data set, covering the entire spectrum of naturally exposed Bed I strata in the Olduvai eastern and the yet underexplored western basin. For the first time, multivariate statistical methods (PCA and DFA) were applied to Olduvai geochemical data, in this case microprobe-derived major-element phenocryst data (augite, anorthoclase, plagioclase), integrated with petrographic and faciesarchitectural analysis. The resulting correlations provide a basin-wide chemostratigraphic framework for Bed I at high lateral and vertical resolution. Based on this we were able to: (I) identify the Orkeri Ignimbrite as the oldest naturally exposed volcanic unit; (II) identify Naabi and CFCT ignimbrites and Bed I lava in proximal settings close to their Ngorongoro volcanic source; (III) newly introduce a Mafic Tuff nomenclature; (IV) identify Ngorongoro as the volcanic source of Mafic tuffs I-III and of the Bed I basalt lava; (V) identify a Ngorongoro sourced volcaniclastic fan delta below Tuff IB, recording bimodal rhyolihic-basaltic volcanism and NW to NE directed drainages; (VI) identify an Olmoti sourced volcaniclastic fan delta, initiating with Tuff IB, and reflecting mainly trachytic volcanism and westward directed drainages. In addition to an improvement of stratigraphic resolution and correlation of Bed I sections, based on geochemical and statistical methods, we applied novel sequence stratigraphic concepts, enabling a reliable tracing of contemporaneous landscapes despite pronounced lateral facies changes. On the basis of unconformity-bounded lake-parasequences we are able to exactly place the DK hominin "occupation" site in a sequence stratigraphic context. The sub Tuff IB volcaniclastic debris and mud flows at DK site were identified as the oldest lahar inundation, modification and preservation of a hominin "occupation" site yet known, age-bracketed between ~1.88 Ma (Bed I Basalt) and ~1.85 Ma (Tuff IB). For the first time, integrated sedimentological and vegetation studies were applied to lower Bed I strata to reconstruct the palaeoenvironments and palaeolandscapes of Olduvai Gorge. At DK hominin site, phytolith analyses of the basalt lava to Tuff IB stratigraphic interval show diverse vegetation, which includes grasses, probably sedges, few palms, as well as trees/shrubs, associated with a fresh water pool. Thus the DK site would have provided plant foods for hominins, such as fruits from trees and shrubs and starch-rich rhizomes and tubers from sedges and reeds. The discovery of fossil rooted tree stumps in the yet underexplored western Olduvai Basin, age-bracketed by the Naabi Ignimbrite (~2.04 Ma) and Tuff IA (~1.89 Ma), provides the first direct, in situ, and to date oldest evidence of living trees at Olduvai Gorge. Phytolith analyses carried out at the tree level imply a pronounced seasonality and indicate a wooded landscape with grasses, shrubs, and sedges growing nearby. Repeated development of grassland paleosols within the western basin fan toe succession would have provided sustained grazing opportunities for Early Pleistocene fauna, with nearby ephemeral streams as freshwater sources. Among the tree stump cluster were found outsized lithic clasts and those consisting of quartzite were identified as Oldowan stone tool artifacts. At an other western basin locality, but at about the same stratigraphic level, the oldest Oldowan archaeological and faunal assemblage yet known from Olduvai Gorge was discovered ~160,000 years older than the next youngest reported from the DK site.
Projektbezogene Publikationen (Auswahl)
-
2013. Use of single-grain geochemistry of cryptic tuffs and volcaniclastic sandstones improves the tephrostratigraphic framework of Olduvai Gorge, Tanzania. Quaternary Research 80: 235-249
McHenry, L.J., Stollhofen, H., Stanistreet, I.G.
-
2015. Multivariate analyses of phenocryst compositional data refine the Bed I tephrostratigraphic framework of Olduvai Gorge, Tanzania. The 17th annual conference of the International Association for Mathematical Geosciences, Freiberg, Germany
Habermann, J.M., Stollhofen, H., McHenry, L.J.
-
2015. Vegetation landscape at DK locality, Bed I, Olduvai Gorge (Tanzania).- 5th East African Association for Palaeoanthropology and Palaeontology (EAAPP) Conference, Dar es Salaam, Tanzania, 3-6 August 2015
Albert, R.M., Bamford, M.K., Stanistreet, I., Stollhofen, H., Rivera-Rondón, C., and Rodríguez-Cintas, A.
-
2015. Vegetation landscape at DK locality, Olduvai Gorge, Tanzania.- Palaeogeography, Palaeoclimatology, Palaeoecology 426: 34-45
Albert, R.M., Bamford, M.K., Stanistreet, I., Stollhofen, H., Rivera-Rondón, C., Rodríguez- Cintas, A.
-
2016. Discrimination, correlation, and provenance of Bed I tephrostratigraphic markers, Olduvai Gorge, Tanzania, based on multivariate analyses of phenocryst compositions. Sedimentary Geology 339, 115-133
Habermann, J.M., McHenry, L.J., Stollhofen, H., Tolosana-Delgado, R., Stanistreet, I.G., Deino, A.L.
-
2016. In situ ~2.0 Ma trees discovered as fossil rooted stumps, lowermost Bed I, Olduvai Gorge, Tanzania. Journal of Human Evolution 90, 74-87
Habermann, J.M., Stanistreet, I.G., Stollhofen, H., Albert, R.M., Bamford, M.K., Pante, M.C., Njau, J.K., Masao, F.T.
-
2016. Pleistocene volcanism of Bed I, Olduvai Gorge, Tanzania: chemostratigraphy, sedimentology, and paleoecology. PhD thesis, Faculty of Sciences, Friedrich-Alexander University (FAU) Erlangen-Nürnberg, 246 p.
Habermann, J.M.
