Browsing by Subject "LATE MIOCENE"

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  • Shang, Yuan; Prins, Maarten A.; Beets, Christiaan J.; Kaakinen, Anu; Lahaye, Yann; Dijkstra, Noortje; Rits, Daniel S.; Wang, Bin; Zheng, Hongbo; van Balen, Ronald T. (2018)
    The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the south bank of the lower reach of the Yellow River provide high-resolution records of Quaternary climate change. In addition, substantial increases in grain-size and accumulation rate have been inferred in the upper part of the loess sequence, above palaeosol layer S2. This study investigates the sources of the long-term dust supply to the MLP and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since S2 (similar to 240 ka) by using end member modelling of the loess grain-size dataset and single-grain zircon U-Pb dating. Our results indicate that the lower Yellow River floodplain, directly north of the MLP, served as a major dust supply for the plateau at least since the deposition of loess unit L9 and indirectly suggest that the integration of the Yellow River and the disappearance of the Sanmen palaeolake took place before L9 (similar to 900 ka). The sudden change in sedi-mentology of the Mangshan sequence above palaeosol unit S2 may result from an increased fluvial sediment flux being transported to the lower reaches of the Yellow River because of tectonic movements (initiated) in the Weihe Basin around 240 ka. Furthermore, sediment coarsening can be explained by the gradual southward migration of the lower Yellow River floodplain towards the MLP since the deposition of palaeosol S2. The migration is evidenced by the formation of an impressive scarp, and is likely caused by tectonic tilting of the floodplain area. (C) 2018 Elsevier Ltd. All rights reserved.
  • Bernor, Raymond L.; Kaya, Ferhat; Kaakinen, Anu; Saarinen, Juha; Fortelius, Mikael (2021)
    Nearly five decades ago Berggren and Van Couvering proposed an Old World "Hipparion Datum" wherein a North American Hipparion extended its range across Eurasia and Africa as an "instantaneous prochoresis" populating the Old World. Four decades ago Woodburne and Bernor examined European and North African hipparion assemblages and proposed a number of distinct hipparion lineages, sharply departing from the mono-generic paradigm of previous work. Through the 1980s until now, hipparion systematic studies have delineated multiple superspecific groups of hipparions. Herein, we define 10 recognizable genus-rank Eurasian and African taxa delineating their chronologic occurrences, geographic extent and where data exists, their body mass and paleodietary preferences. Our study supports the current interpretation that a species of North American Cormohipparion extended its range into the Old World in the early late Miocene. Regional first occurrences of Cormohipparion are recognized in the Potwar Plateau, Pakistan and Sinap Tepe, Turkey 10.8 Ma. The slightly derived lineage Hippotherium is recorded earlier in the Pannonian C of the Vienna Basin, 11.4-11.0 Ma marking the chronologic "Hipparion" Datum at the lower boundary of Mammal Neogene (MN) Unit 9. Within MN 9, 11.2-9.9 Ma, Cormohipparion underwent a minor diversification whereas Hippotherium diversified in Central and Western Europe and China and Sivalhippus (S. nagriensis) originated in the Indian Subcontinent. Whereas Cormohipparion did not survive into the late Vallesian, MN10 (9.9-8.9 Ma), Hippotherium and Sivalhippus did and the Cremohipparion and Hipparion s.s. lineages originated. During the early and middle Turolian (MN11-12, 8.9-6.8 Ma) Hippotherium, Sivalhippus, Cremohipparion and Hipparion persisted and new lineages, Eurygnathohippus, Plesiohipparion, Baryhipparion and Shanxihippus originated. An initial extinction interval occurred at the end of the Miocene, MN13 (6.8-5.3 Ma) wherein all but one endemic species of Hippotherium, H. malpassi (Italy), Hipparion and several species of Cremohipparion became extinct. Lineage and species reduction continued across the MioPliocene boundary so that by the beginning of the Pliocene (MN14, 5.3 Ma) only African species of Eurygnathohippus, Chinese Plesiohipparion houfenense and Proboscidipparion sinense remained. The later Pliocene (MN15-16, ca. 5.0-2.5 Ma) documents the persistence of endemic Chinese Baryhipparion insperatum, modest diversification of African Eurygnatohippus spp. and Chinese Plesiohipparion and Proboscidipparion spp. Eurygnathohippus made a limited geographic extension into the Indian subcontinent during MN16, whereas Pleisohipparion and Proboscidipparion extended their ranges into Eurasia during MN15 and MN16. The latest occurring hipparions are Proboscidipparion sinense at 1.0 Ma in China and Eurygnathohippus cornelianus in Africa 300 kg), with the smaller forms being predominately grass feeders and larger ones being mixed feeders. Decreased hipparion lineage and species diversity in the Pliocene was accompanied by increased average body size and hypsodonty probably in response to more seasonal Eurasian and African environments. There is no evidence that hipparions ever adapted to cold and dry Old World Pleistocene environments.
  • Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.; Koptev, Alexander (2018)
    Focused, rapid exhumation of rocks is observed at some orogen syntaxes, but the driving mechanisms remain poorly understood and contested. In this study, we use a fully coupled thermomechanical numerical model to investigate the effect of upper-plate advance and different erosion scenarios on overriding plate deformation. The subducting slab in the model is curved in 3-D, analogous to the indenter geometry observed in seismic studies. We find that the amount of upper-plate advance toward the trench dramatically changes the orientation of major shear zones in the upper plate and the location of rock uplift. Shear along the subduction interface facilitates the formation of a basal detachment situated above the indenter, causing localized rock uplift there. We conclude that the change in orientation and dip angle set by the indenter geometry creates a region of localized uplift as long as subduction of the down-going plate is active. Switching from flat (total) erosion to more realistic fluvial erosion using a landscape evolution model leads to variations in rock uplift at the scale of large catchments. In this case, deepest exhumation again occurs above the indenter apex, but tectonic uplift is modulated on even smaller scales by lithostatic pressure from the overburden of the growing orogen. Highest rock uplift can occur when a strong tectonic uplift field spatially coincides with large erosion potential. This implies that both the geometry of the subducting plate and the geomorphic and climatic conditions are important for the creation of focused, rapid exhumation.
  • Fortelius, Mikael; Bibi, Faysal; Tang, Hui; Zliobaite, Indre; Eronen, Jussi; Kaya, Ferhat (2019)
  • Morales-Garcia, Nuria Melisa; Saila, Laura K.; Janis, Christine M. (2020)
    Savanna-like ecosystems were present at high latitudes in North America during much of the Neogene. Present-day African savannas, like the Serengeti, have been proposed to be modern analogs of these paleosavannas, particularly those from the middle Miocene of the Great Plains region of the United States. Both these extant and extinct savannas contain a preponderance of artiodactyl (even-toed ungulate) species; however, the taxonomic composition of each fauna is different. While present-day African savannas are dominated by ruminants (primarily bovids), the Neogene savannas of North America were dominated by a diversity of both camelid and non-bovid ruminant families. This study provides a quantitative test of the similarity of the artiodactyl faunas of the North American Neogene paleosavannas to those of the modern-day African savannas. A correspondence analysis of ecomorphological features revealed considerable overlap between modern and fossil faunas. The morphospace occupation of the extinct North American ruminants falls within that of the African bovids. Some of the extinct camelids also fall within this same morphospace, but many do not, perhaps indicating an environmental difference such as greater aridity in Neogene North America. The diversity and disparity of artiodactyl faunas through the Neogene of North America changed along with changing temperatures and precipitation regimes. The taxonomic and ecomorphological diversity of the Serengeti ruminant fauna is statistically comparable to those North American paleofaunas occurring during or immediately after the Middle Miocene Climatic Optimum (MMCO), but the later, more depauperate faunas are no longer comparable. This study quantitatively analyzes artiodactyl communities as they changed with the cooling and drying trend seen during the Neogene.
  • Kaya, Ferhat; Bibi, Faysal; Zliobaite, Indre; Eronen, Jussi T.; Hui, Tang; Fortelius, Mikael (2018)
    Despite much interest in the ecology and origins of the extensive grassland ecosystems of the modern world, the biogeographic relationships of savannah palaeobiomes of Africa, India and mainland Eurasia have remained unclear. Here we assemble the most recent data from the Neogene mammal fossil record in order to map the biogeographic development of Old World mammalian faunas in relation to palaeoenvironmental conditions. Using genus-level faunal similarity and mean ordinated hypsodonty in combination with palaeoclimate modelling, we show that savannah faunas developed as a spatially and temporally connected entity that we term the Old World savannah palaeobiome. The Old World savannah palaeobiome flourished under the influence of middle and late Miocene global cooling and aridification, which resulted in the spread of open habitats across vast continental areas. This extensive biome fragmented into Eurasian and African branches due to increased aridification in North Africa and Arabia during the late Miocene. Its Eurasian branches had mostly disappeared by the end of the Miocene, but the African branch survived and eventually contributed to the development of Plio-Pleistocene African savannah faunas, including their early hominins. The modern African savannah fauna is thus a continuation of the extensive Old World savannah palaeobiome.