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The history of the civilizations of the oases of Bukhara and Qaraqöl (southeastern Uzbekistan) since the Neolithic in relation to environmental changes is studied by the French/Uzbekistan Archaeological Mission in Bukhara 1 following pioneering Russian studies 2. Using a methodology tested in Afghanistan, the geoarchaeological side of the program focused on the drawing of a regional geomorphological map then on the identification, mapping and dating of the paleochannels of the river Zerafshan. We established the chronology of several generations of fluvial channels in relation to archaeological settlements of different eras (Early Neolithic, Neolithic, Bronze Age, Iron Age and Islamic period) and with optically stimulated luminescence dating of alluvial deposits. Based on preliminary results of these OSL dates we propose and discuss a regional environmental reconstruction. We hypothesize that the main cause of avulsion could be catastrophic floods generated by collapse of natural dams in the upper part of the Zerafshan River.

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Abstract. Thermal stress on the biosphere during the extreme warmth of the Paleocene-Eocene Thermal Maximum (PETM) was most severe at low latitudes, with sea surface temperatures at some localities exceeding the 35 °C at which marine organisms experience heat stress. Relatively few equivalent terrestrial sections have been identified, and the response of land plants to this extreme heat is still poorly understood. Here, we present a new PETM record from the peak ring of the Chicxulub impact crater that has been identified based on nannofossil biostratigraphy, an acme of the dinoflagellate genus Apectodinium, and a negative carbon isotope excursion. Geochemical and microfossil proxies show that the PETM is marked by elevated TEX86H-based sea surface temperatures (SSTs) averaging ~37.8 °C, an increase in terrestrial input, surface productivity, salinity stratification, and bottom water anoxia, with biomarkers for green and purple sulfur bacteria indicative of photic zone euxinia in the early part of the event. Pollen and plants spores in this core provide the first PETM floral assemblage described from México, Central America, and the northern Caribbean. The source area was a diverse coastal shrubby tropical forest, with a remarkably high abundance of fungal spores indicating humid conditions. Thus, while seafloor anoxia devastated the benthic marine biota, and dinoflagellate assemblages were heat-stressed, the terrestrial plant ecosystem thrived.

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