Age constraints for the Trachilos footprints from Crete

We present an updated time frame for the 30 m thick late Miocene sedimentary Trachilos section from the island of Crete that contains the potentially oldest hominin footprints. The section is characterized by normal magnetic polarity. New and published foraminifera biostratigraphy results suggest an age of the section within the Mediterranean biozone MMi13d, younger than ~ 6.4 Ma. Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma. By integrating the magneto- and biostratigraphic data we correlate the Trachilos section with normal polarity Chron C3An.1n, between 6.272 and 6.023 Ma. Using cyclostratigraphic data based on magnetic susceptibility, we constrain the Trachilos footprints age at ~ 6.05 Ma, roughly 0.35 Ma older than previously thought. Some uncertainty remains related to an inaccessible interval of ~ 8 m section and the possibility that the normal polarity might represent the slightly older Chron C3An.2n. Sediment accumulation rate and biostratigraphic arguments, however, stand against these points and favor a deposition during Chron C3An.1n.

Size and shape variation in the calcareous nannoplankton genus Braarudosphaera following the Cretaceous/Paleogene (K/Pg) mass extinction: clues as to its evolutionary success

Calcareous nannoplankton have been one of the dominant primary producers in the surface oceans since the late Triassic. The bolide impact at the Cretaceous/Paleogene (K/Pg) boundary ~66.0 Ma, led to the elimination of >90% of nannoplankton species: the largest extinction event in their evolutionary history. One of the few nannoplankton genera to survive the K/Pg mass extinction and even thrive in its aftermath was Braarudosphaera, which precipitates pentagonal calcite plates (pentaliths). The only Braarudosphaera species to span the K/Pg boundary (B. bigelowii) is extant and has formed geographically and temporally restricted “blooms” throughout geologic time. Four morphologically and genetically distinct cryptic species of B. bigelowii have been identified in the modern ocean. However, it is uncertain whether these cryptic species have disparate ecophysiological tolerances that have allowed them to adapt to varying environmental conditions. For the first time, we assess changes in the size and shape of Braarudosphaera pentaliths following the K/Pg mass extinction at three geographically and environmentally disparate sites that have early Paleocene Braarudosphaera blooms. Our results show that different Braarudosphaera morphotypes were dominant in the Gulf of Mexico compared with the Tethys Ocean, likely due to regional environmental differences. In addition, we provide evidence that the dominant Braarudosphaera morphotypes shifted in response to changes in upper water column stratification. This ability to rapidly adapt to unstable environments likely helped Braarudosphaera thrive in the aftermath of the K/Pg extinction and explains why this lineage has enjoyed such a long evolutionary history.

Calcareous nannoplankton paleofluxes in the early Pliocene sapropels of the South Aegean Sea, NE Mediterranean: biogenic carbonate contribution and paleoecological implications

<p>Calcareous nannoplankton, one of the major contributors to marine primary production, not only responds quickly to variations in environmental conditions, but provides excellent means of first-order biostratigraphy. In our study we use early Pliocene sediments from the Cretan Sea (South Aegean; DSDP- Leg 42A, Site 378). The location of the record allows us to investigate formation processes of the Zanclean sapropelic layers in South Aegean Sea, and unravel the effects of monsoonal activity, as well as characterize any high latitude teleconnections of the area, prior to the mid-Pliocene warm period. The obtained nannofossil biostratigraphy provided the first-order bed-to-bed age control during the time interval of 5.08-3.98 Myrs, enabling the astronomical tuning of the marly–sapropelic cycles 12-59 to the target-curves.</p><p>Geochemical analysis  (total organic carbon, oxygen, nitrogen, organic and carbonate carbon stable isotopes) were performed, revealing variations in carbon cycle and paleoceanographic conditions, as also variability in the redox conditions of the basin. Planktonic foraminifera δ<sup>18</sup>O and δ<sup>13</sup>C records are comparable to the global and Mediterranean Sea stacks, revealing warmer conditions in between approx. 5.08-4.9, in accordance to high summer insolation variation values. The quantification of the early Pliocene nannoplankton paleofluxes, indicated approximately two times higher average accumulation rates for the past export production during the sapropelic layers in respect to the non-sapropelic intervals; suggesting that primary productivity was a major component of the sapropelic formation procedures. Overall, calcareous nannofossil assemblage was dominated by <em>Reticulofenestra </em>spp. <5μm (up to 74%) followed by <em>Florisphaera profunda</em> (up to 64%). Other major species of the assemblage composition were <em>Umbilicosphaera</em> spp., <em>Calcidiscus </em>spp. and <em>Helicosphaera</em> spp. <em>F. profunda</em> showed an increase in paleofluxes within the sapropelic layers, coupled with relatively decreased accumulation rates of the upper photic zone taxa and high stratification index, thus suggesting an ecological depth-separation of the water column and a nutrient-rich lower photic zone.</p><p> </p><p>Acknowledgments<br>We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – CLIMPACT’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments). E. Skampa has been granted with a scholarship from the State Scholarships Foundation. This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme « Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (ІΚΥ).</p>

RESPONSE OF CALCAREOUS NANNOPLANKTON TO PALEOCENE–EOCENE THERMAL MAXIMUM IN NORTHERN IRAQ

The Paleocene–Eocene Thermal Maximum (PETM) was an abrupt global warming event in the geological record. Based on calcareous nannofossils from thirteen samples of Aaliji Formation from K-116 well, Northern Iraq, sixty species are identified and can be used to divide the studied section into five biozones. Especially, the transition in the Discoaster multiraditus Biozone (CP8) occurred which is marked by higher speciation for calcareous nannofossils and the occurrences of Discoaster Tan. Such atransition is closely related to global warming during the transition from Paleocene to Eocene.