Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): Douaa Fathy, Michael Wagreich, Susanne Gier, Ramadan S.A. Mohamed, Rafat Zaki, Mohamed M. El Nady A comprehensive set of organic and inorganic geochemical proxies, clay mineralogy, and molecular fossils are presented from two biostratigraphically well-dated oil shale horizons of Egypt, within the Upper Cretaceous Duwi and Dakhla formations. The studied oil shales were deposited within intracratonic sedimentary basins in a broad northern African epeiric sea. Calcareous nannofossil biostratigraphy indicates that the oil shales range from early to late Maastrichtian in age, covering nannofossil zones UC18, UC19, and UC20. The oil shales contain smectite and kaolinite as the main clay minerals that formed by weathering of precursor basement rocks. The relative abundances of clay minerals and several geochemical proxies (e.g. C-value, CIA, Ga/Rb, Rb/Sr and Sr/Cu), along with the occurrence of warm-water nannofossil taxa, demonstrate that the Maastrichtian oil shales accumulated under a warm, arid to humid greenhouse climate during a general Maastrichtian cooling trend. This episode of oil shale deposition in Egypt coincided with the first potential imprint of the global warming, that has been recorded during early-to-late Maastrichtian times (~70.6–67.7 Ma). Elevated eolian terrigenous input was recorded within the Duwi Formation oil shales, shown by high Ti/Al, Si/Al, Zr/Al and low La/Lu ratios. The Duwi Formation environment was characterized by enhanced salinity and a stratified water column, compared to that of the Dakhla Formation, shown by elevated values of the gammacerane index, tetracyclic terpane, β‑carotene and Sr/Ba ratio. The CaCO 3 content and carbonate/siliciclastic ratio indicate that the Dakhla Formation oil shales were deposited during a relative sea-level rise in a deeper marine setting than the Duwi Formation oil shales. The data further imply a wind-driven upwelling scenario of nutrient input s that simulated primary production and increased organic matter fluxes. Thus, paleoclimate and paleoceanography had a considerable impact on organic matter enrichment.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): Tomi P. Luoto, Antti E.K. Ojala Arctic freshwater basins are diversity hotspots and sentinels of climate change, but their long-term variability and the environmental variables controlling them are not well defined. We examined four available lake sediment sequences from High Arctic Svalbard for their subfossil Chironomidae communities, biodiversity and functional traits and assessed the influence of climatic and limnological variability on the long-term ecological dynamics. Our results indicated that collector-filterers had an important role in the oligotrophic sites, whereas collector-gatherers dominated the nutrient-enriched sites with significant bird guano inputs. In the oligotrophic sites, benthic production, taxon richness and taxonomic and functional diversity were highest during the early Holocene, when temperatures showed a rapid increase. An increase in subfossil abundance and diversity metrics was also found in recent samples of the oligotrophic sites, but not in the bird-impacted sites, where the trends were decreasing. When partitioning out the environmental forcing on chironomid communities, the influence of climate was significant in all the sites, whereas in-lake production (organic matter) was significant in two of the sites and catchment erosion (magnetic susceptibility) had only minor influence. The findings suggest that major changes in Arctic chironomid assemblages were driven by climate warming with increasing diversity in oligotrophic sites, but deteriorating ecological functions in environmentally stressed sites. We found that although taxonomic and functional diversity were always coupled, taxonomical and functional turnovers were coupled only in the oligotrophic sites suggesting that the ecological functions operated by chironomids in these low-productivity sites may not be as resilient to future environmental change.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): A.A. Vela-Pelaez, N. Torrescano-Valle, G.A. Islebe, J.F. Mas, H. Weissenberger Holocene fossil pollen samples ( n  = 38) from Lake Silvituc in Mexico were analyzed with the analog technique using modern pollen samples ( n  = 98) of the Yucatán Peninsula, Mexico. Calculated dissimilarity indices allow us to reconstruct the vegetation and to develop a precipitation record for the last 7900 years. The Middle Holocene shows a gradual increase of precipitation and a marked drop in reconstructed precipitation around 4200 BCE. During the Late Holocene two phases were identified: Phase I (2500 BCE – 1 CE) shows the greatest increase in precipitation with four peaks around 1200 BCE, 650 BCE, 200 BCE and 1 CE. Also a period of increased precipitation resulted for the period between 200 and 500 BCE. Periods of reduced precipitation were detected at 900–1100 BCE, 500–600 BCE and 100–190 BCE. Phase II (1–2000 CE) encompasses several strong dry events during the following periods: 150–300 CE, 750–900 CE, 1050–1180 CE, and 1530–1580 CE. A strong reduction of 32% in precipitation in the late Preclassic Period (100–300 CE) was detected. Non-analogs of Phase II are associated with periods of reduced precipitation and fall into time periods of extended droughts related to the Maya Late Classic and the Little Ice Age. A limiting factor on the use of analogs for tropical forests is that a combination of different analogs for the same fossil pollen signal exists. Interpretation under these circumstances requires good knowledge of the ecology of the taxa and a priori characterization of the modern samples.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): Aura Cecilia Salocchi, Nereo Preto, Daniela Fontana The evolution of the San Marino carbonate succession, developed on a wedge-top basin of the northern Apennines during the Middle Miocene (Torriana outcrop, Marecchia Valley), was studied through a high-resolution stable isotope analysis on different carbonate components. A marked positive carbon isotopic excursion is identified at ca. 16 Ma. The excellent correlation of the San Marino δ 13 C carbonates with the global δ 13 C reference curve from Zachos et al. (2008) allows to link the marked positive δ 13 C present in the San Marino section with the global carbon isotope maximum of the Monterey event. Subordinate long-eccentricity-driven δ 13 C cycles (~405 kyr) as recorded by Holbourn et al. (2007) were also identified. The correlation with carbon signatures of coeval successions of the Mediterranean region shows that this main carbon isotopic excursion at the Burdigalian–Langhian boundary is widely recorded and predates the crisis of these heterozoan shelves. The demise of the San Marino shelf resulted from a combination of global and regional factors that controlled the nutrient budget, the detrital input and the subsidence of the basin. The high-resolution chemostratigraphy of San Marino succession shows that even though the shelf evolved in the complex setting of a wedge-top basin, which should be largely influenced by local factors (i.e. tectonic subsidence and detrital input), it records the Monterey event and its eccentricity paced rhythms with high precision. This highlights the strong connection of the Monterey event with the development and subsequent demise of shallow water carbonate depositional systems in the Mediterranean, irrespective of variable and changing local conditions.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): N. Allison, C. Cole, C. Hintz, K. Hintz, A.A. Finch Coral skeletal Ba/Ca is a proxy for seawater Ba/Ca, used to infer oceanic upwelling and terrigenous runoff while [Mg 2+ ] is implicated in the control of coral biomineralisation. We cultured large individuals (>12 cm diameter) of 3 genotypes of massive adult Porites spp. corals over a range of seawater pCO 2 to test how atmospheric CO 2 variations affect skeletal Ba/Ca and Mg/Ca. We identified the skeleton deposited after a 5 month acclimation period and analysed the skeletal Ba/Ca and Mg/Ca by secondary ion mass spectrometry. Skeletal Mg/Ca varies significantly between some duplicate colonies of the same coral genotype hampering identification of genotype and seawater pCO 2 effects. Coral aragonite:seawater Ba/Ca partition coefficients (K D Ba/Ca) do not vary significantly between duplicate colonies of the same coral genotype. We observe large variations in K D Ba/Ca between different massive Porites spp. coral genotypes irrespective of seawater pCO 2 . These variations do not correlate with coral calcification, photosynthesis or respiration rates or with skeletal K D Mg/Ca or K D Sr/Ca. Seawater pCO 2 does not significantly affect K D Ba/Ca in 2 genotypes but K D Ba/Ca is significantly higher at 750 μatm seawater pCO 2 than at 180 μatm in 1 P . lutea genotype. Genotype specific variations in K D Ba/Ca between different Porites spp. could yield large errors (~250%) in reconstructions of seawater Ba when comparing Ba/Ca between corals. Analysis of fossil coral specimens deposited at low seawater pCO 2 , may underestimate past seawater Ba/Ca and ocean upwelling/freshwater inputs when compared with modern specimens but the effect is small in comparison with the observed difference between coral genotypes.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): William Hardy, Fabienne Marret, Aurélie Penaud, Priscilla le Mézo, Laurence Droz, Tania Marsset, Masa Kageyama In order to better explore quantitative reconstructions of net primary productivity (NPP) conditions using a dinoflagellate cyst (dinocyst)-based transfer function method, we revised the tropical Atlantic modern dinocyst database n  = 208 (Marret et al., 2008). Modern assemblages from the worldwide dinocyst atlas (Zonneveld et al., 2013) were added to provide a better geographical coverage of the South Atlantic Ocean. The environmental dataset was updated using the World Ocean Atlas 2013 for sea-surface temperature (SST) and sea-surface salinity (SSS) data, as well as for 1997–2017 mean NPP values recorded during SeaWifs and MODIS spatial programs. New environmental datasets were tested using anomalies regarding mean latitudinal SST as a potential index to track past upwelling activity. Finally, preindustrial NPP values, simulated with the IPSL-CM5A-LR model developed at the Institut Pierre Simon Laplace (IPSL) have been added to the dinocyst environmental database to provide NPP values consistent with the mean age of “modern” dinocyst assemblages. The transfer function method using the updated modern database was then applied to fossil dinocyst assemblages of core KZAI-01, retrieved off the Congo River mouth and covering the last 43.2 kyr. Our results indicate a dominant orbital forcing, with higher primary productivity values reconstructed during precession minima (MIS 3 and the last deglaciation) and enhanced by a maximum of obliquity during the last deglaciation and the Holocene. The synchronicity between high upwelling intensity and high terrigenous inputs during high NPP period (e.g. during the last Deglaciation) highlighted the prevalent role of river-induced upwelling activity, which is specific to the Congo River. These results have improved our understanding of the environmental forcing leading to major trophic changes in the intertropical area.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): Lu Sun, Chenglong Deng, Xiaoming Wang, Qian Li, Huafeng Qin, Huiru Xu, Yanfen Kong, Bailing Wu, Suzhen Liu, Rixiang Zhu Detailed understanding to the evolution of Neogene land mammals in East Asia and its intercontinental correlation has been impeded by the absence of an integrated biochronological system of this region. The numerous and diverse records of Neogene vertebrate fossils preserved in Inner Mongolia of northern China play a key role in the establishment of an independent biochronological framework in East Asia. However, most of these faunas are poorly constrained by independent chronological controls due to the scattered distribution of fossil localities and insufficient exposure of the fossiliferous strata. Additionally, age estimates by mammalian evolution and correlation often have uncertainties greater than ~1–2 million years. Here we present new magnetostratigraphic results of the Baogeda Ula Fauna, which was generally assigned an early Baodean Age (Late Miocene), or equivalent to the European MN12 zone (middle Turolian). Hipparion remains and associated vertebrate fossils were excavated from the upper part of the fluvio-lacustrine Baogeda Ula Formation near Abaga Banner, central Inner Mongolia of northern China. At least two layers of basalt sheet flows can be observed on top of the Baogeda Ula Formation. Our magnetostratigraphy, aided by published biochronology data and K–Ar ages of the lower basalt layer suggests that the Baogeda Ula Fauna consisting of three fossiliferous horizons can be placed within chron C4n.1n with an age range of 7.642–7.528 Ma. Thus, the Baogeda Ula Fauna becomes the first and only Baodean assemblage that is constrained by both magnetostratigraphy and radiometric ages, offering an anchoring point for future biochronological correlations.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): Karen J. Taylor, Seamus McGinley, Aaron P. Potito, Karen Molloy, David W. Beilman This study provides the first mid to late Holocene chironomid-inferred temperature (C-IT) model for northwest Ireland, creating a valuable climatic context for the development of Irish society during the Neolithic and Bronze Age. Using a lake sediment core from an isolated catchment, Lough Meenachrinna in northwest Ireland, a multi-proxy approach of chironomid (Diptera: Chironomidae) subfossils, sediment geochemistry (δ 13 C, δ 15 N, C:N) and pollen analysis was used to assess any potential limnological impact from prehistoric human activity in the region and provide a quantitative summer temperature estimate for the late Mesolithic to the Iron Age (7050–2050 cal yr BP). The pollen record provides a local signal of human activity, showing low levels of pastoral indicators in the early Neolithic, with increased evidence for pastoral and arable farming during the Bronze Age and in particular the Iron Age. Human activity does not appear to be a driving force in lake system change at Lough Meenachrinna, as peaks in farming indicators (e.g. pastoral pollen indicators and increased δ 15 N values) were not concurrent with major fluctuations in the chironomid assemblages. C-ITs provide evidence of multiple fluctuations in temperature during the mid to late Holocene with a cold phase during the late Mesolithic (6800–5890 cal yr BP), followed by a warming period during the early Neolithic (5890–5570 cal yr BP). C-ITs reflect a relatively warm climate during the middle Neolithic, with a substantial warming from the late Neolithic into the early Bronze Age (4630–3810 cal yr BP). C-ITs show a general cooling trend from the Bronze Age into the Iron Age, with a cold event occurring at 3340 cal yr BP during the middle Bronze Age and second cold event at 2430 cal yr BP during the Iron Age. The multi-proxy approach has proven an effective strategy for untangling human and climate influences on the chironomid record, and is recommended as a methodological approach in future Holocene climatic reconstructions where prehistoric human influence is a factor.

Description: Publication date: 15 September 2018 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 505 Author(s): Changqun Cao, Can Cui, Jun Chen, Roger E. Summons, Shuzhong Shen, Hua Zhang A new carbon isotope excursion was recovered from the Capitanian marine carbonates at the Rencunping (RCP) section of South China. Significantly, a pronounced excursion with elevated δ 13 C carb values over +5‰ was coeval with the conodont Jinogondolella prexuanhanensis Zone and resembles the Kamura event recorded in Tethys. The excursions in δ 13 C carb , constrained by conodont biostratigraphy, however, present inconsistent carbon cycle behaviors, especially between the separated basins in South China, and evidently reflect regional litho-facies controls. In addition, a transitional environment in association with a fall in sea level, was recovered from deposits of anoxic cherty carbonates subsequent to shallow-water carbonates around the positive excursion in δ 13 C carb . Accordingly, instead of this being a signal of global-scale climatic cooling, we suggest that the positive excursion in δ 13 C carb can be attributed to eutrophication effects regionally along a continental shelf. In this scenario, the increasing dissolved O 2 level in the mixing zone that induced by the initial sea-level fall will efficiently impede denitrification and increase the bio-available N in N:P ratio to satisfy the demands of primary producers in surface waters. Subsequently, deposits of shallow-water carbonates comprising calcareous algae and massively-bedded lime muds accumulated widely around South China. These deposits appear to represent an unusual environment and ecosystem fertilized, perhaps, by the weathering products from the earliest stages of volcanism prior to the main Emeishan flood basalt eruptions at the Guadalupian-Lopingian boundary (GLB). Graphical abstract