A 60-million-year Cenozoic history of western Amazonian ecosystems in Contamana,eastern Peru

We provide a synopsis of ~ 60 million years of life history in Neotropical lowlands, based on a comprehensive survey of the Cenozoic deposits along the Quebrada Cachiyacu near Contamana in Peruvian Amazonia. The 34 fossil-bearing localities identified have yielded a diversity of fossil remains, including vertebrates, mollusks, arthropods, plant fossils, and microorganisms, ranging from the early Paleocene to the late Miocene–?Pliocene (> 20 successive levels). This Cenozoic series includes the base of the Huchpayacu Formation (Fm.; early Paleocene; lacustrine/fluvial environments; charophyte-dominated assemblage), the Pozo Fm. (middle + ?late Eocene; marine then freshwater environments; most diversified biomes), and complete sections for the Chambira Fm. (late Oligocene–late early Miocene; freshwater environments; vertebrate-dominated faunas), the Pebas Fm. (late early to early late Miocene; freshwater environments with an increasing marine influence; excellent fossil record), and Ipururo Fm. (late Miocene–?Pliocene; fully fluvial environments; virtually no fossils preserved). At least 485 fossil species are recognized in the Contamana area (~ 250 ‘plants’, ~ 212 animals, and 23 foraminifera). Based on taxonomic lists from each stratigraphic interval, high-level taxonomic diversity remained fairly constant throughout the middle Eocene–Miocene interval (8-12 classes), ordinal diversity fluctuated to a greater degree, and family/species diversity generally declined, with a drastic drop in the early Miocene. The Paleocene–?Pliocene fossil assemblages from Contamana attest at least to four biogeographic histories inherited from (i) Mesozoic Gondwanan times, (ii) the Panamerican realm prior to (iii) the time of South America’s Cenozoic “splendid isolation”, and (iv) Neotropical ecosystems in the Americas. No direct evidence of any North American terrestrial immigrant has yet been recognized in the Miocene record at Contamana.     

Environmental history,palaeoecology and human activity at the early Neolithic forager/cultivator site at Kuahuqiao,Hangzhou, eastern China

The date and location of the adoption of rice cultivation by foraging cultures in China are of considerable current interest but its understanding is hampered by lack of information regarding its palaeoenvironmental context. We present detailed multi-proxy palaeoecological research at the earliest-dated site of rice cultivation in the coastal littoral of east China which has revealed the precise environmental setting of this early Neolithic settlement and its incipient cultivation at ca 7750 cal BP. Regional and local environmental changes governed the character of the site and the duration of human activity. After an episode of marine conditions, natural hydrological succession and terrestrialisation of the site preceded fire clearance of marsh fen-carr alder scrub that prepared the ground for cultivation and then maintained a reedswamp-type wet grassland in which rice was grown. Cropping of Typha stands may have formed part of the subsistence base before the site was overwhelmed by marine inundation ca 7200 cal BP, after which rice cultivation spread to Neolithic sites of Hemudu type elsewhere in the coastal lowlands. We suggest that integrated multi-proxy palaeoecological studies are vitally important for the full understanding of such key wetland archaeological sites.     

Bearing up well? Understanding the past,present and future of Australia's koalas

The modern Koala Phascolarctos cinereus is the last surviving member of a once diverse family Phascolarctidae (Marsupialia, Phascolarctomorphia). Nine genera and at least 16 species of koala are known. Late Oligocene sediments of central Australia record the oldest fossils and highest species diversity. Five species are known from the early to middle Miocene rainforest assemblages of the Riversleigh World Heritage Area, Queensland. With the onset of dryer conditions after the middle Miocene climatic optimum (~ 16 Ma), rainforest habitats contracted resulting in the apparent extinction of three koala lineages (Litokoala, Nimiokoala, Priscakoala). Phascolarctos first appears in the fossil record during the Pliocene and the modern species around 350 ka. Despite a dramatic decline in taxonomic diversity to a single extant species, the fossil record indicates that at most only three koala species coexisted in any given faunal assemblage throughout their 24 million year history. Within these assemblages, the vast majority of extinct koalas are extremely rare (some known from only a single specimen) which may reflect a general rarity within their palaeohabitats compared with the modern species which is represented by an estimated 400,000 individuals spread over most of eastern mainland Australia. Be that as it may, P. cinereus, although once geographically more widespread, occurring for example in Western Australia in the Pleistocene, underwent significant range contractions and localized population extinctions during the stressful climatic conditions of the late Pleistocene and more recently through human-induced habitat destruction. Combined with threats of disease, reduced genetic diversity and climate change, the survival of this iconic Australian marsupial is arguably a cause for concern.     

Pacing of the Toarcian Oceanic Anoxic Event (Early Jurassic) from astronomical correlation of marine sections

The Early Toarcian Oceanic Anoxic Event (OAE) in the Early Jurassic Period is associated with a major negative carbon isotope excursion (CIE), mass extinction, marine transgression and global warming. The Toarcian OAE is thought to have been caused by flood basalt magmatism, and may have been a trigger for mass extinction. However, these proposed causes of the Toarcian OAE and associated biotic crisis are not adequately resolved by a precise chronology. The duration of the Toarcian OAE has been estimated to be anywhere from ~ 0.12 to ~ 0.9 Myr, most recently 0.74 to 3.26 Myr from U–Pb dating. The CIE associated with the Toarcian OAE has a similar pattern at numerous localities, and there is evidence that the marine carbon isotope variations recorded astronomical forcing signals. Here we estimate a duration of ~ 620 kyr for the main negative CIE, ~ 860 kyr for the polymorphum zone and > 1.58 Myr for the levisoni zone based on 405-kyr astronomical eccentricity tuning of the marine section at Peniche (Portugal). This 405-kyr tuned series provides a ~ 2.5 Myr continuous high-resolution chronology through the Early Toarcian. There are 6, or possibly 7 short eccentricity cycles in the main CIE interval at Peniche. To confirm this astronomically based estimate, we analyzed three other sections at Yorkshire (UK), Dotternhausen (Germany), and Valdorbia (Italy) from marine carbon isotopic series. These four stratigraphic sections from Early Jurassic western Tethys record the Toarcian OAE with ~ 6 prominent carbon isotope cycles in the CIE that span a 600 ± 100 kyr duration. The Peniche 405-kyr tuned series indicates that the pre- and post-CIE intervals experienced strong precession–eccentricity-forced climate change, whereas the CIE interval is marked by dominant obliquity forcing. These dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the Early Toarcian paleoclimate system that was directly linked to the global carbon cycle.     

Current perspectives on the Permian–Triassic boundary and end-Permian mass extinction: Preface

The end-Permian mass extinction is now robustly dated at 252.6 ± 0.2 Ma (U–Pb) and the Permian–Triassic (P–T) GSSP level is dated by interpolation at 252.5 Ma. An isotopic geochronological timescale for the Late Permian–Early Triassic, based on recent accurate high-precision U–Pb single zircon dating of volcanic ashes, together with calibrated conodont zonation schemes, is presented. The duration of the Early Triassic (Induan + Olenekian stages) is estimated at only 5.5 million years. The duration of the Induan Stage (Griesbachian + Dienerian sub-stages) is estimated at ca. one million years and the early Olenekian (Smithian sub-stage) at 0.7 million years duration. Considering this timescale, the “delayed” recovery following the end-Permian mass extinction may not in fact have been particularly protracted, in the light of the severity of the extinction. Conodonts evolved rapidly in the first 1 million years following the mass extinction leading to recognition of high-resolution conodont zones. Continued episodic global environmental and climatic stress following the extinction is recognized by multiple carbon isotope excursions, further faunal turnover and peculiar sedimentary and biotic facies (e.g. microbialites). The end-Permian mass extinction is interpreted to be synchronous globally and between marine and non-marine environments. The nature of the double-phased Late Permian extinction (at the Guadalupian–Lopingian boundary and the P–T boundary), linked to large igneous provinces, suggests a primary role for superplume activity that involved geomagnetic polarity change and massive volcanism.     

New U/Th ages for Pleistocene megafauna deposits of southeastern Queensland,Australia

Arguments over the extinction of Pleistocene megafauna have become particularly polarised in recent years. Causes for the extinctions are widely debated with climate change, human hunting and/or habitat modification, or a combination of those factors, being the dominant hypotheses. However, a lack of a spatially constrained chronology for many megafauna renders most hypotheses difficult to test. Here, we present several new U/Th dates for a series of previously undated, megafauna-bearing localities from southeastern Queensland, Australia. The sites were previously used to argue for or against various megafauna extinction hypotheses, and are the type localities for two now-extinct Pleistocene marsupials (including the giant koala, Phascolarctos stirtoni). The new dating allows the deposits to be placed in a spatially- and temporally constrained context relevant to the understanding of Australian megafaunal extinctions. The results indicate that The Joint (Texas Caves) megafaunal assemblage is middle Pleistocene or older (>292 ky); the Cement Mills (Gore) megafaunal assemblage is late Pleistocene or older (>53 ky); and the Russenden Cave Bone Chamber (Texas Caves) megafaunal assemblage is late Pleistocene (～55 ky). Importantly, the new results broadly show that the sites date prior to the hypothesised megafaunal extinction ‘window’ (i.e., ～30–50 ky), and therefore, cannot be used to argue exclusively for or against human/climate change extinction models, without first exploring their palaeoecological significance on wider temporal and spatial scales.     

The Bonneville Estates Rockshelter rodent fauna and changes in Late Pleistocene–Middle Holocene climates and biogeography in the Northern Bonneville Basin,USA

Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,500 ¹⁴C yr BP (14,800 cal yr BP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 9000 ¹⁴C BP (10,200 cal yr BP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene–early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 9500 ¹⁴C yr BP (10,800 cal yr BP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.     

Shifting zonal patterns of the southern boreal forest in eastern Canada associated with changing fire regime during the Holocene

This research aims at uncovering the stand-scale Holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub-continental shift in past fire activity that could have triggered a change in the Holocene zonal pattern. In eastern Canada, the extant closed-crown boreal forest corresponds to two ecological regions separated along 49°N, the northern black spruce zone and the southern balsam fir zone. We sampled balsam fir stands from the southern fir zone (n = 7) and among the northernmost patches of fir forest located far beyond the fir zone boundary, into the spruce zone (n = 6). Macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand-scale and regional Holocene fire histories. Data were interpreted in the context of published palaeoecological evidence. Stands of the balsam fir zone were submitted to recurrent fire disturbances between c. 9000 and 5000 cal. yr B.P. Local fire histories suggested that four sites within the fir zone escaped fire during the Holocene. Such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape. Stands of the spruce zone have been affected by recurrent fires from 5000 cal. yr B.P. to present. Local fire histories indicated that no site escaped fire in this zone. Published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200 cal. yr B.P. A change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest. The consequence was a sub-continental reshuffling of the fir and spruce zones within the closed-crown boreal forest. The macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand-scale Holocene fire history at sites where no other in situ fire proxies were available.     

Biometry of the Late Cretaceous Arkhangelskiella group: ecophenotypes controlled by nutrient flux

This study focuses on the morphometry and taxonomy of the Late Cretaceous coccolith genus Arkhangelskiella. Sixty samples from the Campanian–Maastrichtian interval of DSDP Hole 390A (Blake Nose) were investigated for their contents of Arkhangelskiella spp. In each sample one hundred specimens of Arkhangelskiella spp. were examined by measuring the coccolith length and width, as well as the length and width of the central area. In the samples investigated the Arkhangelskiella group exhibits a large size variation, specimens length varies from 4.95 μm to 14.52 μm. Former taxonomic concepts, based on morphometry, subdivided the Arkhangelskiella group into three species: Arkhangelskiella maastrichtiana, Arkhangelskiella confusa and Arkhangelskiella cymbiformis. Our data show a large variability of the morphometric data (coccolith length, width of the outer rim). There is no indication for three independant species; two of the quoted taxa (1. thick outer rim = Arkhangelskiella maastrichtiana; 2. very thin outer rim = Arkkhangelskiella cymbiformis) seem to be extreme forms of a continuous morphometric lineage. The lower part of the investigated succession (139.92–133.42 mbsf) is dominated by small specimens with an average length of 6.8 μm whereas the upper part (132.86–126.15 mbsf) is characterized by larger specimens (mean 8.7 μm). In DSDP Hole 390A the size increase appears to be very abrupt, within two samples (samples 133.42 mbsf, 132.86 mbsf) the mean size increases by 1.51 μm. Previous morphometric studies of Arkhangelskiella indicate a more continuous size increase throughout the late Campanian–Maastrichtian. The abrupt size increase observed here hints toward a minor hiatus in DSDP Hole 390A separating upper Campanian from lower Maastrichtian sediments. It seems likely that the size increase of Arkhangelskiella reflects changes of various environmental factors like nutrient supply and sea water chemistry (Mg/Ca ratio; Ca concentration). A comparison of morphometric results with previous palaeoecological studies documents a nutrient control for the growth of Arkhangelskiella. Small specimens can be related to more mesotrophic conditions whereas large specimens are linked to oligotrophic surface waters.     

A sustained +21 m sea-level highstand during MIS 11 (400 ka): direct fossil and sedimentary evidence from Bermuda

A small, protected karstic feature exposed in a limestone quarry in Bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase, still-stand, and regressive phase of a sea-level in excess of 21.3 m above present during Marine Isotope Stage (MIS) 11 (400 ka) as determined by U/Th dating and amino acid racemization. Cobbles and marine sediments deposited during the high-energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment. This was succeeded stratigraphically by a still-stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates, probably upogebiid shrimp, that could not be produced under any condition other than sustained marine submergence. Overlying this were pure carbonate beach sands of a low-energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates. The considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run-up waves over a minimum duration of months, if not years. The maximum duration has yet to be determined but probably did not exceed one or two thousand years. The most abundant snails in this fauna are two species indicative of brackish water and high-tide line showing that a Ghyben-Herzberg lens must have existed at > + 20 m. The nature of these sediments and fossil accumulation is incompatible with tsunami deposition and, given the absence of evidence for tectonic uplift of the Bermuda pedestal or platform, provide proof that sea-level during MIS 11 exceeded +20 m, a fact that has widespread ramifications for geologists, biogeographers, and human demographics along the world's coastlines.     

Western Palaearctic palaeoenvironmental conditions during the Early and early Middle Pleistocene inferred from large mammal communities,and implications for hominin dispersal in Europe

Large-scale fluctuations in global climate and resulting changes in ecology had a profound effect on human evolution and dispersal. Though hominin remains are scarce, studies focussing on the more abundant records of fossil land mammal communities can contribute greatly to our knowledge of the palaeoenvironmental circumstances that influenced and directed the global spread of hominins. To produce a comprehensive and accurate account of the evolution of western Palaearctic habitat diversity between 2.6 and 0.4 Ma BP, information generated from large mammal communities from 221 key sites has been included in this study.The palaeoecological conditions of the western Palaearctic during the Early and early Middle Pleistocene were principally controlled by the following key factors: (1) a widespread trend of temperature decrease, (2) the periodicity of the global temperature record, (3) the intensity of single climatic stages, (4) the temporal pattern of climatic variation, (5) geographical position, and (6) the distribution of continental water resources. A general picture of the evolution of western Palaearctic habitat diversity saw the replacement of extensive forested terrain by an alternating sequence of varied savannah-like and forested habitats during the 2.6–1.8 Ma span, as well as an alternation between different types of predominantly open habitats between 1.8 and 1.2 Ma. Both of these processes were governed by 41 ka temperature periodicity. During the 1.2–0.9 Ma time span, irregular climatic fluctuations were more common and habitat variability increased. The subsequent 0.9–0.4 Ma interval, a period controlled by 100 ka periodicity, was by comparison more stable, with longer climatic cycles alternating between open and forested landscapes. During the entire Early and early Middle Pleistocene, assemblages of large mammal communities reveal a distinct trend of decreasing continentality between Eastern and South-Eastern Europe on the one hand, and South-Western and North-Western Europe on the other. This trend was due to the effect of the Atlantic Ocean, while in Southern Europe the relatively low continentality was balanced by influences from the Mediterranean Sea.When plotted against evidence of hominin occurrence, the data on western Palaearctic habitat diversity inferred from large mammal communities indicate clear environmental stimuli for the earliest human dispersal in Europe. These are: (1) a wide range of habitats, implying a high diversity of resources; (2) mild climates with low seasonality, implying a lack of strong environmental fluctuations. Around 1.8 Ma at the latest, hominins of African origin entered the western Palaearctic for the first time, taking advantage of the diversity of habitats and resources, particularly along large river systems. Their subsequent westward spread between 1.7 and 1.3 Ma was restricted to Mediterranean-influenced areas, which offered a high variability of habitats and relatively low seasonality. The increase in environmental diversity, which occurred from 1.2 Ma onwards, opened up South-Eastern and Eastern Europe for hominin occupation. According to the available records, North-Western and Central Europe were initially colonized during late Early to early Middle Pleistocene interglacials, when these regions experienced periods of low seasonality and considerable habitat diversity.     

Extinction of deep-sea foraminifera as a result of Pliocene–Pleistocene deep-sea circulation changes in the South China Sea (ODP Sites 1143 and 1146)

During the Late Pliocene–Middle Pleistocene, 56 species and 15 genera of elongate, cylindrical benthic foraminifera disappeared from the deep sea in the South China Sea (ODP Sites 1143 and 1146) as part of the last global extinction in the deep sea. This extinction group (Ext. Gp) exhibited a pulsed decline in abundance and species richness mostly during glacials, and often associated with periods of expansion of polar ice that resulted from increased cooling of the Earth's climate since ∼2.5 Ma, particularly during the Mid-Pleistocene Climate Transition (MPT, 1.2–0.6 Ma). We infer that the Ext. Gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep-sea water masses. The detailed record of withdrawal of the Ext. Gp differs between the two sites, with far more disappearances occurring prior to the MPT in the deeper Site 1143 (2772 m) than in the shallower Site 1146 (2092 m). The Late Pliocene and Early Pleistocene declines in deeper parts of the South China Sea (Site 1143) may have resulted from enhanced glacial production of deep, southern-sourced water passing over the sill into the basin from the North-west Pacific. During the MPT however, the Ext. Gp declines and disappearances were of similar timing and magnitude in both sites, implying that both were influenced by the same deep-water mass during glacials at this time. This could have been North Pacific Deep Water, which many workers infer was formed in the northern Pacific during the last glacial, and may have begun forming during MPT glacials, in association with the progressively enhanced cooling of the Northern Hemisphere.     

Stable isotopes reflect the ecological stability of two high-elevation mammals from the late Quaternary of Colorado

The vertebrate fossil record of Cement Creek Cave, Colorado, spans from > 45,000 yr ago to the present and represents the richest stratified series of high-elevation (> 2900 m) mammal remains known from the late Quaternary of North America. Stable carbon and oxygen isotope analyses of tooth enamel were used to assess potential ecological responses of two species found commonly throughout the cave, Yellow-bellied marmots (Marmota flaviventris) and Bushy-tailed woodrats (Neotoma cinerea), to late Quaternary climate and environmental changes of the Southern Rocky Mountains. Results indicate that despite such perturbations, the dietary ecologies of both species were maintained across this period. Neither taxon shifted to consuming C₄ taxa or different C₃ functional groups; similarly, no significant shifts in surface water use were detected. Variations in enamel δ¹³C were observed, however, that represent the physiological responses of high-elevation plants to changing levels of late Quaternary atmospheric CO₂. While our findings extend both the geographic and elevational record of this plant CO₂ response, they simultaneously highlight the ecological stability of high-elevation M. flaviventris and N. cinerea during climate changes of late Quaternary magnitude.     

贵州水城仲河剖面二叠纪-三叠纪之交底栖群落的物种多样性与功能多样性转变

为了定量化恢复晚二叠世末期生物大灭绝对底栖群落的物种多样性和功能多样性的影响,对浅海碎屑岩台地相区的贵州水城仲河剖面开展宏体化石采集和分析,识别和划分古群落,选择优势度、香农指数、均匀度等代表物种多样性指数,生态功能群数量和功能均匀度代表功能多样性指数. 共采集1 340枚化石标本,经鉴定得到30属33种,其中双壳类可归纳为两个生物带:晚二叠世长兴期的Hunanopecten exilis顶峰带和早三叠世Griesbachian早期的Pteria ussurica variabilis顶峰带. 根据化石属种的地层分布、保存状况,结合聚类分析方法识别出3个古群落:Astartella obliqua-Tethyochonetes quadrata群落、Pteria ussurica variabilis-Claraia wangi群落和Pteria ussurica variabilis-Unionites canalensis群落. 自晚二叠世长兴期末期至早三叠世Griesbachian早期,古群落的优势度上升、香农指数降低、均匀度下降,功能群丰富度降低,功能均匀度上升,这指示晚二叠世末生物大灭绝对浅海碎屑岩相区的底栖群落的组成和功能均有显著的破坏. 此外,结合华南浅海和深海相区的古群落数据,发现底栖群落的物种多样性指数和功能多样性指数在晚二叠世末生物大灭绝中均遭受损失,但是浅海底栖群落受影响较高.      

The spatial characteristics and pollution levels of metals in urban street dust of Beijing,China

The components and concentrations of metals in street dust are indictors of environmental pollution. To explore the pollution levels of Cd, Cr, Cu, Mn, Ni and Pb in street dust and their spatial distribution characteristics, 220 dust samples were collected in a grid pattern from urban street surfaces in Beijing. Multivariate statistics and spatial analyses were adopted to investigate the associations between metals and to identify their pollution patterns. In comparison with the soil background values, elevated metal concentrations were found, except those for Mn and Ni. The results of the geo-accumulation index (I_geo) and the potential ecological risk index (Erⁱ) of the metals revealed the following orders: Cd > Cu > Cr > Pb > Ni > Mn and Cd > Cu > Pb > Cr > Ni. Levels of I_geo ranging from 0 to 5 were found and about 80% of the samples were below the moderately polluted level. The Erⁱ values of single elements were within the low ecological risk level in most sampling sites. Most of the metals in the street dust of Beijing were statistically significantly correlated. It is hard to clearly identify the sources of each metal in the street dust since local environments are very complex. Cadmium, Cu, Cr, Mn and Pb showed medium spatial autocorrelations within the sampling region. Similar spatial distribution patterns were observed for Cu, Cr and Pb, and these metals had relatively high spatial variabilities and were enriched in the center of the city with several peaks scattered in the suburbs. Metal pollution anomalies were identified by using cluster and outlier analyses. Locations identified as clusters with high values indicated non-point source pollution, while locations identified as outliers with high values indicated point source pollution. Traffic, construction, and other human activities influenced these high values. In addition, the locations identified as outliers with low values in urban areas might benefit from less transportation and better management.     

End-cretaceous cooling and mass extinction driven by a dark cloud encounter

We have identified iridium in an ~ 5 m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K–Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co–Ir diagram, calling it the “extraterrestrial index” f_EX. This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of ~ 100 pc and the central density of over 2000 protons/cm³. Kataoka et al. (2013, 2014) pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as − 9.3 W m^− 2, the dark cloud would have caused global climate cooling in the last 8 Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen (Barrera and Huber, 1990; Li and Keller, 1998; Barrera and Savin, 1999; Li and Keller, 1999) and strontium (Barrera and Huber, 1990; Ingram, 1995; Sugarman et al., 1995). The resulting growth of the continental ice sheet also resulted in a regression of the sea level. The global cooling, which appears to be associated with a decrease in the diversity of fossils, eventually led to the mass extinction at the K–Pg boundary.     

Climate forcing and Neanderthal extinction in Southern Iberia: insights from a multiproxy marine record

Paleoclimate records from the western Mediterranean have been used to further understand the role of climatic changes in the replacement of archaic human populations inhabiting South Iberia. Marine sediments from the Balearic basin (ODP Site 975) was analysed at high resolution to obtain both geochemical and mineralogical data. These data were compared with climate records from nearby areas. Baexcces was used to characterize marine productivity and then related to climatic variability. Since variations in productivity were the consequence of climatic oscillations, climate/productivity events have been established. Sedimentary regime, primary marine productivity and oxygen conditions at the time of population replacement were reconstructed by means of a multiproxy approach. Climatic/oceanographic variations correlate well with Homo spatial and occupational patterns in Southern Iberia. It was found that low ventilation (U/Th), high river supply (Mg/Al), low aridity (Zr/Al) and low values of Baexcess coefficient of variation, may be linked with Neanderthal hospitable conditions. We attempt to support recent findings which claim that Neanderthals populations continued to inhabit southern Iberia between 30 and ∼28 ky cal BP and that this persistence was due to the specific characteristics of South Iberian climatic refugia. Comparisons of our data with other marine and continental records appear to indicate that conditions in South Iberia were highly inhospitable at ∼24 ky cal BP. Thus, it is proposed that the final disappearance of Neanderthals in this region could be linked with these extreme conditions.     

Changes of environments and human activity at the Sannai-Maruyama ruins in Japan during the mid-Holocene Hypsithermal climatic interval

Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabi1ted the Sannai-Maruyama site from 5.9 to 4.2 ± 0.1 cal kyr BP However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C₃₇ alkenone SSTs showed clear fluctuations, with four periods of high (8.4–7.9, 7.0–5.9, 5.1–4.1, and 2.3–1.4 cal kyr BP) and four of low (?8.4, 7.9–7.0, 5.9–5.1, and 4.1–2.3 cal kyr BP) SST. Thus, each SST cycle lasted 1.0–2.0 kyr, and the amplitude of fluctuation was about 1.5–2.0 °C. Total organic carbon (TOC) and C₃₇ alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal kyr BP, but was clearly increased between 5.9 and 4.0 cal kyr BP, because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 ± 0.1 cal kyr BP), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal kyr BP, in spite of warm terrestrial climates, the C₃₇ alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 ± 0.1 cal kyr BP, abrupt marine and terrestrial cooling, indicated by a decrease of about 2 °C in the C₃₇ alkenone SST and an increase in the pollen of taxa of cooler climates, led to a reduced terrestrial food supply, causing the people to abandon the site. The timing of the abandonment is consistent with the timing (around 4.0–4.3 cal kyr BP) of the decline of civilizations in north Mesopotamia and along the Yangtze River. These findings suggest that a temperature rise of ～2 °C in this century as a result of global warming could have a great impact on the human community and especially on agriculture, despite the advances of contemporary society.     

Rerewhakaaitu Tephra,a land–sea marker for the Last Termination in New Zealand,with implications for global climate change

The Rerewhakaaiutu Tephra erupted from Okataina Volcanic Centre, North Island, New Zealand, at 14,700±95 ¹⁴C yr BP (ca 17,600 cal yr BP) at a time of rapid re-organisation of Earth's climate system at the end of the Last Glacial (Termination I). It provides a distinctive isochron in a range of different environments in North Island and in adjacent South Pacific Ocean sediments. Terrestrial evidence, based on fluvial aggradation and downcutting relationships, loess accumulation rates, palaeovegetation patterns, and buried soil development and mineralogy, shows that marked amelioration of climate occurred shortly before the Rerewhakaaitu Tephra was deposited. Similarly, marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms, while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the Rerewhakaaitu Tephra. These changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms. The re-organisation of climate commencing at ca 15,000–14,500 ¹⁴C yr BP (ca 18,000–17,400 cal yr BP) is detected elsewhere in the Southern Hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres.     

Repeated anoxia–extinction episodes progressing from slope to shelf during the latest Cenomanian

Oceanic Anoxic Event 2 (OAE 2) during the Cenomanian–Turonian (C/T) transition caused stepwise marine extinctions. Using organic compounds, stable carbon and oxygen isotopes, and foraminifera from three depth-transect sections in northern Spain, this study revealed repeated anoxic/euxinic events coinciding with warming and stepwise extinctions of planktonic and/or benthic foraminifera within intermediate to surface waters in the proto-North Atlantic during the C/T transition. Those short-duration euxinic events occurred four times: at 93.95 Ma, marked by the extinction of Rotalipora greenhornensis; at 93.90 Ma, marked by the extinction of Rotalipora cushmani; at the mid-time maximum of the plateau of the δ¹³C of carbonates (93.70 Ma); and at the time of the C/T boundary (93.55 Ma). Furthermore, the main benthic foraminiferal extinctions occurred during the first and second euxinic events in the upper slope, during the second and third euxinic events in the outer to middle shelf, and during the third and fourth events in the middle shelf. The main euxinic events in each section also showed a progression to the shallow shelf. The main anoxia–extinction events occurred in the upper slope and outer shelf then moved to the middle shelf. The shallowest section had relatively weak anoxia and a proportionally low extinction rate. These new findings indicate that foraminiferal extinctions started from the intermediate water and the continental slope and then moved to the continental shelf. This was the result of the repeated progression of euxinic–anoxic water from the upper slope to the middle shelf on the eastern continental margin of the proto-North Atlantic four times during a 400 kyr period, to the end of the Cenomanian.