Geological Time Frame Research Articles

Assessment of Toxicity Potential of Sedimentary PAHS from Refome Lake, South-East Nigeria over the Last Century

In this study, toxic equivalent factors and sediment quality guidelines were employed for the assessment of toxicity potential of PAHs in 2 sediment cores collected from the center (RC) and shoreline (RS) of Reforme lake, SE Nigeria over the last ~1 century. Boundary cross plots of isomeric ratios such as Ant/Ant + Phe (>0.1) vs. Fl/Fl + Pyr (>0.4) and BaA/BaA + Chry (>0.35) vs. Icdp/Icdp + Bper (>0.2) indicated biomass combustion/domestic coal utilization as the main sources of PAHs input. The result revealed toxicity unit indices (TU1, 1.22 - 1.57) for the two cores were above the thresholds of no effect. The highest TU1 value found in the near-bottom layer (RS5, 20 - 25 cm) of the RS corresponding to geological time-frame ~1930-1947 coincided with the period of inhabitation by the European settlers along the lake’s catchments when coal or coal products utilization for domestic and recreational purposes was at its peak. On the other hand, TU2 values were <1 at all depth intervals, revealing unlikely PAH effects to resident organisms. Total toxicity equivalency factors (TEqFs) for the surface sediment of RS and RC were 9.29 ng/g TEqFs and 9.16 ng/g TEqFs, respectively, and indicated that more attention should be paid to BaPyr accumulation in the lake’s sediment.

Big brains reduce extinction risk in Carnivora.

Why are some mammals more vulnerable to extinction than others? Past studies have explored many life history traits as correlates of extinction, but have not been successful at developing a unified understanding of why some species become extinct while other species persist despite living at the same time, under similar conditions, and facing equivalent challenges. I propose that the lens of wildlife behavior may bring into focus a more comprehensive view of why some species have gone extinct while others persist. The fossil record has recorded extinction events over carnivoran history; unfortunately, behavior is not well recorded in the fossil record. As a proxy for behavior, I examine relative encephalization (RE), brain size after controlling for body mass and phylogeny, as it has been found to be biologically relevant in understanding a wide variety of animal behavioral traits. I focus on the data-rich order Carnivora for which there are comprehensive data on brain size and extinction between 40 and 0.012million years ago. I use Cox proportional-hazards models to assess the role that RE and body size have played on extinction risk for 224 species in the order Carnivora that existed between 40 and 0.012 million years ago. I show generally that carnivoran species with reduced RE had higher relative risks of extinction. Additionally, I find an interaction between RE and body size such that RE had the largest effects on relative extinction risk in the smallest-bodied species. These results suggest that RE is important for understanding extinction risk in Carnivora over geologic time frames.

Evolutionary history of herbivory in the Patagonian steppe: The role of climate, ancient megafauna, and guanaco

Herbivory is an important ecological process than has influenced the evolution of grassland-savannah systems. The evolutionary history of herbivory largely determines how resilient plant communities are to herbivory, with communities evolving with a long history generally possessing plant adaptations that make them able to cope with such disturbance. Thus, the evolutionary history of herbivory can serve as an indicator of a system’s resilience to modern grazing. Determining this history, however, is problematic because quantitative measures of herbivory and knowledge of plant origin are needed over appropriate evolutionary time frames. Paleoecology offers a useful framework for assessing this evolutionary history of plant-herbivore interactions. The Patagonian steppe is a phytogeographic province of South America whose evolutionary history of herbivory has been debated. Past discussions have focused completely on the abundance of its sole large ungulate herbivore—the guanaco (Lama guanicoe Müller 1776)—since European colonization of the continent. Here we use a paleoecological approach to reconstruct the evolutionary history of herbivory and plant evolution in the Patagonian steppe over a much broader, geologic time frame (Cenozoic) to shed light on the matter. We examine the role of past climate, ancient megafauna, and guanaco in shaping the vegetation and briefly discuss how present land use may be misaligned with the steppe’s evolutionary history of herbivory.

Evolutionary Roots of Plant Microbiomes and Biogeochemical Impacts of Nonvascular Autotroph-Microbiome Systems over Deep Time

Since rooted vascular plants rose to dominance, associated microbiota have powerfully influenced global biogeochemistry by mobilizing N and P and otherwise aiding plant health, thereby fostering sequestration of CO2 into coal and soil organics. Less well understood are evolutionary history and biogeochemical roles of microbiomes of ecologically significant nonvascular plants and related algae, whose lineages penetrate more deeply into time. Because analyses of diverse host-microbiome systems indicate that evolutionary history commonly influences microbiome composition and function, we mapped onto a geological time frame biogeochemical features inferred in our previous metagenomic studies of a phylogenetic spectrum of multicellular, freshwater-terrestrial, nonvascular autotroph-microbiome systems: Nostoc commune, representing microbialite-forming cyanobacteria; the Nostoc lichen Peltigera ponojensis; chlorophyte Cladophora glomerata; streptophyte alga Coleochaete pulvinata; moss Sphagnum fimbriatum; and liverwort Conocephalum conicum. Widespread and often abundant today, these species represent ancient lineages of minimal ages ranging from 1450 to 380 Ma, information we used to estimate present global annual magnitudes of organic/inorganic C sequestration, N fixation, and methane oxidation and to calculate biogeochemical impacts during periods from lineage origin to the rise of vascular plants and from lineage origins to present. Functional comparisons indicated that (1) functionally diverse bacterial associates have likely enhanced global C- and N-cycle roles of cyanobacteria for ∼1.5 billion years; (2) by 700–800 Ma, chlorophyte microbiomes retaining ancient functional features (e.g., vitamin B12 biosynthesis and N fixation) had added diverse methane-oxidizing bacteria and eukaryotes, including early metazoans; (3) by ∼500 Ma, streptophyte algal microbiomes possessing ancient functions had incorporated early-diverging fungi; (4) by 450 Ma, microbiomes of early plants included diverse prokaryotes, protists, fungi, and early terrestrial animals; and (5) by 385 Ma, plant microbiomes included P-mobilizing fungi. Autotroph-microbiome systems appear to have accreted functions of global significance over deep time, a new concept that illuminates the early evolution of terrestrial life and that aids modeling past, present, and future biogeochemical impacts.

Investigation of Vial Position Controls for the Development of a Cave Auto-Sampler

Researchers at the University of Waikato visit caves on a periodic basis to collect samples of drip water, which over geological timeframes form stalagmites and other formations. However, most caves are remotely located, which makes it an arduous task to reach the study site and is economically unfeasible for frequent visits. This paper presents the position control aspect of the cave auto-sampler, which is a crucial operation to store water samples in an airtight container. The primary challenge was to position airtight sample vials under the needles for sample collection, within 3.5mm from the centre of the silicone septa. Various methods and makes of stepper motors were tested to find the balance between precision and power saving. A high gear ratio stepper motor was chosen as the primary drives due to its high precision and its ability to hold position when power is turned off between operations. Testing in lab conditions showed satisfactory consistency regarding position control and is integrated into the auto-sampler.

Selling Anthropocene space: situated adventures in sustainable tourism

The Anthropocene is a proposed technical term for a new geological timeframe, but it is also a conceptual tool with the potential to redefine the stakes of contemporary environmental politics. One facet that is often overlooked is that the Anthropocene is a concept with commercial potential, even if the term itself has not been widely adopted. This article presents an investigation of the commercial potential of the Anthropocene idea through the lens of self-described sustainable tourism ventures in The Bahamas. These examples demonstrate some of the ways in which Anthropocene imaginaries participate in the recreation, redesign, and rebranding of specific spaces as emergent “tourism products”, specifically the small island farm and the anthropogenic coral reef. The goal is twofold: (1) to explore the symbolic and material creativity of the Anthropocene idea as its themes are used to extend capitalist innovation, and (2) to examine the Anthropocene idea as a strategy that builds upon existing histories of inequality to enable transnational accumulation in particular locales. As a situated adventure, this article articulates a reflexive mode of political ecological research for the Anthropocene that is equipped to critically articulate emergent practices at the intersection of postcolonial tourism, environmental conservation, and sustainable development.

Source Characterization and Historical Trend of Sedimentary PAHs from Refome Lake, South–South Nigeria

Polycyclic aromatic hydrocarbons (PAHs) released from diverse sources passing through water column carry information into the sediment where they can be used to assess the environmental status of an ecosystem over specified geologic time frame. The vertical distributions of PAHs in two recent sediment cores (RS and RC, 30 cm long) from Refome Lake, South–South Nigeria, were investigated using gas chromatography–mass spectrometry in order to evaluate their sources and historical trends of deposition over the last ca. century. The total PAHs (TPAHs—sum of parent and retene) concentrations ranged from 66.99 ng/g dry weight (dw) at the middle layer of RC core (RC3 10–15 cm) to 182.24 ng/g dw at the near-bottom layer of RS core (RS5 20–25 cm) with a mean of 102.21 ± 24.32 ng/g. The elevated TPAH level at the near-bottom layer of the RS core, corresponding to geologic time-frame ca. 1930–1947, coincided with the period of inhabitation of the European settlers along the lake’s catchments when utilization of coal and/or coal products for domestic/recreational activity was at its peak. A decline in TPAH levels up-cores thereafter reflected the periods of gradual evacuation of inhabitants of the lake area hinterland following the departure of the White after the Nigerian independence in 1960. Evaluation of PAH category according to ring size coupled with data from specific molecular ratios revealed inputs dominated by wood/coal combustion with a moderate contribution from petrochemical/liquid fossil fuel exhaust emissions and a minor diagenetic sources. Principal component analysis result not only distinctively separated RS from RC core samples but also revealed that the RS samples were more impacted by wood/coal combustion emissions than the RC, while liquid fossil fuel exhaust emission dominated the RC over the RS samples. Although short-range eolian transport did play a role in the delivery of PAHs to the lake, localization of source contamination was more important.

Role of the Qinghai-Tibetan Plateau uplift in the Northern Hemisphere disjunction: evidence from two herbaceous genera of Rubiaceae

To assess the role of the Qinghai-Tibetan Plateau uplift in shaping the intercontinental disjunction in Northern Hemisphere, we analyzed the origin and diversification within a geological timeframe for two relict herbaceous genera, Theligonum and Kelloggia (Rubiaceae). Phylogenetic relationships within and between Theligonum and Kelloggia as well as their relatives were inferred using five chloroplast markers with parsimony, Bayesian and maximum-likelihood approaches. Migration routes and evolution of these taxa were reconstructed using Bayesian relaxed molecular clock and ancestral area reconstruction. Our results suggest the monophyly of each Theligonum and Kelloggia. Eastern Asian and North American species of Kelloggia diverged at ca.18.52 Mya and the Mediterranean species of Theligonum diverged from eastern Asian taxa at ca.13.73 Mya. Both Kelloggia and Theligonum are Tethyan flora relicts, and their ancestors might have been occurred in warm tropical to subtropical environments along the Tethys coast. The Qinghai-Tibetan Plateau separated the eastern and western Tethyan area may contribute significantly to the disjunct distributions of Theligonum, and the North Atlantic migration appears to be the most likely pathway of expansion of Kelloggia to North America. Our results highlight the importance role of the QTP uplift together with corresponding geological and climatic events in shaping biodiversity and biogeographic distribution in the Northern Hemisphere.

Dating early animal evolution using phylogenomic data

Information about the geological timeframe during which animals radiated into their major subclades is crucial to understanding early animal ecology and evolution. Unfortunately, the pre-Cambrian fossil record is sparse and its interpretation controversial. Relaxed molecular-clock methods provide an alternative means of estimating the timing of cladogenesis deep in the metazoan tree of life. So far, thorough molecular clock studies focusing specifically on Metazoa as a whole have been based on relatively small datasets or incomplete representation of the main non-bilaterian lineages (such as sponges and ctenophores), which are fundamental for understanding early metazoan evolution. Here, we use a previously published phylogenomic dataset that includes a fair sampling of all relevant groups to estimate the timing of early animal evolution with Bayesian relaxed-clock methods. According to our results, all non-bilaterian phyla, as well as total-group Bilateria, evolved in an ancient radiation during a geologically relatively short time span, before the onset of long-term global glaciations (“Snowball Earth”; ~720–635 Ma). Importantly, this result appears robust to alterations of a number of important analytical variables, such as models of among-lineage rate variation and sets of fossil calibrations used.

Hydrogen isotope ratios of terrestrial leaf wax n-alkanes from the Tibetan Plateau: Controls on apparent enrichment factors, effect of vapor sources and implication for altimetry

Empirical evidence suggested that the altitudinal dependence of hydrogen isotope ratios of leaf wax n-alkanes (δDwax) can be used to estimate paleoaltitudinal changes. However, the application of δDwax-based paleoaltimetry remains difficult, as the impacts of evaporative, transpirative and biosynthetic processes on hydrogen isotope fractionations in changing environments and the influence of likely changing water vapor sources are not well explored. For this study, we sampled stream waters, soils and plant leaves along two transects spanning large gradients of altitude, precipitation amount, vapor source, temperature and vegetation type on the Tibetan Plateau (TP). δD values of stream water (as an approximation for δDp), soil water (δDsw) and plant leaf water (δDlw) as well as leaf wax n-alkanes were measured in order to quantify isotopic fractionations in the formation of leaf waxes.Most interestingly, we found a strong negative correlation between the evapotranspirative enrichment of leaf water against precipitation (εlw-p), which combines the effects of soil evaporation and leaf transpiration, and the biosynthetic hydrogen isotope fractionation (εwax-lw), which describes isotopic enrichment between leaf wax and leaf water. The relationship yields a steady apparent isotopic enrichment factor (εwax-p) between leaf wax and precipitation, which is independent from climatic parameters and has an average value of −107±26‰ for grasses (monocotyledons) and −77±22‰ for trees (dicotyledons). Since the terrestrial n-alkanes, especially n-C27 and n-C29, in sediments are derived from trees and grasses, the likely change of the vegetation type in the uplift of mountains can change the isotopic estimates by about ±30‰, which corresponds to an altitudinal change of ∼1600m. We, therefore, suggest that hydrogen isotope ratio of sedimentary n-C31 alkane, which is mainly derived from grasses might be better proxies to reconstruct paleoaltitudes.Our large dataset of δDwax from trees and grasses that aimed to mirror the variability of environmental factors over geological time frames showed the lapse rates were significant, but much smaller than in previous studies. Most importantly our result demonstrated that the lapse rate significantly differed for both transects (p=0.0068), i.e. 0.87±0.71‰/100m (R2=0.28, p=0.2841, n=6) and 2.28±0.82‰/100m (R2=0.34, p=0.0135, n=17) for Indian monsoon and Westerly dominated areas, respectively. This suggests that different moisture sources might strongly affected the observed lapse rates. In consequences altitude reconstructions are strongly complicated in areas with likely changing air masses like the Tibetan Plateau.

The Effect of Bromide on Oxygen Yields in Homogeneous α-radiolysis

ABSTRACTIn a scenario where ground water enters a canister for spent nuclear fuel in a deep geological repository, the presence of dissolved ions in the water could possibly influence the fuel dissolution due to effects on radiolysis yields. One species of particular interest in this context is bromide, which has a proven ability to scavenge hydroxyl radicals much faster than molecular hydrogen does. As a result, bromide could inhibit the beneficial effect of dissolved hydrogen, which has been shown in γ-radiolysis experiments. However, already a few hundred years after repository closure, α-decay starts to dominate in the radiation field from the spent fuel. Hence, the effects of α-radiolysis are expected to govern the fuel dissolution over the geological timeframes of the repository. In the present work, α-radiolysis experiments have been performed to determine the effect of bromide ions on the yield of hydrogen peroxide by mass spectrometric measurement of its decomposition product oxygen. The use of high activity 238Pu solutions has made it possible to study this effect during pure α-radiolysis from a homogeneously distributed radiation field. To simulate deep bedrock repository conditions, and to minimize the influence of in-leaking O2 from air, the studies were performed using graphite sealed stainless steel autoclaves with an initial atmosphere of 10 bar H2. The results show that addition of 1 mM Br- to the solution gives no significant effect on the O2 yield for radiation doses up to 2 MGy. This lack of effect is most likely explained by the limited radical escape yields from radiation tracks in pure α-radiolysis.

Toward a conceptual model relating chemical reaction fronts to water flow paths in hills

Both vertical and lateral flows of rock and water occur within eroding hills. Specifically, when considered over geological timeframes, rock advects vertically upward under hilltops in landscapes experiencing uplift and erosion. Once rock particles reach the land surface, they move laterally and down the hillslope because of erosion. At much shorter timescales, meteoric water moves vertically downward until it reaches the regional water table and then moves laterally as groundwater flow. Water can also flow laterally in the shallow subsurface as interflow in zones of permeability contrast. Interflow can be perched or can occur during periods of a high regional water table. The depths of these deep and shallow water tables in hills fluctuate over time. The fluctuations drive biogeochemical reactions between water, CO2, O2, and minerals and these in turn drive fracturing. The depth intervals of water table fluctuation for interflow and groundwater flow are thus reaction fronts characterized by changes in composition, fracture density, porosity, and permeability. The shallow and deep reaction zones can separate over meters in felsic rocks. The zones act like valves that reorient downward unsaturated water flow into lateral saturated flow. The valves also reorient the upward advection of rock into lateral flow through solubilization. In particular, groundwater removes highly soluble, and interflow removes moderately soluble minerals. As rock and water moves through the system, hills may evolve toward a condition where the weathering advance rate, W, approaches the erosion rate, E. If W=E, the slopes of the deep and shallow reaction zones and the hillsides must allow removal of the most soluble, moderately soluble, and least soluble minerals respectively. A permeability architecture thus emerges to partition each evolving hill into dissolved and particulate material fluxes as it approaches steady state.

Rates and geochemical processes of soil and salt crust formation in Salars of the Atacama Desert, Chile

The hyperarid Atacama Desert contains numerous local basins with surficial salt crusts, known as salars, where evaporation of shallow groundwater drives the major soil processes. We examine chemical and isotopic profiles in two soils of differing ages from the Salar Llamara to determine the geochemical processes involved in their formation. Evaporation, which provides salts to the soils through mineral precipitation, decreases with increasing salt crust thickness, and average~0.03mmm−2d−1 over geological time frames. Salt distribution varies predictably with depth and soil age, with the most soluble compounds concentrated nearest to the land surface, indicating the direction of fluid flow. δ34S values of mineral sulfate tend to decrease with decreasing soil depth, following a pattern indicative of Rayleigh-like fractionation as solute-rich waters migrate toward the land surface. δ13C and δ18O values of carbonate suggest that the uppermost halite layers, which contain very small amounts of carbonate, have a strong biological signature. In contrast, carbonate-rich layers deeper in the profiles consist of largely unmodified lacustrine carbonate that formed in highly evaporitic lake conditions. The continuous upward evaporation of water and dissolved solutes creates a rugged and physically dynamic halite crust composed of rounded salt nodules. The crust undergoes deliquescence as atmospheric relative humidity rises from marine air intrusions, and we found that the halite nodules on the surface of the Salar Llamara are nearly always at or above deliquescence relative humidity. The interiors of these nodules are therefore able to buffer the large diurnal changes in atmospheric relative humidity allowing for the survival of halophilic microbial communities in an otherwise very dry environment. Radiocarbon measurements of occluded organic C in the surface crusts indicate that C cycling occurs at differing rates depending on local micrometeorological conditions, and that a given salt crust feature may persist for thousands of years once formed.

Geological and Exploration Models of Beach Placer Deposits, Integrated from Case-Studies of Southern Australia

The processes leading to the formation of beach placer deposits generally begin inland and terminate at the coast, including source rocks being weathered, eroded and then transported by streams and rivers to the coast, where the sediments are deposited in a variety of coastal environments. The coastal sediments are reworked by the action of waves, tides, longshore currents and wind, which are effective processes for sorting the mineral grains based on differences in their size and density, resulting in laminated or lens-shaped packages of sediments up to tens of meters thick that are rich in heavy minerals. Detailed studies of sedimentary basins, as well as peripheral (paleo-)valleys that drained sediment source areas, are important tools in the exploration for heavy mineral resources. Knowledge of the (paleo-)basin, associated valley architecture and the source of heavy minerals concentrated in the shorelines and valleys are useful guides to the potential for, and location of, economic deposits.Evidence from sedimentology can be combined with that from other geological and geophysical characteristics to arrive at a general reconstruction of basin and paleovalley architecture and depositional environments. Complex paleogeography of the shorelines can influence or determine the sites of heavy mineral concentration. Heavy mineral sands tend to concentrate in certain shoreline settings during storm activity. Repeated storm erosion and reworking over centuries (e.g., the southeastern coast of Australia) or millennia (e.g., the Eucla and Murray Basins of Australia) can progressively enrich heavy mineral sand deposits. Preservation of these deposits over a geological timeframe of millions of years can ensue through subsidence of coastal sediments, and during sea-level change that results in either shorelines migrating inland (marine transgression) or seaward (marine regression), potentially burying or stranding earlier deposits or reworking them to form younger deposits. Refinements in remote sensing and geophysical techniques, data processing, sedimentology and computer-aided interpretations provide effective, economic and efficient methods for modeling coastal reconstructions and for exploring provinces and terrains prospective for heavy mineral sand deposits. Landscape topography analysis, combined with geophysical methods that can resolve physical property contrasts between the shoreline sediments and underlying sequences, are increasingly used in mineral exploration to locate and to reconstruct paleoshorelines and paleovalleys.Australia has modern and ancient beach-placer deposits, both of which show many similar geologic features. The formation of these heavy mineral deposits provides one of the best examples of applying knowledge of modern systems (e.g., the west and east coasts of Australia) as an analogue to interpret and understand the geology and form of ancient deposits (e.g., the Eucla and Murray Basins of southern Australia). This study provides descriptive and exploration models of Australia’s heavy mineral sand deposits formed in coastal environments, which can be applied to similar settings worldwide.

The effect of fuel chemistry on UO2 dissolution

The dissolution rate of both unirradiated UO2 and used nuclear fuel has been studied by numerous countries as part of the performance assessment of proposed geologic repositories. In the scenario of waste package failure and groundwater contact with the fuel, the effects of variables such as temperature, dissolved oxygen, and water and fuel chemistry on the dissolution rates of the fuel are necessary to provide a quantitative estimate of the potential release over geologic time frames. The primary objective of this research was to determine the influence these parameters, with primary focus on the fuel chemistry, have on the dissolution rate of unirradiated UO2 under oxidizing repository conditions and compare them to the rates predicted by current dissolution models.Both unirradiated UO2 and UO2 doped with varying concentrations of Gd2O3, to simulate used fuel composition after long time periods when radiolysis has minor contributions to dissolution, were examined. In general, a rise in temperature increased the dissolution rate of UO2 and had a larger effect on pure UO2 than on those doped with Gd2O3. Oxygen dependence was observed in the UO2 samples with no dopant and increased as the temperature rose; in the doped fuels less dependence was observed. The addition of gadolinia into the UO2 matrix resulted in a significant decrease in the dissolution rate. The matrix stabilization effect resulting from the dopant proved even more beneficial in lowering the dissolution rate at higher temperatures and dissolved O2 concentrations in the leachate where the rates would typically be elevated.

Did a Miocene–Pliocene island isolation sequence structure diversification of funnel web spiders in the Taiwan‐Ryukyu Archipelago?

AbstractAimWe tested the competing hypotheses concerning the relative importance of Pleistocene versus Miocene–Pliocene geological events for the formation of endemism in an Asian archipelago using the Macrothele taiwanensis (Hexathelidae) species group.LocationTaiwan‐Ryukyu Archipelago.MethodsWe estimated phylogenetic trees from cytochrome oxidase I subunit (COI) and 16S rRNA (16S) gene regions and employed Bayesian ancestral range reconstructions to investigate previously debated models of lineage diversification in the Taiwan‐Ryukyu Archipelago. To evaluate alternative geological timeframes for their importance in shaping the genetic structure of funnel web spiders, we used five time calibration schemes to estimate timing of divergence, infer ancestral distributions, and to reconstruct historical demographic changes in each lineage. We tested taxonomic boundaries with two species delimitation procedures.ResultsOur results indicate a north‐to‐south isolation sequence of the M. taiwanensis group: the Amami lineage diverged first, then Yaeyama, and finally the Taiwanese lineages. Divergence time estimation and population demographic change analyses indicate that Pleistocene climate fluctuations minimally impacted the genetic structure of these spiders. Instead, estimated divergence events correspond to Miocene–Pliocene geological events, strongly supporting a much older timeframe for diversification. The results of species delimitation analyses coincide well with morphological differences observed among the island populations, reinforcing inferred species boundaries, and at least three potential cryptic species were statistically detected within Taiwan.Main conclusionsMiocene–Pliocene geological events appear to have contributed disproportionately to diversification in the M. taiwanensis species group. The clear association between geographical area, genetic structure and statistical species delimitation strongly supports an interpretation of allopatric speciation. We advocate comparing our results with those derived from additional study organisms with similar life histories to further explore the Miocene–Pliocene diversification hypothesis.

About this title ‐ The Value of Outcrop Studies in Reducing Subsurface Uncertainty and Risk in Hydrocarbon Exploration and Production

Field studies over a range of scales have been important in the upstream oil and gas industry for decades. Advances in digital outcrop characterization and data capture, coupled with increased computational capabilities, have resulted in a resurgence in fieldwork; these field studies are required to develop depositional, stratigraphic and structural concepts and provide the data which underpin the current generation of complex, computer generated, 3D subsurface models. These models provide an informed means of benchmarking the subsurface along with a more considered view of subsurface uncertainty and management of the risks identified. The papers in this volume cover safety in the field, frontier basin petroleum system assessment, field appraisal and development including unconventional resources, applications of techniques such as LiDAR and 3D photogrammetry, and uncertainty characterization. The studies were undertaken in diverse locations such as the Faroe Islands, Italy, Algeria, India, the USA and Trinidad; they represent a range of tectonic settings and a wide geological time frame. The spectrum of papers is testament to the value and integral position that fieldwork occupies within the modern hydrocarbon industry.

Neogene Deep Water Agglutinated Foraminiferal Biostratigraphy and Biozonation in Niger Delta, Nigeria

This study entails the biostratigraphy of benthic agglutinating foraminifera of four wells in the deep water of the Niger Delta. A total of 453 ditch cuttings were analysed for wells A, B, C and D. Eighty-five and 164 ditch cuttings from the intervals of 4900–9920 ft. and 4530–14600 ft. of wells A and well B respectively, while 92 and 112 cuttings from 5760–11400 ft. and 6000–12750 ft. were analysed in wells C and D respectively. These samples were processed and analysed at 60 feet intervals. . The analysed sections of the wells are composed of shale, mudstones and sand deposited in the upper to lower bathyal environments. The agglutinating foraminifera recovered were fairly well preserved. Total foraminifera percentages recovered from wells A, B, C and D wells are 31%, 34%, 24% and 27% respectively. Marker species were identified and used to erect biozones. The following six agglutinated foraminiferal zones beginning from the oldest have been proposed, Eggerella scrabra Taxon Range Zone, and Ammobaculites strathearnensis–Eggerella scabra, Haplophragmoides narivaensis - Eggerella scabra, Cyclammina cancellata–Ammobaculites strathearnensis, Cyclammina complanata–Glomospira gordiales, Cyclammina cf. minima–Ammobaculites strathearnensis Interval Range Zones. The agglutinated foraminifera assemblages were calibrated to the geologic timeframe by means of planktic foraminifera and calcareous nannofossils. The studied wells penetrated a sedimentary succession of Late Miocene to Early Pliocene age. Taxonomic notes on some of the observed species have also been provided.

Biosignatures on Mars: What, Where, and How? Implications for the Search for Martian Life.

The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is the concept of habitability, the set of conditions that allows the appearance of life and successful establishment of microorganisms in any one location. While environmental conditions may have been conducive to the appearance of life early in martian history, habitable conditions were always heterogeneous on a spatial scale and in a geological time frame. This “punctuated” scenario of habitability would have had important consequences for the evolution of martian life, as well as for the presence and preservation of traces of life at a specific landing site. We hypothesize that, given the lack of long-term, continuous habitability, if martian life developed, it was (and may still be) chemotrophic and anaerobic. Obtaining nutrition from the same kinds of sources as early terrestrial chemotrophic life and living in the same kinds of environments, the fossilized traces of the latter serve as useful proxies for understanding the potential distribution of martian chemotrophs and their fossilized traces. Thus, comparison with analog, anaerobic, volcanic terrestrial environments (Early Archean >3.5–3.33 Ga) shows that the fossil remains of chemotrophs in such environments were common, although sparsely distributed, except in the vicinity of hydrothermal activity where nutrients were readily available. Moreover, the traces of these kinds of microorganisms can be well preserved, provided that they are rapidly mineralized and that the sediments in which they occur are rapidly cemented. We evaluate the biogenicity of these signatures by comparing them to possible abiotic features. Finally, we discuss the implications of different scenarios for life on Mars for detection by in situ exploration, ranging from its non-appearance, through preserved traces of life, to the presence of living microorganisms. Key Words: Mars—Early Earth—Anaerobic chemotrophs—Biosignatures—Astrobiology missions to Mars. Astrobiology 15, 998–1029.

Uncertainty in the Timing of Origin of Animals and the Limits of Precision in Molecular Timescales

SummaryThe timing of divergences among metazoan lineages is integral to understanding the processes of animal evolution, placing the biological events of species divergences into the correct geological timeframe. Recent fossil discoveries and molecular clock dating studies have suggested a divergence of bilaterian phyla >100 million years before the Cambrian, when the first definite crown-bilaterian fossils occur. Most previous molecular clock dating studies, however, have suffered from limited data and biases in methodologies, and virtually all have failed to acknowledge the large uncertainties associated with the fossil record of early animals, leading to inconsistent estimates among studies. Here we use an unprecedented amount of molecular data, combined with four fossil calibration strategies (reflecting disparate and controversial interpretations of the metazoan fossil record) to obtain Bayesian estimates of metazoan divergence times. Our results indicate that the uncertain nature of ancient fossils and violations of the molecular clock impose a limit on the precision that can be achieved in estimates of ancient molecular timescales. For example, although we can assert that crown Metazoa originated during the Cryogenian (with most crown-bilaterian phyla diversifying during the Ediacaran), it is not possible with current data to pinpoint the divergence events with sufficient accuracy to test for correlations between geological and biological events in the history of animals. Although a Cryogenian origin of crown Metazoa agrees with current geological interpretations, the divergence dates of the bilaterians remain controversial. Thus, attempts to build evolutionary narratives of early animal evolution based on molecular clock timescales appear to be premature.