Geological Time Spans Research Articles

Improving deformation models by discounting transient signals in geodetic data: 2. Geodetic data, stress directions, and long‐term strain rates in Italy

AbstractThe lithosphere of Italy is exposed to a number of different short‐term strain transients, including but not limited to landslides, postseismic relaxation, and volcanic inflation/deflation. These transients affect GPS velocities and complicate the assessment of the long‐term tectonic component of the surface deformation. In a companion paper we present a method for anticipating the principal patterns of nontectonic, short‐term strains and building this information into the covariance matrix of the geodetic velocities. In this work we apply this method to Italian GPS velocities to build an augmented covariance matrix that characterizes all expected discrepancies between short‐ and long‐term velocities. We find that formal uncertainties usually reported for GPS measurements are smaller than the variability of the same benchmarks across a geologic time span. Furthermore, we include in our modeling the azimuths of most compressive horizontal principal stresses (SHmax) because GPS data cannot resolve the active kinematics of coastal and offshore areas. We find that the final tectonic model can be made relatively insensitive to short‐term interfering processes if the augmented covariance matrix and SHmax data records are used in the objective function. This results in a preferred neotectonic model that is also in closer agreement with independent geologic and seismological constraints and has the advantage of reducing short‐term biases in forecasts of long‐term seismicity.

541. Use of Endogenous Viral Elements to Deduce the Sequence of an Ancient Adeno-Associated Virus That Circulated Amongst Australian Marsupials ~30 Million Years Ago

Vectors based on adeno-associated viruses (AAVs) have been successfully applied in clinical trials and pre-clinical settings. AAV capsid proteins are the primary determinants of vector tropism and immunogenicity, and are continually being developed to impart desirable properties, such as immune evasion and specificity for selected target tissues in humans and those of model organisms. One approach that was recently adopted by at least two groups to generate novel capsid variants is the computational deduction of putative ancestral AAV sequences, based upon observable genetic diversity amongst closely related contemporary AAV isolates. Such inferred ancestral sequences potentially recapitulate the evolutionary history of AAVs for hundreds or possibly thousands of years. Germline endogenous viral elements (EVEs) can compensate for the lack of a viral fossil record by genetically preserving viral nucleotide sequences over a geologic time span. Here we describe an AAV-EVE (mAAV-EVE1) that is lineage-restricted to the germlines of members of the Australian marsupial suborder Macropodiformes (present-day kangaroos, wallabies, and related macropodoids), to the exclusion of other Diprotodontian marsupial lineages. Orthologous mAAV-EVE1 sequences from sixteen macropodoid species, representing a speciation history spanning an estimated 30 million years, facilitated in silico reconstruction of an inferred ancestral AAV sequence. This sequence represents the genome of an ancient marsupial AAV that circulated among Australian metatherian fauna sometime during the late Eocene to early Oligocene. The deduced ancient AAV bears remarkable resemblance to modern AAVs in its predicted structural and non-structural genes, underscoring the concept that despite their relatively rapid mutation rates, AAVs have evolved under tight constraints imposed by both form and function. Moreover, the evolutionary history of mAAV-EVE1 since its integration into the pro-macropodoid lineage reflects that of the respective host species. In addition to providing an inferred ancient AAV capsid sequence for future transduction studies, this sequence can serve as input for the generation of further novel capsids by approaches such as capsid shuffling and directed capsid engineering/evolution. Furthermore, by comparing it to contemporary AAV capsids, this sequence can inform rational capsid design approaches by providing insights into long-term capsid evolution.

Evolution of sealing efficiency for CO2 geological storage due to mineral alteration within a hydrogeologically heterogeneous caprock

In CO2 geological storage (CGS) context, the evolution of the caprock sealing capacity has received increasing attention, particularly on a geological time span (thousands of years). At this time scale, geochemical reactions may enhance or weaken the caprock quality. It is widely recognized that, for the reservoir, geological heterogeneities affect the concentration and spatial distribution of CO2, and then affect the extent of gas–water–rock interactions, which in turn alters the hydrogeological properties of the reservoir. However, much less attention of these effects has been paid to the caprock. In this study, we presented and applied a novel approach to evaluate the effects of permeability and porosity heterogeneities on the alteration of minerals, the associated evolution of the caprock sealing efficiency and the containment of supercritical CO2 (scCO2) within the caprock. Even though this is a generic study, several conditions and parameters such as pressure, permeability, and mineral composition, were extracted from a caprock layer of the Shiqianfeng Formation in the Ordos Basin demonstration site in China. For the sake of simplification, a 2-dimensional model was designed to represent the caprock domain. We firstly generated an appropriate heterogeneous random field of permeability with the average permeability taken from the uppermost mudstone layer of the Shiqianfeng Formation, and then the heterogeneity in porosity was incorporated using a joint normal distribution method based on the available data. Homogeneous mineral compositions of the reservoir and caprock were used in all simulations. Simulations of three cases were performed, including a homogeneous case, a case with only permeability heterogeneity and a case with both permeability and porosity heterogeneities. The results demonstrate dramatic influences of permeability and porosity heterogeneities on the migration of scCO2 within the caprock, the alteration of minerals, and therefore the evolution of the caprock sealing quality. Specific to the data used in this study, hydrogeological heterogeneities facilitated the overall penetration of scCO2 within the caprock and promoted the alteration of minerals, thereby weakening the caprock sealing efficiency over the simulation time.

Is the Anthropocene really worthy of a formal geologic definition?

Scientists are actively debating whether the Anthropocene, the geologic time span (GTS) we are now living in, should be considered a period, epoch, or age in the geologic timescale. The solution is not easy, because the beginning of this GTS is undefined and the end unknown. In fact, there is no agreement on when the Anthropocene began, the proposed dates ranging from the Second World War, when radioactive fallout branded soils and sediments all over the world, to little after the end of the last glacial period, i.e. 11.7 thousand years ago, therefore coinciding with the onset of the Holocene. We are in favour of a concurrence of the Anthropocene with the Holocene, although a major impact of people on the environment began diachronically in different parts of the world. This single GTS should be named Anthropocene because it is chiefly characterized by a peculiar process of change for the planet: human impact. Nevertheless, a pivotal hindrance for the Anthropocene to be worthy of a formal geologic definition remains. The Anthropocene is open ended, therefore its real duration is unknown.

Temperature dependence of biological processes: Implications for food quality, safety and security

Nutrition is well outside my area of expertise although my first degree was in Agriculture in which Animal Physiology and nutrition was an important part of the course. More recently at UTas we have had several research projects the aim of which was to discover microbial sources of polyunsaturated fatty acids. Thraustochytrids were the most promising organisms and an interesting outcome was that these grew in media with no added salt without affecting PUFA production. Several studies have optimised PUFA production by varying media composition, salinity and temperature. Optimum growth rates were at 25e30 oC and continued to a minimum of 5e10 oC, similar to many other marine organisms including bacteria. That is they fit into the thermal category of psychrotropic organisms which merge with mesophiles as temperatures increase. Temperature plays a major role in the rate at which biological populations develop and potentiates the effect of other factors such as oxygen availability, salinity, hydrostatic pressure and pH. In microbiology time scales range from milliseconds for enzyme catalysed reactions to doubling times of ~7 minutes for Clostridium perfringens, to days, weeks or months for psychrophilic bacteria growing optimally, to > 3.5 billion years to reach the current level of evolutionary adaptation. The temperature dependence of biological process rates requires knowledge of microbial ecology (rate of population increase) and physiology (biochemical reaction rates and physiological control in individual cells). The integration of these disciplines into ecophysiological studies supported by omics technologies is necessary to underpin advances in understanding how to inhibit or stimulate microbial growth. At UTas we have studied the ecophysiology of food borne bacteria including pathogens and spoilage organisms for 40 years. The original aim was to produce mathematical models to predict the rate of growth or decline of populations in foods, and this continues but in the last decade we have expanded into other ecosystems. The field of Predictive Microbiology has changed the paradigm of foodmicrobiology from one of testing and retrospective reporting of results to prospective reporting based on the temperature history of a process interpreted by a predictive model. A major outcome of this work was mandating the use of the Refrigeration Index by The Australian Quarantine Inspection Service in the revised Export Control Meat and Meat Products) Order, AQIS 2005(http://www.daffa.gov.au/aqis/export/meat/elmer-3). The models developed and validated to that time were empirical and the current state of the art can be found in Corkrey et.al 2014, the abstract of which is reproduced below: “Life on Earth is capable of growing from temperatureswell below freezing to above the boiling point of water, with some organisms preferring cooler and others hotter conditions. The growth rate of each organism ultimately depends on its intracellular chemical reactions. Here we show that a thermodynamic model based on a single, rate-limiting, enzyme-catalysed reaction accurately describes population growth rates in 230 diverse strains of unicellular and multicellular organisms. Collectively these represent all three domains of life, ranging from psychrophilic to hyperthermophilic, and including the highest temperature so far observed for growth (122 C). The results provide credible estimates of thermodynamic properties of proteins and obtain, purely from organism intrinsic growth rate data, relationships betweenparameterspreviously identifiedexperimentally, thusbridgingagap between biochemistry and whole organism biology. We find that growth rates of both unicellular and multicellular life forms can be described by the same temperature dependence model. The model results provide strong support for a single highly-conserved reaction present in the last universal common ancestor (LUCA). This is remarkable in that itmeans that the growth rate dependence on temperature of unicellular and multicellular life forms that evolved over geological time spans can be explainedby the samemodel”. Progress in integrating applications in food quality, safety and security will be reported in November.

OMANASTER IMBRICATUS (ECHINODERMATA, ASTEROIDEA), A NEW GENUS AND SPECIES FROM THE SAKMARIAN (LOWER PERMIAN) SAIWAN FORMATION OF OMAN, ARABIAN PENINSULA

Omanaster imbricatus is a new genu s and species of Sakmarian (Early Permian) asteroids collected from the basal Pachycyrtella Bed of the Saiwan Formation of Oman, Arabian Peninsula; the family Omanasteridae is recognized. Late Paleozoic and especially Permian asteroids are rare and O. imbricatus differs significantly from those previously described, thereby providing an important addition to known late Paleozoic diversity. Unfortunately the single available specimen is incomplete with remaining ossicles both leached and partially fused, and available data are limited. Adambulacral form and arrangement of O. imbricatus are both suggestive of corresponding expressions of certain earlier Paleozoic species and unlike those of the crown-group, suggesting an enduring Paleozoic lineage but one not phylogenetically a part of the Mesozoic diversification. The Pachycyrtella Bed has been interpreted as recording a succession of pioneer palaeocommunities colonizing a turbulent, shallow-water settingaffected by oscillatory flows. The apparently flattened appearance of O. imbricatus is suggestive of appearances of certain Cretaceous and extant species recovered from similar environments thus suggesting both homoplasy and the versatility of asteroid evolution across extended spans of geologic time.

Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru

Non-pathological densification (osteosclerosis) and swelling (pachyostosis) of bones are the main modifications affecting the skeleton of land vertebrates (tetrapods) that returned to water. However, a precise temporal calibration of the acquisition of such adaptations is still wanting. Here, we assess the timing of such acquisition using the aquatic sloth Thalassocnus, from the Neogene of the Pisco Formation, Peru. This genus is represented by five species occurring in successive vertebrate-bearing horizons of distinct ages. It yields the most detailed data about the gradual acquisition of aquatic adaptations among tetrapods, in displaying increasing osteosclerosis and pachyostosis through time. Such modifications, reflecting a shift in the habitat from terrestrial to aquatic, occurred over a short geological time span (ca 4 Myr). Otherwise, the bones of terrestrial pilosans (sloths and anteaters) are much more compact than the mean mammalian condition, which suggests that the osteosclerosis of Thalassocnus may represent an exaptation.

Protein thermodynamics can be predicted directly from biological growth rates.

Life on Earth is capable of growing from temperatures well below freezing to above the boiling point of water, with some organisms preferring cooler and others hotter conditions. The growth rate of each organism ultimately depends on its intracellular chemical reactions. Here we show that a thermodynamic model based on a single, rate-limiting, enzyme-catalysed reaction accurately describes population growth rates in 230 diverse strains of unicellular and multicellular organisms. Collectively these represent all three domains of life, ranging from psychrophilic to hyperthermophilic, and including the highest temperature so far observed for growth (122°C). The results provide credible estimates of thermodynamic properties of proteins and obtain, purely from organism intrinsic growth rate data, relationships between parameters previously identified experimentally, thus bridging a gap between biochemistry and whole organism biology. We find that growth rates of both unicellular and multicellular life forms can be described by the same temperature dependence model. The model results provide strong support for a single highly-conserved reaction present in the last universal common ancestor (LUCA). This is remarkable in that it means that the growth rate dependence on temperature of unicellular and multicellular life forms that evolved over geological time spans can be explained by the same model.

The vertebrates of the Jurassic Daohugou Biota of northeastern China

ABSTRACT The Early Cretaceous Jehol Biota of northeastern China has become famous over the last two decades as a source of feathered avialan and non-avialan theropods, preserved alongside an array of other fossil vertebrates, invertebrates, and plants. Still more recently, a rich assemblage referred to in this paper as the Daohugou Biota has begun to emerge from Jurassic strata in the same region. Like their counterparts from the Jehol Biota, Daohugou Biota vertebrate specimens are typically preserved in fine-grained lacustrine beds and often retain feathers and other soft-tissue features. At present, 30 vertebrate taxa (five salamanders, one anuran, two lizards, 13 pterosaurs, five dinosaurs, and four mammals) are known from the Daohugou Biota, which was first recognized at the Daohugou locality in Inner Mongolia. The presence of the salamander Chunerpeton tianyiensis, proposed in this paper as an index fossil for the Daohugou Biota, links the Daohugou locality to five other fossil-producing areas in the provinces of Hebei and Liaoning. The strata containing the Daohugou Biota are close to the Middle–Upper Jurassic boundary and belong at least partly to the regionally widespread Tiaojishan Formation. In general, the vertebrate fauna of the Daohugou Biota is strikingly different from that of the Jehol Biota, although paravian dinosaurs, anurognathid pterosaurs, and salamanders with cryptobranchid and hynobiid affinities occur in both. Nevertheless, the Daohugou Biota and the Jehol Biota are two successive Lagerstätte assemblages that collectively offer a taphonomically consistent window into the Mesozoic life of northeast Asia over a significant span of geologic time.

Taxonomic diversity, stratigraphic range, and exceptional preservation of Juro-Cretaceous salamanders from northern China

Since the late 1990s, eight localities in volcanic shale-rich lacustrine deposits of Middle Jurassic through Early Cretaceous age in northern China (western Liaoning Province, northern Hebei Province, and southern Inner Mongolia) have yielded thousands of exceptionally well-preserved salamander specimens. With 10 species published and several new taxa yet to be named and described, the fossil samples from northern China represent the most species-diverse, individually abundant, and exquisitely preserved salamander fossil assemblage known from the Mesozoic Era. The stratigraphic range of the fossil record covers a geologic time span of roughly 40–45 million years from the Middle Jurassic (Bathonian) through the Early Cretaceous (Aptian). In contrast to the well-known stem-group salamanders Karaurus and Kokartus from the Middle to Late Jurassic of Middle Asia, the Chinese record contains the earliest known crown-group salamanders, including Jurassic representatives of both Cryptobranchoidea and Salamandroidea. The Chinese Mesozoic record includes numerous examples of virtually complete larval, juvenile, young adult, and fully grown adult individuals that collectively provide key information on the life histories and developmental patterns of the earliest known crown-group salamanders. Many specimens show preservation of soft tissue structures, including body outline, eye, liver, and external gill filaments. This kind of soft tissue preservation is unusual for fossil salamanders, so the Chinese Mesozoic specimens are important for furnishing otherwise unavailable information on the life history, diversity, and ecological adaptations of early crown-group salamanders.

An Analytical Model to Evaluate the Static Soil Pressure Throughout Geological Era

In this study, the time dependent characteristics of the soil pressure coefficient is theoretically investigated and a new model is developed to evaluate the static soil pressure in a normally consolidated soil deposit during geological era. The volumetric deformation of soil is described by the Kelvin model, while its shear deformation is represented by the modified Maxwell model assuming the shear- creep relationship as a linear function of the time logarithm. By employing the “elastic-viscoelastic correspondence principle”, the coefficient of soil pressure is found as a function of time, indicating an increase within the geological time span

Ontogenetic and stratigraphic influence on observed phenotypic integration in the limb skeleton of a fossil tetrapod

Understanding morphological integration is one of the central goals of evolutionary developmental biology. Despite its applicability to questions of paleontological interest, there are few studies on integration in fossil vertebrates. In this study, we examine limb integration in the Lower Jurassic ichthyosaurStenopterygius quadriscissus, with the aim of examining the effect of ontogeny and anagenetic changes over short geological time spans on metrics of limb integration. Both ontogenetic and stratigraphic effects had a significant influence on measured values of integration, the identity of strongly integrated elements, and some common ratio values such as the relative integration of the forelimb to the hind limb, or within-limb to between-limb integration. Ontogenetic effects were relatively greater, although this could be linked to sample size. Although adults showed the lowest levels of overall integration, they possessed high levels of integration between serially homologous elements, something that was unexpected due to strong divergence in limb size and perhaps functional differences in derived ichthyosaurs. Ontogenetic differences in the relative integration of the forelimb to the hind limb are probably related to early locomotor demands on the forelimb. We conclude that if samples are pooled, the resulting pattern of integration may not reflect any one subsample but will be a composite created through the superposition of several variables. Pooling data in paleontological studies of integration has a non-trivial effect on the results obtained.

Time-dependent convection models of mantle thermal structure constrained by seismic tomography and geodynamics: implications for mantle plume dynamics and CMB heat flux

SUMMARY One of the outstanding problems in modern geodynamics is the development of thermal convection models that are consistent with the present-day flow dynamics in the Earth’s mantle, in accord with seismic tomographic images of 3-D Earth structure, and that are also capable of providing a time-dependent evolution of the mantle thermal structure that is as ‘realistic’ (Earth-like) as possible. A successful realization of this objective would provide a realistic model of 3-D mantle convection that has optimal consistency with a wide suite of seismic, geodynamic and mineral physical constraints on mantle structure and thermodynamic properties. To address this challenge, we have constructed a time-dependent, compressible convection model in 3-D spherical geometry that is consistent with tomography-based instantaneous flow dynamics, using an updated and revised pseudo-spectral numerical method. The novel feature of our numerical solutions is that the equations of conservation of mass and momentum are solved only once in terms of spectral Green’s functions. We initially focus on the theory and numerical methods employed to solve the equation of thermal energy conservation using the Green’s function solutions for the equation of motion, with special attention placed on the numerical accuracy and stability of the convection solutions. A particular concern is the verification of the global energy balance in the dissipative, compressible-mantle formulation we adopt. Such validation is essential because we then present geodynamically constrained convection solutions over billion-year timescales, starting from present-day seismically constrained thermal images of the mantle. The use of geodynamically constrained spectral Green’s functions facilitates the modelling of the dynamic impact on the mantle evolution of: (1) depth-dependent thermal conductivity profiles, (2) extreme variations of viscosity over depth and (3) different surface boundary conditions, in this case mobile surface plates and a rigid surface. The thermal interpretation of seismic tomography models does not provide a radial profile of the horizontally averaged temperature (i.e. the geotherm) in the mantle. One important goal of this study is to obtain a steady-state geotherm with boundary layers which satisfies energy balance of the system and provides the starting point for more realistic numerical simulations of the Earth’s evolution. We obtain surface heat flux in the range of Earth-like values : 37 TW for a rigid surface and 44 TW for a surface with tectonic plates coupled to the mantle flow. Also, our convection simulations deliver CMB heat flux that is on the high end of previously estimated values, namely 13 TW and 20 TW, for rigid and plate-like surface boundary conditions, respectively. We finally employ these two end-member surface boundary conditions to explore the very-long-time scale evolution of convection over billion-year time windows. These billion-year-scale simulations will allow us to determine the extent to which a ‘memory’ of the starting tomography-based thermal structure is preserved and hence to explore the longevity of the structures in the present-day mantle. The two surface boundary conditions, along with the geodynamically inferred radial viscosity profiles, yield steady-state convective flows that are dominated by long wavelengths throughout the lower mantle. The rigid-surface condition yields a spectrum of mantle heterogeneity dominated by spherical harmonic degree 3 and 4, and the plate-like surface condition yields a pattern dominated by degree 1. Our exploration of the time-dependence of the spatial heterogeneity shows that, for both types of surface boundary condition, deep-mantle hot upwellings resolved in the present-day tomography model are durable and stable features. These deeply rooted mantle plumes show remarkable longevity over very long geological time spans, mainly owing to the geodynamically inferred high viscosity in the lower mantle.

Exceptional preservation of Mn-oxidizing microbes in cave stromatolites (El Soplao, Spain)

Many ferromanganese stromatolites of El Soplao Cave (N Spain) are characterized for the exceptional preservation and high diversity of microbial fossils, probably representing the best example of microbial preservation described in ferromanganese deposits so far.The El Soplao stromatolites are mainly formed by polymetallic Mn-rich oxides with subordinate and variable amounts of detrital material, and consist of both dendritic and laminar microfacies. In both microfacies, microbial forms are abundant in the relatively pure Mn-oxide rich material, whereas they are scarce in areas with significant detrital material. Microbial forms are observed either in cross section, completely embedded in the Mn-oxide-rich matrix, or in three dimensions lining the walls of pores. Based on their morphology, we have separated the most abundant microbial forms into six main morphotypes and six additional submorphotypes, most of which can be assigned to bacteria. Most morphotypes consist of coccoid, coccobacilus, or filamentous forms. Therefore they are not diagnostic of any particular bacterial group. However, the ovoid cells of morphotype B show cylindrical polar protuberances typical of prosthecate alpha-Proteobacteria. On the basis of characteristic morphological features, three submorphotypes of morphotype B can be assigned to three alpha-Proteobacteria genera: Hyphomicrobium, Pedomicrobium, and Caulobacter. This ascription is supported by the well known Mn-oxidizing behavior of both Pedomicrobium and Caulobacter, and by the common presence of Hyphomicrobium in ferromanganese deposits elsewhere.The excellent microbial preservation is partly related to the origin of the ferromanganese oxides, i.e. extracellular precipitation induced by microbial metabolism. Other factors contributing to the good microbial preservation are the relatively low degree of diagenetic alteration, and the relatively high accretion rates of stromatolites compared to other ferromanganese deposits. The generally low degree of diagenesis is likely because the stromatolites have remained relatively stable and at a rather low temperature since they were formed at least 1Ma ago. Still, some stromatolites have suffered diagenetic alteration (partial dissolution and replacement by calcium carbonates and Fe-rich oxides), obscuring or even obliterating their bioforms. The El Soplao case represents an example of how easily biogenic Mn oxides can be altered, and their bioforms blurred, in a relatively short geological time span in spite of being in a relatively stable, alkaline, and low-temperature setting. A geological implication is that the absence of bioforms in other ferromanganese deposits, including rock varnish and Precambrian iron formations, does not disprove their possible biogenic origin, since the high chemical reactivity of biogenic manganese oxides makes them highly vulnerable to diagenesis.

Geochemical study of laterites of the Jamnagar district, Gujarat, India: Implications on parent rock, mineralogy and tectonics

The laterite deposits occur in a linear stretch along the northern Arabian Sea coast in the Jamnagar and Porbandar districts of, Gujarat state, India. These deposits are characterised by presence of gibbsite, kaoline, calcite, quartz, anatase, natroalunite, goethite and hematite, and relicts of mafic minerals and plagioclase. On the basis of petro-mineralogy and geochemistry, these deposits are grouped as aluminous laterites (Fe 2O 3 – 1.45–3.84%, Av. 3.13, Al 2O 3 – 39.31–57.24, Av. 45.80) and laterites (Fe 2O 3 – 9.84–32.21, Av. 25.13%, Al 2O 3 – 34.74–49.59, Av. 41.27). The major, trace and REE characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic/andesitic composition, and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation. The correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements. The Jamnagar laterite deposits occur as capping over the Deccan Trap basaltic lava flows and pyroclasic deposits. Lateritisation prevailed during Palaeocene age when India was separated from the Seychelles and passing over the equator. During this time climate, morphology and drainage conditions were favourable for lateritisation that result in the formation of Jamnagar and other laterite deposits within the Deccan Province. Flood basaltic provinces of Deccan, Columbia, North Australia and Hawaii appear good location for hosting laterite deposits due to their wide areal extent, small geological time span and uniform chemical composition. However, comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate, morphology and drainage are equally important factors for facilitating lateritisation.

Tectonic-Diffusion Estimate of Orogenic Gold Resources

Age-frequency data are used to determine amounts of vertical tectonic displacement experienced by the global population of orogenic gold deposits following their emplacement at a crustal depth of 10 ± 1 km. Knowledge of this tectonic dispersion allows for an estimate of the total crustal endowment of gold in orogenic gold deposits. This estimate is based on a compilation of data on 365 orogenic gold deposits, of which gold contents are available for 314 deposits and good age control is available for 126 deposits. Ages of well-dated deposits form three clusters that range in age from 47 to 850 Ma (primarily Phanerozoic; 69 deposits), 1730 to 2090 Ma (Proterozoic; 13 deposits), and 2540 to 3107 Ma (Archean; 44 deposits). Gold endowments do not vary significantly among the three age groups and average 155 tonnes (t) per deposit for the entire population for which data on gold tonnages are available. Owing to the distinct tripartite nature of the age frequency distribution, it is not possible that orogenic gold deposits represent largely invariant rates of ore formation and destruction (uninterrupted tectonic dispersion would have resulted in the destruction of essentially all Proterozoic and Archean deposits). Separate tectonic-diffusion calculations for each of the three deposit age populations were carried out while constraining biases to tectonic diffusion (i.e., the most suitable ratios of uplift and erosion versus subsidence and burial), with continental crustal thicknesses on the order of several tens of kilometers. The results of these calculations indicated that a total of ~25,236 orogenic gold deposits formed over the full span of geologic time, that ~23,664 of these (~94%) were destroyed during subsequent uplift and erosion, and that ~1,572 deposits remain at depth in Earth’s crust. If all 365 known orogenic gold deposits have the same mean gold content as the deposits for which gold contents are available, then ~706,439 t of gold remain at depth in Earth’s crust. Gold in orogenic deposits constitutes about 0.0022 percent of the total gold content of the crust. Using estimates of gold released by prograde metamorphism of the Otago Schist, gold in the deposits that remain in the crust could have been released from about 1,413,000 km3 of amphibolite facies rocks, which constitute only about 12 percent of currently exposed metamorphic rocks. If we assume a maximum depth of ~3 km for future mining of these deposits, the model results indicate that deposits containing almost 113,000 t of gold exist within crustal rocks above this depth. Discovered deposits make up about 8 percent of this endowment. In the context of spatial density, the areal concentration of orogenic gold deposits along Phanerozoic metamorphic belts is about ten times that in Proterozoic terranes and about three times higher than in Archean belts. This suggests that exploration for the next generation of orogenic gold deposits should be focused on Phanerozoic terranes.

Multiscale magmatic cyclicity, duration of pluton construction, and the paradoxical relationship between tectonism and plutonism in continental arcs

The close relationship between crustal magmatism, an expression of heat dissipation, and tectonics, an expression of stress dissipation, leads to the question of their mutual relationships. Indeed, the low viscosity of magmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization in magmas, and then possible “magmatic” initiation of structures at a wide range of scales. However, new data about 3-d pluton shape and duration of pluton construction perturb this simple geological image, and indicate some independence between magmatism and tectonics. In some cases we observe a direct genetic link and strong arguments for physical interactions between magmas and tectonics. In other cases, we observe an absence of these interactions and it is unclear how magma transfer and emplacement are related to lithospheric-plate dynamics. A simple explanation of this complexity follows directly from the pulsed, incremental assembly of plutons and its spatial and temporal characteristics. The size of each pluton is related to a magmatic pulsation at a particular time scale, and each of these coupled time/space scales is related to a specific process: in small plutons, we can observe the incremental process, the building block of plutons; in larger plutons, the incremental process is lost, and the pulsation, which consists of a cycle of injections at different timescales, must be related to the composition and thermal regime of the source region, itself driving magmatic processes (melting, segregation, and transfer) that interact with tectonic boundary conditions. The dynamics of pulsed magmatism observed in plutonic systems is then a proxy for deep lithospheric and magmatic processes. From our data and a review of published work, we find a positive corelation between volume and duration of pluton construction. The larger a pluton, the longer its construction time. Large/fast or small/slow plutons have not been identified to date. One consequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamic setting to another and also over various geologic time spans. A second consequence of this correlation is that small plutons, which are constructed in a geologically short length of time, commonly record little about tectonic conditions, and result only from the interference between magma dynamics and the local geologic setting. The fast rate of magma transfer in the crust (on the order of cm/s) relative to tectonic rates (on the order of cm/yr) explain why the incremental process of pluton construction is independent of – but not insensitive to – the tectonic setting. However, in large plutonic bodies, which correspond to longer duration magmatic events, regional deformation has time to interact with the growing pluton and can be recorded within the pluton-wall rock structure. Magma transfer operates at a very short timescale (comparable to volcanic timescales), which can be sustained over variable periods, depending on the fertility of the magma source region and its ability to feed the system. The fast operation of magmatic processes relative to crustal tectonic processes ensures that the former control the system from below.

Intraspecific variation and micro-macroevolution connection: illustration with the late Miocene genusProgonomys(Rodentia, Muridae)

Recent progresses in our knowledge of mouse odontogenesis have enhanced rodent tooth morphology as a model for Evo-Devo studies. Deciphering the connection between macroevolution and microevolution, however, especially in the case of mammalian teeth, requires examples to illustrate how morphological differences among species, or higher taxa, can stem from population-level processes. In this paper we use paleontological material to study intraspecific variation of tooth morphology in the late Miocene speciesProgonomys clauzoni, over a short span of geological time in a restricted area.Progonomysis of particular interest as a stem genus of all murine rodents (Old World rats and mice). We use morphometrical and statistical methods to illustrate how change in the amplitude in variation at the population level through geological time is associated with the emergence of new characters. Some of these new characters, including functional ones, become fixed in parallel in distinct murine lineages. Nine million years ago,Progonomys clauzonidisplayed variational properties of the developmental system shared by the Murinae, which can also explain some singular tooth characteristics that now are scattered among the diverse lineages. Further morphometric studies, however, are necessary to explain how the variety of cusp patterns observed inProgonomys clauzonican be explained by developmental properties.

Precambrian geotectonic units of the Río de La Plata craton

The main Precambrian tectonic units of Uruguay include the Piedra Alta tectonostratigraphic terrane (PATT) and Nico Pérez tectonostratigraphic terrane (NPTT), separated by the Sarandí del Yí high-strain zone. Both terranes are well exposed in the Río de La Plata craton (RPC). Although these tectonic units are geographically small, they record a wide span of geologic time. Therefore improved geological knowledge of this area provides a fuller understanding of the evolution of the core of South America. The PATT is constituted by low- to medium-grade metamorphic belts (ca. 2.1 Ga); its petrotectonic associations such as metavolcanic units, conglomerates, banded iron formations, and turbiditic deposits suggest a back-arc or a trench-basin setting. Also in the PATT, a late to post-orogenic, arc-related layered mafic complex (2.3–1.9 Ga), followed by A-type granites (2.08 Ga), and finally a taphrogenic mafic dike swarm (1.78 Ga) occur. The less thoroughly studied NPTT consists of Palaeoproterozoic high-grade metamorphic sequences (ca. 2.2 Ga), mylonites and postorogenic and rapakivi granites (1.75 Ga). The Brasiliano-Pan African orogeny affected this terrane. Neoproterozoic cover occurs in both tectonostratigraphic terranes, but is more developed in the NPTT. Over the past 15 years, new isotopic studies have improved our recognition of different tectonic events and associated processes, such as reactivation of shear zones and fluids circulation. Transamazonian and Statherian tectonic events were recognized in the RPC. Based on magmatism, deformation, basin development and metamorphism, we propose a scheme for the Precambrian tectonic evolution of Uruguay, which is summarized in the first Palaeoproterozoic tectonic map of the Río de La Plata craton.

Stress change over short geological time: the case of Scandinavia over 9000 years since the Ice Age

Abstract Palaeoseismological investigations are used in many regions of the world to extend back in time the earthquake statistics of historical written or oral records as well as instrumental information. This is very valuable for discussions of earthquake hazard, but it only applies to areas of stable stress regime. Although the intraplate areas of Scandinavia and Greenland have experienced only rather small earthquakes within the human timescale, they serve as a clear warning on the application of palaeoseismology for hazard studies in regions where the stresses have changed. In a small part of Scandinavia, where recent earthquake activity is not significantly different from that of its surroundings, large faults have been discovered and several have been investigated via palaeoseismology. They are interpreted to show the occurrence of large earthquakes about 9000 years ago. Signs of this are coincident landslides as well as liquefaction in loose sediments, which are well dated through varve-counting. In contrast to this the present-day stress release in earthquakes and in surface rock deformations is mainly caused by plate motion. Regional investigations in Scandinavia and Greenland/North America, as well as those included in the World Stress Map Project of the 1990s, have shown compression within the plate, mainly in the direction of absolute plate motion. The ice cap influence has disappeared. So stress reorganization is clearly indicated over the short geological timespan of 9000 years. Into this argument goes the observation from Greenland and Antarctica, that no earthquakes occur under the ice caps. For Scandinavia the argument is that no earthquakes occurred under the ice sheet during the Ice Age, and that the stored stresses were released when the ice sheet melted 9000 years ago. This does emphasize a warning. There are regions of the globe where palaeoseismological investigations can give a fantastic extension of the short-term historical earthquake records. But in some regions stress reorganization has changed this condition.