Towards an astronomical age model for the Lower to Middle Pleistocene hominin-bearing succession of the Sangiran Dome area on Java, Indonesia

Well-dated paleoanthropological sites are critical for studying hominin evolution and dispersal, especially when related to regional or global climate change. For the rich hominin fossil record of Africa, this has been facilitated by the development of high-resolution astronomically tuned age models. So far, such age models are lacking for the Pleistocene of SE Asia with its similarly rich fossil hominin record. This study aims to develop an astronomical age model for the classical Sangiran Dome area of central Java, using a semi-quantitative grain size record of the hominin-bearing Sangiran and Bapang Formations. Two initial age models were established based on two different sets of tie points and approaches (constant sedimentation rate and Bayesian age modelling). These models, which correspond to the paleoanthropological short and long chronologies for the arrival of Homo erectus on Java, were used to convert the grain size record into a time series for time series analysis. The preferred initial age model was then used as a starting point to correlate or tune the grain size record to the LR04 benthic δ18O isotope stack. This tuning was constrained by the sudden switch in grain size from obliquity to double obliquity related cycles; this switch can be linked to the onset of the Mid-Pleistocene Transition at ∼1.2 Ma marked by a similarly abrupt change in ice age history. Two slightly different astronomical age models are presented, while a one cycle hiatus at the base of the Grenzbank cannot be excluded. These age models are in better agreement with the short paleoanthropological chronology, arguing for a late arrival of H. erectus on Java. Finally, such astronomical age models, when finalized, will provide the accurate, precise, and high-resolution age control required to gain insight into the influence of both regional and global climate change on the Pleistocene paleoenvironment and potentially the hominin population of Java

Palaeoenvironmental reconstruction of a middle Miocene alluvial fan to cyclic shallow lacustrine depositional system in the Calatayud Basin (NE Spain)

The middle Miocene sedimentary fill of the Calatayud Basin in north-eastern Spain consists of proximal to distal alluvial fan-floodplain and shallow lacustrine deposits. Four main facies groups characteristic of different sedimentary environments are recognized: (1) proximal and medial alluvial fan facies that comprise clast-supported gravel and subordinate sandstone and mudstone, the latter exhibiting incipient pedogenic features; (2) distal alluvial fan facies, formed mainly of massive mudstone, carbonate-rich palaeosols and local carbonate pond deposits; (3) lake margin facies, which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system, i.e. front (lithofacies A), comprising massive siliciclastic mudstone and tabular carbonates, or lateral (lithofacies B) showing laminated and/or massive siliciclastic mudstone alternating with tabular and/or laminated carbonate beds; and (4) mudflat–shallow lake facies showing a remarkable cyclical alternation of green-grey and/or red siliciclastic mudstone units and white dolomitic carbonate beds. The cyclic mudflat–shallow lake succession, as exposed in the Orera composite section (OCS), is dominantly composed of small-scale mudstone–carbonate/dolomite cycles. The mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods, the deposits evolving either under subaerial exposure or water-saturated conditions, depending on their location on the lacustrine mudflat and on climate. The dolomite intervals accumulated during lake-level highstands with Mg-rich waters becoming increasingly concentrated. Lowstand to highstand lake-level changes indicated by the mudstone/dolomite units of the small-scale cycles reflect a climate control (from dry to wet conditions) on the sedimentation in the area. The spatial distribution of the different lithofacies implies that deposition of the smallscale cycles took place in a low-gradient, shallow lake basin located in an interfan zone. The development of the basin was constrained by gradual alluvial fan aggradation. Additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of δ18O and δ13C values varying from )-7.9 to 3.0‰ PDB and from -9.2 to -1.7‰ PDB respectively. More negative δ18O and δ13C values are from carbonate-rich palaeosols and lakemargin carbonates, which extended in front of the alluvial fan systems, whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment. The results show a clear trend of δ18O enrichment in the carbonates from lake margin to the centre of the shallow lake basin, thereby also demonstrating that the lake evolved under hydrologically closed conditions

Early to Middle Miocene Astronomically Paced Climate Dynamics in the Eastern Equatorial Atlantic

Detailed analysis of tropical climate dynamics is lacking for the Early to Middle Miocene, even though this time interval bears important analogies for future climates. Based on high-resolution proxy reconstructions of sea surface temperature, export productivity and dust supply at Ocean Drilling Program Site 959, we investigate astronomical forcing of the West African monsoon in the eastern equatorial Atlantic across the prelude, onset, and continuation of the Miocene Climatic Optimum (MCO; 18–15 Ma). Along with previously identified eccentricity periodicities of ∼400 and ∼100 kyr, our records show that climate varied on ∼27–17 kyr, ∼41 kyr, and ∼60–50 kyr timescales, which we attribute to precession, obliquity, and their combination tones, respectively. The relative contribution of these astronomical cycles differed between proxies and through time. Three intervals with distinct variability were recognized, which are particularly clear in the temperature record: (a) strong eccentricity, obliquity, and precession variability prior to the MCO (18.2–17.7 Ma), (b) strong influence of obliquity just after the onset of the MCO (16.9–16.3 Ma) concurring with a 2.4 Myr eccentricity minimum, and (c) dominant eccentricity and precession variability during the MCO between 16.3 and 15.0 Ma. Sedimentation at Site 959 was influenced by astronomically paced variations in upwelling intensity and North African aridity related to West African monsoon dynamics. Continuously present patterns of precession imply low-latitude forcing, while asymmetric eccentricity and obliquity imprints and strong obliquity influence suggest that Site 959 was also affected by high-latitude, glacial-interglacial dynamics

Astronomical forcing of sedimentary cycles in the middle to late Miocene continental Calatayud Basin (NE Spain)

A high-resolution cyclostratigraphic and magnetostratigraphic study was carried out on cyclically bedded successions of middle Miocene lacustrine to distal alluvial fan-floodplain deposits from the Calatayud basin, in northeast Spain. Eight (partially overlapping) subsections near the village of Orera are correlated in detail using distinct sedimentary cycle patterns or by following marker beds in the field. Together they form the Orera Composite Section (OCS). Sedimentary cycles are recognised on at least two different scales. The basic small-scale cycles in the OCS consist of an alternation of grey and, occasionally, red clays with white, dolomite-rich, carbonate beds. They are arranged in largerscaled, so-called large-scale cycles based on repetitive changes in the overall carbonate-clay lithology. Two other, but less distinct, types of intermediate scale cyclicity are also recognised. In terms of depositional environment, the cycle hierarchy is interpreted to represent periodic lake expansion over the palaeo-alluvial fan-floodplain area. The palaeomagnetic results yield a reliable magnetostratigraphic record, which confirms the cyclostratigraphic correlations between the subsections in detail. Rock magnetic experiments reveal that haematite is the main magnetic carrier of the primary component. The magnetostratigraphy of the OCS is correlated straightforwardly with the geomagnetic polarity time scale. This resulted in an age of 10.7^12.8 Ma for the entire succession, which is supported by fossil micromammal findings. In addition, it also reveals the presence of two, possibly three, short new polarity intervals. Based on the number of cycles in the OCS the average periodicity of the basic small-scale cycles is approximately 23 000 yr, while the large-scale cycle indicates a periodicity of 400 000 yr. This suggests that these sedimentary cycles are controlled by astronomically induced climate changes causing lake-level fluctuations and thus resulting in the deposition of carbonate-clay cycles. The continental sequences of the OCS provide a unique opportunity to extend the astronomical polarity time scale into the middle Miocene. The overlap of such continental sequences in the Mediterranean area with time-equivalent astronomically induced marine sequences is fundamental for establishing marine^continental, bed-tobed, correlations and for understanding regional climate change

Milankovitch cycles in banded iron formations constrain the Earth-Moon system 2.46 billion years ago

The long-term history of the Earth-Moon system as reconstructed from the geological record remains unclear when based on fossil growth bands and tidal laminations. A possibly more robust method is provided by the sedimentary record of Milankovitch cycles (climatic precession, obliquity, and orbital eccentricity), whose relative ratios in periodicity change over time as a function of a decreasing Earth spin rate and increasing lunar distance. However, for the critical older portion of Earth's history where information on Earth-Moon dynamics is sparse, suitable sedimentary successions in which these cycles are recorded remain largely unknown, leaving this method unexplored. Here we present results of cyclostratigraphic analysis and high-precision U-Pb zircon dating of the lower Paleoproterozoic Joffre Member of the Brockman Iron Formation, NW Australia, providing evidence for Milankovitch forcing of regular lithological alternations related to Earth's climatic precession and orbital eccentricity cycles. Combining visual and statistical tools to determine their hierarchical relation, we estimate an astronomical precession frequency of 108.6 ± 8.5 arcsec/y, corresponding to an Earth-Moon distance of 321,800 ± 6,500 km and a daylength of 16.9 ± 0.2 h at 2.46 Ga. With this robust cyclostratigraphic approach, we extend the oldest reliable datum for the lunar recession history by more than 1 billion years and provide a critical reference point for future modeling and geological investigation of Precambrian Earth-Moon system evolution

Initial cyclostratigraphy of the middle Nama Group (Schwarzrand Subgroup) in southern Namibia

The Ediacaran Period includes critical evolutionary trends of early complex life as well as climatic variations associated with ocean oxygenation, glaciations, and carbon cycling, which are still poorly understood in terms of astronomical climate forcing. The middle Nama Group in southern Namibia was deposited during the late Ediacaran in mainly shallow marine environments within a foreland basin and consists of hierarchically arranged depositional sequences. Here, we test a possible astronomical origin of these sedimentary variations by developing an initial cyclostratigraphic framework based on satellite images integrated with recently published high-precision U-Pb zircon ages. Regular sedimentary alternations occur dominantly on scales of several tens of meters, accompanied by smaller- and larger-scale variations, and are correlatable over distances of ∼50 km. Throughout the studied succession, 35 to 39 alternations are recognized on this dominant scale, which have an average duration of ∼120–180 k.y. This duration corresponds well with the period of short eccentricity (∼100 k.y.), given the likely presence of hiatuses, or alternatively, the period of obliquity amplitude modulation (∼173 k.y.), which would imply no time is missing on this scale. The dominant alternations are consistent with previously identified medium-scale sequences in this succession, which have been interpreted to record fluctuations in relative or eustatic sea level. We hypothesize that astronomically-forced fluctuations in eustatic sea level modulated deposition of the middle Nama Group. Geochemical studies suggested a relation between fossil distribution, redox variability and sea level, implying that astronomical forcing may have played a role in the distribution of early complex life

Análisis sedimentológico y caracterización paleoclimática de la sucesión cíclica de Orerà, Mioceno continental de la Cuenca de Calatayud

The representation of continental and continuous cyclically bedded sequences for long time intervals in the sedimentary record of the Iberian Peninsula is very scarce. The middle Miocene sedimentary fill o f the Calatayud Basin (NE Spain) consists of proximal to distal alluvial fanfloodplain and shallow lacustrine deposits. A 160 m-thick lacustrine succession showing an exceptional cyclical bedding (Orera Composite Section, OCS) is exposed close to the Orera Village, in the northern margin of the basin. The correlation of the magnetostratigraphy of the OCS with the Geomagnetic Polarity Time Scale (GPTS), resulted in an age o f 10.7-12.8 Ma for the entire section, which is supported by biostratigraphical data. The cyclic shallow lacustrine succession comprises 91 superposed small-scale cycles, each consisting mainly of an alternation of greygreenish mudstone and white dolomite beds. Based on the number of cycles, the average periodicity of the basic small-scale cycles is approximately 23,000 yr. This periodicity suggests that deposition of the sedimentary cycles was controlled by astronomically induced climate changes causing lake-level fluctuations. The deposition of these cycles took place in a low gradient, shallow lake basin developed in an "inter-fan" zone (Miedes and Orera alluvial fans). The small-scale cycles are interpreted as a result of the evolution from mudflat deposits (red and green-grey clays), accumulated in lowstand periods o f the lake, to shallow lake deposits (dolomites) during relatively high lake level stages

Precessional pacing of early Proterozoic redox cycles

Regularly alternating reduction-oxidation (redox) patterns attributed to variations in the Earth's orbit and axis (Milankovitch cycles) are widely recorded in marine sediment successions of the Phanerozoic and attest to a dynamic history of biospheric oxygen in response to astronomically forced climate change. To date, however, such astronomical redox control remains elusive for much older, Precambrian intervals of the geological record that were characterized by a globally anoxic and iron-rich ocean, i.e., prior to Earth's atmospheric oxygenation (ca. 2.4–2.2 billion years ago). Here we report a detailed cyclostratigraphic and geochemical investigation of marine-sedimentary redox cycles identified in the ca. 2.46 billion-year-old Joffre Member of the Brockman Iron Formation, NW Australia, suggesting the imprint of Earth's climatic precession cycle. Around the base and top of regularly intercalated mudrock layers, we identify sharp enrichments in redox sensitive elements (Fe, S, Ca, P) that appear to represent chemical reaction fronts formed during nonsteady state diagenesis. Using a reactive transport model, we find that the formation of characteristic double S peaks required periods of increased organic matter deposition, coupled to strongly declining Fe2+ concentrations in the overlying water column. This combination, in turn, implies a periodic deepening of the iron chemocline due to enhanced oxygenic photosynthesis in marine surface waters, and is interpreted as the result of precession-induced changes in monsoonal intensity that drove variations in runoff and associated nutrient delivery. Our study results point to a dynamic redox evolution of Precambrian oceanic margin environments in response to Milankovitch forcing, and offer a temporal framework to investigate linkages between biological activity and the early build-up of oxygen in Earth's ocean-atmosphere system

Tropical Warming and Intensification of the West African Monsoon During the Miocene Climatic Optimum

Studying monsoon dynamics during past warm time periods such as the Miocene Climatic Optimum (MCO; ∼16.9–14.5 Ma) could greatly aid in better projecting monsoon intensity, in the context of future greenhouse warming. However, studies on regional MCO temperature change and its effect on the monsoons during this time period are lacking. Here, we present the first high-resolution, low-latitude record of sea surface temperature (SST) and paleoceanographic change covering the Miocene Climatic Optimum, in the eastern equatorial Atlantic, at Ocean Drilling Program Site 959, based on TEX86 paleothermometry. SSTs were ∼1.5°C warmer at the onset of the MCO (16.9 Ma) relative to the pre-MCO (∼18.3–17.7 Ma). This warming was accompanied by a transient increase in %total organic carbon. Prior to the MCO, sediment composition, geochemical proxy data as well as dinoflagellate cyst assemblages imply a productive surface ocean at Site 959. Immediately following the MCO onset (∼16.9–16.5 Ma), we record an intensification of the West African Monsoon (WAM) characterized by higher amplitude variability in all proxy records on precession to obliquity timescales. We interpret increased orbital-scale SST, biogenic Ba and dinocyst assemblage variability to represent intensification of equatorial upwelling, forced by the WAM strength. Furthermore, higher SSTs during eccentricity maxima correlate to increased relative abundances of the warm and stratification-favoring dinocyst Polysphaeridium zoharyi, during periods of low WAM intensity. Finally, while long-term SSTs decline toward the middle Miocene, maximum SSTs and Polysphaeridium zoharyi abundances occur during MCO peak warming at ∼15.6 Ma

Заява Спілки Археологів України щодо проекту Закону України “Про відродження унікального Символу православ’я — церкви Богородиці (Десятинної) в місті Києві” (№ 9196)

The Milankovitch theory of climate change is widely accepted, but the registration of the climate changes in the stratigraphic record and their use in building high-resolution astronomically tuned timescales has been disputed due to the complex and fragmentary nature of the stratigraphic record. However, results of time series analysis and consistency with independent magnetobiostratigraphic and/or radio-isotopic age models show that Milankovitch cycles are recorded not only in deep marine and lacustrine successions, but also in ice cores and speleothems, and in eolian and fluvial successions. Integrated stratigraphic studies further provide evidence for continuous sedimentation at Milankovitch time scales (10^4 years up to 10^6 years). This combined approach also shows that strict application of statistical confidence limits in spectral analysis to verify astronomical forcing in climate proxy records is not fully justified and may lead to false negatives. This is in contrast to recent claims that failure to apply strict statistical standards can lead to false positives in the search for periodic signals. Finally, and contrary to the argument that changes in insolation are too small to effect significant climate change, seasonal insolation variations resulting from orbital extremes can be significant (20% and more) and, as shown by climate modelling, generate large climate changes that can be expected to leave a marked imprint in the stratigraphic record. The tuning of long and continuous cyclic successions now underlies the standard geological time scale for much of the Cenozoic and also for extended intervals of the Mesozoic. Such successions have to be taken into account to fully comprehend the (cyclic) nature of the stratigraphic record