Geological Past Research Articles

Hydrothermal alteration episodes reflect multiple Proterozoic tectonic and magmatic events in the Kangdian region, western Yangtze Block

Hydrothermal fluids are major agents for mass and heat transfer in the upper crust. Precise age dating and tracing of the origins of fluid fluxes can provide vital information on the geological past, yet detailed reconstructions of past hydrothermal fluid activity in Precambrian terranes are commonly hindered by multistage overprints and recrystallization events. In this contribution, we present integrated U-Pb and Re-Os isotopic analyses of texturally resolved hydrothermal minerals including allanite, monazite, apatite, rutile, and sulfides, in order to constrain the timing of hydrothermal activity in the 1710−1660 Ma Dahongshan Group, which hosts the largest Fe-Cu-Au deposit in the Kangdian region of the western Yangtze Block, South China. We identify six discrete periods of fluid activity at ca. 1650, 1140, 1040, 930, 870, and 830 Ma, as well as several other cryptic hydrothermal events in metasomatised rocks, all of which can be correlated with regional tectonic and magmatic events. Our reconstruction provides a framework for evaluating Proterozoic hydrothermal and metallogenic histories of the Kangdian region along the western margin of the Yangtze Block. Furthermore, our results highlight the sensitivity of minerals to the hydrothermal response of regional tectonomagmatic events. Demonstration of these relationships is further ascertained by contrasting hydrothermal histories among the Kangdian region and other Paleoproterozoic terranes that have similar polymetallic Fe-Cu mineralization worldwide. An additional implication is that hydrothermal archives hold potential to serve as unique fingerprints to aid recognition of geological events, complementary to conventional detrital and lithotectonic records.

A New Geosite as a Contribution to the Sustainable Development of Urban Geotourism in a Tourist Peripheral Region—Central Poland

The article presents a new geosite in a small provincial town in central Poland. It contains twelve Scandinavian erratic boulders from the area, deposited by the Pleistocene ice sheet about 130,000 years ago. The geotrail is equipped with three informative boards, a folder, and each boulder has its own identifier. The article also draws attention to petrographic types and types of erratic boulders among the collected boulders. Their basic dimensions, age, and source area are given. Specific features of rock morphology are discussed. Records of sub/inglacial processes, periglacial processes affecting the forefield of the melting ice sheet, and contemporary morphogenetic processes are also analyzed. The recipient/beneficiary of such information can be anyone who is sensitive to the beauty of abiotic nature, feels heir to the geological past of his region, or wants to broaden his horizons with knowledge from the ice age. The recognized and disseminated heritage of abiotic objects in nature through the transfer of expert knowledge has great potential to become an effective generator of sustainable socio-economic development of peripheral tourist areas. The paper presents in detail expert knowledge and specific examples of improving the quality of life with the creation of this geosite. The tool to be used here is geotourism; it deals with the study of geodiversity and the development of elements of abiotic nature to perform tourist functions in accordance with the principles of nature protection. It protects the geological heritage by effectively securing geosites, widely disseminating geological sciences, and promoting their educational and tourist functions.

Clay mineral assemblages of late Holocene turbidites in the Gaoping Submarine Canyon of the northeastern South China Sea and their responses to typhoon activities

Submarine canyons are the principal conduits for turbidity currents transporting sediments to the deep sea. Thus, turbidites, as sedimentary products of turbidity currents, can be used to trace sediment sources and transport processes and to reconstruct mechanisms of turbidity currents in submarine canyons during the geological past. Herein, clay mineral assemblage of late Holocene turbidites at Core MD18–3565 in the Gaoping Submarine Canyon is investigated to reveal the triggering mechanisms of turbidity currents. High-resolution grain-size analysis of typical coarse-grained layers characterized by basal erosion surface and fining-upward sequence in the core verifies their turbidity current origin. A total number of 318 such turbidite layers, covering ∼30% of the total thickness (19.68 m) of the core, are recognized in the late Holocene sediments (33–3954 cal yr BP). Clay mineral assemblage of the turbidites is composed mainly of illite (52–60%) and chlorite (35–45%), with small quantities of smectite (0–5%) and kaolinite (0–4%), while clay mineral assemblage of the non-turbidite sediments (hemipelagites) is composed of approximately the same contents of illite (51–62%) and chlorite (34–43%), but with slightly higher smectite (0–10%) and kaolinite (1–6%). Despite the small differences in smectite and kaolinite contents, the provenance analysis identifies the Gaoping river as the predominant source of sediments in the turbidite layers, while the hemipelagite layers receive small amounts of sediments from the neighboring Erhjen, Tsengwen, and Pachang rivers besides the Gaoping river in southwest Taiwan. In combination with clay mineral compositions of surface sediments in the adjacent continental shelf and slope, as well as in-situ observational results by subaqueous moorings, we believe that the turbidity currents, in which the Gaoping river directly supplied clay minerals to the submarine canyon to form the turbidites, have been triggered mainly by typhoons passing through Taiwan. The frequency of turbidites generally keeps pace with long-term variations of El Niño-Southern Oscillation (ENSO) events, implying the potential modulation of ENSO on occurrences of late Holocene typhoon activities in the Western Pacific.

Wildfire associated with a deciduous broadleaved forest from the Neogene Baoshan Basin at the southeastern margin of the Tibetan Plateau

Wildfire bears a close relationship with vegetation as its fuel source. The southeastern margin of the Tibetan Plateau witnesses frequent wildfires among various types of vegetation, whereas such wide interactions between wildfire and vegetation remain poorly studied from geological times. In this study, we reported a local fire using sedimentary macroscopic charcoals from the latest Miocene to early Pliocene of the Baoshan Basin in this region, and then inferred the local vegetation at the time of the fire event based chiefly on the coexistent fruit and seed fossil assemblage. Our taxonomic results show that the charcoal assemblage is probably dominated by broadleaved plants and the fruit and seed fossil assemblage is apparently dominated by Salix (Salicaceae) followed by Sambucus (Adoxaceae), suggesting a deciduous broadleaved forest in which the fire likely occurred. Under a seasonally dry climate associated with the Asian monsoon, this type of vegetation might be prone to natural fire, because in the wet rainy season the plants grew well to accumulate biofuel and in the dry season abundant ground litter resulting from leaf decay would be desiccated to become highly flammable. Due to the fire-tolerant habit of Salix as the dominant plant, the forest might be in return adapted to the fire event or even more fires that potentially followed. All these may suggest a close relationship between the fire event and the reconstructed vegetation. Our finding documents a new type of wildfire–vegetation interaction, namely the interaction between wildfire and deciduous broadleaved forest, from the geological past at the southeastern margin of the Tibetan Plateau. It therefore sheds new light on the wildfire history coupling vegetation change in the region.

Organic Carbon Distribution in Cambrian Deposits of the cis-Yenisei Subbasin

Abstract —The study considers the distribution of organic carbon in different formations and facies of Cambrian age identified in the cis-Yenisei subbasin. Two groups of depositional environments were recognized in the deepwater perioceanic and epicontinental basins, which accumulated sediments with elevated and sometimes anomalously high concentrations of planktonic and benthic organic matter. These are 1) local centers in the Tommotian (Oksym Formation) and Botomian stages of the lower Cambrian, Mayan (Elogui and Pudzhelga formations) and Ayusokkanian (Kondes Formation) stages of the middle Cambrian; 2) regional Kuonamka horizon, which is composed of Toyonian and Amgian deposits and occurs along the margins of the Siberian Platform; it is represented by the Inikan and Kuonamka formations in the east of the Siberian Platform and by the Paidugina Formation in the study area. The study shows that the organic matter has undergone a high degree of transformation and reached the apocatagenesis grade. The results of the study assume that the hydrocarbon generation intensity was high in the Cambrian formations of the cis-Yenisei subbasin in the geological past.

Active faults studies in Delhi and national capital region (NCR): Inferences from satellite data and field investigations

In recent years, the National Capital Region (NCR) of Delhi has experienced several earthquakes ranging in magnitude from 1.0 to 6.7. According to the last 50 years of earthquake data, the majority of earthquakes in the NCR have occurred near the Mahendragarh Dehradun Fault (MDF) and the Sohna Fault (SF). The region is bounded by a number of subsurface Ridges, Faults, and Lineaments, which are also influenced by the active plate boundary of the Indian and Eurasian plates. Active fault mapping is critical for the precise identification and marking of active fault traces in the NCR area for a precise seismic hazard assessment. We used high resolution Cartosat-1 stereopair data obtained from NRSC, Hyderabad, and Anaglyph (A 3D representation of the surface) and DEM prepared with ENVI software to map the active faults. We identified 12 sites in the NCR region based on satellite data interpretation, primarily along the MDF and Sohna Fault and their extensions. The presence of tectono-geomorphic markers along the MDF and Sohna Fault, such as warped surfaces indicative of fault scarps, stream offsets, gully erosion, and sag ponds, suggests active tectonic movement along these faults, most likely in the recent geological past. We believe the MDF is a right-lateral strike-slip fault with a compressional component on the western side and an extensional component on the eastern side. It acts as a segment boundary between compressional and extensional boundaries. We also identified the right lateral Nuh-Jhirka fault (NJF), which can be the Sohna Fault’s southern extension from Nuh to Jhirka. The western limb of the Delhi Mega fold has also seen a few right-lateral strike-slip movements that have extended up to the eastern bank of the Yamuna River, where the river reflects the base-level change and tight meandering on its upward side and a straight pattern on its downward side. This fault is known as the Delhi Fault (DF). The findings are preliminary, and further research would be required to create a detailed active fault map of the Delhi-NCR region to conduct a precise Seismic Hazard Assessment (SHA) of the region.

Discharge timing and origin of fluids at methane seeps in the late Cretaceous subduction zone of Hokkaido, Japan: Coupling U–Pb calcite dating with Sr–Nd isotope analysis

Seepage of methane-rich fluids is common in subduction zones throughout Earth's history. However, the causes and hydrogeological regimes of methane seepage in the geological past are commonly elusive. To provide insights into the hydrogeological regime and structural evolution of the Cretaceous subduction zone of Hokkaido, Japan, this study investigates the timing of discharge and migration pathways of fluids emitted at five ancient methane seeps using U–Pb dating and coupled Sr, Nd, C, and O isotope analyses of the authigenic seep carbonates. The carbonates were collected from forearc-basin sediments of the Yezo Group, which are underlain by a mafic igneous basement (lower Sorachi ophiolite) detached from the subducting plate. The subduction zone is known to have experienced intermittent accretionary and non-accretionary stages, and the U–Pb dates determined for seep carbonates document two fluid discharge events, ∼100 and ∼80 Ma, falling within the accretionary periods. The 87Sr/86Sr ratios (0.70682–0.70781) and εNd values (−5.9 to −0.1) of the carbonates show significant variability, indicating the seeping fluids experienced interactions with the mafic rocks of the lower Sorachi ophiolite and with siliciclastic sediments of the Yezo Group. The δ13C values of the carbonates, as low as −49‰, suggest a primarily microbial origin of the seeping methane, which makes methane migration from the underplating materials at high temperatures (>100 °C) unlikely. These results demonstrate that the episodic expulsion of the methane-rich fluids, originating from within the forearc basin rather than from the underplating materials, occurred during the accretionary stages and played a major role in methane seepage in the Cretaceous subduction system.

“Geo-Archaeo-Routes” on the Island of Lemnos: The “Nalture” Experience as a Holistic Geotouristic Approach within the Geoethical Perspective

The geosites of Lemnos represent local touristic products that, beyond their high aesthetic value, display significant scientific links to the geological past as well as prehistory and history, archaeology, mythology and religious heritage of the island. The unique wealth of Lemnos geosites in combination with the abundance of archaeological sites, cultural monuments and museums composes the basis of what we define here as “Geo-Archaeo-Routes”: certain routes that can be geographically defined, offered, guided and finally followed by the touristic masses. The outcome of the performed quantitative Lemnos geosite assessment enables decision making, thus providing a toolbox useful for sustainable Geo-Archaeo-tourism development at a local level and forms the basis for designing “Geo-Archaeo-Routes”. “Geo-Archaeo-Routes” are particularly favorable of environmentally friendly alternative types of tourism, attracting naturalists, hikers, fans of cultural or religious tourism and many others who represent a major part of the touristic needs of the 21st century. The established hiking and road “Geo-Archaeo-Routes” on Lemnos Island may represent a distinctive touristic product as they offer a high level of “nalture” entertainment, blending “nature with culture” in the framework of a holistic geotouristic approach.

Aliens and dragons: purposefully-framed play and non-standard learning methods in teaching evolutionary processes to primary school pupils

Evolutionary processes lie at the base of the entire observable biodiversity, both at present and in the geological past (i.e., in the fossil record). For this reason, the teaching of evolution should receive more recognition than it currently has (e.g., in Poland) and become accurately applied from the early formal education stages onwards. To test the possibility of effective teaching of evolution to primary school pupils, workshops using non-standard learning methods (‘purposefully-framed play’) were organised during childrens’ university (UNIKIDS) courses of one-hour sessions for 33 groups, comprising several to 20 participants, aged 7 to 12. The final task for all participants was to predict future evolutionary processes by creating new species adapted to given environmental factors. Pupils effectively completed this task, but a few misconceptions also become clear. These workshop scenarios suggest that evolution can be taught effectively at least in extracurricular settings to primary school pupils, but for a detailed insight, a quantitative analysis and application of such scenarios in school programmes should be tested in future.

What the geological past can tell us about the future of the ocean’s twilight zone

Paleontological reconstructions of plankton community structure during warm periods of the Cenozoic (last 66 million years) reveal that deep-dwelling ‘twilight zone’ (200–1000 m) plankton were less abundant and diverse, and lived much closer to the surface, than in colder, more recent climates. We suggest that this is a consequence of temperature’s role in controlling the rate that sinking organic matter is broken down and metabolized by bacteria, a process that occurs faster at warmer temperatures. In a warmer ocean, a smaller fraction of organic matter reaches the ocean interior, affecting food supply and dissolved oxygen availability at depth. Using an Earth system model that has been evaluated against paleo observations, we illustrate how anthropogenic warming may impact future carbon cycling and twilight zone ecology. Our findings suggest that significant changes are already underway, and without strong emissions mitigation, widespread ecological disruption in the twilight zone is likely by 2100, with effects spanning millennia thereafter.

Effects of redox variability and early diagenesis on marine sedimentary Hg records

Volcanism is a dominant natural source of mercury (Hg) to the atmosphere, biosphere, ocean and sediments. In recent years, sedimentary Hg contents have emerged as a tool to reconstruct volcanic activity, and particularly activity of (subaerially emplaced) large igneous provinces in geological deep time. More specifically, Hg has shown potential as a useful proxy to illuminate the previously elusive impact of such large-scale volcanism on marine and terrestrial paleo-environments. While Hg is now widely applied as volcanism tracer, non-volcanic factors controlling sedimentary Hg content are generally not well constrained. Part of this uncertainty stems from our inability to directly observe a natural unperturbed “steady-state” environment as a baseline, as the modern Hg cycle is heavily influenced by anthropogenic activity. Here we focus on the effects of ambient redox conditions in the water column and shallow sediments (early diagenesis), quantify their influence on the geological Hg record and thereby contribute to constraining their potential impact on the use of Hg as a proxy for deep-time volcanic activity. Constraining these factors is of critical importance for the application of Hg as such a proxy. Many periods in the geological past for which records have been generated, such as the Mesozoic Oceanic Anoxic Events, are marked by a variety of high-amplitude environmental perturbations, including widespread deoxygenation and deposition of organic-rich sediments. We estimate the impact of redox changes and early diagenesis on the geological Hg record using a suite of (sub)recent–Pleistocene and Upper Cretaceous sediments representing oxic to euxinic marine conditions. Our sample set includes a transect through an oxygen minimum zone and cores that record transient shifts in oxygenation state, as well as post-depositional effects – all unrelated to volcanism, to the best of our knowledge. We find substantial alterations to the Hg record and the total organic carbon and total sulfur content, which are typically assumed to be the most common carrier phases of Hg in marine sediments. Moreover, these biases can lead to signal alteration on a par with those interpreted to result from volcanic activity. Geochemical modifications are ubiquitous and their potential magnitude implies that the factors leading to biases in the geological record warrant careful consideration before interpretation. Factors of particular concern to proxy application are (1) the disproportionate loss of organic carbon and sulfur relative to Hg during oxidation that strongly modulates normalized Hg records, (2) the evasion of Hg in anoxic and mildly euxinic sediments and (3) sharp focusing of Hg during post-depositional oxidation of organic matter. We suggest that paired analyses of additional redox-sensitive trace elements such as molybdenum, and organic-matter characteristics, particularly the type of organic matter, could provide first-order constraints on the role that redox and diagenetic changes played in shaping the Hg record as part of checking the attribution of enrichments to volcanic activity.

Viruses of sulfur oxidizing phototrophs encode genes for pigment, carbon, and sulfur metabolisms

Viral infections modulate bacterial metabolism and ecology. Here, we investigated the hypothesis that viruses influence the ecology of purple and green sulfur bacteria in anoxic and sulfidic lakes, analogs of euxinic oceans in the geologic past. By screening metagenomes from lake sediments and water column, in addition to publicly-available genomes of cultured purple and green sulfur bacteria, we identified almost 300 high and medium-quality viral genomes. Viruses carrying the gene psbA, encoding the small subunit of photosystem II protein D1, were ubiquitous, suggesting viral interference with the light reactions of sulfur oxidizing autotrophs. Viruses predicted to infect these autotrophs also encoded auxiliary metabolic genes for reductive sulfur assimilation as cysteine, pigment production, and carbon fixation. These observations show that viruses have the genomic potential to modulate the production of metabolic markers of phototrophic sulfur bacteria that are used to identify photic zone euxinia in the geologic past.

THE VOLGA-DON COLLISIONAL OROGEN IN THE EAST EUROPEAN CRATON AS THE PALEOPROTEROZOIC ANALOGUE OF THE HIMALAYAN-TIBETAN OROGEN

The ca 2.0 Ga Volgo-Don fold-and-thrust belt, about 500 km in width and at least 600 km in length, covering an area of about 300000 square kilometers intervenes between the Archean Sarmatian and Volgo-Uralian proto-cratonic blocks of the East European Craton, both of which are coupled with 200–300 km thick sub-continental lithospheric mantle keels. The focus of this paper is the elucidation of its nature in order to answer the basic question how this and other thrust-and-fold belts could be formed in the Paleoproterozoic, and whether they are the same as or different from modern collision orogens. The active Himalayan-Tibet orogen is commonly thought of as the most extensively studied large, bi-verging fold-and thrust belt continental collision zone which may provide insight into key tectonic mechanisms for an understanding of orogenic processes in the Earth’s geological past. Precambrian orogens are tentatively perceived yet as something that was distinct from recent orogenic styles and was due to the initial elevated geotherm and higher radio-genic heat production in the early Earth.In this paper we report for the first time the revealation of the large, slightly eroded divergent Paleoproterozoic Volgo-Don orogen which is mostly composed of juvenile metasediments and comprises well-preserved patterns of the crustal orogenic architecture which are characteristic of the archetypal Himalayan-Tibet collisional orogen rather than of hot/ultra-hot Precambrian orogens based on numerical modeling.

High altitude Pliocene to Pleistocene vegetation and climate change of the Kunlun Pass Basin, NE Tibetan Plateau

The world largest alpine permafrost region, the Tibetan Plateau, will experience amplified warming under global climate change scenarios. Studying its environmental evolution in the geological past is crucial to further our understanding of mechanism and thresholds of climate change. Here we present a 3.5-million-year-long, high-altitude vegetation and climate record from the Kunlun Pass Basin to reconstruct the transition from the sustained warm, high carbon dioxide environment of the Pliocene to the cool glacial and interglacial periods of the Pleistocene, 4.31 to 0.85 million years (Ma) ago. The Early Pliocene pollen record indicates the occurrence of patches of broadleaved and coniferous forests in a semi-desert shrubland at this high-altitude site. Pollen derived quantitative climate estimates based on modern pollen rain transfer functions suggest a moister climate before 4.0 Ma with mean annual temperatures (MATs) > 14 °C warmer than today. The retreat of broadleaved and coniferous forests from the Kunlun Pass Basin area is linked to stepwise cooling at ∼4.0 Ma and during the Plio-Pleistocene transition between 2.7 and 2.6 Ma. Pollen derived climate estimates and Δ47-palaeothermometry indicate an abrupt cooling of ∼4–8 °C resulting in the onset of permafrost condition on the Tibetan Plateau after 2.7 Ma. An expansion of Chenopodioideae dominated xerophytic shrublands after 3.8 Ma and 2.15 Ma indicates a reduction in precipitation on the NE Tibetan Plateau, which appears to be linked to a weakening of the East Asian Summer Monsoon at the Plio-Pleistocene transition. The reconstructed cooling at the Kunlun Pass Basin site reflects the regional expression of global climate change with high-elevation temperature amplification hence rejecting the notion of a major tectonic uplift of the Tibetan Plateau during the Plio-Pleistocene.

Constraints on the Timing and Extent of Deglacial Grounding Line Retreat in West Antarctica

AbstractProjections of Antarctica's contribution to future sea level rise are associated with significant uncertainty, in part because the observational record is too short to capture long‐term processes necessary to estimate ice mass changes over societally relevant timescales. Records of grounding line retreat from the geologic past offer an opportunity to extend our observations of these processes beyond the modern record and to gain a more comprehensive understanding of ice‐sheet change. Here, we present constraints on the timing and inland extent of deglacial grounding line retreat in the southern Ross Sea, Antarctica, obtained via direct sampling of a subglacial lake located 150 km inland from the modern grounding line and beneath >1 km of ice. Isotopic measurements of water and sediment from the lake enabled us to evaluate how the subglacial microbial community accessed radiocarbon‐bearing organic carbon for energy, as well as where it transferred carbon metabolically. Using radiocarbon as a natural tracer, we found that sedimentary organic carbon was microbially translocated to dissolved carbon pools in the subglacial hydrologic system during the 4.5‐year period of water accumulation prior to our sampling. This finding indicates that the grounding line along the Siple Coast of West Antarctica retreated more than 250 km inland during the mid‐Holocene (6.3 ± 1.0 ka), prior to re‐advancing to its modern position.

Quantifying Continental Crust Thickness Using the Machine Learning Method

AbstractCrustal thickness plays a key role in many geological processes. However, it remains challenging to quantify crustal thickness in the geological past. Here we propose an Extremely Randomized Trees algorithm‐based machine learning model to recover crustal thickness of old geological regions. The model is trained using major oxide and trace element compositions of 1,480 young intermediate to felsic rocks from global arcs and collisional orogens and geophysical measurements of crustal thickness. The model provides better estimations of crustal thickness than the commonly used methods based on Sr/Y and (La/Yb)N when applied to the testing data. The validity of this model is further demonstrated by its applications to the Kohistan–Ladakh, Gangdese and Talkeetna arcs, where paleocrustal thicknesses have been well constrained. We then use this model to construct the Mesozoic crustal thickness evolution of the Erguna Block in the southeast of the Mongol–Okhotsk suture belt. The closure time of the suture zone is still debated. Our results suggest that the crustal thickness of the Erguna Block increased from 43 ± 9 km at 210 Ma to 62 ± 7 km at 180 Ma, remained constant between 180 and 150 Ma, and then thinned to 36 ± 4 km at 120 Ma. These results suggest that the Mongol–Okhotsk Ocean closed in the Early–Middle Jurassic and the thickened crust was stretched during the Cretaceous. We show that the thick crust and compression‐extension transition seem to be favorable for the formation of porphyry copper deposits in the Erguna Block during the Late Jurassic.

Optically stimulated luminescence dating and paleoclimatic implications of the Holocene dune sands in the Hunshandake Sandy Land, Northeast China

Aeolian sediments are important geological archives of paleoclimate changes. Due to the fragile ecosystem of desert, sand dune mobility is particularly sensitive to climate change, and is thus important for revealing the stabilization and mobilization processes of dunes during the geological past. In northeastern China, several sandy lands are located in the East Asian monsoonal region, and desert evolution has been used to infer the waxing and waning of monsoonal climate. However, the relationship between dynamic aeolian landscapes and forcing mechanisms is still under debate due to the complex nature of the aeolian dune systems. In this study, we analyse two aeolian sand dune sections in the Hunshandake Sandy Land, northeast China, located at the northern edge of the East Asian summer monsoon, explore regional paleoclimatic changes during the Holocene. We carried out high-resolution optically stimulated luminescence (OSL) dating to develop a well-constrained chronology for the dune sands, as well as analyses of multiple climatic proxies including magnetic susceptibility, particle size, and color parameters, to obtain knowledge about dune mobility and climatic changes. Our results indicate that the early Holocene was characterized by the accumulation of aeolian dune sands, implying an arid climate, driven by an enhanced East Asian winter monsoon. Paleosols were generally developed in the mid-Holocene (∼8 and 4 ka) when the sand dunes were stabilized by vegetation under a relatively warm and humid climate driven by an enhanced East Asian summer monsoon. In the late Holocene, from ∼4 ka to the present, climate returned to an arid and semi-arid phase, marked by aeolian dune sands with some weakly-developed paleosols. Through comparison of the aeolian record with the other East Asian monsoonal records and the sea-surface temperature of the North Pacific, we suggest that the evolution of the East Asian monsoon, which was paced by both the melting and expansion from the Northern Hemisphere ice sheet as well as the changes of solar radiation, played an important role in driving climate change in the Hunshandake Sandy Land during the Holocene.

Provenance evidence for the early-to-middle Pleistocene drainage reorganization of the Songhua River, NE China

The Songhua River, one of seven major water systems in China, is the most famous river in Northeast China. However, it is still unclear whether the paleo-Songhua River had a reversed flow direction in the geological past and what mechanisms controlled changes in the flow direction. This study presents new results utilizing detrital zircon U-Pb geochronology and heavy mineral composition retrieved from a well-dated 102-m sediment core and from fluvial sediments in the Songhua River drainage basin, to reveal the evolution of the river system. A shift in Precambrian (>600 Ma) and 100–400 Ma age spectra can be observed at 62.2 m (∼0.94 Ma) in the core, and the heavy mineral composition also shows remarkable variations above and below 62.2 m. Provenance analysis shows that the sediments above 62.2 m in the core originated from the west (i.e., from the direction of the Songnen Plain), but below 62.2 m were fed from areas in the east (i.e., from the direction of the Jia-Yi divide), indicating that the paleo-Songhua River flowed westwards into the Songnen Plain before 0.94 Ma. A conceptual model is therefore proposed for the Songhua River drainage evolution over the early-to-middle Pleistocene. The westward-flowing paleo-Songhua River was captured by the eastward-flowing paleo-Sanjiang River at the Jia-Yi divide due to headward erosion of the paleo-Sanjiang River, leading to the initiation of a unified eastward flowing river system at ∼ 0.94 Ma. The second reorganization of the Songnen river system occurred at 0.46 Ma, characterized by the termination of the Songnen paleolake and the disintegration of the centripetal river system. The tectonics and climate were the main drivers controlling the evolution processes of the paleo-Songhua River before 1.2 Ma and after 0.94 Ma, respectively, whereas they acted together during 1.2–0.94 Ma. The tectonic uplifting of the Songliao divide and the long-term aridification in the Songnen Plain collectively controlled the second drainage reorganization in the Songnen Plain at 0.46 Ma.

Evolution of complex giant seafloor depressions at the northern Argentine continental margin (SW Atlantic Ocean) under the influence of a dynamic bottom current regime

Seafloor depressions (SD) are features commonly observed on the ocean floor. They often occur as circular, small-sized (up to 10 s of m) incisions caused by fluid expulsion. Larger depressions (100s m to km) are considerably less abundant, and their origin and development have been scarcely studied. This study investigated two giant morphological depressions (>5 km) using recently acquired multibeam bathymetry and backscatter, sediment echosounder, and high-resolution seismic data. An arc-shaped (SD-N) and a sub-circular depression (SD-S) are located on the Ewing Terrace at the Argentine Continental Margin north and south of the Mar del Plata Canyon, respectively. The study area is influenced by the Brazil-Malvinas Confluence, where major counterflowing ocean currents affect sedimentation, and northward flowing currents form a large contourite depositional system. Using an existing seismo-stratigraphy, the onset of SD-N was dated to the middle Miocene (∼15–17 Ma), whereas SD-S started developing at the Miocene/Pliocene boundary (∼6 Ma). Acoustic anomalies indicate the presence of gas and diffuse upward fluid migration, and therefore seafloor seepage is proposed as the initial mechanism for SD-S, whereas we consider a structural control for SD-N to be most likely. Initial depressions were reworked and maintained by strong and variable bottom currents, resulting in prograding clinoform reflection patterns (SD-N) or leading to the build-up of extensive cut-and-fill structures (SD-S). Altogether, this study highlights the evolution of two unique and complex seafloor depressions throughout the geologic past under intense and variable bottom current activity in a highly dynamic oceanographic setting.

Eco-ISEA3H, a machine learning ready spatial database for ecometric and species distribution modeling

We present the Eco-ISEA3H database, a compilation of global spatial data characterizing climate, geology, land cover, physical and human geography, and the geographic ranges of nearly 900 large mammalian species. The data are tailored for machine learning (ML)-based ecological modeling, and are intended primarily for continental- to global-scale ecometric and species distribution modeling. Such models are trained on present-day data and applied to the geologic past, or to future scenarios of climatic and environmental change. Model training requires integrated global datasets, describing species’ occurrence and environment via consistent observational units. The Eco-ISEA3H database incorporates data from 17 sources, and includes 3,033 variables. The database is built on the Icosahedral Snyder Equal Area (ISEA) aperture 3 hexagonal (3H) discrete global grid system (DGGS), which partitions the Earth’s surface into equal-area hexagonal cells. Source data were incorporated at six nested ISEA3H resolutions, using scripts developed and made available here. We demonstrate the utility of the database in a case study analyzing the bioclimatic envelopes of ten large, widely distributed mammalian species.