Tuff Layers Research Articles

Miocene Petit-Spot Basanitic Volcanoes on Cretaceous Alba Guyot (Magellan Seamount Trail, Pacific Ocean)

New data obtained from core samples of two boreholes and dredged samples from the Alba Guyot in the Magellan Seamount Trail (MST), Western Pacific, including the 40Ar/39Ar age determinations of basanite, and the mineralogy of basanite, tuff, tuffite, mantle-derived inclusions in basanite and tuff (lherzolite xenolith and Ol, Cpx, and Opx xenocrysts), and calcareous nannofossil biostratigraphy, have implications for the guyot′s development and history. Volcanic units in the upper part of the Alba Guyot main edifice and its Oma Vlinder satellite, at sea depths between 3600 and 2200 m, were deposited during the Cretaceous 112 to 86 Ma interval. In the following ~60 myr, the Alba Guyot became partly submerged and denuded with the formation of a flat summit platform while the respective fragment of the Pacific Plate was moving to the Northern Hemisphere. Volcanic activity in the northeastern part of the guyot summit platform was rejuvenated in the Miocene (24–15 Ma) and produced onshore basanitic volcanoes and layers of tuff in subaerial and tuffite in shallow-water near-shore conditions. In the Middle-Late Miocene (10–6 Ma), after the guyot had submerged, carbonates containing calcareous nannofossils were deposited on the porous surfaces of tuff and tuffite. Precipitation of the Fe-Mn crust (Unit III) recommenced during the Pliocene–Pleistocene (<1.8 Ma) when the guyot summit reached favorable sea depths. The location of the MST guyots in the northwestern segment of the Pacific Plate near the Mariana Trench, along with the Miocene age and alkali-basaltic signatures of basanite, provide first evidence for petit-spot volcanism on the Alba Guyot. This inference agrees with the geochemistry of Cenozoic petit-spot basaltic rocks from the Pacific and Miocene basanite on the Alba Guyot. Petit-spot volcanics presumably originated from alkali-basaltic melts produced by decompression partial melting of carbonatized peridotite in the metasomatized oceanic lithosphere at the Lithosphere–Asthenosphere Boundary level. The numerous volcanic cones with elevations of up to 750 m high and 5.1 km in basal diameter, discovered on the Alba summit platform, provide the first evidence of voluminous Miocene petit-spot basanitic volcanism upon the Cretaceous guyots and seamounts of the Pacific.

Mercury isotopes of the Late Ordovician to Middle Triassic tuff layers in South China link the fate of ancient volcanism and the mass extinction

Mercury (Hg) anomalies in sedimentary records are a newly developed proxy of large volcanism in the geological past. Tuff layers host abundant volcanic ash and record key information on the type of volcanic emission (e.g., arc volcanism and large igneous province eruptions). Here, we measured the Hg isotopic compositions of several tuff layers in South China. Tuff samples in the Late Ordovician Wufeng Formation and the Middle Triassic Guanling Formation mostly show positive Δ199Hg values of – 0.01 to 0.10‰ and – 0.06 to 0.16‰, respectively, suggesting arc volcanism occurred during these two periods. Tuff samples in the Middle Permian Dachang Layer mostly show near-zero Δ199Hg values (– 0.08 to 0.00‰), suggesting volcanism was driven by the Emeishan large igneous province eruption. Results of this study verify Hg isotopes as a useful proxy in revealing the type of volcanism in geological history.

New U-Pb zircon tuff ages and revised stratigraphic correlations in the Superior craton during the Great Oxidation Episode

Major environmental changes during the Great Oxidation Episode are recorded in 2.5–2.0 Ga sedimentary successions across the world. In North America, the Huronian Supergroup is the most complete succession, preserving three glacial intervals with possible equivalents in the Lake Superior region. The third and youngest glacial unit (Gowganda Formation, Cobalt Group) of the Huronian Supergroup has been correlated with glacial deposits of the Chocolay Group in the Lake Superior region. Here we present the results of in situ SHRIMP U-Pb geochronology of zircon in thin tuff layers from the basal Wewe Slate, Chocolay Group, from drill-core in the Marquette Range area, upper Michigan. Zircon U-Pb data from two intervals ∼16 m apart yielded weighted mean 207Pb/206Pb ages of 2174 ± 9 Ma and 2172 ± 6 Ma, which define the depositional ages of the Wewe Slate and the conformably underlying Kona Dolomite. In the Huronian Supergroup, SHRIMP U-Pb dating of zircon in a tuff bed from the Gordon Lake Formation, Cobalt Group, yielded a weighted mean 207Pb/206Pb age of 2318 ± 8 Ma, interpreted to be the age of deposition. Re-examination of previously published U-Pb zircon data from the Gordon Lake Formation (Rasmussen et al., 2013) yields a slightly older weighted mean 207Pb/206Pb age of 2310 ± 5 Ma. Our results show that the Wewe Slate, and probably the Kona Dolomite, are ∼150 million years younger than the ∼2.32 Ga Gordon Lake Formation, with which they were previously correlated. Our results suggest that the glacial deposits in the Lake Superior region represent a fourth Paleoproterozoic glaciation in North America, whose age range corresponds to that of the fourth and final early Paleoproterozoic glaciation in southern Africa. We propose that the Chocolay Group was deposited after the Huronian Supergroup and is broadly coeval with the rift-passive margin succession (Cycle 1 of the Kaniapiskau Supergroup) in the New Québec Orogen, Canada, whose deposition has been linked to rifting and breakup along the eastern margin of the Superior craton at ∼2.22 Ga.

Stratigraphic evidence for a major unconformity within the Ediacaran System

The subdivision and correlation of the Ediacaran System within the geologic timescale is desirable, but challenging. The Ediacaran Doushantuo Formation (∼635–550 Ma) in South China is one of the most important sedimentary successions for studying the co-evolution of Earth's environment and life at that time. However, its stratigraphic continuity is confusing and deserves scrutiny. In this study we evaluate stratigraphic continuity of the Doushantuo Formation from a key section deposited in an alleged deep-water “basinal” setting. Using litho-, chemo-, and chrono-stratigraphic data anchored by two new CA-ID-TIMS U-Pb zircon dates of 629.7 Ma and 556.4 Ma from two tuff layers, we reveal that this section contains a cryptic subaerial unconformity with a >44 Myr gap in the sedimentary record. The unconformity occurs immediately prior to the EN3/Shuram δ13C excursion in the mid-Ediacaran, and can be traced regionally and may be correlative to other mid-Ediacaran unconformities globally. We suggest that its development is related to glacio-eustatic sea-level changes during the mid-Ediacaran. This finding provides a critical stratigraphic boundary for future subdivision and correlation of the Ediacaran System in South China, and we advocate for a reconsideration of the completeness of the Ediacaran stratigraphic record in this area.

Middle Neoproterozoic (Tonian) Polar Wander of South China: Paleomagnetism and ID‐TIMS U‐Pb Geochronology of the Laoshanya Formation

AbstractPaleomagnetic records of middle Neoproterozoic (820 to 780 Ma) rocks display high amplitude directional variations that lead to large discrepancies in paleogeographic reconstructions. Hypotheses to explain these data include rapid true polar wander (TPW), a geomagnetic field geometry that deviates from a predominantly axial dipole field, a hyper‐reversing field (>10 reversals/Ma), and/or undiagnosed remagnetization. To test these hypotheses, we collected 1,057 oriented cores over a 85 m stratigraphic succession in the Laoshanya Formation (Yangjiaping, Hunan, China). High precision U‐Pb dating of two intercalated tuff layers constrain the age of the sediments between 809 and 804 Ma. Thermal demagnetization isolates three magnetization components residing in hematite which are not time‐progressive but conflated throughout the section. All samples possess a north and downward directed component in geographic coordinates at temperatures up to 660°C that is ascribed to a Cretaceous overprint. Two components isolated above 660°C reveal distinct directional clusters: one is interpreted as a depositional remanence, while the other appears to be the result of a mid‐Paleozoic (460 to 420 Ma) remagnetization, which is likely widespread throughout South China. The high‐temperature directions are subtly dependent on lithology; microscopic and rock magnetic analyses identify multiple generations of hematite that vary in concentration and distinguish the magnetization components. A comparison with other middle Neoproterozoic paleomagnetic studies in the region indicates that the sudden changes in paleomagnetic directions, used elsewhere to support the rapid TPW hypothesis (ca. 805 Ma), are better explained by mixtures of primary and remagnetized components, and/or vertical axis rotations.

Identification of Deep Groundwater Aquifer Zones with Geoelectrical Method in Sukadanaham Area Bandar Lampung, Indonesia

Research on groundwater aquifers using the geoelectric method has been carried out in the Sukadanaham area, Tanjung Karang Barat District, Bandar Lampung City. This Research Objectives This research aims to identify the lithology and depth of groundwater aquifer zones based on resistivity values ​​and geological literature. Data acquisition was carried out using the Schlumberger configuration of 3 points in the young Betung volcanic formation (Qhvb). The data used is the resistivity value. Resistivity value data is modeled vertically with inverted results. The resistivity value of each point is adjusted and interpolated based on the literature on rock resistivity values. Based on the identification results, 4 types of subsurface rock lithology were found, namely top soil, tuff, breccia, and andesite. The lithology of the layers at point 1, point 2 and point 3 is dominated by tuff and breccia layers. The resistivity value of the andesite layer obtained has a high value, which is > 300 Ωm. The resistivity value of the tuff layer for the waterproof layer has a value of 200-250 Ωm. The breccia layer acts as a groundwater aquifer zone with a low resistivity value of 15-60 Ωm. The rock resistivity value with the lowest value is at a depth of 40-95 m which is a compressed aquifer layer with andesite and tuff layers as a waterproof layer above and below.

Radon revealed: The hidden connection between construction and contamination in Jazan region

Indoor radon levels, when high, can silently set the stage for lung cancer. Many are actively searching for the reason behind these spikes in radon in our living spaces. The investigation includes buildings in the picturesque Jazan region, where we use the advanced CR-39 solid-state detector. We explored houses built using two interesting methods: traditional soil compaction, innovative pore filling, and simple columns only. Surprisingly, houses built using soil pressure have always remained safe. However, as summer arrived in the Jazan region, 16% of homes with columns revealed radon levels above international safety lines. Even more surprising is that the summer radiation doses in 32% of these homes exceeded international standards. In contrast, pore-filling homes showed unwavering integrity throughout the year. The results showed that the average concentration of radon gas in the first type decreased from 358.97 Bq/cm3 in summer to 209.36 Bq/cm3 in winter. As for the second type, the concentration of radon gas decreased from 153.67 Bq/cm3 in the summer to 88.67 Bq/cm3 in the winter. This study highlights the profound impact of building and home ventilation strategies on radon levels. By combining soil compaction and the tuff layer, we ensure that Jazan homes have a healthy, radon-free environment. Furthermore, constant, up-to-date ventilation is key to staying healthy and radon-free during the hot summer months. It is advised that research into various building types worldwide be continued to determine the most secure method of construction that can lessen gas leakage from the ground and preserve public health. Future research should also look into how different building designs and ventilation systems affect radioactive contamination levels.

Aquifer potential investigation applying vertical electrical sounding in Bango sub-catchment area

The freshwater requirement in the Bango sub-catchment is rising along with land use change. The main source of freshwater that can be used is groundwater in the aquifer layer. The research on aquifer potential was conducted using the vertical electrical sounding (VES) method. Vertical electrical sounding is a geoelectric method to measure the resistivity of the rocks. This instrument is used to obtain subsurface information about aquifer depth. The measurements along fourteen measurement points that the length of each track used is a maximum of 4 km. The layer which is the potential to be an aquifer is a tuff layer with resistivity values for tuff layer at each measurement point varying from 20,2 to 78,16 Ωm. The results showed that the rock lithology is influenced by volcanic activity and there is a layer suspected of being a potential shallow aquifer. The potential shallow groundwater in the Bango sub-catchment is approx. 5,73 billion cubic meters.

Hydrogeology Conceptual Model of Meninting Dam and Its Surrounding Area, West Lombok Regency, West Nusa Tenggara, Indonesia

The Meninting Dam is one of the dams recently built in West Lombok, Indonesia. Hydrogeologically, this dam was built on the Mataram-Selong Groundwater Basin, which is known to be a highly productive aquifer. However, in this area, no extensive research in terms of hydrogeological conditions has been conducted. Therefore, the objective of this research is to present a conceptual model of the hydrogeology of the Meninting Dam and its surrounding area. This study was carried out by collecting primary and secondary data on the geological, hydrological, and hydrogeological conditions in the research area. Results show that there are two layers of unconfined aquifer, one layer of aquitard, and one layer of confined aquifer in this area. The unconfined aquifer is built by layers made up of pebbles, sand, clay, gravel, and boulders, but also a layer of pumiceous tuff with a thickness up to 40 m and a hydraulic conductivity value between 10-1 mm/s and 5x10-2mm/s. The confined aquifer is composed of pumiceous tuff and has a thickness range of up to 100 m and a K value of about 5 x 10-3 mm/s. Between unconfined and confined aquifers, there is a thick layer of aquitard made up of laharic breccia.

Middle Miocene volcanic flare up preceding and synchronous with the Langhian/Serravallian sea‐level decline in the North Pannonian Basin: Insights from 40Ar/39Ar dating, geo‐seismic analysis and 3D visualization of the subterranean Kráľová stratovolcano

AbstractThe Pannonian Basin System originated from the collision of the African and European tectonic plates, followed by the Miocene extensional collapse that led to the development of a back‐arc basins. Accurate dating is essential to comprehend the tectono‐volcanic evolution of the region, particularly in the under‐studied Danube Basin. Single‐grain 40Ar/39Ar dating has revealed that volcanic activity in the Danube Basin commenced around 14.1 million years ago, aligning with previous biostratigraphic and radioisotope data from nearby volcanic fields. The initial Middle Miocene pyroclastic deposits were generated by intermediate high K calc‐alkaline magmas, contributing significantly to the deposition of thick layers of fine vitric tuffs. The timing and chemistry of the volcanism are consistent with the Badenian rift phase in the Middle Miocene within the Carpathian–Pannonian region, suggesting an intraplate back‐arc volcanic environment. Three‐dimensional imaging has exposed the buried Kráľová stratovolcano, revealing its impressive scale with a thickness between 2620 and 5000 m and a base diameter of 18–30 km. Such dimensions place it among the ranks of the world's largest stratovolcanoes, indicating its substantial impact on the evolution of the Carpathian–Pannonian area. The complex formation history of the stratovolcano points to multiple phases of growth. Furthermore, the basin controlling Mojmírovce‐Rába fault's intersection with the stratovolcano implies that fault activity was subsequent to the volcanic activity, being younger than 14.1 million years. Regional age data consistently indicates that volcanic activity in the Danube Basin reached its zenith just prior to and during the lower/upper Badenian sea‐level fall (Langhian/Serravallian). K‐metasomatism is unique to the stratovolcanic structures and is not observed in the wider regional setting. This study supports the notion of an intricate, interconnected subterranean intrusive system within the stratovolcano, underscoring the complex interplay between geological structures and volcanic processes.

Influence of Reservoir Water Level Fluctuations of Reservoir B (Rusunawa) on Groundwater Availability at the Environment of Lampung University

The presence of four reservoirs as rainwater collection infrastructure at the University of Lampung is expected to enhance the infiltration process and recharge the groundwater aquifers. However, the threat of water scarcity in the area may arise due to the reduction of recharge areas. Therefore, a comprehensive study is necessary to understand the important factors in maintaining groundwater availability. This research aims to analyze groundwater aquifers, identify fluctuations in the water level of Reservoir B, and analyze the relationship between the elevation of the water level in the reservoir and the availability of groundwater in the University of Lampung environment. The research methodology involves the interpretation of geoelectric data and the calculation of water level fluctuations in the reservoir. The analysis results indicate that the shallow groundwater aquifer is estimated to be located at depths ranging from 10 to 30 meters, while the deeper aquifer is situated at depths of 80 to 130 meters with a layer of sandy tuff. The highest fluctuation in water level is recorded at 14 cm during rainfall with an intensity of 52.1 mm/day. There were no significant changes in the water level observed during rainfall with intensities ranging from 0 to 2.4 mm/day, and the average fluctuation observed is approximately 0.5 cm every 8 hours.

40Ar/39Ar and U-Pb age correlations of the large Rupelian Rhodope Massif eruptions with airfall tuffs in SE, S and Central Europe

Numerous Eocene and Oligocene volcanic tuff layers within the Eastern, Central and Southern Europe sedimentary basins attest to extensive volcanic activity. Tephra dispersal of these tuffs covers areas of more than 1 000 000 km2, and the volume of erupted material to 1000s of cubic kilometers. The sources of the eruptions, however, remain unknown. Using precise 40Ar/39Ar and U-Pb radiometric dating, we correlate some of these tuff layers to three silicic Rhodope Massif Rupelian (еarly Oligocene) supereruptions dated at 33.2 Ma, 32.8 Ma and 31.6 Ma and named Dazhdovnitsa, Borovitsa and Perelik. Hence, these tuff layers can now be used as regional stratigraphic isochronous marker horizons for correlating, dating and synchronizing deposits and events in geologic and paleoenvironmental studies.

Identification of Geothermal System in Cisolok, West Java based on the Correlation of Gravity Method, ADMT (Active Directory Magnetotelluric), and Drill Log Data

Indonesia has 40% geothermal potential of the world’s geothermal potential. One proof of its potential is in Cisolok, West Java. The method used in this study is the gravity method from 2013 GGMPlus satellite with First Horizontal Derivative (FHD) analysis which is correlated with ADMT and drill log data. Based on overlaid between Land Surface Temperature (LST) map and residual anomaly map, Cisolok has a temperature of around 23.8 – 26.5 °C. These correlations describe the normal fault structure in the south that controls the Cisolok geothermal system. The results of the 3D inversion modeling show alternating layers of tuff, tuff breccia and silt as a cap rock with a density contrast of 0 – 0.2 gr/cc at a depth of 0 – 325 m, thick limestone layers with a density contrast of -0.1 – (-0.05) gr/cc at a depth of 325 – 700 m, and a layer of granodiorite rock as an intrusion body with a density contrast of -0.2 – (-0.15) gr/cc at a depth of 700 – 900 m. Based on the results obtained, it can be proven that the gravity method and the ADMT method have a fairly good correlation in geothermal exploration activities.

Identification of Geothermal Potential in Block Ciasmara Sector II, Mount Salak Area, Based on the Correlation of the Active Directory Magnetotelluric (ADMT) and Self-Potential Methods

Indonesia possesses significant geothermal potential, with the largest share located in West Java, accounting for up to 21.7% distributed across 44 locations in 11 regencies. One such location with geothermal potential is in Block Ciasmara Sector II, the Mount Salak area, Bogor Regency, characterized by manifestations such as hot spring bathing pools. This research aims to understand the distribution of geothermal reservoirs in the study area, where these reservoirs contain hot fluids that can be harnessed for renewable energy generation. The methodology used in this research involves a correlation between the Active Directory Magnetotelluric (ADMT) and Self-Potential (SP) methods. A total of 3 ADMT measurements were conducted along tracks ranges from 5-8 meters, while the SP method involved 7 measurement points with coordinates distributed around the geothermal manifestations in the Mount Salak area. The data obtained were then visualized in 2D and 3D to gain insights into the distribution and orientation of the reservoir layers in the study area. The results indicate a correlation between the ADMT and Self-Potential methods. In Line 01 of the ADMT, located in the western part, there is a correlation with high potential difference values on the SP map ranges from 47.6-82.1 mV, suggesting the presence of tuff layers rich in alteration minerals. This is confirmed by the 2D ADMT modeling, which shows that the clay cap is thicker compared to Line 02 and Line 03, associated with the presence of alteration minerals in the clay cap. This correlation also applies to Line 03, which has low potential difference values ranges from 4.9-25.3 mV, indicating a response from lapilli rocks. This is corroborated by the 2D model, which reveals thickening of the lapilli rock layer on Line 03.Keywords: ADMT, Geothermal, Mount Salak, Reservoir, Self-Potential.

Unravelling the pre-eruptive conditions of the rhyolitic Šumovit Greben lava dome from clinopyroxene-dominant glomeroporphyritic clots

Detailed analyses of mineral composition and whole-rock geochemical data helped to unravel the volcanic plumbing system beneath the rhyolitic Šumovit Greben lava dome, the westernmost member of the Kožuf-Voras volcanic system (N. Macedonia). It is characterized by high SiO2 content (> 70 wt%) coupled with low MgO (< 1 wt%) and Sr (< 500 ppm) suggesting fractionation of clinopyroxene and plagioclase at depth forming a crystal mush and a crystal-poor rhyolitic lens by fractional crystallization and melt extraction on top of it. The crystal mush is composed of mainly clinopyroxene, biotite and plagioclase, whereas sanidine and plagioclase are the most abundant phenocrysts of the rhyolitic lens. The main dome forming event occurred at ca. 2.9 Ma, which sampled the crystal-poor rhyolitic lens. After a short quiescence time, an explosive eruption occurred depositing a massive lapilli tuff layer northwest of the lava dome, and an extrusion of a small-volume lava flow on the northern side of the lava dome at ca. 2.8 Ma. This latter sampled also the crystal mush, as it contains abundant glomeroporphyritic clots of clinopyroxene ± plagioclase ± biotite. The clinopyroxene phenocrysts are chemically homogeneous, their crystallization temperature is ca. 900 °C representing the crystal mush, whereas the plagioclase and the sanidine crystallized at a lower temperature (ca. 790 °C) representing the rhyolitic lens. Noble gas isotopic composition of the clinopyroxene indicate no mantle-derived fluids (< 0.5%) having an R/Ra of ca. 0.04 Ra. The rejuvenation of the system probably occurred due to implementation of mafic magma at depth leading to a heat transfer and partial melting of the cumulate. This led to crystallization of Ba-rich rims of the sanidine and An- and Sr-rich rims of the plagioclase. The crystal mush zone beneath Šumovit Greben might be connected to the nearby, more mafic volcanic centers, and the eruption of Šumovit Greben could have been the start of the last cycle in the lifetime of the Kožuf-Voras volcanic system.

Guadalupian–Lopingian (Middle–Late Permian) radiolarians from clastic rocks and zircon U–Pb ages of intercalated tuff and tuffaceous sandstone on Sado Island, central Japan

We investigated Permian strata in the Ota area of the Kosado Hills, Sado Island, central Japan, and their depositional ages were determined based on radiolarian biostratigraphy and zircon U–Pb dating. We also focused on the geology of the region and its lithologic correlation with other geological units in the Inner Zone of Southwest Japan. The radiolarian analysis identified the presence of Follicucullus porrectus and F. dilatatus in mudstone exposed on the coastline of Ota, indicating a middle–late Capitanian to early Changhsingian age. Mudstone exposed along the forest road in the Ota area contained Cariver charveti, suggesting a late Capitanian–early Changhsingian age. Zircon U–Pb dating of the tuff layer intercalated within the Follicucullus-bearing mudstone yielded a weighted-mean age of 259.9 ± 2.0 Ma, corresponding to a Capitanian–Wuchiapingian age. The tuffaceous sandstone interbedded with mudstone containing C. charveti yielded a weighted-mean age of 264.1 ± 6.3 Ma, which covers the Roadian to Wuchiapingian ages. The youngest model peak age (256.6 ± 2.6 Ma; Wuchiapingian) provides the most reliable estimate of the maximum depositional age. The Paleozoic strata in the Kosado Hills have previously been correlated with the Ultra-Tamba and Maizuru belts in Southwest Japan based on fossil occurrences. Our findings indicate that the Permian rocks in the Kosado Hills exhibit differences in lithology from those in the Ultra-Tamba belt but share similarities with the upper Guadalupian–Lopingian strata in the Maizuru belt.

THE OLDEST TRACE FOSSILS IN ASSOCIATION WITH EDIACARA-TYPE BIOTA IN THE UPPER VENDIAN OF THE SOUTH URALS

Trace fossils and palaeopascichnids have been studied from the Basa Formation of the Vendian Asha Group of the South Urals (southwestern periphery of the Suleiman Anticline, Shubino quarry in the Ust’-Katav city, Chelyabinsk Region. The general morphology and preservation of ichnofossils was shown to be similar to the Late Vendian-Early Cambrian subhorizontal bilobate burrows of Didymaulichnus. The paleontological remains were found to be confined to extremely shallow depositional settings and located stratigraphically below the volcanic tuff layer, the zircon from which has a U–Pb isotopic age of 578 ± 7 Ma. Until now, the first occurrence of trace fossils and the associated “Agronomic Revolution” were thought to be timed to the interval of ~560–550 Ma. Our results show that mobile benthos and biological mixing of sediments may have occurred 20–30 Ma earlier and support the hypothesis that the onset of the first “Agronomic Revolution” and the “Cambrian Explosion” were not significantly coincident in time.

A chronostratigraphic and biostratigraphic framework for the Yanliao Biota of northeastern China: Implications for Jurassic terrestrial ecosystems and evolution

The terrestrial Yanliao Biota in northeastern China represents a Jurassic biodiversity hotspot. Abundant and diverse fossils include the oldest known representatives of several groups of plants, invertebrates, and vertebrates that thrived in a forest ecosystem under a humid and warm climate. Since the early 21st century, discoveries associated with the Yanliao Biota have significantly improved our understanding of Jurassic terrestrial ecosystems. However, a robust chronostratigraphic framework is required to calibrate the biota with key evolutionary events and to improve understanding of possible links between evolution and tectonism. In this paper, we report novel 40Ar/39Ar ages for two tuff layers (161.4 ± 0.8 Ma and 161.6 ± 0.6 Ma) positioned directly above the less-studied but salamander fossil-rich beds in Reshuitang, near Lingyuan, Liaoning Province, China. These new age data improve knowledge of the timing of diversification of early salamanders. We also review all reported age data and summarize significant fossils from classic Yanliao outcrops. Our study indicates that the Reshuitang fossil beds were deposited slightly later than the well-known Daohugou fossil beds situated ∼15 km away in Inner Mongolia and somewhat earlier than the Linglongta fossil beds in western Liaoning Province. These findings advance understanding of the Jurassic world during an episode of pronounced climatic warming.

The Oldest Trace Fossils in Association with an Ediacara-Type Biota in the Upper Vendian of the South Urals

Trace fossils and palaeopascichnids have been studied in the Basa Formation of the Vendian Asha Group of the South Urals (southwestern periphery of the Suleiman Anticline, Shubino quarry in Ust’-Katav, Chelyabinsk Region of Russia). The general morphology and preservation of ichnofossils have been shown to be similar to the Late Vendian–Early Cambrian subhorizontal bilobate burrows of Didymaulichnus. The paleontological remains have been found to be confined to extremely shallow deposition settings and located stratigraphically below the volcanic tuff layer with a zircon U–Pb isotopic age of 578 ± 7 Ma. Until now, the first occurrence of ichnofossils and the associated “Agronomic Revolution” were dated at ~560–550 Ma. According to our study results, mobile benthos and biological mixing of sediments could have occurred 20–30 Ma earlier. The hypothesis that the onset of the “First Agronomic Revolution” and the “Cambrian Explosion” were far from being close in time was confirmed.

Root-Layer Fungi Native to Four Volcanic Topographies on Conserved Ocean Islands: Another Clue to Facilitate Access to Newer Natural Microbial Resources in the Extreme Terrains

This study hypothesized that geographic segregation of certain extreme natures of the same kind could be an indicator of access to new natural microbial resources. Root-layer fungi and soil properties native to well-conserved volcanic topographies from two geographically segregated ocean volcanic islands beside the Korean Peninsula were analyzed. Four segregated sampling sites that represented the ocean volcanoes’ unique natural characters (tuff layer, caldera, and two steep cliffs) were examined. A total of 1356 operational taxonomic units classified into 7 phyla and 196 genera were obtained. Soil analysis showed that the sand proportion varied from 32.0–57.4%, and silt, 39.4–64.8%. The tuff layer terrain was the only terrain classified as silt soil. Soil Corg contents ranged from 2.78–15.12%; TN, 0.159–0.843; salinity, 0.001–0.019; and pH, 5.0–7.4. The larger the island area, the less oceanic salinity inflow, but TN and Corg decreased, and pH increased. The Shannon diversity index varied from 4.81–5.23 and was higher at the larger or center of larger islands. As geographic segregation (distance) increased, the proportion of taxa commonly identified decreased. Thus, geographic isolation of certain natural features (e.g., volcanic islands) may be a preferential clue to accessing a broader range of potential microbial resources.