Search Results (10)

The interglacial period of the Cryogenian glaciation is a pivotal interval in geological history, marked by two “Snowball Earth” events and the emergence of early animals. Currently, there is considerable debate regarding the paleo-oceanic environment and the dominant factors controlling organic matter enrichment. Here, based on inorganic geochemical data and mineral composition from the Datangpo Formation in Xiangtan (South China), combined with previous research, we have analyzed the paleo-climate, redox condition, seawater restriction, and primary productivity across different sedimentary facies during this critical interval. The results exhibit that the Datangpo Formation can be divided into three members (Da1–Da3) based on lithology. Paleoclimatic proxies suggest the environment was relatively cold during the deposition of the Da-1 Member, while it was relatively warm and humid during the deposition of the Da 2–3 members. Compared to shallow water areas, deep-water areas experienced a more rapid transition in paleotemperature following the Sturtian glaciation event. Combining Mo-U elements, Ce_N/Ce*_N, and C_org/P ratios, the environment was characterized by an oxic environment during the early deposition period of the Datangpo Formation, then gradually transitioned to suboxic, and finally anoxic conditions. Furthermore, the decompression of terrestrial magma chambers led to intense volcanic/hydrothermal activity during the deglaciation period. Hydrothermal activity was most intense during the Da-1 depositional period, followed by Da-2, and gradually declined during Da-3 depositional period. Hydrothermal activity not only provided essential materials for the formation of Mn carbonate ores but also significantly enhanced the primary productivity by introducing large amounts of nutrients in the paleo-ocean. The primary productivity indicators (Ni/Al, Cu/Al) exhibited an obvious coupling with Ce_N/Ce*_N and C_org/P ratios in the Datangpo Formation, indicating that oxygen-rich environments were favorable for biological proliferation, thereby providing abundant organic matter. Anoxic conditions further facilitated the preservation of organic matter, which may be the primary factor driving organic matter enrichment in the Datangpo Formation. Full article

The trend in partial pressure of atmospheric CO₂, P(CO₂), across the 66 MYr of the Cenozoic requires elucidation and explanation. The Null Hypothesis sets sea surface temperature (SST) as the baseline driver for Cenozoic P(CO₂). The crystallization and cooling of flood basalt magmas is proposed to have heated the ocean, producing the Paleocene–Eocene Thermal Maximum (PETM). Heat of fusion and heat capacity were used to calculate flood basalt magmatic Joule heating of the ocean. Each 1 million km³ of oceanic flood basaltic magma liberates ~5.4 × 10²⁴ J, able to heat the global ocean by ~0.97 °C. Henry’s Law for CO₂ plus seawater (H_S) was calculated using δ¹⁸O proxy-estimated Cenozoic SSTs. H_S closely parallels Cenozoic SST and predicts the gas solute partition across the sea surface. The fractional change of Henry’s Law constants, ${\displaystyle \frac{{\mathrm{H}}_{\mathrm{n}}-{\mathrm{H}}_{\mathrm{i}}}{{\mathrm{H}}_{\mathrm{n}}-{\mathrm{H}}_0}}$ is proportional to ΔP(CO₂)_i, and ${\displaystyle \frac{{\mathrm{H}}_{\mathrm{n}}-{\mathrm{H}}_{\mathrm{i}}}{{\mathrm{H}}_{\mathrm{n}}-{\mathrm{H}}_0}}\times ∆\mathrm{P}\left(\mathrm{C}{\mathrm{O}}_2\right)+\mathrm{P}(\mathrm{C}{\mathrm{O}}_2{)}_{\mathrm{m}\mathrm{i}\mathrm{n}}$, where ΔP(CO₂) = P(CO₂)_max − P(CO₂)_min, closely reconstructs the proxy estimate of Cenozoic P(CO₂) and is most consistent with a 35 °C PETM ocean. Disparities are assigned to carbonate drawdown and organic carbon sedimentation. The Null Hypothesis recovers the glacial/interglacial P(CO₂) over the VOSTOK 420 ka ice core record, including the rise to the Holocene. The success of the Null Hypothesis implies that P(CO₂) has been a molecular spectator of the Cenozoic climate. A generalizing conclusion is that the notion of atmospheric CO₂ as the predominant driver of Cenozoic global surface temperature should be set aside. Full article

The Middle-Upper Cambrian Xixiangchi Formation in the Sichuan Basin is regarded as an important reservoir with great potential for hydrocarbon exploration. It is previously indicated that the Xixiangchi carbonates have experienced extensive dolomitization, however, the origin of dolomitizing fluids and the dolomitization mechanism still remain uncertain. In this study, a set of petrographic and geochemical examinations, including rare earth elements (REE) and isotopic (C, O, and Sr) compositions were used to trace the origins of dolomitizing fluids and associated diagenetic processes. The petrographic examination revealed three types of matrix dolomites (D1, D2, D3) and one cement saddle dolomite (SD). These phases have crystal size ranges of less than 30 μm (very fine to fine crystals, D1), 30–100 μm (fine to medium crystals, D2), 100–300 μm (medium to coarsely crystalline dolomite, D3), and 0.3–4 mm (fracture filling cements, SD), respectively. D1 is characterized by non to very weak luminescence, weakly negative Ce anomalies (Ce/Ce* = 0.84 ± 0.02), strongly negative Eu anomalies (Eu/Eu* = 0.65 ± 0.03), and high ⁸⁷Sr/⁸⁶Sr ratios (0.71062 ± 0.00122). In combination with δ¹³C (−1.5‰ ± 0.2‰) and δ¹⁸O (−9.7‰ ± 0.5‰) compositions, D1 is interpreted to be formed by penecontemporaneous dolomitization in the near-surface environment with seawater as the dolomitizing fluid. In contrast, D2 is characterized by intercrystalline pores, dirty crystal surfaces, similar δ¹³C (−1.4‰ ± 0.4‰) compositions but higher δ¹⁸O (−8.9‰ ± 0.7‰) compositions, and lower ⁸⁷Sr/⁸⁶Sr ratios (0.70992 ± 0.00035), similar Ce anomalies (Ce/Ce* = 0.87 ± 0.04) and higher Eu anomalies (Eu/Eu* = 0.85 ± 0.04). The coarser D2 is regarded to be formed by the post-penecontemporaneous seepage-reflux dolomitization or by recrystallization of D1 dolomite in a near-surface or shallow burial environment. D3 is distinguished by a cloudy core with clear rims, showing slightly higher Eu anomalies (Eu/Eu* = 0.88 ± 0.02) and similar Ce anomalies (Ce/Ce* = 0.88 ± 0.02) than those of D1 and D2. Combined with the δ¹⁸O compositions (−10.4‰ ± 0.4‰) and ⁸⁷Sr/⁸⁶Sr ratios (0.70989 ± 0.00048), D3 is thought to be formed by the overgrowth or recrystallization of D1 and D2 dolomites in a shallow to moderate burial environment. The fractures filling SD dolomite consists of nonplanar and much coarser crystals with undulatory extinctions and brighter red luminescence. The lower δ¹⁸O (−11.1‰ ± 0.3‰) compositions, lower negative Eu anomalies (Eu/Eu* = 0.70 ± 0.01) of SD than the matrix dolomites, and similar Ce anomalies (Ce/Ce* = 0.83 ± 0.01) are indicative of hydrothermal dolomitization, with possible fluids associated with the magma during the period of Emei taphrogenic movement. In addition, the ⁸⁷Sr/⁸⁶Sr ratios (0.70941 ± 0.00003) of SD suggest probable origin from the coeval seawater partially. Therefore, SD dolomite is interpreted to be formed by hydrothermal dolomitization with mixed dolomitizing fluid of seawater and hydrothermal fluids. In summary, all the matrix dolomites have almost the same ΣREE concentrations and exhibit similar near-flat REE partition patterns with weak LREE enrichments, weakly negative Ce anomalies, and negative Eu anomalies. Such characteristics of REE compositions are indicative of similar evolved dolomitizing fluid, such as seawater or seawater- derived fluids. By contrast, SD dolomites have a different REE partition pattern with left-leaning characteristics, LREE depletions, and negative Eu anomalies, thus suggesting a different dolomitizing fluid source from the matrix dolomites. In addition, the development of intercrystalline pores associated with D2 dolomite makes it more likely to be a potential reservoir, indicating that the dolomitizing history of carbonate has a strong influence on the quality of potential dolomite reservoirs. Full article

As one of the youngest back-arc basins, the evolutionary behavior of magmatic volatiles in the Eastern Manus Basin has been poorly studied. Recently, apatite has received widespread attention for its powerful function in recording information on magmatic volatiles. In this paper, by determining the major element compositions and primary volatile abundances (F, Cl, SO₃) of apatites in dacite, we analyze the compositions of volatiles before magma eruption in the Eastern Manus Basin, as well as their indications for magmatic oxygen fugacity and petrogenesis, so as to improve the study about the evolution of magmatic volatiles in this region. Experimental data indicate that apatite saturation temperatures range from 935 to 952 °C. All the apatites are magmatic apatites with F contents of 0.87−1.39 wt.%, Cl contents of 1.24−1.70 wt.%, and SO₃ ≤ 0.06 wt.%. Analysis reveals that the apatites in this study crystallized from volatile-undersaturated melts, so their chemical compositions can be used as indicators of magmatic compositions. According to calculations, the minimum S concentrations of the host melts range from 2−65 ppm or 8−11 ppm. The crystallization and separation of magnetite caused the reduction state of melts, and the relatively low oxygen fugacity (ΔFMQ = −0.2 ± 0.9) caused low SO₃ contents in apatites. In addition, F and Cl contents of the host melt were calculated to be 185−448 ppm and 1059−1588 ppm, corresponding to the H₂O contents of 1.4−2.1% and 1.2−1.5% (error ± 30−40%), respectively. The high Cl/F ratio and H₂O contents of samples indicate the addition of slab-derived fluids in the mantle source region of the Eastern Manus Basin. High F contents of the melts may be influenced by F-rich sediments, as well as the release of F from lawsonite and phengite decomposition. High Cl appears to originate from the dual influence of subduction-released fluids and Cl-rich seawater-derived components. Further, it is estimated that 14−21% of the total Cl concentrations in melts were added directly from subduction-released fluids, or higher. Full article

Melanin protects skin from ultraviolet radiation, toxic drugs, and chemicals. Its synthesis is sophisticatedly regulated by multiple mechanisms, including transcriptional and enzymatic controls. However, uncontrolled excessive production of melanin can cause serious dermatological disorders, such as freckles, melasma, solar lentigo, and cancer. Moreover, melanogenesis disorders are also linked to neurodegenerative diseases. Therefore, there is a huge demand for safer and more potent inhibitors of melanogenesis. In the present study, we report novel inhibitory effects of Jeju magma-seawater (JMS) on melanogenesis induced by α-melanocyte stimulating hormone (α-MSH) in B16F10 melanoma cells. JMS is the abundant underground seawater found in Jeju Island, a volcanic island of Korea. Research into the physiological effects of JMS is rapidly increasing due to its high contents of various minerals that are essential to human health. However, little is known about the effects of JMS on melanogenesis. Here, we demonstrate that JMS safely and effectively inhibits α-MSH-induced melanogenesis via the CaMKKβ (calcium/calmodulin-dependent protein kinase β)-AMPK (5′ adenosine monophosphate-activated protein kinase) signaling pathway. We further demonstrate that AMPK inhibits the signaling pathways of protein kinase A and MAPKs (mitogen-activated protein kinase), which are critical for melanogenesis-related gene expression. Our results highlight the potential of JMS as a novel therapeutic agent for ameliorating skin pigmentation-related disorders. Full article

Trace and rare earth elements (REEs) are considered to be reliable indicators of chemical processes for the evolution of carbonate systems. One of the best examples of ancient carbonate successions (Berdiga Formation) is widely exposed in NE Turkey. The Lower Cretaceous limestone succession of Berdiga Formation may provide a case study that reveals the effect of ocean paleoredox conditions on diagenetic alteration. Measurement of major, trace and REEs was carried out on the Lower Cretaceous limestones of the Berdiga Formation, to reveal proxies for paleoredox conditions and early diagenetic controls on their geochemistry. Studied micritic limestone microfacies (MF-1 to MF-3) indicate deposition in the inner platform to a deep shelf or continental slope paleoenvironment during the Hauterivian-Albian. The studied limestone samples mainly exhibit low Mg-calcite characteristics with the general chemical formula of Ca_{98.35–99.34}Mg_0.66–1.65(CO₃). They are mostly represented by a diagnostic REE seawater signature including (1) slight LREE depletion relative to the HREEs (ave. 0.72 of Nd/Yb_N and ave. 0.73 of Pr/Yb_N), (2) negative Ce anomalies (Ce/Ce* = 0.38–0.81; ave. 0.57), (3) positive La anomaly (La/La* = 0.21–3.02; ave. 1.75) and (4) superchondritic Y/Ho (ave. 46.26). Studied micritic limestones have predominantly low Hf (bdl to 0.5 µg/g), Sc (bdl to 2 µg/g) Th (bdl to 0.9 µg/g) contents suggesting negligible to minor shale contamination. These findings imply that micritic limestones faithfully record chemical signals of their parental and diagenetic fluids. The succession also exhibits high ratios of Eu/Eu* (1.01–1.65; ave. 1.29 corresponding to the positive Eu anomalies), Sm/Yb (1.26–2.74; ave. 1.68) and La/Yb ratios (0.68–1.35; ave. 0.9) compared to modern seawater and wide range of Y/Ho ratios (29.33–70.00; ave. 46.26) which are between seawater and hydrogenetic Fe-Mn crusts. Several lines of geochemical evidence suggest water-rock interaction between parental seawater and basaltic rocks at elevated temperatures triggered by hydrothermal activity associated with Early Cretaceous basaltic magma generation. The range of Ce/Ce* values is suggestive of mostly oxic to dysoxic paleoceanographic conditions, with a sudden change to dysoxic conditions (Ce/Ce* = 0.71–0.81), in the uppermost part of the MF-1. This is followed by an abrupt deepening paleoenvironment with a relative increase in the oxic state of the seawater and deposition of deeper water sediments (MF-2 and MF-3) above a sharp transition. The differences in microfacies characteristics and foraminifera assemblage between MF-1 and overlying facies (MF-2 and MF-3) may also confirm the change in paleoceanographic conditions. Therefore, REEs data obtained from studied limestones have the potential to contribute important information as to regional paleoceanographic conditions of Tethys during an important period in Earth history. Full article

Mid-ocean ridge basalts (MORB) in the South China Sea (SCS) record deep crust-mantle processes during seafloor spreading. We conducted a petrological and geochemical study on the MORBs obtained from the southwest sub-basin of the SCS at site U1433 and U1434 of the International Ocean Discovery Program (IODP) Expedition 349. Results show that MORBs at IODP site U1433 and U1434 are unaffected by seawater alteration, and all U1433 and the bulk of U1434 rocks belong to the sub-alkaline low-potassium tholeiitic basalt series. Samples collected from site U1433 and U1434 are enriched mid-ocean ridge basalts (E-MORBs), and the U1434 basalts are more enriched in incompatible elements than the U1433 samples. The SCS MORBs have mainly undergone the fractional crystallization of olivine, accompanied by the relatively weak fractional crystallization of plagioclase and clinopyroxene during magma evolution. The magma of both sites might be mainly produced by the high-degree partial melting of spinel peridotite at low pressures. The degree of partial melting at site U1434 was lower than at U1433, ascribed to the relatively lower spreading rate. The magmatic source of the southwest sub-basin basalts may be contaminated by lower continental crust and contributed by recycled oceanic crust component during the opening of the SCS. Full article

Magnetite is an iron oxide mineral component of primitive Earth. It is naturally synthesized in different ways, such as magma cooling as well as olivine decomposition under hydrothermal conditions. It is probable magnetite played a significant role in biogenesis. The seawater used in the current work contained high Mg²⁺, Ca²⁺ and SO₄²⁻ concentrations, unlike the seawater of today that has high Na⁺ and Cl⁻ concentrations. It is likely that this seawater better resembled the ion composition of the seas of the Earth from 4 billion years ago. Cyanide and thiocyanate were common molecules in prebiotic Earth, and especially in primitive oceans, where they could act on the magnetite mechanism synthesis via Fe²⁺ interaction. In this research, magnetite samples that were synthesized under prebiotic conditions in the presence of cyanide or thiocyanate, (both with and without artificial seawater), showed that, besides magnetite, goethite and ferrihydrite can be produced through different Fe²⁺-ion interactions. Cyanide apparently acts as a protective agent for magnetite production; however, thiocyanate and seawater 4.0 Gy ions produced goethite and ferrihydrite at different ratios. These results validate that Fe³⁺ oxides/hydroxides were possibly present in primitive Earth, even under anoxic conditions or in the absence of UV radiation. In addition, the results show that the composition of water in early oceans should not be neglected in prebiotic chemistry experiments, since this composition directly influences mineral formation. Full article

Thioacetamide (TAA) is known to induce lipid accumulation in the liver. In the present study, we investigated the effects of magma seawater (MS) rich in minerals on hepatic lipid metabolism by evaluating lipogenic enzymes regulated by sterol regulatory element-binding proteins (SREBPs). Rats (n = 10 per group) were intraperitoneally injected with TAA (200 mg/kg bw) thrice a week for seven weeks in combination with a respective experimental diet. Rats in the TAA-treated group received either a chow diet (Control group) or a chow diet containing MS (TMS group, 2.05%) or silymarin (TSM group, 0.05%). Rats in the normal group were injected with PBS as a vehicle and received a chow diet. Rats in the TMS group showed significantly lower hepatic lipid concentrations than rats in the control group (p < 0.05). Hepatic protein expression levels of fatty acid synthase, SREBP-1, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and SREBP-2 were significantly downregulated in the TMS group, whereas carnitine palmitoyltransferase 1 levels were upregulated (p < 0.05). Hepatic thiobarbituric acid reactive substances levels were lower in the TMS group, whereas protein levels of glutathione peroxidase and catalase were elevated (p < 0.05). The effects of MS were comparable to those of silymarin. Our results evidently showed that MS inhibits hepatic lipid accumulation by suppressing lipid synthesis, accompanied by lipid oxidation and elevation of antioxidative status. Full article

The three volcanoes that are the object of this paper show different types of activity that are representative of the large variety of volcanism present in the Central Mediterranean area. Etna and Stromboli are sub-aerial volcanoes, with significant part of their structure under the sea, while the Marsili Seamount is submerged, and its activity is still open to debate. The study of these volcanoes can benefit from multi-parametric observations from the seafloor. Each volcano was studied with a different kind of observation system. Stromboli seismic recordings are acquired by means of a single Ocean Bottom Seismometer (OBS). From these data, it was possible to identify two different magma chambers at different depths. At Marsili Seamount, gravimetric and seismic signals are recorded by a battery-powered multi-disciplinary observatory (GEOSTAR). Gravimetric variations and seismic Short Duration Events (SDE) confirm the presence of hydrothermal activity. At the Etna observation site, seismic signals, water pressure, magnetic field and acoustic echo intensity are acquired in real-time thanks to a cabled multi-disciplinary observatory (NEMO-SN1 ). This observatory is one of the operative nodes of the European Multidisciplinary Seafloor and water-column Observatory (EMSO; www.emso-eu.org) research infrastructure. Through a multidisciplinary approach, we speculate about deep Etna sources and follow some significant events, such as volcanic ash diffusion in the seawater. Full article