This research aims to understand the genesis and diagenetic pathway of dolomite in the Lower Cretaceous oilfield carbonates of Abu Dhabi (United Arab Emirates) based on its petrographical and geochemical signatures. The “A Formation dolomite” occurs as multiple stratiform beds associated commonly with evaporites (anhydrite nodules). Petrographic observation indicates that dolomite mainly occurs in mud-dominated facies, such as wackestone and mudstone deposited under a sabkha environment. This occurrence implies the dolomitization of precursor carbonates by hypersaline seawater immediately after the deposition at the intertidal to supratidal sabkha environment. This interpretation is supported by a high Na concentration of up to 5,000 ppm. The ⁸⁷Sr/⁸⁶Sr of the dolomite falls in a range of coeval seawater of the Lower Cretaceous. Hence, the dolomitizing fluid was originated from the evaporative seawater. The low δ¹⁸O values of the dolomite imply an overprint of the original geochemical signatures by diagenetic processes in burial settings. The dolomites were subjected to dedolomitization in burial settings, as proven by the depletion of trace elements and precipitation of calcite cements. The slightly increased Fe and slightly decreased Sr concentrations indicate that the dolomite interacted with another fluid such as an interstitial water in the buried depth. The deep burial diagenesis is confirmed by the high dolomite formation temperatures in a range of the reservoir temperature. This is because dolomite δ¹⁸O is largely reset by the ongoing dolomite-to-dolomite recrystallization, and the δ¹⁸O values no longer keep the initial values of evaporative dolomitization at the surface. The diagenetic pathway of the dolomite yielded different petrographic textures and, consequently, porosity and permeability of the reservoir rock. During the deep burial phase, geochemical compositions (δ¹⁸O and trace elements) were modified through dolomite-to-dolomite recrystallization, but there was no significant new dolomite formation as indicated by the initial seawater ⁸⁷Sr/⁸⁶Sr of the dolomite. Therefore, the main determining factor of the petrographic texture was the degree of dolomitization (= formation and supply of hypersaline water) in surface environments. As dolomitization progresses in mud-dominated facies, the permeability first increases as the fine-grained matrix micrite is replaced by larger dolomite crystals. However, as dolomitization progresses further, both porosity and permeability decrease due to dolomite cementation and to the replacive dolomitization. Therefore, the degree of evaporative dolomitization should not be too strong or too weak for the excellent reservoir rock properties of the “A Formation dolomite".

Hornblende peridotite occurs in the Nishidohira metamorphic rocks in the southern Abukuma Mountains (Tagiri, 1971 Jour. Japan. Assoc. Min. Petrol. Econ. Geol.; Tanaka et al., 1982 Jour. Japan. Assoc. Min. Petrol. Econ. Geol.). This peridotite is characterized by large poikilitic hornblende grains with rounded olivine (± pyroxenes) grains (we call poikilitic hornblende peridotite hereafter). Poikilitic hornblende peridotite is frequently associated with granitic and metamorphic belts (e.g., Tiepolo et al., 2011 Jour. Petrol.; Itano et al., 2021 Lithos) and in the lower crust to upper mantle sequence of ophiolites (Ozawa, 1984 Jour. Geol. Soc. Japan; Ishiwatari 1985 Jour Petrol.) as a minor component. Poikilitic hornblende peridotite is also found as a sub-arc xenolith (Ishimaru et al., 2009 Jour. Mineral. Petrol. Sci.). The origin and tectonic implications of the poikilitic hornblende peridotite are unclear. The geochronological relationships of poikilitic hornblende peridotite and surrounding rocks provide essential information about their origin and tectonic implications. U-Pb zircon dating provides the timing of magmatic and metamorphic events. We report petrological characteristics and U-Pb zircon ages of the Nishidohira poikilitic hornblende peridotite. Poikilitic hornblende grains exhibit zoning in color and chemical composition, such as a dark core of high TiO₂-Al₂O₃ and a green margin of low TiO₂-Al₂O₃. The dark-colored core of hornblende contains numerous small ilmenite lamellae. Clinopyroxene often occurs in vermicular form with hornblende. Melt compositions calculated from hornblende and pyroxene core compositions based on melt-mineral partitioning (Shimizu et al., 2017 Geochim. Cosmochim. Act for amphibole, and Hart & Dunn, 1993 Contrib. Mineral. Petrol for clinopyroxene) are characteristic of continental arc magmas. The U-Pb zircon age for poikilitic hornblende peridotite is about 120 Ma, which is interpreted as a magmatic age. This period of arc magmatism is consistent with the U–Pb zircon age of gneissic granitic rocks in the studied area (Tagiri et al., 2011 Island Arc), suggesting the development of lower curst in prior to the widespread granitic plutonism in the southern end of the Abukuma Mountains at ca. 110–100 Ma (Takahashi et al., 2016 Island Arc).

Magnetic analysis of soil and sediment in room temperature is a non-destructive method, therefore it has been used geological and environmental investigations. Many illegal activities have been occurred in beach. In order to verify the usefulness of magnetic analysis in forensic research, the beach sediments were collected at nine sites from Shimokita Peninsula in Japan, were measured, and discussed whether the results reflect to regional characteristics. Concentration-dependent magnetic parameters: low-field magnetic susceptibility, anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM) indicated relative higher values at sites where were located near the sedimentary mines of titanium (Ti) and iron (Fe). Results of thermo magnetometry suggest that magnetic carriers of the sediments are mainly magnetite (Fe₃O₄), and pyrrhotite (Fe₇S₈) is recognized around Ti-Fe mines sites. Result of the concentration-dependent magnetic parameter imply that the amount of magnetic minerals in the beach sediments will be regionally characterized. The IRM curves in low temperature are also characteristic per the sampling sites. The comparison of the magnetic grain size parameters to the Curie points also could characterize per the sampling sites. We think that magnetic analysis of the beach sediments will be an effective method to estimate the provenance of beach sediments in forensic research.

Project COESS (Chemistry, Observation, Ecology of Submarine Seeps) was founded and endorsed by UNESCO in 2022 as part of the UN Decade of Ocean Science for Sustainable Development. The project currently involves 27 researchers from 16 research institutions with the goal of studying cold seeps and hydrothermal vents and promoting education of the public regarding these unique ecosystems.

In October, 2023 we deployed to Fugro Shallow Environmental Landers (SFEL) on Torigakubi Spur, offshore Joetsu in order to do long-term monitoring of an active methane seep area. The two SFEL are still deployed and will be recovered in October, 2024. During the past year they have been measuring changes in salinity, temperature, pressure, turbidity, pH, oxygen, and methane. Located roughly 60 km from the epicenter of the Noto earthquake in January, the landers also will provide an opportunity to see the effects of seismic activity on methane seeps.

In June, 2024 we deployed a prototype Full Depth Drone to document the conditions of the landers prior to recovery. We found the landers covered with dark sediment or biofilm, while the internal parts appear to be colonized by microbial mats. Squid, sea cucumbers, whelks, snow crabs and shrimp were also found living near or on the landers (Fig. 1). We also noted several interesting features in the area including a fresh exposure of shallow gas hydrate and a “garden” of cnidarians. A number of cnidarians occurring in Torigakubi Spur exist in solitary and branching tubular form and also host a number of other macrofaunal species clinging to their surface including other cnidarian epibionts. During the same drone deployment, we also observed seafloor markers left by earlier ROV deployments and hope to compare our new video footage with video footage collected by members of our team over 10 years ago.