The Oligocene provides an important interval for examining climatic and sedimentary variability following the Eocene–Oligocene transition, but the expression of orbital forcing in low-latitude marginal seas remains incompletely understood. We integrate natural gamma-ray (GR) logging and microfossil records from Well L9 in the Pearl River Mouth Basin, northern South China Sea, to establish a cyclostratigraphic framework spanning approximately 34.6–21.7 Ma. A floating chronology based on 405 kyr cycle counting was anchored using an independently constrained Oligocene–Miocene boundary horizon. Spectral analyses identify approximately 405 kyr, 100 kyr, and 40 kyr components, together with longer-period variability near 2.4 Myr and 1.2 Myr. Amplitude-modulation analysis reveals an approximately 1.2 Myr component in the 40 kyr envelope, supporting an obliquity-related interpretation. In contrast, the 100 kyr envelope contains approximately 1.6 Myr variability rather than a clear 2.4 Myr component, leaving the eccentricity-modulation origin of the latter unresolved. Palynological evidence indicates generally cool and humid conditions during the early–middle Oligocene, followed by late Oligocene warming. Comparison with published climate records suggests correspondence with six recognized cooling episodes, although chronological uncertainty limits precise event alignment. These results provide a regional chronological and paleoenvironmental framework and highlight the need to distinguish observed long-period sedimentary variability from its proposed orbital origin.
The Sakmara thrust–accretionary zone of the Mugodzhar segment, Southern Urals, preserves Precambrian–Lower Paleozoic volcanic and metasedimentary complexes whose hydrothermal evolution remains poorly constrained. This study compares aqueous fluid inclusions in quartz from the Lushnikov and Akai formations and amygdale-filling calcite from the Sugralin Formation. Homogenization temperatures (Th), final ice-melting temperatures, and NaCl-equivalent salinities were used to characterize contrasting fluid populations. Lushnikov quartz records Th of 95–119 °C. Akai sample E14 contains two populations at 165–178 °C and 240–280 °C, while samples E15 and E17 yield 190–200 °C and 235–250 °C, respectively. Sugralin calcite contains populations at 231–240 °C and 340–357 °C. Salinities range overall from 3.4 to 13.4 wt.% NaCl eq. The populations are consistent with repeated hydrothermal circulation influenced by volcanic heat supply, permeability, fracture reactivation, and later tectonic modification. Their chronology and trapping depths remain independently unconstrained. High Th in Sugralin calcite is compatible with submarine hydrothermal circulation, although natural post-entrapment re-equilibration cannot be excluded. The data provide a basis for evaluating polyphase thermal-fluid evolution in the Sakmara zone.
Fayalite (Fe2SiO4), the Fe-rich end-member of the olivine solid-solution series, is a key mineral in governing the thermodynamic behavior of Fe-rich planetary mantles. Here, using an iterative numerical approach constrained by previous experimental data, we extracted the volume, elastic properties, and, most importantly, the thermodynamic properties, including thermal expansion, isobaric heat capacity, entropy, and the Grüneisen parameter of fayalite up to 20 GPa and 2000 K. Our results demonstrate that all these thermodynamic properties are positively correlated with temperature but negatively correlated with pressure. Also, thermal expansion, isobaric heat capacity, entropy, and the Grüneisen parameter of fayalite are generally higher than those of San Carlos olivine, but show lower pressure dependence. This work provides a comprehensive thermodynamic dataset for modelling phase equilibria in the Fe–Mg olivine system and for refining interpretations of the thermal state of iron-rich planetary mantles.
In October 2016, Hurricane Matthew passed along the east coast of Florida, USA. Intense coastal erosion by storm waves made sandy beaches to reveal a multitude of trunk molds of ancient palm trees that once flourished along what is now the intertidal zone. A combination of coastal engineering efforts and natural processes caused the ancient palms to be reburied by beach sand. Fortunately, two retired geologists quickly responded after the hurricane ended, conducting a detailed investigation of the fossil palms. The trunk molds occur in two adjacent parallel zones that have an overall length of 1.4 km. The seaward-facing zone contains trunk molds where wood has been mineralized by calcite, enclosed within a coquinoid outer zone. The molds are associated with areas of gray coquina. In contrast, the landward-facing zone is characterized by trunk molds that contain mummified wood tissues within a weakly cemented sand matrix. These molds have thin coquina outer boundaries, but they occur within loose beach sand. Geological and botanical characteristics suggest a Holocene age for the ancient palm groves; their occurrence and demise are associated with small-scale regression/transgression cycles. A 14C radiocarbon age of 160 yrs BP for one of the younger cycles suggests the possibility that the landward- facing coastal palm growth was related to tidal changes that were related to the temperature fluctuations of the Little Ice Age (1300–1850).
Acid mine drainage (AMD) produces iron (Fe)-rich precipitates that retain arsenic (As), forming contaminant stores susceptible to disturbance during mine rehabilitation. We re-examined aqueous As partitioning and solid-phase geochemical evidence from a 1996–1998 investigation at the abandoned Pintor W–As mine, Portugal. During two 1996 sampling campaigns, adit drainage had pH 3.1–3.9 and operationally dissolved As concentrations of 1126–2208 µg L−1. These concentrations decreased by 99.5–99.8% over 1.8 km, but corresponding changes in As loads could not be determined without concurrent flow measurements. Streambed coatings contained 2.9–4.0 times more As than paired sediments, and an Fe-rich outlet crust had 3.85% aqua regia-extractable As. Dark-oxalate extraction accounted for 48–82% of recovered As across the analysed solids. The concentration gradient coincided with As enrichment in Fe-rich deposits, consistent with Fe-associated retention. Later investigations commissioned by Empresa de Desenvolvimento Mineiro, S.A. (EDM) confirmed that acidic, As-bearing drainage remained present in 2007 and 2022–2024. The historical evidence identifies priorities for pre-intervention characterisation of As-bearing deposits, monitoring particulate As export during excavation, evaluating dissolved and particulate As loads through the proposed treatment system, and assessing As accumulation in channel deposits and treatment residues.
