The paleoenvironmental interpretation of fossil soils is enhanced by the identification of clay minerals formed in situ, as these phases provide important constraints on the chemical and climatic conditions prevailing during pedogenesis. Nevertheless, distinguishing between authigenic and allochthonous clays remains a notable challenge in paleopedology, particularly in soils where mineral assemblages commonly reflect mixtures of inherited and neoformed components. In this context, thermodynamic equilibrium offers a useful reference framework to evaluate the stability of mineral phases under defined geochemical conditions and to assess the degree to which natural systems deviate from these idealized states. In the La Tatacoa region of Colombia, mineral stability diagrams were used to assess clay provenance in gray bed paleosol successions of the La Victoria Formation ( 13.6–13.1 Ma) and red bed paleosol successions of the Villavieja Formation ( 13.1–12.0 Ma). A mineral stability model was developed for Al2O3–MgO–Na2O–K2O–SiO2–H2O systems, supported by X-ray diffraction (XRD) and X-ray fluorescence (XRF) data. Stability fields were constructed based on phyllosilicate dissolution equilibria (Al2O3–SiO2–H2O) and thermodynamically plausible assemblages constrained by the activity of Na, K, and Mg, while soil pH—reconstructed from geochemical proxies—was used to approximate paleoenvironmental conditions. The results show that Villavieja red bed paleosol successions formed under well-drained conditions exhibit mineral assemblages broadly consistent with the modeled equilibrium fields. In contrast, gray bed La Victoria waterlogged paleosol succession display departures from these fields, characterized by nontronite enrichment and smectite dominance, indicating mineralogical disequilibrium and suggesting the addition of fluvially deposited volcaniclastic material. These findings underscore the importance of thermodynamic modeling in identifying mineral provenance as well as transformation pathways and environmental shifts associated with water regime and climate variability in the Miocene paleosols of La Tatacoa.
Lake Öhningen (Middle Miocene, Mammal Neogene Zone MN7) on the southern flank of the Schiener Berg (SW Germany) is one of the most iconic European Fossil-Lagerstätten, yet the depositional environment and age of its sediments have remained poorly constrained. In 2021, a new excavation in the historical upper quarry exposed 8 m of lacustrine sediments, representing the upper part of the known deposits. The succession comprises calcareous laminites, unstructured and laminated clays and silts, marls and limestones, a conspicuous interval of micaceous fine sands and calcarenites with well-developed ripple marks, and several tuffite layers. The laminites are largely unfossiliferous and lack petrographically resolvable varve couplets, contrasting sharply with the organic-rich, varved laminites of ‘textbook’ meromictic maar-lake Fossil-Lagerstätten. The rippled sandstones document phases of shallow, higher-energy conditions and significant input of reworked Molasse sand from the catchment, most likely via tributaries and weather-generated inflow. Together with the mixed facies pattern, this challenges the traditional interpretation of Öhningen as a classic maar lake. Two brown tuffites interbedded within the lacustrine succession yield apatite fission-track ages of 13.7 ± 0.5 Ma (lower Serravallian), providing the first robust absolute ages for the Öhningen Beds. These ages are slightly older than the Herrentisch Deckentuff (12.6 ± 0.4 Ma) and overlap with published ages of the Wangen tuff cone, placing Lake Öhningen within an early phase of Hegau volcanic activity and confirming its MN7 assignment from biochronology. We interpret Lake Öhningen as a small, stratified but hydrologically open lake influenced by episodic volcanic, fluvial, and storm events, and recommend the neutral term ‘Lake Öhningen’ rather than ‘Öhningen Maar’ for this depositional system.
Located in the southern Aegean Sea, the Santorini volcanic complex represents one of the most geodynamically active and hazardous volcano–tectonic systems in the Mediterranean. Following the Late Bronze Age caldera-forming eruption ( 1600 BCE), the Kameni volcanic edifice emerged within the central caldera. On the northwestern flank of Nea Kameni, lava flows are superposed on unconsolidated pyroclastic deposits, primarily pumice and ash attributed to the 726 CE submarine explosive eruption. These units reside on a topographic step coincident with a major volcano–tectonic lineament, a geomorphological configuration that exhibits structural parallels to the pre−2018 sector collapse state of Anak Krakatau. Here, we employ the Landslide-HySEA numerical code to simulate tsunami generation and propagation resulting from various potential flank instability scenarios of Nea Kameni. Three distinct collapse volumes were modeled: 0.057 km3, 0.077 km3, and 0.13 km3. The simulations demonstrate substantial hazardous potential; a flank failure of 0.13 km3 has the potential to generate maximum coastal wave amplitudes of up to 39 m. Furthermore, all modeled scenarios result in tsunami heights exceeding 2 m at multiple critical coastal locations. These results indicate that such events would inflict severe damage on critical infrastructure and high-density maritime hubs situated along the inner caldera cliffs. Seafloor microbathymetry acquired through a photogrammetric tow-sled system suggests little remobilization despite ongoing volcano–seismic activity. Yet, our findings underscore the necessity for continuous monitoring of the structural stability of the Kameni volcanic edifice and emphasize the requirement to integrate flank-collapse mechanisms into the tsunami hazard assessment frameworks for Santorini.
The Eastern Bavarian Molasse Basin is used for geothermal energy, natural gas, and hydrogen storage, making constraints on the present-day stress field essential for assessing borehole stability and fault integrity. We integrate borehole breakout (BO) observations from 70 wells with formation integrity tests (FITs), an extended leak-off test (XLOT), drilling-mud pressures, RACOS® measurements, and geomechanical constraints to characterize stress orientation and magnitude. Oriented four-arm caliper data from 20 wells reveal BOs in 19 wells. The results confirm a regional N–S-oriented maximum horizontal stress ( S_Hmax ) but also document local stress rotations of up to 70–90° within the Aquitanian and Chattian. These rotations are associated with fault displacement, structural geometry, and the juxtaposition of mechanically contrasting units, indicating that mechanical heterogeneity can be as important as fault-related effects for local stress orientations. The XLOT at 1484 m TVD constrains S_hmin to approximately 28.2 MPa ( 19 MPa/km), while S_V is 33.7 MPa. Depending on pore pressure and XLOT uncertainties, S_Hmax ranges from 34.1–42.9 MPa, consistent with an independent frictional-limit estimate of 32.4–44.8 MPa, resulting in a strike-slip regime close to normal-faulting with relatively low differential stresses. BO formation at approximately 400 m, is facilitated by low strength. The value of integrating heterogeneous legacy datasets within a consistent geomechanical framework, providing a transferable workflow for stress characterization in mature hydrocarbon fields is demonstrated. The suggested low differential stresses in the uppermost 1.5 km provide favorable conditions for subsurface utilization of Eastern Bavarian Molasse Basin with a low likelihood of inducing significant seismicity.
ID-TIMS U–Pb isotope data were obtained for mini-fractions (1–5 grains) of accessory monazite extracted from various crystalline rocks of the Moslavačka Gora Massif in central Croatia (Tisza–Adria boundary). Based on these measurements, the following geological events could be constrained: the monazite-bearing, central S-type granite pluton of the massif (the Central Granite) intruded and crystallized at 82.5 ± 0.4 Ma. A penetrative low-pressure/high-temperature (LPHT), granulite facies metamorphic/anatectic event in metapelitic to metagranitic country rocks led to monazite growth also, likely between 82 and 83 Ma (Concordia age pooled from 6 fractions: 82.3 ± 0.9 Ma). Surprisingly, older monazite relics are unusually abundant in these rocks as well. Inconsistent (sub) concordant monazite ages between 85 and 95 Ma are interpreted as geologically meaningless mix ages of 82–83 Ma old monazite domains and relictic cores. In one of the metamorphic/anatectic rocks (Vrtlinska metagranite), two consistent concordant Lower Cretaceous ages (U238–Pb206 ages 123 and 124 Ma) were measured, hinting at a cryptic geological event at that time. In another anatectic granitoid rock, the Jelen grad metagranite (formation age ca. 490 Ma), two monazite fractions gave concordant Variscan ages (U238–Pb206 ages 311 and 337 Ma), evidencing a so far unknown Variscan regional metamorphism. With regard to its pre-Mesozoic geochronological record (Cambro-Ordovician granitic magmatism, Variscan regional metamorphism), the Moslavačka Gora Massif shows affinities to the Slavonian sector of the Tisza plate. Therefore, we propose it was positioned in the upper (Tisza) plate during the Upper Cretaceous, above the Sava Subduction Zone. We argue that the 82–83 Ma metamorphic/magmatic coining of the Moslavačka Gora Massif took place when subduction of oceanic crust under Tisza was about to end, giving way to a slab break-off/slab roll-back situation and an increased mantle heat flow with basaltic underplating near the Tisza plate edge.
