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Geologica Acta, vol. 23, no. 19, 18 p. TomÁs S., Parcerisa, D. Cantarero I., Baqués V., Salas R. & Travé A. (2025).- Linking early diagenesis and relative sea-level changes in ancient corals: a multiproxy approach from the Benassal Formation (Lower Cretaceous, Maestrat Basin, E Spain)- The Aptian shallow-water carbonate platform of the Benassal Formation in eastern Spain (Maestrat Basin) contains facies dominated by scleractinian corals. Corals and coral reefs are widely used as environmental archives; however, the effects of their complex diagenetic evolution are a major factor impacting reliable reconstructions of the environments. This study addresses the environmental signatures (i.e. relative sea-level changes) and burial conditions that controlled the various diagenetic minerals present in the Aptian coral facies. A multiproxy approach including petrographic and geochemical evaluation reveals the diagenetic pathways, fluid compositions and timing accounting for the syn- to post-depositional history of this ancient coral facies. Cc1, which shows low Fe and Mn content and high Na content, precipitated within the primary porosity, alongside the replacement of coral skeletons, in a mixing zone dominated by marine waters. Cement Cc2, characterized by its higher Fe and Mn content and low Na values, precipitated in the mixing zone dominated by meteoric waters related to a relative sea-level drop. Cement Cc3, distinguished by low Fe and Mn content and high Na content, reflects a subsequent phase of increased marine influence, likely associated with a relative sea-level rise. Silica and isolated rhombohedral dolomite crystals formed concurrently in this mixing zone. During intermediate burial, saddle dolomite and cement Cc4 precipitated from high-temperature formation brines. Finally, during uplift, meteoric fluids caused the calcitization of previously formed dolomite rhombohedra. Geologica Acta, vol. 23, no. 20, 17 p. Sethy P.C., Naik A. & Nayak R. (2025).- Geochemical characterization and tectonic significance of the granite gneiss in the Tikiba Granitic Complex, Northwest Odisha, India- The study explores the Precambrian tectonic evolution and the growth of continental crust in the southern region of the North Odisha Singhbhum Craton (NOSC), delving into the potential petrogenetic processes and source characteristics. The Tikiba Granitic Complex (TGC) is in the contact area of the Eastern Ghat Mobile Belt (EGMB) and the NOSC. The present study involves the geochemical characteristics of TGC granitoids and their geochemical variations. Petrographically, the TGC is comprised of alkali feldspar granite, monzogranite to granodiorite. The major element geochemistry reveals calc-alkalic, ferroan to magnesian affinities, and a metaluminous, peraluminous and peralkaline character. It is enriched in LILE and HFSE like Yb, Sm, Zr and Y. The (La/Yb)N values range from 4.0–26.1 and exhibit distinct negative Eu anomalies (Eu/Eu*) (0.4-0.6). This granitic complex shows high ?REE contents of 176-860ppm with variable enrichment in LREE. Both REE and other incompatible element compositions define an A-type affinity. Based on geochemical data, we conclude that these granitoids have probably derived from a predominant crustal source with variable mantle characteristics in a post-orogenic setting. Geologica Acta, vol. 23, no. 21, 42 p. Albert-Villanueva E., Bover-Arnal T., Ferràndez-Cañadell C., GonzÁlez L., Esteban M. & Salas R. (2025).- Lower Miocene carbonate platforms of the Falcòn Basin (NW Venezuela) compared to the offshore Perla Field reservoir- Based on field data collected in the northern and southern Falcòn Basin (Venezuela), this paper presents a comprehensive monograph that reports on the age and sedimentary evolution of the San Luis and Churuguara formations. It integrates platform-to-basin depositional models through facies distribution and stratal architecture, a palaeogeographic reconstruction, larger foraminifera biostratigraphy, sequence stratigraphy, and the evaluation of the accommodation history. An additional aim is to compare these onshore mixed carbonate-siliciclastic systems with the Oligo-Miocene subsurface carbonate reservoir of Perla in offshore Gulf of Venezuela, considered the largest gas discovery ever in Latin America. The carbonate platforms studied formed as a result of a second-order transgressive event, and corresponded to distally steepened or undifferentiated ramps dominated by coralline algae and larger foraminifera. The presence of Miosorites americanus and Annulosorites spiralis dates the San Luis and Churuguara formations to the Early Miocene. The miogypsinid associations identified further distinguish between the Aquitanian and Burdigalian stages. The San Luis and Churuguara platforms exhibit a general aggradational trend, while the Perla carbonates have been interpreted as a retrogradational unit. Third-order T-R sequences interpreted from these successions were mainly influenced by differential tectonic subsidence. Additionally, major regional regressive events in the Falcòn Basin and Perla Field coincide with global glaciations, highlighting the influence of eustatic changes. However, the Perla reservoir exhibits significant differences in thickness, spatial extent and sedimentary architecture compared to the onshore equivalents. The differences arise from variations in tectonic and palaeotopographic settings, accommodation and sedimentation rates and influence of adjacent siliciclastic systems. As a result, predicting the sedimentary architecture of carbonate reservoirs in this region using a generalized depositional model has proven to be challenging. Geologica Acta, vol. 23, no. 22, 18 p. Canales-García I., Pérez-Cruz G., Orozco-AlmazÁn L. & Urrutia-Fucugauchi J. (2025).- Basement structural controls on the Jurassic sedimentary sequences in the Tampico-Misantla Basin, northeastern Mexico from a 3-D seismic reflection study- The Tampico-Misantla basin is a mature oil rich province in northeastern Mexico with large unconventional oil plays currently being explored. Results of a 3-D seismic reflection study of the basement and Jurassic sequences are used to analyze the basement influence on the sedimentary sequence and basin structure, by mapping the seismo-stratigraphic horizons for the (Tithonian) Pimienta, (Kimmeridigian) Taman/San Andrés, (Oxfordian) Santiago, (Callovian) Tepexic/Huehuetepec and (Bathonian) Cahuasas formations. The basement is characterized by stepped NW-SE tilted blocks of horst and grabens. The horst sections to the northeast are found at depths of 3,200m and get deeper up to 6,500m to the southwest. Blocks bounded by planar curved high angle normal faults with NW-SE and NE-SW orientation form a Triassic-Jurassic system, with two major pulses during the Bajocian and Oxfordian. Vertical slips of main faults are variable and may reach 2,000m. Basement blocks play major roles in defining the depositional processes, with thickness and distribution of overlying sedimentary units. Based on our analysis the Middle Jurassic Cahuasas Formation units were deposited predominantly in continental environments and exhibit large thickness variations. The Callovian Tepexic and Huehuetepec formations were deposited in transitional and shallow marine environments, with relatively uniform thickness and distribution. The Oxfordian to Tithonian Santiago, Taman/San Andres and Pimienta formations were deposited in marine environments, showing multiple fault deformation with tendency of progressively pinching out against the topographic highs. The thickness variation in the Santiago Formation suggests episodes of increasing subsidence and fault reactivation. The seismic volume models constraint the basement structures and Jurassic sequence stratigraphy in the Tampico-Misantla basin Geologica Acta, vol. 23, no. 23, 27 p. Mutlu S. (2025).- Tectonic geomorphology of theSemdinli Yüksekova Fault Zone (SYFZ) and Baskale Fault Zone (BFZ) (SE Turkey): Evidence from morphometric analysis and neotectonic structures- The collision between the Arabian and Eurasian plates resulted in the uplift of The East Anatolian Province of Shortening (EAPS). Within the EAPS, the faulting mechanism is characterized by right- and left-lateral strike-slip faults, thrust faults, and a relatively limited occurrence of normal faults. When examined on a regional tectonic scale, about 70% of the deformation of the EAPS is controlled by strike-slip faults. However, the proportion of right- and left-lateral strike-slip faults contributing to this deformation remains unknown and is poorly understood. Two adjacent fault zones located at the southeastern margin of EAPS were selected to investigate the deformation associated with right- and left-lateral strike-slip mechanisms using morphometric analysis along with field observations. These fault zones are the Semdinli Yüksekova Fault Zone (SYFZ), which exhibits right lateral deformation and is defined as a seismic gap, and the Baskale Fault Zone (BFZ), which has a left lateral deformation and that caused a destructive earthquake in (23/02/2020, Mw: 5.9). To elucidate the relative degree of active tectonics of both fault zones, morphometric analysesis were applied alongside field surveys. An adaptation of the relative active tectonic Index (Iat) was computed for Baskale and Yüksekova-Semdinli sub-basins in the region. The results supported by field observations indicate that the drainage basins are largely controlled by fault activity and exhibit a youthful topographic character. Moreover, quantitative data derived from the Index of Active Tectonics (IAT) reveal that the SYFZ demonstrates very high tectonic activity, while the BFZ displays moderate levels of active tectonic deformation. These numerical findings, which indicate ongoing deformation, are further corroborated by field observations that clearly reflect the surface expressions of tectonic activity. Geologica Acta, vol. 23, no. 24, 17 p. Machek M., RoxerovÁ Z., Kusbach V., KucerÁkovÁ M. & Vratislav S. (2025).- Evolution of microstructure and texture in a small-scale high-temperature marble shear zone from the Ossa-Morena Zone (Iberian Variscan Belt)- This research investigates microstructures and crystallographic preferred orientation in a high-temperature Variscan small-scale shear zone within marbles from the south-western Ossa-Morena Zone (Iberian Variscan Belt). Quantitative microstructural analysis, and crystallographic preferred orientation data obtained via neutron diffraction and electron backscatter diffraction mapping allowed to infer the deformation mechanisms and active slip systems. The primary S2 foliation, formed during the Variscan D2 deformation phase, is characterized by high-temperature grain boundary migration recrystallization mechanism, coupled with intracrystalline slip on the c(0001)<-12-10> system. Ductile shear zone development, marked by a coarse-grained microstructure with pronounced shape preferred orientation parallel to the shear plane, involved both high-temperature grain boundary migration recrystallization and intracrystalline dislocation creep, accommodated by f{-1012} <10-11> and r{10-14} <-2021> slip systems. These results indicate a high-temperature extensional origin for the S2 foliation and the shear zone formation during the D2 deformation event of the Ossa-Morena Zone, linked to thermal effects from the Beja Igneous Complex plutonism and regional partial melting driven by asthenosphere upwelling (~353–335Ma). Geologica Acta, vol. 23, no. 25, 19 p. Oliva-Urcia B., RomÁn-Berdiel T., Torres-Lòpez S. & Villalaín J.J. (2025).-Shortening-controlled magnetic fabrics in the Alpine thrust front of the Cantabrian Mountains- The magnetic fabrics (or anisotropy of magnetic susceptibility) are used in this work to decipher thrust kinematics in the Cantabrian Mountains (western Pyrenees). Most of the analyzed rocks (total of 51 sites) correspond to the Mesozoic rifting and post-rifting stages (Triassic, Jurassic and Cretaceous) rocks in the Asturian-Leonese region, whose alpine structure is controlled by south-verging, basement-involved thrusts. Paramagnetic minerals are scarce as shown by the thermomagnetic analyses, and maghemite/hematite predominates as carriers of the magnetic fabric. The rifting phase is recorded by a primary fabric that remained unaltered during the alpine contraction, whereas the magnetic fabric of the Albian and Upper Cretaceous rocks show a reorientation due to contraction, which is better recorded in the fine grained continental facies of the Utrillas Group than in the carbonatic rocks overlying them. In the contractional fabrics found, the magnetic lineation delineates the thrust front enhancing the changes of the local shortening direction along strike. This reinforces the hypothesis of a strong control of the thrust direction by inherited structures. Geologica Acta, vol. 23, no. 26, 11 p. Ruh J.B. (2025).-Grain-size reduction diminishes the impact of viscous shear heating in lithospheric mantle shear zones- Active plate tectonics require weak boundaries that accommodate large strain over long time periods. Many studies argue that shear heating converted from dissipated mechanical energy may be responsible for the necessary weakening in the mantle lithosphere to initiate and sustain weak plate boundaries. Here, I present simple numerical simulations of pure olivine systems with a composite diffusion-dislocation creep rheology coupled to a self-consistent grain-size evolution model to investigate the effect of grain-size reduction on shear heating. Results demonstrate that the weakening related to grain-size reduction and the activation of grain-size-sensitive diffusion creep undermines the importance of shear heating in mantle shear zones. Depending on shear zone width, shear velocity and apparent stresses, estimations on ideal shear zone widths and viscosities are presented. Geologica Acta, vol. 23, no. 27, 21 p. Bover-Arnal T., Pascual-Cebrian E., Moreno-Bedmar J.A. & Salas R. (2025).- Strontium-isotope stratigraphy of the Aptian–Albian transition in the western Maestrat Basin (E Iberia)- The Aptian–Albian transition in the Maestrat Basin (E Iberian Chain) encompasses two lithostratigraphic units: the Benassal and Escucha formations. In some sectors of the basin, such as the western Galve and Las Parras sub-basins, this stratigraphic interval recorded a progressive shift from widespread carbonate platform settings to coastal siliciclastic-influenced and coal-bearing environments. Due to the transitional nature of this interval, establishing a clear stratigraphic boundary between the upper part of the Benassal Formation and the lower part of the Escucha Formation is challenging. Additionally, there is no unanimous agreement on the age range of these formations. To shed light on the stratigraphic location of the boundary between the Aptian and the Albian, strontium-isotope analyses were carried out on thirteen low-Mg calcite oyster shells to derive numerical ages. In the Las Parras Sub-basin, the 87Sr/86Sr values obtained from the siliciclastic-influenced transitional deposits between the Benassal and Escucha formations, as well as from the lowermost part of the Escucha Formation, range from 0.707282±0.000002 to 0.707410±0.000002. These Sr-isotope ratios translate into numerical ages that constrain this stratigraphic interval to the early Albian. The oyster shells collected in the Galve Sub-basin exhibit a higher degree of diagenetic alteration. Nevertheless, the least altered specimens analysed from the lower part of the transitional facies between the Benassal and Escucha formations in this latter sub-basin yielded Sr-isotope ratios between 0.707197±0.000003 and 0.707256±0.000002. These values correspond to ages spanning from the latest Aptian to the earliest Albian. Accordingly, in most sectors of the western Maestrat Basin, the Aptian–Albian boundary is likely to be stratigraphically located at the lowermost part of the transitional facies between the Benassal and Escucha formations. Geologica Acta, vol. 23, no. 28, 18 p. Calugaru M.E., Munteanu M., Wäll M. & Isac A. (2025).- Trace element contents in bornite, chalcopyrite and pyrite (LA-ICP-MS) from Miocene porphyry copper-gold deposits from Metaliferi Mountains, Romania- In porphyry systems, valuable elements such as Au, Ag, Te, Se and Bi are found in trace contents associated with Cu and Fe sulfides. The relations between sulfide and the trace element contents, as well as the role of physicochemical factors in the uptake of different trace elements are still being assessed. This study focused on understanding how these elements are concentrated in selected sulfides (pyrite, chalcopyrite and bornite) and on the relation between the measured trace element composition of these sulfides and the hydrothermal alteration types in six porphyry deposits from Romania: Roșia Poieni, Bucium-Tarnița, Colnic, Rovina, Valea Morii and Bolcana. Based on LA-ICP-MS micro-analytical data, bornite is revealed as the main host for Bi (1077ppm), Se (810ppm), Ag (312ppm) and Te (43.73ppm). Chalcopyrite is also relatively rich in Se (199-403ppm), Ag (1.88-49.97ppm) and Te (1.95-36.06ppm). Pyrite is enriched in Co (98.81-704ppm), Ni (3.81-20.68ppm), As (2.13-166ppm), Se (24.65-729ppm) and Te (0.99-11.75ppm). These elements occur in the host sulfides as solid solution and as mineral microinclusions. Gold content is <0.2ppm in both Cu-Fe sulfides and pyrite. There is no significant variation in trace element ratio in chalcopyrite (Se/In) and in pyrite (Co/Ni, Co/Cu, Ag/Co) when comparing results from potassic-altered with chloritic-sericitic altered samples. Based on trace element results and micro-textural features of studied minerals, we suggest that these elements were initially incorporated in the crystal lattice during the potassic alteration and the overprinting of chloritic-sericitic alteration caused the exsolution and redistribution of trace elements within their host minerals. | |
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