The Upper Oligocene-Neogene collisional succession in the SE segment of the Zagros Fold-Thrust Belt records progressive flexural subsidence related to topographic loading along the Main Zagros Thrust. Detailed analysis of lithofacies and clay mineral assemblages reveals vertical and lateral changes in the depositional environment of the foreland sedimentary rocks, spanning the shallow-marine carbonates of the Jahrum Formation and the alluvial-fan strata of the Bakhtyari Formation. Tectonic uplift and associated activity along the Main Zagros Thrust to the northeast have driven this shallowing-upward transition. The relatively uniform distribution of clay minerals suggests that mineralogy is primarily controlled by provenance rather than environmental fluctuations. The sedimentary environment can be generally modeled as a fan delta with various facies belts, i.e., proximal fan delta, mid fan delta, transition facies, delta slope, distal fan facies, shallow marine, and fluvial-alluvial systems. Lateral irregular variations in the sedimentary environment and thickness (10-250 m) during the Late Oligocene to Early Miocene along the Main Zagros Thrust can be attributed to the irregular shape of the Arabian plate and differing subsidence rates. However, the significant thickening of the Guri Member from the northwest to the southeast (2 to 700 m), coupled with a deepening sedimentary environment trend toward the southeast of the MZT, suggests that the Minab-Zendan Fault may have contributed to modulating accommodation space from the Middle Miocene onward. While this structure likely influenced the subsequent deposition of the Mishan and Aghajari formations, these patterns may also reflect broader regional subsidence variations.
The Late Mesozoic marks an important period in the tectonic evolution of southern Tibet. We examine the Late Mesozoic sedimentary sequences of the back-arc basins in southern Tibet using over 1000 detrital zircon U–Pb ages with in-situ Lu–Hf isotopic data, to fingerprint sediment provenance and reconstruct basin evolution. Our new geochronological results establish a refined chronostratigraphic framework and constrain the maximum depositional ages from ca. 157 to 84 Ma. Specifically, the Late Jurassic–Early Cretaceous successions (Quesangwenquan to Takena Formations; dated at 157–105 Ma) record multiple major zircon age peaks between 151 and 571 Ma with enriched Hf isotopic compositions (-24.56 to -0.13), indicating derivation mainly from the central Lhasa sub-terrane. In contrast, the Late Cretaceous Shexing Formation (ca. 84 Ma) exhibits a prominent age peak at ca. 125 Ma and predominantly positive ɛ Hf (t) values (+ 0.37 to +14), indicating a provenance shift toward the south Lhasa sub-terrane. This provenance turnover documents a major tectonic transition from an extensional back-arc basin to a compressional retro-arc foreland basin. These results provide key constraints on the paleotectonic architecture of the back-arc basins and highlight the Neo-Tethys Ocean northward subduction and the Lhasa–Qiangtang collision in driving changes in sedimentary provenance and paleogeography.
Accurately constraining the provenance of geological materials from archaeological contexts is critical for the subsequent interpretation of their significance. Stonehenge, the iconic Neolithic monument on Salisbury Plain, is significant in terms of well-documented long-distance transport of geological materials used in its construction, with many of the bluestones transported c. 225 km from West Wales. One stone at Stonehenge, the Altar Stone, is distinctive in terms of its composition, being composed of a well-sorted fine- to very fine-grained calcite-cemented sandstone. Its purpose at the monument, and when it was transported to the site, is unknown. Early interpretations of a provenance from West Wales have previously been discounted based on both geochemical and mineralogical data. More recently, the age of detrital zircon, rutile and apatite grains in the Altar Stone were used to infer a provenance from the Orcadian Basin of NE Scotland. This paper presents a detailed multi-proxy characterization of the sedimentology, geochemistry, detrital and diagenetic mineralogy of the Altar Stone based on both in situ analysis along with the analysis of museum samples confidently attributed to the Altar Stone, as direct sampling is not possible. While the previously published detrital grain dating supports a Laurentian source for the heavy minerals present in the Altar Stone, the overall petrology, heavy mineral assemblage, clay mineralogy and geochemistry show that many outcrops of the Old Red Sandstone (ORS) in the Orcadian Basin could not have been the source of the Altar Stone. To date, no examined outcrop area of the UK ORS can be shown to have the same suite of lithological and geochemical characteristics as documented for the Altar Stone. Consequently, this integrated dataset shows that the exact provenance of the Altar Stone is as yet unknown.
This study investigates Paleoproterozoic magmatic dynamics in the Ritápolis Arc of the Mineiro Belt, focusing on the Rhyacian (2.15–2.10 Ga) Rio Grande Pluton and Macuco de Minas granitoid. These rocks record part of the Paleoproterozoic magmatic evolution of the Brazilian sector of the São Francisco–Congo Paleocontinent, specifically within the southern sector of the Minas-Bahia Orogen. By integrating detailed field observations with petrographic, geochemical, and geochronological data, we constrain the processes of enclave formation and magma interaction and their implications for open-system magmatic evolution during the Rhyacian. The Rio Grande Pluton contains hornblendite enclaves displaying fragmentation, angular boundaries and pervasive felsic net-veining, locally forming hybrid rocks. The Macuco de Minas granitoid records magma interaction through cuspate–lobate diorite/tonalite–granite contacts, granitic back-veining, mechanical transfer of K-feldspar megacrysts into mafic enclaves and titanite-centered ocelli. Both plutons preserve microscale disequilibrium textures, including mineral resorption, zoning, and mafic clots. These observations indicate that the hornblendite enclaves are fragments of older hydrous mafic cumulate rather than in situ cognate cumulates. Repeated interaction between Rio Grande and Macuco de Minas magmas drove magma mixing and mingling highlighting the importance of open-system dynamic in the Paleoproterozoic.
Continental rift basins commonly exhibit strong lateral variability in subsidence rates during syn-rift deposition, but the extent to which this affects stratigraphic correlation and depositional architecture remains ill-constrained. We integrate wireline logs, core data and structural interpretations across the Horda Platform, northern North Sea, to examine the evolution of the Permian–Triassic syn- to post-rift alluvial systems. The syn-rift succession is characterised by weak continuity and correlation of stratigraphic units owing to localised fault-controlled accommodation. In contrast, post-rift successions display greater lateral continuity and more consistent proximal–distal trends as basin relief diminished and eustatic influence increased. Sediment flux and autogenic processes further modulated the stratigraphic expression of base-level change, locally obscuring tectonic and eustatic signals. Sedimentological analysis records a transition from dryland fluvial and aeolian systems to wetter fluvial and coastal-marine environments, while palaeosols and floodplain deposits record a corresponding transition from arid to humid climatic conditions during the Permian–Triassic time. Overall, stratigraphic and facies architecture observed in wells penetrating syn-rift successions is strongly dependent on well position relative to active faults and sediment-source areas. These results highlight the importance of detailed structural analysis for stratigraphic correlation in syn-rift basins, particularly where stratigraphic dating and well data are limited.
