Search Results (60)

Synthesis of published and new data from the Govorov and Kocebu guyots provide geochemical and chronostratigraphic constraints on hydrogenetic cobalt-rich Fe-Mn crusts from the Western Pacific Magellan Seamount Trail (MST). The history of the crusts began about 65–60 Ma, when the relict layer R was deposited in the Campanian—Maastrichtian and Late Paleocene along the shores of guyots. The growth of the old-generation crusts continued in the Late Paleocene—Early Eocene (Layer I-1) and in the Middle—Late Eocene (Layer I-2) in a shallow-water shelf environment. The younger layers formed in the Late Oligocene—Early Miocene (Layer I-2b), Miocene (Layer II), and Pliocene—Pleistocene (Layer III) at depths about the present sea level. The precipitation of Fe and Mn oxyhydroxides from seawater was interrupted by several times, with the longest gap from 38 to 26.5 Ma between the old (R, I-1, and I-2) and young (I-2b, II, and III) layers. Fe and Mn oxyhydroxides in the crusts were affected by two global events of phosphogenesis in the Pacific: Late Eocene—Early Oligocene, from 43 to 39 Ma (Layers R, I-1, I-2) and Late Oligocene—Early Miocene, from 27 to 21 Ma (Layer I-2b). The trace element patterns in different layers of the Co-rich Fe-Mn crusts are grouped using factor analysis of principal components (varimax raw) into four factors: (1) +(all REEs except Ce and La); (2) +(Ce, La, Ba, Mo, Sr, Pb); (3) +(Zr, Hf, Nb, Rb, As)/-Pb; (4) +(U, Th, Co, As, Sb, W)/-Y. The factor score diagrams highlight fields which are especially contrasting for Layers I-1, I-2, and II + III according to factors 2 and 4. Consistent REE and Y variations in Layers I-2b → II → III of the crust from Pallada Guyot correlate with gradual ocean deepening between the Late Oligocene—Early Miocene and Present when the MST guyots were submerging. Large variations in the trace element contents across coeval layers may be due to the hydrodynamics of currents on the guyot surfaces. Furthermore, the geochemistry of the crusts bears effects from repeated episodes of Cenozoic volcanism in the MST region of the Pacific Plate. Higher contents of Nb, Zr, As, Sb, and W in the younger layers II and III may result from large-scale volcanism, including Miocene eruptions of petit-spot volcanoes. Full article

The rich Eocene larger benthic foraminiferal (LBF) assemblages in the vicinity of Verona have long been well known. However, they are described in detail only from the Ypresian to Bartonian interval. Here, we present the results of our morphometrically based study of Priabonian LBF. The lowermost part of the succession, just above the uppermost occurrence of giant Nummulites (N. biedai), outcrops at Monte Cavro and contains Heterostegina reticulata multifida and Nummulites hormoensis as major constituents. These taxa clearly determine the earliest Priabonian Shallow Benthic Zone (SBZ) 18C. Slightly younger strata can be analyzed in the other three studied exposures on the northern side of Castel San Felice. These beds already represent the early Priabonian SBZ 19A Zone based on the first appearing Spiroclypeus sirottii and the presence of Heterostegina reticulata mossanensis and Nummulites fabianii (replacing H. r. multifida and N. hormoensis, respectively). The most abundant LBF in these beds are the very diverse and well-preserved orthophragmines represented the families Discocyclinidae (genera Discocyclina and Nemkovella) and Orbitoclypeidae (genera Orbitoclypeus and Asterocyclina). They determine the Orthophragmine Zone (OZ) 14. The distinction of six species of the genus Discocyclina (especially that of D. euaensis from D. dispansa) is discussed in detail. The exposures around Castel San Felice are considered as key localities for the SBZ 19A and OZ 14 Zones, containing their key LBF assemblages. Consistently, both orthophragmine and LBF range charts for the late Lutetian to Priabonian are updated. Full article

The Eastern Carpathians are thrust to the east and north over their Eastern European foreland, tectonically covering it over an area several hundred kilometers across. Information about the nature of the underthrust part of the Carpathian foreland can be obtained from the rock fragments preserved in the sedimentary successions of the Carpathian fold and thrust belt, specifically in the Outer Dacides and the Moldavides. Fragments of felsic rocks occurring within the sedimentary units of the Upper Cretaceous successions of the Moldavides have long been attributed to the Cuman Cordillera—an intrabasinal ridge in the Eastern Outer Carpathians. This work is the first complex geochemical and geochronological study on the exotic igneous clasts of the Cuman Cordillera. Igneous clasts from the southern part of the Moldavides (Variegated clay nappe/formation) are investigated here. They include mainly granites and rhyolites. Phaneritic rocks are composed of cumulus plagioclase, albite, amphibole and biotite, and intercumulus quartz and potassium feldspar, with apatite, magnetite, sphene, and zircon as main accessories, while the porphyritic rocks have a mineral assemblage similar to that mentioned above, displayed in a porphyritic texture with a usually crystallized groundmass. SHRIMP U-Pb zircon dating indicated the 583–597 Ma age interval for magma crystallization. Based on calcareous nannofossils, the depositional age of the investigated igneous clasts is Cenomanian to Maastrichtian, implying that the Cuman Cordillera was an emerged piece of land, herein an active source of sediments in the flysch basin for at least 40 Ma, from the Early Cretaceous (Aptian) to the Late Cretaceous (Maastrichtian). The intrusive and subvolcanic rocks show similar trends for trace and major elements, evincing their comagmatic nature. The enrichment in LILE and LREE relative to HFSE and HREE, as well as the element anomalies (e.g., negative Nb, Ta, and Eu and positive Rb, Ba, K, and Pb) suggest a convergent continental plate margin tectonic setting. Mineral chemistry suggests magma crystallization in relatively oxic conditions (magnetite series), during ascent within a depth of 15 km to 5 km. The igneous rocks attributed to the Cuman ridge display compositional and geochronological features similar to Brno and Thaya batholiths in the Brunovistulian terrane, which could be a piece of the Carpathian foreland not covered by the Tertiary thrusts. Our data confirm the non-Carpathian origin of the igneous clasts, revealing a Neoproterozoic history of the Carpathian foreland units, which include a Cadomian/Pan-African continental arc, exposed mainly during the Late Cretaceous as an intrabasinal island of the Alpine Tethys, traditionally known as the Cuman Cordillera. Full article

The Cretaceous oceanic red beds (CORBs) and their implications for “oceanic oxic events” have been widely studied by geologists globally. In southern Tibet, CORBs are extensively distributed within the Upper Cretaceous strata of the northern Tethyan Himalaya (NTH). A well-exposed, CORB-bearing, mixed carbonate–shale sequence is found in the Zhangguo section of Rilang Township, Gyangze County. The Chuangde Formation in this section is characterized by well-preserved CORBs, which include reddish shale, limestone, marlstone, and interbedded siltstone. These CORBs are stratigraphically overlain by the Jiabula/Gyabula Formation (predominantly shale) and underlain by the Zongzhuo Formation (“mélange”). However, the precise age, depositional environments, and regional/global correlations of these CORBs, as well as their implications for synchronous versus diachronous oceanic oxic events, remain to be fully understood. In this study, a comprehensive analysis of foraminiferal biostratigraphy and microfacies is conducted for the CORB-bearing Chuangde Formation and the upper Jiabula (Gyabula) Formation in the Zhangguo section. Five planktic foraminiferal biozones including Dicarinella asymetrica, Globotruncanita elevata, Contusotruncana plummerae, Radotruncana calcarata, and Globotruncanella havanensis are identified through detailed biostratigraphic analysis, confirming a Campanian age for the Chuangde Formation and its CORBs. These findings are broadly correlated with typical Upper Cretaceous CORBs in pelagic–hemipelagic settings across the NTH in southern Tibet. Nine microfacies and four facies associations are identified within the Upper Cretaceous strata of Gyangze and adjacent areas through field and petrographic analyses. Notably, it is indicated that planktic foraminiferal packstone/grainstone CORBs were deposited in outer shelf to upper slope environments, while radiolarian chert CORBs are inferred to have formed in deep-water, basinal settings below the carbonate compensation depth (CCD). Full article

The Placerias quarry is a dicynodont-dominated bonebed in Upper Triassic Chinle Group strata near St. Johns in east-central Arizona, USA. Though long identified as being in strata of the lower Chinle Group, recently published numerical ages apparently indicate a stratigraphically much higher (younger) position in the Chinle section for the Placerias quarry. Nevertheless, recent analysis of outcrop and subsurface (hydrologic) data in the vicinity of the Placerias quarry confirms its stratigraphic position very low in the Chinle Group section, close to the base of the Bluewater Creek Formation. A regional Upper Triassic lithostratigraphy has been established across east-central Arizona and west-central New Mexico by nearly a century of stratigraphic studies and geologic mapping by diverse workers, and is supported by biostratigraphy; in this lithostratigraphy the Placerias quarry is near the Chinle Group base. However, U/Pb ages on zircons from Upper Triassic strata in eastern Arizona/western New Mexico have been used to reorganize this lithostratigraphy to indicate intertonguing and dramatic lithofacies changes over relatively short lateral distances. But, if the well-established lithostratigraphy is followed, the U/Pb ages are problematic, particularly where younger ages (such as at the Placerias quarry) are stratigraphically below older ages. A handful of numerical ages should not be used to over-rule well-established understanding of lithostratigraphy and biostratigraphy, unless the lithostratigraphy and biostratigraphy need to be modified based on stratigraphic data. Numerical ages need to be used judiciously and evaluated critically with regard to established lithostratigraphy, biostratigraphy and other age constraints. Full article

The middle and upper Eocene sedimentary successions exposed along the northwestern and northeastern portions of the Nile Valley, Egypt, have been thoroughly examined for their ostracod assemblages. This study enhances the understanding of biostratigraphic zonations and evaluates the paleobiogeographic distribution and paleoenvironmental conditions that prevailed during the deposition of this sedimentary record. Lithostratigraphically, the studied successions are subdivided into four stratigraphic units, arranged in ascending order as follows: the Qarara, the El Fashn, the Gehannam, and the Beni Suef formations. A total of 125 rock samples were selected and well analyzed, resulting in the identification of sixty-five ostracod species and subspecies belonging to thirty-three genera, fifteen families, and three superfamilies. The stratigraphic distribution of the recorded ostracod taxa contributed to the construction of four local biozones, spanning the interval from the upper Lutetian to lower Priabonian: Schizocythere fadlensis Zone (upper Lutetian–lower Bartonian), Loxoconcha pseudopunctatella Zone, Dygmocythere ismaili Zone (Bartonian), and Asymmetricythere hiltermanni Zone (Bartonian–Priabonian). These biozones are well described, discussed, and correlated with those previously documented in different areas of Egypt and neighboring countries. The statistical analysis, supported by ternary plot diagrams, indicates that the depositional environments of the studied rock units fluctuated between shallow inner neritic and deeper outer neritic marine environments. The identified taxa display a wide geographic distribution and show a significant similarity with those identified in the southern, northern, and eastern Tethyan provinces, suggesting a direct marine connection during the Eocene. Full article

The Palaeocene Lockhart Formation, a carbonate-rich succession abundant in Larger Benthic Foraminifera, represents a significant potential hydrocarbon reservoir extending throughout the Kohat, Potwar and Hazara basins of Pakistan. This study examines two stratigraphic sections of the Lockhart Formation in the Hazara Basin—Bagran and Karhaki—providing crucial insights into its biostratigraphy and microfacies analysis. The formation comprises medium- to fine-grained limestone with shale intercalations, exhibiting argillaceous to compacted textures. Biostratigraphic analysis revealed a diverse assemblage of Larger Benthic Foraminifera, with 23 species identified across 9 genera, including Miscellanea miscella, Lockhartia haimei, Lockhartia conditi and Ranikothalia sindensis. These fossils indicate deposition within Shallow Benthic Zone (SBZ) 4 during the Late Thanetian, suggesting a dynamic palaeoenvironment. Seven distinct microfacies types were identified: bioclastic mudstone, mixed bioclastic wackestone, miliolidal bioclastic wackestone, foraminiferal wackestone–packstone, foraminiferal wackestone, foraminiferal packstone and bioclastic foraminiferal packstone. These microfacies indicate varied depositional settings, from shallow subtidal and lagoonal to shallow restricted and open marine environments, spanning inner ramp to distal mid-ramp conditions. This research advances our understanding of Late Thanetian depositional environments within the Lockhart Limestone, with implications for regional sedimentology, palaeogeographic reconstruction and reservoir characterisation. Full article

This study investigates the depositional environments and soft sediment deformation within the Early Jurassic Ammonitico Rosso Formation in the External Ionian Basin (Western Greece), focusing on its biostratigraphy, sedimentology, and tectonic activity. This research provides new insights into the depositional environment of the Ammonitico Rosso Formation and its transitions with the underlying and overlying formations. Syn-rift tectonics at the time of deposition formed half-grabens, which influenced sedimentary processes and created conditions for seabed slumping. Detailed field mapping and microfacies analysis revealed two distinct depositional environments: deep-water to open-shelf settings and platform-margin reefs. The entire Ammonitico Rosso Formation is allochthonous, deposited as repetitive slices of little-disturbed stratified sediments capped by debrites near the toe of a complex submarine landslide. The presence of well-preserved fossils, such as planktonic and benthic foraminifera, Radiolaria (both Spumellaria and Nassellaria), and ammonites, allowed precise age determinations, suggesting that the first appearance of Globuligerina might predate previous records, occurring first in the Pliensbachian rather than the Toarcian. These findings contribute to the ongoing debate on the depth and conditions of Ammonitico Rosso deposition, supporting the hypothesis of a relatively deep, open-shelf environment influenced by slope instability. Full article

This study presents the first U-Pb (CA-ID-TIMS) radioisotopic dating of zircon grains extracted from tonsteins within the uppermost Permian coal interval of the Minusinsk Coal Basin (Siberia, Russia). Petrographic, structural, and mineralogical analyses confirm the volcanic ash origin of the tonsteins. The parent pyroclastic materials are identified as rhyolite–pantellerite for tonstein I-22 and dacite–rhyodacite for tonstein I-12. Morphological analysis of zircon crystals, along with cathodoluminescence and melt inclusion studies, confirms their volcanic origin and crystallisation temperatures of 700–900 °C. New radioisotopic dates of 261.4 ± 0.7 Ma and 261.3 ± 0.4 Ma clarify the age of the Izykh Formation, enabling its direct correlation with the Capitanian Stage of the International Chronostratigraphic Chart. The results emphasise the possible discontinuity of the coal-bearing succession of Siberian palaeocontinent and highlight the potential for further stratigraphic refinement through continued radioisotopic dating of tonsteins. Full article

New data obtained from core samples of two boreholes and dredged samples from the Alba Guyot in the Magellan Seamount Trail (MST), Western Pacific, including the ⁴⁰Ar/³⁹Ar age determinations of basanite, and the mineralogy of basanite, tuff, tuffite, mantle-derived inclusions in basanite and tuff (lherzolite xenolith and Ol, Cpx, and Opx xenocrysts), and calcareous nannofossil biostratigraphy, have implications for the guyot′s development and history. Volcanic units in the upper part of the Alba Guyot main edifice and its Oma Vlinder satellite, at sea depths between 3600 and 2200 m, were deposited during the Cretaceous 112 to 86 Ma interval. In the following ~60 myr, the Alba Guyot became partly submerged and denuded with the formation of a flat summit platform while the respective fragment of the Pacific Plate was moving to the Northern Hemisphere. Volcanic activity in the northeastern part of the guyot summit platform was rejuvenated in the Miocene (24–15 Ma) and produced onshore basanitic volcanoes and layers of tuff in subaerial and tuffite in shallow-water near-shore conditions. In the Middle-Late Miocene (10–6 Ma), after the guyot had submerged, carbonates containing calcareous nannofossils were deposited on the porous surfaces of tuff and tuffite. Precipitation of the Fe-Mn crust (Unit III) recommenced during the Pliocene–Pleistocene (<1.8 Ma) when the guyot summit reached favorable sea depths. The location of the MST guyots in the northwestern segment of the Pacific Plate near the Mariana Trench, along with the Miocene age and alkali-basaltic signatures of basanite, provide first evidence for petit-spot volcanism on the Alba Guyot. This inference agrees with the geochemistry of Cenozoic petit-spot basaltic rocks from the Pacific and Miocene basanite on the Alba Guyot. Petit-spot volcanics presumably originated from alkali-basaltic melts produced by decompression partial melting of carbonatized peridotite in the metasomatized oceanic lithosphere at the Lithosphere–Asthenosphere Boundary level. The numerous volcanic cones with elevations of up to 750 m high and 5.1 km in basal diameter, discovered on the Alba summit platform, provide the first evidence of voluminous Miocene petit-spot basanitic volcanism upon the Cretaceous guyots and seamounts of the Pacific. Full article

Recent investigations in the upper Lower–Middle Pleistocene deposits of the Megalopolis Basin (Greece) led to the discovery of several sites/findspots with abundant faunal material. Here, we provide an updated overview including new results on the micro- and macro-mammal fauna. Important new discoveries comprise partial hippopotamus skeletons from Marathousa 1 and the new Lower Pleistocene site Choremi 6, as well as a second partial elephant skeleton from Marathousa 1, including a complete tusk and the rarely found stylohyoideum. Based on the first results from the newly collected micromammals, we discuss age constraints of the sites, and we provide biostratigraphic/biochronologic remarks on key mammal taxa for the Middle Pleistocene of Greece and southeastern Europe. The presence of mammals highly dependent on freshwater for their survival, together with temperate-adapted ones in several stratigraphic layers of the basin, including those correlated with glacial stages, when conditions were colder and/or drier, indicate the capacity of the basin to retain perennial freshwater bodies under milder climatic conditions, even during the harsher glacial periods of the European Middle Pleistocene, and further support its refugial status. Yet, the smaller dimensions of the Megalopolis hippopotamuses may represent a response to the changing environmental conditions of the epoch, not optimal for hippopotamuses. Overall, the Megalopolis Basin comprises a unique fossil record for southeastern Europe and provides valuable insights into the Middle Pleistocene terrestrial ecosystems of Europe, and hominin adaptations in particular. Full article

The Croatian Natural History Museum (CNHM) houses rich fossil collections from the Neogene deposits of Northern Croatia, comprising numerous scallops (Bivalvia: Pectinidae). During the Middle Miocene (Badenian = Langhian and early Serravallian), this region was located at the southwestern margin of the Central Paratethys. The value of the CNHM’s historical collections has been presented through taxonomic revisions and biostratigraphic, paleoenvironmental and paleogeographic study. Methods included the cross-checking of specimens from museum boxes with all available published data, systematic revision of scallops, recording the abundance of each taxon, defining the preservation state of the specimens, measuring the morphometric elements and taking photographs of each specimen. After the conducted revision of 624 specimens, the number of registered taxa in the collections was reduced from 52 to 33, and their stratigraphic distribution has been updated. The species Lissochlamys excisa (Bronn, 1831) has been recorded for the first time at the southwestern part of the Central Paratethys. The southernmost Badenian record of Delectopecten vitreus (Gmelin, 1791) known so far has been described. Six types of pectinid habitats have been distinguished, based on the provided paleontological and lithological data, also estimating the scallops’ abundance in each of them. Bioerosion and encrustation traces on scallops’ shells represent an additional contribution to paleoecological studies. Full article

A reliable character system is crucial to taxonomy and systematics, and it promises valid downstream inferences, e.g., estimates of diversity and disparity, reconstruction of evolutionary history, and even stratigraphic correlations. Modern taxonomy and systematics of extant cockroaches requires an integrative study involving multiple lines of evidence with emphasis on genital and reproductive characteristics and molecular data. In contrast, many fossil cockroach taxa published recently are based solely on forewings. Many studies have shown that forewing-based taxa are questionable. In order to find out how much of the phylogenetic signal we could ascertain from venational similarity, and how confident we could be, this study used forewing characters to reconstruct phylogenies of the genera of well-recognized family-group taxa. The intuitively reconstructed phylogeny of 75 extant genera failed to recover those taxa or their relationships. Parsimony analyses of various datasets all yielded strong polyphyly and chaotic relationships. In conclusion, the forewing of cockroaches is not a universally competent character system. The underlying causes are the complicated nature of veins and the limitations of current analytical techniques. The uncertainty in forewing-based taxonomy and systematics has been underestimated in the literature. Forewing-based fossil taxa warrant re-evaluation; some of them are herein deemed nomina dubia in their current state. Full article

The comment by Yin (2024) referred to the systematic morphology and identification of the newly recovered in situ ammonite assemblage Tiltoniceras sp. and Hildoceratidae sp. from the Bilong Co section in the Qiangtang Basin. Yin (2024) suggests that Tiltoniceras sp. should be assigned to Oxycerites aspidoides. Upon re-examination of our paper and the reply to the released comment, it is demonstrated that the morphologic characteristics of the recovered ammonites are more consistent with Tiltoniceras rather than Oxycerites aspidoides. These ammonites, along with in situ calcite U–Pb age (ca. 181 Ma), carbon isotope stratigraphy, and age-diagnostic palynomorphs, constrain the age of the Bilong Co oil shale to the Lower Jurassic (Toarcian) with plausible credentials. Full article