Stratotype Research Articles

Introduction to the Khalij Limestone Member Type Section in the Gadvan Formation of Iran: A Comprehensive Analysis Utilizing 38 Exploration and Development Wells and 1 Surface Section of Gadvan

The Khalij limestone member, well-known for its abundant benthic facies, is situated in the middle segment of the Gadvan shaly formation, boasting an average thickness of approximately 14 meters. This specific member is exclusively found below the surface, devoid of any exposed outcrops, and is characterized by the presence of easily identifiable orbitolinid limestone. Well logging techniques, such as Gamma Ray and Density measurements, prove particularly effective in identifying this distinct layer. The primary objective of this study was to conduct a comprehensive analysis of the lithostratigraphy and microstratigraphy within the Gadvan formation, with a specific emphasis on the Khalij limestone member. A regional stratigraphic assessment covered an extensive area of about 100,000 square kilometers in the Fars and Dezful regions within the Zagros region. To achieve this, data from 38 exploration and development wells were utilized, and approximately 1,400 microscopic thin sections from the Gadvan formation were meticulously examined. The paramount contribution of this research lies in the establishment of a representative type section for the Khalij limestone member, characterized by a thickness of 13 meters. Detailed microscopic analysis has revealed that this member predominantly comprises wackestone carbonate, featuring microfossils, particularly foraminifera from the orbitolindae family. Based on the observed species index, it has been determined to be of Barremian age and linked to a lagoon-like depositional environment.

New advances on the carbon isotope and rare earth elements chemostratigraphy of the late Ediacaran Tamengo Formation (Corumbá Group, Brazil)

The Tamengo Formation (Corumbá Group, midwest Brazil) is a carbonate-dominated succession of major importance to unravel the environmental and biological changes during the Ediacaran–Cambrian transition in Gondwana. Although it has been extensively studied in terms of sedimentology, isotope geochemistry, biostratigraphy, and geochronology, these studies are constrained to the Corumbá region. This work presents new sedimentological, C and O isotope chemostratigraphy, and rare earth elements (REE) plus yttrium (REY) data of four sections of the Tamengo Formation in the Serra da Bodoquena region, approximately 200 km south of Corumbá, discussing how these new data are related to the type sections. The sections present ooid grainstones, with hummocky, swaley, and wavy structures, interbedded with mudstones and shales, indicating deposition of fine particles by suspension fallout in-between periods of high-energy, with reworking by storm waves. The δ13Ccarb curves show positive plateaus with minor, short-lived negative excursions linked to facies variations, which are related to a large δ13Ccarb depth gradient in a redox-stratified water column. The REY profiles present middle REE (MREE)-bulge patterns and absent to slightly positive Ce anomalies, consistent with MREE adsorption onto Fe–Mn oxyhydroxides in the water column followed by release in pore waters. Subsequently, REY remobilization during anoxic diagenetic stages resulted in the MREE-bulge pattern and overprinted some of the original seawater REY features, including the Ce anomalies. The Tamengo Formation in the Serra da Bodoquena region represents a storm-dominated carbonate ramp, as previously interpreted for this unit in the Corumbá region. Nevertheless, there is a significant shift of 2 ‰ in the peaks of δ13Ccarb data between both localities, which may be related to differences in the overall sector of the carbonate ramp. There are also substantial variations in the δ13Ccarb record of the Tamengo Formation and other coeval Gondwana basins, such as the Nama and Itapucumi groups, with different peak values, which may be related to latitudinal differences on the inorganic carbon isotope composition or to the degree of basin restriction.

Saussurea arctecapitulata Lipsch. – new species for the flora of Russia

Saussurea arctecapitulata, a herbaceous perennial species, belonging to the type section of the genus Saussurea, previously known only from a few localities in the northern Mongolia, has been found in the Naryn River Valley during field trips to the territory of Republic of Tuva. This article presents an updated description accompanied by photos of the species in nature, updated data on the distribution of the species, as well as phylogenetic relationships with morphologically similar species of the section based on the variability of the site ITS1-5.8S-ITS2.

The Neogene–Quaternary boundary at its type locality, Monte San Nicola, Sicily, southern Italy: X-ray computed tomography and ichnofabric signals of the sapropelic Nicola bed

A new low-cost method is described for obtaining narrow blocks of the friable Nicola bed, the local marker for the Neogene–Quaternary system (Pliocene–Pleistocene series) boundary at the type section at Monte San Nicola, southern Sicily. The Global boundary Stratotype Section and Point (GSSP), which also defines the Gelasian Stage and is dated at 2.58 Ma, is placed at the base of a marly layer immediately overlying the sapropelic microlaminated Nicola bed. Sedimentary structures and ichnofabrics revealed by X-ray computed tomography (CT) and polished surface observations show the rapid onset of anoxia marking the base of the Nicola bed, followed by progressive dysoxia indicated by the trace fossil Chondrites isp. alone. The top of the Nicola bed is bioturbated over an interval of several centimeters, which obscures precise recognition of the GSSP horizon. The overlying marl is characterised by the presence of Chondrites isp. accompanied by Planolites isp. and Thalassinoides isp. indicating a return to higher oxygen levels in the bottom waters, although a brief return to poor oxygenation is interpreted from the temporary absence/rarity of Chondrites isp. Trichichnus isp. is prevalent throughout the interval immediately above the Nicola bed, and its lowest extent revealed by CT may serve at least locally as an independent marker for the GSSP level. In general, we recommend the careful study of any sapropel before placing a GSSP at its upper or lower boundary or midpoint.

Microfossils, High-Resolution Stratigraphy, Geochemistry and Lithology of the Upper Jurassic and Lower Cretaceous (Urdyuk-Khaya and Paksa Formations) in the Nordvik Peninsula, Anabar Bay, Laptev Sea

Abstract —The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic–Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.

Constitutional amendments as a mechanism to pursue different goals in the context of internal and external challenges

This article reviews the constitutional evolution of Russia and Mexico in order to determine the causes for their current differences regarding their policies and governance systems after sharing similar characteristics during their political and economic liberalization period over three decades ago. The subject of this research are constitutional amendments, their frequency by type (article or section) and initiators (institutions and actors) in both countries. Results are compared with the main theories of the main experts in the field as well as speeches by leading government figures to identify and explain discrepancies. The goal consists in finding the causes and purposes of constitutional amendments to determine a hierarchy of actors and their capacity and instruments required in establishing national policies. In order to achieve the research goal, the author carries out a comparative analysis regarding the evolution of both nations at a political and constitutional level, furthermore, external threats are analyzed regarding their ability to influence the decisions behind the main actors regarding the overall course of both nations. In conclusion, the author underlines the importance in initial position of the country within the larger order of nations as a determinant in its course regardless of the implementation of foreign policies and practices. In the same manner, the role of the Mexican and Russian presidents as regulators of the internal power dynamics and overall system of governance is noted in both countries. This article represents a conceptual framework for supporting constitutional studies in the context of comparative analysis to assess the capacity of government institutions in reacting to the challenges of their external context. The detailed theoretical and practical approach towards analyzing constitutional amendments was conducted by means of comparing a quantitative and qualitative analysis that allowed determining the prospects of a standardized system for future comparative studies.

New insights into the conodont biostratigraphy and paleobiogeography of the Katkoyeh Formation (Lower–Upper Ordovician) at the Katkoyeh Section, East-Central Iran

The Katkoyeh Formation comprises most of the Ordovician strata in the Kerman Province of East-Central Iran. However, determining its depositional timing remains challenging due to conflicting biostratigraphic ages, regional stratigraphic gaps, and tectonic complexities in the area. To enhance the understanding of the Katkoyeh Formation, a new conodont sampling was conducted at the Katkoyeh type section, which revealed 1,937 conodont elements belonging to 31 species of 26 genera. They allow the recognition of the Juanognathus variabilis Range Zone (middle–upper Floian) and the Icriodella superba Range Zone (Katian–?Hirnantian) in the Katkoyeh Formation, leading to better biostratigraphic and intercontinental correlations of the Ordovician strata in East-Central Iran with the Precordillera, the Famatina System, and the Central Andean Basin of northwestern Argentina, as well as with North American Midcontinent and North Atlantic basins, and South China. Moreover, the oral structure of Juanognathus variabilis Serpagli is reassessed based on the new Iranian records, recognizing 7 morphotypes in its apparatus structure, referred to the M, Pa, Pb, Sa, Sba, Sbb and Sc positions.

Bashkirian foraminifera in the Sanandaj-Sirjan Zone (Iran): Their importance in taxonomy, biostratigraphy, and palaeobiogeographic reconstruction of the southern margin of Western Palaeotethys

A noteworthy Lower Pennsylvanian fusulinid fauna is, for the first time, reported from the Sanandaj-Sirjan Zone in Iran. From the main outcrop, eighty five species of thirty genera belonging to two classes, five orders, five suborders, seven superfamilies, sixteen families, and seven subfamilies are examined. The present fusulinids are assigned to the early–late Bashkirian (Syuranian, Akavassian, and Askynbashian substages). The characteristic taxa include Semistaffella spp., Plectostaffella varvariensis, Millerella marblensis, Pseudostaffella spp., Profusulinella cf. parva, and Ozawainella spp. Three successive assemblages spanning the early–late Bashkirian are proposed: (1) Assemblage with Semistaffella variabilis-S. minuscilaria-Plectostaffella seslavica (Syuranian age); (2) Assemblage with Pseudostaffella antiqua-P. compressa (Akavassian age); and (3) Assemblage with Ozawainella mosquensis-Profusulinella cf. parva (Askynbashian age). The new found fusulinid assemblages of the Sanandaj-Sirjan Zone have close resemblance and are well correlative with the Bashkirian standard and reference sections of the Russian Platform, Donets Basin, Urals, Southern Turkey, and Central Asia. The Iranian Bashkirian foraminiferal faunas, furthermore, exhibit very similar compositions to their counterparts in other areas of the Western Palaeotethys Region; many foraminifers, both smaller foraminifers and fusulinids, are in common between them. The new findings, in addition to clarifying the biostratigraphic correlation with the well-known type sections of the same age, are also important for reconstructing the palaeoposition of the Sanandaj-Sirjan Zone as a southern margin of Western Palaeotethys.

Revised stratigraphic sequence and type sections of the Southern Bida Basin, Nigeria

A reassessment of the stratigraphy of the Southern Bida Basin has been attempted among various disagreements. For this work, field geological mapping and stratigraphic descriptions of exposed lithologic types on outcrop sections were used. Section-by-section descriptions of important outcrops based on field observations aided in identifying lithologic units and delineating the boundaries of the sub-basin's three formations (Lokoja, Ahoko, and Agbaja). The type sections for formations in the sub-basin were not properly erected, so Jones (1958) type section has been supplemented by a more comprehensive hypostratotype, and the name Patti Formation, which is considered a misnomer in this context, has been replaced with Ahoko Formation proposed by Rahaman et al. (2019). Ahoko village is the type locality. The Agbaja Plateau, where the Agbaja Formation is best exposed, has been presented as the lectostratotype for the formation, while the revised stratigraphic succession of the Lokoja region shows the Lokoja Formation directly encompassing the Paleozoic Basement terrain, with the Maastrichtian Agbaja and Ahoko Formations (former Patti) overlying it sequentially.

Geological Assessment of Turonian - Coniacian terrestrial sedimentation records during climatic recovery, Moreno Hill Formation, Zuni Basin

Understanding of Upper Cretaceous terrestrial sediments within the Western Interior Basin is advancing; however, the Turonian–Coniacian transition remains enigmatic. Recent chronometry of the Moreno Hill Formation indicates that sediment deposition took place during this interval of geodynamic upheaval and climatic recovery immediately following the peak of the Cretaceous Thermal Maximum (CTM). To decipher these effects, the sedimentary record of the Moreno Hill Formation was reassessed near the type section, and near Quemado, New Mexico (USA) using facies analysis and architectural reconstruction. Seven facies types (thirteen lithofacies codes), eleven architectural elements, and three facies associations were identified. Sedimentation within the floodplain of the lower Moreno Hill Formation was affected by the east-migrating forebulge of the Western Interior Basin. Furthermore, increasingly bedload-rich multi-story channel complexes and a transition from near-coastal to alluvial coals reflect gradual climatic cooling and overall regression of the Western Interior Seaway (with interruption by a regional [T2–R2] transgressive-regressive sequence). This is consistent with more subaerial conditions indicative of continued regression reflected within the floodplain sediments of the upper Moreno Hill Formation. Whilst diversion of westerly fluvial feeder systems by ongoing forebulge migration also affected sediment transport and deposition, a return to more suspended-load-rich single-story channels and thin coals are tied to an intervening (T3) transgression. Repetitive paleosol sequences throughout the Moreno Hill Formation indicate groundwater fluctuation in response to these base level changes. Together with detrital zircon-based geochronology, these slight sedimentary differences support a revised subdivision from three into two members: lower and upper. Beyond feeding the seaward Gallup Delta, the newly defined lower member correlates to the Toreva, Straight Cliffs (Smoky Hollow member), Ferron Sandstone, Funk Valley and Frontier formations (Dry Hollow Member) and the upper member to the Wepo and Straight Cliffs (John Henry Member) formations within the Kaiparowits, Notom, Last Chance and Vernal fluvio-deltaic systems. Landward sediments of the Cardium Formation (Canada) correlate with the lower and upper members of the Moreno Hill Formation.

Cenomanian Radiolarians and Stratigraphy of the Sel’-Bukhra Section, Republic of Crimea

New radiolarian data from the type section of the middle Cenomanian Pseudoaulophacus lenticulatus Zone located on the northern and southern slopes of the Sel’-Bukhra Mountain section (southwestern Crimea) are reported. The Pseudoaulophacus lenticulatus Zone radiolarians have been studied and analyzed in this section for the first time. Five species previously unknown in this region have been found here. Lithology of the lower part of the upper Cenomanian Triactoma parva Zone from the southern slope of the Sel’-Bukhra Mountain section is reported. Both Pseudoaulophacus lenticulatus and Triactoma parva Zones have more than 60% species distributed in the Tethyan Superrealm.

The helochelydrid turtle Helochelydra nopcsai from the Early Cretaceous (late Barremian – early Aptian) fissure fills of Balve, North Rhine-Westphalia, Germany, including a large sample of granicones

Early Cretaceous (late Barremian – early Aptian) fissure fill deposits near Balve, North Rhine Westphalia, Germany, have yielded a rich continental vertebrate fauna over the course of the last two decades. More than 250 fragmentary specimens, including more than 150 osteoderms (i.e., granicones), represent the late Early Cretaceous helochelydrid Helochelydra nopcsai, which had previously been reported from the UK, France, and Spain. The new material mostly differs from that from the type section by exhibiting a reduced to absent entoplastral scute and by displaying distinct cranial scute sulci, both of which are interpreted as intraspecific variation. Although morphological insights are limited, the new material reveals that the visceral cavity extends anteriorly and posteriorly to the bridge, a relatively novel feature previously reported for an eclectic mix of compsemydids, pleurosternids, and other helochelydrids. The available sample of granicones reveals great shape diversity, but a morphometric analysis concludes that no distinct morphotypes exist.

Centennial scale sequences of environmental deterioration preceded the end-Permian mass extinction

The exact drivers for the end-Permian mass extinction (EPME) remain controversial. Here we focus on a ~10,000 yr record from the marine type section at Meishan, China, preceding and covering the onset of the EPME. Analyses of polyaromatic hydrocarbons at sampling intervals representing 1.5–6.3 yr reveal recurrent pulses of wildfires in the terrestrial realm. Massive input pulses of soil-derived organic matter and clastic materials into the oceans are indicated by patterns of C2-dibenzofuran, C30 hopane and aluminum. Importantly, in the ~2,000 years preceding the main phase of the EPME, we observe a clearly defined sequence of wildfires, soil weathering, and euxinia provoked by the fertilization of the marine environment with soil-derived nutrients. Euxinia is indicated by sulfur and iron concentrations. Our study suggests that, in South China, centennial scale processes led to a collapse of the terrestrial ecosystem ~300 yr (120–480 yr; ± 2 s.d.) before the onset of the EPME and that this collapse induced euxinic conditions in the ocean, ultimately resulting in the demise of marine ecosystems.

Stratigraphical, microfacies, and ichnological characteristics and depositional environments of the Permo‒Carboniferous Aheimer Formation, western side of the Gulf of Suez, Egypt

The palaeoenvironments of the upper Palaeozoic succession in the eastern foot slopes of the Northern Galala Plateau, west of the Gulf of Suez, Egypt, are interpreted based on a detailed study of the sequence-stratigraphic framework, sedimentary facies and trace fossils. The upper Carboniferous–lower Permian Aheimer Formation has been studied in its type section exposed in Wadi Aheimer. Three unconformities bound four 3rd-order depositional sequences, including the upper Carboniferous DS NG 1, and the lower Permian DS NG 2‒4. These sequences are correlated with their counterparts on the North African and Arabian plates. The sedimentary facies characteristics indicate palaeoenvironments ranging from fluvial, estuarine, intertidal, shallow subtidal, shoreface to offshore transitional settings. The abundant and diverse ichno-assemblages are composed of horizontal, vertical and sub-vertical traces. At least 26 ichnotaxa have been identified, representing suites of the Glossifungites, proximal Cruziana, and proximal-archetypal Cruziana ichnofacies. Ichnofabric analysis revealed three distinct ichnofabrics: Tisoa, Schaubcylindrichnus and Zoophycos ichnofabrics. The trace and body fossil distribution and trophic structure of some of the recorded faunal assemblages confirm relatively stable and low-stress shallow-marine environments. In contrast, the trophic structure of some other assemblages indicates the influence of particular environmental parameters, including substrate consistency, bathymetry, water energy, productivity, rate of sedimentation, salinity and oxygen availability. The integrated results indicate that the sequences were formed during an interval dominated by different perturbations that resulted in a wide spectrum of depositional features. Moreover, evidence for Carboniferous–Permian glaciation is tentatively established in North Egypt but require further investigations.

New fossil remains of proboscideans from the Siwalik group of Pakistan

ABSTRACT We have described here proboscideans fossil remnants which belong to six species: Prodeinotherium pentapotamiae, Gomphotherium browni, Choerolophodon corrugatus, Protanancus chinjiensis, and Elephas planifrons. The described specimens are collected from six different localities of the Siwaliks. These localities are Bhilomar, Chinji type section, Lawa, Dhok Bun Ameer Khatoon (Chinji Formation), Ochri (Dhok Pathan Formation) and Rathian (Pinjor Formation), belongs to the Lower to Upper Siwaliks, district Chakwal and Jhelum, Punjab, Pakistan. The specimens were collected from these localities after extensive fieldwork from 2015 to 2020, which confirms the presence of large mammalian fauna during the Middle Miocene to Late Pleistocene. Prodeinotherium pentapotamiae is rare taxa in the Middle Siwaliks of Pakistan, first time discovered from new fossil section Satroma wali dhal in the vicinity of the Dhok Bun Ameer Khatoon locality. Bhilomar is a less explored fossil locality belongs to the Chinji Formation, Gomphotherium browni and Choerolophodon corrugatus is reported from the Chinji type section. A beautiful juvenile mandibular ramus of Protanancus chinjiensis has been recovered first time from Lawa and Elephas planifrons were recovered from Rathian which belongs to Pinjor Formation dated as Plio-Pleistocene age of Upper subgroup of Siwaliks. Based on palaeoenvironment and stratigraphy the age of these localities is suggested as Miocene to Pleistocene. The recovered proboscideans fossil fauna indicates about the climatic changes and confirms that more seasonal extensive grasslands and savannah like ecosystem were present at that time.

Biostratigraphy of the Numidian Formation and its underlying Tellian unit, based on calcareous nannofossils in Northern Tunisia: Implication on their stratigraphic vs. tectonic relationships

A detailed biostratigraphic study, based on calcareous nannofossils, was performed to re-evaluate the stratigraphic interpretation of the Numidian Formation and its structural relationship with the underlying El Haria, Boudabbous and Souar formations Tellian units (i.e., stratigraphic vs. tectonic). The new biostratigraphic results indicate that the Numidian Formation is not restricted to a Miocene age as considered in some recent works but spans from Oligocene (Rupelian and Chattian, NP23 to NP25) to early Miocene (Aquitanian and Burdigalian, NN1 to NN3). The Cap Serrat succession can be retained as the type section for the Tunisian Numidian Formation, where both the Chattian-Aquitanian (Oligocene/Miocene boundary) and the Aquitanian-Burdigalian transitions have been characterized.Based on the new calcareous nannofossil findings, several duplications of the sedimentary succession were identified. They include the thick shales and marls of El Haria (Maastrichtian-Paleocene) and Souar (Eocene) formations, thrusted by the Numidian Formation. The updated regional structural cross-sections, confirm that the Numidian Formation is currently juxtaposed by southward major thrust contact to the underlying Kasseb structural unit in the studied area. The latter is intensively affected by poly-phased tectonics, resulting in the thrust events associated with the Alpine phase inversion. This has to be taken into consideration in oil and gas exploration in the area of the fold-thrust belt system, in both onshore and offshore Northern Tunisia.

New Five Southern Tethyan Agglutinated Foraminiferal Species

Benthic foraminifera was studied as part of an investigation of the Dababiya section (Egypt), which was undertaken to document a candidate section for the Global Stratotype Section and Point (GSSP) for the base of the Ypresian Stage, Thanetian/Ypresian boundary, Late Campanian Dokan and Azmer sections of Kurdistan (NE Iraq), and the type section of Khangiran Formation of Khangiran section (NE Iran). Five new species of the genera Pseudogaudryina and Pseudogaudryinella are proposed, from three countries Egypt, Iraq and Iran, and from Campanian and Ypresian sediments. Three species of Pseudogaudryina: P. dababiyaensis (from Egypt), P. kurdistanensis and P. iraqensis (from Iraq), two species from Iran: Pseudogaudryinella iranica and Pseudoclavulina iranica. The Tethyan continental shelf fauna Midway-Type Fauna (MTF) of deep middle neritic to the upper bathyal environment is interpreted.

Stratigraphic revision of the early Miocene Kiahera Formation from Rusinga Island, Lake Victoria, Kenya

Decades of research in Early Miocene deposits on Rusinga Island, Lake Victoria, Kenya, have made its fossil record pivotal for interpreting floral and faunal evolution in eastern Africa during the early Neogene. Paleontological research has largely focused on Rusinga Island's fossil-rich Hiwegi Formation, and because that work has largely motivated geological research a similar bias can also be found in stratigraphic studies of the island's deposits. Hence, the resolution of paleoclimate, paleohabitat, and floral and faunal community reconstructions from other formations is limited, and discrepancies in stratigraphic placement and correlations among outcrops limit our ability to fully assess the interplay of climate and evolution.New lithostratigraphic and sedimentologic analyses of the Kiahera Formation on Rusinga Island clarify these discrepancies. Our work demonstrates that the Kiahera Formation comprises ten facies and can be divided into three discrete clastic units (from bottom to top): Nyamita Spring Member, Ukowe Member, and Rondo Member. The lithofacies in the formation are composed of conglomerates, sandstones, airfall tuffaceous units, and paleosols. Conglomerates, sandstones, and paleosols are found primarily within fluvially-dominated sediments in the Nyamita Spring and Rondo Members, interpreted to represent little to no volcanic input. Tuffaceous units occur within the middle Ukowe Member and record a series of eruptions of the neighboring Kisingiri Volcano. Importantly, reassessment of the type section of the Wayando Formation, which previous researchers identified as the oldest formation on Rusinga Island, demonstrates that it is stratigraphically and lithologically equivalent with the upper member of the Kiahera Formation. Other deposits historically attributed to the Wayando Formation can likewise be correlated with sections of the Kiahera Formation. Hence, the Kiahera Formation represents the oldest sediments on Rusinga. Finally, our revised descriptions and analysis enabled us to identify the basal member of the Kiahera Formation in outcrops on neighboring Mfangano Island, but stratigraphically well above where previous researchers had positioned them. This provides a new basis for interpreting the relationship between Mfangano Island's important fossil assemblages and the better-known assemblages from Rusinga Island. In total, clarification and consolidation of Rusinga Island's Kiahera Formation significantly impact paleontological and paleoecological characterizations of this unit and of the entire Early Miocene geological sequence on the island, further informing interpretations of how Rusinga's fossil sites formed with respect to the evolving Kisingiri Volcano.

Palynological Study and Age Dating of the Early Miocene Dukku Claystone Type Section of Gwandu Formation, Sokoto Basin, Northwestern Nigeria

Outcrop samples were collected from Dukku area for the purpose of subjecting them to palynological analysis in order to determine the relative age of Gwandu Formation and palaeoenvironment of deposition of the deposit. Field and laboratory methods were carried out in order to obtain lithological sequence description of the outcrop. The samples obtained went through processes of acid digestion with hydrochloric acid, hydrofluoric acid and separation of macerals by floatation with the use of zinc bromide. The prepared slides were observed under microscope for palynomorph contents. Diagnostic palynomorphs that are stratigraphically important for palynozonation were retrieved such as Belskipollis eligans, Verrutricolporites laevigatus. Striamonocolpites sp., Retibrevitricolporites sp., Retibrevitricolporites obodoensis, Retistephanocolpites sp., Cingulatisporites ornatus, Longapertites marginatus and Proteacidites sp. The marker fossils belong to Magnatariatites horwardii zone; Zone P600 and Subzone P630 and C1 Zone of Nigerian Niger Delta sedimentary basin zonal schemes, dated Early Miocene age. Dinoflagellate forms recovered include Batiacasphaera sp., Senegalinium sp., Andalusiella polymorpha Selenophemphix nephroides, Andalusiella sp., Andalusiella laevigata, Histrichosphaera turocona and undifferentiated dinoflagellate cysts of peridinacean forms that belong to marginal marine setting.

Climate and Atlantic sea-level recorded in Southwestern Spain from 6.3 to 5.2 Ma. Inferences on the Messinian Crisis in the Mediterranean.

The Mio-Pliocene succession of Andalusia on the Atlantic coast (Guadalquivir Basin) is known as one of the former stratotype candidate for the Andalusian Stage, proposed during the seventies as the last stage of the Miocene. Its type section is located in Carmona, east of Seville. Our investigation includes the drilling of three cored boreholes, which provide bio- and magnetic-stratigraphic data in complement to pre-existing industrial information, and a high-resolution palynological analysis (pollen grains, spores and dinoflagellate cysts). The pollen flora and its climatic quantification provide the mean to correlate the section to the oxygen isotope curve from the Montemayor-1 borehole, located about 80 km to the West of Carmona. The variations in the ratio between dinoflagellate cysts and pollen grains are used to identify high and low oceanic levels, consistently with a recent paleobathymetric reconstruction based on foraminifera: the two lowest levels being successively marked by the deposit of a littoral calcarenite (the Calizza Tosca Formation) then by a subaerial erosive episode. Based on the correlation with the Montemayor-1 regional drilling, the two major lowerings in oceanic level observed at Carmona are linked with the two episodes of the Messinian Crisis. The interlocking position of the high-energy sandstone deposits inscribed in the Messinian valley leads to an assessment of a drop in the global oceanic level of about 114 m at the beginning of the paroxysm of the Messinian Crisis, amplitude to be moderated with respect to the potential effect of isostatic readjustements due to the Messinian Crisis. Comparisons are discussed with the amplitude of the Messinian Erosional Surface in the West-Alboran Basin which potentially remained suspended and fed with Atlantic waters during the height of the crisis and isolated from the rest of the almost totally dried Mediterranean Basin. The quantified climate constructed from the pollen records confirms that dry conditions existed before the Messinian Crisis in Southern Mediterranean latitudes including the Atlantic side, making the Mediterranean Sea climatically predisposed to desiccation. Atlantic sea-level variations observed in the Guadalquivir region and measured at Carmona suggest that global glacio-eustatism somewhat facilitated the onset and completion of the Messinian Crisis in the Mediterranean Basin. At last, this work allows to discriminate two regional erosive events: the first one, dated at 5.60 Ma, of fluvial origin in relation with global eustasy; the second one, submarine, occurred just before 5.33 Ma, and referred to the strain exerted by the Guadalquivir olistostrome.