The uppermost Rhuddanian to upper Aeronian largely black-shale succession exposed in section 5 on the northeastern shore of El Pintado reservoir in northern Seville Province, Spain is described with particular reference to graptolites and graptolite biostratigraphy. It complements published data from the neighbouring El Pintado section 1 ratified by the IUGS in 2024 as the base Telychian GSSP. The uppermost Rhuddanian part of the continuously graptolitic, but stratigraphically incomplete section is assigned to the Coronograptus cyphus Biozone. Black-shale sedimentation continued across the Rhuddanian-Aeronian boundary, but the succession is interrupted by a significant stratigraphical gap commencing in the middle of the lower Aeronian Demirastrites triangulatus Biozone. Largely uniform black-shale sedimentation revived in the lower part of the middle Aeronian Pribylograptus leptotheca Biozone and continued through the Lituigraptus convolutus and Stimulograptus sedgwickii biozones to the latest Aeronian Stimulograptus halli Biozone. A short gap in sedimentation may potentially be present in the lower-middle sedgwickii Biozone, suggested by a rusty, pyrite-rich silty layer and the atypical course of the Late Aeronian Carbon Isotope Excursion (LACIE) in the local delta 13Corg curve. Eighty-five graptolite species have been recorded in this succession, including six new taxa: Neodiplograptus nanus sp. nov., Pernerograptus roquei sp. nov., P.? praecipuus sp. nov., Torquigraptus cracens sp. nov., T. pilatus sp. nov. and Aeronites circinatus gen. et sp. nov., with twelve left in open nomenclature. The new genus and new species are described here.
The East Pisco Basin of southern Peru is renowned worldwide for its exceptionally well-preserved marine vertebrate fossils, recovered from sedimentary successions spanning the middle Eocene to the early Pliocene. Although the lower Eocene-Oligocene deposits of the Otuma Formation have been extensively investigated, the uppermost Eocene to lower Oligocene strata remain comparatively understudied. Notably, these strata encompass the Eocene-Oligocene transition (similar to 34 Ma), a critical interval characterized by profound global climatic and ecological changes. This study presents an integrated biostratigraphic analysis of the Otuma Formation based on calcareous nannofossils, diatoms, and silicoflagellates. The investigated deposits were laid down in two distinct sub-basins: an eastern, land-proximal sub-basin at Cerro Tiza and a western, more distal sub-basin at Quebrada Perdida (Media Luna). In addition, Ar-39-Ar-40 dating of a volcanic ash layer provides an independent chronological tie point for the age model at Cerro Tiza. At both localities, the Otuma Formation comprises calcareous siltstones and diatomite layers deposited from the Priabonian to the Rupelian. Sedimentation rates derived from the age model average 75.5 m/My at Cerro Tiza and 8.1 m/My at Media Luna. A progressive shift from calcareous nannofossil-dominated assemblages to diatom-dominated assemblages throughout the sections reflects a general trend toward cooler conditions and increased nutrient availability, consistent with global patterns during this interval. However, diatom assemblages do not indicate the establishment of permanently eutrophic conditions. Differences in microfossil assemblages, together with an order-of-magnitude contrast in sedimentation rates between Cerro Tiza and Media Luna, point to markedly distinct palaeoenvironmental conditions in the two sub-basins. These differences are interpreted as the result of tectonic controls and contrasting positions within the Peruvian forearc system.
The Puertollano Coalfield succession corresponds to the Late Carboniferous Stephanian Stage of the West European chronostratigraphic framework, but the position within this unit, based on megafloral biostratigraphy, has been ill-defined; attributed ages have ranged from Stephanian A (now Barruelian) to Stephanian C. During working of the Mina Emma opencast site, samples of volcanic tuff were collected from bands in the two principal coals, the Tercera (sample P173) and Segunda (sample P172) seams, separated by some 24 m. These seams lie near the middle of a total stratigraphic column of around 600 m. These samples were submitted for CA-ID-TIMS high precision U-Pb radiometric dating, which gave corresponding absolute ages: P173-303.48 Ma +/- [0.44] and P172-303.19 Ma +/- [0.42]. These dates correspond to the earliest Gzhelian Stage of the global chronostratigraphic timescale, close to its limit with the underlying Kasimovian. In the West European framework, constrained by radiometric dates from stratotypes in the Cantabrian Mountains, this succession falls in the earliest part of the proposed Saberian substage, closely above the contact with the preceding Barruelian substage. The Puertollano palaeobotanical record comprises a hygrophile biome related to the coal swamp environment and also, in the upper part of the succession, elements of a mesophile flora largely comprising conifer taxa. The latter have suggested the significantly younger age, in contrast to the hygrophile flora which largely corresponds to the older Saberian age. The palaeobotanical record contributes to discussion on the influence on climate as a driver of mixed floral biomes and relevance of the concept of an extrabasinal derivation of some taxa. The new dates provide the basis for on-going review of the floral dynamics and stratigraphical significance of the palaeobotanical record in the Puertollano succession, and also a framework for the unique vertebrate fauna.
The Black Hills, South Dakota, USA, expose thick packages of Devonian-Carboniferous carbonates that represent the shallow-water succession on the NW margin of the Transcontinental Arch. These carbonates are the up-ramp facies of the well-studied Devonian-Carboniferous Boundary succession in the Williston Basin farther to the NW. This basin margin succession is critical to developing a detailed sequence stratigraphic history of the Williston Basin and the U.S. Midcontinent but little chronostratigraphic information is available from these strata beyond their designation to the Mississippian Subsystem. Here, we sampled the uppermost beds of the Englewood Formation and similar to 60 m of the Pahasapa Formation for integrated conodont and carbon isotope biochemostratigraphy at the Spearfish Canyon section in the Black Hills including a total of 34 conodont and 203 carbonate carbon isotope samples. Conodont yields were generally poor, but the Mickelson Member of the Englewood Formation contained conodonts of the Siphonodella sandbergi Zone and the lower portion of the Pahasapa Formation contained Siphonodella crenulata Zone fauna. No discernable carbon isotope excursion was identified, and delta C-13 values persist above +3 parts per thousand throughout the top of the sampled interval. The Kinderhookian-Osagean Regional Stages boundary could not be placed precisely at the outcrop. However, there is no evidence that the portion of the Pahasapa Formation sampled extends any higher than within the global Tournaisian Stage.
In recent years, cyclostratigraphy has significantly improved the accuracy and precision of the Devonian timescale, especially at stage boundaries. Yet, the body of Devonian stages often remains undefined in terms of cyclostratigraphy. Here, we present a new astrochronological framework for the upper to uppermost Famennian based on XRF-derived elemental proxy records from two rhythmic marine successions in the Rhenish Massif (Germany). The composite record spans the interval from the Annulata Events to the Hangenberg Crisis (the end-Devonian extinction pulse) and reveals a 5.7 +/- 0.4 Myr duration. We resolve a 2.3 Myr interval between the Annulata and Dasberg black shales, and 2.4 Myr between the Dasberg and Hangenberg black shales. There is an estimated 67 kyr between the Lower and Upper Annulata black shales. Additionally, we constrain the durations of nine conodont biozones. Our results are consistent with several previous studies and strengthen the case for integrating multiple astrochronologies and to construct correlatable astrochronozones between globally distributed sections. The emerging 2.3-2.4 Myr rhythm of the Annulata-Dasberg-Hangenberg sequence supports the hypothesis that Late Devonian anoxic events were modulated by long-eccentricity forcing, underscoring a strong astronomical pacing of Late Devonian palaeoenvironmental change.
Biostratigraphy is one of the most applied methods in stratigraphy and is therefore a main component in the International Stratigraphic Guide (ISG). The principles of biostratigraphy are reevaluated here and considered generally valid as described in the ISG and in general use. The basic unit is the biozone which can be subdivided into Range Zones (Taxon Range Z., Concurrent Range Z.), Interval Zones (Base Z., Top Z., Base-Top Z., Partial Range Z.), Acme Zones and Assemblage Zones. A special biozone is the Lineage Zone which is based on phylogenetic relationships of species. Biozones are bounded by biohorizons which may be defined by the lowest occurrence and highest occurrence of a taxon. In contrast to frequent use the lowest occurrence should be named Base (B) and highest occurrence Top (T) to avoid confusion with other definitions/abbreviations. First Appearance Datum (FAD) and Last Appearance Datum (LAD) are reserved for the Lineage Zones but should be used with caution. For main fossil groups biozones are presented and examples are provided. The definition of biohorizones is not consistently used in various fossil groups, in particular, in ammonites biostratigraphy/biochronology horizons are not considered surfaces within rocks but described as beds or even a set of beds. An application consistent with the general usage is recommended and in addition to sub-subbiozones the already existing rank 'zonule' should be added. The sequence of biozones represents a biozonation which is together with the biohorizons the most important correlation tool. The strong influence of several parameters such as phylogeny, paleoecology, paleobiogeography and paleogeography are discussed resulting in the fact that no global biozonation can exist. As pragmatic but insufficient option 'standard biozonations' are established which represent, however, only a fraction of existing biozonations. Correlation of biohorizons and biozones can and should be supported by numerical methods to gain geochronologic results. The step from biostratigraphy to biochronology is described and the differentiation of both approaches is considered very important. For biochronology numerical age dating is required for which several methods exist but basically dating by radiogenic elements or by astrochronology and (as indirect method) by magnetochronology is applied. The final step is to interrelate biostratigraphy/biochronology with other stratigraphic methods to end up with a well based high-resolution integrative stratigraphy. Biostratigraphy plays an important role for chronostratigraphy because 80% of the defined GSSPs are based on bioevents.
This study analyzes foraminiferal assemblages in the Middle Jurassic upper Dhruma Formation in Central Saudi Arabia to support the refinement of the Jurassic sequence stratigraphic interpretation in the region. The disaggregation-acetic acid leaching technique was applied to 62 lithified limestone and marl samples to recover foraminifera, facilitating morphogroup analysis, species composition assessment, and the vertical distribution of species for paleoenvironmental interpretation, depositional sequence analysis, and maximum flooding horizon identification. The studied section covers the Atash and lower part of the Hisyan members of the D7 unit of the Dhruma Formation. The succession is dominated at the base of the Atash Member by calcareous epifaunal benthic species, transitioning to a diverse assemblage of shallow and deep infaunal agglutinated and calcareous benthic foraminifera, along with planktonic taxa, in the middle part of the Atash Member. This part of the section marks peak transgression and coincides with the J40 maximum flooding surface (MFS). A return to epifaunal foraminiferal dominance in the lower part of the overlying Hisyan member probably reflects a shallowing. Morphogroup and species composition analyses reveal significant environmental shifts, correlating with a transgressive-regressive cycle. Biodiversity indices and cluster analysis further delineate depositional settings, supporting a refined stratigraphic framework. A conceptual paleobathymetric model indicates progressive deepening in an epicontinental ramp setting, emphasizing the role of sea-level fluctuations and suggesting that the clay-rich unit (Hisyan Member) may represent a shallowing rather than a deepening trend. These findings enhance our understanding of Jurassic shallow marine carbonate platform dynamics and their broader implications for regional sequence stratigraphy.
This study examines the biostratigraphy and chronostratigraphy, using ammonoids, of the interval between lower Pliensbachian (Davoei Chronozone, Figulinum Subchronozone) and lower Toarcian (Serpentinum Chronozone, Elegantulum Subchronozone), in four sections of Asturias, located between the west of Punta de Rodiles (Villaviciosa) and Playa de Vega (Ribadesella). The collection of ammonoids in more than 130 successive levels allowed the establishment of a reference scale, which is compared with those defined in other basins of Iberia and the western Tethys. The lower limit of the upper Pliensbachian is marked with the first occurence of Protogrammoceras (Matteiceras) occidentale, above the last Oistoceras, and the lower limit of the lower Toarcian is marked with the first occurrence of Dactylioceras (Eodactylites), which in Asturias corresponds to D. (E.) simplex. In addition, all the chronozones and subchronozones proposed in the standard scales of NW Europe have been characterised. In general, the ammonoids identified are similar to those of the Subboreal and Submediterranean Provinces, although there are some intervals where taxa typical of, or common in, the Mediterranean Province are recorded. The most significant are registered in the Margaritatus Chronozone (Gibbosus Subchronozone), Spinatum Chronozone (terminal Hawskerense Subchronozone) and Tenuicostatum Chronozone (Paltum/Mirabile Subchronozone). Based on the succession of the recorded ammonoid species, 21 chronostratigraphic horizons have been characterised, the calibration of regional or global biotic events that occurred in the Asturian Basin, such as the extinction of Amaltheidae and Hildoceratidae (Arieticeratinae) in the upper part of the Hawskerense Subchronozone, the expansion of the Dactylioceratinae Subfamily from the beginning of the Tenuicostatum Chronozone, the extinction of Protogrammoceratinae (Lioceratoides) and Dactylioceras (Eodactylites) in the transition between the Paltum/Mirabile and Semicelatum subchronozones, and the extinction of Protogrammoceratinae (Protogrammoceras) and other groups, such as Hildoceratinae (Neolioceratoides) and almost all Dactylioceras (Orthodactylites) during the transition between the Tenuicostatum and Serpentinum chronozones, coinciding with the final stage of the Jenkyns Event.
. Calcareous nannofossil and planktonic foraminifera biohorizons constitute the backbone for Cenozoic stratigraphic studies. However, most bioevents have been calibrated in equatorial regions, with much scarcer data available at higher latitudes. This introduces a latitudinal bias particularly in the Indian Ocean. In this study, we quantitatively analyse Middle to Late Miocene calcareous nannofossil abundances, as well as first and last occurrences at ODP Site 752 (Broken Ridge, 30 degrees S Indian Ocean). Specifically, the focus lies both on stratigraphically relevant, as well as on rare taxa. Complementary to the nannofossil biostratigraphy, we also evaluated planktonic foraminifera to obtain an integrated biostratigraphic dataset. This new re-calibrated Middle to Late Miocene bioevent framework for the mid-latitude Indian Ocean region gives way to a new regional biozonation scheme for both fossil groups. The comparison of these bioevents with previously published data also provides new insight into the origin and evolutionary patterns of calcareous nannofossil and planktonic foraminifera species. Specifically, Base G. nepenthes and Base D. kugleri showed an earlier occurrence (12.36 and 12.78 Ma, respectively) at Site 752 compared with the available literature data for the equatorial areas. The earlier occurrence of G. nepenthes at our location suggests an evolutionary origin in the mid-latitude Indian Ocean. The Base of D. kugleri on the other hand suggests an origin in the high-latitude regions. The Top D. kugleri aligns with the equatorial data. Finally, the Top of G. panda is traditionally placed at 11.93 Ma, yet G. panda continuously occurs at ODP Site 752 until 10.54 Ma. Top G. panda thus is an unreliable marker in the higher mid-latitudes and needs further revision. We conclude that this work constitutes an important step towards a regionally applicable biozonation for the mid-latitude Indian Ocean across the Middle and Late Miocene.
Biostratigraphic resolution of the Early Miocene planktonic foraminiferal zonations is relatively low compared to younger Neogene intervals, and high-resolution quantitative records of planktonic foraminifera are scarce. Additionally, there is an ongoing debate about which bioevents best approximate the Aquitanian/Burdigalian boundary, although the Base of the calcareous nannofossil Helicosphaera amplia perta (20.43 Ma) has been provisionally adopted to mark the base of the Burdigalian Stage. Here, the results of a high-resolution quantitative analysis of planktonic foraminiferal assemblages from Site 926 (ODP Leg 154, Ceara Rise, equatorial Atlantic Ocean) for the interval from 21.5 to 17.6 Ma are presented. Following the astronomically calibrated composite section of Site 926, samples were selected from nannofossil-foraminiferal chalk levels with a time resolution of similar to 30 kyr. This study provides the quantitative distribution patterns of the biostratigraphic marker species of the studied interval and allows the refinement of the stratigraphic position and age of the main bioevents. Age calibration of some identified bioevents, such as Top (T) Paragloborotalia pseudokugleri, Base (B) Globigerinoides altiaperturus s.l., B Globigerinatella sp. and B Globorotalia praescitula, is nearly consistent with the current biochronology. Conversely, T P. kugleri, which defines the M1b/M2 zonal boundary, is younger than what is reported in literature and postdates B H. am pliaperta. Notably, the age calibration of T P. kugleri and B G. altiaperturus s.l. is close to the age of the top of magnetic polarity Chron C6An (19.97 Ma), possibly offering new perspectives on the selection of criteria for defining the base of the Burdigalian Stage. Further identified events, Top common (Tc) Paragloborotalia kugleri, Tc Tenuitella munda, T Paragloborotalia mendacis and T Ciperoella fariasi, enhance the biostratigraphic resolution of the studied interval. Finally, quantitative records of other biostratigraphic markers, such as Catapsydrax dissimilis, Paragloborotalia siakensis, P. birnageae, P. nana, Trilobatus trilobus gr. and Globigerinoides neoparawoodi/G. joli gr., reveal details of their distribution patterns within the studied interval. Biostratigraphic correlation of Site 926 with other low-latitude (I)ODP Sites is hindered by inconsistencies in the relative stratigraphic positions of T P. pseudokugleri, T P. kugleri and calcareous nannofossil events, partly due to different resolution of the biostratigraphic analysis and partly due to the absence of important events (e.g., B Globigerinatella sp., B H. ampliaperta) at some of the considered sites. Overall, the high-resolution planktonic foraminiferal quantitative record of Site 926 obtained in this study may contribute to improving biostratigraphic resolution and enhancing the accuracy of Early Miocene standard zonation and biochronology.
Core RH-323 drilled in the Revivim Valley, southern Israel, provides an expanded upper Paleocene to middle Eocene sedimentary succession, deposited in an upper-middle slope environment on the southern margin of the Tethys. We present high resolution lithological, bulk geochemical and biostratigraphic data for the lower Eocene to optimize stratigraphic constraints on the sequence. Variability in magnetic susceptibility (MS) is pervasively controlled by astronomical forcing. The identification of a clear short eccentricity signal in the MS record provides a foundation for the astronomical tuning of the surveyed interval guided by calcareous nannofossil and dinoflagellate cyst biostratigraphy. On this basis, the available delta 13C record has been independently tuned to the La2010b astronomical solution, which allowed for an orbital scale correlation of a series of negative carbon isotope excursions (CIEs) recorded in bulk sediment calcium carbonate to the well-known series of CIEs in the global exogenic carbon pool, associated with global warming. Interestingly, spectral analysis suggests a potential presence of a half-precession signal, and an enhancement of the obliquity signal across the CIEs.
Exceptionally preserved fossils from the Toarcian (Lower Jurassic) black shales of Bascharage in southeast Luxembourg have been known for decades, but stratigraphy and palaeontological implications of these deposits have remained poorly understood. Recent attempts to describe the litho- and biostratigraphy of these black shales have yielded controversial or ambiguous results. Here, we present and discuss new data collected in May 2022 during a large-scale scientific excavation at the Bommelscheuer industrial zone in Bascharage, a campaign that was led by the National Museum of Natural History Luxembourg. A previously unexplored area of 40 m x 80 m was decorticated layer by layer, with the aim to expose a continuous section and record a maximum of geological data. We provide here a high-resolution litho-, bio-and chemostratigraphic survey and assessment of the Bascharage succession, comprising the upper Tenuicostatum and lower Serpentinum Zones and therewith the period before and during the initiation of the Toarcian oceanic anoxic event (T-OAE). This critical endeavour enables stratigraphic correlations with coeval successions, in particular with the SW-German Posidonia Shale. The high-resolution bulk carbonate carbon isotope record shows the four-step negative excursion in the initial T-OAE reported for coeval successions in the Paris and the Swabian basins. The course of the delta C-13(carb) trend suggests that the investigated site at Bascharage represents a largely continuous and complete T-OAE succession. It furthermore suggests that the base of the Serpentinum Zone coincides with the 2(nd) step of the negative carbon isotope excursion, the latter therefore representing an important chemostratigraphic marker. The nodule layer - called the insect nodule horizon in the present paper - may represent the stratigraphic equivalent to the SW-German "Unterer Stein" and with that also to the "Whale Stones" of Yorkshire, providing therefore a lithological reference horizon across Europe. Palaeontological evidence suggests that the Bascharage site can be qualified as a Lagerst & auml;tte because of the abundance and extraordinary preservation of the fossils, including 3D and soft tissue preservation. The biotic spectrum shows a combination of features typically found in near-shore settings. Due to the abundance and excellent preservation of insect fossils, the Bascharage Lagerst & auml;tte ranks among the most important Lower Toarcian insect taphocoenoses in Europe. This succession was deposited in a marginal near-shore setting close to the emerged London-Brabant landmass but still within the Central European areas of black shale depositions. Seawater current indicators based on 32 occurrences of wood fragment accumulations around ammonite shells recorded in the lower 30 cm of the Serpentinum Zone and three wood logs recorded at different levels of the succession show that the Lower Toarcian sea floor was swept by very gentle SSE currents in the investigated area, providing unusual palaeocurrent insights into a low-energy depositional setting.
Integrated chronostratigraphy of core WPGPC230202, which was taken from the summit of seamount KC-7 located in the Magellan Seamounts of the western Pacific Ocean, was established using planktonic foraminifera biostratigraphy, calcareous nannofossil biostratigraphy, and magnetostratigraphy. Planktonic foraminiferal biostratigraphy clearly shows 17 biohorizons from Pliocene Zones PL1 to Pleistocene Subzone PT1b. Calcareous nannofossils yielded 12 biostratigraphic index taxa, revealing 15 biohorizons from Plio-Pleistocene Zones CNPL2 to CNPL11. In addition, 6 paleomagnetic reversal events were recorded, which correlate continuously to the geomagnetic polarity time scale, ranging from the Brunhes (C1n) to the upper Gilbert (C3n.1n). As a result, the integrated chronostratigraphy provided an age of-4.3 Ma, which can be applied to regional stratigraphic correlations and to better understand Late Neogene paleoceanographic changes in the study area. The age-depth model of core WPGPC230202 shows the distinct decrease of sedimentation rates from-0.19 to-0.07 cm/kyr at-2.4 Ma, which corresponds to the Northern Hemisphere Glaciation (NHG). Core WPGPC230202 primarily consists of biogenic carbonate ooze (foraminifera and nannofossils) and due to the shallow water depth at the core site limiting the effect of dissolution, the sedimentation rate is mainly dependent on the degree of paleoproductivity. The NHG is characterized by the gradual global cooling and change in the deep-water circulation patterns. During the NHG, surface water cooling and reduced formation of the North Pacific Deep Water may degrade carbonate productivity in the subtropical ocean including the study area, similar to what is recorded in the subarctic North Pacific.
Ammonoids have long held a central position in stratigraphic research, having served as one of the principal fossil groups since the early development of the discipline. These extinct cephalopods developed a rich morphological diversity with exceptionally high evolutionary rates, resulting in a rapid turnover of species. From the Early Devonian through to the end of the Cretaceous, ammonoids were one of the most important groups for the subdivision of sedimentary sequences. In recent decades, however, their dominance in biostratigraphy has diminished in favour of other fossil groups, particularly microfossils. Despite this, ammonoids still play a crucial role in the regional definition of very short stratigraphic intervals. In many cases, their precision in stratigraphic subdivision exceeds that of both macrofossil and microfossil groups. Ammonoids remain unparalleled in their utility for stratigraphic schemes, especially in the Late Devonian, selected intervals of the Carboniferous and Triassic, the entire Jurassic and parts of the Cretaceous. Stratigraphic units based on ammonoids are sometimes between 50 kyr and 100 kyr in duration. However, the often-limited geographic distribution of ammonoid species restricts their potential for interregional or global correlation.
The Late Pliocene was characterized by a warmer climate than today, followed by pronounced cooling toward the Early Pleistocene; thus, the Late Pliocene is a critical period for understanding Earth's climate evolution and assessing the impacts of future global warming. Although the contribution of the western boundary currents in the northwestern Pacific is essential for the warm climate and subsequent glacial expansion in the Northern Hemisphere, the evolution of these surface/deep current systems remains unclear owing to the lack of continuous paleoceanographic records in this region. In this study, we provide a new Late Pliocene benthic oxygen isotope (818O) stratigraphy, with assistance from paleomagnetic polarity transitions and zircon U-Pb dating from on-land marine successions in central Japan that were rapidly deposited in a forearc basin in the northwestern Pacific margin. We measured the stable 818O composition of four infaunal benthic foraminiferal taxa obtained from three sections in the Boso and Miura peninsulas, Japan. Interspecies offsets and the influence of depositional paleodepth on the benthic 818O were corrected to construct a composite 818O stratigraphy. The resultant 818O stratigraphy, robustly constrained by magnetostratigraphy and zircon U-Pb ages, ranges from Marine Isotope Stage (MIS) Gi1 (3604 ka) to G15 (2898 ka). These sections cover the age interval around the onset of the Northern Hemisphere Glaciation and most of the mid-Piacenzian Warm Period (missing MIS KM6 due to slumping). A clear increase in 818O during MIS MG4-M2 (3390-3250 ka) is similar to that in the western subpolar Pacific, indicating that cold/high-818O deep-water occurred along the northwestern Pacific margin during that period. The change in bottom-water properties coincided with enhancement of the latitudinal thermal gradient in the North Pacific, and recovery of abyssal ventilation into the tropical eastern Pacific in association with cooling around Antarctica and resulting activation of bottom-water formation. These observations suggest that cooling around Antarctica and resulting activation of bottom-water formation in the Southern Ocean during MIS MG4-M2 led to northward expansion of high-density deep-water to the subarctic North Pacific along the western margin and interruption of the weak latitudinal thermal gradient in the North Pacific. Further paleoceanographic and paleoclimatic studies using our delta 18O stratigraphy will facilitate understanding of the North Pacific surface and deep western boundary current systems during the Late Pliocene.
A high-resolution bio- and chemostratigraphic study based on planktonic foraminifera and carbon stable isotope of the late Cenomanian-late Turonian time interval of the Sarvak Formation was undertaken in the Zagros Basin (SW Iran). In this research, a hemipelagic succession, named the Tang-e Bawlek section, was inspected. Significant documented bio-events in stratigraphic order include lowest occurrence (LO) of Praeglobotruncana algeriana, the highest occurrences (HO) of Thalmanninella appenninica, Th. deeckei, Rotalipora montsalvensis, Th. greenhornensis and R. cushmani, LO of Helvetoglobotruncana praehelvetica, helvetica. These bio-events have led to the recognition of four biozones (from Rotalipora cushmani Zone to Dicarinella primitiva-Marginotruncana sigali Zone) from the Tethyan realm. Integrating of the well-documented bio-events with a high-resolution 813C curve, particularly around the Cenomanian/Turonian boundary (CTB), enabled comprehensive documentation of OAE2 and its three distinct associated peaks (a, b and c) as well as facilitated correlation with key reference curves. These results reveal that in contrast to the other parts of the Zagros Basin, where the CTB is represented by a marked disconformity or sea level fall, this portion of the Lurestan Subzone exhibits evidence of deep marine conditions. However, the detailed lithological and microfacies observations point to the development of a condensed horizon with a low sedimentation rate, rich in glauconite and phosphate located just above the peak c of the 813C curve, which can be associated with a short hiatus close to the CTB. Palaeoecological reconstructions of the studied interval revealed three major changes in the depositional conditions, establishing a notable eutrophic condition during the OAE2 interval accompanied by a well-developed oxygen minimum zone (OMZ).
Over the past 70 years, the potential of organic-walled dinoflagellate cysts (or dinocysts) for the dating and correlation of marine deposits from the Upper Triassic onwards has been increasingly realized, and dinocyst biostratigraphy has developed into a valuable stratigraphic method both in academic and industrial applications. Its utility is traditionally considered to be greatest in shelfal settings, but dinocyst biostratigraphy has also been successfully applied to deep-ocean sedimentary successions. As such, dinocystderived age information is complementary to that of other microfossil groups with typically more offshore distribution centers such as planktonic foraminifera, calcareous nannofossils, diatoms, and radiolaria. Due to the limited preservation potential of calcareous and siliceous microfossils in high-latitude settings, dinocysts are particularly important for age determinations in polar to sub-polar regions. The versatility of dinocyst signals is further enhanced in microscope slide preparations containing these microfossils because they typically also include terrestrial palynomorphs such as pollen and spores, yielding direct land-sea correlations. Regardless of its impressive potential, dinocyst biostratigraphy comes with specific challenges. The present article aims to provide a critical and comprehensive review of dinocyst biostratigraphy. It first discusses the principles of dinocyst morphology and taxonomy, as well as current concepts in dinoflagellate (cyst) paleo-ecology, because accurate identification and an understanding of environmental tolerances are indispensable for successful dinocyst-based biostratigraphic analysis. It then considers the suitability of dinocysts as bi-ostratigraphic markers in terms of morphological distinctiveness and abundances, taxonomic diversity, strati-graphic ranges, and (paleo-) geographic distributions. Finally, it identifies perspectives and potential for fu-ture work.
