Short research note

Supplementary modification and introduction of code numbers to the low-latitude coccolith biostratigraphic zonation (Bukry, 1973; 1975)

The Late Miocene-Early Pliocene Biogenic Bloom (ca. 9.0–3.5 Ma) was a phase of high marine biological productivity documented globally at multiple ocean sites, related to an increase in nutrient input and/or a significant reorganization of nutrients in the oceans. Here, we studied the Biogenic Bloom at Ocean Drilling Program (ODP) Site 1085 in the Southeast Atlantic Ocean, additionally providing an updated age model based on calcareous nannofossil biostratigraphy. During the event, we identified four intervals characterised by distinct benthic foraminiferal assemblages, suggesting changes in paleoenvironmental/paleoceanographic conditions. The Biogenic Bloom extends from 8.1 to 3.0 Ma at Site 1085, as detected by different proxies such as linear sedimentation rates, carbonate mass accumulation rates, benthic foraminiferal indices and assemblage data. The inferred paleoenvironmental changes allowed us to differentiate four intervals within the Biogenic Bloom. From 8.1 to 5.2 Ma and from 3.8 to 3.0 Ma, the high benthic foraminiferal accumulation rates (BFARs) and the abundance of phytodetritus-exploiting taxa point to highly seasonal phytoplankton blooms. Between 5.2 and 4.8 Ma, we document short-term fluctuations between well‑oxygenated conditions with transient input of phytodetritus and phases of low oxygen eutrophic conditions. Between 4.8 and 3.8 Ma, a decrease in opportunistic species and an increase in eutrophic taxa likely suggest a switch to a higher food supply to the seafloor. Our data shows that the onset of the Biogenic Bloom was synchronous with other global well-dated records and its end appears to align with other Atlantic records. Lastly, our findings support the hypothesis that the Biogenic Bloom was not a single productivity event, but a complex event made up of several short-lived, high-productivity regimes with different driving forces.

A high-resolution quantitative nannoplankton biostratigraphy has been established in four wells based on a total of 1241 subsurface samples to understand and improve hydrocarbon exploration and recovery in the offshore Nile Delta. Ninety-two nannofossil species were used to delineate stages/ages boundaries of the Miocene-Pleistocene succession and to construct the age-depth model. Empirical, semi-quantitative (Graphic Correlation), and quantitative (Unitary Associations ‘UA’) methods retained comparable results, suggesting that the data quality is a master variable in the biostratigraphic resolution of the studied sequence. The UA method retained a sequence of 22 UAs, which exceeded the empirical zones (15; CNM6-CNPL9 = NN4-NN19). However, these UAs were merged into 14 zones (UAZ) to enable correlation among sections. Age-depth models and the nannofossil abundance were used to estimate the sedimentation rates and identify the system tracts within the depositional cycles. The variation in sedimentation rate was attributed to the interplay between the sea level and Nile flooding, which controlled the terrigenous influx. Furthermore, the nannofossil diversity was linked to the sequence stratigraphic framework, where seven 3rd order sequences were identified and correlated with the Global Tethyan sequences. Moreover, the extinction rate has increased after the Messinian and is attributed to the Pliocene-Pleistocene sea-level highstand and invasion of deeper water rich in nutrients from the upwelling zone.

The Early Eocene Kuldana Formation (KF) consists of variegated color shales, mudstone, and sandstone with limestone interbeds/lenses in the Yadgar area, Muzaffarabad, of Sub-Himalayan foreland basin. We report, for the first time, 20 nannofossil species of 9 genera, discovered from carbonate units of KF. Based on this calcareous nannofossil assemblage, an Early Eocene Ypresian age (NP10) is determined. The presence of Coccolithus, Fasciculithus, Rhomboaster, Tribrachiatus and Sphenolithus indicates dominantly warm water and oligotrophic conditions during deposition of the carbonate units, while the presence of Zeugrhabdotus and Neococcolithes suggests minor cool-water, eutrophic to mesotrophic conditions. Five microfacies were identified based on the field and petrographic investigations of the study section, namely, Nummulitic wacke-packstone microfacies (KMF-1), Assilina wacke-packstone microfacies (KMF-2), Molluscan microfacies (KMF-3), Lime mudstone microfacies (KMF-4), and Ostracode wackestone microfacies (KMF-5), suggesting that the deposition occurred in inner to middle shelf, shallow marine environment.

Precise taxonomy and the chronostratigraphic calibration of the Middle Eocene Alveolina from Central Iran is here undertaken from the Chah-Talkh section of the southern Sabzevar region (Central Iran). We have identified Alveolina kieli, Alveolina stercusmuris and Alveolina nuttalli along with the new species Alveolina ozcani n. sp. that we include into the Alveolina elliptica group. We have also found Nummulites uroniensis, Nummulites obesus and Nummulites cf. verneuili and associated calcareous nannofossils that look reliable to make thoughtful correlations with the Shallow Benthic Zones (SBZ). The foraminiferal biostratigraphy suggests an assignment to the upper part of the lower Lutetian–lower part of the middle Lutetian, SBZ13 (Middle Eocene), further strengthened through the identification of the calcareous nannofossil NP14b–NP15b or CNE8–CNE10 biozones, providing a solid correlation with the global stratigraphic standards.

Despite extensive chronological studies, the relationship between the age and sub-seafloor depth of Arctic Ocean sediments remains ambiguous. This prevents confident identification of paleoceanographic changes in the Arctic during the Quaternary. Currently, age-depth models derived from uranium-series decay in Arctic sediments diverge by hundreds of thousands of years compared to those built on known evolutionary appearances and extinctions of calcareous nannoplankton, a group of globally valuable age-markers. Here we report on high-resolution biostratigraphic analysis of late Quaternary sediments in six cores from the central Arctic Ocean (CAO). We applied paired light microscope (LM) and scanning electron microscope (SEM) imaging to improve nannofossil diagnosis. We argue that low abundances and poor preservation have led to misidentification of the true stratigraphic depth of the critical Pleistocene nannofossil bio-events that have underpinned age models for many Arctic sedimentary records for decades. The revised calcareous nannofossil biochronology provides a radically different geochronological framework for CAO sediments – indicating that what had previously been identified as Marine Isotope Stage (MIS) 7 (191–243 ka) in many sedimentary records is older than MIS 12 (424–478 ka). Furthermore, it suggests that previously inferred sub-stages of MIS 5 could represent full interglacial periods rather than interstadials. The results help reconcile the different dating approaches and provide a transformative step towards resolving the disparity in Quaternary Arctic age-depth models, bringing us one step closer to accurate paleoceanographic reconstructions based on sediment cores.

High-resolution chronostratigraphy is fundamental for a refined interpretation of the evolution of sedimentary basins and, consequently, for generating more accurate geological models, which are essential for oil and gas exploration. This study provided an innovative integration of seismic reflectors interpretation, a biostratigraphic framework and 405-kyr astronomically-tuned age models from three wells, arranged in a dip section comprising Miocene deposits in the slope break of the Albacora Field, Campos Basin, Brazil. We (i) to provide a high-resolution, 2D astrochronologic model from the combination of three astronomical timescales (ATSs) – comprising a timespan of ∼3 Myr for the dip section; (ii) infer that the studied section comprises the middle Miocene deposits and records the Miocene Optimum Climate, and the significant eustatic falls that delimit this event; and (iii) provide refined age estimates for the seismic reflectors near the biozones.