Calcareous Nannofossil Biostratigraphy Research Articles

Miocene Petit-Spot Basanitic Volcanoes on Cretaceous Alba Guyot (Magellan Seamount Trail, Pacific Ocean)

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.

Tectonically-controlled biofacies distribution in the Eocene Foraminiferal Limestone (Pag, Croatia): A quantitative-based palaeontological analysis

This paper analyses the lower to middle Eocene carbonate succession exposed at the Island of Pag (Croatia), in the External Dinarides, providing its palaeoenvironmental, palaeobathymetric, and stratigraphic reconstruction. A total of 125 samples have been collected within the Foraminiferal Limestone and the overlying Transitional Beds units cropping out in the sites of Vrčići and Pag for the quantitative analysis of the skeletal assemblage (point counting) and the foraminiferal association (area counting), including both large benthic and small benthic foraminifera. Further samples were collected from the overlying Dalmatian Flysch, to constrain the age of the top of the succession using calcareous nannofossil biostratigraphy. On these bases, the Foraminiferal Limestone has been dated from the Ypresian to the middle Eocene (late Lutetian/early Bartonian). Thanks to the analysis of the skeletal and foraminiferal assemblages, and the use of multivariate statistics, seven main biofacies were identified within the Foraminiferal Limestone and one biofacies within the Transitional Beds. The porcelaneous and agglutinated benthic foraminifera biofacies (BF1) indicates a well-illuminated, oligotrophic to mesotrophic, shallow water, lagoonal environment. The hyaline SBF and encrusting benthic foraminifera biofacies (BF2) developed in a shallow water, inner-ramp environment, and is related to a vegetated seafloor. The nummulitid biofacies (BF3) indicates a moderately high energy, shallow water environment, whereas the comminuted bioclasts and nummulitid biofacies (BF4) corresponds to a low-energy, shallow water environment, and both deposited in inner-to-middle ramp settings. The nummulitid and orthophragminid biofacies (BF5) indicates a moderate energy environment, deposited in middle ramp settings. The nummulitid and serpulid biofacies (BF6) consists of transported material from the inner ramp deposited in middle ramp settings. The orthophragminid and nummulitid biofacies (BF7) indicates a below-wave base, outer shelf setting and the planktic foraminifera biofacies (BF8), recorded in the Transitional Beds, indicates a hemipelagic environment. Based on the foraminiferal counting, quantitative parameters such as the orthophragminids/nummulitids ratio, the planktic/benthic foraminifera ratio, and the hyaline/porcelaneous foraminifera ratio were calculated. These parameters indicate that the succession formed along a distally steepened ramp profile, showing a progressively tectonically-controlled deepening of the depositional environment, culminating with the final drowning of the carbonate ramp. Quantification serves as a crucial instrument for a precise and reliable palaeoenvironmental reconstruction, allowing the comparison amongst different successions.

Calcareous nannofossil biostratigraphy, bioevents, and palaeoecological interpretation of the lower-middle Miocene outcrops in west central Sinai (Egypt)

The Burdigalian/Langhian (B/L) boundary has not yet been designated as a Global Stratotype Section and Point (GSSP), despite various proposed zonal schemes. In the Gulf of Suez region of Egypt, the Burdigalian-Langhian successions are notable for hosting significant hydrocarbon reservoirs within a tectonic rift setting. Therefore, biostatigraphy plays a crucial role in exploration endeavors in this area. The nannofossil biostratigraphy is investigated in two sections, Wadi Baba and Wadi Gharandel, of the lower-middle Miocene from west-central Sinai. Three biozones, NN3 (Sphenolithus belemnos) Zone, NN4 (Helicosphaera ampliaperta) Zone, and NN5 (Sphenolithus heteromorphus) Zone, are identified from the studied interval. The NN4 Zone could be divided into MNN4a/b and MNN4c. Important biovents are discussed, such as the S. heteromorphus paracme interval and the first occurrence and evolution of the Discoaster exilis and Discoaster variabilis groups. Based on the cluster analysis, the recorded taxa can be subdivided into four groups that reflect their palaeoclimatic preferences. The paleoecological interpretation of the studied Rudies Formation indicates prevailing cool and eutrophic nutrient conditions based on the dominance of taxa such as Coccolithus pelagicus, Reticulofenestra minuta, and Cyclicargolithus floridanus. The nannofossil taxa responses to sea level curve are interpreted. Fluctuations in taxa abundance and diversity indicate a slight rise in the sea level at the base of the Burdigalian followed by sudden drop in the sea level at the middle Burdigalian. High sea-level conditions prevailed again until the B/L boundary. During the Langhian period, many small-scale fluctuations in sea-level curve are detected.

Unravelling changes in the productivity regime during the Late Miocene-Early Pliocene Biogenic Bloom: Insights from the western equatorial Pacific (IODP Site U1488)

The Late Miocene-Early Pliocene Biogenic Bloom (9.0–3.5 Ma) is a widespread paleoceanographic phenomenon marked by increased marine biological productivity and by high accumulations of biological components documented at multiple open ocean sites in the Indian, Pacific, and Atlantic oceans. We investigate the expression of the Biogenic Bloom at International Ocean Discovery Program (IODP) Site U1488 in the western equatorial Pacific Ocean. We generated an improved age model based on calcareous nannofossil biostratigraphy and a quantitative benthic foraminiferal record across the Late Miocene to the Early Pliocene. Increased carbonate mass accumulation rates suggest the Biogenic Bloom occurs between 8.1 and 4.0 Ma at Site U1488. We described four intervals with paleoenvironmental significance: Interval 1 (8.1–6.2 Ma), Interval 2 (6.2–5.5 Ma), Interval 3 (5.5–4.5 Ma), and Interval 4 (4.5–3.1 Ma), the Biogenic Bloom spans across Interval 1 and 3. Intervals 1, 3, and 4 are marked by high abundance of phytodetritus exploiting taxa, related to phases of El Niño-like conditions. The highest abundance of these species during Interval 1 has been related to a phase of higher seasonality. In contrast, intervals 3 and 4 show reduced seasonality and a steadier input of food to the seafloor, associated with increased dust supply through wind transport and/or increased continental weathering during the Pliocene. Interval 2 stands out as the sole interval encompassing La Niña-like conditions, marked by a shift in the nutrient composition reaching the seafloor, from labile phytodetritus to refractory organic matter, and possibly a decrease in seasonality.

Multiproxy faunal analysis of the middle – upper Eocene deposits in the Fayum area, Egypt: Insights into sequence stratigraphy, trophic conditions, and oxygenation

The Eocene epoch experienced significant fluctuations in climate, ranging from intense greenhouse warming to icehouse cooling, which profoundly impacted the global depositional systems. The middle – upper Eocene deposits in Garet Gehannam, Fayum area, Egypt, present an exciting opportunity to explore paleoenvironmental dynamics using a multiproxy dataset of calcareous nannofossils, benthic foraminifera, ostracods, and molluscan assemblages. Calcareous nannofossil biostratigraphy constrained the studied sequence to the NP17 and NP-19-20 zones. Furthermore, three 3rd-order depositional sequences, BAR.SQ.1, BAR.SQ.2, and PR.SQ.3 were identified. The BAR.SQ.1 sequence encompasses the Gehannam Formation, with a transgressive systems tract (TST) and a highstand systems tract (HST). The BAR.SQ.2 sequence corresponds to the lower Birket Qarun Formation and exhibits a TST/HST pattern. The PR.SQ.3 sequence, however, consists solely of a TST spanning the upper Birket Qarun and Qasr El Sagha formations. The main trend of our multiproxy-based sea level curve shows an overall stepped Tethyan sea level regression within the 2nd-order cycle. This regression is characterized by a transition from outer neritic to inner settings, interrupted by two minor 3rd-order transgressive pulses. This sea level trend was likely driven by global eustatic changes and regional tectonic uplift related to the final collisional phase between Africa/Arabia and Eurasia, which led to the closure of the Neotethys Ocean. Multiproxy faunal analysis reveals a pronounced upsection shift from low-oxic and mesotrophic conditions to well-ventilated, oligotrophic settings tracking long-term sea level fall. The lowering of the sea level may have expanded aerobic ventilation windows on the continental shelf while potentially reducing nutrient influx. Our multiproxy sequence stratigraphic and paleoenvironmental analysis provides insights into the complex interplay of tectonic, eustatic, and climatic influences on the region during the middle – late Eocene episode along the southern Tethyan margin.

Biostratigraphy of the Eocene shallow-water succession of the south Sabzevar area (Central Iran) based on larger benthic foraminifera and calcareous nannofossils

A rich larger foraminifera assemblage from the Eocene carbonates of the south Sabzevar region (Now-Deh section) in central Iran indicates a late Ypresian to early Lutetian age. Nine species of Alveolina d’Orbigny are studied for systematics and biostratigraphy. The assemblage includes A. minuta, A. decastroi, A. cremae, A. cremae elongata, A. decipiens ayrancensis, A. celali, A. rugosa, A. cuspidata, A. frumentiformis. We have also found nummulitids (genus Nummulites and Assilina) and orthophragmines identified as N. campesinus, N. praediscorbinus, A. placentula, A. praespira, A. reicheli, A. ex. intrec. laxispira-maior and Discocyclina archiaci bartholomei. The recovery of Alveolina cremae elongata, A. decipiens ayrancensis, A. celali, A. rugosa, A. cuspidata and Assilina praespira has permitted for the first time to extend their geographical distribution outside of the classical peri-Mediterranean area to the central Tethys regions. The obtained biostratigraphy points to the Shallow Benthic Zones SBZ11 to SBZ13, indicating the occurrence of a Lower–Middle Eocene carbonate system. Part of the age model is supported by the calcareous nannofossil biostratigraphy that belong to the NP14b and CNE8 biozones, recorded from the central portion of the studied section. Issues regarding the application of the SBZ into the Middle East domains are discussed in terms of relative stratigraphic position and biogeographic dispersal of some significant Alveolina species.

A benthic foraminifera perspective of the Late Miocene-Early Pliocene Biogenic Bloom at ODP Site 1085 (Southeast Atlantic Ocean)

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.

Calcareous nannofossil biostratigraphy and biochronology across the Eocene-Oligocene transition: the record at IODP Site U1509 (Tasman Sea) and a global overview

Calcareous nannofossil biostratigraphy and biochronology across the Eocene-Oligocene transition: the record at IODP Site U1509 (Tasman Sea) and a global overview

New insights on calcareous nannofossil biostratigraphy and paleoecology around the Pliensbachian/Toarcian boundary in the South Iberian paleomargin.

New insights on calcareous nannofossil biostratigraphy and paleoecology around the Pliensbachian/Toarcian boundary in the South Iberian paleomargin.

Revised calcareous nannofossil biostratigraphy and chemostratigraphy for the late Turonian–early Campanian at Seaford Head (southern England).

Revised calcareous nannofossil biostratigraphy and chemostratigraphy for the late Turonian–early Campanian at Seaford Head (southern England).

Middle to Late Miocene calcareous nannofossil biostratigraphy and paleoecology at Broken Ridge, eastern Indian Ocean (ODP Site 752).

Middle to Late Miocene calcareous nannofossil biostratigraphy and paleoecology at Broken Ridge, eastern Indian Ocean (ODP Site 752).

Oligocene–Early Miocene calcareous nannofossil biostratigraphy and paleoenvironment from the northern South China Sea.

Oligocene–Early Miocene calcareous nannofossil biostratigraphy and paleoenvironment from the northern South China Sea.

Cretaceous and Cenozoic calcareous nannofossil biostratigraphy of the northwestern inland basins of Colombia.

Cretaceous and Cenozoic calcareous nannofossil biostratigraphy of the northwestern inland basins of Colombia.

Upper Paleocene–lower Eocene calcareous nannofossil biostratigraphy at Nukhul, West Central Sinai, Egypt

This research offers a comprehensive examination of calcareous nannofossils, isotopic ratios (δ18O and δ13C), and carbonate content spanning the critical Paleocene-Eocene transition at Gebel Nukhul. The study covers three lithostratigraphic formations: Tarawan, Esna, and Thebes. By meticulous analysis, we’ve identified five distinct calcareous nannofossil zones, including NP7/8 and NP9-12. Zone NP9 is further divided based on the lowest occurrences of specific nannofossils (Discoaster anartios, D. araneus, and/or Rhomboaster spp.), while Zone NP10 is subdivided using Tribrachiatus contortus as a marker. We discussed the significance of various calcareous nannofossil taxa in biostratigraphy, highlighting their role as valuable stratigraphic markers. Our research precisely locates the base of the Eocene at the onset of Subzone NP9b within the Esna Formation, revealing no discernible lithological changes coinciding with this boundary. Additionally, our findings align with the global record, indicating significant decreases in δ13C, δ18O, and calcium carbonate (CaCO3) content during the Paleocene–Eocene transition. These changes underscore the climatic and environmental perturbations during this pivotal geological phase. This study provides valuable insights into the stratigraphy and paleoclimatology of the Paleocene–Eocene transition, contributing to our understanding of past climatic variations on Earth.

Biostratigraphy of calcareous nannofossils and their distribution in Tonasa Formation, Mallasoro area Jeneponto, South Sulawesi

The age studies of the Tonasa Formation have been carried out from various relative ages, including using large foraminifera, small foraminifera, and nannofossil. Field and laboratory data were collected to observe the age and distribution of nannofossils in the study area. The results of observations from nannofossils in the Mallasoro section of the Jeneponto area are as many as 20 species were identified and examined in three markers of Sphenolithus pseudoradians (NP.22-NP.24), and the Last Occurrence of Dictyococcites scrippsae (NP.25-NN. 1). The age zonation of Tonasa Formation in this area is determined from the three datums is the Late Oligocene to Early Miocene (NP. 21 – NN.1) or correlated to CP.16c – CP.19a. The nannofossil abundances are distributed from bottom to top of the section is common to a few species, they are Cyclicargolithus floridanus, Sphenolithus moriformis, and Sphenolithus predistentus, respectively. Then followed by Zygrhabilithus bijugatus, Discoaster deflandrei, Dictyococcites scrippsae, and Coccolithus pelagicus in rare to present distributions and the others are present to single.

Biostratigraphy of calcareous nannofossils and palaeoenvironments in the Lower Miocene of the Albanian–Thessalian Basin (Albania)

Biostratigraphy of calcareous nannofossils and palaeoenvironments in the Lower Miocene of the Albanian–Thessalian Basin (Albania)

Middle-late Eocene to Early Miocene micropaleontology of the ANH–TIERRALTA–2–X–P well: Biostratigraphic implications for southwestern deposits of the Sinú-San Jacinto belt (Colombian Caribbean)

The Eocene and Oligocene deposits of the southwestern region of the Sinú-San Jacinto Belt (SSJB) in NW South America were formed in marine environments influenced by fluvial discharges from the northern Andes of Colombia. However, these deposits are not well-exposed on the surface, which has limited the study of micropaleontological assemblages that could improve our understanding of the chronostratigraphic and paleoenvironmental characteristics of these rocks. In this study, we analyzed two cores of one of the thickest Cenozoic stratigraphic sections in the Caribbean region, from the ANH-TIERRALTA-2-X-P stratigraphic well, using palynomorphs and calcareous nannofossils. Our analysis allowed us to determine the age of deposition and understand the biostratigraphic patterns of marine and terrestrial microfossils in these nearshore deposits. We found that the first cored interval, from 2122 m to 2026.9 m, corresponds to marine rocks accumulated between the middle and late Eocene. The second interval, from 1130 m to 731.6 m, showed patterns of terrestrial and marine microfossils, which indicate the middle-late Eocene to the Early Miocene age. Palynological and calcareous nannofossil biostratigraphy were consistent in the middle to upper Eocene and Lower Miocene deposits, but discrepancies were observed in the Oligocene deposits. We attributed this to reworking or broader biostratigraphic ranges of certain palynological markers used in the biozones. Determining the age of the middle to upper Eocene and upper Eocene to lower Oligocene deposits was challenging due to the limited number of well-calibrated biostratigraphic markers. As a result, accurate correlation with the late Eocene – early Oligocene stratigraphic record from other parts of the SSJB is hindered, demonstrating that regional stratigraphic correlations based on biostratigraphy alone are problematic.

Spatial variations in the consolidation of sediments in the Neogene Miyazaki forearc basin, Southwest Japan

The Neogene Miyazaki Group comprises forearc basin sediments exposed onland in South Kyushu in Southwest Japan, and is characterized by significant spatial variations in consolidation despite the minor differences in depositional ages. The Miyazaki Group is divided into three lithofacies (the Aoshima, Miyazaki, and Tsuma facies) from south to north. To evaluate the factors controlling lithification in the basin, the physical properties of the sedimentary rocks and the calcareous nannofossil biostratigraphy were investigated. The upper parts of the Aoshima and Miyazaki facies and the lower part of the Tsuma Facies were deposited at the same time (5–6 Ma), and have minor differences in maximum paleo-temperatures (97–116, 85–99, and 80–94 °C, respectively), but major differences in porosity (15.9%, 25.5%–26.9%, and 26.1%–31.6%) and consolidation yield stress (38.2, 13.8–16.2, and 13.6–15.5 MPa). These findings indicate that the porosity reduction associated with consolidation is a more important control on the lithification than the depositional age and maximum temperature. There is a large difference in maximum burial depth between the Aoshima (>3500 m) and Miyazaki facies (<1600 m). It represents variations in sedimentary depositional environments in the Miyazaki Group: the Aoshima Facies were deposited in the deep-marine depocenter and deeply buried, whereas the Miyazaki and Tsuma facies were in the shallower marine facies and shallowly buried. After the deposition, only the southern part of the Miyazaki forearc basin was largely uplifted, making distribution of the highly consolidated sedimentary rocks there. The large amount of uplift in the Aoshima Facies was apparently due to the subduction of the Kyushu–Palau Ridge beneath the forearc basin.

High-resolution calcareous nannofossil biostratigraphy and facies of Nimar Sandstone Formation (Bagh Group), central India and its bearing on Oceanic Anoxic Event 2

It is proposed to consider Narmada Valley Late Cretaceous sequences in three sectors with proper selection of stratotype in each sector: Eastern Sector: comprising of Lameta group of rocks with type area in Jabalpur area, essentially laid down in lacustrine-paedogenic milieu and containing a variety of fossils including dinosaur remains of Late Maastrichtian age. No evidence of sea incursion is available in the Eastern Sector either via the Narmada lineament or the K-G Basin. Central Sector: comprising of the Bagh Group in ascending order of: Nimar Sandstone Formation–Nodular Limestone Formation–Coralline-Bryozoan Limestone Formation, laid down in estuarine complex entirely within Turonian without any evidence of Cenomanian and Coniacian age calcareous nannofossils or other fossils being present. In the western part of Central Sector: Siliciclastic rocks and limestones referred to as Nimar Sandstone Formation curiously lack Late Cenomanian marker species, hence could be of Early Turonian age. Western Sector: comprises of Lacustrine sediments associated with Deccan Flood Basalt. The absence of the Cenomanian/Turonian Boundary and Black shales negates the presence of global OAE2 events in the Narmada lineament, but several OAE events are recognised in the Cauvery Basin, southeastern India. Uranium- and Thorium-rich Lower and Upper Nimar Sandstone Formation overlying crystalline basement are interpreted to have been essentially laid down in a fully marine estuarine milieu with reworked plant, and palynofossils including dinosaur remains. Calcareous nannofossils recovered from Upper Nimar Sandstone Formation over four decades ago and assigned Late Turonian age is revised based on modern data incorporating calcareous nannofossil and planktonic foraminifera datum and now suggest an older age of Early Turonian matching a zone with FAD of Quadrum gartneri at the base and FAD of H. helvetica at the top. It must be emphasised that except for the solitary and unique incursion of Early Turonian (ca. 93.9 Ma) sea along the Narmada lineament reaching eastward (&gt;300 km) up to the present town of Indore, no other marine intrusion ever took place on Indian shield except along collision facing Subathu–Dogadda lineament during Late Maastrichtian. It would be erroneous to suggest that the global eustatic rise of sea level caused the entry of the Turonian sea along the Narmada lineament; instead, it was earlier speculated by me that Large Igneous Province activity of Mahajanga Flood Basalt of Madagascar (ca. 93.9 Ma) could have most probably caused a short-lived Turonian sea to enter Narmada lineament from the west around C/T boundary.

Basin-wide erosion and segmentation of the Plio-Pleistocene forearc basin in central Japan revealed by tephro- and biostratigraphy

The basement of the Tokyo metropolitan area consists of the Miocene–Pleistocene forearc basin fills that are well exposed around Tokyo Bay, especially on the Miura and Boso peninsulas. The forearc basin fills on these two peninsulas are called the Miura and Kazusa groups, and they were deposited during the late Miocene–Pliocene and Pliocene–middle Pleistocene, respectively. Because many biostratigraphic datum planes, paleomagnetic reversal events, and other chronostratigraphic tools are available for these deposits, they provide the “type stratigraphy” of other equivalent sedimentary sequences on the Japanese islands and in the northwest Pacific. However, the use of such stratigraphic markers has not been fully applied to understand the architecture of a basin-wide unconformity between the Miura and Kazusa groups called the Kurotaki unconformity. For our study, we made correlations among the Pliocene vitric tephra beds based on their stratigraphic levels, lithologic characteristics, the chemical compositions of glass shards, and calcareous nannofossil biostratigraphy. As a result, we were able to correlate tephra beds Ng-Ky25 just above the C3n.3n normal subchronozone (4.7 Ma), IkT16-An157.5 and IkT19-An158.5 near the top of the Mammoth reverse polarity subchronozone (3.21 Ma), and Ahn-Onr (2.6–2.7 Ma) across Tokyo Bay on the Miura and Boso peninsulas. We were able to recognize erosional surfaces and coeval mass-transport deposits immediately below the top of the Mammoth reverse polarity subchronozone, which suggests that submarine landslide(s) may have produced the lack of stratigraphic horizons (4.5–3.2 Ma) in the Miura and eastern Boso regions. Basal pebbly sandstone beds pervasively cover the erosional surfaces, and they show lateral variations into the thick (up to 60 m) mass-transport deposits and overlying turbidite sandstones. The lateral variations in sediment thickness of the post-failure deposits suggest that the basin-wide erosion was associated with the initial growth of a basin-bounding structural high that separates two distinct sub-basins in the forearc basin, which resulted in the subsequent onlapping deposition in the earliest stage of the Kazusa forearc basin. The basin-wide erosion marks the initiation of tectonic reconfigurations that led to segmentation of the forearc basin around the Tokyo Bay region.