SSP2.1

The Phanerozoic sedimentary record documents a diverse series of cyclic patterns of sedimentation that reflect multiple drivers of change (e.g. climate, eustasy, tectonics, biotic evolution) operating over a range of time scales (days to hundreds of million years). While short-term cycles can be easily identified within the rock record and have frequently been related to the Milankovitch cycles, medium-term (a few tens of million years) and long-term (hundreds of million years) cycles are less-well-resolved. Notably the identification of medium- and long-term cycles are reliant upon global scale studies, which are typically hampered by low stratigraphic resolution or address sedimentary changes indirectly through proxies (e.g. sea-level models, geochemical trends). Moreover, such difficulties have resulted in uncertainties as to the drivers and durations of medium- and long-term cycles.

To adequately address this challenge, an integrated approach is required, combining 1) large sedimentary and global events datasets, 2) a high-resolution sequence stratigraphic model, and 3) plate tectonic and digital palaeo-elevation modelling.

We present the preliminary results of an industry-led study of medium- to long-term Phanerozoic cycles in global sedimentation and an assessment of the drivers of these cycles. Our study is based upon a spatially- and temporally-enabled global dataset of sedimentary records, obtained from over 8,500 wells. The sedimentary data contained within the wells have been standardised using a hierarchical classification of sediment types and divided into time slices based upon sequence stratigraphic interpretations, and the identification of age calibrated maximum flooding surfaces derived from the Neftex Global Sequence Stratigraphic Model. This approach allows the Phanerozoic sedimentary record to be subdivided into 132 time slices and the proportion of different sedimentary compositions preserved for each time slice can be reported as a percentage. The resultant analysis identifies medium- to long-term cycles in the proportions of siliciclastics, carbonates and evaporites.

There are two long-terms trends apparent from our data, and these have been analysed by a palinspastic reconstruction of each time slice using our digital palaeo-elevation and tectonic models. The first trend is a progressive decrease in the proportion of carbonates relative to siliciclastics, such that carbonates represent ~50% of Cambrian sediments and ~30% of Neogene sediments. This appears linked to early Palaeozoic low latitude continental configurations favouring carbonate sedimentation. The second trend is a notable increase in evaporites from the Late Permian to Late Jurassic (5% to 10%, from a Phanerozoic average of <2%) this appears linked to the Pangea super-continent configuration and persists until its breakup. In addition, other lesser breakup events appear linked to increases in evaporites.

Medium-term cycles are identifiable as significant shifts in the global proportions of siliciclastics relative to carbonates. There is a hierarchical arrangement to these cycles, both in terms of duration and severity of change, suggestive of multiple drivers. An initial comparison with known glaciations, major biotic events impacting carbonate producers and orogenies appears to explain many of these cycles.

How to cite: Wrobel-Daveau, J.-C., Ray, D., Carroll, G., Tetley, M. G., Baines, G., Simmons, M., and van Buchem, F.: Long-term sedimentary cycles of the Phanerozoic; insights from the integration of global stratigraphic datasets and tectonic modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4555, https://doi.org/10.5194/egusphere-egu21-4555, 2021.

The Algarve Basin is a Mesozoic sedimentary basin located in southern Portugal. The basin was initiated by rifting associated with the opening of the North and Central Atlantic Ocean during the initial breakup of Pangea. Sedimentation commenced with continental red beds, which unconformably overlie folded and faulted late Carboniferous strata. The red bed succession (Silves Sandstones) consists mainly of sandstones and conglomerates at the base, overlain by variegated mudstones interbedded with siltstones and dolomites (Silves Mudstones, Siltstones and Dolomites). The sandstones were deposited in alluvial environments, and the mudstones in alluvial to shallow lacustrine environments. Upper Triassic (Carnian to Norian) macrofossils are scarce in the red bed succession, occurring predominantly in the upper beds of the succession above the Silves Sandstones, and do not accurately constrain the age of the beginning of the Algarve Basin.

A palynological study of a new road cut outcrop of Silves Sandstones, located in central Algarve, was undertaken in order to ascertain its age. A 3 m thick bed of grey siltstones located ca. 2.5 m above the unconformity yielded age-diagnostic palynomorphs, which date the onset of sedimentation in the basin. Samples from the latter bed yielded a moderately well preserved, low diversity palynomorph assemblage, which is dominated by Aulisporites astigmosus, Converrucosisporites sp. and Tulesporites briscoensis. Other taxa present in the assemblage include Alisporites sp., Calamospora sp., Cycadopites sp., Deltoidospora sp., Ovalipollis cf. ovalis, Triadispora sp., and Vallasporites ignacii.

The dominance of A. astigmosus together with V. ignacii is indicative of an early Carnian age based on comparison with independently dated sections described elsewhere in Europe. This new dating evidence thus constrains the beginning of sedimentation in the Algarve Basin to the earliest Late Triassic. The co-occurrence of T. briscoensis and A. astigmosus suggests a mixing of palynofloral elements typical of North American and central European Carnian assemblages respectively, which is consistent with the intermediate position of Portugal between those regions. The dominance of phytoclasts and the absence of marine palynomorphs confirms a continental depositional environment as also suggested by sedimentary lithofacies.

Acknowledgements

The authors would like to acknowledge the financial support of the Portuguese Foundation of Science and Technology (FCT) with the scholarship with the reference SFRH/BD/144125/2019 and would also like to acknowledge the financial support of the FCT to CIMA through UIDP/00350/2020.

How to cite: Vilas-Boas, M., W. Paterson, N., Pereira, Z., Fernandes, P., and Cirilli, S.: Constraining the age of the first pulse of continental rifting associated with the breakup of Pangea in Southwest Iberia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1346, https://doi.org/10.5194/egusphere-egu21-1346, 2021.

Greenhouse climates are periods characterized by high atmospheric CO₂ levels and the absence of large continental icecaps, conditions that define most of the Phanerozoic eon. Fossil record and proxy data from the Cretaceous-Early Paleogene (145-33 My) greenhouse interval suggest increased polar warmth and reduced latitudinal gradient. Such features are challenging for most climate models. They imply either misinterpretation of paleoenvironmental data or an underestimation of climate sensitivity under greenhouse climate. Here we present a new record from polar (>80°) paleolatitudes of the Early Jurassic (~180My) global warming episode known as the Toarcian Oceanic Anoxic Event. Carbonate clumped isotope (Δ47) thermometry and stable isotope analyses (δ¹⁸O_c, δ¹³C) were performed on pristine aragonite bivalve shells from the Polovinnaya River succession (N Siberia) recording exceptionally low burial. Reconstructed growing season temperatures of 9.7±5.2 to 19.0±3.4 °C and water δ¹⁸O_w values of −4.6±1.2 to −2.2±0.8‰VSMOW imply increased warmth and significant freshwater contribution in the Toarcian Arctic seas, in line with coeval Siberian paleobotanical data. The unusually low δ¹⁸O_w values confirm the incorrectness of assuming a spatially uniform δ¹⁸O_sw value for calculation of δ¹⁸O-derived paleotemperatures. The inferred Early Jurassic polar sea surface temperatures are in good agreement with independent high latitude proxy data from Cretaceous and Eocene warming events. Together with coeval sea surface temperatures data from the western Tethys Ocean, our new data suggest a strong reduction of latitudinal temperature gradients during the Toarcian relative to modern gradients. The reconstructed polar warmth and reduction in latitudinal temperature gradient are substantially higher than those simulated by most climate models of the Jurassic to Eocene greenhouse periods, and support the increasing amount of data and models indicating an increase of climate sensitivity with CO₂ levels. Our results bring critical new constraints for model simulations of Jurassic temperatures and δ¹⁸O_sw values and suggest that high climate sensitivity is the hallmark of greenhouse climates since at least 180 My.

How to cite: Letulle, T., Suan, G., Rogov, M., Daëron, M., Vinçon-Laugier, A., Reynard, B., Montagnac, G., and Lécuyer, C.: Clumped isotope evidence for polar warmth and reduced salinity during the Early Jurassic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14318, https://doi.org/10.5194/egusphere-egu21-14318, 2021.

The Jurassic was punctuated by several episodes of abrupt environmental changes associated with climatic instabilities, severe biotic crisis, and perturbations of the global carbon cycle. Over the last decades, the Toarcian Oceanic Anoxic Event (Early Jurassic, ~183 Ma) and the early Bajocian Event (Middle Jurassic, ~170–168 Ma) have attracted much attention because they represent such episodes of global and severe environmental change. Bracketed in between the Toarcian and the Bajocian, the Aalenian stage (Middle Jurassic, ~174-170 Ma) has received less attention, although there is some evidence from Tethyan and Boreal records that it was a time of environmental changes marked by marine biotic turnovers. The lack of knowledge about the Aalenian palaeoenvironments leaves a gap in our understanding of the wider context of the Toarcian and Bajocian events and hence of environmental feedback mechanisms surrounding Mesozoic carbon cycle perturbations. In this study, we provide a high-resolution, biostratigraphically well-defined carbon isotope records (δ¹³C_org and δ¹³C_carb) combined to Rock-Eval data for the upper Toarcian–lower Bajocian interval from two expanded marl/limestone alternation successions from France (French Subalpine Basin) and Chile (Andean Basin). The comparison with available records from the Tethyan and Boreal domains highlights that medium-term δ¹³C fluctuations are reproducible across different palaeoceanographic settings from both hemispheres and between different carbon substrates. The new high-resolution dataset highlights the complexity of the Aalenian δ¹³C record, including previously identified δ¹³C shifts and hitherto undescribed fluctuations. This study provides one of the most expanded high-resolution chemostratigraphic reference records for the entire Aalenian stage, and shows compelling evidence from both hemispheres that it was a time marked by recurrent perturbations to the global carbon cycle and environmental changes.

How to cite: Fantasia, A., Adatte, T., Spangenberg, J. E., Mattioli, E., Bernárdez, E., Thibault, N., Krencker, F.-N., and Bodin, S.: Recurrent global carbon cycle disturbances during the Aalenian: Evidence from France and Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8206, https://doi.org/10.5194/egusphere-egu21-8206, 2021.

Arctic carbon cycling and its regional climate have been observed to deviate from global trends in the Late Jurassic and across the Jurassic–Cretaceous boundary interval, but appear to recouple with global trends in the Early Cretaceous (Galloway et al., 2019; Jelby et al., 2020). We investigate the possible link between these observed trends and volcanism by examining the mercury (Hg) and other element records from Arctic sites in Svalbard (Norway) and the Queen Elizabeth Islands, Canada. We assess whether pulsed phases of the High Arctic Large Igneous Province, or the globally significant emplacement of Paraná-Etendeka or Greater Ontong-Java Plateau, are expressed by stratigraphic Hg trends recorded in the studied sites of Arctic Canada and Svalbard, and how any signals correlate with the regional stable carbon-isotope (δ¹³C) record. We compare these new data to Hg and δ¹³C records from other globally distributed sites, focusing on the carbon isotope excursion (CIE) intervals: the Arctic-wide Volgian CIE (“VOICE”), the global Valanginian positive CIE (“Weissert Event”), and the global early Aptian CIE associated with Ocean Anoxic Event 1a (OAE1a).

How to cite: Vickers, M. L., Jelby, M. E., Galloway, J. M., Percival, L., Wang, F., Sanei, H., Śliwińska, K. K., Price, G. D., Ullmann, C. V., Hougård, I. W., Midtkandal, I., Mather, T., and Korte, C.: Volcanism and carbon cycling in the High Arctic during the Late Jurassic – Early Cretaceous, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1279, https://doi.org/10.5194/egusphere-egu21-1279, 2021.

Although anoxia is rare in modern oceans, the marine stratigraphic record is punctuated by sedimentary and geochemical evidence for episodes of widespread oceanic anoxia. The last time in Earth history that a large volume of the ocean became anoxic was in the middle Cretaceous: black organic-carbon-rich muds were repeatedly preserved on the deep seafloor during oceanic anoxic events (OAEs).

Sedimentary and geochemical evidence for oceanic anoxia during OAEs comes mainly from the Atlantic and Tethys Oceans. Data from the Pacific Ocean, which was the largest ocean basin in the middle Cretaceous, is scarce and equivocal. Based on black shales deposited at depths of about 500–1500 m on seamounts, Monteiro et al. (2012) have suggested that at least 50 vol% of the ocean was anoxic at the climax of Cretaceous oceanic anoxia during the late Cenomanian. They also included a single black shale at DSDP Site 585 in the Mariana Basin as evidence for anoxia in the deep Pacific. We will show, however, that this is a mud turbidite reworked from shallower water.

For this study, we reviewed all available data and publications from scientific drilling that recovered Cretaceous sediments in the Pacific Ocean. The little available Cretaceous record from the Pacific consists mainly of well-oxidized sediments. The exceptions are black shales that occur at depths of about 500–1500 m on seamounts. Takashima et al. (2011) have shown that the Asian and North American continental margins of the Pacific were indeed oxic for most of the late Cenomanian OAE. 

We used a new paleomagnetic reconstruction of the Pacific plate back to 150 Ma to show that all investigated Cretaceous organic-carbon-rich sediments in the Pacific Ocean were deposited while the site was located in the Equatorial Divergence Zone (10°S to 10°N). We therefore argue that organic matter deposition in the Pacific Ocean might not have been directly related to OAEs, but rather be associated with the passage of seamounts beneath the equatorial belt of high productivity.

Several authors have challenged suggestions that OAEs were characterized by globally pervasive anoxic deep water and pointed to the difficulty in sustaining whole-ocean anoxia, even in warm oceans. We agree and our results show that oceanic anoxia in the Pacific is a local phenomenon superposed on a global trend of expanded oxygen minima in the ocean.

How to cite: Bouwmeester, M. J., Boschman, L., Berends, N., Owens, J. D., Gill, B. C., and Trabucho Alexandre, J. P.: Cretaceous Black Shales in the Pacific: The Equatorial Position Hypothesis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10135, https://doi.org/10.5194/egusphere-egu21-10135, 2021.

The Postalm section in the Gosau Group (Northern Calcareous Alps) exposes pelagic deposits of northwestern Tethyan origin. We present a magneto-, bio- and chemostratigraphic assessment of this Santonian to uppermost Campanian record, as well as a cyclostratigraphic model for the Tethyan Campanian based on three independently assessed proxies; the δ¹³C signature, the elemental ratio of Fe and the thickness of limestone/marl couplets (Wolfgring et al., 2021).

The Santonian/Campanian transition is characterised by condensed greyish packstones, the Campanian strata exhibit a succession of limestone-marl couplets that represent orbital precession of an approximate duration of 20ka. A magneto- and biostratigraphic (based on planktonic foraminifera and calcareous nannofossils) framework is supported by carbon isotope and strontium stratigraphy.

The Sr isotope record matches the data for the Upper Cretaceous and suggests no major gaps in the Postalm succession. A robust cyclostratigraphic assessment of three independently assessed data series (L/M couplets, Fe and δ¹³C) resulted in the identification of eighteen 405 ka eccentricity cycles spanning the middle to upper Campanian (Contusotruncana plummerae to Gansserina gansseri Zones or CC17/UC15 to CC23/UC16 nannofossil zones).

Carbon isotope stratigraphy identifies the LCE (Late Campanian Event) and possibly the SCBE (Santonian Campanian Boundary Event). Magneto- and biostratigraphic data, in particular the position of the top of the R. calcarata planktonic foraminifera Zone, the position of the LCE and the top of Chron C32r.1r served as primary tie points and constraints to match the floating cyclostratigraphic model to the Laskar solution and to compare it to other cyclostratigraphic solutions and reference sections for the upper Campanian.

References: Wolfgring, E., Wagreich, M., Hohenegger, J., Böhm, K., Dinarès Turell, J., Gier, S., Sames, B., Spötl, C., Jin, S., 2021. An integrated multi-proxy study of cyclic pelagic deposits from the north-western Tethys: The Campanian of the Postalm section (Gosau Group, Austria), Cretaceous Research, 120, 104704, doi.org/10.1016/j.cretres.2020.104704.

How to cite: Wagreich, M., Wolfgring, E., Hohenegger, J., Dinarès-Turell, J., Spötl, C., and Sames, B.: A multistratigraphic study of the Campanian Postalm section (Northern Calcareous Alps, Austria), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12656, https://doi.org/10.5194/egusphere-egu21-12656, 2021.

The main trigger for the Cretaceous/Paleogene boundary (KPB) mass extinction is still subject of intense debate. The co-occurrence of the Chicxulub impact (Yucatan, Mexico) and massive Deccan Traps volcanism (India) during Chron C29r hinders disentangling their climatic and environmental effects. Unravelling the influence of Deccan volcanism on the KPB extinction and other Maastrichtian and Danian perturbations requires more accurate age calibrations and duration estimates of biotic and climatic events. Here we integrate existing astrochronologies of the Zumaia section, allowing us to produce a refined cyclostratigraphic calibration of the main planktic foraminiferal and paleoclimatic events recorded across the KPB in the well-know Zumaia section (NW, Spain).

At Zumaia, the KPB is marked by a ~8 cm-thick dark clay bed, with low values of %CaCO₃ and δ¹³C. The Chicxulub ejecta-rich airfall layer has been identified at the base of the dark clay bed, but it is partially masked within a 1–2 cm-thick diagenetic calcitic layer. At Zumaia, the KPB has been astronomically calibrated at 66 Ma (compatible with radioisotopic ages), and the duration of dark clay bed is estimated at ~10 kyr. The first appearances (FA) of the Danian planktic foraminiferal index-species Parvularugoglobigerina longiapertura, Parvularugoglobigerina eugubina, Eoglobigerina simplicissima, Parasubbotina pseudobulloides, Subbotina triloculinoides and Globanomalina compressa have been orbitally tuned at Zumaia, to have occurred at 8, 30, 45, 70, 210, and 475 kyr after the KPB. Specimens of Plummerita hantkeninoides have been identified for the first time in the Maastrichtian of Zumaia, and its first occurrence is dated at ~100 kyr before the KPB. Based on d¹³C data, we have identified the late Maastrichtian Warming Event (LMWE), the early Danian Dan-C2 and the Lower-C29N events. Additionally, a bloom of the eutrophic/opportunist genus Chiloguembelitria, interpreted as a period of environmental stress, has also been recognized above and separate from the KPB clay bed. Besides the KPB, the main paleoclimatic/paleoenvironmental events have been astronomically calibrated at Zumaia as follows: the LMWE between 270 and 120 kyr before the KPB, the Dan-C2 event between 205 and 305 kyr after the KPB, the Lower-C29N event between 520 and 595 kyr after the KPB, and the Chiloguembelitria bloom between 100 and 305 kyr after the KPB. According to this chronology, we conclude that the LMWE and early Danian Chiloguembelitria bloom seems to coincide in time with major volcanic pulses of the Deccan Traps, unlike the Dan-C2 and Lower-C29N events, which appear to have been driven by orbital forcing. Regardless of the cause of climatic and environmental events, all these perturbations appear unrelated to the KPB mass extinction event. It supports the hypothesis that the influence of Deccan volcanism on planktic foraminiferal assemblages during the Maastrichtian and Danian was limited.

How to cite: Gilabert, V., Batenburg, S. J., Arenillas, I., and Arz, J. A.: Astronomical calibration of paleoclimatic and planktic foraminiferal events of the Cretaceous-Paleogene transition at Zumaia, Spain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8008, https://doi.org/10.5194/egusphere-egu21-8008, 2021.

The Eocene ‘‘blue hole” freshwater limestones from the bauxite cover-sequence at the Gánt karst system (Vértes Hills), Transdanubian Central Range, north-western Hungary, have yielded rich charophyte assemblages of higher taxonomic and biostratigraphic interest. The taxonomic study of this flora allows revision and emendation of the species Raskyella peckii and facilitates the definition of a new evolutionary anagenetic lineage based on three successive anagenetic varieties of this species which were formerly considered as separate species or subspecies: Raskyella peckii var. peckii (early Lutetian–early Bartonian), Raskyella peckii var. caliciformis (early Bartonian), and Raskyella peckii var. vadaszii (late Bartonian). Based on these, we propose a new local charophyte biozonation with the new Raskyella peckii Superzone (Lutetian–Bartonian), subdivided into three successive charophyte partial range zones: The ‘Raskyella peckii peckii Zone’ (Lutetian–lowermost Bartonian) is locally characterized by an assemblage of R. peckii peckii, Gyrogona caelata forma caelata, G. caelata forma monolifera and Nitellopsis (Tectochara) palaeohungarica. The ‘Raskyella peckii caliciformis Zone’ (lower Bartonian) includes the local assemblage of R. peckii var. caliciformis, G. caelata forma caelata, G. caelata forma monolifera, G. caelata forma baccata, Nitellopsis (Tectochara) palaeohungarica and Chara media. The ‘Raskyella peckii vadaszii Zone’ (upper Bartonian) is composed of the local assemblage of R. peckii var. vadaszii, G. caelata forma bicincta, G. caelata forma baccata, G. caelata forma fasciata, G. tuberosa, Psilochara polita, Psilochara sp., Chara media and Chara subcylindrica. Future research may show the new local biozonation as applicable to whole Europe and complementing the current European charophyte biozonation. Our results show that the sequences from Gánt previously regarded as upper mid-Eocene (upper Lutetian–lower Bartonian) appear to comprise a longer chronostratigraphic interval, i.e. lower Lutetian till upper Bartonian, with also has implications on the understanding of the regional stratigraphy of the Transdanubian Central Range during the Eocene.

How to cite: Trabelsi, K., Sames, B., Wagreich, M., Kázmér, M., Mindszenty, A., and Martín-Closas, C. M.-C.: Charophyte biostratigraphy of continental deposits in a filled-karst system: A case study from the Eocene bauxite cover-sequence at Gánt (Vértes Hills, Hungary), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12976, https://doi.org/10.5194/egusphere-egu21-12976, 2021.

About 34 Ma, the Warmhouse climate state switched into the Coolhouse state, when a rapid drop in temperature and the establishment of permanent continental ice-sheet on the Antarctic continent occurred (1).

This event, which is referred to as the Eocene-Oligocene transition (EOT; lasted ~500 ka) represents one of the most prominent transitions of the entire Cenozoic. During the EOT, calcareous nannoplankton experienced significant changes in the assemblage coinciding with the long-term cooling and modifications in the sea-surface water conditions (2, 3), suggesting a cause-effect relationship between the onset of the first sustained Antarctic glaciation and the response of phytoplanktonic communities.

We generated a high-resolution calcareous nannofossil and geochemical datasets (δ¹⁸O, δ¹³C and % CaCO₃) from IODP Site U1509 (New Caledonia Trough) (4) with the final aim to provide an overview of the paleoclimatic and paleoceanographic evolution of the study area across the EOT. Our bio-magnetostratigraphic results, consistent with shipboard data (5), were compared along with other existing records recovered from Indian Ocean, Equatorial Pacific and Atlantic Ocean in order to critically evaluate the reliability, reproducibility and synchroneity of all the biohorizons taken into consideration and to obtain a clearer global perspective. 

According to major trends and shifts in the assemblage, the ~5 Myr study interval was subdivided into 4 distinct phases, which were also identified based on changes observed in 1) a number of diversity indices (i.e., species richness, dominance, H-index and evenness), 2) the warm-oligotrophic taxa abundance (Discoaster saipanensis, D. barbadiensis and Ericsonia formosa), 3) the principal component (PC1 and PC2) scores, and 4) bulk stable isotopes and carbonate content. The observed changes are interpreted as an overall decline of warm-oligotrophic communities and, conversely, the incoming of genera better adapted to cooler and more eutrophic conditions.

The most prominent shift in the assemblage occurred during a time window of ~520 kyr, the precursor phase, with relatively high bulk δ¹⁸O and % CaCO₃ values, that predated the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum – EOGM) (6) and documented the permanent loss of the late Eocene k-selected community, characterized by warm and oligotrophic taxa.

References

1. T. Westerhold et al., Science. 369, 1383–1388 (2020).

2. T. Dunkley Jones, P. R. Bown, P. N. Pearson, J. Syst. Palaeontol. 7, 359–411 (2009).

3. H. K. Coxall, P. N. Pearson, in Deep-Time Perspectives on Climate Change: Marrying the Signal from Computer Models and Biological Proxies, Micropaleontology Society Special Publication, M. Williams, A. M. Haywood, J. Gregory, D. N. Schmidt, Eds. (Geological Society, London, 2007), pp. 351–387.

4. R. Sutherland, G. R. Dickens, P. Blum, the Expedition 371, Int. Ocean Discov. Progr. (2017), doi:10.14379/iodp.pr.371.2018.

5. R. Sutherland et al., Tasman Front. Subduction Initiat. Paleogene Clim. Proc. Int. Ocean Discov. Program, 371 Coll. Station. TX (International Oce. 371, 1–35 (2019).

6. Z. Liu, S. Tuo, Q. Zhao, X. Cheng, W. Huang, Chinese Sci. Bull. 49, 2190–2197 (2004).

How to cite: Viganò, A., Dallanave, E., Alegret, L., Westerhold, T., Sutherland, R., Dickens, G. R., and Agnini, C.: Calcareous nannofossils from the Tasman Sea (IODP Site U1509): biochronology, paleoclimatic evolution and bulk stable isotopes across the Eocene-Oligocene Transition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10985, https://doi.org/10.5194/egusphere-egu21-10985, 2021.

The latest Miocene-early Pliocene biogenic bloom is a poorly understood paleoceanographic event that has been traditionally related to increased primary productivity; and associated changes in the marine carbon cycle. In order to identify this event in the Tasman Sea, we carried out an integrated study at IODP Site U1506. First, we have constructed an age model based on an integrated approach (i.e. biostratigraphy, astrocyclostratigraphic tuning). This permits the identification of the precise position as well as the duration of the biogenic bloom in the Tasman Sea but also the calculation of sedimentation rates across the study interval. In this framework, we generated quantitative micropaleontological records (benthic and planktic foraminifera and calcareous nannofossils) and a low-resolution carbon and oxygen stable isotope records on Cibicidoides mundulus and Trilobatus sacculifer across an interval spanning from 233.50 to 81.75 m CSF-A (Tortonian, late Miocene to Zanclean, early Pliocene). Quantitative assemblage work and statistical analyses on the resulting dataset point to increased export productivity in the lower part of the interval (between CNM15 and CNM18, Backman et al., 2012), as inferred from benthic foraminiferal assemblages dominated by taxa (e.g. Uvigerina and Ehrenbergina) that have been reported to be common across the biogenic bloom in the Indian Ocean (Dickens and Owen, 1999). The paleoecological analysis of these assemblages suggests eutrophic conditions at the seafloor and low oxygen concentration of bottom waters.

Reference

Backman, J., Raffi, I., Rio, D., Fornaciari, E., & Pälike, H., 2012. Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes. Newsletters on Stratigraphy, 45(3), 221–244.

Dickens, G.R. and Owen, R.M., 1999. The latest Miocene-early Pliocene biogenic bloom: A revised Indian Ocean perspective. Marine Geology, 161: 75-91.

Acknowledgments

University of Padova DOR grant, CARIPARO Foundation Phd scholarship.

Spanish Ministry of Economy and Competitiveness and FEDER funds (PID2019-105537RB-I00).

How to cite: Gastaldello, M. E., Agnini, C., Dallanave, E., Westerhold, T., Lam, A. R., Drake, M. K., Dickens, G. R., Sutherland, R., and Alegret, L.: Hunting down the late Miocene-early Pliocene biogenic bloom in the Tasman Sea: an integrated study at IODP Site U1506, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10907, https://doi.org/10.5194/egusphere-egu21-10907, 2021.

The Middle Pleistocene Subseries and Chibanian Stage were officially defined in 2020 through ratification of the Global Boundary Stratotype Section and Point (GSSP) at Chiba, Japan (Suganuma et al., in press).  Their shared base at 774.1 ka represents the approximate midpoint of the Early–Middle Pleistocene transition, a 1.4–0.4 ka interval marked by a progressive increase in the amplitude of climate oscillations and shift towards a quasi-100 ky frequency.  They currently both extend to the base of the Upper Pleistocene Subseries dated provisionally at ~129 ka (Head et al., in press).  Global stages have not traditionally been employed for the Quaternary owing to the long use of global subseries and regional stages.  Global stages are nonetheless required for formal subdivision of the International Chronostratigraphic Chart, and their acceptance in subdividing both the Holocene and Pleistocene Series has become increasingly evident.  The Middle Pleistocene Subseries and Chibanian Stage are currently identical in extent.  With this in mind, we consider the possibility of subdividing the Middle Pleistocene by introducing a second stage, which would shorten the duration of the Chibanian and increase its utility.  There has been increasing recognition of the ‘Mid-Brunhes Event’ (Jansen et al., 1986) more recently termed the ‘mid- Brunhes Transition’ (Yin, 2013; Barth et al., 2018), an abrupt step-change to increased amplitude of the quasi-100 kyr cycles and warmer interglacials from MIS 11 onwards. The base of this new stage would reasonably be placed around the MIS 12–MIS 11 transition (Termination V, ~420 ka), a level clearly recognised in the marine record. This level appears to approximate the bases of the Holsteinian, Hoxnian, Likhvinian, and Zavadivian regional stages across northwestern and central Europe, the Russian Plain, and the Ukrainian Loess Plain; and can be traced across the Chinese Loess Plateau (Cohen and Gibbard, 2020).  The possibility of a second stage will initially be explored by publication of a position paper. If this attracts sufficient support, a Working Group of the International Subcommission on Quaternary Stratigraphy will be established to analyse the case more formally.

Barth, A.M., Clark, P.U., Bill, N.S., He, F., Pisias, N.G., 2018.  Climate evolution across the Mid-Brunhes Transition. Climate of the Past 14, 2071–2087.

Cohen, K., Gibbard, P., 2020. Global chronostratigraphical correlation table for the last 2.7 million years v.2019 (Poster version), Mendeley Data, V3, doi: 10.17632/dtsn3xn3n6.3

Head, M.J., Pillans, B., Zalasiewicz, J.A., in press. Formal ratification of subseries/subepochs for the Pleistocene Series/Epoch of the Quaternary System/Period. Episodes.

Jansen, J.H.F., Kuijpers, A., Troelstra, S.R., 1986. A mid-Brunhes climatic event: Long-term changes in global atmosphere and ocean circulation. Science 232, 619–622.

Suganuma, Y., Okada, M., Head, M.J. et al., in press. Formal ratification of the Global Boundary Stratotype Section and Point (GSSP) for the Chibanian Stage and Middle Pleistocene Subseries of the Quaternary System: the Chiba Section, Japan.  Episodes.

Yin, Q., 2013. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature. Nature 494: 222–225.

How to cite: Head, M. J., Zalasiewicz, J., Bertini, A., and Zhou, L.: The Mid-Brunhes Event: a second stage for the Middle Pleistocene Subseries?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6900, https://doi.org/10.5194/egusphere-egu21-6900, 2021.