Priabonian Research Articles

Ypresian–Lutetian platform evolution in the Indus Basin, Southwestern Pakistan: An interplay between local and regional tectonic changes

The present investigation aims to analyze the depositional environment, sequence stratigraphy, and geochemistry of the Early–Middle Eocene succession in the Laki Range of the Southern Indus Basin, Pakistan. The sequence is subsequently correlated with other sections within the Southern Indus Basin, Central Indus Basin, Upper Indus Basin, and Hazara Basin in Pakistan. For this study, the Lakhra and Laki formations were sampled from four sections in the Laki Range. Based on detailed outcrop observations, eight lithofacies were identified including four clastic lithofacies (CLF-1 to 4) and four limestone lithofacies (LLF-1 to 4). Similarly, based on detailed petrographic examination, seven microfacies were identified in limestone units. Considering the biotic paleoecology, facies texture, and chemical composition, depositional environments were assigned to the microfacies and lithofacies. All the microfacies, and the shale and sandstone lithofacies (CLF-1 and CLF-4) represent shallow inner to deeper outer-shelf settings whereas the other two lithofacies (CLF-2 and CLF-3) represent deltaic and tidal flat settings, respectively. All the microfacies and lithofacies information was used to establish sequence stratigraphy for the studied strata. The top of the Lakhra Formation and the whole of the Laki Formation in the Bara Nala Section (BNS) represent two complete, and two partial, third-order sequences, further divided into fourth order and small-scale cycles. The sequence's development is primarily influenced by regional and local tectonics. The regional correlation of the Indus Basin and Hazara Basin indicates that the regional basin's bathymetry and resultant depositional sequence were significantly influenced by the Himalayan Orogeny. The regional depositional pattern indicates that subsequent to India–Asia collision, the closure of eastern Tethys took place in a temporal succession from northwestern to the southwestern parts of the Indus Basin. In the Central Indus Basin, marine environments persisted until the Priabonian Stage (SBZ20) compared to those of the Upper (SBZ11–12) and Southern (SBZ13–14) Indus basins. This study offers valuable insights into both the local and regional depositional frameworks and the influence of local and regional tectonics on a carbonate platform evolution.

Upper Eocene benthic foraminiferal assemblages from Western Siberia (Trans-Ural Region): a multi-proxy approach to infer environmental changes

During the Late Eocene, the West Siberian Basin became increasingly isolated from the Peri-Tethys Ocean. The final stage of this marine connection is marked by sediments of the Tavda Formation thatwere deposited during the Bartonian and Priabonion. We have analyzed the composition, structure and diversity of benthic foraminiferal assemblages in core material from the Kyshtyrla Quarry located in the southwest of Western Siberia to reconstruct the depositional environment during the terminal phase of marine sedimentation in theWest Siberian Basin (Upper Tavda Subformation). The foraminiferal record was jointly used with lithological and geochemical multi-proxy data to infer the chronology of events that shaped the critical transition until the complete closure of the basin. Based on stratigraphic index markers, a Priabonian age is indicated for sediments of the Upper Tavda Subformation. From the bottom to the top of the core, the foraminiferal biotas progressively shift from shallow subtidal to low-diverse and stress-tolerant intertidal assemblages, indicative for an increasing isolation of the West Siberian Basin. The increasing shallowing of the marine basin is accompanied by a gradual shift in grain size, and the continuous presence of benthic foraminifera and ratios of geochemical proxies (Sr/Ba, Si/Al, Ti/Al, Zr/Al, K/Al, and U/Th) indicate that mainly marine to brackish water conditions prevailed.

Paleogene turtles of Eastern Europe: new findings and a revision

The article provides an overview of all known 39 localities of the Paleogene turtles of Eastern Europe. Numerous remains of turtles are described for the first time from 19 localities, of which six are new, and 13 are the localities from which materials were only mentioned previously. Among them are Pan-Trionychidae indet., Pan-Cheloniidae indet., Dermochelyidae indet. and Pan-Testudines indet., as well as pan-cheloniids Argillochelys sp. from the Ypresian Novoivanovka and the Ypresian or Lutetian Gruzinov localities. Several indeterminate specimens from Eocene localities show similarity to pan-cheloniids Argillochelys cuneiceps (Owen, 1849) and Puppigerus camperi (Gray, 1831) or Tasbacka aldabergeni Nessov, 1987, and dermochelyids Natemys peruvianus Wood et al., 1996 or “Psephophorus” rupeliensis van Beneden, 1883. One specimen of costal 1 of Pan-Testudines indet. from the Lutetian Krasnorechenskoe locality resembles that of pleurodires Eocenochelus spp. and Neochelys spp. In addition, new materials of turtles are described from five previously known localities. Among them, new and additionally restored specimens from the Bartonian Ak-Kaya 1 locality of the pan-cheloniid Argillochelys sp., and the dermochelyid Cosmochelys sp., which expand data on their morphology and intraspecific variability. The specimens of pan-cheloniids with deep and dense sculpturing of the external shell surface from the Bakhmutovka, Bulgakovka, Krasnorechenskoe and Tripolye localities clearly belong to a new species, not described due to fragmentary material. It is supposed that Anhuichelys-like pan-testudinoids migrated from Asia in Eastern Europe in the Danian age, and were preserved as relict Dithyrosternon valdense Pictet et Humbert, 1855 until the Priabonian age.

Turbiosphaera archangelskyi sp. nov. and a morphological complex from the late Middle to Late Eocene of southern high latitudes: Biostratigraphic, palaeoenvironmental and palaeoceanographic implications

We record a morphological complex of species of the dinoflagellate-cyst genus Turbiosphaera from the uppermost Río Turbio Formation, considered to be of late Priabonian age, and from equivalent units of the Austral-Magallanes Basin, southern Argentina and southern Chile. Previously, specimens now assigned to Turbiosphaera archangelskyi sp. nov and Turbiosphaera sarrisii were assigned to the cosmopolitan latest Maastrichtian to Middle Eocene species Turbiosphaera filosa. We now identify three species in our Turbiosphaera archangelskyi species complex, which excludes Turbiosphaera filosa. At one end of the complex is Turbiosphaera sarrisii with incipient processes, and at the other end, with well-developed individual processes, is Turbiosphaera sagena. The new species, Turbiosphaera archangelskyi, represents the intermediate stage and is the most abundant form. These three species have only been recorded together in the Austral-Magallanes Basin; their earliest occurrences are slightly asynchronous: Turbiosphaera sarrisii and Turbiosphaera archangelskyi have earliest occurrences in the late Bartonian, but that of Turbiosphaera sarrisii is slightly older. The earliest occurrence of Turbiosphaera sagena is recorded in the middle Priabonian. Our results highlight the biostratigraphic value of these species and their limited palaeogeographical distribution. The morphological variability exhibited by the Turbiosphaera archangelskyi species complex in the latest Eocene may be environmentally influenced, perhaps reflecting the deepening of the Drake Passage and the consequent influx of low-salinity water from the shelf and nearshore regions of the southeastern Pacific onto the Patagonian Shelf.

New Spore and Pollen Data from the Upper Eocene Deposits of the Sambian Peninsula, Kaliningrad Oblast

The article presents the results of the study of continental palynomorphs from the amber-bearing Upper E-ocene deposits in the Primorsky quarry (Kaliningrad Oblast, southeastern coast of the Baltic Sea). Three spore and pollen assemblages were identified and calibrated with the dinoflagellate cyst Rhombodinium perforatum and Thalassiphora reticulata zones. The “Blue Earth” Member of the Prussian Formation of the early Priabonian age is characterized by the Tricolporopollenites exactus–T. retiformis–Quercoidites microhenrici assemblage. The upper Priabonian “Upper Quicksand” and “White Wall” members of the Prussian Formation and the Palvé Formation are characterized by the Platanipollis ipelensis–Castaneoideaepollis oviformis–Tricolpopollenites foraminatus assemblage. The Inaperturopollenites–Sciadopityspollenites–Sequoiapollenites assemblage was recognized in the uppermost Palvé and lowermost Kurshskaya formations of the terminal Priabonian age. During the late Eocene the climatic conditions on the territory of the modern southern Baltic area were quite warm and humid, close to subtropical ones. Mixed coniferous-broad-leaved forests grew along the shores of the marine paleostrait, while the open spaces were occupied by heat-loving evergreen and moderately heat-loving deciduous shrubs and low-lying land areas were swamped. At the end of the Priabonian, a gradual regression of the sea basin began, which led to an increase in swampy areas on land, while the climate was still quite warm and humid.

First records of aneuretine ants (Hymenoptera: Formicidae: Aneuretinae) in late Eocene Rovno amber (Ukraine)

Aneuretinae is an enigmatic ant subfamily with poorly defined morphological boundaries. Aneuretus simoni Emery, 1893, found only in Sri Lanka, is a “living fossil”, the only known extant species of Aneuretinae. In the distant past, however, Aneuretinae was more diverse and widespread, including eight extinct genera spread across North America, Europe, and the Russian Far East. Here, we report two fossil Aneuretinae species, Protaneuretus succineus Wheeler, 1915 and Paraneuretus tornquisti Wheeler, 1915, found in late Eocene (Priabonian, 37.8–33.9 Ma) Rovno amber (Ukraine), providing distinguishing morphological features and measurements. These species, the first recorded Aneuretinae in Rovno amber, were originally described from Baltic amber of similar Priabonian age. These new records raise the number of reported ants in Rovno amber to 77 species from 39 genera and 9 subfamilies, and indicate that in the late Eocene Aneuretinae were distributed both on the northern and southern coasts of the Paratethys. Fossil evidence suggests that Aneuretinae originated in the Northern Hemisphere and only entered India and Sri Lanka after the Indian subcontinent collided with Asia ~59 Ma. Why Aneuretinae survived to the present only in Sri Lanka remains a mystery.

Palynostratigraphy, biochronology and palaeobathymetry of a section of Awaizombe-1 well, eastern Niger Delta, Nigeria

ABSTRACTDitch cuttings (69 samples) from a section of Awaizombe-1well located in the Northern Depobelt of the eastern Niger Delta Basin were used for this study. The lithology of the studied interval 1373–1812 m (439 m thick) consists of fissile grey shale and mudstone units. The scid method of sample preparation for palynormorphs’ recovery was adopted. Analysis recorded a well-preserved and diverse assemblage of palynomorphs, rich in pollen, spores and dinoflagellate cysts (dinocysts). First and last occurrences of marker and age diagnostic species were used for palynostratigraphic interpretation. Four palynostratigraphic interval range zones were established: Psilatriporites sp.–Racemonocolpites hians Zone; early Oligocene (Rupelian age), Praedapollis africanus–Doualaidites laevigatus Zone; late Eocene (Priabonian age), middle Eocene (Lutetian and Bartonian ages), Doualaidites laevigatus–Praedapollis flexibilies Zone; and early Eocene (Ypresian age), Verrucatosporites usmensis–Retitricolpites ituensis Zone. The first downhole occurrence of D. laevigatus at the 1482 m marks the late Eocene/early Oligocene boundary. Established zones are useful for inter and intra basins correlation. Lithology and age of the studied section are suggestive of the lower Agbada Formation. Palaeoenvironmental interpretations using diagnostic species revealed two environments: brackish and inner neritic to upper bathyal (0–600 m) under relatively warm-water marine condition indicated by thermophilic dinocyst taxa, such as Lingulodinium machaerophorum, Polysphaeridium zoharyi and Homotryblium spp. The lithology and these types of environments are good sites for hydrocarbon generation.

Morphology and Putative Ecology of Eocene Ant Agroecomyrmex duisburgi (Hymenoptera: Formicidae: Agroecomyrmecinae)

Agroecomyrmecinae is a poorly-known subfamily of ants that includes just two extant genera and species, Tatuidris tatusia Brown et Kempf, 1968, a leaf-litter dweller from the Neotropics, and Ankylomyrma coronacantha Bolton, 1973, an arboreal inhabitant from West Africa. Two Agroecomyrmecinae genera have been described from Eocene fossils: Agroecomyrmex Wheeler, 1910 found in European amber (Baltic and Bitterfeld), and Eulithomyrmex Carpenter, 1935 found in North American shale (Florissant). There are published records of just seven specimens of Agroecomyrmex duisburgi (Mayr, 1868), the sole member of its genus. We found four additional A. duisburgi specimens, three from Baltic amber and one from Rovno (Ukraine) amber of similar age (Priabonian stage, 37.8–33.9 Ma). This increases number of known ant subfamilies in Rovno amber to 10, and indicates that Agroecomyrmecinae were distributed in the late Eocene on both the northern and southern coasts of the Paratethys Sea. Based on morphological features and the rarity of fossil remains, we suggest that Agroecomyrmex and Eulithomyrmex were most likely neither litter-dwelling nor arboreal, but were epigean species, living on the soil surface.

Bolide impact effects on the West Florida Platform, Gulf of Mexico: End Cretaceous and late Eocene

Abstract This study documents seismic reflection evidence that two different bolide impacts significantly disrupted stratigraphic and depositional processes on the West Florida Platform (Gulf of Mexico). The first impact terminated the Late Cretaceous Epoch (Chicxulub impact, Mexico; ca. 66 Ma; end-Maastrichtian age). The second took place in the late Eocene (Chesapeake Bay impact, Virginia, USA, portion of the Chesapeake Bay; ca. 35 Ma; Priabonian age). Both impacts produced far-reaching seismic shaking and ground roll followed by an impact-generated tsunami, the effects of which are evident in the seismostratigraphic record. The Chicxulub seismic shaking caused collapse and shoreward retreat of the Florida Escarpment and widely disrupted (faulting, folding, slumping) normal flat-lying shelf beds. The associated tsunami currents redistributed these shelf deposits and mixed them together with collapse debris from the escarpment to form a thick wedge of sediments along the base of the escarpment. The Chesapeake Bay impact created a mounded sedimentary deposit near the outer edge of the late Eocene ramp slope. This deposit also has a bipartite origin. A lower layer is marked by en echelon faulting created in situ by seismic shaking, whereas an upper layer represents sediments redistributed from the late Eocene shelf and upper ramp slope by tsunami-driven bottom currents (debris flows, contour currents, slumps). This is the first report of seismic effects from the Chesapeake Bay impact in the Gulf of Mexico. These results further demonstrate that large-scale marine bolide impacts have widespread effects on the stratigraphic and depositional record of Earth.

The Guinardera quarry (Sant Martí de Tous, Barcelona): A new chert exploitation location during historical times

In 2014, an anthropic accumulation of chert material was discovered in La Guinardera area, at the southwest of the Sant Martí de Tous town (Barcelona, NE Iberian Peninsula). In 2018 a first archaeological intervention was carried out in two locations: La Guinardera and La Guinardera Nord. After the fieldworks, these two accumulations were interpreted as chert workshops. These workshops are in the St. Genís Formation, included within La Noguera lacustrine system and dated to the Priabonian age (upper Eocene). The St. Martí de Tous area presents shallow lacustrine conditions typical of sabkha environments, in which layers of gypsums and sandy lutites are interspersed with tabular red sandstone levels, yielding different varieties of chert.
 The Guinardera chert is characterized by a fairly homogeneous matrix, presenting a fine texture, with a microcrystalline and spherulitic length-slow chalcedony matrix, and a combination of grey colours, in general of dark hues, with an opaque diaphaneity but translucent at the edges.
 The archaeological assemblage from La Guinardera Nord site allows us to identify a chert workshop for the production of gunflints. The heterogeneity of the assemblage at La Guinardera site precludes assigning it to any single chrono-cultural period or function.
 The technological characterization of La Guinardera Nord site reveals distinctive attributes of a gunflint workshop that can be differentiated from prehistoric workshops. The presence of square and thick preforms, oxide traces on butts and ventral faces, marked bulbs and thick platforms, together with fresh edges on flakes and blades and the near-absence of patinated materials, corroborate it.
 The presence of these two deposits within the above-mentioned formation shows us a repeated landscape exploitation pattern for raw material extraction, since references chert use range from the Middle Palaeolithic (e.g., Abric Romaní) to historical times (e.g., La Guinardera Nord).

A new species of Maomingosuchus from the Eocene of the Na Duong Basin (northern Vietnam) sheds new light on the phylogenetic relationship of tomistomine crocodylians and their dispersal from Europe to Asia

Maomingosuchus acutirostris sp. nov. is a new tomistomine crocodile from the middle–upper Eocene deposits (late Bartonian–Priabonian age, 39–35 Ma) of the Na Duong Basin in northern Vietnam. M. acutirostris can be differentiated from the type species Maomingosuchus petrolicus by having an acute anterior tip of the premaxilla. Both species differ from another Maomingosuchus from Krabi (Thailand) by differences in the surangular–dentary suture and maxillary alveoli. According to our phylogenetic results, M. acutirostris seems to be the sister species to the group M. petrolicus + Krabi-Maomingosuchus. The close relationship between those three tomistomines is supported in the present phylogenetic analysis by three synapomorphies. In our phylogenetic analysis, Maomingosuchus was retrieved in a basal position forming the sister group to Paratomistoma + Gavialosuchus + Melitosaurus + Tomistoma, including the extant Tomistoma schlegelii. This phylogeny indicates three different dispersal events of Tomistominae from Europe towards eastern Asia: 1) for the stem lineage of Maomingosuchus, no later than the late Eocene; 2) for the stem lineage of Penghusuchus pani + Toyotamaphimeia machikanensis, no later than the early–middle Miocene; and (3) for the stem lineage of T. schlegelii, during the Neogene. http://zoobank.org/urn:lsid:zoobank.org:pub:19B27C1E-0A3F-4425-AA8C-F904277DF327

Phosphogenesis in the Zagros Fold-Thrust Belt, Iran: The link between the Tethyan paleoenvironment and phosphate ore deposition

The Zagros phosphogenic horizon, hosted by the Eocene-Oligocene Pabdeh Formation, is located in the NW-SE-trending Zagros Fold-Thrust Belt (ZFTB), Iran. These phosphorites, which formed along the Tethyan Realm, are the most important and highest-grade phosphatic resources of Iran. This paper discusses the evolution and depositional paleoenvironment of the Zagros phosphogenic horizon. Petrographic studies indicate that the main components of the ZFTB phosphatic horizons are pellet, ooid, intraclasts, and bone fragments and various microfossils, which are common in other Tethyan phosphorites. Post-Archean Australian Shale-normalized patterns of REE in these rocks show HREE enrichment, a negative Ce anomaly in all studied samples and a positive Eu anomaly in the majority of the studied samples. These patterns are interpreted to reflect the original REE signature of the paleo-seawater rather than any significant effect of diagenetic changes on the geochemistry of the Zagros phosphorites. Comparison of measured 87Sr/86Sr values with the Eocene secular seawater curve suggests a Lutetian age (47.8 and 41.2 m.y.) for the Sheykh-Habil deposit and a Priabonian age (37.8 and 33.9 m.y.) for the Kuh-e-Sefid and Kuh-Rish deposits. The Zagros and eastern Mediterranean phosphorites form part of the Tethyan Phosphogenic Province which, over a period of ∼ 50 m.y., developed in a long (∼7000 km) and narrow (<800 km) east–west trending marine channel system. Additionally, the δ18OCarb values from the studied samples indicate minimal weathering, while the obtained δ13CCarb values support an unaltered authigenic origin, as has been proposed for other eastern Mediterranean phosphorites. Our findings suggest that the paleoenvironmental conditions during formation of the Zagros phosphorites varied from oxic-suboxic to anoxic during microbial decomposition of organic compounds and/or bacterial reduction of sulfate. The negative shifts evident in the δ13CCarb data and presence of glauconite are consistent with precipitation of the Zagros phosphorites in a shallow marine environment, most likely a mid- to outer ramp setting at a depth of ∼ 150 m within which the Pabdeh Formation is believed to have been deposited.

Integrated stratigraphy of the middle-upper Eocene Souar Formation (Tunisian dorsal): Implications for the Middle Eocene Climatic Optimum (MECO) in the SW Neo-Tethys

Calcareous nannofossil biostratigraphy and carbon-isotope stratigraphy on bulk organics of the middle-upper Eocene Souar Formation (Tunisia) allow for a refined stratigraphy of this interval in the southwestern Neo-Tethys margin. The Souar Formation represents the deepest sedimentary deposits of the central northern Tunisian Basin and was only dated previously by coarse data on planktonic foraminifera. Together with our new data, a correlation is proposed to previous Tunisian records of the Halk El Menzal carbonate platform to the NE and shallow-water deposits of central Tunisia to the SW, which leads us to the erection of a synthetic stratigraphic chart of the middle-upper Eocene in central and northeastern Tunisia. Our results allow for a review of the accurate position of the Lutetian / Bartonian and the Bartonian / Priabonian stage boundaries in Tunisia relative to calcareous nannofossil biohorizons. We apply Bayesian statistics to build our age-depth model which points to a hiatus in the Lutetian (CNE12 Zone) that we relate to the middle Lutetian regressive sequence leading to the Lu-4 M-cycle. Radiolarian-rich sediments and cherts of the late Lutetian and early Bartonian are interpreted as a response to an increase in productivity, tied to the seasonal upwelling of nutrient-rich waters. Correlation to other sections in Tunisia highlights the strong contrast in facies between the carbonate-rich sequences of the edges of the dorsal and the silica-rich deposition in the Souar Formation. This contrast is particularly pronounced in the interval before and across the Middle Eocene Climatic Optimum (MECO) characterized by a maximum of nummulitic carbonate production on the platform and a minimum of carbonate production in the deep basinal parts of the Tunisian dorsal, rather dominated by silica-rich sediments. • Middle-Late Eocene calcareous nannofossil biostratigraphy in the SW Neo-Tethys. • The MECO corresponds to the Reneiche member in the Tunisian stratigraphic chart. • The MECO is characterized by a δ 13Corg excursion and biosiliceous productivity. • Increase in terrigenous flux to the Tunisian dorsale during the MECO. • Major sedimentation rate variations due to changes in the on-land weathering.

Stratigraphic architecture of a saline lake system: From lake depocentre (Alès Basin) to margins (Saint‐Chaptes and Issirac basins), Eocene–Oligocene transition, south‐east France

ABSTRACTChanges in sedimentary profiles and stratigraphic architecture over time in lake basins are shown to be relevant markers of climate changes in terrestrial palaeoenvironments. The stratigraphic architecture of the Priabonian (late Eocene)–early Rupelian (early Oligocene) Alès–Saint‐Chaptes–Issirac saline lake system has been reconstructed from the sedimentological, biostratigraphic and magnetostratigraphic analysis of outcrops and well cores. As a function of the inflow–evaporation balance, three distinct depositional models have been proposed for the Priabonian Alès–Saint‐Chaptes–Issirac lake system which is characterized by both fault‐controlled and low‐angle ramp‐like margins: (i) freshwater to oligohaline lake; (ii) oligohaline to mesohaline closed‐lake; and (iii) hypersaline, evaporitic closed‐lake. Two major stages of lake spreading (possibly middle Priabonian and late Priabonian–early Rupelian) separated by two stages of significant lake closure represented by evaporite succession in the Alès Basin depocentre (middle to late Priabonian) have been evidenced. Regional tectonics and climate induced changes in inflow–evaporation balance of the lake and controlled the development of transgressive–regressive cycles with calcium‐sulphate sedimentation during regression in the lake depocentre (Alès Basin) and during early transgression in lake margins (Saint‐Chaptes and Issirac basins). The correlation between the palaeohydrological cycles inferred for the Alès–Saint‐Chaptes–Issirac lake system and the regional climate changes of Priabonian stage, prior to the Eocene–Oligocene transition, strongly suggests that climate significantly impacted the nature of lacustrine depositional models and the depositional architecture of Palaeogene, syn‐rift, saline lake basins from Western Europe.

CeutorhynchusGermar (Coleoptera, Curculionidae) as proxy for Eocene core Brassicaceae: first record of the genus from Rovno amber

AbstractThe beetleCeutorhynchusis used as a proxy for Eocene core Brassicaceae. The age of Brassicaceae has been strongly debated because their fossil record is scanty. There are four species ofCeutorhynchus inaffectatusspecies-group known in the Priabonian:Ceutorhynchus zerovaenew species in Rovno amber and three in Baltic amber. There are numerous extant members of the group, all of which feed on core Brassicaceae. Together with differentiation of Brassicaceae-feeding Pierinae (Lepidoptera) in the Priabonian, the strong presence ofCeutorhynchusindicates at least an early Priabonian age of core Brassicaceae. The oldest fossil Brassicaceae is not known in the late Eocene of Europe, but was recorded in Montana, dated in some studies as late Oligocene, but recently as Priabonian (34 Ma).Ceutorhynchus zerovaen. sp. is very close toC.electrinusfrom Baltic amber.UUID:http://zoobank.org/7f10761f-463d-44c5-9eef-bb4697bfb116.

Orbital tuning for the middle Eocene to early Oligocene Monte Cagnero Section (Central Italy): Paleoenvironmental and paleoclimatic implications

During the middle Eocene to early Oligocene Earth transitioned from a greenhouse to an icehouse climate state. The interval comprises the Middle Eocene Climatic Optimum (MECO; ~40 Ma) and a subsequent long-term cooling trend that culminated in the Eocene-Oligocene transition (EOT; ~34 Ma) with the Oi-1 glaciation. Here, we present a refined calcareous nannofossil biostratigraphy and an orbitally tuned age model for the Monte Cagnero (MCA) section spanning the middle Eocene to the early Oligocene (~41 to ~33 Ma). Spectral analysis of magnetic susceptibility (MS) data displays strong cyclicities in the orbital frequency band allowing us to tune the identified 405 kyr eccentricity minima in the MS record to their equivalents in the astronomical solution. Our orbitally tuned age model allows us to estimate the position and duration of polarity chrons (C18 to C13) and compare them with other standard and orbitally tuned ages. We were also able to constrain the timing and duration of the MECO event, which coincides with a minimum in the 2.4 Myr and 405 kyr eccentricity cycles. Our study corroborates the previous estimated age for the base of the Rupelian stage (33.9 Ma) and estimates the base of the Priabonian stage in the MCA section to be at 37.4 Ma. Finally, calcareous nannofossils with known paleoenvironmental preferences suggest a gradual shift from oligotrophic to meso-eutrophic conditions with an abrupt change at ~36.8 Ma. Besides, nannofossil assemblages suggest that enhanced nutrient availability preceded water cooling at the late Eocene. Altogether, this evidence points to a poorly developed water column stratification prior to the cooling trend.

Proposal for the Global Boundary Stratotype Section and Point (GSSP) for the Priabonian Stage (Eocene) at the Alano section (Italy)

Claudia Agnini, Jan Backman, Flavia Boscolo-Galazzo, Daniel J. Condon, Eliana Fornaciari, Simone Galeotti, Luca Giusberti, Paolo Grandesso, Luca Lanci, Valeria Luciani, Simonetta Monechi, Giovanni Muttoni, Heiko Pälike, Maria Letizia Pampaloni, Cesare A. Papazzoni, Paul N. Pearson, Johannes Pignatti, Isabella Premoli Silva, Isabella Raffi, Domenico Rio, Lorenzo Rook, Diana Sahy, David J.A. Spofforth, Cristina Stefani, Bridget S. Wade. Episodes 2021;44:151-73. https://doi.org/10.18814/epiiugs/2020/020074

The transition from Pyrenean shortening to Gulf of Lion rifting in Languedoc (South France) – A tectonic-sedimentation analysis

The Pyrenean orogen extended eastward, across the present-day Gulf of Lion margin. The late or post-orogenic dismantling of this orogen segment, contemporaneous with ongoing shortening in the Spanish Pyrénées, is still debated. Understanding the transition between the two geodynamic events requires to document the precise timing of the succession of the tectonic processes involved. We investigate the superposition of rifting structures over Pyrenean thrusts and folds in the onshore Languedoc. Compilation and reassessment of the regional chronostratigraphy, in the light of recent biostratigraphic dating and new mapping of Paleogene basins, lead to date the transition to the Priabonian. Tectonic-sedimentation relationship in the Eocene to Oligocene depocentres are analysed in surface exposures as well as in seismic reflection surveys. Bed-to bed mapping allowed us to: i) characterise an intermediate sequence of Priabonian age, bounded at the base and the top by unconformities; ii) evidence syn-depositional deformation within the Priabonian; iii) define the axes of Priabonian deformation. Interpretation of seismic reflection profiles, across the onshore basins covered by syn- and post-rift sequences, reveals the existence of an intermediate sequence displaying similar features, and that is correlated to the Priabonian. Syn-depositional deformation of some Priabonian basins correspond to extensional structure, whereas neighbouring, contemporaneous basins, reveal compressional deformation. The distribution of such apparently conflicting observations across the studied area provides evidence for left-lateral strike-slip deformation between two major regional faults (Cévennes and Nîmes faults). Left-lateral strike-slip along NE-trending faults accommodates E-W extension of the West European Rift (ECRIS) and part of the ongoing N-S shortening in the Central and Western Pyrénées. Priabonian clastic sedimentation and deformation in Languedoc witness the initial stages of the dismantling of the Languedoc-Provence Pyrénées, prior to Oligocene-Aquitanian back-arc rifting.

LATE EOCENE BIOSTRATIGRAPHIC AGE FOR ANDESITIC VOLCANIC HOST ROCKS FORMED IN AN ISLAND ENVIRONMENT AT THE COBRE PANAMA PORPHYRY Cu-Mo-Au-Ag DEPOSIT, PANAMA

Abstract The giant Cobre Panama porphyry Cu-Mo-Au-Ag deposit in western Panama is hosted by an undated andesitic volcanic sequence, the Petaquilla batholith (32.20 ± 0.76–28.28 ± 0.61 Ma), and porphyry stocks (28.96 ± 0.62–27.48 ± 0.68 Ma). Here we present a biostratigraphic age for the volcanic sequence based on stratigraphically diagnostic large foraminifera from thin limestone beds within kilometer-thick andesitic rocks. These yield a late middle to late Eocene biostratigraphic age (41.2–33.9 Ma), with a probable late Eocene age (Priabonian stage, 37.8–33.9 Ma), which is slightly older than the age of the batholith and porphyry intrusions. The volcanic sequence is dominated by fine-grained, massive basalt to andesite lavas with subordinate volcaniclastic deposits. A preliminary description of volcanic textures based on macroscopic observation of drill core and quarry/road exposures supports the occurrence of lavas, fallout tuffs, volcanic breccias, and possible pyroclastic density current deposits. Rare polymictic conglomerates with well-rounded clasts of igneous rocks attest to minor sedimentary reworking from a nearby subaerial volcanic environment. The dated limestone that is interbedded with the submarine volcanic sequence was deposited in an estimated water depth of 50 to 80 m, probably in a middle- to outer-shelf large foraminiferal shoal. These results support deposition on the flank of an active volcanic island during early shallowing of the Isthmus of Panama. The Cobre Panama volcanic center is interpreted to have formed in the final stages of the latest Cretaceous-Eocene volcanic arc before, or possibly during, the 175-km sinistral offset of the Panama volcanic front in the late Eocene-Oligocene. However, it remains unclear whether the volcanic center formed on the western continuation of the San Blas-Chagres arc segment or the eastern termination of the Azuero-Soná arc segment and whether it was emplaced during broadening of the pre-Oligocene volcanic front or in a back-arc setting.

10 Myr evolution of sedimentation rates in a deep marine to non‐marine foreland basin system: Tectonic and sedimentary controls (Eocene, Tremp–Jaca Basin, Southern Pyrenees, NE Spain)

AbstractThe propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone.