A tectonic inversion by steps during the Cenozoic : the Dover Strait

Abstract The Boulonnais is a dome incised by a former marine gulf inset into a zone of tectonic inversion from the Middle Eocene, which was already partly excavated at least at the Upper Eocene. New sedimentological and paleopedological data obtained within the Boulonnais, completed with old seismic profiles, allow a better understanding of the inversion process which developed step by step. The initial breaching probably took place in the late Eocene. The Dover Strait was probably opened during the Lutetian, a part of the Oligocene and the late Neogene. Oligocene and Pliocene faunal assemblages are identical on both sides of the Strait. It was closed again for tectonic and eustatic reasons in the early Quaternary and reopen subsequently just before the Last Interglacial. The opening is related to the evolution of the Western Channel and of its paleovalley system. The inversion of the Variscan front accommodates most of the shortening induced by the Pyrenean Orogen on the western border of the European plate. The inversion of the Dover Strait region is almost synchronous with those of other basins of the Channel and North Sea areas. Tectonic, geomorphologic and climatic implications of this dynamic are discussed within the western European context.

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New microplanktonic biostratigraphy and depositional sequences across the Middle–Late Eocene and Oligocene boundaries in eastern Jordan

GeoArabia ◽

10.2113/geoarabia2003145 ◽

2015 ◽

Vol 20 (3) ◽

pp. 145-172

Author(s):

Sherif Farouk ◽

Mahmoud Faris ◽

Fayez Ahmad ◽

John H. Powell

Keyword(s):

Middle Eocene ◽

Planktonic Foraminifera ◽

Eastern Desert ◽

Late Eocene ◽

Arabian Plate ◽

Rapid Decline ◽

Calcareous Nannofossil ◽

Upper Eocene ◽

Depositional Sequences ◽

Global Correlation

ABSTRACT The first detailed calcareous nannofossil and planktonic foraminiferal biostratigraphic and integrated lithofacies analyses of the Eocene–Oligocene transition at the Qa’ Faydat ad Dahikiya area in the Eastern Desert of Jordan, on the border with Saudi Arabia, is presented. Three calcareous nannofossil zones namely: Discoaster saipanensis (NP17), Chiasmolithus oamaruensis (NP18) and Ericsonia subdisticha (NP21), and three planktonic foraminiferal zones: upper part of Truncorotaloides rohri (E13), Globigerinatheka semiinvoluta (E14) and Cassigerinella chipolensis/Pseudohastigerina micra (O1) are identified. Calcareous nannofossil bioevents recorded in the present study show numerous discrepancies with the Standard biostratigraphic zonal schemes to detect the Middle/Upper Eocene boundary (e.g. the highest occurrences (HOs) of Chiasmolithus solitus, C. grandis, and lowest occurrences (LOs) of C. oamaruensis, Isthmolithus recurvus are not considered reliable markers for global correlation). The Middle/Upper Eocene boundary occurs in the current study above the extinctions of large muricate planktonic foraminifera (large Acarinina and Truncorotaloides spp.) which coincide within the equivalent calcareous nannofossil NP18 Zone. These microplanktonic bioevents seem to constitute more reliable markers for the base of the Upper Eocene in different provinces. The uppermost portion of the Middle Eocene is characterized by an observed drop in faunal content and, most likely, primarily denotes the effect of the major fall in eustatic sea level. A major unconformity (disconformity) marked by a mineralized hardground representing a lowstand is recorded in the present study at the Eocene–Oligocene transition that reveals an unexpected ca. 2.1 Myr duration, separating Eocene (NP18/E14 zones) from Oligocene (NP21/O1 zones). Furthermore, the microfossil turnover associated with a rapid decline of the microfossil assemblages shows a distinct drop in diversity and abundance towards the Eocene/Oligocene unconformity and is associated with a sharp lithological break marked, at the base, by a mineralized hardground representing a major sequence boundary. These bioevents, depositional sequences and the depositional hiatus correlate well with different parts of the Arabian and African plates, but the magnitude of the faunal break differs from place to place as a result of intraplate deformation during the regional Oligocene regression of Neo-Tethys on the northern Arabian Plate. The presence of the Lower Oligocene shallow-marine calcareous planktonic assemblages in the study area indicate that communication between the eastern and western provinces of the western Neo-Tethys region still existed at this time.

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Inversion tectonics at the northern margin of the Paris basin (northern France): new evidence from seismic profiles and boreholes interpolation in the Artois area

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.181.5.429 ◽

2010 ◽

Vol 181 (5) ◽

pp. 429-442 ◽

Cited By ~ 7

Author(s):

Bruno Minguely ◽

Olivier Averbuch ◽

Marie Patin ◽

David Rolin ◽

Franck Hanot ◽

...

Keyword(s):

Middle Eocene ◽

Paris Basin ◽

Inversion Process ◽

Seismic Profiles ◽

Localized Deformation ◽

Borehole Data ◽

Northern Margin ◽

Northern France ◽

Thrust Front ◽

Northern Border

AbstractA synthesis of existing borehole data and seismic profiles has been conducted in the Artois area (northern France), along the northern border of the Paris basin, in order to explore the possible control exerted at depth by the Upper Carboniferous Variscan thrust front on the distribution of Late Paleozoic-Mesozoic depositional centers and their subsequent uplift in Tertiary times. Such control was demonstrated recently in the Weald-Boulonnais basin (Eastern Channel area) that forms the western prolongation of the area under study but was so far poorly constrained in the Artois area. Presented data provide evidence for the topography of the Artois hills and the altitude of sedimentary layers to be controlled by the activity of a network of relaying WNW-ESE striking faults inducing the systematic uplift of the southern fault blocks. Those steeply S-dipping faults branch downward onto the ramp of the Variscan thrusts forming listric faults that locally limit to the north buried half-graben structures, filled with fan-shaped fluviatile Stephanian-Permian deposits. Such clear syn-rift geometry shows that the ramp of the main Variscan frontal thrust (the Midi thrust) has been reactivated as a normal fault in Stephanian-Permian times thus forming a very demonstrative example of a negative inversion process. The reverse offset of the transgressive Middle Cretaceous-Lower Eocene layers covering unconformably the Paleozoic substratum argue for a Tertiary (Middle Eocene-Late Oligocene?) contractional reactivation of the fault network thereby documenting a repeated inversion process along the Artois Variscan thrust front. The Variscan frontal thrust zone is thus shown here to represent a prominent crustal-scale mechanical discontinuity that localized deformation in the Artois-Boulonnais area since Upper Paleozoic times.

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New discoveries concerning the geology of the central and eastern parts of the English Channel

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1975.0048 ◽

1975 ◽

Vol 279 (1288) ◽

pp. 155-167 ◽

Cited By ~ 25

Keyword(s):

Upper Cretaceous ◽

Middle Eocene ◽

Geological Structure ◽

English Channel ◽

Total Thickness ◽

Upper Eocene ◽

The South ◽

Seismic Profiles ◽

Isle Of Wight ◽

Geological Map

A study of rock-samples collected at 26 stations and continuous seismic profiles taken over a distance of 2000 km in the eastern part of the English Channel reveals the existence of a large flat-floored Tertiary syncline which forms an easterly extension of the Hampshire Basin of Southern England. The newly delineated basin, which is here referred to as the Hampshire—Dieppe Basin, forms part of the well-known Palaeogene Anglo-Paris-Belgian depositional basin. The total thickness of Palaeogene strata in the eastern part of the basin is about 380 m and the youngest beds present are probably of Upper Eocene age. Upper Cretaceous strata are exposed around the edges of the basin; the thickness of the Chalk varying from about 250 m in the south and east to 420 m in the northwest. The basin is bounded to the northeast by the Weald—Artois anticline and a strong flexure, the Bembridge—St Valery line, which is a continuation of the Isle of Wight monocline, controls the position of much of its southwestern boundary. To the south of the Hampshire-Dieppe basin lies the Baie de la Seine Tertiary syncline. Here, freshwater limestones of presumed Oligocene age overlie a Middle Eocene marine sequence. Lithologies and microfaunas of the samples are described and related to those of sequences of similar age on nearby land, and some conclusions are drawn about the palaeogeography of the area. The geological structure of the area is elucidated, the paths of faults and fold axes are traced and a geological map is presented.

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Paleoecology of the Upper Eocene-Lower Oligocene Malcov Basin based on the calcareous nannofossils: a case study of the Leluchów section (Krynica Zone, Magura Nappe, Polish Outer Carpathians)

Geologica Carpathica ◽

10.2478/v10096-012-0012-8 ◽

2012 ◽

Vol 63 (2) ◽

pp. 149-164 ◽

Cited By ~ 3

Author(s):

Marta Oszczypko-Clowes ◽

Bartłomiej Żydek

Keyword(s):

Middle Eocene ◽

Late Eocene ◽

Calcareous Nannofossils ◽

Late Oligocene ◽

Upper Eocene ◽

Early Oligocene ◽

Lower Oligocene ◽

Quantitative Analyses ◽

Outer Carpathians

Paleoecology of the Upper Eocene-Lower Oligocene Malcov Basin based on the calcareous nannofossils: a case study of the Leluchów section (Krynica Zone, Magura Nappe, Polish Outer Carpathians)During the period of ca. 20 Ma (Middle Eocene-Chattian) the Leluchów Succession of the Magura Basin passed through drastic changes of sedimentary condition and paleobathymetry from well oxygened red shales withReticulofragmium amplectens, deposited beneath CCD, redGlobigerinaoozes, to oxygen depleted organic-rich menilite-type shales and finally to flysch deposition of open marine conditions. The biostratigraphic and lithostratigraphic scheme is well established with the Leluchów Marl Member — Zones NP19-20 to NP22 (Late Eocene-Early Oligocene), Smereczek Shale Member, Zone NP23 (Early Oligocene) and the Malcov Formation s.s., Zone NP24 (Early-Late Oligocene). The aim of the paper is to present the quantitative analyses as the basis for paleoecological changes in the Magura Basin during the Late Eocene-Late Oligocene period. The changes manifest themselves through a decrease in the water temperature and progressing eutrophication. Species typical of brackish water conditions and restricted to the Paratethys region were identified from the NP23 Zone.

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Eocene echinoids of Texas

Journal of Paleontology ◽

10.1017/s0022336000044206 ◽

2003 ◽

Vol 77 (3) ◽

pp. 491-508

Author(s):

Louis G. Zachos ◽

Ann Molineux

Keyword(s):

New Species ◽

New Taxa ◽

Depositional Environment ◽

Middle Eocene ◽

Late Eocene ◽

Marine Environments ◽

Upper Eocene ◽

Texas Coast ◽

Lower Eocene

Fourteen species of echinoids ranging in age from early to late Eocene, including four new species, are described from Texas. New taxa include Schizaster (Schizaster) caddoensis from the Reklaw and Weches Formations (Claiborne Group, middle Eocene), Schizaster (Schizaster) stenzeli and Eupatagus texanus from the Weches Formation, and Schizaster (Paraster) susana from the Caddell Formation (Jackson Group, upper Eocene). Fibularia meyeri (Aldrich, 1921) and Fibularia alabamensis Cooke, 1959 are synonymized with Fibularia texana (Twitchell, 1915) from the Weches and Cook Mountain Formations (Claiborne Group, middle Eocene). Other reported species are Linthia hollandi Barry, 1942, from the Sabinetown Formation (Wilcox Group, lower Eocene); Gagaria sp., Protoscutella tuomeyi (Twitchell, 1915), Protoscutella mississippiensis mississippiensis (Twitchell, 1915), Maretia arguta (Clark, 1915), and Linthia? sp. from the Weches Formation; Spatangus? sp. and Eupatagus carolinensis? Clark, 1915 from the Cook Mountain Formation, and Periarchus lyelli (Conrad, 1834) from the Cook Mountain and Caddell Formations. These echinoids are sensitive indicators of depositional environment, in particular their distribution serves as a marker for stenohaline (open marine) environments and illustrates the biogeographic variability along the northeast Texas coast during the Eocene.

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Geographic contingency, not species sorting, dominates macroevolutionary dynamics in an extinct clade of neogastropods (Volutospina; Volutidae)

Paleobiology ◽

10.1017/pab.2020.60 ◽

2021 ◽

pp. 1-15

Author(s):

Dana S. Friend ◽

Brendan M. Anderson ◽

Warren D. Allmon

Keyword(s):

Middle Eocene ◽

Ecological Factors ◽

Geographic Range ◽

Late Eocene ◽

Range Size ◽

Species Sorting ◽

Extinction Rates ◽

Geographic Range Size ◽

Speciation Rates ◽

Planktotrophic Larvae

Abstract Rates of speciation and extinction are often linked to many ecological factors, traits (emergent and nonemergent) such as environmental tolerance, body size, feeding type, and geographic range. Marine gastropods in particular have been used to examine the role of larval dispersal in speciation. However, relatively few studies have been conducted placing larval modes in species-level phylogenetic context. Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades have not considered both phylogenetic context and net speciation (speciation–extinction) rates. This study utilizes Eocene volutid Volutospina species from the U.S. Gulf Coastal Plain and the Hampshire Basin, U.K., to explore the relationships among larval mode, geographic range, and duration. Based on the phylogeny of these Volutospina, we calculated speciation and extinction rates in order to compare the macroevolutionary effects of larval mode. Species with planktotrophic larvae had a median duration of 9.7 Myr, which compared significantly to 4.7 Myr for those with non-planktotrophic larvae. Larval mode did not significantly factor into geographic-range size, but U.S. and U.K. species do differ, indicating a locality-specific component to maximum geographic-range size. Non-planktotrophs (NPTs)were absent among the Volutospina species during the Paleocene–early Eocene. The relative proportions of NPTs increased in the early middle Eocene, and the late Eocene was characterized by disappearance of planktotrophs (PTs). The pattern of observed lineage diversity shows an increasing preponderance of NPTs; however, this is clearly driven by a dramatic extinction of PTs, rather than higher NPT speciation rates during the late Eocene. This study adds nuance to paleontology's understanding of the macroevolutionary consequences of larval mode.

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Impact of mid Eocene greenhouse warming on America’s southernmost floras

Communications Biology ◽

10.1038/s42003-021-01701-5 ◽

2021 ◽

Vol 4 (1) ◽

Cited By ~ 1

Author(s):

Damián A. Fernández ◽

Luis Palazzesi ◽

M. Sol González Estebenet ◽

M. Cristina Tellería ◽

Viviana D. Barreda

Keyword(s):

Middle Eocene ◽

Pollen Grains ◽

Late Eocene ◽

Significant Rise ◽

Spores And Pollen ◽

Deep Time ◽

Nonparametric Estimators ◽

Southern Patagonia ◽

Marine Realm ◽

High Diversity

AbstractA major climate shift took place about 40 Myr ago—the Middle Eocene Climatic Optimum or MECO—triggered by a significant rise of atmospheric CO2 concentrations. The biotic response to this MECO is well documented in the marine realm, but poorly explored in adjacent landmasses. Here, we quantify the response of the floras from America’s southernmost latitudes based on the analysis of terrestrially derived spores and pollen grains from the mid-late Eocene (~46–34 Myr) of southern Patagonia. Robust nonparametric estimators indicate that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The high atmospheric CO2 and increasing temperatures may have favored the combination of neotropical migrants with Gondwanan species, explaining in part the high diversity that we observed during the MECO. Our reconstructed biota reflects a greenhouse world and offers a climatic and ecological deep time scenario of an ice-free sub-Antarctic realm.

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Falcatifolium (Podocarpaceae) macrofossils from paleogene sediments in south-eastern Australia: a reassessment

Australian Systematic Botany ◽

10.1071/sb97014 ◽

1998 ◽

Vol 11 (6) ◽

pp. 711 ◽

Cited By ~ 5

Author(s):

Robert S. Hill ◽

Leonie J. Scriven

Keyword(s):

Leaf Morphology ◽

Middle Eocene ◽

Late Eocene ◽

South Eastern ◽

Early Oligocene ◽

Extant Species ◽

Eastern Australia ◽

South Eastern Australia

A re-investigation of macrofossils previously referred to the extantpodocarpaceous genus Falcatifolium Laubenfels shows thatno records can be sustained. Falcatifolium australisD.R.Greenwood from Middle Eocene sediments in Victoria bears littleresemblance to extant species in the genus and is transferred to the newfossil genus Sigmaphyllum R.S.Hill & L.J.Scriven.Specimens from Early Oligocene sediments in Tasmania previously assigned toFalcatifolium are described as a second species ofSigmaphyllum, S. tasmanensisR.S.Hill & L.J.Scriven, and specimens from mid to late Eocene sediments inTasmania previously assigned to Falcatifolium do notbelong to that genus, although their true generic affinities are uncertain.Dispersed cuticle specimens from Late Eocene–Oligocene sediments inSouth Australia referred to Falcatifolium are notreliable records of the genus and require further investigation. However,Dacrycarpus eocenica D.R.Greenwood, from Middle Eocenesediments in Victoria is transferred to Falcatifolium,and is similar to the extant species F. angustumLaubenfels, which has a leaf morphology unusual for the genus.Falcatifolium eocenica (D.R.Greenwood) R.S.Hill & L.J.Scriven is the only reliable record of the genus in the Australian fossilrecord to date.

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Late Paleogene paleotopographic evolution of the northern Cordilleran orogenic front: Implications for demise of the orogen

Geological Society of America Bulletin ◽

10.1130/b35919.1 ◽

2021 ◽

Author(s):

Majie Fan ◽

Kurt N. Constenius ◽

Rachel F. Phillips ◽

David L. Dettman

Keyword(s):

Initial Phase ◽

Middle Eocene ◽

High Elevation ◽

Late Eocene ◽

Crustal Extension ◽

Late Oligocene ◽

Slab Rollback ◽

Basin Floor ◽

Climate Cooling ◽

High Range

The paleotopographic history of the North American Cordilleran orogen holds the key to understanding mechanisms of orogenesis and subsequent orogenic collapse. It has been suggested that the orogenic front in western Montana (USA) and Alberta (Canada) was more than 4 km high during Late Cretaceous−early Eocene contractional deformation and during the initial phase of extension in the middle Eocene; however, the late Eocene−Oligocene topographic evolution during continued extensional collapse remains poorly constrained. Here we extend the paleotopographic record in the Kishenehn Basin in northwestern Montana and southeastern British Columbia (Canada) to the late Oligocene by studying δ18O values of fossil mollusks and cement and paleosol carbonates. The molluscan taxa changed from three sympatric groups with preferred habitats ranging from tropical wet, semi-arid subtropical, and temperate during the middle and late Eocene, to mainly a single group associated with temperate environment during the Oligocene, reflecting a decline in molluscan biodiversity induced by climate cooling across the Eocene−Oligocene transition. Reconstructed δ18O values of alpine snowmelt and basinal precipitation decreased by 1.4‰ and 3.8‰, respectively, from the middle to late Eocene, reflecting climate cooling and ∼1 km surface uplift of the basin floor. The reconstructed alpine snowmelt δ18O values then increased by 2.9‰ in the Oligocene suggesting a ∼0.5 km drop in elevation of the orogenic front. Collectively, the results of our new and previously published δ18O data chronicle the paleotopographic response to the change from flat-slab subduction to slab rollback over a 45 m.y. period. These data suggest that the orogenic front was characterized by high elevation (>4 km) in the ancestral Lewis-Clark-Livingston ranges during latest Cretaceous−early Eocene (ca. 75−52 Ma) contraction. The initial phase of extension related to the Kishenehn Basin created a lowland basin with a surface elevation of only ∼1.5 km during the early middle Eocene (ca. 46−44 Ma) whereas the ranges remained >4 km high. The high range elevations were sustained for at least 12 m.y. in the middle to late Eocene concurrent with extension, while the basin floor elevation was uplifted to ∼2.5 km by the latest Eocene (ca. 36−34 Ma). Basin aggradation can explain at most half of the 1 km basin floor uplift. The remaining amount (at least 0.5 km) and sustained high range elevation suggest that range denudation and crustal extension was compensated by the isostatic and thermal effects of slab rollback and/or passage of a slab window and infusion of hot asthenosphere beneath the continent. The range elevation in the orogenic front decreased ∼0.5 km by the late Oligocene (ca. 28 Ma), associated with a decrease in rock uplift rate associated with extension. A post-Oligocene elevation drop of ∼1 km resulted in both the ranges and basin floor reaching modern topography in the Kishenehn Basin drainage, likely due to the regional effect of Neogene Basin and Range extension. This study, along with the previous investigation of the Kishenehn Basin by Fan et al. (2017), are the first studies that systematically investigate paleorelief of the orogenic belt by reconstructing paleoelevations of the mountains and the basin at the same time. The results highlight that the Cordilleran orogenic front of northern Montana and southern British Columbia sustained its high elevation edifice for at least 12 m.y. after the start of extension. We suggest that initial crustal extension did not result in orogenic demise because of concurrent thermal and isostatic uplift.

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The first damselfly (Odonata, Lestidae) from the upper Eocene of Monteils (Gard, France)

Zootaxa ◽

10.11646/zootaxa.4750.3.9 ◽

2020 ◽

Vol 4750 (3) ◽

pp. 432-436

Author(s):

ROMAIN JATTIOT ◽

BENJAMIN LATUTRIE ◽

ANDRÉ NEL

Keyword(s):

Western Europe ◽

Late Eocene ◽

Type Locality ◽

Upper Eocene ◽

Isle Of Wight ◽

Type Series ◽

Lacustrine Basin ◽

Southern Area

The discovery of the first damselfly Lestes regina Théobald, 1937 from Monteils (Gard, France) supports the identity of late Eocene age of this outcrop with the historical outcrop of Célas, type locality for the type series of this species. Lestes regina is also documented from the late Eocene Isle of Wight basin, confirming the presence of significant contacts between this southern area and the anglo-Parisian lacustrine basin at that time. Nearly all the Eocene and Oligocene fossil Lestes from Western Europe have a particular character, viz. the presence of a supplementary row of cells between the veins MP and CuA. This character is much less frequent in extant Lestes and is still unknown among Neogene representatives of the genus.

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