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Eocene initiation of Nile drainage due to East African uplift.
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The Late Eocene and Early Oligocene sedimentary succession in the Fayum, Egypt records the progressive development of northerly flowing Nile-type African drainage. New biostratigraphic dating of these units allows the calibration of the paleomagnetic record, the combination of dating methods enabling a detailed chronology of events to be studied. Between about 38 and 35 Ma there was a dramatic change in sedimentary regime and vast quantities of clasticmaterial were transported into the area, smothering the underlying carbonate platform and initiating a stepwise progradation of clastic units. The sudden change in sediment availability coincideswith the beginning of uplift and volcanic activity in the Turkana region of East Africa, cutting off preexisting easterly drainage from the middle of the continent. The Fayum succession therefore records the initiation of northerly drainage of central and eastern Africa, and the origins of themodern Nile watershed. The development of the current route of the Nile, with the incision of the current Nile Valley, was slightly later and related tomid Oligocene uplift of the Red Sea margins and Messinian base level fall.
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Unraveling the PETM in shallow marine Tethyan environments: the Tunisian stratigraphic record.
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Despite the increasing understanding of the Paleocene-Eocene thermal maximum (PETM) in open marine environments, shallow marine settings remain relatively unexplored. We investigated an upper Paleocene to lower Eocene shallow-water sequence near Kalaat Senan in Tunisia (Sidi Nasseur and Wadi Mezaz sections)in order to generate a stratigraphic framework of the PETM in shallow marine fine-grained siliciclastic setting on the Southern Tethys. These sections expose the top part of the El Haria Formation (Fm.), the Chouabine Fm. and the lower part of the limestone bearing El Garia Fm., covering the upper Paleocene - lower Eocene (NP9a to NP11). The PETM interval is situated near the top of the El Haria Fm. and the regional stratigraphy is compared to the well-known Egyptian setting. The isotope record of total organic carbon (δ13Corg)reveals the characteristic negative carbon isotope excursion(CIE), comparable to the δ13Corg record of the Global Boundary Stratotype Section and Point of the Eocene at Dababiya (Egypt). Although the Tunesian PETM interval is quite expanded, no anomalous beds are observed and only the "CIE" core is partly represented as the top part of the PETM is truncated. In addition to a well-expressed CIE, the position of the Paleocene-Eocene boundary is supported by the appearance of nannoplankton (Discoaster araneus)and foraminiferal (e.g. Acarinina multicamerata)marker taxa. Furthermore, ostracode and benthic foraminiferal turnovers coincide with the onset of the PETM and are characterized by the disappearance of many common Paleocene taxa (e.g. Frondicularia aff. phosphatica) in this area. The lowest occurrences of Alocopocythere attitogonensis and Buntonia ? tunisiensis (ostracodes), Reophax sp. 1 (benthic foraminifera) and Fasciculithus tonii (calcareous nannplankton) may be applicable for regional correlation. These results indicate that characteristic PETM taxa evolved and/or dispersed immediately after the main δ13Corg shift.
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In search of the Latest Danian Event in a paleobathymetric transect off Kasserine Island, north-central Tunisia.
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Danian (lower Paleocene) sequences in north-central Tunisia are dominantly composed of marls and shales but a conspicuous, indurated glauconite-bearing marker bed is associated with the P3a–P3b transition. This glauconite bed is considered to correlate with the Latest Danian Event (LDE) described from the Nile Basin in Egypt, with the ‘top Chron C27n event’ (Atlantic and Pacific Oceans) and with the ‘CIE-DS1’ (Zumaia, Spain). The LDE is thought to reflect a short period of global warming, similar to the Paleocene Eocene Thermal Maximum, but of lesser magnitude. The presence of a glauconitic bed at the P3a/P3b transition in Tunisia suggests that the sequence is condensed, which is confirmed by planktic foraminifer and nannofossil biostratigraphy, and by the absence of the typical LDE beds found in most Egyptian sections. Benthic foraminiferal assemblages were quantitatively analyzed in three sections in north-central Tunisia (Sidi Nasseur, Garn Halfaya, Elles) in order to characterize the paleoenvironmental evolution during the late Danian and compare this with sections in Egypt. The benthic foraminiferal assemblages indicate that the Tunisian sections were located along a depth- and a paleoenvironmental gradient on the shelf north of Kasserine Island. The reconstructed depth range is comparable with sections in Egypt, and encompasses middle neritic (Sidi Nasseur section) to shallow upper bathyal depths (Elles section,with up to 16% Gavelinella beccariiformis below the P3a/P3b). Like in Egypt, assemblage shifts across the P3a/P3b subzonal transition indicate shallowing and a transition to amore eutrophic paleoenvironment, characterized by relatively high abundances of buliminids and Stainforthia sp. The δ13C and δ18O records generated on well-preserved specimens of the ostracode species Bairdia failed to demonstrate the presence of the carbon isotope excursion (CIE) associated with the LDE at the base of Subzone P3b. A condensed section or a hiatus associated with the glauconite bed would explain why the CIE is not recorded in the Tunisian sections.
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New Paleocene Sepiid Coleoids (Cephalopoda) from Egypt: Evolutionary Significance and Origin of the Sepiid ‘Rostrum’.
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New coleoid cephalopods, assignable to the order Sepiida, are recorded from the Selandian/Thanetian boundary interval (Middle to Upper Paleocene transition, c. 59.2 Ma) along the southeastern margin (Toshka Lakes) of the Western Desert in Egypt. The two genera recognised, Aegyptosaepia n. gen. and ?Anomalosaepia Weaver and Ciampaglio, are placed in the families Belosaepiidae and ?Anomalosaepiidae, respectively. They constitute the oldest record to date of sepiids with a ‘rostrum-like’ prong. In addition, a third, generically and specifically indeterminate coleoid is represented by a single rostrum-like find. The taxonomic assignment of the material is based on apical parts (as preserved), i.e., guard, apical prong (or ‘rostrum-like’ structure), phragmocone and (remains of) protoconch, plus shell mineralogy. We here confirm the shell of early sepiids to have been bimineralic, i.e., composed of both calcite and aragonite. Aegyptosaepia lugeri n. gen., n. sp. reveals some similarities to later species of Belosaepia, in particular the possession of a distinct prong. General features of the phragmocone and protoconch of the new form are similar to both Belocurta (Middle Danian [Lower Paleocene]) and Belosaepia (Eocene). However, breviconic coiling and the presence of a longer ventral conotheca indicate closer ties with late Maastrichtian–Middle Danian Ceratisepia. In this respect, Aegyptosaepia n. gen. constitutes a link between Ceratisepia and the Eocene Belosaepia. The occurrence of the new genus near the Selandian/Thanetian boundary suggests an earlier origin of belosaepiids, during the early to Middle Paleocene. These earliest known belosaepiids may have originated in the Tethyan Realm. From northeast Africa, they subsequently spread to western India, the Arabian Plate and, probably via the Mediterranean region, to Europe and North America.
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Integrated bio-chemostratigraphical correlations and climatic evolution across the Danian–Selandian boundary at low latitudes.
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The Global Boundary Stratotype Section and Point for the base of the Selandian Stage is defined in the Zumaia section (Spain) at an abrupt change in lithology (base of Itzurun Formation), which coincides with the onset of a negative carbonate carbon isotope shift. However, this lithological change is not always very well expressed in other sections. In order to document the stratigraphic position of the Danian/Selandian boundary (DSB) on a more global scale, we have investigated three sections across the DSB, the Zumaia reference section (GSSP), the Loubieng section (auxiliary DSB reference section, France) and the Sidi Nasseur section (Tunisia). The Danian/Selandian boundary interval is subdivided and correlated throughout low latitudes, from the Altlantic Bay of Biscay to the Southern Tethys, on the basis of seven calcareous nannofossil and planktonic foraminiferal events (E-events). The base of the Selandian is proved to coincide with the end of the Braarudosphaera acme, which correlates with the lowest consistent occurrence (LCsO) of Lithoptychius aff. bitectus (=Fasciculithus janii sensu Steurbaut and Sztrákos, 2008) (event E4), but which is slightly posterior to the second radiation of the fasciculiths, up to now considered to represent the primary correlation tool of the DSB. A short-term δ13Corg negative excursion, associated with an increase in pCO2 is recorded at the very base of the Selandian. It is interpreted as a short period of global warming (hyperthermal), the duration of which is estimated at ~30 kyr. It is followed in all the three studied sections by a long-term decoupled carbon isotope event, marked by increasing δ13Corg and decreasing δ13Ccarb values. It may reflect a period of climatic cooling of a few 100 kyr, interpreted as a possible precursor of the global cooling event, marking the late Paleocene in the North Atlantic realm. The integration of the biostratigraphic and the isotope data indicates major differences in sedimentation rates during the early Selandian in the studied sections, but there is no evidence of substantial breaks in sedimentation in any of the sections during this interval. The lithological shift at the base of the Selandian points to an abrupt palaeoenvironmental reorganisation, although our integrated bio-chemostratigraphical investigation does not allow for estimating its duration nor the presence of a hiatus at that time.
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Early Eocene environmental development in the northern Peri-Tethys (Aktulagay, Kazakhstan) based on benthic foraminiferal assemblages and stable isotopes (O, C).
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The Aktulagay section in Kazakhstan provides an expanded northern Tethyan record of the middle Ypresian (calcareous nannoplankton zones NP11-13, ~ 54-50 Ma), including the Early Eocene Climatic Optimum (EECO). The marl sequence features a series of sapropel beds, observed throughout the Peri-Tethys, indicative of the basin-wide occurrence of episodic hypoxic events. In order to unravel the paleoenvironmental evolution at Aktulagay during this period of global warming, we investigated the benthic foraminiferal record by means of a detailed multivariate analysis of the > 63 μm fraction, as well as through stable isotopic (C, O) investigations on excellently preserved benthic foraminiferal specimens. The Alashen Formation (NP11 to lower NP12; ~ 54 to 52.5 Ma), in the lower part of the sequence, contains a diverse assemblage of deep outer neritic (~ 200-250 m) benthic foraminifera, with common Pulsiphonina prima and Paralabamina lunata. The sea-floor conditions are interpreted as initially (54 Ma) well-ventilated and oligo- to mesotrophic, gradually changing to more eutrophic and oxygen-limited, culminating in more permanent low-oxygen conditions and eutrophy in the sapropel-bearing Aktulagay B1 unit (middle NP12; ~ 52.5-52 Ma). The latter conclusion is corroborated by the dominance of Anomalinoides acutus and Bulimina aksuatica and the lower diversity. Also the upward migration of endobenthic species to the sediment-water interface, as suggested by rising δ13Cendobenthic values, supports this interpretation. A transgression, which flooded lowlands, might have caused this development. In the Aktulagay B2 unit (top NP12-NP13; ~ 52-50 Ma), benthic foraminiferal assemblages dominated by Epistominella minuta suggest an oligotrophic environment, with transient pulses of phytodetritus and moderate ventilation. The Aktulagay B2 unit coincides with the peak temperature interval of the EECO, as indicated by its position close to the base of NP13 and rising δ13Cepibenthic values. Large river plumes, episodically reaching the area, in a monsoonal climatic context, might explain this basin development. Although it is not unlikely that some of the observed patterns are related to long-term climate change, it can currently not be excluded that changing paleogeography and variable connections to the Tethys, Atlantic and the Arctic Ocean were responsible for the long-term period with dysoxia and anoxia during deposition of the sapropel beds at the Peri-Tethyan seafloor. The evolution of the basin as observed in Aktulagay shows similarities to the evolution of the North Sea Basin as observed in Denmark, suggesting that these basins were connected during the Early Eocene.
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Eocene stratigraphy of the Wadi Al-Hitan World Heritage Site and adjacent areas (Fayum, Egypt).
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A transient deep-sea circulation switch during Eocene Thermal Maximum 2.
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Ever since its discovery, Eocene Thermal Maximum 2 (ETM2; ~53.7 Ma) has been considered as one of the “little brothers” of the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) as it displays similar characteristics including abrupt warming, ocean acidification, and biotic shifts. One of the remaining key questions is what effect these lesser climate perturbations had on ocean circulation and ventilation and, ultimately, biotic disruptions. Here we characterize ETM2 sections of the NE Atlantic (Deep Sea Drilling Project Sites 401 and 550) using multispecies benthic foraminiferal stable isotopes, grain size analysis, XRF core scanning, and carbonate content. The magnitude of the carbon isotope excursion (0.85–1.10‰) and bottom water warming (2–2.5°C) during ETM2 seems slightly smaller than in South Atlantic records. The comparison of the lateral δ13C gradient between the North and South Atlantic reveals that a transient circulation switch took place during ETM2, a similar pattern as observed for the PETM. New grain size and published faunal data support this hypothesis by indicating a reduction in deepwater current velocity. Following ETM2, we record a distinct intensification of bottom water currents influencing Atlantic carbonate accumulation and biotic communities, while a dramatic and persistent clay reduction hints at a weakening of the regional hydrological cycle. Our findings highlight the similarities and differences between the PETM and ETM2. Moreover, the heterogeneity of hyperthermal expression emphasizes the need to specifically characterize each hyperthermal event and its background conditions to minimalize artifacts in global climate and carbonate burial models for the early Paleogene.
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Revision of the Frasnian marine deposits from the Booischot borehole (Campine Basin, Belgium).
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Reconsideration of the systematics and distribution of the rhynchonellid brachiopod Atrypa mesacostale Hall, 1843 from the Late Givetian and Early Frasnian of New York.
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