Pirkenseer C.M.,University of Fribourg |
Steurbaut E.,Royal Belgian Institute Of Natural Sciences |
Steurbaut E.,Catholic University of Leuven |
Abels H.A.,University Utrecht |
And 2 more authors.
Newsletters on Stratigraphy
The early Eocene is characterized by a succession of orbitally-controlled global stable carbon isotope excursions, with some being linked to climatic and related biotic perturbations. The impact of these isotopic excursions has been primarily studied in deep-sea sections under comparably stable conditions. In order to investigate the impact of global post-PETM isotopic signals on shallow marine settings, the Ypresian neritic 'Blue Marls' of the Corbières (SW France) were investigated. High-resolution records of microfossil biota and stable carbon and oxygen isotopes pinpoint biostratigraphic, paleoecologic and geochemic constraints. Calcareous nannofossil biostratigraphy positions the sequence in the upper part of zone NP11, possibly ranging into basal NP12, which is conformable with larger benthic foraminifera data indicating shallow benthic zone SBZ8. This implies a time span of about 0.4 Myr and high overall sedimentation rates of about ~ 32 cm/kyr for the section. A shallowing upward trend from outer neritic to coastal settings is observed in the development of the lithostratigraphy and the microfossil assemblage. The assemblages can be subdivided in seven larger biofacies and four ostracod assemblage zones. The lower third of the section is characterized by strongly fluctuating and partly high plankton/benthos-ratios for neritic settings. A final pronounced peak in plankton occurrence is associated with strong decrease of benthic biota, suggesting anoxic conditions in the outer neritic environment. Several local negative δ13C- and δ18O-excursions can be identified in the section. The upper, most pronounced and consistent negative δ13C excursion is tentatively linked to global carbon isotope excursion K (ETM3) based on the biostratigraphic constraints. © 2013 Gebrüder Borntraeger, Stuttgart, Germany. Source
Sliwinska K.K.,University of Aarhus |
Dybkjaer K.,Geological Survey of Denmark |
Schoon P.L.,Netherlands Institute for Sea Research |
Beyer C.,CB Magneto |
And 3 more authors.
A multidisciplinary study of the Oligocene/Miocene (O/M) transition was carried in two boreholes (Harre-1 and Horn-1) from the Danish land area in order to improve the understanding of the paleoclimatological and environmental changes across the Mi-1, the earliest Miocene cooling event. Dinoflagellate cyst (dinocyst) biostratigraphy, supported by re-evaluation of the foraminiferid biostratigraphy, a new set of magnetic data and stable carbon isotope (δ13C) records were applied to improve the age model for the studied succession; as well as the positioning of the O/M boundary. These data further enabled a correlation of the two investigated profiles with the well-established stratigraphical framework for the Danish area. The BIT index (an organic proxy indicating the relative input of soil-derived organic matter), dinocyst assemblages and palynofacies have been applied for establishing the paleoenvironmental changes across the Oligocene/Miocene (O/M) boundary. Our data indicate a shallowing upward trend in the latest Oligocene, resulting in the establishment of a very restricted marine setting in the earliest Miocene. Our study confirms that the O/M boundary is located at a sequence boundary (the local sequence boundary B - SB B) and corresponds to an increase in terrestrial organic matter input. A mean air temperature record based on the MBT'/CBT proxy reveals an ~. 2. °C drop in temperature at the O/M and the sequence boundary. Our findings confirm previous suggestions that this sequence boundary is a result of the glacio-eustatic sea level fall related with the Mi-1 cooling event. The unconformity at the sequence boundary probably correlates with the coldest part of Mi-1, and thus no deposits from this period have been preserved. This suggests that the temperature drop might have been greater than 2. °C. © 2014 Elsevier B.V. Source
Deprez A.,Catholic University of Leuven |
Tesseur S.,Catholic University of Leuven |
Tesseur S.,Ghent University |
Stassen P.,Catholic University of Leuven |
And 7 more authors.
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 52.5Ma), in the lower part of the sequence, contains a diverse assemblage of deep outer neritic (~200-250m) benthic foraminifera, with common Pulsiphonina prima and Paralabamina lunata. The seafloor conditions are interpreted as initially (54Ma) 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; ~52.5-52Ma). 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; ~52-50Ma), 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. © 2014 Elsevier B.V. Source
Dybkjaer K.,Geological Survey of Denmark |
King C.,16A Park Rd. |
Sheldon E.,Geological Survey of Denmark
Palaeogeography, Palaeoclimatology, Palaeoecology
For the first time a combined palynological and δ 13C-isotope study has identified the Oligocene-Miocene boundary - and thus the base of the Neogene - within the North Sea Basin. The type section, the Lemme-Carrosio section in northern Italy, is correlated with the Frida-1 well in the eastern (Danish) part of the North Sea Basin using a combination of data from a previous dinocyst stratigraphic study and new δ 13C-isotope data. The results show that the Oligocene-Miocene boundary is located at a depth of 1440m in the Frida-1 well. The Frida-1 δ 13C-isotope curve further reflects the Mi-1 glaciation event also recorded in the Lemme-Carrosio section. The dinocyst events bracketing the boundary in Frida-1 are; the last occurrence (LO) of Distatodinium biffii at 1630. m, below the boundary, the LO of Chiropteridium spp. at 1370. m and first occurrence (FO) of Ectosphaeropsis burdigalensis at 1330. m, both above the boundary. An influx of Deflandrea phosphoritica is found in an interval immediately below the boundary (1532-1490. m), while the genus Homotryblium occurs abundantly in a broader interval (1650-1330. m) encompassing the boundary. Hitherto unpublished data combined with new data provide a series of stratigraphically important nanno- and micropalaeontological events that frame/characterise the Oligocene-Miocene boundary within the North Sea Basin; an almost monospecific assemblage of Reticulofenestra bisecta at 1630. m, the LO of Elphidium subnodosum at 1625. m, the LO of Aulacodiscus insignis quadrata (Diatom sp. 3 of King, 1983) at 1610. m, the LO of Karreriella seigliei at 1580. m and the LO of Pararotalia canui at 1570. m, all below the boundary, and the FO of Aulacodiscus aemulans (Diatom sp. 5 of King, 1983) at 1410. m and the LO of Aulacodiscus aemulans at 1250. m, both above the boundary. The dinocyst, nanno- and micropalaeontological studies thus provide a series of bioevents and abundance variations which can be used to locate and to correlate the Oligocene-Miocene boundary within the eastern North Sea Basin more precisely than was previously possible. © 2012 Elsevier B.V. Source
Berggren W.A.,Rutgers University |
Berggren W.A.,Woods Hole Oceanographic Institution |
Alegret L.,University of Zaragoza |
Aubry M.-P.,Rutgers University |
And 17 more authors.
Austrian Journal of Earth Sciences
The Dababiya corehole was drilled in the Dababiya Quarry (Upper Nile Valley, Egypt), adjacent to the GSSP for the Paleocene/ Eocene boundary, to a total depth of 140 m and bottomed in the lower Maastrichtian Globotruncana aegyptiaca Zone of the Dakhla Shale Formation. Preliminary integrated studies on calcareous plankton (foraminifera, nannoplankton), benthic foraminifera, dino-flagellates, ammonites, geochemistry, clay mineralogy and geophysical logging indicate that: 1) The K/P boundary lies between 80.4 and 80.2 m, the Danian/Selandian boundary between ~ 41 and 43 m, the Selandian/Thanetian boundary at ~ 30 m (within the mid-part of the Tarawan Chalk) and the Paleocene/Eocene boundary at 11.75 m (base [planktonic foraminifera] Zone E1 and [calcareous nannoplankton] Zone NP9b); 2) the Dababiya Quarry Member (=Paleocene/Eocene Thermal Maximum interval) extends from 11.75 to 9.5 m, which is ~1 m less than in the adjacent GSSP outcrop.; 3) the Late Cretaceous (Maastrichtian) depositional environment was nearshore, tropical-sub tropical and nutrient rich; the latest Maastrichtian somewhat more restricted (coastal); and the early Danian cooler, low(er) salinity with increasing warmth and depth of water (i.e., more open water); 4) the Paleocene is further characterized by outer shelf (~ 200 m), warm water environments as supported by foraminifera P/B ratios > 85% (~79-28 m), whereas benthic foraminifera dominate (>70%) from ~27-12 m (Tarawan Chalk and Hanadi Member) due, perhaps, in part to increased dissolution (as observed in nearby outcrop samples over this interval); 5) during the PETM, enhanced hydrodynamic conditions are infered to have occurred on the sea-floor with increased river discharge (in agreement with sedimentologic evidence), itself a likely cause for very high enhanced biological productivity on the epicontinental shelf of Egypt; 6) correlation of in situ measured geophysical logs of Natural Gamma Ray (GR), Single-Point Resistance (PR), Self-Potential (SP), magnetic susceptibility (MS), and Resistivity, and Short Normal (SN) and Long Normal (LN) showed correspondence to the lithologic units. The Dababiya Quarry Member, in particular, is characterized by very high Gamma Ray and Resistivity Short Normal values. Source