136 research outputs found
Calcareous nannofossil assemblages of the Late Cretaceous Fiqa Formation, north Oman
This study presents the
first detailed calcareous nannofossil assemblage data from the Late
Cretaceous succession of the subsurface Aruma Basin, north Oman. The
taxonomic description and documentation of assemblage composition are based
on extensive quantitative analysis of ditch cuttings and side-wall samples
from eight hydrocarbon exploration wells across north Oman. The samples
studied from those wells cover the Coniacian to earliest Maastrichtian deep
marine shales and marls of the subsurface Fiqa Formation. These fine-grained
siliciclastic deposits often yield moderately to well-preserved nannofossil
assemblages, especially in the Campanian intervals. Consequently, diverse
assemblages have been recorded from the Fiqa Formation, with a total
diversity of ∼200 species, including two new species,
Staurolithites ormae sp. nov. and Chiastozygus fahudensis
sp. nov., which are illustrated and described. Extensive imaging of this
diversity is provided here, as are stratigraphic distributions of the main
components from a key reference well in north Oman, W-4. Poorly described
groups such as Staurolithites are closely investigated and their
utility for stratigraphic applications is highlighted. Relative abundances of
nannofossil taxa with strong palaeoenvironmental preferences have revealed
new insights into the palaeo-productivity of the basin. High-fertility
species like Discorhabdus ignotus, Biscutum constans and
Zeugrhabdotus erectus show substantial variations in abundance
throughout the Fiqa Formation, reflecting long-term shifts in the
productivity conditions of the basin. This is supported by abundance patterns
of Watznaueria barnesiae and Micula staurophora that show a
broadly inverse correlation with the high-fertility species. The Fiqa
Formation represents a key regional seal unit for the Cretaceous hydrocarbon
reservoirs of Oman, as well as being a productive unit elsewhere in the
Arabian Peninsula. Beyond the Aruma Basin of Oman, this study will provide a
key reference point for future biostratigraphic or palaeoenvironmental
analyses of the Late Cretaceous calcareous nannofossil assemblages across the
Middle East and other southern Tethyan areas.</p
Climate model and proxy data constraints on ocean warming across the Paleocene-Eocene Thermal Maximum
Constraining the greenhouse gas forcing, climatic warming and estimates of climate sensitivity across ancient large transient warming events is a major challenge to the palaeoclimate research community. Here we provide a new compilation and synthesis of the available marine proxy temperature data across the largest of these hyperthermals, the Paleocene-Eocene Thermal Maximum (PETM). This includes the application of consistent temperature calibrations to all data, including the most recent set of calibrations for archaeal lipid-derived palaeothermometry. This compilation provides the basis for an informed discussion of the likely range of PETM warming, the biases present in the existing record and an initial assessment of the geographical pattern of PETM ocean warming. To aid interpretation of the geographic variability of the proxy-derived estimates of PETM warming, we present a comparison of this data with the patterns of warming produced by high pCO2 simulations of Eocene climates using the Hadley Centre atmosphere-ocean general circulation model (AOGCM) HadCM3L. On the basis of this comparison and taking into account the patterns of intermediate-water warming we estimate that the global mean surface temperature anomaly for the PETM is within the range of 4 to 5°C
Late Neogene evolution of modern deep-dwelling plankton
The fossil record of marine microplankton provides insights into the evolutionary drivers which led to the origin of modern deep-water plankton, one of the largest components of ocean biomass. We use global abundance and biogeographic data, combined with depth habitat reconstructions, to determine the environmental mechanisms behind speciation in two groups of pelagic microfossils over the past 15 Myr. We compare our microfossil datasets with water column profiles simulated in an Earth system model. We show that deep-living planktonic foraminiferal (zooplankton) and calcareous nannofossil (mixotroph phytoplankton) species were virtually absent globally during the peak of the middle Miocene warmth. The evolution of deep-dwelling planktonic foraminifera started from subpolar–mid-latitude species, during late Miocene cooling, via allopatry. Deep-dwelling species subsequently spread towards lower latitudes and further diversified via depth sympatry, establishing modern communities stratified hundreds of metres down the water column. Similarly, sub-euphotic zone specialist calcareous nannofossils become a major component of tropical and sub-tropical assemblages during the latest Miocene to early Pliocene. Our model simulations suggest that increased organic matter and oxygen availability for planktonic foraminifera, and increased nutrients and light penetration for nannoplankton, favoured the evolution of new deep-water niches. These conditions resulted from global cooling and the associated increase in the efficiency of the biological pump over the last 15 Myr
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