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  • Articles  (2)
  • Egypt  (1)
  • Extant coccolithophorids  (1)
  • 1
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 284 (2009): 88-113, doi:10.1016/j.palaeo.2009.08.020.
    Description: Smaller size is generally seen as a negative response of organisms to stressful environmental conditions, associated with low diversity and species dominance. The mean size of the coccolithophorids decreased through the Neogene, leading to the prediction that their extant representatives are characterized by poor diversification and low specialization. The study of the (exo)coccospheres of selected taxa in the order Syracosphaerales negates this prediction, revealing that on the contrary some extant lineages are highly diversified and remarkably specialized. Whereas the general role of coccoliths remains indeterminate, this analysis suggests that some highly derived coccoliths may be modified for the collection of food particles, including picoplankton, thus implying that mixotrophy may characterize these lineages. In the extant coccolithophorids, species richness of genera is inversely correlated with the size of cells, definitive evidence that small size is part of a morphologic strategy rather than a sign of evolutionary failure. Because of their extreme minuteness, the extant nannoplankton can be well compared to Lilliputians, but the trend toward size decrease in Neogene lineages is not attributable to the Lilliput effect described by Urbanek (1993).
    Keywords: Extant coccolithophorids ; Neogene ; Size ; Exococcospheres ; Functional morphology ; Mixotrophy
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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  • 2
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Journal of African Earth Sciences 136 (2017): 61-108, doi:10.1016/j.jafrearsci.2017.05.008.
    Description: We present a detailed geologic study of the Thebes Formation at Gebel Gurnah in its locus typicus on the West Bank (opposite Luxor) of the Nile River in the Upper Nile Valley, Egypt. This is the first detailed measurement and lithologic description of the ~ 340 m thick (predominantly) carbonate section. The Thebes Formation is divided into thirteen major lithic units (A to M). We interpret data on the lithologic succession and variations, whole rock/clay mineralogy, and macro/micropaleontology in terms of deposition on a shallow carbonate platform episodically influenced by continental runoff, and describe six depositional sequences that we place in the global framework of Lower Eocene (Ypresian) sequence stratigraphy. We note however significant incompatibilities between the Thebes depositional sequences and the global sequences. We emend the definition of the Thebes Formation by defining its top as corresponding to level 326 m at the top of Nodular Limestone ‘L’ (NLL), and assigning the overlying beds to the Minia Limestone Formation. New biostratigraphic data and revision of previous studies establish the direct assignment of the Thebes Formation to planktonic foraminiferal Zones E4/P6b (upper part), E5/P7 and (indirectly) Zone E6/P8, and (probably, indirectly) Zone E7a/”P9”, and to calcareous nannofossil Zone NP12 and lower Zone NP13 of the Lower Eocene (Ypresian) and provide a temporal framework spanning ~ 2.8 Myr from 〈52.45 to ~49.6 Ma for the deposition of the Thebes Formation prior to the prominent sea level fall (~ 49.6 Ma) towards the end of the Early Eocene. Dominantly carbonate deposition, with a strongly reduced detrital influx, occurred on a very wide shelf (probably) at least ~ 100 km from the coastline. The thick sedimentary succession and the marked vertical lithologic variations are interpreted as resulting from sea level fluctuations imprinted on a long-term decrease in sea-level associated with rapid subsidence reflecting tectonic relaxation after the major Late Paleocene tectonic reorganization of the Syrian Arc.
    Description: National Geographic Society for financial support
    Keywords: Thebes Limestone ; Lower Eocene ; Gebel Gurnah ; Egypt ; Sequence stratigraphy
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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