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A revision of the Early Palaeogene nummulitids (Foraminifera) from northern Oman, with implications for their classification

By
J. R. Haynes
J. R. Haynes
1
Institute of Geography and Earth Sciences, Aberystwyth University, Ceredigion SY23 3DB, UK
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A. Racey
A. Racey
2
BG Group, 100 Thames Valley Park Drive, Reading, Berkshire RG6 1PT, UK
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J. E. Whittaker
J. E. Whittaker
3
Department of Palaeontology, The Natural History Museum, London SW7 5BD, UK
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Published:
January 01, 2010

Abstract

Fifteen nummulitid species are described from the Late Paleocene and Early Eocene of northern Oman. These comprise Operculina (five species), Assilina (one), Planocamerinoides (two), Ranikothalia (one), Nummulitoides (three), Palaeonummulites (one) and Chordoperculi-noides (two). The taxa Nummulitoides margaretae, Chordoperculinoides bermudezi, Palaeonum-mulites thalicus gwynae, Assilina ranikoti and Operculina libyca are recorded from the Middle East for the first time. Operculina canalifera and O. inaequilateralis are reassigned to Nummuli-toides; Operculina jiwani and Assilina dandotica are transferred to Planocamerinoides, and Rani-kothalia sahnii is placed in Chordoperculinoides. Some revisions to the generic classification are proposed, with these simple forms being removed to the Palaeonumulitinae, new subfamily herein, genera with lateral chamberlets being confined to the Nummulitinae, and genera with subdivided equatorial chambers being assigned to the Heterostegininae. Enrollment of the lamina and height of the coil (opening rate) is taken into account, as well as the presence or absence of vertical canals and the thickness of the marginal cord. On these grounds, a new genus, Caudrina (type species C. soldadensis), is formally described to include sub-evolute descendants of involute Chordoperculinoides. Trabeculae and trabecular canals are redefined and the problem of their mis-identification in terms of presence/absence as a criterion in the systematics of the Nummulitidae is discussed.

The biostratigraphical and palaeobiogeographical implications of this early nummulitid fauna are significant. The presence of Chordoperculinoides bermudezi in Oman is considered to be of particular importance, since it has previously been considered to be restricted to the Caribbean faunal province. The occurrence also of Ranikothalia nuttalli kohatica extends the geographical distribution of this taxon, which hitherto was only known from NW Pakistan, while Nummulitoides was previously only recorded with certainty from West Africa, Libya, Pakistan, the Pyrenees and from off western Ireland. Other taxa such as Assilina ranikoti and Palaeonummulites thalicus gwynae, and Operculina libyca, were previously only known from Pakistan and Libya, respectively. The fauna therefore shows a marked mixing of taxa from the Indian Subcontinent, the Mediterranean/North Atlantic and West African regions, as well as including a taxon previously considered endemic to the Caribbean.

Forms with a massive marginal cord such as Chordoperculinoides, Ranikothalia and Nummuli-toides indicate an age close to the Paleocene-Eocene boundary (nannoplankton zones NP8– NP10) with Nummulitoides possibly ranging as high as top NP11. Assilina, Palaeonummulites and Planocamerinoides have a first occurrence in the latest Paleocene (within NP9/P5a). Most of the genera studied first appear in the Late Thanetian (NP8/P4b-c) and were probably derived from a tightly coiled ancestor of Palaeonummulites earlier in the Paleocene. Possible lines of descent between these genera are also discussed.

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Contents

The Micropalaeontological Society, Special Publications

Micropalaeontology, Sedimentary Environments and Stratigraphy: a Tribute to Dennis Curry (1912–2001)

Geological Society of London
Volume
4
ISBN electronic:
9781862396227
Publication date:
January 01, 2010

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