Neorotalia omanensis and Operculina musawaensis from the Sultanate of Oman

Two new species of larger benthic foraminifera, Neorotalia omanensis n. sp. and Operculina musawaensis n. sp. are described and illustrated from the eastern Oman Mountains. N. omanensis n. sp. occurs in the Musawa Formation in association with the planktonic foraminifera Morozovella edgari and Truncarotaloides topilensis indicating an early to middle Eocene age (P10P13). Operculina musawaensis n. sp. occurs in the Abat Formation in association with the planktonic foraminifera Acarinina esnaensis and A. soldadensis indicating an early Eocene age (P6). This is the first known record showing the presence of genus Neorotalia in the Middle East. Representatives of the larger foraminiferal genus Linderina sp. are also described and illustrated from the Musawa Formation and compared with the published Linderina species in the surrounding countries.


Introduction
he genus Neorotalia sp. is poorly known from Arabia.The only published record from the northern Oman Mountains is Linderina rajasthanensis (Singh, 1953), found by White (1989) in Wadi Rusayl.White (1989) synonymized all four of Singh's (1953) species (rajasthanensis, bikanerensis, kolayatensis, kirtharensis) under one name (rajasthanensis) stating that test size, and shape (globular to discoidal with central boss, depending on the amount of lateral thickening) are insignificant as the means of discriminating species.The geographic distribution of the recorded species is very broad, including southern Europe (England to Romania), the Middle East, the Indian Sub-continent, Indonesia, Australia, Western Pacific and the Caribbean, possibly reflecting the presence of different genera with similar features (Ferrandex-Canadell and Serr-Kiel, 1999).In this paper the author reports two new species of large foraminifera in the Abat and Musawa Formations in the eastern part of the northern Oman Mountains.

T 2. Geological Setting
The section studied is located in the Jabal Ja'alan area of the Sharqiyah region, in the foothills of the eastern Oman Mountains, north Oman (Figure 1).The samples studied were collected from the Abat and Musawa Formations outcropping along the southern side of Wadi Musawa (Figure 1).Here a 1220 m thick mixed clastic-carbonate succession of Tertiary age rests unconformably on an older granitic basement.The Tertiary strata comprise, from bottom to top, the Abat, Musawa and Tahwah Formations (Figure 2).The samples yielding the new taxa described herein were collected from unit D of the Abat Formation and Unit H of the Musawa Formation (Figure 2).The Abat Formation comprises interbedded marine limestone (mudstone to packstone) and shale.The Musawa Formation contains three fluvial units, each of which is ferruginous towards its base and contains coal towards its top.The fluvial units are overlain by marine limestone and shale.The Abat Formation is Late Palaeocene to Early Eocene and the Musawa Formation is Early to Late Eocene based on planktonic foraminiferal assemblages.Previous work in the area was mainly focused on geological mapping (Villey et al., 1986;Filbrandt et al., 1990;Roger et al., 1991).Although Villey et al. (1986) include micropalaeontological data, these data are limited to faunal lists and broad age assignments and do not include illustrations and descriptions of the taxa recorded.
Figure 1.Location map of the study area (modified after Montenat et al., 1977).

Lithostratigraphy
This section describes the lithostratigraphic units containing the microfossils reported in the present study.

Abat Formation
Type-Locality: Wadi Musawa -Latitude 22 0 19' N and Longitude 58 0 23' E This unit unconformably overlies Maastrichtian sandstone turbidite and marl of the Fayah Formation, and is conformably overlain by sandstone of the Musawa Formation within which it interdigitates in its upper part.The lower part of the Abat Formation consists of thinly interbedded shale and mudstone overlain by planktonic foraminiferabearing wackestone with interbeds of mudstone and calcarenite.These beds pass upwards (across a 9 m unexposed section) into resedimented wackestone and packstone comprising six depositional cycles.The middle part of the Abat Formation is characterized by thinly bedded wackestone overlain by shale and followed by an upper unit of limestone and dolomite capped by a palaeosol horizon.Planktonic foraminifera, including Morozovella sp. and Subbotina sp., are common in the mudstone and shale of the lower part of the formation.Larger foraminifera, including Discocyclina sp., Daviesina sp., Miscellanea sp., Nummulites sp. and Assilina sp.together with small rotaliids, textulariids, calcareous red algae, echinoids and corals are common in the limestone of the upper part of the Abat Formation (Figure 3).The larger foraminifera commonly appear to have been penecontemporaneously redeposited and become progressively more abraded up section.Reworked Cretaceous radiolaria and charophytes also occur within this interval.
The Abat Formation has been dated as Late Palaeocene to Early Eocene (Thanetian to Ypresian) on the basis of its planktonic foraminifera, and comprises a thick sequence of open-marine basinal sediments.Common deep-marine planktonic-foraminiferal shale and mudstone form the lower part of the Abat Formation which shoals upwards into high-energy middle to outer shelf limestone.The latter is dominated by larger and smaller benthonic foraminifera with subordinate dasycladacean algae, calcareous red algae, echinoid plates and corals.The specimens of Operculina musawaensis n. sp.described herein were collected from the lower part of Unit D of the Abat Formation (Figure 2).

UNIT D
Description: This unit begins with packstone and mudstone separated by a very thin (7 cm thick) distinctive silicified mudstone from an overlying a 24 m thick massive larger foraminiferal limestone (wackestone-packstone).The basal part of Unit D comprises bioturbated limestone (packstone) overlain by mudstone rich in planktonic foraminifera (Acarinina sp. and Morozovella sp.) and larger foraminifera including Alveolina sp., Nummulites sp., Discocyclina sp. and Operculina musawaensis n. sp.This passes upwards into shale containing Nummulites and small rotaliids.The unit becomes more indurated up-section and rich in larger foraminifera, ostracods, corals, bivalves, gastropods and oysters.Lithoclasts and foraminifera are less abundant in the uppermost part of the unit, where clasts of grey chert are common, together with rare silicified burrows.Bivalves (often disarticulated) are also common in the uppermost part of the unit.
The characteristic microfossils in the Abat Formation include larger foraminifera (Alveolina sp., Nummulites honogoensis, N. globulus, Discocyclina sp., Assilina ex.gr.exponens, Somalina sp., Actinocyclina sp., Operculina musawaensis n. sp., Ranikothalia sp.) together with planktonic foraminifera (Acarinina esnaensis, A. soldadoensis and Morozovella aragonensis) which occur in the basal part of this unit.Other fossil fragments present include gastropods, and rare brachiopods, with smaller rotaliids, miliolids and textulariids.Rare dasycladacean algae occur in the middle to upper part of this unit, together with ostracods (Bairdia sp., Cytherella sp., Phalococythere sp. and Xestoleberis sp.).Age: An Early Eocene age is indicated by the presence of Morozovella marginodentata, M. aragonensis, Acarinina esnaensis, and A. soldadoensis along with associated larger foraminifera, including Nummulites cf.globulus.Although Somalina is typically considered to be Middle Eocene in age, White (1989) found Somalina hottingeri in late Early -Eocene rocks from the northern Oman Mountains.This unit corresponds to the Morozovella aragonensis Zone (P8) of Blow (1969) and Berggren and Miller (1988).Thickness: 33 m.Environment: The unit shows a gradual change from deep marine basinal facies rich in planktonic foraminifera in its lower part into shallow marine mid-outer shelf limestone with Nummulites sp., Assilina sp. and Discocyclina sp., and rare dasycladacean green algae (fragments) in its upper part.The Abat Formation is capped by non-fossiliferous shale of probable fluvial origin and palaeosols.Ostracods (Bairdia sp., Cytherella sp., Phalcocythere sp. and Xestoleberis sp.) suggest a shallow marine environment.

Musawa Formation
Type-Locality: Wadi Musawa -Latitude 22 0 19' N and Longitude 58 0 23' E The Early to Late Eocene (Ypresian to upper Bartonian) Musawa Formation comprises a regressive siliciclastic package at its base and a transgressive interval at its top.It contains fluvial sandstones, palaeosoland coal and shale, together with marine mudstone bearing planktonic foraminifera and re-deposited larger foraminifera and radiolaria.Reworked radiolaria and charophytes tend to occur together, especially in the fluviatile, coal-bearing beds.The middle part of the Musawa Formation represents an outer shelf environment.The lower part of the Musawa Formation is characterised by deep, open marine planktonic foraminifera including Morozovella sp.. Its middle part is dominated by planktonic foraminifera (M.edgari, Globigerinatheka sp., Truncorotaloides sp. and Turborotalia blowcentralis).
The upper part of the Musawa Formation represents a shallow marine, outer shelf environment with common insitu larger foraminifera including Nummulites sp., Operculina sp., Discocyclina sp., Dictyoconus sp., Coskinolina sp, and Neorotalia omanensis n. sp.Bivalves and gastropods, including Bicorbula sp., lucinids and naticids (N.Morris, 1998), are indicative of an intertidal to tidal-flat environment.The uppermost part of the formation consists of innershelf facies with miliolids and molluscs.It becomes more estuarine-dominated towards its top as indicated by the presence of coal seams and the presence of ostracods such as Neocyprideis sp., Bythocypris sp., Hornibrookella sp. and Paracosta sp.Neorotalia omanensis n. sp. and Linderina sp.specimens were collected from Unit H of the Musawa Formation.
Planktonic foraminifera.including Morozovella sp, Truncorotaloides libyaensis, and Globigerina sp., occur in the middle of the unit.The larger foraminifera include Nummulites maculatus, Nummulites cf.schaubi, Discocyclina dispansa, Assilina sp., Alveolina sp., Neorotalia omanensis n. sp., Operculina sp., Linderina sp., Nonionella sp., Pararotalia sp. and miliolids and rare ostracods.Burrows and macrofossils, including gastropods (i.e.Natica sp.), oysters and corals occur throughout.Age: Middle Eocene (upper Lutetian) age is indicated by the presence of the planktonic foraminifera: Truncorotaloides libyaensis, Truncorotaloides topilensis, Morozovella bolivariana, Globigerinatheka barri, Globigerinatheka curryi and Globigerinatheka sp.. Benthonic foraminifera (Nummulites schaubi and N. maculates) were recorded by Racey (1995) from the Middle Eocene (lower and middle Lutetian) of the northern Oman Mountains.The unit ranges within the Truncorotaloides topilensis Zone to the Truncorotaloides libyaensis/Morozovella bolivariana Zone, representing the local expression of the standard zones, the Globigerinatheka subconglobata subconglobata Zone to the Orbulinoides beckmanni Zone (P13), of Blow (1969) and Berggren and Miller (1988).Thickness: 81 m Environment: This is an outer shelf environment which was deeper at the base of the unit.It is indicated by abundant and diverse planktonic foraminifera.The topmost part of the unit is characterized by a low-intertidal to sub-tidal molluscan assemblage (N.Morris, Personal commun. 1998) Diagnosis: A distinctive large (2.3 mm diameter) planoconvex species of Neorotalia with 9-13 chambers in the last whorl.Surface coarse and pustulate, umbilical region characterised by a rosette pattern of plugs.Description: Test trochoid, rounded planoconvex.Periphery lobate to subcircular.There are 3-3.5 whorls with 9-13 triangular chambers in the last whorl in the equatorial section.Umbilical side strongly convex with large pillars on the umbilical shoulder surrounded by fine pustules.Spiral side flat to slightly convex with pustules coarser towards centre.Aperture is extraumbilical-umbilical.Dimensions: Holotype Diameter 2.3 mm.thickness 1.3 mm Paratypes Diameter 2.2 mm.thickness 1.1 mm Neorotalia omanensis n. sp.specimens are slightly different from Neorotalia aticantina, as described by Colom (1954), which is biconvex and smaller in size (0.5 to 0.7 mm in diameter and 0.4 to 0.6 mm thick).The Omani species have fine pustules at the periphery coarsening towards the centre on both sides, and a greater number of whorls than Neorotalia aticantina (Colom,1954) and Neorotalia mexicana (Nuttall, 1952).The N. omanensis shows a greater number of chambers in the last whorl than N. aticantina (Colom, 1954) and has an equal number of chambers in the last whorl to N. mexicana (Nuttall, 1952).The genus Neorotalia shows some similarities with Daviesina, although Daviesina is restricted to the Palaeocene and has a circular to subcircular, slightly trochospiral test with large pillars on umbilical shoulders.

Geographic distribution and stratigraphic range:
The genus Neorotalia is previously unknown from the Middle East, having been reported from the Oligocene of southern Mexico (Nuttall, 1952) and the Ypresian/Lutetian boundary in Spain (Colom, 1954).

Genus Operculina )d'Orbigny 1826(
Type species Lenticulites complanatus )Defrance, 1822( Description Planispirally coiled, evolute with flat to flattened lenticular to compressed test; loosely coiled with rapidly opening spire, comprising few whorls and subdivided by numerous high chambers.Wall calcareous, perforate with smooth or pustulose surface.Diagnosis: A small heavily pustular species with a distinctive large polar pustule, relatively few chambers per whorl and a markedly tight spire (4 whorls in a radius of about 1 mm).Description: A-form.Test discoidal, flat with polar region thickened by secondary lamellation.Marginal cord is well-developed with septal sutures radial and recurved towards the periphery.Chambers are 1.5-2 times higher than wide with twenty four arcuate chambers in the last whorl.The spire is tight and opens uniformly.The proloculus has an internal diameter of 0.035-0.043mm.

Generic description of Linderina
Test large up to 3.5 mm in diameter, discoidal, centrally thickened.Periphery rounded, peripheral outline lobate, wall calcareous and test surface covered with small pustules.Early chambers of microspheric test form an irregular cluster, rather than a distinct spire.Megalospheric test with bilocular embryo followed by a nepionic ring of seven to eight small chambers with a concentric series of small arched chambers in a single equatorial layer.Younger chambers are progressively larger and alternating in position.Early stage is covered by numerous layers of calcite resulting in an inflated central region traversed by fine pores connecting the chambers to the exterior.Apertures and intercameral openings occur at the base of the chamber against the chambers of the previous whorl.

Discussion
Illustrations in the Ellis and Messina Catalogue (1940) and observations during this study suggest that the globular forms with umbonal lamellar thickening (e.g.Plate 2, Figures 3-4; Plate 3. Figure 5) are all megalospheric, whereas the discoidal forms (without or with very little umbonal lamellar thickening e.g.Plate 2, Figures 1-2, Plate 3, Figures 1-4) appear to be microspheric.
Linderina sp.B. Plate 2, Figures 3-4, Plate 3, Figure 5 Material: Twenty five specimens from sample WME 182.Description: Test large, discoidal with rim encircling the central area and with a slightly wavy periphery.Equatorial chambers arcuate, large and arranged overlapping alternately, increasing in size towards the center varying in size from 0.09 mm to 0.12 mm across.In axial section the test is thick at the centre and narrows towards the margins.Pillars are fine, radial over most of the test.Protoconch is about 0.11 mm in axial section, and 0.08 mm in equatorial section.

Figure 3 .
Figure 3. Distribution chart of the key taxa of benthonic foraminifera.