A new species of Omphalocyclus (Foraminiferida) from the Upper Cretaceous of Jamaica and its stratigraphical significance

The orbitoidal larger foraminifer Omphalocyclus maldonensis n. sp. is described from the Maldon Inlier of northwestern Jamaica, being the first record of this genus from the island. The limestone in which it occurs contains the Upper Cretaceous (Upper Maastrichtian) Titanosarcolites rudist fauna, together with larger foraminiferal specimens identified as Orbitoides megaloformis Papp & Küpper. The new species differs from Omphalocyclus macroporus, the only other widely recognized species, in possessing a much smaller nucleus. At least some of the earlier records of Omphalocyclus from the Upper Cretaceous of Venezuela and Cuba should probably be referred to O. maldonensis.


INTRODUCTION
Larger foraminifera belonging to the Family Orbitoidae achieved circum-tropical distributions in the late Cretaceous (Dilley, 1973). Many of the species, particularly Orbitoides and Omphalocyclus have been used as biostratigraphic indicators in the platform limestone successions of the Mediteranean Tethys where ammonites and inoceramids are rare (e.g. Küpper, 1954; van Hinte, 1966;Dilley, 1973;Caus et al., 1996). Omphalocyclus has been widely recognized in Upper Cretaceous rocks in many parts of the Tethyan region, usually as O. macroporus (Lamarck) the type species (El-Asa'ad, 1989;Matsumaru, 1997). In most cases, the presence of Omphalocyclus has been used to indicate a Late Cretaceous, Maastrichtian, age for the rocks in which it occurs.
During the course of re-mapping the Upper Cretaceous rocks of the Maldon Inlier, northwest Jamaica (Chubb, 1958;Meyerhoff & Krieg, 1977;Fig. 1) two of us (GCG & SFM) sampled a layer containing numerous specimens of the larger foraminiferal genus Omphalocyclus. This is the first record of this genus from Jamaica. However, the specimens from the Maldon Inlier differ from typical O. macroporus and are described herein as O. maldonensis. We further discuss the biostratigraphical significance of the orbitoidal foraminifera in the Caribbean.

GEOLOGICAL SETTING
Upper Cretaceous sedimentary rocks are well exposed in the Maldon Inlier in the Parish of St. James (western Jamaica: Fig. 1). The inlier has previously been mapped by Sawkins (1869), Bailey (Chubb, 1958) and Atkinson (1969). The succession, named informally by Chubb (1958), consists of two limestones, the Maldon Limestone and Vaughansfield Limestone, within a thick succession of volcaniclastic shales and sandstones (Fig. 2). These sediments were deposited in a shallow tropical sea, close to active volcanoes of a Cretaceous island-arc complex (Coates, 1977;Draper, 1987;Mitchell, in press). The limestones contain abundant rudist bivalves, including Titanosarcolites giganteus (Whitfield), Biradiolites jamaicensis Trechmann, Chiapasella sp., Antillocaprina spp., Thyrastylon spp., Bournonia spp. and Plagioptychus spp. (Chubb, 1971;Kauffman & Sohl, 1974). This is a typical assemblage of the Titanosarcolites fauna (Chubb, 1971) and is traditionally considered to indicate a Maastrichtian age (Chubb, 1971;Sohl & Kollman, 1985), although Jiang & Robinson (1987) suggested it may also be partly Late Campanian. New strontium isotopic dates indicate a late Maastrichtian age (Steuber et al., 2002). Corals, gastropods and ostracodes are also present (Coates, 1977;Sohl & Kollman, 1985;Hazel & Kamiya, 1993;Sohl, 1998). The intervening clastics yield gastropods, corals, ostracodes and the larger foraminifera Kathina jamaicensis (Cushman & Jarvis) and Ayalaina rutteni (Palmer) (Robinson, 1968;Atkinson, 1969;Hazel & Kamiya, 1993). Hazel & Kamiya (1993)    Type locality and horizon. The specimens were collected c. 9 m below the top of the Maldon Limestone ( Description. Externally the test is disk shaped, bilaterally depressed in the centre, more or less circular in outline. Many tests are asymmetrical, one side being flat to slightly depressed in the centre, the opposite side with a markedly depressed centre. Surface ornamented with a cellular pattern of low ridges mimicking the internal pattern of septa separating the chambers; periphery bluntly rounded, with two to three rows of coarse pores; smaller specimens with two rows of pores, frequently separated by a more or less prominent keel. Diameters of 176 measured specimens range from 1.2 mm to 6.6 mm and maximum thicknesses (at or near the periphery) from 0.24 mm to 0.98 mm (Fig. 3). Equatorial sections of well preserved megalospheric individuals exhibit a quadrilocular nucleus, similar in pattern to that of Orbitoides (e.g. Caus et al., 1996), surrounded by a thickened wall. Internal nuclear diameters of 11 sectioned individuals range from 0.16 mm to 0.30 mm. Adauxiliary chambers (sensu Caus et al., 1996, p. 128) are generally 8 to 9 (observed range 6 to 10) in number, surrounded by about 7 or 8 cycles of orbitoidal chambers. In the outer part of the test, the equatorial layer consists of chambers with a more or less square cross-section (chessboard pattern of Höttinger, 1981).

SYSTEMATIC PALAEONTOLOGY
In axial section, the nucleus is succeeded variably by 2 to 4 cycles of normal uniserial orbitoidal chambers, then by 5 to 10 cycles of biserial orbitoidal chambers of the type illustrated by Höttinger (1981, fig. 7); a third, somewhat irregular layer of equatorial chambers is inserted between the last 3 to 6 cycles of orbitoidal chambers in the peripheral region. These are of the kind described by Höttinger (1981, figs 5 & 6). The more numerous triserial cycles are seen preferentially in microspheric specimens. No lateral chambers of the orbitoidal kind are present.
Equatorial sections of the microspheric generation show a tiny, apparently biserial embryonic stage, surrounded by a low trochospiral coil of about 6 to 8 chambers. These are succeeded in turn by from five to as many as 12 or more cycles of orbitoidal equatorial chambers, similar to those of the megalospheric generation. These may be followed, in the distal part of the test, by several cycles of chambers of the chessboard pattern of Höttinger (1981).

Dimensions. Measurements of the nucleus of specimens of
Omphalocyclus from Jamaica and The Netherlands (early late Maastrichtian, ENCI quarry) is given below. The terminology, Li and li, follows that used by van Hinte (1966) for the nucleus of Orbitoides and is illustrated with reference to Figure 4. Measurements in mm.

SIGNIFICANCE OF OMPHALOCYCLUS MALDONENSIS
In the upper part of the Maldon Limestone, O. maldonensis occurs with rare specimens of Orbitoides. Equatorial thin sections of these Orbitoides (Pl. 1, fig. 7) are comparable with examples of Orbitoides megaloformis collected from the Guinea Corn Formation at Logie Green (e.g. Krijnen et al., 1993, figs 22-6,7) in the Central Inlier (central Jamaica: Fig. 1). Van Hinte (1966) demonstrated that within the Orbitoides lineage there is an increase in the size of the nucleus and number of epi-auxillary chamberlets as one passes from more primitive to more advanced species through the late Cretaceous. Based on the nuclear characteristics, Jiang & Robinson (1987, fig. 8) suggested that the Logie Green Orbitoides might indicate a stratigraphic position near the Campanian-Maastrichtian boundary. Krijnen et al. (1993) noted that the specimens of O. megaloformis from the Central Inlier partly fit the limits set by Van Hinte (1966) for that taxon and suggested that the fauna might be slightly more advanced and, therefore, represented the very Early Maastrichtian. Caus et al. (1996), in a review of the biostratigraphic value of species of the genus Orbitoides, proposed that Orbitoides megaloformis Papp & Küpper characterized the latest Campanian of Europe. Independent age dating of the Logie Green site comes from nannofossils (Robinson, 1988, p. 59 (Renz, 1955, pl. 6, fig. 3) suggest that this designation may be a synonym of O. megaloformis. Examination of the specimens, however, would be required to confirm these interpretations. It is, therefore, possible that this Venezuelan fauna contains the same assemblage of orbitoid foraminifera as the upper Maldon Limestone. Renz (1955)  In the type Maastrichtian in The Netherlands, O. macroporus is associated with O. apiculata Schlumberger (Hardenbol et al., 1998). This association has also been reported from elsewhere,  including Saudi Arabia (El-Asa'ad, 1989), Turkey (Matsumaru, 1997) and, significantly, Cuba (Seiglie & Ayala-Castañares, 1963). Hardenbol et al. (1998) indicated that O. macroporus appeared in the upper Lower Maastrichtian.
In the Caribbean, therefore, there appear to be two orbitoid faunas, a fauna with O. megaloformis and O. maldonensis (Jamaica and possibly northern Venezuela); and a fauna with O. apiculata and O. macropora (Cuba).