Odontochitina tabulata sp. nov. A Late Santonian–Early Campanian dinoflagellate cyst from SE Sirte Basin, Libya

Odontochitina tabulata, a new tabulated ceratioid species, has been recorded and described from core samples in Well C3-65 in the SE Sirte Basin. This species is characterizd by parasutural and pandasutural features reflecting clear gonyaulacacean paratabulation. It has a short stratigraphic range and is considered as a valuable stratigraphic marker for the Late Santonian–Early Campanian. The diagnosis of the genus Odontochitina Deflandre, 1935 is emended to include forms having a well defined gonyaulacacean paratabulation and narrow pandasutural and parasutural ridges.


INTRODUCTION
The presented taxon is one of many new genera and species recovered by the author during a study of the Upper Cretaceous sediments subcropping in the SE Sirte Basin, Libya. The new taxon is recovered from the Upper Cretaceous succession of Well C3-65 in the Sarir area, SE Sirte Basin (Fig. 1). This well belongs to the Arabian Gulf Oil Company (AGOCO) Libya and was drilled by British Petroleum (BP) in 1961, and six cores were cut in the Upper Cretaceous sediments. These cores are barren of any age diagnostic foraminifera. The palynological analyses of these cores have yielded a richassemblage of diverse and well preserved palynomorphs. The newly recorded taxa include many peridinioid and gonyaulacoid species. The latter includes a distinctive tabulated ceratioid species of the genus Odontochitina Deflandre, 1935, emend. nov., identified as 0. tabulura sp. nov. This species is recorded from three successive samples from core # 4 (depths 8517 feet, 852&8523 feet, 8524-8527 feet) which have been assigned to a Late Santonian-Early Campanian age by the author. This age interpretation is based on the presence of stratigraphically important species such as Nelsoniella aceras Cookson & Eisenack, 1960, N . tuberculata Cookson & Eisenack, 1960, Eucladinium cf. gambangense (Cookson & Eisenack, 1970) Stover & Evitt, 1978, E. madurense (Cookson & Eisenack, 1970) Stover & Evitt, 1978, Exochosphaeridium bijidium (Clarke & Verdier, 1967 Clarke et al., 1968, Nematosphaeropsis grande Davey, 1975. The detailed palynostratigraphy of these samples is under preparation by the author to be published in a separate paper.

Material
The samples were treated with standard palynological techniques, including a treatment with HCL (35%), H F (40%) and oxidation with Schultze solution. Strong oxidation is used to liberate the palynomorphs which are locked up inside the organic material. They are then stained using Safranin-0 to make them more visible. All type slides are housed in the palynological collection of the Centre for Palynological Studies, Sheffield University, England.
Archeopyle. Apical, type [tA], principle archeopyle parasuture smooth, weakly angular to zigzag with an offset parasulcal notch; operculum free or attached. Paracingulum. If present indicated by faint features or by low relief parasutural ridges. Parasulcus. Indicated anteriorally by an offset parasulcal notch, or by two parallel longitudinal parasutural ridges in the ventral side of the hypocyst.
Remarks and comparison. Odontochitina Deflandre; emended herein closely resembles Xenascus Cookson & Eisenack, 1969emend. Stover & Helby (1987, as both have a ceratioid cyst. The latter differs from Odontochitina in having a circumcavate to a cornucavate cyst with variable, large periphragmal processes, whereas the former has a cornucavate to bicavate cyst with very rarely homogeneous, small, closed, spinose processes.
Discussion. This genus is emended to include species with a cornucavate, and occasionally an epicavate, tabulate cyst in which the paratabulation is defined by parasutural features.

Parasulcal notch
1.  fig. I; PI. 2, fig. 6). The periphragm is smooth to scabrate. paratabulation formula is 4, 6 , 5-6c, 6", Ip, l"", Xs. About 2/3 of the distal part of the apical, antapical and lateral Archeopyle. Apical, type [tA], principal archeopyle parasuture horns are ornamented with numerous perforations which are smooth or zigzag with slightly offset parasulcal notch; operaligned alongside the ridges on the horns. These perforations are culum free. subcircular to subrectangular and < 0.5 m to > 3 m in diameter. Paracingulum. Distinct and delineated by shallow transverse Paratabulation. Gonyaulacacean, normally indicated by para-depression and two parallel parasutural ridges which may also sutural ridges, archeopyle and paracingulum. The derived indicate the presence of 5 4 paraplates. Paracingular notch is always present at the point of re-curvature of the lateral horn. Parasulcus. Delimited by parasutural features and shallow longitudinal depression on the mid-ventral surface of the hypocyst and on the anterior part of the epicyst by the parasulcal notch. Dimensions. Overall length (without apical horn) 210 (265) 320pm; endocyst length 54 (64) 74pm, width 42 (54) 74pm; apical horn length 100 (104) 108pm; antapical horn length 40 (62) 82pm; lateral horn length 34 (57) 80pm; specimens measured 19. Dimensions of holotype; overall length (without apical horn) 250pm; endocyst length 74pm, width 72pm; antapical horn length 76 pm; lateral horn length 60 pm. Dimension of paratype; overall length (without apical horn) 21 0 pm; endocyst length 64 pm, width 70 pm; antapical horn length 62 pm; lateral horn length p34 m. Remarks. Odontochitina tabuluta sp. nov. a species of Odontochitina Deflandre, 1935 emend., is characterized by possessing pandasutural and parasutural ridges reflecting clear gonyaulacacean paratabulation. Odonrochitina tabulata sp. nov. is similar to 0. cribropoda Deflandre & Cookson, 1955 and 0. p o r f e r a Cookson, 1956 in the general morphology, but the former differs from the two latter species in having paratabulation reflected by panda-and parasutural features, which the latter species are lacking. The new species also differs from 0. p o r f e r a in that the perforations are restricted to the 2/3 of the distal part of the apical, lateral and antapical horns.