Ostracoda from the Miocene Marada Formation of Libya

The ostracods of the Miocene Marada Formation from three wells in the east of the Sirt Basin are described. These indicate ages ranging from Aquitainian to Tortonian. Four biozones are recognised: Pokornyella deformis minor (=Aquitainian), Aurilla soummamensis (=Burdigalian), an interval zone of Mid Miocene age, and Ruggieria tetraptera tetraptera (=Tortonian). 55 species have been identified, 22 of which are known from other Mediterranean localities. Six new species are described: Actinocythereis sirtensis sp. nov, Bythocypris tripoliensis sp. nov, Cyprideis maradaensis sp. nov, Cytheridea joshensis sp. nov, Gammudi, Hermanites zaltanensis sp. nov, and Paijenborchellina keeni sp. nov, Gammudi.


INTRODUCTION
The Sirt Basin is one of several sedimentary basins developed on the East Saharan Craton (Fig.1). Subsidence began in the Cretaceous, continued through the Tertiary, with the accumulation of more than 6000m of sediment. Miocene sediments are only present in Libya in the northern Sirt Basin, adjacent areas of the Cyrenaica Platform, and a small area around A1 khums which is 120km east of Tripoli. During the Early-Mid Miocene a shallow marine gulf, fringed by lagoons and bordered by a coastal plain existed over the northern Sirt Basin (Fig 1) . The deposits of the Cyrenaica Platform are shallow marine carbonates, while the thicker sediments of the Sirt Basin include shales as well as clastics and carbonates. The Miocene of the Cyrenaica Platform is entirely Middle Miocene in age (Desio, 1928). while that of A1 Khums (A1 khums Formation) has recently been dated on the basis of foraminifera (Innocenti & Pertusati, 1984) and ostracods (A1 Waer, 1988(A1 Waer, , 1992 as Late Miocene, although they were previously believed to be Mid Miocene. The Marada Formation is traditionally regarded as being Early-Mid Miocene in age. The Miocene is usually unconformable with the underlying rocks, except in the south central Sirt Basin where it is conformable with the Oligoccne Diba Formation. The wells studied here were drilled by the Wintershall Company in the eastern Sirt Basin on onshore concession 97 ( Fig. l.), and penetrate some 1200ft. of sediment referred to the Marada Formation. The samples are ditch cuttings, each representing 30-60ft of well drilling. While it is impossible to determine the true distribution of microfossils in the wells, the first appearance downhole can be ascertained, and features such as numerical abundance and nature of preservation give some clues as to. the probability of in situ occurrence. The ostracod fauna recovered from these samples is a typically diverse infralittoral fauna, with many species in common with the Miocene of the Mediterranean area in general.

THE MARADA FORMATION
Desio introduced the name Marada Series for the succession of Dor Marada, some 50km northwest of Jabal Zaltan ( Fig.1). The type section consists of 80m of shale interbedded with sand and limestone, with some gypsum layers. It contains a marine fauna which Desio considered indicated a Langhian(Burdiga1ian) -Helvetian age, ie. Early to mid Miocene. Mammalian studies (Aramborg & Magnier, 1961;Magnier, 1964;Savage & White, 1965;and Savage & Hamilton, 1973) suggest Early Miocene, including Burdigalian, for the formation at Jabal Zaltan. Hughes (1974 unpublished internal report B. G. S. No PDL 74/5 , in Benfield and Wright 1980) studied core samples taken from about 60-70 ft below the top of the Marada Formation in Borehole J(C1-95) ( Lat, 27O 27", Long, 20° 43"), located 85km North West of well F1-97 studied here. On the basis of foraminiferal species such as Borelis melo (Fichtel & Moll) he suggested a Middle Miocene age for this part of the Marada Formation. Innocenti & Pertusati (1984) studied the Marada Formation of the area immediately to the north of the type area, using both macro and microfossils, including ostracods, and recognised two foraminiferal assemblages.  Selley (1969) and El-Hawat (1980) studied the sedimentary facies of the Marada Formation in its type area, recognising fluviatile, estuarine channels, tidal inlets and flats, lagoons, barrier bar and beaches, marine banks, and marine delta fans. The succession in the type area has a thickness of 80-150m; it increases in thickness northwards into the centre of the basin, with a maximum recorded thickness of 2800ft (853m) (Wright & Benfield 1980).
The wells studied here were drilled to the east of the type area, in a regiom which was a trough during the Miocene where some 365m (1200ft) of sediment accumulated. The sediments penetrated by the wells differ from those of the type area; most of the succession consists of fossilifeous limestones (marly calcarenites, some calcilutites) with common shale horizons. It is not easy to correlate these sediments with the facies described by Selley (1969) and El-Hawat (1980). The fauna (see below ) indicates the predominance of shallow marine conditions, probably infralittoral, throughout the succession. Brackish water ostracods such as Cyprideis and Neocyprideis occur commonly in the lower part of the Marada Formation in the wells studied, but there is no correlation between their abundance and type of sediment. Therefore they cannot be regarded as representative of the lagoonal shale facies of Selley and El-Hawat. Lagonal facies however were clearly present in the vicinity of the wells. There is no evidence of barrier bar, beach, tidal flat, estuarine channels or fluviatile facies, because the area was presumably seaward of these facies.

PREVIOUS STUDIES OF T H E MIOCENE OSTRACODS OF LIBYA
While the Miocene ostracods of the Mediterranean area have been widely studied during the past 100 years, only four studies have been published on the Miocene ostracods of Libya. The first was by Van Hinte et a1 (1980) who recorded ostracod faunas from the side wall core of the offshore well Bl-NC35A, located about 140km north east of Tripoli on the Pelagian platform. The lithology of the core shows intercalation of anhydrite between marl beds. The marls above the anhydrite were considered to be Pliocene in age, and marls below the anhydrite Miocene. The evaporites are probably evidence of the Messinian event in the area. 41 species of ostracods were recorded, including 23 named species. 11 species were only present above the evaporites, and of 30 species recorded from the Miocene only Acantkocytkereis kystriw, Ckrysocytkere catapkracta and Neomonoceratina laskarevi have been found in this study. The reason for this great difference in faunas is partly due to stratigraphy as the faunas of Van Hinte et a1 are mostly younger than those of the Marada Formation, and partly due to facies where the samples of Van Hinte et a1 indicate predominantly circalittoral-upper bathyal (75-500m) conditions. El-Waer (1988, 1992 (Sissingh), Aurila impressa (Ruggieri), Aurila longa Ruggeiri, Aurila Punctata (Von Munster), Aurila trigonella (Reuss), Bairdia subdeltoidea (Von Munster), Bairdoppillata octopunctata Ruggieri, Chyso cythere cataphracta (Ruggieri), Cletocythereis minor (Ruggieri) Cnestocythere truncata ( Reuss), Cytheridea acuminata Bosquet, Kangarina coarctata Ruggieri, Loxoconcha punctatella (Ruggieri), Loxoconcha variesculpata (Ruggieri) Neomonoceratina mediterranea (Ruggieri), Neomonoceratina mouliana (Sissingh), Ruggieria tetraptera tetraptera (Seguenza), Tenedocythere mediterranea (Ruggieri). This list of species is so different from that recorded in t h s study that, because they are not illustrated, it is impossible to make any valid comparisons.

SYSTEMATIC DESCRIPTIONS
The material described here is stored in the collections of the Hunterian Museum, University of Glasgow, and the numbers refer to its catalogue. Subclass Ostracoda Latreille, 1806. Order Podocopida Miiller, 1894. Suborder Platycopa Sars 1866. Family Cytherellidae Sars, 1866. Three species of Cytherella Jones 1849 have been recognised (Fig.2). Cytherella cf. pulchella Ruggieri 1967 differs from the type material from the Upper Tortonian of Italy in the arrangement of the pits and in lacking a truncated posterior in dorsal view; it is more similar to C. pulchella described by Amta (1982) from the Middle-Upper Miocene of Sicily, differing in its smaller size and less truncated posteroventral margin. Six specimens were recovered; five of these are punctate, the sixth is smooth, and is interpreted as polymorphism (See Keen 1982 Edwards, 1944 is conspecific with the species described under this name by Keij (1955) and   Moyes (1965) from the Aquitanian of southwest France, but it is not clear whether these should really be placed into Edwards' species which was described from the Miocene of North Carolina, U.S.A. Bairdoppilata sp. B and differs from Bairdoppilata sp.A in its smaller size and in having a more evenly curved dorsal margin, more pointed posterior, and a less upwardly curved postero-ventral area.  Carbonnel(1986), although the outline is not quite the same, the species described here being more elongate. It is also similar in size to Disopontocypris schwejeri Van Den Bold (1966), but differs from the latter in the outline of the dorsal and anterior margins; in B. tripoliensis the dorsal margin slopes downwards towards the anterior giving a more tapered anterior in the female, and has a more humped dorsal margin.

Length
Height L/HH Superfamily Cypridacea Baird, 1845 Family Cyprididae Baird, 1845 Subfamily Disopontocypridinae Mandelstam, 1956 Genus Disopontocypris Mandelstam, 1956 Disopontocypris schwejeri Van Den Bold, 1966 (Pl. 1, fig. 10) Material. 9 carapaces and 1 valve; only present in Well Cla-97 between 770-950 ft.; No A12674-76. Remarks. This was originally described from the Neogene of Gabon (Van Den Bold 1966), and subsequently from the Burdigalian of Algeria (Coutelle & Yassini, 1974) and the Neogene of Senegal (Carbonnel 1986  Family Paracyprididae Sars, 1923 Genus Purucypris Sars, 1866 Three species of this genus have been recognised. Purucypris aff P. politu Sars 1866 resembles Purucypris politu Sars (1866) described from the Burdigalian of South West Anatolia, Turkey, by Gokcen (1986); the latter differs in lateral outline, being more elongate and having a more tapered posterior margin and more obliquely rounded anterior margin. Purucypris politu described from the Upper Oligocene-Helvetian of the Aquitaine Basin (Keij, 1955 andMoyes 1965), differs in being more elongate and in having a highly tapered posterior. Purucypris sp. A shows similarities with Purucypris roseFeldensis described from the lower Miocene of Southern Trinidad (Van Den Bold, 1957) but the latter has a more pointed posterior and it is larger. I? sp. A differs from Propontocypris sp. in the pointed posterior margin and smaller size. Purucypris sp. shows some similarities to Purucypris sp described' from the Neogene of Rhodes (Mostafawi, 1989), but the latter differs in having maximum height at 1 / 3 length of carapace from anterior, dorsal margin is slightly rounded, and postero-dorsal margin slightly curved rather than straight. This species also shows some similarities with Purucypris politu Sars described from the Burdigalian of south west Anatolia, Turkey (Gok~en1986), but differs in having a longer and curved antero-dorsal margin. Remarks. This widespread species, first described from the Tortonian of the Vienna Basin (Reuss 1850) is also recorded from the Aquitanian-Burdigalian of France (Keij 1955, Moyes 1965, and Carbonnel 1969 from the Tortonian of central Sicily (Ruggieri 1962), from the Upper Miocene of Libya (El-WaerJ992) and from the ?middle Miocene Marada Formation and Hommath Formation of Egypt (Szczechura & Abd-Elshafy 1989). Triebel (1950) described two species from the Tortonian of the Vienna Basin: Cnestocythere lumellicostu n.sp. and C. truncutu (Reuss); the former has sharp and high ridges while the latter has low rounded ridges, our specimens have low and rounded ridges.
Family Cytherettidae Triebel, 1952 Genus Cytherettu G. W. Muller, 1894 Two species are recorded, Cytherettu cf. semipunctutu Bomemann, 1885 and Cytherettu sp. A. The former is similar to Cytherettu aff semipunctutu described from the Lower Miocene of the Rhone Basin in France (Carbonnel1969), but differs in shape and arrangement of punctae. In our specimens these are variable in size, forming four rows in the postero-central area and extending both posteriorly and anteriorly as scattered and smaller sized punctae; the remainder of the carapace is smooth. Cytherettu sp. A has an ornamentation consisting of seven longitudinal ridges in the posterior part of the carapace, with weakly developed reticulation between them; one specimen also has very indistinct rows of punctae in the antero-ventral part of the valve. It is similar to Cytherettu ishizukii Bonaduce at ul 1992, described from the Sahelian of offshore Tunisia. It differs in lacking the postero-ventral punctae which characterise C. ishizukii. El Waer (1992) described two species, Cytherettu sp. A and Cytherettu sp.B from the late Miocene of Libya.They appear to us to be conspecific, the only difference being the greater prominence of the punctae in Cytherettu sp.A. Our species lacks the punctae present in the postero-dorsal, central, and ventral areas of El Waers's species. The presence of these punctae also separates El Waer's species from C. ishizukii. These three taxa do appear to be closely related however.     Carbonnel (1969)  Remarks. This is similar to Cytheridea josephinae Kollmann 1960, recorded from the middle Tortonian of Austria, but differs in the postero-ventral area being broadly rounded as well as in the Ornamentation which consists of different sized weak punctae situated in the centre of the valves, the remainder of the carapace being smooth.  centre of the carapace; anterior margin broadly rounded with some seven small spines on both valves; posterior margin obliquely rounded; ventral margin nearly straight but slightly concave in the antero-ventral area while in the left valve weakly convex; Surface of carapace has scattered punctae; some of these are seen to be sieve type normal pore canals, others are too ill preserved to be sure whether they are pore canals. Internal feature very clear and typical of the genus. Males smaller and slightly more elongate than females.  Van Den Bold. (1963) from the Upper Miocene and Pliocene of Trinidad. The latter species differs in having a more truncated posterior end and lacks the small postero-ventral flangepresent in our species. The carapace is smooth to slightly pitted, and sexual dimorphism is not pronounced. Remarks. This species is very similar to Cyprideis sp. A in lateral outline; it differs in having an ornamentation of prominent pits; finer pits arranged in four rows parallel to the anterior and posterior margins, and coarse pits over the remainder of the carapace; it is also has a small posteroventral spine in the right valve. No internal features have been observed.

Genus Neocypridies Apostolescu,l956
Neocyprideis sp (P1.2, fig. 6) Material. 5 carapaces; No A12590-91. Wells Cla-97 at depth,1280,1550; G1-97,880; F1-97,840 ft. Remarks. This is placed in Neocypridies on the basis of lateral outline; no internal feature have been observed. It shows some similarity to Neocyprideis rura Goerlich,l953 subspecies cerestel in Carbonnel (1969) Szczechura, 1980 (P1.3, figs 14, 17) Material. 5 carapaces and 1 valve; No A12688-689 from Wells Cla-97 at depth 1400, 1610ft, G1-97 at 1470ft and F1-97 at 780,810 ft. Remarks. This was described from outcrops of the Upper Miocene of the northern Sirt Basin between Marada Oasis and the Dahra oil fields (Szczechura, 1980 Description. Carapace pear shaped in lateral view; anterior margin slightly obliquely rounded; dorsal margin rounded and saddle like; ventral margin straight; maximum height at antero-dorsal area one third from anterior, i.e. at maximum curvature dorsally; reticulation over entire carapace surface. One specimen (P1.3, fig. 20) is poorly reticulate but has well developed reticulation around the anterior margin; this may be due to preservation or indicate infraspecific variation. Central area with longitudinal ribs, ventral most of which is clearly defined at posterior where it bends sharply downwards; there is a weak depression parallel to the anterior margin. Internal features not known. Sexual dimorphisim is distinct, with more elongate males.  Yassinil974) and Turkey (Bassiouni, 1969, Gokcen 1984 Description. Carapace triangular in lateral view; dorsal margin rounded to arched; maximum height slightly behind centre of carapace; anterior margin obliquely rounded; posterior margin truncate with very short caudal process; ventral margin concave in the anterior part and slightly convex posteriorly; left valve larger than right valve and strongly overlaps the right; the surface is ornamented by variable sized punctae; anterior margin with four parallel rows of quadrate reticulation. No internal feature were observed. Sexual dimorphisim is distinct, males being more elongate than females. Remarks. Aurila gr convexa is similar to Aurila (Aurila) maculosa (Uliczny 1969) in lateral outline but the latter has its maximum height located at the mid length of the carapace while in our specimens the maximum height is situated just to the posterior of mid length.

Material. 25 carapaces and 4 valves from all wells; No
Remarks. Pokornyella deformis minor Moyes is smaller than the nominate subspecies. It is recorded from the lower Miocene of the Aquitain Basin in France (Moyes, 1965), the lower Miocene of Turkey (Bassiouni, 1979), the lower Aquitanian to Burdigalian of the Kale-Yensehir region of Turkey (Gokcen 1985-86) and is described from ?middle Miocene of the central Sirt Basin and western coast of the Gulf of Suez, Egypt (Szczechura & Abd-Elshafy 1989). Ruggieri, Russo & Bossio (1977), have illustrated topotype material of both Pokornyella deformis deformis and Pokornyella deformis minor. The diagnostic feature of P. deformis minor, apart from smaller size, is the presence of a short ridge at the postero-dorsal angle. Remarks. This is similar to Procythereis sulcatopunctatus (Reuss 1850) described from the middle Miocene of Turkey by Bassiouni (1979), but differs in having a more curved dorsal margin, and a more obliquely rounded anterior margin. This is very similar to Procythereis sulcatopuntatus of El-Waer (1992)) from the Upper Miocene A1 khums Formation of Libya.
Genus Urocythereis Ruggieri, 1950 (P1.3, fig.6) Material.One carapace from Borehole G1-97 at depth of 1190 ft; No A12706. Remarks. This shows great similarities in lateral outline to Urocythereis sorocula from the Pliocene of Reggio di Calabria  but the latter differs in having elongate groove more or less parallel to the anterior margin which is weakly developed in our species, as well as differences in the pattern of reticulation. U. sororcula is also described from the Pliocene of Spain (Carbonnel & Magne, 1977).
Urocythereis cf. U. sorocula Uliczny,1969Family Loxoconchidae Sars, 1925 Genus Loxoconcha SarsJ866 Loxoconcha gr ovulata (Costa), 1853 (Pl.l, fig. 18 97,960,990,1080,1230,1260,1440,1500,1560-1620. Family Schizocytheridae Howe, 1961Genus Neomonoceratina Kingma, 1948 Neomonocera tina keiji Szczechura, 1989 (P1.3, fig.13) 1989 Neomonoceratina keiji pl. 8,ll. Material.190 Carapaces and 20 valves from all wells and all depths; No A12606-611. Diagnosis. A species of Neomonoceratina with reticulation present but poorly developed; reticulation is strongest to the posterior of dorsal sulcus and below the ventral ridge; much of the surface is smooth with prominent pore cones. Remark. This is similar to Neomonoceratina miocaenica (El-Waer 1988) from the Upper Miocene of N.W Libya. El-Waer's species differs in having stronger reticulation present over the whole surface, a less accentuated ventral ridge and the antero-dorsal ridge running from eye tubercle to join with the median ridge. The variation in the reticulation in figured species compared with N. miocaenica is suggestive of ecophenotypic variation. However, no variation has been observed in the specimens studied and as tlus common species is found throughout the wells, reticulation is regarded as a genuine character for differentiating species. This species occurs throughout the Marada Formation as well as in the Hommath formation of ?middle Miocene age of the western coast of the Gulf of Suez (Egypt).  Aruta, 118, p1.4, figs 15-17. 1985 Neomonocwatina mouliana Sissingh, El-Waer, 40, pl. 4, figs 36. 1988 Paijenborchellina laskarevi Krstic & Pietrzeniuk, Bonaduce et al, pl. 1, fig. 5. 1989 Neomonoceratina ruggierii Szczechura, 293-294, pl. 8, figs. 1, ?8,9,12-15. Material. 34 carapaces and 4 valves from all wells and horizons; No A12602-05. Remarks. The reticulation is not as prominent as that illustrated by other workers, while the pore conuli are more prominent. The specimens figured by Van Hinte (1980) and Bonaduce, et al. (1988) are very similar to the specimens studied here; it is not clear whether the differences noted warrant specific or subspecific separation. The figured specimen differs from typical N. laskarevi in having a more ornamentated posterodorsal area, and a more prominent median ridge.
Genus Actinocythereis Puri, 1953 Actinocythereis Iibyaensis El-Waer, 1992 (P1.4, fig. 5) Material. 4 carapaces from Well Cla-97 at depth of 770 feet; No A12551-553. Remarks. This was described from the Upper Miocene A1 Khums Formation of North west Libya (Al-Waer, 1992). El-Waer, 1988. (P1.4, fig.7) Material. One left valve from Well G1-97 at depth of 1040 feet; No A12550. Remarks. El-Waer based his new species on 3 left valves from the Late Miocene A1 khums Formation. These are all more elongate than the specimen described here, so there is the possibility of sexual dimorphisim, those figured by El-Waer being male while that described here is female. A feature not mentioned by El-Waer is the presence of reticulation at the posterior as well as anterior. with spines. Carapace ornamented by three longitudinal rows of spines or nodes; dorsal row consists of six spines, some being bifid; median row starts from antero-central area and consists of six spines formed into two groups of three spines separated by a small gap; seven spines form the median row which ends in a central posterior position; ventral row is the shortest, consists of eight spines starting at the middle of the ventral margin runnings backwards ending in the postero-ventral area. The remainder of carapace reticulate with subrounded pits. Internal features not known. Sexual dimorphisim is distinct, males being more elongate. Remarks. This differs from Actinocytkereis spinosa El-Waer, 1988 in having a well defined median row of spines, while A. spinosa lacks the well defined reticulation of A. sirtensis; A. libyaensis differs in the arrangement of the median large spines as well as having a smooth carapace.

Dimensions of figured specimens (in Fm
Length Height L / H Genus Carinovalva Sissingh, 1973 Carinovalva carinata (Moyes), 1965 (P1.1, fig.19) Material. 30 carapaces and two valves distributed throughout all three wells; No A12597-601. Remarks. T h s species was first described from the Upper Miocene of the Aquitain Basin and is also recorded from the Rhone Basin (Carbonnel, 1969), from the Upper Miocene Tortonian of Portugal (Nascimento, 1983) and from the Upper Miocene of A1 Khums Formation of North West Libya (El-Waer, 1988).
Genus Chrysocythere Ruggieri, 1962 Remarks. Species of Ckrysocytkere are separated on the basis of lateral outline, the exact pattern of the median longitudinal ridge, and details of the intercostal Ornamentation. Using these criteria three distinct species can be recognized in the material studied. The first of these is regarded as being conspecific with Ckrysocytkere catapkracta catapkracta Ruggieri, 1962 in which the median ridge ends before reaching the posterior, and the intercostal ornamentation is dominated by vertical connecting ribs giving rise to vertically oriented elongate reticulation. The second species is placed in C. paradisus Doruk,1973; the ornamentation is identical, although the posterior dorsal angle is less rounded than in Doruk's illustration. C. paradisus differs from C. catapkracta in having smaller, more even reticulation between the longitudinal ridges. C. catapkracta muricata El-Waer 1992 differs from C. paradisus in being slightly elongated and in details of ornamentation. The third species is identified as C. alkkumia El-Waer 1992 which is similar to C. catapkracta, but has a prominent downturned median ridge at the posterior giving a very characteristic outline to the median ridge. Ckysocytkere cataphracta of Bassiouni (1979) differs from all these Libyan specimens in details of longitudinal ridges and intercostal ornamentation. Variation in the intercostal ornament is seen in illustrations of C. catapkracta given by various authors. The longitudinal ridges are connected by a series of vertical ribs giving the impression of very coarse vertically orientated elongate reticulae; in Ruggieri's original illustration these elongate reticulae can be seen to be subdivided by weak horizontal reticulation; this character appears to vary in strength, i.e. in Aruta (1982), the intercostal ornamentation seems to consist of small even reticulation, while in Carbonnel (1986), the reticulation is almost non existent as in the Libyan specimens. The dorsal margin of the left valve is parallel to the ventral margin and does not show the slight posterior tapering seen in the illustration of Ruggieri (1962) and of Aruta (1982) but is similar to those of  and Carbonnel(l986). Well Cla-97, 770,1160, 1340, 1400, 1730Well G1-97, 640, 1130Well G1-97, 640, , 1350Well F1-97, 990, 1020Well F1-97, 990, . 1170C. paradisus, 8 carapaces and 1 valve, Well Cla-97, 770;Well F1-97, 600, 660, 690, 900, 930, 1140Well F1-97, 600, 660, 690, 900, 930, , 1530Cdkkumia, i valve, Well F1-97, 930. Genus Cistacythereis Uliczny, 1969 Cistacythereis qabilatashurfuhensis El-Waer, 1992. (P1.4, fig.12) Material. Six carapaces from Wells Cla-97 at 770 and 1160 ft and F1-97 at 1260-1290 ft; No A12594-596. Diagnosis. A species of Cistacythereis with three strong longitudinal ridges and a fourth ridge parallel to the anterior margin; prominent deep fossae and strong muri. Remarks. This was described from the Upper Miocene A1 khums Formation, N.W. Libya.
Neocaudites nudicosta (Yassini 1979) (P1.2, fig. 18 Remarks. This was first described from the Upper Miocene of the Vienna Basin (Reuss, 1850). The specimens studied here differ from Hermanites haidingeri described from the Pliocene of Algeria (Yassini, 1979-80)  Description. Carapace elongate to subrectangular in lateral outline; the maximum height at anterior cardinal angle; dorsal margin appears to be humped at posterior due to the overhanging of the dorsal ridge; ventral margin straight to slightly concave in the middle; anterior margin broadly rounded; posterior margin concave in the upper part, while the ventral part possesses five short spines; three longitudinal ridges are present; the dorsal ridge is curved, ending in a slight node which connects the dorsal and median ridges; a weak median ridge runs from the subcentral tubercle towards the posterior and is nearly parallel to the dorsal ridge; the ventral ridge is strongly developed and almostly straight, starting from anteroventral area and running backwards nearly parallel to the ventral margin, ending in a small node in the posteroventral area.  Khalaf, 1982 from the middle Miocene of Iraq differs in the outline of the ventral and anterior margins, and in having much coarser surface reticulation. H. zaltanensis is very similar in lateral outline to H. tschopi (Van Den Bold, 1946) described from the Neogene of Senegal and Guinea (Carbonnel, 1985), but the latter differs in being shorter than our specimens, and the ventral ridge connects with the anterior ridge. There is doubt about the generic assignment; we have followed El Waer 1992. present in the central anterior area; remainder of carapace is smooth. Some specimens bear spines along the anterior and posterior margins. Sexual dimorphism is pronounced, males being more elongate than females. Remarks. This species was first described from the Tortonian of Scrivia, Italy (Capeder 1902) and is also recorded from the Upper Miocene of Malta (Keen 1987). It is very similar to Keijella hodgii Bradley, but differs in having larger areas of ornamentaion, and also in lateral outline .
Family Xestoleberididae Sars, 1928 Genus Xestoleberis Sars, 1866 Xestokberis cf. reyrnenti Ruggieri, 1967 (P1.4, fig.36 Family uncertain Genus Ruggieria Keij, 1957. Ruggieria tetraptera tetraptera Sequenza, 1869 (P1.4, fig.14) Material. 41 carapaces and two valves from all wells and horizons; No A12636-640. Remarks. The figured specimen is close to Ruggieria tetraptera tetraptera figured by Keen (1987)   Ruggieria aff dorukae Bassiouni, 1979 (P1.4, fig.10) Material. Two carapaces and one valve from Well G1-97 at depth 1260 ft; No A12641-643 Remarks. Ruggieria dorukae was recorded from Lower Miocene of Turkey (Bassiouni,l979) and subsequently recorded from the Burdigalian of south west Anatolia, Turkey ( Gok~enJ986). The Libyan specimens differ from these in the presence of a smooth area in the anterior region; this feature is original, but preservation in two of the specimens makes it difficult to describe. It is not clear whether this is of specific importance or not, and lack of material makes it impossible to discern whether or not variation exists within the Libyan material. Mostafawi( 1987) figured specimens of Ruggieria dorukae from the Middle Miocene of Kos, Greece, which also have a smooth area at the anterior, although this area is smaller than in the Libyan specimens.

OSTRACOD FAUNAS FROM M E MARADA FORMATION
The ostracod fauna described here differs from previously described Miocene faunas from Libya (Bellini 1969;Van Hinte et a1 1980;Innocenti and Pertusati 1984;El-Waer 1988, 1992 due to differences in age and facies. It also differs from the fauna described by Szczechura & Abd-Elshafy (1989) from the Miocene of Egypt and the Marada Formation of the north central Sirt Basin. It is difficult to account for this latter difference; the presence of Pokornyella deformis minor and Aurila cf soummamensis in their samples suggests an Aquitanian age, i. e Lower Miocene. If this is correct, this could be a factor in accounting for the differences, i.e their fauna is of Aquitanian age while the majority of the species recorded here come from Burdigalian or later sediments. Slight differences in facies and geographical location may also be involved. Fifty five species have been identified in this study; twenty two of which have been described from various localities in the Mediterranean area and north Africa; six species are new; the remainder are left in open nomenclature, although some of these are very similar to species already described. Sixteen species are important for stratigraphical age Aquitainian determination; four of these are restricted to the Lower Miocene, nine to the Upper Miocene, while three species have longer ranges but still provide stratigraphical information. In general the species recorded in Fig.3 are part of a widespread Mediterranean fauna, and most of the remaining species are closely related to widespread species. The fauna is markedly different from that described from Iraq (Khalaf,1982) where there are no species found in common to the two countries. The Libyan fauna also differs from those of central and northern Europe.
The stratigraphical range of the ostracods is based on published records from localities in Algeria, Austria, Belgium, Cyprus, Egypt, France, Greece, Italy, Libya, Malta, Tunisia, and Turkey. The stratigraphical and geographical distribution of each species has been discussed in the systematic section. Lower Miocene species. The typical species is Aurila sournmumensis, described from the Burdigalian of Algeria, and from the lower Miocene of Turkey (Bassiouni, 1979). Gokcen (1984) used this species to define the Lower Miocene (Burdigalian) Biozone in the Neogene sequences of Turkey. Pokornyella dejormis minor (Moyes 1965), described from the lower Miocene of Aquitain, France, and the lower Miocene of Turkey (Bassiouni, 1979 andGokcen 1984) is also a useful marker species, restricted to the Aquitanian. Middle Miocene. No species have been found in this study which are restricted to the Middle Miocene; three species are present which are recorded from the Middle Miocene, but range into later periods: Cnestocythere truncata, (Aquitanian-Tortonian), Chrysocythere paradisus (Langhain-Tortonian), and Acanthocythereis hystrix (Langhain-Pliocene). Thus, although they are not restricted to the Middle Miocene, their first appearance indicates Middle Miocene or later periods, and the interval between their first appearance and first appearance of typical Upper Miocene ostracods can be regarded as Middle Miocene. Ostracod biozones are proposed for the Marada formation in the eastern Sirt Basin based on the first appearance downhole of one or more index species. The species chosen are known to have a wide geographical distribution, their stratigraphic ranges are short and well documented, they are easily identified, and they are reasonably abundant.

Interval zone
Several biozonations based on ostracods have been published for different provinces of the Mediterranean Neogene: Carbonnel (1969) on the Aquitanian-Tortonian of the Rhone basin in France,  on the late Cenozoic of the south Aegean Islands, and Jircek (1974), on the Neogene sediments of the Czechoslovakia and Paratethys. Gokcen (1984) recognised a Burdigalian-early Langhian zone based on Neomonoceratina helvetica (Oertli) and Aurila soummamensis in the Neogene sequences of Turkey (Fig.4). The following four biozones have been recognised in the Marada Formation of the sequences studied, in ascending order (Fig. 3.). A-Pokornyella deformis minor Biozone. The top of this zone is recognised by the first occurrence downhole of Pokornyella deformis minor; its base has not been determined. This zone is probably equivalent to the Aquitanian. B-Aurila soummamensis Biozone. The top of this zone is recognised by the first occurrence downhole of Aurila sournmumensis; the base is defined by the first appearance downhole of Pokornyella deformis minor. This is equivalent to the Burdigalian. C-An interval Biozone. This zone lies between the top of