North Africa GeoNet - Cyrenaica abstracts

Presented by the Libyan Biostratigraphy Group (LBG)
and the North Africa Research Group (NARG)

The Dynamic Stratigraphy of Cyrenaica:
An Implication of the Mediterranean Tectonics

Ahmed S. El Hawat
Consultant Geologist, PO Box 543 , Benghazi , Libya . Email: ashawat@lttnet.net

The North African coastal promontory of Cyrenaica , NE Libya, consists of two distinct tectonic provinces separated by a hinge line of the Cyrenaican fault system. These are the northern, and presently active inverted basin of Al Jabal al Akhdar; and the more stable Cyrenaica platform to the south. Cyrenaica represents a topographic, geological as well as a geophysical anomaly in the Mediterranean basin as consequence of the direct impact of compressive forces induced by the convergence between the European - Aegean and African plates.

The northern limit of Al Jabal al Akhdar inversion anticlinorium is down faulted to the coastal plain, which extends northward to the offshore to form a narrow, steep, faulted and folded continental margin. It is separated from the Mediterranean Accretion Ridge by an east west trending, narrow furrow at 2500 to 3000 meters of water depth. It represents a scare of a major fault system running in the offshore parallel to the Cyrenaican coast and is referred to as north Cyrenaica fault system. Significantly, the Cyrenaican continental slope is being differentially overthrusted by the Mediterranean Ridge in what is regarded as active incipient continental collision processes.

These ongoing tectonic activities were impacted on the stratigraphic record of northern Cyrenaica and were manifested in the recurring upward shallowing sequences and associated unconformities. Constrained temporal palaeogeographic maps and cross sections demonstrate dynamic stratigraphic changes of palaeotopography attributed to changing structural configurations through time. These were often associated with reworking and syndepositional mass movement of sediments, as well as development of post depositional structural deformation, which are observed in the Cyrenaican stratigraphic record since the Upper Cretaceous. Furthermore, younger tectonic signatures are recorded as up faulted Pleistocene coastal terraces, and in the destruction of Cyrenaican towns from antiquity to present. Finally, an integrated approach to the study of geology and biostratigraphy in Cyrenaica taking into account analysis of associated tectonic events and signatures is urgently required in order to reach a rational interpretation of stratigraphy.

The stratigraphic positions of Wadi Dukhan and Al Uwayliah Formations, north-east Libya – A review

Nationaal Natuurhistorisch Museum, Naturalis, P.O. Box 9517, 2300 RA Leiden - The Netherlands, E-mail address: aftmalla@yahoo.co.uk

The stratigraphic positions of Wadi Dukhan Formation and Al Uwayliah Formation have been reviewed. Diagnostic Maastrichtian larger foraminiferal species are illustrated, for the first time, from the Wadi Dukhan Formation in well B7 – 41 (Cyrenaica) and in well U2 – 6 (northeastern Sirt Basin ). These species are Omphalocyclus macroporus (Lamarck) Siderolites cf. calcitrapoides Lamarck, and Orbitoides sp.

Following the rules of nomenclature the type section of Al Uwayliah Formation should be considered a composite-stratotype. The section east of al Uwayliah village is the holostratotype (upper part of the formation) and the Jrdas al Jarrari section is the parastratotype (lower part of the formation). The combined thickness of the two component-stratotypes seems to be too thin to represent the whole Paleocene Series. Paleontologic evidence also suggests that parts of the Paleocene standard foraminiferal zones are not represented in either of the two component- stratotypes. Most probably a middle part of Al Uwayliah Formation, below the holostratotype and above the parastratotype, (late Danian to Selandian), has not yet been recognized. More paleontologic work is needed to clarify this point.

Biostratigraphic review of the Al Athrun and Apollonia formations, Cyrenaica, NE Libya, based on calcareous nannofossils

Arabian Gulf Oil Company, Geol. Lab., P.O. Box 263 , Benghazi , Libya E-mail: a_mehhagnan@yahoo.com

The Al Athrun and Apollonia Formations at two locations in Wadi Al Athrun area in Cyrenaica , NE Libya, have been reviewed biostratigraphically, based on their calcareous nannofossil content. i) Wadi al Athrun section, representing the upper part of Al Athrun Formation, is assigned to the Quadrum trifidium CC22 Zone of Campanian age,while, has been the lower part of the Apollonia Formation is assigned to Discoaster multiradiatus zone NP9 of Late Paleocene age. An undifferentiated Apollonia horizon belongs to Eocene Tribrachiatus contortus to Discoaster binodosus zones NP10-NP12. ii) The a slump section representing a part of the Al Athrun Formation also contains Quadrum trifidium CC22 zone, previously assigned to late Coniacian to late Maastrichtian age based on the study of their planktonic foraminiferal content (Barr and Hammuda, 1971). However, Barr and Berggren (1980) and Haq and Aubry (1980) interpreted the typical Palaeocene planktonic foraminifera and calcareous nannofossil assemblages present in both sections of the Apollonia Formation as being reworked. The present study proves that this conclusion is unreliable and the interpretations were based on inadequate results.

Biostratigraphic analysis of the upper part of Apollonia Formation in Northeastern Libya

1 Arabian Gulf Oil Company, Exploration Division, Geological Laboratory, P. O. Box 263 , Benghazi- , Libya . 2 University of Tanta , Department of Geology, Tanta , Egypt .

Thirty calcareous nannoplankton species, retrieved from the upper part of Apollonia Formation at the Wadi Bacur road-cut (Al Jabal al Akhdar), have been documented. The diagnostic nannofossil species: Cyclicargolithus floridanus, Reticulofenestra bisecta, Cribrocentrum reticulatum, Reticulofenestra umbilica, Dictycoccites scrippsae, Reticulofenestra pelycomorpha and Discoaster saipanensis confirms Late Eocene Sphenolithus pseudoradians (NP20) zone. The presence of very rare Tribrachiatus orthostylus and T. bramlettei points to Early Eocene, at this stratigraphic level is considered to be a result of reworking of older sedimentary deposits.

Palynological Analysis of the Upper Cretaceous Al Hilal Formation, Ras Al Hilal area, Al Jabal Al Akhdar, NE Libya

Arabian Gulf Oil Company, Geological Lab, P.O. Box: 263, Benghazi , Libya , GSLAJ.
E-mail: amehdawi@yahoo.com

Twelve surface samples from the Al Hilal Formation, exposed in Ras Al Hilal area, Al Jabal Al Akhdar, NE Libya have been palynologically examined. Productive samples yielded a low recovery of organic matter dominated by herbaceous debris including low abundance and diversity of palynomorphs, dominated by pale dinoflagellate cysts, with rare terrestrial miospores. About thirty species of dinoflagellate cysts and miospores were recognised . The most characteristic species are peridinioid forms including Chatangiella biapertura , C. ditissima , C. serratula , C. cf. tripartita , Eucladinium cf. gambangense , E. madurense , Isabelidinium acuminatum , I . belfastense , I. Cooksoniae , and Other chorate, marginate, ceratioid, and gymnodinoid species such as Cannosphaeropsis cf. utinensis, Nematosphaeropsis sp., Tanyosphaeridium cf. regulare , Cyclonephelium vannophorum , Senoniasphaera sp. A, Xenascus sarjeantii, Dinogymnium acuminatum, D . cf. cooksoniae , and D . undulosum . Two important Upper Cretaceous terrestrial miospores Araedinaesporites sp., and Foveotriletes margaritae are also recognized.
Based on the recorded dinoflagellate cyst assemblage, the examined stratigraphic section is assigned to the Santonian-early Campanian? age.
The type of palynodebris and associated dinoflagellate cyst groups, dominated by peridinioid forms present in the upper part of the formation, would indicate an upward shallowing of depositional environment, from deep marine, bathyal to deep neritic.

Palynological Contribution to the Stratigraphy of the Al Faidiyah Formation, Al Jabal Al Akhdar, NE Libya

1 Arabian Gulf Oil Company, Geology Department, Geological Lab, P.O.Box: 263, Benghazi , Libya , GSLAJ. E-mail: amehdawi@yahoo.com

2 Department of Geology, Faculty of Science, University of El Mansoura , El Mansoura , 35516 , Egypt . E-mail: syelbeialy@mans.edu.eg

Well preserved palynomorphs (dinoflagellate cysts, tasmanites, microforaminiferal test lingings and rare sporomorphs) of moderate abundance and diversity have been recognized from eight surface samples . These were nearly eight metres thick collected from the Al Faidiyah Formation exposed at the Cyrene-Apollonia road cut, Al Jabal Al Akhdar, NE Libya.
The dinoflagellate cysts are the dominant palynomorph group and is characterized by the presence of Deflandrea phosphoritica , Pentadinium laticinctum , Adnatosphaeridium multispinosum , Wetzeliella articulata , W. symmetrica , Homotryblium floripes subsp. breviradiatum, Homotryblium plectilum , Selenopemphix sp. 2, Dapsilidinium pastielsii , D. pseudocolligerum , Systematophora placacantha , Palaeocystodinium golzowense , Operculodinium centrocarpum , Polysphaeridium cf. zoharyi, Lingulodinium machaerophorum and Hystrichokolpoma cinctum. Terrestrial sporomorphs are represented by the presence of some angiosperm and gymnosperm pollen such as Monocolpopollenites sp., Retitricolpites sp., Salixipollenites sp., Ambrosia sp., Ilexpollenites sp. and Inaperturopollenites spp.
The recorded dinoflagellate cyst assemblage is in favor of late Oligocene to early Miocene age, and not early Miocene. This age assessment is in accordance with similar findings obtained from calcareous nannofossils and forams.
The type of palynodebris and the associated palynomorphs reveal that the Al Faidiyah sediments have been deposited i n shallow inner-neritic environment, under freshwater runoff influence.

Biostratigraphic and sedimentological analyses of the Al Abraq Formation in Jabal Al Akhdar, NE Libya

Ali A. El-Mehaghag 2 , Ahmed M. Muftah 1 , Salem Bushiha 1 and Abuessoud A. Addaloush 2

1 University of Garyounis, Faculty of Science, Department of Earth Sciences, P. O. Box 9480, Benghazi-Libya.
2 Arabian Gulf Oil Company, Exploration Division, Geological Laboratory, P. O. Box 263, Benghazi-Libya.

Three road-cut sections of Al Abraq Formation at (Daryanah-Abyar, Shahhat-Susa and Dabousseyiah) and the Type Locality, has been examined on the basis of its calcareous nannoplankton and foraminiferal contents. The examined sections yield few calcareous nannofossils, with the exposure at Dabousseyiah being barren.
The presence of the zonal markers Dictyococcites bisectus , Sphenolithus ciproensis and Cyclicargolithus abisectus places the sampled Al Abraq stratigraphic horizon within the Sphenolithus distentus (NP24) to Sphenolithus ciperoensis (NP25) of the Late Oligocene age range zone. However, since the overlying Al Faidiyah Formation has unequivocally been determined as belonging to the NP24 zone, it follows that the Al Abraq Formation's age would be restricted to an earlier part of the NP24 zone.
The presence of Nummulites fichteli at this level, points to Early Oligocene. However, the absence of marker planktic foraminifers and the low diversity of some benthic foraminiferids, such as Nummulites fichteli, Operculina complanata, Amphestigina spp., and miliolids make the foraminiferal zonation difficult to apply. By contrast, age-diagnostic nannofossils indicate a Late Oligocene. Based on the integration of interpretations using these two biostratigraphical tools, the presence of Nummulites fichteli is considered to be a result of reworking of older beds.
Six sedimentological microfacies have been recognized at the type locality, starting from base: nummulitho-echinoidal packstone, foraminiferal wackestone, miliolid-echinoidal packstone (becoming pelloidal at the top), peloidal-miliolid garinstone (grading to foraminiferal-glauconitic grainstone at top), and peloidal-operculinid wackestone. These mcirofacies reflect three cycles of upward shallowing conditions.

1 Arabian Gulf Oil Company, Exploration Division, P.O. Box 263 , Benghazi Libya . < a_mehagnan@yahoo.com >
2 Garyounis University , Faculty of Science, Department of Earth Sciences, P. O. Box 9480 , Benghazi Libya . < a_muftah@yahoo.com >

Tukrah Formation was assigned to the Late Cretaceous age by some authors, and to the Eocene by others, based mainly on its macrofossils, foraminiferal and calcareous nannofossil content. The present study is based on the nannofossil and foraminiferal content of this formation in two localities. Calcareous nannofossils in Tukrah samples from the Tukrah coastal plain indicate a range of Late Eocene to Early Oligocene age. The presence of moderate to poorly preserved and rare small benthic foraminifera such as Bulimina sp. and bolivinids confirms the nannoplankton dating. Tukrah argillaceous bioclastic packstones from an exposure at the ancient ruins of Greek City , yielded moderate to good preserved diagnostic calcareous nannoplanktons, including Cyclicargolithus floridanus, Dictyococcites bisectus and Cribrocentum coenurum. Accordingly, the age of this formation ranges from Late Eocene ( Sphenolithus pseudoradians NP20) to Oligocene ( Sphenolithus distentus NP24),based on Martini's (1971).zones. Tukrah samples, retrieved from areas between these two localities, yielded a Late Eocene-Oligocene age range, based on micropaleontological, analysis .

1 University of Garyounis, Faculty of Science, Department of Earth Sciences, P. O. Box 9480, Benghazi-,Libya. <a_muftah@yahoo.com>
2 Arabian Gulf Oil Company, Exploration Division, Geological Laboratory, P. O. Box 263 , Benghazi- , Libya . <a_mehagnan@yahoo.com>

Ten planktic and forty benthic foraminifera species, together with twenty-seven calcareous nannoplankton species, retrieved from Al Faidiyah Formation, at a Shahhat-Susa road cut (Al Jabal al Akhdar) and a shallow water borehole in the proximity of Al Qawarishah area, have been documented. The diagnostic planktic species Globigerina ciperoensis ciperoensis, G. ciperoensis angulisuturalis and Globorotalia opima nana assign the sampled stratigraphic horizon at the Shahhat-Susa road cut to the G. ciperoensis ciperoensis zone. By comparison, the diagnostic nannofossil species: Sphenolithus ciperoensis, S. predistantus, Cyclicargolithus abisectus, Reticulofenestra bisecta and Zygrhablithus bijugatus assign the same horizon to the S. distantus zone (NP24). The integration of these results confirms early Late Oligocene age for that part of Al Faidiyah Formation exposed at the Shahhat-Susa locality.
The First occurrence of Sphenolithus abies and the presence of the zonal marker Orbulina universa assign the sampled part of Al Faidiyah Formation at Al Qawarishah subsurface section to the Middle Miocene's Discoaster hamatus zone (NN9), which is equivalent to the upper part of the O. universa zone. This age supports Eliagoubi's results.

Palynological age dating and facies analysis of the Nubian Group,
SE Sirte Basin, Libya

(2) North Africa Research Group, www.narg.org.uk, University of Bremen, FB5, P.O. Box: 330 440, 28334 Bremen – Germany, E-mail address: Sebastian.Luning@gmx.net

The Nubian Group in the Hameimat Trough is subdivided into the three units Lower Nubian Sandstone, Varicoloured Shale and Upper Nubian Sandstone. Core slabs from 271 feet of cored intervals from the Lower Nubian Sandstone in well R9-82 and 424 feet of cored intervals from the Upper Nubian Sandstone in well A1-NC125 have been analysed. Nine lithofacies have been identified and classified according to their lithological characteristics and sedimentary and biogenic structures. These include (1) conglomeratic sandstone with mud rip-up clasts, (2) trough cross bedded sandstone, (3) planar cross-bedded sandstone, (4) poorly stratified sandstone with rare flaser bedding, (5) ripple cross laminated sandstone, (6) silty mudstone, (7) mudstone, (8) deformed fine sandstone and mudstones, and (9) interbedded fine sandstone and mudstone with marine trace fossils. Sandstones in the Lower Nubian are interbedded with muds, but display braid channel characteristics. They were deposited in a subsiding basin which created ample accommodation space for fines to accumulate. The overlying sandstones were most likely laid down in lagoonal/marginal flood plain environments. Trace fossils indicate harsh, restricted marine environments for the sand bodies and they are interpreted as shoreline or barrier shoals to lagoons and marshes. Escape structures indicate storm events. The topmost sand show a return to fluvial influence but interbedded shales and the succeeding Varicoloured Shale contain lagoonal palynofacies. The Upper Nubian Sandstone comprises of two sand bodies and an intervening thick shale. The sandstones are fluvial braided deposits; the shale is brackish/lagoonal. The overall environment for the group is interpreted as marginal marine to flood plain. Palynological age dating indicate an Early Cretaceous age, the Varicoloured Shale being most probably Aptian. The dinoflagellate Lagenorhytis sp and the presence of Odontoihina sp indicate an age range from Barremian to Campanian. The large number of Ephederites sp strongly point to Aptian.

An Early–Middle Miocene dinoflagellate cyst biozonation for the Gulf of Suez, Egypt

1 Institut für Erdewissenschaften (Geologie und Paläontologie), Karl-Franzens Universität GRAZ, Heinrichstrasse 26, A- 8010 Graz (Austria), ali. soliman@uni-graz.at ; werner.piller@uni-graz.at .
2 Geology Deaprtment, Faculty of Science, Tanta University, Tanta 31527, Egypt.
3 Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN (England), mh300@hermes.cam.ac.uk .
4 Department of Geology, Faculty of Science, El Mansoura University, El Mansoura 35516 (Egypt), syelbeialy@mans.edu.eg

A new dinoflagellate cyst zonation for the Early-Middle Miocene of the Gulf of Suez is proposed. The zonation is constructed using biostratigraphic data obtained from five deep wells in the southern Gulf of Suez, Egypt, and is based on the highest occurrences of selected dinoflagellate cyst taxa. The zonation is tied to a chronostratigraphic framework by using correlation to calcareous nannoplankton datums. The presence of diverse dinoflagellate cyst taxa allows the establishment of four interval zones covering the late Aquitanian? to Serravallian. The oldest is the Cordosphaeridium cantharellus Zone of late Aquitanian?–early Burdigalian age (NN2). This is followed by the Apteodinium spiridoides Zone of Burdigalian age (NN2–NN4) and the Selenopemphix denticulatum n. sp. Zone of Langhian age (NN4). The youngest interval zone is the Cleistosphaeridium spp. Zone of late Langhian–Serravallian age (NN5). Comparisons with other Miocene zonations from the Mediterranean, North Atlantic, eastern USA and central Paratethys indicate that the highest occurrences of Cordosphaeridium cantharellus, Exochosphaeridium insigne, Distatodinium paradoxum and Apteodinium spiridoides , and the lowest occurrences of Hystrichosphaeropsis obscura , Sumatradinium soucouyantiae , Sumatradinium druggii , Labyrinthodinium truncatum are important horizons. This is the first study to demonstrate the applicability of Early and Middle Miocene dinoflagellate cyst markers for detailed stratigraphic correlation in the Gulf of Suez, Egypt.

The study area in the northern Western Desert lies at the eastern margin of the Abu Gharadig Basin and at the northern marhin of the El Gindi Basin. Three exploration wells were selected from the area to the north of Lake Qarun (wells 1-BRE 6-1, 1-BRE 3-1, and WD 19-2). The Cenomanian - Turonian successions were studied in detail (lithologic description, faunal content, biostratigraphic age dating), and the results were correlated with surface and subsurface sections in the Western Desert, Sinai, Palestine, Jordan and Kuwait. The Cenomanian is characterized by two rock units: the Bahariya Formation (Late Albian to Early Cenomanian) and the Abu Roash “ G” Member of Late Cenomanian age. The Early and Middle Turonian is represented by the Abu Roash “ D “, “ E “, “ F “ members. Palaeontologically the Rotalipora brotzeni Zone (international zone of Late Albian - Early Cenomanian age) is recorded within the Cenomanian sequence.
Charentia cuvillieri / Mayncina orbignyi Zone (Local zone): (Upper most part of Early Cenomanian). This biozone extends from the first occurrence of Rotalipora reicheli to the last occurrence of Favusella washitensis with a common occurrence of the Charentia cuvillieri and Mayncina orbignyi assemblage. The Biozone is introduced and identified based on the richness of the benthonic foraminifera and the occurrence of short range planktonics which can be used as a marker for the top Bahariya Formation in the different locations in the Western Desert, Egypt and nearby areas.
In the Upper Cenomanian, two Biozone are recognized, which are Rotalipora cushmani (International Zone of Middle - Late Cenomanian age). In the present study it is proved that only the upper part of this zone is present, while its lower part (Middle Cenomanian) is absent. Whiteinella archaeocretacea (International Zone of Late Cenomanian to Early Turonian age) is recorded for the first time in the Western Desert, Egypt.
The International Zone Helvetoglobotruncana helvetica (Middle Turonian) is subdivided into three local subzone, these are from older to younger:
1- Heterohelix acme subzone that was recognized by different authors is modified and correlated with the previous studies.
2- Helvetoglobotruncana praehelvetica subzone: (Middle part of Middle Turonian). Extends from the last occurrence of the abundant Heterohelix spp. to the last occurrence of Helvetoglobotruncana praehelvetica.
3- Discorbis spp. - Ostracoda subzone: (Upper most part of Middle Turonian). It extends from the last occurrence of Helvetoglobotruncana praehelvetica to the last occurrence of Helvetoglobotruncana helvetica with the abundant occurrence of Discorbis spp. and common occurrence of diagnostic Ostracoda.

Subsurface Upper Cretaceous successions in the northern Western Desert, Egypt, in relation to global sea level changes and sedimentation

Upper Cretaceous units from the subsurface were studied in three selected wells to the north of Lake Qarun in the eastern part of the North Western Desert, Egypt (1- BRE 3-1, 1- BRE 6-1 and WD 19-2 Wells). The lithology, log characteristics and faunal content was studied with special attention to sedimentary breaks. Nine breaks in sedimentation are recognized within the Upper Cretaceous sequences of the study area.
Their possible duration and relationship with eustatic sea level changes are tentatively calculated based on the EXXON chart ( Haq et al. 1988 ) and on the high resolution biostratigraphic analyses and the integration between palaeontological results (Planktonic, Benthonic and Ostracoda), and lithological characters.
• The first Break is suggested between the Lower and the Upper Members of the Bahariya Formation, (within the Early Cenomanian), and is proved by the absence of the upper part of the Rotalipora brotzeni Zone and is confirmed by a change in lithofacies. This unconformity is widely recognized in the Western, Eastern Desert of Egypt and Sinai
• The second Break is suggested between the Upper unit of the Bahariya Formation and the Abu Roash “ G ” Member, (Early / Late Cenomanian), and is confirmed by the complete absence of the Middle Cenomanian sequence (lower part of Rotalipora cushmani Zone)
• A local break in sedimentation is suggested with the end of deposition of the A/R “F” and A/R “E” Member, as the upper part of Whiteinella archaeocretacea Zone is absent, indicating a period of erosion due to uplift in the area.
• With the end of the Middle Turonian, the area had suffered from lowering in sea level or uplifting of the succession which led to non-deposition of the Late Turonian sequence ( Sigalitruncana sigali Zone and the basal part of Dicarinella primitiva Zone) resulting in the absence of the upper part of the A/R “D” and the lower part of the AR ”C” Member.
• The fifth break in sedimentation is recognized with the end of the Coniacian, between Abu Roash “ B ” and “ A ” Members, and is proven by the partial absence of the upper part of the Dicarinella concavata Zone.
• The sixth unconformity is recognized between the Abu Roash “ A “ Member and the Khoman “ B “ Member, (Santonian – Campanian) which depends on the complete absence of the Globotruncanita elevata Zone and the partial absence of the Dicarinella asymetrica Zone.
• The seventh unconformity encountered, is noticed between the Campanian, Khoman “B” and Maastrichtian Khoman “ A ” members. A non-deposition period is documented by the complete absence of the Late Campanian Radotruncana calcarata Zone and the Early Maastrichtian Globotruncanella havanensis Zone.
• The eighth break in sedimentation is described within the Maastrichtian sequence, Khoman “ A “ Member, which is documented by the partial absence of the upper part of the Globotruncana Egyptiaca Zone, and is confirmed by the red soil and conglomeratic deposits within the Maastrichtian sequence encountered in well WD-19-2.
• The ninth and youngest unconformity detected, is that recognized between the Maastrichtian and the Tertiary sequences and is confirmed by the complete absence of the Abathomphalus mayaroensis Zone which represents the latest Maastrichtian.
The time duration of these breaks in sedimentation is tentatively calculated according to EXXON chart (Haq et. Al.1988). A correlation between the three wells has been carried out and resulted in conclusion that:
• An increase in thickness, which means an increase in basin depth is noticed towards the northwest, this is confirmed by the high level of the Precambrian basement in the southern Well (1-BRE 6-1) while decreasing towards the northwest in WD 19-2 Well.
• The variation in thickness of the Cenomanian in the different studied wells indicate that the bottom topography was tectonically controlled.

By Prof. Joseph Salaj
Geological Institute of the Slovak Academy of Sciences
Dubravska cesta, 840 05 Bratislava

Proved specimens of the genus Whiteinella Pessagno, 1967 from the Zone of Whiteinella gigantea Lehmann, 1964 (= syn.: Whiteinella archaeocretacea Pessagno, 1967) without Helvetoglobotruncana helvetica (Bolli) confirm that the Helvetoglobotruncana helvetica Zone in the area of Marsa al Hilal (Barr 1972) is not closely overlying the Rotalipora cushmani Zone. Otherwise in Cyrenaica we should accept the existence of a stratigraphical hiatus and specimens of the genus Whiteinella Pessagno, 1967 would belong to the Helvetoglobotruncana helvetica Zone, in which the species Helvetoglobotruncana helvetica (Bolli) occurs sporadically or as a consequence of unfavourable ecological conditions is not present.
In the frame of the Helvetoglobotruncana helvetica Zone the species Sigalitruncana sigali (Reichel) is always found in its upper part and never present at primary occurrence in the Upper Turonian. As for its occurrence in the Upper Turonian, it always has two keels (Barr 1972) and therefore corresponds to a different, new species, Falsomarginotruncana barri Salaj and Gasparikova, 2005.
In the Upper Campanian – Lower Maastrichtian in the area of Jabal Akhdar as a consequence of lagoonal sedimentation (development of foraminifers of the family Rhapidioninidae Keizer, 1945; Salaj and Röhlich, 1999) in the course of pelagic sedimentation there was distinct shallowing in the Marsa al Hilal area in the equal time section.
For this reason oceanic species as Globotruncanita subspinosa (Pessagno), Radotruncana calcarata (Cushman) and Globotruncana gagnebini Tilev are missing and /or extraordinarily scarcely found.
Similarly these oceanic species are also missing in Upper Campanian – Maastrichtian sediments of the Al Gharbiyah Formation (Nairn and Salaj, 1992), in the northern part of Al Hammadah al Hamra. They are lacking as a consequence not only of shallow water neritic development, but also of the existence of minimally at least three proved stratigraphical hiatuses. In the lower part of the Middle Maastrichtian the species Globotruncana lugeoni Tilev and in the Upper Maastrichtian Abathomphalus mayaroensis Bolli and Kassabiana falsocalcarata (Kerdany and Abdel Salam) are missing.
As a consequence of the Upper Senonian stratigraphical hiatuses in the Hammadah al Hamra area is an incomplete biostratigraphical division, also on the basis of important groups of benthonic foraminifers. From orbitoid foraminifers the Lower Maastrichtian Orbitoides apiculata Zone is missing. Equally many forms of the genera Neoflabellina Bartenstein, 1949 and Bolivinoides Cushman,1927, significant for stratigraphy, are missing.

* Geology Department, Arabian Gulf Oil Company, P.O. Box 263, Benghazi , Libya.
** Geology Department, University of Southampton , Southampton Oceanography Centre, Southampton SO143ZH, England

Detailed sedimentological studies of the Paleogene section from both the subsurface (14 boreholes) and surface outcrops (5 localities) have shown that the western margin of the Cyrenaica Platform was rimmed by a shallow-water carbonate bank. Characteristic features of bank facies include an abundant shallow marine fauna (nummulites, algae, mollusks, miliolids, echinoderms) and dominant packstone to grainstone textures, interbedded with minor bioclastic wackestones. These data together with evidence from red algae and micro-borings suggest deposition in the lower aphotic zone above storm wave base. The fore-bank region is characterized by chalk, shale and lithoclastic packstone facies that accumulated by both pelagic processes and downslope re-sedimentation, whereas the back-bank region comprises a restricted fauna (miliolids and mollusks) and interbedded dolostone/evaporite facies indicative of a moderately to hypersaline lagoonal environment. A double cycle of high to low stand system tracts characterize the Paleocene succession in NE Libya and are approximately coincident with eustatic changes of sea level. Expansion of the nummulites bank facies association occurred during relative high-stand deposition, whereas a greater extent of lagoonal dolostone and evaporates is evident during low stands. Local tectonic activity was a secondary control on facies distribution, thicknesses and rates of accumulation. Despite a complex diagenetic history, porosity-permeability data show that the nummulitic limestone and parts of the dolostone section have good reservoir potential. Both structural and stratigraphic trap types can be identified on seismic sections and known hydrocarbon shows suggest mid Miocene generation and migration.

Microfacies and palaeoenvironment analysis of the algal Limestone Member of the Al Bayda FormationI, Al Jabal Al Akhdar, NE Libya.

Department of Earth Science, University of Garyounis , P.O. Box 9480 , Benghazi , Libya .

Two sections of the Algal Limestone Member of Al Bayda Formation have been examined along Daryanah–Al Abyar road-cut (17 samples) and Susa-Shahhat road-cut (31 samples) in Al Jabal al Akhdar region, northeast Libya . This study aims to review the depositional environment of this member based on lithofacies and micropaleontological content, with particular reference to coralline red algae. Extreme indurations have prevented desegregations and recovery of individual foraminiferal specimens, consequently this study is limited to thin sections of the rock samples. Some encrusting coralline red algal species have been documented and illustrated, belong to some genera such as Sporolithon, Lithoporella, Lithophyllum, Lithothamnion, Mesolphyllum , Neogoniolithon as well as Corallina . The associated benthic foraminifers are rare to spares with general aspects of marginal to shallow marine forms in which dominated by nummulitids, miliolids and gypsinids with few amphisteginids.
Five microfacies have been recognized based on Dunham's method, These are from bottom to top as follows: 1) nummulitic wackestone-packstone, 2) algal rudstone-boundstone, 3) algal wackestone-packstone, 4) bryozoan-algal boundstone and 5) foraminiferal-algal rudstone The Algal Limestone Member is unconformably underlain by the deeper marine Shahhat Marl Member of Al Bayda Formation. The stratigraphic distribution of rock units and fossil contents of Al Bayda Formation indicate an upward shallowing trend from a lower outer ramp to shallow inner ramp depositional setting.
An Early Oligocene age is suggested due to the presence of Oligocene-nummulitids such as Nummulites vascus, Nummulites fichtelli, and Operculina complanata; beside the absence of Eocene-nummulitids.
The documented algal assemblage fit strongly to the suggested age. The stratigraphic range of the genus Neogoniolithon has been extended back to be Early Oligocene- Recent, as indicated by the studied area.

The Biostratigraphy of the Early Cretaceous Sarir Group of the Maragh Low and Western Cyrenaican Platform , Libya

Palynological analysis of twenty-three Pre- Tertiary well sections from the Maragh Low and surrounding area, has allowed high resolution biostratigraphical correlations to be undertaken. Pre-Sirt Unconformity two superimposed rifting cycles have been identified. The oldest of Cambrian to Triassic age is represented by the Amal Group and the youngest of Early Cretaceous age belongs to the Sarir Group.
The Early Cretaceous phase of rifting was associated with Neo- Tethyan margin development and a northwest to southeast fault trend that probably rejuvenated older basement faults. Syn-rift and post- rift sequences of lacustrine and alluvial deposition with occasional marine influences can be identified. This rift sequence is of late Neocomian to early Aptian age and was associated with igneous intrusive granites and extrusive basalts. The rift sequence was terminated by movements relating to the Sirt Unconformity. At a formation level an informal lithostratigraphy still prevails for the Sarir Group. Identified and correlated in this area from oldest to youngest are the Neocomian Sandstone, the Early Barremian Shale, the Barremian Sandstone, the Late Barremian Shale and the Aptian Sandstone.
The Neocomian Sandstone is represented by a colourless to white, fine to medium grained, sub-angular to angular sandstone with a kaolinitic cement. Typically it grades into a dark brown to grey siltstone towards its base. Coaly and asphaltic horizons are common. Recovered and diagnostic miospores include Concavisporites juriensis , Gleicheniidites circinidites and Contignisporites cooksoniae.
The overlying Early Barremian Shale is identified only in the central parts of the Maragh Low. It is represented by a varicoloured silty shale interbedded with thin, fine grained, sub-rounded to sub-angular, silica cemented, clear to translucent sandstones and conformably overlies the Neocomian Sandstone. The early Barremian age of this shale is based on the highest occurrences of the miospore taxon Dicheiropollis etruscus . Also present in the assemblage is Afropollis operculatus , abundant Cupresaccites oxycedroides , Pilosisporites cf. verrus and an abundance of the freshwater algae Pediastrum bifidites . The sediment type, the organic richness of this unit and the recovered palynomorph assemblages all indicate that it was deposited in a lacustrine palaeo-environment.
The overlying Barremian Sandstone is represented by a sandstone which is colourless to translucent, fine to medium grained and sub-angular to sub-rounded. Interbedded are minor siltstones which are light to dark brown and friable with a siliceous cement. Glauconite is sometimes present. There are also shale stringers which are grey, green to red brown and firm to sub-fissile and sometimes silty. The age of the Barremian Sandstone is Early Cretaceous, Barremian, this is based on the highest occurrences of the miospore taxon Alisporites spp. Associated palynomorphs in the assemblages include the miospore taxa Inaperturopollenites crisopolensis , Callialasporites dampieri and Appendicisporites spp. and the marine dinoflagellates Phoberocysta neocomica and Aptea anaphrissa.
Deposition of the Barremian Sandstone was mainly in a terrestrial alluvial palaeoenvironment although recovery of marine palynomorphs from the top of the formation and the presence of glauconite indicates a marine Barremian cycle. This entered the Maragh Low from the north. This unit lies unconformably on Lower Palaeozoic aged sediments on the western Cyrenaican Platform. This transgressive, marine Barremian cycle was deposited due probably to a combination of a eustatic sea level rise and to local tectonic movement associated with post rift sag.
The conformably overlying Late Barremian Shale is represented by a grey, to brick red, brown, green soft shale which is occasionally silty, pyritic and micaceous. Interbedded are thin sandstones which are white to grey, sub-rounded and fine to medium grained. These have fair sorting. The Late Barremian Shale is present only in the central Maragh Low. The palynomorph assemblage recovered is typified by the presence of the miospore taxa Aequitriradites spp. and Cicatricosisporites spp. The presence of the freshwater algae Pediastrum bifidites and of brackish water ostracods indicates that the depositional palaeoenvironment of this unit varied between brackish-lagoonal to lacustrine.
The youngest identified Sarir Group unit present only in the central part of the Maragh Low is the Aptian Sandstone. Interbedded fine grained, white to brown, fairly sorted, kaolinitic sandstones with thin interbeds of gray to red silty shale typify this unit. Palynomorphs from the Aptian Sandstone are generally of low abundance and diversity. This is probably related to a rapid rate of deposition. The Aptian Sandstone was deposited as a last cycle of post rift sag before uplift and truncation by the Sirt Unconformity. Age diagnostic palynomorphs recovered from the Aptian Sandstone include the miospore taxa Concavissimisporites spp., Inaperturopollenites spp., Balmeisporites holodictyus and Dictyophyllidites spp. The recovery of terrestrial palynomorphs and the mainly arenaceous sediment are consistent with this interval being deposited in a braided stream and the sediment represents alluvium and overbank deposits.