Corals studies in Libya are very limited, although they play an important role in the oil exploration as they form excellent reservoirs of coral reef buildups at some oil fields of Sirt Basin (e.g. Intisar “Idris” and Sahabi Fields). Both fields are produced from Paleocene coral reefs. Meanwhile, in Cyrenaica, corals are of less importance as they are not reported in subsurface tertiary rocks, which probably in the environmental settings of these sediments out of the core of reef as occurred in the surface. Meanwhile, corals are reported from older (Jurassic) subsurface successions as in Concession NC-152, but the cementation diagenesis leads to blocking and destroying the porosity. This study presents the first surface documentation work of eight scleractinian coral species from the exposed sediments in northern Libya, where sixtaxa is reported from Al Jabal al Akhdar region, these include a) an association of huge colonies of Caulastrea sp. and Stylophora sp., from the Middle Eocene Darnah Formation at West Darnah road cut section. Theco-existence of the fast Caulastrea sp. with the slow Stylophora sp. is due to the competition strategy; b) Antiguastrea sp. which is reported from the Oligocene Algal Limestone of Al Bayda Formation at Daryanah-Abyar Roadcut section; c) Cyphastrea sp. and Aleveopora sp. from Oligo-Miocene Al Faidiyah Formation at Al Fatayah cement quarry and d) Tarbellastraea sp. From Middle Miocene Benghazi Formation at Benghazi Cement Quarry. In addition, two species Astraeaopora sp. and Actinacis parorai are reported from the Upper Miocene sediments of formation “M” in As Sahabi area.
This paper deals with corals built up in the Cyrenaica. Coral refers to coral carbonate accumulation which has original topographic relief that lives in association with other organisms including algae and foraminifers as major contributor Guilcher [
The documented subsurface coral occurrences in Libya are very limited and are mainly obtained from the oil exploration activities, where coralreef forms an excellent reservoir as evidenced from some previous reports of oil fields in Sirt Basin (e.g. Intisar “Idris”) [
However, the most comprehensive surface coral occurrences in the previous works that are presented by [
The studied corals are obtained from two regions:
1) The Al Jabal al Akhdar region which is located in northern Cyrenaica. It is a huge anticlinorium extending in SW-ENE ridge located between 32˚ to 33˚N and latitudes and 20˚ to 23˚E longitudes. The documented corals herein are from four well known localities, these are: a) West Darnah Roadcut section; b) Daryanah-Abyar Roadcut section; c) Al Fatayah cement quarry; iv) Benghazi (Hawari) cement Quarry in
2) The As Sahabi region, which is located in the northeastern corner of Sirt Basin, covering an area of about 375 km2. It is bounded by longitudes 20˚48'08" to 20˚54'45"E and latitudes 30˚10'58" to 30˚17'36"N, within a tectonic province called the Ajdabiyah Trough. The documented coral specimens came from the scattered clusters of patch coral reef P53 and P119 area at the western edge of the Sabkhat al Qunayy in
The Al Jabal al Akhdar area in Cyrenaica region, northeastern Libya has a long geologic history, ranging from the Paleozoic to Late Miocene. The tertiary exposed rocks in this area are represented by nine rock units separated from each other by unconformity surfaces in
1) Al Uwayliah Formation composes of chalky limestone, soft and enriched with planktic and calcareous nannofossils of Landenian age at its upper exposed section, However, it is well bedded and hard with rare planktic foraminifers of Danian age at its lower exposed part, although its middle part is not exposed, a series problem in the definition of Al Uwayliah Formation, this issue was discussed by [
2) Apollonia Formation is a well bedded chalky limestone, of mudstone-wackestone texture, with common chert nodules. The foraminifers are indicative of Ypresian―Lutetian age. There are no reefal facies in this formation. This formation exhibits interfingering relationship with the overlying Darnah Formation.
3) Darnah Formation is a thick bedded to massive limestone of grainstone to Packstone locally becoming rudstone in texture, this Formation is enriched in larger benthic foraminifers (Nummulites, Discocyclina, Orbitolites, Sphaerogypsina, etc.) with coralline red algae and/or coral facies at some places. This formation is dated as Middle Eocene based on the Nummulites gizehensis as example. Corals are among the local bioclasts occurrence as in West Darnah Roadcut section.
4) Shahhat Marl is dated as Late Eocene based on the presence of Nummulites fabianii and Gaziryinabulchellus [
5) Al Bayda Formation, the lower member “Algal Limestone Member” of Al Bayda Formation [
6) Al Abraq Formation is dated as Middle-Late Oligocene, it is skeletal limestone with abundant Operculinacomplanata africana and Lepidocuclina spp. It is deposited under shoal-channel complex [
7) Al Faidiyah Formation is dated as Late Oligocene―Early Miocene which was updated by [
8) Benghazi Formation is dated as Early-Middle Miocene [
Wadi al Qattarah Formation is dated Late Miocene [
The As Sahabi area according to Muftah [
a) Formation “M” (Tortonian); it consists of semi-consolidated bioclasts exposed in the floor of the Sebkhat, totally or partially decalcified and gypsified. Erosional relief of shallow Miocene coral reef, echinoids Clypeaster and Echinolampas and pelecypods, gastropods, bryozoans and Balanus.
b) Formation “P” (Messinian); it consists of lattice of gypsum crystals in a very sparse mineral matrix of dark sand and clay with very few fossils.
c) Sahabi Formation (Messinian-Pliocene); it was subdivided into six members:
i) Member “T”. It consists of cross bedded sand with abundant marine fauna and trace fossils (e.g. Ophiomorpha).
ii) Member T.X. Reddish clay and vertisol with cracks accessible in one area only.
iii) Member U-1. Sands with clay lenses and clay balls incorporating with common well preserved bones, teeth, jaws and skulls of land mammals.
iv) Member U-D. Cross bedded and bioturbated sandy dolostone.
v) Member U-2. Interbeddedsand and clay with dolomitic crusts with mammals remains.
vi) Member V. Sands and sandy clays with lenses of dolomite and gypsum crystals common root casts.
d) Formation “Z” (Pleistocene) is the youngest formation and consists of very complex fossil soil with paleo-caliche and terrestrial snail (e.g. Helix sp.).
The collected coral specimens used in this study are mainly derived from four localities located in the North east Libya (Cyrenaica) and one locality in As Sahabi area in
The Eocene rocks of Al Jabal al Akhdar in
The Oligocene rocks of Al Jabal al Akhdar in
The reef framework in Upper Oligocene Al Faidiyah Formation at Al Fatayah cement quarry is constructed of two genera of corals Cyphastrea sp.
The Miocene Tarbellastraea sp. coral of Benghazi Formation in
The As Sahabi coral reef is mainly of scleractinian type. They are growing in forms of small scale patch reefs extending parallel to the western edge of Sabkhat al Qunayyin, in NNE-SSW trending pattern. The diversity of the As Sahabi corals is very low, restricted to only two species in the Tortonian formation “M”. The first type is Astraeaopora sp.
The Al Jabal al Akhdar area and As Sahabi area display conspicuous exposures of the scleractinian coral reef. Only eight species are documented herein, six from The Al Jabal al Akhdar area and two from the As Sahabi area.
The reefal facies of Al Jabal al Akhdar is restricted to the Middle Eocene Darnah Formation, Early Oligocene
Al Bayda Formation; Upper Oligocene Al Faidiyah Formation and Middle Miocene Benghazi Formation. Only the Upper Miocene formation “M” is developed in As Sahabi area.
Diagenetic processes at some subsurface records rule the effectiveness of coral buildups to be good reservoirs, although in the surface show excellent porosity and permeability.
We would like to thank the Arabian Gulf Oil Company in Ganfouda for their assistance in sample preparation and providing some subsurface data. The authors wish to thank the University of Benghazi for the logistical support during field trips. Dr. James Pollard of the University of Manchester is appreciated for the identification of Oligo-Miocene coral specimens.
Belkasim Khameiss,William Hoyt,Saad K. El Ebaidi,Ahmed M. Muftah,James Klaus,Ann Budd, (2016) A Preliminary Documentation of the Coral Reefs from Libya. Open Journal of Geology,06,260-269. doi: 10.4236/ojg.2016.64023