Papers by Ahmed S El-Hawat
Early silicification of the Cyrenaican chert, Libya: The importance of moganite as a transitional silicon dioxide phase, 2021
The Messinian lagoonal carbonate-evaporite sequence of Cyrenaica, northeast Libya, hosts: (i) opa... more The Messinian lagoonal carbonate-evaporite sequence of Cyrenaica, northeast Libya, hosts: (i) opaline nodules in gypsiferous microbial-rich mudstone; (ii) nodules replacing poikilotopic gypsum cementing bioclastic carbonates; and (iii) bedded porcelanite with large lenticular gypsum pseudomorphs intercalated with recrystallized microbial mats. Optical microscopy, scanning electron microscopy, backscattered electron imagessecondary electron images, X-ray fluorescence, X-ray diffraction and cathodoluminescence techniques were employed to elucidate on the early stages of chert diagenesis and demonstrate the role of moganite in the formation of varieties of chalcedony during silicification. The opaline nodules composed of opal-A, exhibit shrinkage cracks lined by isopachous fibrous quartzine underlain by a thin birefringent zone. This suggests that quartzine may develop by crystallization and conversion of opal-A through a transitional moganite. The quartzine is followed by amorphous silica gel that converts into length-fast chalcedony. By contrast, lutecite evolved by silica replacement of gypsum through a transitional moganite phase, which forms an amorphous zone in apparent optical continuity with the fibrous lutecite; as moganite advances by pseudo-crystalline terminations controlled by the gypsum cleavage. In gypsified oyster shells, intercrystalline organic matter enveloping pseudomorphed shell microstructures enabled moganite nucleation that merges syntaxially around the gypsum crystal rim. The associated lutecite occurs as radial-fibrous beekite aggregates that are consistent with early shell silicification. The bedded porcelanite consists of opal-CT groundmass undergoing recrystallization and enclosing micro-cavities lined by quartzine. The associated pseudomorphs display phases of gypsum replacement by moganite and lutecite at the outer margin, followed by dissolution and cavity filling by quartz varieties in response to fluid flushing. In all cases, organic matter and microbes played a vital role in the silicification process.
We propose a novel method to evaluate regional palaeoclimate that can be used to alleviate the pr... more We propose a novel method to evaluate regional palaeoclimate that can be used to alleviate the problems caused by the discontinuous nature of palaeoenvironmental data found in deserts. The technique involves processing satellite imagery and DEM's to map past rivers, catchments and evaluate the areas and volumes of palaeolakes. This information is used to determine the new Lake Evaluation Index (LEI) that allows a qualitative estimate of the amount of sediment received by lakes and how long-lived those lakes are. Lakes with considerable longevity and large sediment stores are selected for study. Validation is performed using image interpretation of remote sensing data, UltraGPR surveys and fieldwork. These techniques are also used to identify and study spring deposits and fluvial landforms that provide valuable palaeoclimate information. The method is applied to the Fezzan Basin in southern Libya focusing on the Wadi ash Shati and Wadi el-Agial catchments. Results indicate that the palaeohydrology is accurately mapped except within dune fields. We analysed the sedimentology of the key deposits identified by this methodology, developing a chronology using optically stimulated luminescence (OSL) and radiocarbon dating. We find evidence for relatively humid conditions during MIS 5c/d and e, as well as during the early to middle Holocene. Larger lakes and more extensive river systems were present during MIS 5 than are found during the Holocene, suggestive of greater humidity. The Holocene humid period started at ~11 ka and continued until ~5 ka being interrupted by abrupt periods of aridity at ~8.2 ka and ~6 ka that coincide with North Atlantic cooling. After each of these arid events the climate was less humid than previously, suggesting that they were superimposed upon an overall drying trend. The termination of the Holocene humid period in the Sahara has received much scrutiny in recent years, and sediments of Palaeolake Shati provide a continuous record of this. We do not find evidence to support the hypothesis of either sudden or gradual aridification of the Sahara at ~5 ka, instead we find that that aridity started to develop at ~6.5 ka, whereupon the lake levels oscillated until finally drying-up by 5.3 ka. Most of the other lakes in the Fezzan also dried up at ~ 5ka. We suggest that thousands of years of aridification prior to 5 ka shrunk these lakes so that additional aridity at this time led to their final desiccation. Because lakes are prodigious dust sources this mechanism potentially explains the rapid rise in dust flux to the
Terrestrial and lacustrine Neogene and Quaternary sediments in the Libyan Fezzan provide key evid... more Terrestrial and lacustrine Neogene and Quaternary sediments in the Libyan Fezzan provide key evidence for paleoclimate changes in the central Sahara, associated with Lake Megafezzan. Understanding of Holocene and late Pleistocene deposits is resolved, but the age of older sediments is not. We provide the first high-resolution chronology and stratigraphy of the Neogene deposits in the Fezzan Basin, and so also the central Sahara. The sediments are divided into three unconformity-bounded units, the oldest unit, comprising the Shabirinah and Brak formations, is dated using magnetostratigraphy. The Shabirinah Formation is a succession of lacustrine and fluvial units, locally with humid and arid paleosols, which progressively show evidence of increasing aridity up through the succession. The overlying Brak Formation is a pedogenically modified palustrine limestone at basin margin locations. All these units are dated to the early Aquitanian to late Serravallian in the early to mid-Miocene, having formed prior to major volcanic fields to the east. During the mid-late Aquitanian widespread stromatolitic lake sediments developed in SE Fezzan. In the late Burdigalian palustrine carbonate units developed that typically pass laterally into mixed clastic-paleosol-carbonate units that characterise basin margin situations. The Serravallian-aged Brak Formation is a highstand deposit developed during maximum lake extent, which formed due to restriction of basin drainage to the north and east, due to growth of the Jabal as Sawda volcanic centre and uplift of the SW shoulder of the Sirte Basin. Gradual aridification of the central Sahara occurred from the early Miocene, but this trend was periodically interrupted by humid phases during which Lake Megafezzan developed. The hyperaridity of the central Sahara must have developed after 11 Ma and the main drainage networks from the Fezzan Basin were established before 23 Ma, in the Oligocene indicating the great antiquity of major central Saharan river basins.
This paper reports the results of fieldwork conducted
in the 2010 and 2011 DMP field seasons and ... more This paper reports the results of fieldwork conducted
in the 2010 and 2011 DMP field seasons and of analysis
of samples collected during these and previous years.
Research has involved 1) studying palaeolake sediment
outcrops, 2) using ground penetrating radar (GPR) to
determine their extent under the Daha¯n Uba¯rı¯, and
3) coring palaeolakes in order to determine their palaeoenvironmental
records. Research on these samples
is continuing but some initial findings are discussed in
this paper. The most extensive palaeolake sediments are
found within the al-Mahruqah Formation and were deposited
by a giant lake system that developed in the Fazza¯n
Basin during past humid periods. Stratigraphic analysis of
Lake Megafazza¯n sediments suggests two different sedimentary
successions, a lake margin succession distinctive
for its lacustrine and palaeosol carbonates, and a clasticdominated,
intensely rootleted, basin-centre succession
which has terrestrial intervals (aeolian and palaeosols)
as well as in the upper parts lacustrine limestones. Both
basin margin and basin centre successions are underlain
by fluvial deposits. Magnetostratigraphy suggests that
the formation may be as old as the mid-Pliocene. After
the Lake Megafazza¯n phase, smaller palaeolakes developed
within the basin during subsequent humid periods.
One of the largest is found in the Wa¯dı¯ al-Haya¯t in the
area between Jarma and Uba¯rı¯. Similar deposits further
west along the Wa¯dı¯ at progressively higher altitudes are
interpreted as small lakes and marshes fed by springs
issuing from aquifers at the base of the escarpment, last
replenished during the Holocene humid phase. Dating
of sediments suggests that this was between c. 11 and
c. 8 ka. The Wa¯dı¯ ash-Sha¯t¸ı¯ palaeolake core also provides
a Holocene palaeoclimate record that paints a slightly different
picture, indicating lake conditions until around 7
ka, whereupon it started oscillating until around 5.5 ka
when sedimentation terminates. The reasons for the differences
in these records are discussed.
The January 2009 fieldwork season conducted geomorphological and palaeoenviromental surveys in as... more The January 2009 fieldwork season conducted geomorphological and palaeoenviromental surveys in as yet unexplored parts of the Lake Megafazzan Basin, as well as continuing research in the Wadi al-Hayat and Ubari Sand Sea. Lake Megafazzan sediments were investigated at two sites on the eastern margin of the basin. At the first site, east of Tamessah, 24 m of stratigraphy was investigated and found to consist of a lacustrine carbonate unit at the base progressing into a fluvial unit and then an upper carbonate unit. The sediments were sampled for magnetostratigraphy and cosmogenic nucleide dating in order to determine their age. Similar studies were undertaken in the vicinity of the Arial Agricultural Project, where 31 m of section were logged and sampled. Here the sediments were quite different, being composed of a deltaic sequence consisting of stacked channels and palaeosols, thought to represent the outflow delta of the palaeolake. Many new Holocene lake sediment deposits were discovered and sampled in the Wadi al-Hayat and the Ubari Sand Sea, including a 5 m section through Jarma Playa that appears to record the last arid-humid cycle. Lake Gabr 'Awn and the moat round Old Jarma were cored in order to gather a detailed picture of recent palaeoenvironmental change. Finally, we implemented a pilot geophysical survey to test the ability of state-of-the-art Ground Penetrating Radar (UltraGPR) technology for detecting and mapping buried palaeolake sediments under the dunes of the Ubari Sand Sea. The UltraGPR was found to be very effective, detecting palaeolake sediments as much as 60 m beneath the surface. Preliminary results suggest such sediments underlie much of the region.
The Geology of Sirt Basin, Vol II, 1996
VIII Congress of the Regional Committee on the Mediterranean Neogene Stratigraphy, 1987
The Geology of Western Libya, 2003
The Geology of Sirt Basin, 1996
The Geology of Libya Vol. II, 1980
Palaeogeography, Palaeoclimatology, Palaeoecology, 2008
We have integrated information on topography, geology and geomorphology with the results of targe... more We have integrated information on topography, geology and geomorphology with the results of targeted
fieldwork in order to develop a chronology for the development of Lake Megafazzan, a giant lake that has
periodically existed in the Fazzan Basin since the late Miocene. The development of the basin can be best
understood by considering the main geological and geomorphological events that occurred thought Libya
during this period and thus an overview of the palaeohydrology of all Libya is also presented. The origen of
the Fazzan Basin appears to lie in the Late Miocene. At this time Libya was dominated by two large rivers
systems that flowed into the Mediterranean Sea, the Sahabi River draining central and eastern Libya and
the Wadi Nashu River draining much of western Libya. As the Miocene progressed the region become
increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked
the River Nashu in Late Miocene or early Messinian times forming a sizeable closed basin in the Fazzan
within which proto-Lake Megafazzan would have developed during humid periods. The fall in base level
associated with the Messinian desiccation of the Mediterranean Sea promoted down-cutting and extension
of river systems throughoutmuch of Libya. To the south of the proto Fazzan Basin the Sahabi River tributary
know as Wadi Barjuj appears to have expanded its headwaters westwards. The channel now terminates at
Al Haruj al Aswad. We interpret this as a suggestion that Wadi Barjuj was blocked by the progressive
development of Al Haruj al Aswad. K/Ar dating of lava flows suggests that this occurred between 4 and 2Ma.
This event would have increased the size of the closed basin in the Fazzan by about half, producing a
catchment close to its current size (~350,000 km2). The Fazzan Basin contains a wealth of Pleistocene to
recent palaeolake sediment outcrops and shorelines. Dating of these features demonstrates evidence of
lacustrine conditions during numerous interglacials spanning a period greater than 420 ka. The middle to
late Pleistocene interglacials were humid enough to produce a giant lake of about 135,000 km2 that we have
called Lake Megafazzan. Later lake phases were smaller, the interglacials less humid, developing lakes of a
few thousand square kilometres. In parallel with these palaeohydrological developments in the Fazzan
Basin, change was occurring in other parts of Libya. The Lower Pliocene sea level rise caused sediments to
infillmuch of theMessinian channel system. As this was occurring, subsidence in the Al Kufrah Basin caused
expansion of the Al Kufrah River system at the expense of the River Sahabi. By the Pleistocene, the Al Kufrah
River dominated the palaeohydrology of eastern Libya and had developed a very large inland delta in its
northern reaches that exhibited a complex distributary channel network which at times fed substantial
lakes in the Sirt Basin. At this time Libyawas a veritable lake district during humid periods with about 10% of
the country underwater.
The Middle Miocene Marada Formation is a second-order stratigraphic sequence bound by well-define... more The Middle Miocene Marada Formation is a second-order stratigraphic sequence bound by well-defined unconformable boundaries. It forms a terminal phase in the post-rift megasequence infilling the Sirt Basin, and consists of vertically arranged lowstand (LST), transgressive (TST) and highstand (HST) systems tracts. These constitute six vertically stacked carbonate-siliciclastic genetic depositional units exhibiting lateral facies changes of the carbonate-dominated Marada area to siliciclastics in Jabal Zaltan to the south. The LST consists of fluviatile and fluviomarine deposits rich in vertebrate fauna and flora. These pass laterally northwards into estuarine calcareous sandstone facies infilling a channel system forming the base of the section. To the south, the start of the TST is marked by deposition of thick lagoonal shales over the fluvio-estuarine deposits. These change northward into cross-bedded bioclastic carbonate barrier bars and sandy bioclastic tidal inlets and a delta complex that transgress over the lagoonal shales. Together, these are stacked in repeated transgressive-regressive architecture in response to cyclic influx and cessation of siliciclastic supply and created accommodation space. During maximum flooding carbonate sedimentation extended into the siliciclastic-dominated south and developed a condensed section (CS) to the north. It is characterised by lithification, build-up of oyster banks, and development of a regionally extended Echinolampas marker. The following HST consists of open marine wackestone banks alternating with prograding deltaic marl and calcareous sandstone shoestring facies. Ultimately, the sequence stratigraphic architecture of the Marada Formation and the alternation of carbonate and siliciclastic cyclic sedimentation are attributed primarily to the interplay of steady eustatic sea-level change and overprinting by spasmodic tectonic activity of the Sirt rift complex during the Middle Miocene.
Libyan …, Jan 1, 2009
The January 2009 fieldwork season conducted geomorphological and palaeoenviromental surveys in as... more The January 2009 fieldwork season conducted geomorphological and palaeoenviromental surveys in as yet unexplored parts of the Lake Megafazzan Basin, as well as continuing research in the Wadi al-Hayat and Ubari Sand Sea. Lake Megafazzan sediments were investigated at two sites on the eastern margin of the basin. At the first site, east of Tamessah, 24 m of stratigraphy was investigated and found to consist of a lacustrine carbonate unit at the base progressing into a fluvial unit and then an upper carbonate unit. The sediments were sampled for magnetostratigraphy and cosmogenic nucleide dating in order to determine their age. Similar studies were undertaken in the vicinity of the Arial Agricultural Project, where 31 m of section were logged and sampled. Here the sediments were quite different, being composed of a deltaic sequence consisting of stacked channels and palaeosols, thought to represent the outflow delta of the palaeolake. Many new Holocene lake sediment deposits were discovered and sampled in the Wadi al-Hayat and the Ubari Sand Sea, including a 5 m section through Jarma Playa that appears to record the last arid-humid cycle. Lake Gabr 'Awn and the moat round Old Jarma were cored in order to gather a detailed picture of recent palaeoenvironmental change. Finally, we implemented a pilot geophysical survey to test the ability of state-of-the-art Ground Penetrating Radar (UltraGPR) technology for detecting and mapping buried palaeolake sediments under the dunes of the Ubari Sand Sea. The UltraGPR was found to be very effective, detecting palaeolake sediments as much as 60 m beneath the surface. Preliminary results suggest such sediments underlie much of the region.
searchanddiscovery.com
Forty eight high resolution stratigraphic sections and more than 850 thin sections were used to s... more Forty eight high resolution stratigraphic sections and more than 850 thin sections were used to study the Eocene of Cyrenaica. Sections are located on the northern limb of Al Jabal al Akhdar inversion anticlinorium that formed a series of submerged Cretaceous structural highs and islands. These played an important role in the development of the Eocene nummulitic ramp complex.
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Papers by Ahmed S El-Hawat
in the 2010 and 2011 DMP field seasons and of analysis
of samples collected during these and previous years.
Research has involved 1) studying palaeolake sediment
outcrops, 2) using ground penetrating radar (GPR) to
determine their extent under the Daha¯n Uba¯rı¯, and
3) coring palaeolakes in order to determine their palaeoenvironmental
records. Research on these samples
is continuing but some initial findings are discussed in
this paper. The most extensive palaeolake sediments are
found within the al-Mahruqah Formation and were deposited
by a giant lake system that developed in the Fazza¯n
Basin during past humid periods. Stratigraphic analysis of
Lake Megafazza¯n sediments suggests two different sedimentary
successions, a lake margin succession distinctive
for its lacustrine and palaeosol carbonates, and a clasticdominated,
intensely rootleted, basin-centre succession
which has terrestrial intervals (aeolian and palaeosols)
as well as in the upper parts lacustrine limestones. Both
basin margin and basin centre successions are underlain
by fluvial deposits. Magnetostratigraphy suggests that
the formation may be as old as the mid-Pliocene. After
the Lake Megafazza¯n phase, smaller palaeolakes developed
within the basin during subsequent humid periods.
One of the largest is found in the Wa¯dı¯ al-Haya¯t in the
area between Jarma and Uba¯rı¯. Similar deposits further
west along the Wa¯dı¯ at progressively higher altitudes are
interpreted as small lakes and marshes fed by springs
issuing from aquifers at the base of the escarpment, last
replenished during the Holocene humid phase. Dating
of sediments suggests that this was between c. 11 and
c. 8 ka. The Wa¯dı¯ ash-Sha¯t¸ı¯ palaeolake core also provides
a Holocene palaeoclimate record that paints a slightly different
picture, indicating lake conditions until around 7
ka, whereupon it started oscillating until around 5.5 ka
when sedimentation terminates. The reasons for the differences
in these records are discussed.
fieldwork in order to develop a chronology for the development of Lake Megafazzan, a giant lake that has
periodically existed in the Fazzan Basin since the late Miocene. The development of the basin can be best
understood by considering the main geological and geomorphological events that occurred thought Libya
during this period and thus an overview of the palaeohydrology of all Libya is also presented. The origen of
the Fazzan Basin appears to lie in the Late Miocene. At this time Libya was dominated by two large rivers
systems that flowed into the Mediterranean Sea, the Sahabi River draining central and eastern Libya and
the Wadi Nashu River draining much of western Libya. As the Miocene progressed the region become
increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked
the River Nashu in Late Miocene or early Messinian times forming a sizeable closed basin in the Fazzan
within which proto-Lake Megafazzan would have developed during humid periods. The fall in base level
associated with the Messinian desiccation of the Mediterranean Sea promoted down-cutting and extension
of river systems throughoutmuch of Libya. To the south of the proto Fazzan Basin the Sahabi River tributary
know as Wadi Barjuj appears to have expanded its headwaters westwards. The channel now terminates at
Al Haruj al Aswad. We interpret this as a suggestion that Wadi Barjuj was blocked by the progressive
development of Al Haruj al Aswad. K/Ar dating of lava flows suggests that this occurred between 4 and 2Ma.
This event would have increased the size of the closed basin in the Fazzan by about half, producing a
catchment close to its current size (~350,000 km2). The Fazzan Basin contains a wealth of Pleistocene to
recent palaeolake sediment outcrops and shorelines. Dating of these features demonstrates evidence of
lacustrine conditions during numerous interglacials spanning a period greater than 420 ka. The middle to
late Pleistocene interglacials were humid enough to produce a giant lake of about 135,000 km2 that we have
called Lake Megafazzan. Later lake phases were smaller, the interglacials less humid, developing lakes of a
few thousand square kilometres. In parallel with these palaeohydrological developments in the Fazzan
Basin, change was occurring in other parts of Libya. The Lower Pliocene sea level rise caused sediments to
infillmuch of theMessinian channel system. As this was occurring, subsidence in the Al Kufrah Basin caused
expansion of the Al Kufrah River system at the expense of the River Sahabi. By the Pleistocene, the Al Kufrah
River dominated the palaeohydrology of eastern Libya and had developed a very large inland delta in its
northern reaches that exhibited a complex distributary channel network which at times fed substantial
lakes in the Sirt Basin. At this time Libyawas a veritable lake district during humid periods with about 10% of
the country underwater.
in the 2010 and 2011 DMP field seasons and of analysis
of samples collected during these and previous years.
Research has involved 1) studying palaeolake sediment
outcrops, 2) using ground penetrating radar (GPR) to
determine their extent under the Daha¯n Uba¯rı¯, and
3) coring palaeolakes in order to determine their palaeoenvironmental
records. Research on these samples
is continuing but some initial findings are discussed in
this paper. The most extensive palaeolake sediments are
found within the al-Mahruqah Formation and were deposited
by a giant lake system that developed in the Fazza¯n
Basin during past humid periods. Stratigraphic analysis of
Lake Megafazza¯n sediments suggests two different sedimentary
successions, a lake margin succession distinctive
for its lacustrine and palaeosol carbonates, and a clasticdominated,
intensely rootleted, basin-centre succession
which has terrestrial intervals (aeolian and palaeosols)
as well as in the upper parts lacustrine limestones. Both
basin margin and basin centre successions are underlain
by fluvial deposits. Magnetostratigraphy suggests that
the formation may be as old as the mid-Pliocene. After
the Lake Megafazza¯n phase, smaller palaeolakes developed
within the basin during subsequent humid periods.
One of the largest is found in the Wa¯dı¯ al-Haya¯t in the
area between Jarma and Uba¯rı¯. Similar deposits further
west along the Wa¯dı¯ at progressively higher altitudes are
interpreted as small lakes and marshes fed by springs
issuing from aquifers at the base of the escarpment, last
replenished during the Holocene humid phase. Dating
of sediments suggests that this was between c. 11 and
c. 8 ka. The Wa¯dı¯ ash-Sha¯t¸ı¯ palaeolake core also provides
a Holocene palaeoclimate record that paints a slightly different
picture, indicating lake conditions until around 7
ka, whereupon it started oscillating until around 5.5 ka
when sedimentation terminates. The reasons for the differences
in these records are discussed.
fieldwork in order to develop a chronology for the development of Lake Megafazzan, a giant lake that has
periodically existed in the Fazzan Basin since the late Miocene. The development of the basin can be best
understood by considering the main geological and geomorphological events that occurred thought Libya
during this period and thus an overview of the palaeohydrology of all Libya is also presented. The origen of
the Fazzan Basin appears to lie in the Late Miocene. At this time Libya was dominated by two large rivers
systems that flowed into the Mediterranean Sea, the Sahabi River draining central and eastern Libya and
the Wadi Nashu River draining much of western Libya. As the Miocene progressed the region become
increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked
the River Nashu in Late Miocene or early Messinian times forming a sizeable closed basin in the Fazzan
within which proto-Lake Megafazzan would have developed during humid periods. The fall in base level
associated with the Messinian desiccation of the Mediterranean Sea promoted down-cutting and extension
of river systems throughoutmuch of Libya. To the south of the proto Fazzan Basin the Sahabi River tributary
know as Wadi Barjuj appears to have expanded its headwaters westwards. The channel now terminates at
Al Haruj al Aswad. We interpret this as a suggestion that Wadi Barjuj was blocked by the progressive
development of Al Haruj al Aswad. K/Ar dating of lava flows suggests that this occurred between 4 and 2Ma.
This event would have increased the size of the closed basin in the Fazzan by about half, producing a
catchment close to its current size (~350,000 km2). The Fazzan Basin contains a wealth of Pleistocene to
recent palaeolake sediment outcrops and shorelines. Dating of these features demonstrates evidence of
lacustrine conditions during numerous interglacials spanning a period greater than 420 ka. The middle to
late Pleistocene interglacials were humid enough to produce a giant lake of about 135,000 km2 that we have
called Lake Megafazzan. Later lake phases were smaller, the interglacials less humid, developing lakes of a
few thousand square kilometres. In parallel with these palaeohydrological developments in the Fazzan
Basin, change was occurring in other parts of Libya. The Lower Pliocene sea level rise caused sediments to
infillmuch of theMessinian channel system. As this was occurring, subsidence in the Al Kufrah Basin caused
expansion of the Al Kufrah River system at the expense of the River Sahabi. By the Pleistocene, the Al Kufrah
River dominated the palaeohydrology of eastern Libya and had developed a very large inland delta in its
northern reaches that exhibited a complex distributary channel network which at times fed substantial
lakes in the Sirt Basin. At this time Libyawas a veritable lake district during humid periods with about 10% of
the country underwater.
Thirty eight high-resolution sedimentological sections along 167 km, which were measured and laboratory analysis of samples, indicate that Wadi Yunis Member is divided into two successive shallowing-up sequences consisting of six vertically stacked depositional facies. These are; 1. Oolitic grainstone facies; 2. Oo-skeletal grainstone - packstone facies; 3. Algal pelle-skeletal facies, 4. Bioclastic wackestone facies; 5. Algal stromatolite facies and 6. Coarsely crystalline selenite gypsum facies. These are interpreted as an association of high-energy; wave dominated oolitic shoals–channel complex and low-energy lagoonal facies, constituting a carbonate ramp system. The oolitic shoal palaeocurrents measurements suggest a southwest (206°) vector mean transport direction, a result of a north-easterly dominated Mediterranean wind. Constructed facies ratios, isopach and palaeogeographic maps of the study area demonstrate that the oolitic shoals carbonate factory was located to the northwest, whereas the shelf lagoon was influenced by siliciclastic input from the southeast. At times, during eustatic low-stands the shelf lagoon was subjected to restricted circulation and evaporites precipitation.
Due to environmental compartmentalization and rapid lateral facies changes, a multi-datum technique is used in this study. This carbonate ramp body with its elongated narrow morphology along the NW-SE strike and the SW unimodal palaeocurrent mode of 206° azimuth is the end product of wave dominated sedimentological processes and inherited structures that control to an extent the palaeocurrents flow directions and facies distribution.
However, at some stage in time the basin suffered of restriction and complete isolation. The primary gypsum ratio map shows a bulls-eye pattern with evaporites in the basin centre surrounded completely with carbonates, typical of completely enclosed basins.
Detailed laboratory work for petrographic analysis and diagenesis of the limestone facies has been conducted on 53 representative sample thin sections.
The dolomitization and gypsification ratio maps indicated that the diagenetic patterns are facies controlled in the study area. The dolomitization process is intensive and largely restricted to the permeable high energy deposits that dominated by lime sand-sizes, while the gypsification process is largely restricted to the impermeable low energy deposits that dominated by lime mud-sizes.