PANORAMIC OF PALEOHABITATS OF PLIOCENE SAHABI FORMATION AND RECENT AS-SAHABI AREA, NORTHERN LIBYA

As-Sahabi area is located to the south of Ajdabiyah city in Sirt Basin, Libya. This area considered as a spectacular open Museum of vertebrate remains (i.e. teeth, bones, skulls and skeletons) of mammals, reptiles, aves and fish. This paper presents the methods used during the excavation and lists most of the documented taxa and finally compare these paleo-habitats with the corresponding present-day habitat of As-Sahabi. The As-Sahabi fossils played important role in delineating the paleohabitats and in understanding the migration routes as well as in tracing their evolutionary trends. These remains are preserved in continental deposits (mainly sands and clays) since 5 million years ago. Six paleo-habitats have been suggested “Salt neritic water, Eo-Sahabi River, Riverine forest and river edge, Water's edge and Eo-Sahabi estuary habitats, Savana habitat, and Arid Desert-like habitat. As-Sahabi vertebrates (e.g. crocodiles, hippos, hyena, etc..) are considered to be the ancestral taxa of the descendant vertebrates exist today in other parts of the world. However, some are found to be indigenous taxa due to migration failure such as the gigantic size, Mastodon (Stegotetrabeledon lybicus) and shovel-tusker Proposcidean (Amebelodon cyrenaicus) or medium-sized with short-legged Anthracothere (Libycosaurus petrocchii).


INTRODUCTION
The well-known Neogene paleontological site in Libya, As Sahabi (Fig. 1) has attracted not only paleontologists for its open natural museum of Neogene vertebrates, but also tourists for its fascinating scenery and impressive desert landscape panorama.During the 1920's, Italian soldiers noted by accident the presence of mammal fossil bones in the vicinity of the Qasr as Sahabi, a nowruined fort dating from Roman times, located at the southern part of the present paleontological site.
In the early 1930's, the famed Italian geologist and paleontologist Ardito Desio, with Professor G. D' Erasmo from Naples and geologist G. Stefanini from the University of Pisa, conducted the first geological and paleontological investigation in the As Sahabi area (Petrocchi, 1934).Carlo Petrocchi, DOI: 10.46717/igj.53.1B.1Rz-2020-03-01 a young paleontologist recruited in the 1935 by Desio to study As Sahabi, would become involved for decades in As Sahabi (and Libya), and make discoveries that rendered As Sahabi the most famous Libyan fossil site.Among his first finds (via excavations also), were the skull of the four-tusked elephantid Stegotetrabelodon syrticus and the skull and the in-situ skeleton of a cetacean, a whale (Petrocchi 1934(Petrocchi , 1936(Petrocchi and 1941)).For more on the discovery of the As Sahabi site, see Rook (2008); for a general presentation of the paleontological site, see Boaz (2008).
The as Sahabi area is located in the northeastern part of Sirt Basin, covering an area of about 375 km 2 (Fig. 1).It is bounded by longitudes 20 º 48'08" to 20 º 54'45" E and latitudes 30 º 10'58" to 30 º 17'36" N, within a tectonic province called the Ajdabiyah Trough.The productive samples in terms of vertebrates came from scattered exposures aligned in a N30 º E-trending manner and bounded by the Sabkhat al Qunayyin from the west (Fig. 1).However, the western part of the As Sahabi area is called the Sabkhat Al Qunayyin (Fig. 1).

The Field Work
The visited stratigraphic outcrops in As Sahabi area for this study consist of two profiles named P10 and P28 (Fig. 2).P10 (Jabal Shagig): Coordinates: Latitudes (30º11'12.58"N) and Longitudes (20º49'24.14"E).The measured thickness of this profile is 46 meters, represented by all members of Sahabi Formation (Fig. 2).P28 (Elephant hill): Coordinates: Latitudes (30º13'56.69"N) and Longitudes (20º51'26.71"E).The measured thickness of this profile is 22 m.This section represents by four members of Sahabi Formation, from bottom to top U1 member, UD member, and V member.
At this locality a possible complete skeleton of the Mastodon Stegotetrabelodon is buried, from which the name of the hill was derived.An amazing petrified forest is situated in front of this hill (Fig. 2).

Fig. 2: Jabal Shagig (P10); and Elephant hill (P28)
Excavation Proceedures 1-Sediments (sands) are removed from around the specimen (Fig. 3A) using painting brush with intensive care, because the" skeleton" is very fragile and will be collapsed easly if subjected to very little force (Fig. 3B).
2-when most of the skeleton is exposed (Fig. 3C) the surface covered with thin Paraloid -B72 or any alternative glue and left this cover for many hours (up to 24 hours) to infiltrate and fill the bone tissue (pores) to hardening the skeleton.
3-The glued skeleton is coated with Aluminium foil and covered with wet cloth.All exposed skeleton coated with Gypsum amalgom and left this for 24 hours to solidify (Fig. 3D).
4-The coated and solidified skeleton is turned upside down (Fig. 3E) with care, then the specimen transported to the Laboratory.The gypsum cover is removed in the laboratory to undergoes the required measurments and identifications by the concerned specialists.2016) amended the lithostratigraphic nomenclatures of the As Sahabi area based on stable isotopes dating of few samples to modify formation "M" and regional correlation to introduced new "lower member" and "upper member" of Sahabi Formation, Qarrat Waddah Formation and Z Formation, the latest version (Fig. 4) the composite columnar section having adopted four superimposed formations composing the substratum: 1-M Formation: Semiconsolidated bioclasts exposed in floor of the Sebkhat, totally or partially decalcified and gypsified.Erosional relief of shallow reefs "MR" with corals, echinoids, pelecypods and gastropods (De Heinzelin and El-Arnauti, 1987) (Fig. 4).
2-Sahabi Formation: It can be subdivided into two members: i) the lower member (≈De Heinzelin and El-Arnauti's P member and lowermost part of T member) characterized by semi-consolidated sandy, gypsiferous, and dolomitic limestone.Presence of a large network of fractures (~5 m deep) filled with selenitic gypsum is also a characteristic feature.ii) the upper member (≈De Heinzelin and El-Arnauti's T, U1, UD, and U2 members of Sahabi Formation) and uppermost part of T member) characterized by Sand with abundant marine fauna in places.Often bioturbated, and containing fish teeth and sirenian skeletons with land mammals.Followed by sands with clay lenses and clay balls incorporating well preserved bones.A transgressive bar, followed by interbedding of sand, clay and dolomitic crusts generally bounded between two dolomite beds, the lower one is highly bioturbated (Fig. 4).

Paleontology Flora
The Sahabi fossil flora is largely African in nature, as judged by comparative anatomy of the collected fossil wood with the living African species (Dechamps, 1987a;1987b;Dechamps & Maes, 1987).
Evidence of fossil diatoms undigested within coprolites is also recorded from the Sahabi Formation (Burckle, 1982).

Paleontology Fauna
A large number of mammalian and other vertebrate remains (more than 5000 specimens), have been so far collected and identified from the Sahabi Formation (lower member in the As Sahabi area, with De Heinzelin and El-Arnauti's member "U1" the most prolific in terms of mammalian, reptilian and avian remains.The most common mammalian representatives in the Sahabi Formation after Boaz et al., (2008) are shown on Table (1).Presence of the vertebrate trace fossils (Coprolites) is also common characteristic in the investigated area, which give a clue to the behavior of these organisms (Fig. 5).Carmignani et al., (2009) suggested from remote sensing data that the "Sahabi Channels" of Barr and Walker (1973), which extended by Nicolai (2008) into the Mediterranean Basin by the use of seismic data, represented a late Miocene incursion of the Nile River into Libya.Such a model requires migrate of the Nile from its basin and flow uphill over the higher relief Western Desert to enter the Ajdabya Trough and eventual entry into the Gulf of Sirt.The model is not supported by data on Miocene paleorelief of western Egypt that would make such a hypothesis plausible, and recent remote sensing data (Paillou et al. 2009) support a separate Libyan hydrographic drainage pattern distinct from the Nile.Moreover, Muftah et al., (2013) suggested that the source of the river was Chad mega Lake (Fig. 6) based on geochemical analysis of the clay sediments of Member U1 of Sahabi Formation, where, their geochemical composition might also be explained by an origin from Precambrian outcrops within the Ethiopian highlands near Lake Tana in the catchment area of the Blue Nile, paleontological evidence (Table .1) renders this is an unlikely hypothesis (Muftah et al., 2013).
However, flora is mainly of arid desert plants which are mainly restricted to few annular plants and grasses which strictly growing after short time rainfall in wadis and baltas (Fig. 9A-F), the illustrated flora is not classified herein.

CONCLUSIONS
The following are the main conclusions: 1-Highlight the Eo-Sahabi river with attention to its possible source and its role in creating the six recognized habitats in Pliocene Sahabi Formation of As-Sahabi area.
2-Compare the documented vertebrate fossils remains during the Pliocene time in reconstructing the prevailed habitats in As Sahabi area.RECOMMENDATION 1-The As Sahabi area is highly recommended to be registered as an international natural heritage site in order to conserve the hidden and the exposed vertebrate fossil remains.
2-Protecting vertebrate remains and fossil wood from taking them for any reason.

Fig. 3 :
Fig. 3: The excavation steps of Chelonia from AS Sahabi area near the petrified forest at P28

Fig. 4 :
Fig. 4: Geological map and composite stratigraphic column of As Sahabi area shows the studied profiles (Modified after De Heinzelin and El-Arnauti, 1987)

Fig. 6 :
Fig. 6: Map shows the proposed origin of sediments of the vertebrate bearing member U1 of Sahabi Formation from Chad paleolake (Muftah et al., 2013)