Wadi As Sir Limestone Formation is highly fossiliferous and rich in echinoids and fragmented shells [19]. Macrofossils assemblages include bivalves, gastropods, pelecypods, cephalopoda and echinoderms. The foraminiferal species include; Haplophragmoides gracilis, Ammomarginuluna aburoashensis, and ammobaculites turonicus (Said & Kenawy), Flabellammina aegyptia (Omara), Praebulimia prolixa (Cushman & Parker), Discorbis minutus, Nonion beadnelli, and Gavelinopsis pseudobaccata (Said & Barakat), Heterohelix globulosa (Ehrenberg), Hedbergella delrioensis (Carsey), Helvetoglobotruncana praehelvetica (Trujillo) [20]. The Wadi as Sir Limestone Formation is Turonian in age based on foraminiferas and ostracods [21] [22].

Wadi As Sir Limestone Formation covers the Al-tayyar area and the entire section of the study area comprised of 30 m thick. Wadi As Sir Limestone Formation significantly exposed in the area of study, and it consists of ten layers in the area of study from bottom to top (Table 1).

The lithological units beginning with the Chalky unit, defined by calcite-filled vugs and fractures with white to creamy color and 7.70 m thick which is about 25.6% of the section’s entire thickness.

The section’s second unit is the dolomite unit that consists of alternating dolomitic limestone with yellowish, white to a gray color and is 9.90 m thick which is about 33% of the section. The third unit of the section consists of a 7.60 m thick marl unit, which is about 25.3% of the section. The last top part of the section in the study area is the limestone unit with white partly dirty color and about 16% of the section’s entire thickness is 4.80 m thick.

Thirty-five thin sections are representing Wadi As Sir Formation selected for analysis of the microfacies in the studied area.

Thin sections were examined with Alizarin-Red-S’ before and after the staining [6] [8] carbonate rock classification used to classify the rocks examined.

MF1: Bioclastic Wackestone, Biomicrite Microfacies.

These microfacies represent the chalky unit consisting of chalky limestone alternation. The microfacies are composed of grains (30%) contained in a micritic ground layer. The heterogeneous matrix is mainly made by micrite with less microsparite.

Bioclasts are loose pellet mud grains; (Figure 2(a)), sediment-filled gastropod shells; (Figure 2(b)), echinoderms; (Figure 2(c)), pelecypods; (Figure 2(d) & Figure 2(e)). Silica-filled radiolarian shells; (Figure 2(f)). Cortoids grains; (Figure 2(g)), large bone fragment bioclasts; (Figure 2(h)), rudist fragment; (Figure 3(a)), foraminiferas are present; (Saccaminopsis sp); (Figure 3(b)), and deformed foraminifera’s chambers; (Figure 3(c) & Figure 3(d)), other common allochems are peloids; (Figure 3(e)).

The foraminifers are often fully micritized and their shell partially damaged and can be barely distinguished from peloids that make up (15%) of the rock as vugs, they are mostly spherical and oval, sorted and range from (0.1 to 0.2 mm).

The fracture is filled with iron oxides and calcite; (Figure 3(e) & Figure 3(f) & Figure 3(g)) and the impact of diagenesis processes well illustrated by micritization, inversion, compaction, and dolomitization; SEM image of the types of Wackestone Microfacies (Figure 3(h)).

Some benthic foraminifera species scanned by scanning electron microscope to observe the deformed tests of their surface abnormalities which noted in thin section analysis; (Figure 4(a) & Figure 4(b) & Figure 4(c)), and Wackestone microfacies types; (Figure 4(d)).

MF2: Bioclastic mudstone, Biomicrite Microfacies.

Such microfacies represent a dolomitic unit that consists of alternating calcareous dolomitic. The matrix was bioturbed and mostly composed of micrite (supported by mud); Mudstone containing grains of less than 10%. Iron oxide, calcite cements, and calcite cement post-dolomitization filled cracks and pores; (Figure 5(a) & Figure 5(b) & Figure 5(c)). The allochem assembly consists of some peloids, usually, the result of indurated carbonate mud erosion and abrasion, which are spherical in form and small size; (Figure 5(d) & Figure 5(e)). The bioclasts embedded in a micrite matrix consisting of cephalopods; (Figure 5(f)), benthic foraminifera; (Figure 5(g)). Mollusks shell; (Figure 6(a)), fragmented shell, and other Calcareous Algae (Gymnocodiaceans) allochem assembly; (Figure 6(b)). Lamination is a common feature in the lower beds of these microfacies, these hundreds of micron to about two millimeters thick laminates produced by the concentration of fossils parallel to the bedding planes; (Figure 6(c)). Completely dolomitized foraminiferas; (Figure 6(d) & Figure 6(e)) and textures of the fine dolomite grains are found; (Figure 6(f)). The fossils are not well preserved due to compaction and the micritization process; SEM image of types of Mudstone Microfacies (Figure 6(g)).

MF3: Bioclastic packestone, Biosparite Microfacies.

Such microfacies represent a unit of marls. The calcareous matrix is composed of heterogeneously strongly bioturbed micrite, micro sparite, and less sparry calcite. Bioclast content (50%), consists of two curved bivalve shells containing calcite; (Figure 7(a)), thick bivalves are most common in these microfacies; (Figure 7(b) & Figure 7(c-1) & Figure 7(d-1) & Figure 7(e-1)), gastropods are composed of aragonite; Figure 7(c-2) & Figure 7(f)); crinoid elements-echinoderms embedded in sparry calcite; large micrite-embedded pelecypods; Figure 7(d-2) and (Figure 7(g)). Prismatic brachiopods layer; (Figure 7(h)), stromatoporoids; (Figure 8(a)), and some cortoid grains; (Figure 8(b-1)); shell fragments of molluscs; (Figure 8(b-2)). Calcareous algae (Koninckopora); (Figure 8(c)), intraclast aggregate grain variety; (Figure 8(d)), shell fragments of molluscs; (Figure 8(e)).

The result of the diagenesis cycle well reflected by micritization, dolomitization and some parts of them are dissolved and recrystallized to sparry calcite. SEM image of the Packestone Microfacies types (Figure 8(f)).

MF4: Bioclastic Grainstone, Biosparite Microfacies.

These microfacies depict the limestone unit in some thin sections, the layer composed of about 90% grains embedded in a matrix of neomorphic sparite and microsparite as well as micrite. The bioclastic content consists of thick-shelled Gastropods which replaced the original aragonite shell with blocky calcite; (Figure 9(a) & Figure 9(b-1)), and (Figure 9(c-1)). Bivalves; (Figure 9(b-2)). Worm tubes serpulids; (Figure 9(d)), pelecypods; (Figure 9(c-2)), and plentiful ostracods; (Figure 9(e-2)). Some quartz grains have identified; (Figure 10(a)), the elements of some crinoids (Figure 9(e-1)), and; (Figure 10(b)). Bivalve shell (Oyster) two layers, with a dense, inner layer of calcite and a thinner, outer aragonite layer; (Figure 10(c)). In these microfacies, large amounts of gastropod distinguished; (Figure 10(d)). This microfacies consists of mostly broken angular to rounded skeletons.

Microfacies analysis in comparison with other previous studies [4] recorded the following types of microfacies which are compatible with the present study results; Globigerinid mudstones, bioclastic grainstone, miliolid packestone, peloidal packestone, and pure mudstone. And corresponded with [23] results; Benthic Foraminifera-peloidal-bioclastic wackestone, Benthic foraminifera peloidal-bioclastic mudstone/wackestone, Mollusks-bioclastic wackestone/ packestone, Echinoderm-peloidal-bioclastic wackestone, Peloidal-planktonic foraminifera-bioclastic wackestone/packestone, Bioclastic wackestone, Benthic foraminifera bioclastic wackestone, Peloidal-bioclastic wackestone/packestone, Peloidalbioclastic mudstone/wackestone, and Benthic foraminifera mudstone.

Microfacies analysis of the Turonian succession in the study area (Wadi As Sir Limestone Formation) led to the recognition of four types of microfacies, namely the Bioclastic Wackestone-Biomicrite, Bioclastic Mudstone-Biomicrite, Bioclastic Packestone-Biosparite, and Bioclastic Grainstone-Biosparite (Figure 11) that change laterally as well as vertically. Based on the grain composition (mainly fossil types) and the content of the matrix. Paleoenvironmental interpretation of each microfacies as follows;

Starting with the base of Wadi As Sir Limestone Formation (in the study area), the lowermost 7.7 m thickness consists of Bioclastic Wackestone microfacies, including bivalves, gastropods, echinoderms, pelecypods, peloids, and fossil ostracodes. Wackestone facies, stromatolites, rudist fragments, and other fossils suggest deposition under low energy conditions, salinity, as well as oxygenation, are subject to highly variable, restricted circulation shelves, most likely lagoon environments. The lagoon is a shallow coastal water body separated from the ocean by a barrier, intermittently connected to an ocean exchange by one or more restricted inlets, usually oriented parallel-shore [24]. In general, relatively shallow environments are approximately 50 meters deep and moderate in water energy, temperature, and salinity.

Bioclastic packestone microfacies found in the third part of the section with a thickness of 7.6 m. This type of microfacies is widespread in the Middle East in strata of different geological ages [25], and the type of fossils in this facies suggest that deposition was in shallow, warm, and restricted environments.

The top of the section was a microfacies of Bioclastic grainstone, 4.8 m thick, consisting mainly of fossils, suggesting that it is a result of relatively high energy environments. Current activity is responsible for reworking the underling sediments, and for creating new grains of sediments.

The findings in the present study identified various types of Microfacies, such variations represent a shift in the environmental deposition. Several variables influence the sedimentary environment as a whole, such as water energy, depth, temperature, and salinity. The Wadi as Sir Limestone Formation deposited in shallow shelf environments-back reef (lagoon), moderate saline, and varying energy levels based on the present study [26]. This may mean that a sea level fluctuation during the period of deposition was possibly causing upliftment and subsidence.

The second part of the section in Wadi As Sir Limestone Formation was a bioclastic mudstone microfacies with a thickness of 9.9 m, it indicates deposition in shallow water environments, and a large amount of micrite suggested deposition in low energy conditions and restricted circulation.

Depositional models usually derived from sedimentary environments and can be used for comparison with other ecosystems or systems. Vertical and lateral microfacies and fossil changes in the study area indicated the initiation of the deposition of Wadi as Sir Limestone Formation in the lagoon environment as a consequence of the withdrawal of the sea from the northern part of the study area and its retreat from the east; (Figure 12).

This assumption confirmed by the existence of peloid, microfossils, gastropods, bivalves, pelecypods, echinoderms, and ostracods. Peloids in some varieties of microfacies indicate a shift from low to high energy environments [27]. The lateral distribution of depositional facies relies on the depositional setting, whereas their vertical piling determined by the fluctuation of the sea level, shown in the stratigraphic sequence [28].

The variability of microfacies types in the study area correlated with previous studies showing that the Tethys Ocean has spread and filled both of these areas. The paleodepositional environment in the present study is in accordance with [4] who proposed that the Wadi as Sir Formation (Upper Cretaceous) depositional environment was lagoonal but towards the end of the period in which open shelf conditions prevailed. Correspond to [5] who suggested that the depositional environment of Wadi as Sir Formation was in a shallow marine environment except for the lower part deposited in the outer open sea shelf.

Ref. [1] [19] who proposed that the Wadi As Sir Formation deposited in shallow epicontinental seas and wide shallow carbonate platform. The aforementioned general interpretation may usually agree with, in the case that they used it on a basis for deposition in shallow neritic shelf seas on a platform.