Introduction

Tayiba Formation has a considerable importance to the history of the opening of the Red Sea and the Gulf of Suez. This formation represented a transitional stage between the pre-rifting Eocene marine sediments and the Early Miocene transgression of the newly formed rift (Refaat and Imam 1999).

Lithostratigraphically, the exposed Eocene successions in the south-western part of Sinai are mainly carbonate. The Eocene succession thickness recorded at Wadi Tayiba is about 152 m (Ibrahim et al. 2016).

Tayiba Formation is located at the mouth of Wadi El-Tayiba. It unconformably overlies the Late Eocene Tanka Formation (interbedded chalky limestone and shale with argillaceous limestone) and unconformably underlies the Early Miocene Nukhul Formation. This is significant with polymictic conglomerate beds characteristic of the unconformable surfaces (El Barkooky and El-Araby 1999). Also, they mentioned which conformable up change from shallow marine carbonates (Tanka Formation) to tidally influenced shallow marine clastics and carbonates (Tayiba Formation) indicate a swallowing of water depth during the Late Oligocene. Jackson et al. (2006) revealed that the Tayiba Formation represented slight changes in relative sea level. In addition, Van Wagoner et al. (1988) mentioned that the eustatically or tectonically driven sea-level drop leads to the pre-rift/syn-rift contact unconformity. Refaat and Imam (1999) mentioned that at Wadi El-Tayiba, the Tayiba Formation is composed of marine, yellow red siltstone and mudstone, alternating with reddish-yellow and grayish argillaceous to sandy limestone, highly fossiliferous with reworked Nummulites spp. and molluscan shell fragments.

Materials and methods

Fifteen representative samples were collected from the carbonate rocks of Abu Zenima, Tayiba Formation in West Central Sinai. Mineralogically, three selected samples were investigated by the X-ray technique at the Egyptian Mineral Resources Authority (Dokki, Egypt) using a PAN analytical X-Ray Diffraction equipment model X′Pert PRO with Secondary Monochromator; Cu-radiation (λ = 1.542 Å) at 45 K.V., 35 M.A., and scanning speed 0.02°/s were used. The diffraction charts and relative intensities are compared with ICDD files. Eight samples were selected to determine the chemical composition by using Axios Sequential WD_XRF Spectrometer, Analytical 2005 in the National Research Center laboratories. ASTM E 1621 standard guide for elemental analysis by wavelength dispersive X-Ray Fluorescence Spectrometer, and ASTM D 7348 standard test methods for loss of ignition (LOI) of solid combustion. The fabric and the size of the synthesized samples were characterized via SEM coupled with energy-dispersive spectroscopy EDAX (SEM Model Quanta FEG 250), carried out in the National Research Center laboratories. The samples were selected based on their hand specimen description to represent the formation for chemical and mineralogical studies.

Geologic setting

Abu Zenima area is located on the eastern part of the Gulf of Suez, west-central Sinai (Fig. 1). The stratigraphical sequence ranges in age from late Cretaceous to middle Miocene. In Abu Zenima area, the Tayiba Red Beds (Hume et al. 1920) or Tayiba Formation (Youssef and Abdel Malik 1969) consists generally of red shale and sandstone with polymictic conglomerate and subordinate argillaceous to sandy limestone beds. Two major unconformity surfaces are represented with obvious basal polymictic conglomerate beds. This formation was underlying the Middle Eocene Tanka Formation and overlying the Early Miocene Abu Zenima Formation. Wadi Tayiba is located about 2 km north of the village of Abu Zenima.

Fig. 1
figure 1

Photograph stratigraphic correlation through the Wadi Tayiba. Modified from Jackson et al. (2006)

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All previous studies indicate that the oldest pre-rift unit in the Wadi Tayiba is the Upper Eocene Tanka Formation, which consists of micritic, pelletoidal limestones, containing a range of shallow water benthic foraminifera (e.g., Quingelocuina sp.) According to the faunal assemblage, the Tanka Formation was deposited on a carbonate platform in an upper shelf environment (Abul-Nasr and Thunell 1987).

Late pre-rift marine carbonates, mudstones and sandstones of the Thebes, Khaboba, Tanka and Tayiba formations are erosively overlain by alluvial and volcanic deposits of the early syn-rift Abu Zenima Formation transversely a major sequence boundary (Jackson et al. 2006) (Fig. 2).

Fig. 2
figure 2

Photograph map SE showing the stratigraphic section at the entrance to Wadi Tayiba, appearance Thebes, Khaboba, Tanka and Tayiba formations overlain by alluvial and volcanic deposits of the early syn-rift Abu Zenima Formation across a major sequence boundary (after Christopher Aiden-Lee)

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The aim of the present work is to study the mineral and chemical composition of the carbonate rocks of the Tayiba Formation (Upper Eocene) in Abu Zenima area to reveal their depositional environments and if there is a possibility of utilizing them in some purposes.

Results

Chemically, the studied samples composed mainly of CaO (26.39%), SiO2 (25.93%), Al2O3 (10.67%), Fe2O3 (3.13%), MgO (1.88%), and Na2O (1.26%). Mineralogically, the studied carbonate rocks at Tayiba Formation, Upper Eocene, Abu Zenima area, are consisting of calcite and dolomite as well as clay minerals. Dolomitization was the main diagenetic features encountered in the carbonate rocks of Tayiba Formation. Table 1 shows the chemical analysis data for major, trace, and rare earth elements of the studied carbonate rocks and the relation between them quoted in Table 2.

Table 1 Concentration of major (%), trace, and rare earth elements (ppm) of the studied carbonate rocks as well as ratios
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Table 2 Correlation matrix between the studied elements
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Discussion

Mineralogy

X-ray diffraction XRD analyses were carried out on some selected samples. X-ray patterns revealed that the dominating minerals in the studied samples are mainly dolomite and calcite, quartz in addition to clay minerals.

Geochemistry

Major elements

Chemical analysis data of major, trace, and rare earth elements are quoted in Table 1. The normative dolomite content of the studied samples ranges from 4.3 to 11.44%, averaging 8.61%. Calcite precipitated from seawater would contain from 5.9 to 27.1% MgCO3 by weight, while calcite exposed to meteoric water diagenesis will lose most of its magnesium content (Moore, 1989 and Morse and Mackenzie, 1990). The studied carbonate rocks contain up to 8.67% MgCO3 and 6.52%, in average. This value revealed that the studied calcite was subjected to progressive diagenesis. MgO content varies from 0.94 to 2.5%. The terminal parts of the studied Tayiba Formation are more dolomitized relative to the middle beds. Though, it seems more eligible that the dolomitization process is controlled by the fracture and joint systems in the area, which maintain access to the dolomitizing fluids. Consequently, the dolomitization process was controlled by the fracture and joint in the area, which preserve access to the dolomitizing fluids. This result agrees with X-ray results.

SiO2 content in the studied samples ranges from 24.7 to 27.37% with an average of 25.93%. Al2O3 content ranges from 9.85 to 12.15% with an average 10.67% (Table 1). The carbonate rocks of the studied succession record average 1.26 and 0.69%, respectively of Na2O and K2O. The positive relation between SiO2 and both Al2O3 and K2O (Table 2) can mainly be attributed to the clay content, which is detected by X-ray diffraction analysis. The Eocene marine basin of deposition was relatively alkaline, close to the landmass that supplied the basin of deposition by quartz and clays (Ibrahim et al. 2016).

Fe2O3 content of the studied carbonate sediments ranges from 2.15 to 3.54%, averaging 3.13%. The values for the Tayiba dolomite indicate the formation of dolomite in the near-surface oxidizing environment (Choquette and James, 1990, Loukina and Abou El-Anwar 1994 and Abou El-Anwar 2006 and Abou El-Anwar 2011). The positive correlation between Fe2O3 and SiO2 (r = 0.56), suggests that iron is not completely associated with the terrigenous admixture but is rather a pigment. Also, the strong negative correlation between Fe2O3 and Sr (r = − 0.90) indicates that there is no essential function of many microbes (Abou El-Anwar 2005, 2011, 2014 and Abou El-Anwar 2018a and Abou El-Anwar et al. 2017 and Abou El-Anwar 2018a, 2018b).

The strontium content of the studied carbonate rocks in the studied samples ranges from 964 to 1522 ppm, averaging 1099 ppm, which indicate late diagenetic resulting of dolomitization process (Veizer, et al., 1978 and Tucker and Wright 1990). The positive correlation between Sr and Ca (r = 0.56) signified that calcite is still the main host of strontium in the studied carbonates (Table 2). The values of Sr content can be attributed to the long diagenetic history particularly the dolomitization stages. This agrees with the findings of Brand and Veizer (1980) and Abou El-Anwar (2005 and 2006).

The average Sr content suggests that the dolomitization process has taken place in marine environment (Brand and Veizer 1980 and Abou El-Anwar 2011). The strong negative correlation between Sr and Na (r = − 0.15) indicates that Na does not couple with Sr during dolomitization. This is in disagreement with Moore and Chowdhury (1988), Loukina, et al., (2001), and Abou El-Anwar (2005 and 2006).

Trace and rare earth elements

Geochemical tools are used to identify and construe the parameters of normal environmental and origin. Thus, trace and REE elements are the most geochemical parameters that can be used to illustrate the paleo-climatic environments (Veizer and Mackenzie 2014 and Kamber, et al., 2014).

Carbonate rocks in the Tayiba Formation, Abu Zenima region, are highly enriched in trace elements (Zn = 132.6, Ni = 66.3, I = 27.8, and Mo = 5.1, ppm, Table 1 and Fig. 3) and highly to moderately rare earth elements (La = 31.5, Sc = 28, Y = 23, Sm = 20.1, W = 17.3, Nb = 16, Cs = 7.6, As = 5.5, Sb = 4.2, and Ta = 3.5 ppm, Fig. 4) compared with those of the UCC (Rudnick and Gao 2003).

Fig. 3
figure 3

The concentration of the trace elements of the studied carbonate rocks compared with the UCC (Rudnick and Gao 2003)

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Fig. 4
figure 4

The concentration of the rare earth elements of the studied carbonate rocks compared with the UCC (Rudnick and Gao 2003)

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The strong and moderate positive correlations between Al2O3 and all immobile elements of trace and rare earth elements (Table 2) reveal that these elements are concentrated during weathering processes (Fedo et al. 1996). Almost all the trace and rare earth elements show positive relation with each other in the study carbonate rocks. Thus, these elements may be associated with each other or with the heavy minerals rather than with dolomite and clay minerals (Abou El-Anwar 2018b).

The radioactivity elements in the studied carbonate rocks are ranging from 1.1 to 3.4 with average 2.05 ppm for U and from 7.9 to 10.8 ppm for Th. Therefore, these contents are less than the allowed limits for radioactivity elements of carbonates. Thus, the studied carbonate rocks can be used in cement industries and as building stones (de Silva et al. 2010, Abou El-Anwar et al. 2017 and Abou El-Anwar 2018a).

Environmental condition

Al and Mg oxides are important scavengers for trace and REEs, which observed by the positive correlation among them and Al2O3 and MgO. This finding indicates that the distribution of trace and REEs in the studied carbonate rocks is partly controlled by clays and dolomites.

Pi et al. (2014) mentioned that the content of redox-sensitive elements; V, Ni, Mo, U, Cu, Cr, Re, Cd, Sb, Tl, and Mn can be used to indicate paleo-oceanographic environments. The V/Mo and V/(V + Cr) ratios (14.74 and 0.6, respectively) Table 1 indicates that the studied carbonate rocks were deposited in oxic environments (cf. Gallego-Torres et al. 2010; Pi et al. 2014 and Abou El-Anwar 2018a). U/Mo ratio (0.37) indicates the rocks of the studied area were deposited under an oxic marine transgressive condition (Arning et al. 2009 and Abou El-Anwar 2018b). Depletion of Ce (average = 22.1 ppm) indicated an anoxic environment (De Baar, et al., 1988). Consequently, the studied rocks deposited under anoxic to oxic environment.

The degree of digenesis can be increased during meteoric and burial diagenesis which was accompanied with loss of U (under oxic conditions), and increase of Zn, Mn, and Fe (Halverson et al. 2007; Webb et al. 2009). Thus, depletion of U and enrichment of Zn and Fe revealed that the deposition of the studied carbonates took place under oxic environment. In addition high content of Sr, Zn, and Ni as trace elements indicated that these carbonate rocks deposited in marine environments.

Provence of carbonates

Some of the elements are used to distinguish between deposits formed in freshwater, shallow-marine, and marine environments, as well as precipitated under surface or deeper condition. In addition to the rare earth elements, hydrogenous deposits show high ΣREE and those of hydrothermal deposits are considerably lower (Usui and Someya 1997). The studied carbonate rocks show high ΣREE (average of 426 ppm), compared with those of the total in average of continental crust which is about 125 ppm (Rudnick and Gao 2003). Moreover, Si–Al discrimination diagram (Fig. 5) and the (Ni + Co) against (As+Cu+Mo+Pb+V+Zn) as a binary diagram (Fig. 6) according to Choi and Hariya (1992) and Nicholson (1992), respectively, indicated that the studied rocks are mainly hydrogenous sources. Low La/Ce ratios (1.42) and LREE enriched are suggest hydrogenous the origin of the studied carbonate rocks which conformed with Figs. 5 and 6 (Nath et al. 1997).

Fig. 5
figure 5

Si–Al plot diagram after Choi and Hariya (1992)

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Fig. 6
figure 6

(Ni + Co) versus (As + Cu + Mo + V + Zn) plot diagram after Nicholson (19 92)

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Trace and rare earth element geochemistry can be used as a tool for sediment provenance (Hu, et al., 2017). The elements such as Cr, Sc, Ta, Th, Zr, Hf, As, and Sb, as well as Y and the rare earth elements (REEs), La to Lu have little mobility in low-temperature, near-surface environments, Thus, they can be useful tool for sediment provenance. Fe and Cr enrichment in pyroxenes and chromite, Sc present in pyroxenes, micas, amphiboles, titanite, and clay minerals, Ti and Ta are found in ilmenite, pyroxene, hornblende, and biotite. Th and Ta can be hosted in micas, amphiboles, zircon, sphene, and clay minerals; Zr and Hf are associated with zircon, As, and Sb most likely occurring as substitutes for Fe in magnetite; Sc is enriched in pyroxenes; and Th and La are enriched in granitic rocks. As a result, the trace and rare earth elements in the studied carbonate rocks may be derived from more mafic near sources.

The average of LREE enrichment than HREE (~ 102 and 51 ppm, respectively) and the LREE/HREE ratio (2.00) indicated the effect of weathering process on the REE fractionation in the studied carbonate rocks. Thus, the low mobility of LREE than HREE leads to the LREE enrichment, while HREE depletion accompanying with increase weathering effect (Yusoff et al. 2013 and Cao, et al., 2016). Therefore, it is in compatible to the general distribution of REEs in limestone (Gromet et al. 1984; Condie 1991 and Ketris and Yudovich 2009).

The values of the La, Cs, Sc, and Ga indicated that the investigated carbonate rocks were deposited in marine environment (Alibo and Nozaki 1999).

Conclusions

The closed correlation between the contents of REE and those of Al, Ca, and Mg is probably due to the vigorous role of calcite, dolomites, and clay minerals in the transfer of REE in the carbonate rocks of Tayiba Formation (Upper Eocene) in Abu Zenima area, West Central Sinai. The studied carbonate rocks deposited under anoxic to oxic marine environments.

The low mobility of LREE than HREE in the studied carbonate rocks leads to the enrichment of LREE than HREE and complementary with increase weathering effect. The high concentration of the ΣREE and plot diagrams are indicated to hydrogenous source of the studied carbonate rocks.