Paleoenvironmental and paleoclimatic conditions during the deposition of the bauxite layer (Upper Cretaceous) using multi-proxy geochemical and palynological analyses, in the Zabirah Area, Northern Saudi Arabia

  • Madyan M.A. Yahya
  • Mohammed H. Hakimi
  • Mahmoud A. Galmed
  • Mohamed N. El-Sabrouty
  • Yasamin K. H. Ibrahim
Original Paper
  • 100 Downloads

Abstract

In this research, Cretaceous claystones in the Az Zabirah area, Northern Saudi Arabia were evaluated to investigate the paleoenvironmental and paleoclimatic conditions during deposition of the claystone sediments. Outcrop samples of claystone from the bauxite zone profile in the Az Zabirah area were analyzed using multi-proxy geochemical and coupled with palynological analysis. Palynological analysis suggested that the age of the Az Zabirah claystones is Maastrichtian of Upper Cretaceous. This evidence is valid due to the presence of microspore taxa Gabonisporis sp. The Az Zabirah claystones have abundant angiosperm taxa, indicating a large terrestrial influx in the interval of the claystone. This finding is confirmed from geochemistry of major and trace elements and mineral compositions. The high concentration of terrestrial detritus oxides, such as SiO2, Al2O3, and TiO2, infers that the Az Zabirah claystones were sourced from terrigenous origin. This is consistent with a significant amount of quartz and kaolinite in the Az Zabirah claystones. The claystones could be deposited under oxic paleo-redox and warm-humid with little aridity climatic conditions. This is indicated by their concentration of the trace element concentrations along with their geochemical ratios. Warm-humid climate condition is also largely supported by the presence of a significant amount of kaolinite.

Keywords

Claystone Cretaceous Az Zabirah area Palynology Geochemistry paleoenvironmental Paleoclimate Northern Saudi Arabia 

Introduction

The dataset used herein is from Az Zabirah area in the Ha’il province, Northern Saudi Arabia (Fig. 1). The research area occupies the north part of Saudi Arabia, which lies between 27° 35′ N and 27° 40′ N and 44° 00′ E and 44° 7′ E (Fig. 1) and has an elevation of 628 m above sea level. The Az Zabirah area is located at about 150 km southwest of the Trans-Arabian pipeline (TAP line) and approximately 180 km north of the town of Buraydah the capital city of Al Qassim province in the northeastern region of Saudi Arabia. The Az Zabirah section also lies at about 484 km northwest from the capital of Saudi Arabia, Riyadh (Fig. 1).
Fig 1

Geological map of the Ha’il province, Northern Saudi Arabia, inclusing the study area (Az Zabirah)

Palynological research has gained the distinction of scientific discipline since the decade of 90s,, especially after the remarkable studies of the Swedish geologist Lennart von Post. His pioneer works include the pollen diagrams that assisted in the count and identification of pollen grains from the deposits of peat (Stricto and Lato, 2015).

In view of the exploration of bauxite ore deposit, the Az Zabirah area of Saudi Arabia has attracted the attention of several researchers and explorers (e.g., Al-Bassam, 2005; Al-Mesbah, 2009). However, palynological research of the Cretaceous claystone in the Az Zabirah area has not been reported yet in any of the previous literature. Thus, there is a prominent knowledge gap in the paleoenvironmental and paleoclimatic conditions that prevailed during the deposition of the these claystones. This study aims to make integration between the palynology and inorganic geochemistry to provide a multi-scale view and increase the knowledge about the mineralogy and chemical composition of sedimentary strata and their related depositional environment and paleoclimate conditions in the Az Zabirah area.

Geologic setting

The Az Zabirah bauxite deposit is part of the outcrop of the Stable Shelf of the Arabian Platform, which has not been subjected to major tectonic disturbance since the Cambrian (Powers et a1., 1966). The Az Zabirah bauxite deposits have an overall strike length of approximately 105 km, trending northwest-southeast direction, with an identified width of 5 km. It comprises of three main geographic zones, South zone, Central zone, and the North zone, with each zone being approximately 30 km long (Al-Mesbah, 2009). The stratigraphic sequence exposed in the Az Zabirah area has been grouped into four lithostratigraphic sequences ranging in age from Triassic to Quaternary (Fig. 2). The lower part of the lithostratigraphic sequences is represented by non-marine sandstones of the Manjur Formation. The Manjur sandstone is overlain conformably by Jurassic units. The Jurassic units are composed of carbonates of the Marrat and Dhruma Formations that are in turn overlain conformably by Cretaceous rocks.
Fig. 2

Regional stratigraphic section in the Az Zabirah bauxite area (Black et al., 1982; Bowden, 1981) showing the location of the studied bauxite profile

The lower part of the Cretaceous is represented by Biyadh Sandstone Formation, attaining a thickness of about approximately 5 m. The Biyadh Formation comprises primarily of fine-grained, well-bedded sandstone (15–20 cm) with either a kaolinitic, hematitic, or siliceous matrix (Al-Mesbah, 2009). The Biyadh Sandstones are overlain by the Bauxite deposit zone (Fig. 2). The Bauxite deposit zone comprises mainly of bauxite ore deposit and claystone layers, which are divided into lower and upper clay zones. The lower clay zone is in fact a transition zone between the bauxite ore deposits and the underlying unaltered parent rock, and both of their character and the textures are determined by the permeability of the parent rock. In the case of the permeable sandstone of parent rock, there is a gradual downward transition from sparsely pisolitic, bauxitic clay, kaolinitic clay to unaltered bedrock. In contrast, the upper clay zone capped the bauxite zone. The top of the upper clay zone consists of white claystone, with cuspate, buff-colored flecks, known as flecked clay (Fig. 2). Electron microscope studies show that the buff-colored flecks are titanium rich (Laville, 1982). These claystones of the upper clay zone are target of the present research. The bauxite ore layer zone is characterized by its pisolitic textures and constitutes the potentially economic portion of the Bauxite Zone in the study area. The contact of this zone with the overlying clay zone is relatively sharp with a fairly uneven surface. The pisolitic bauxite zone is generally hard and compact and exhibits a wide variety of pisolitic bauxite textures. It attains a thickness of 6 m in the study area, Az Zabirah, where it was developed into two different rock types (Bowden, 1981; Black et al., 1982). The rocks overlying the bauxite zone belong to the Upper Cretaceous Wasia Formation (Albian to Turonian). The Wasia Formation in the Az Zabirah area can be subdivided into three units: lower, middle, and upper. The lower Wasia Formation immediately overlies the bauxite zone and comprises of fluviatile sandstone, minor siltstone, and lagoonal mudstone; the latter becomes carbonaceous and pyritised where intersected in drill holes below the oxidation zone. The palynology of the carbonaceous mudstone member, which immediately overlies the bauxite, indicates an Albian to Cenomanian age for this mudstone (von A1men, 1983; Fauconnier, 1981, 1982). Also, the Foraminifera of a persistent carbonate marker bed in the middle Wasia Formation, some 40 m above the bauxite, has been definitely dated as Cenomanian (von Almen, 1982; Premo1i-Silva, 1982). The Wasia sediments are themselves overlain by the Late Cretaceous limestone of the Aruma Formation (Fig. 2). This Late Cretaceous limestone of the Aruma Formation is covered by Quaternary deposits, which are composed of unconsolidated Wadi sediments.

Samples and methods

A total of nine outcrop claystone samples were collected from the exposed section of the Bauxite ore deposit layer in the Az Zabirah area, Northern Saudi Arabia (Fig. 2). The samples were collected from a channel after removing the weathered surfaces by digging to about 0.5 m. All the claystone samples were subjected to palynological, X-ray diffraction (XRD), and X-ray fluorescence (XRF) spectrometry analyses.

For palynological analysis, the claystone samples were treated with HCl and HF following the standard procedure outlined by Durand and Nicaise (1980) and Saxby (1970). After each treatment, the residue was washed with distilled water until the pH is 7. Hot HCl (30%) was added after the removal of HF and subsequent rinsing, in order to dissolve any possible insoluble neo-fluorides and fluorosilicates formed during the HF–silicate reaction (Durand and Nicaise, 1980; Ercegovac et al., 1997). The spore and pollen were separated from the remaining residue (containing pyrite and other insoluble heavy minerals) by gravity separation, using ZnCl2 solution (specific gravity ~ 2). The resulting spore and pollen concentrate was sequentially treated with 20% HCl then washed with distilled water and set aside for palynological slide preparation. The palynological slides were studied by scanning electron microscope (SEM) to identify the present spore and pollen.

The SEM (JSM-6380 LA) of high performance Kevex-Ray unit was used in order to help in the identification of the palynomorphs (e.g., spores and pollen). The palynomorphs were prepared for the SEM research by picking up the palynomorphs with aid of a clean pipette. Then, they were deposited on glass slides (32/22 mm) and covered by the cover slide and sealed with paraffin. The slides that separate each palynomorph are picked up and placed on the slide in a drop of distilled water. Glycerine was also used for a good observation in MEB. The palynomorphs were then transferred on aluminum alloy in a vacuum evaporator, for transmission electron microscopy. Finally, the palynomorphs were placed directly on an agar cub, covered with an additional agar drop, and then impregnated with an epoxy resin for ultra-microtone sectioning. These tasks of SEM analysis have been carried out in the Research Center, College of Science, King Saud University.

XRD and XRF spectrometry analyses were carried out on the bulk sediment samples after crushing them to less than 200 mesh. In order to facilitate an accurate mineral identification, XRD analysis was performed on the powdered sample using SIEMENS D5000 X-ray diffractometer. XRF is also the method of choice for the analysis of claystone samples throughout the industry. This XRF analysis was used to determine the oxides of major elements such as SiO2, Al2O3, CaO, K2O, Na2O, Fe2O3, MnO, MgO, TiO2, and P2O5. The XRF analysis is determined in conjunction with a loss-on-ignition at 1000 °C. The data may be normalized (except for the LOI) if required, before the final results are reported. Moreover, concentrations of the trace elements within the studied claystone samples were also determined using an XRF spectrometer. The X-ray fluorescence analysis was conducted at “ALS” Arabia Laboratory at Jeddah, Saudi Arabia.

Results and discussions

Palynological characteristics

On the basis of palynological determinations, the claystone of the Az Zabirah area belongs to the of Maastrichtian age. This is suggested by the presence of the palynomorph taxa such as Gabonisporis sp. (Figs. 1, 2, 5, 6, 9, and 10 of Plate Plate I). The palynological analysis indicates a strong predominance of land-derived microspores. The high abundance of angiosperm taxa suggests that the Az Zabirah claystones were deposited in a terrestrial environment under probably an oxic conditions. The common angiosperm taxa of the terrestrial origin are Gabonisporis bacaricumulus, Hannisporis scollardensis, Dictyophyllidites harrissi, Heliosporites kemensis, Heliosporites altmarkensis, Matonisporites phlebopteroids, Radialisporis radiatus, Retitriletes austroclavatidites, Retitriletes nidus, Triporoletes stellatus, Triporoletes tympanoideus, Trochicola scollardiana, Taxodiaceaepollenites distichiforme, Aquilapollenites pachypolus, Aquilapollenites proteus, Polyvestibulopollenites verus, Simpsonipollis mullensis, Tricolpites dubhensis, and Triporopollenites mullensis (see Plates Plate I, Plate II, Plate III, Plate IV, and Plate V).
Plate I

Spores. Figs. 1, 2, 5, 6, 9, and10: Gabonisporis bacaricumulus. SEM figure magnified ×1500, photomicrograph showing distal face. SEM figure magnified ×4500, photomicrograph showing details of sculpture with damaged area. SEM figure magnified ×1500, photomicrograph showing distal face. SEM figure magnified ×4500, photomicrograph showing details of sculpture with damaged area. SEM figure magnified ×1500, photomicrograph showing distal face. SEM figure magnified ×4500, photomicrograph showing details of sculpture with damaged area. Figures 3 and 4: Hannisporis scollardensis. SEM figure magnified ×1500, photomicrograph showing pattern of muri on proximal face with damaged exine. SEM figure magnified ×1500, photomicrograph showing granular sclerine on distal face with damaged exine. Figure 7: Dictyophyllidites harrisii. SEM figure magnified ×1500, photomicrograph showing lateral view of specimen with damaged exine. Figure 8: Heliosporites kemensis. SEM figure magnified ×1500, photomicrograph showing proximal face with damaged exine. Figures 11 and 12: Matonisporites phlebopteroides. Figures 11 and 12: SEM figure magnified ×1500, photomicrograph showing smooth exine with damage

Plate II

Sporse. Figures 1, 2, 5, and 6: Heliosporites kemensis. SEM figure magnified ×1500, photomicrograph showing of a tetrad. SEM figure magnified ×3000, photomicrograph showing details of exine sculpture with damaged area. SEM figure magnified ×1500, photomicrograph showing of a tetrad. SEM figure magnified ×3000, photomicrograph showing details of exine sculpture with damaged area. Figures 9 and 10: Heliosporites altmarkensis. Figure 9: SEM figure magnified ×1500, photomicrograph showing a tetrad. Figure 10: SEM figure magnified × 3000, photomicrograph showing details of exine sculpture with damaged area. Figures 3 and 4 Radialisporis radiatus. SEM figure magnified ×2000, photomicrograph showing pattern of distal face with damaged exine. SEM figure magnified ×1500, photomicrograph showing granular proximal face with damaged exine. Figures 7 and 8: Retitriletes austroclavatidites. SEM figure magnified ×2000, photomicrograph showing reticulate sculpture on distal face with damaged exine. SEM figure magnified ×6000, photomicrograph showing details of reticulate sculpture on distal face with damaged exine. Figures 11–12: Retitriletes nidus. SEM figure magnified ×1500, photomicrograph showing proximal face with damaged exine. SEM figure magnified ×2000, photomicrograph showing distal face with damaged exine

Plate III

Spores. Figures 1, 2, 5, 6, 9, and 10: Triporoletes stellatus. SEM figure magnified ×1500, photomicrograph showing pattern of proximal face. SEM figure magnified ×2000, photomicrograph showing details of sclerine on and around tetrad-mark with damaged area. SEM figure magnified ×1500, photomicrograph showing proximal face. SEM figure magnified ×3000, photomicrograph showing details of proximal sculpture and tetrad-mark with damaged area. SEM figure magnified ×1500, photomicrograph of a broken specimen showing distal face. SEM figure magnified ×3000, photomicrograph showing details of wall structure with damaged area. Figures 3 and 4: Triporoletes stellatus. SEM figure magnified ×1500, photomicrograph in oblique view. SEM figure magnified ×3000, photomicrograph showing details of sclerine at equatorial margin. Figures 7 and 8: Triporoletes tympanoideus. SEM figure magnified ×1500, photomicrograph showing pattern of proximal face. SEM figure magnified ×10,000, photomicrograph showing details of tetrad-mark and proximal sclerine with damaged area. Figures 11 and 12: Trochicola scollardiana. SEM figure magnified ×1500, photomicrograph showing distal face. SEM figure magnified ×10,000, photomicrograph showing details of of exine invagination in radial areas with damage

Plate IV

Pollen grains. Figures 1, 2, 5, and 6: Taxodiaceaepollenites distichiforme. SEM figure magnified ×1500, photomicrograph showing the split and the position of ligula at the point marked. SEM figure magnified ×3000, photomicrograph showing details of damaged exine. SEM figure magnified ×1500, photomicrograph showing ligula is situated at the end of split. SEM figure magnified ×3000, photomicrograph showing details damaged exine. Figures 9 and 10 Aquilapollenites pachypolus. SEM figure magnified ×1500, photomicrograph showing a part of a broken specimen with inner smooth surface and exine layers. SEM figure magnified ×3000, photomicrograph showing details of the exine layers showing a thickened nexine at the contact area of the equatorial and polar projections, baculate and tegillate layer of the sexine with damaged area. Figures 3, 4, 7, and 8: Aquilapollenites proteus. SEM figure magnified ×1500, photomicrograph showing a complete specimen in equatorial view. SEM figure magnified ×3000, photomicrograph showing details of exine in polar view with an abnormal spinule. SEM figure magnified ×1500, photomicrograph showing a complete specimen in an oblique equatorial view. SEM figure magnified ×3000, photomicrograph showing details of exine on polar projection with occasional punctuate at the base of spinules. Figures 11 and 12: Polyvestibulopollenites verus. SEM figure magnified ×1500, photomicrograph showing of a specimen in polar view and details of exine surface. SEM figure magnified ×3000, photomicrograph showing details of the exine with damaged area

Plate V

Pollen grains. Figures 1 and 2: Polyvestibulopollenites verus. SEM figure magnified ×1500, photomicrograph showing a specimen in polar view and details of exine surface. SEM figure magnified ×3000, photomicrograph showing details of the exine with damaged area. Figures 5, 6, 9, and 10: Simpsonipollis mullensis. SEM figure magnified ×1500, photomicrograph showing a specimen in equatorial view. SEM figure magnified ×3000, photomicrograph showing details of exine in with damaged area. SEM figure magnified ×1500, photomicrograph showing a tetracolporate specimen in polar view. SEM figure magnified ×3000, photomicrograph showing details of exine with damaged area. Figures 3, 4, 7, and 8: Tricolpites dubhensis. SEM figure magnified ×1500, photomicrograph showing a complete specimen in polar view. SEM figure magnified ×3000, photomicrograph showing details of exine on polar view with damaged area. SEM figure magnified ×1500, photomicrograph showing a complete specimen in polar view. SEM figure magnified ×3000, photomicrograph showing details of exine on polar view with damaged area. Figures 11 and 12: Triporopollenites mullensis. SEM figure magnified ×1500, photomicrograph showing of a specimen in polar view. SEM figure magnified ×3000, photomicrograph showing details of the exine on polar view with damaged area

Mineral composition characteristics

The XRD analysis revealed that the Cretaceous claystones in the Az Zabirah area consist of clay minerals, which are mainly of kaolinite (Figs. 3 and 4). Non-clay minerals such as quartz, calcite, and goethite are also found (Fig. 3). The XRD results are generally compatible with the chemical analysis data and the mineralogical variations comparable with the major element compositions (see Section 4.3). The higher amounts of detrital kaolinite in the studied claystones indicate the prevalence of a humid-warm climate (Chamley, 1989). The presence of iron minerals like goethite (Fig. 3) indicates that the studied claystones were formed under suitable Eh–pH conditions (Karadag et al., 2009). Calcite is also present in the studied claystones (Fig. 3) as filling components for cavities and cracks that developed during and after bauxitization. In addition, non-clay minerals such as quartz are land-derived detritus.
Fig. 3

X-ray diffractograms of the some claystones in the Az Zabirah showing the presence of quartz (Q), goethite (Ga), gibbsite (G), calcium carbonate (Ca), and kaolinite (K)

Fig. 4

X-ray diffractograms and SEM image of the one claystone samples with rich kaolinite (K)

Geochemistry of elements and oxides

In this study, inorganic geochemistry elements and oxides including total sulfur content, major oxides, and some trace elements of the analyzed claystone samples were measured, and derivative geochemical ratios were calculated as shown in Tables 1 and 2.
Table 1

Major (wt%) oxide elements with sulfur content (S wt%) of the Cretaceous claystones in the Az Zabirah

Sample ID

Minor oxide elements (wt%)

Geochemical ratios

Sulfur (S %)

SiO2

Al2O3

CaO

Fe2O3

MgO

TiO2

K2O

Na2O

P2O3

K/N

K/A

Ti/Al

Al + K + N

UPCZ1

41.1

28.8

23.1

4.5

0.82

1.4

0.09

0.03

0.06

3.0

0.003

0.05

28.9

0.06

UPCZ2

35.4

48.3

1.1

8.7

0.82

4.8

0.47

0.07

0.30

6.7

0.010

0.10

48.8

0.09

UPCZ3

35.8

37.3

0.5

20.2

0.61

3.5

1.08

0.34

0.38

3.2

0.029

0.09

38.7

0.21

UPCZ4

32.0

33.8

21.7

4.5

0.83

4.1

1.10

0.84

0.61

1.3

0.033

0.12

35.7

1.05

UPCZ5

49.9

42.4

0.5

2.1

0.81

4.0

0.19

0.06

0.04

3.2

0.004

0.09

42.7

0.03

UPCZ6

41.7

11.8

31.1

13.5

0.81

0.20

0.08

0.09

0.10

0.9

0.007

0.02

12.0

0.14

UPCZ7

57.2

6.0

0.4

35.0

0.86

0.20

0.05

0.06

0.07

0.8

0.008

0.03

6.1

0.06

UPCZ8

47.0

39.6

0.3

7.8

0.67

4.2

0.34

0.05

0.05

6.8

0.009

0.11

40.0

0.04

UPCZ9

48.9

8.2

22.0

19.8

0.39

0.40

0.02

0.07

0.10

0.3

0.002

0.05

8.3

1.18

Average

43.2

28.5

11.2

12.9

0.70

2.5

0.40

0.20

0.20

2.9

0.012

0.07

29.0

0.32

Al + K + N: (Al2O3 + K2O + Na2O), K/A: (K2O/Al2O3), K/N: (K2O/Na2O), Ti/Al: (TiO2/Al2O3)

The average values is presented in bold text

Table 2

Some trace elements (ppm) of the Cretaceous claystones in the Az Zabirah

Sample ID

Trace element compositions (in ppm)

Geochemical ratios

V

Co

Ni

Cu

Sr

Ba

Th

U

Ga

Ni/Co

Sr/Cu

UPCZ1

67

39

17

6

120

170

20

10

8

0.44

20.0

UPCZ2

150

9

17

12

263

100

30

< 10

10

1.89

21.9

UPCZ3

25

261

25

25

25

60

25

10

25

0.10

1.0

UPCZ4

149

24

22

18

583

80

20

< 10

10

0.92

32.4

UPCZ5

125

29

30

24

127

80

20

< 10

9

1.03

5.3

UPCZ6

33

10

1

2

166

30

30

< 10

9

0.10

83.0

UPCZ7

376

32

86

63

45

30

20

< 10

8

2.69

0.7

UPCZ8

119

10

12

8

41

20

20

< 10

10

1.20

5.1

UPCZ9

50

4

8

18

920

140

20

< 10

10

2.00

51.1

Average

121.6

46.4

24.2

19.6

254.4

78.9

22.8

8.8

11.0

1.2

24.5

The average values is presented in bold text

The sulfur (S wt%) content of the studied claystones is generally low and ranges from 0.03 to 1.18%, with an average value 0.32% (Table 1), suggesting that the claystones were likely to have been deposited in a principally non-marine environment and this is consistent with the interpretation of a freshwater environment (e.g., Berner and Raiswell, 1983; Wenger and Isaksen, 2002). However, there are different sources of sulfur (S), including inorganically and organically bound S (Urban et al., 1999). The low of organic matter in the analyzed claystones may indicate that the majority of sulfur is not associated with sedimentary organic matter (OM). Therefore, the total sulfur in the analyzed claystone samples is considered as a strong measure for the degree of marine influence than the organic or pyritic sulfur during the sediemnation.

In the current research, major element data in conjunction with mineralogical data may be used to establish the element–mineral associations for the Cretaceous claystones in the Az Zabirah area. Major oxides of the studied claystone samples and thier geochemical ratios are listed in Table 1. The claystone samples contain SiO2, Al2O3, Fe2O3, and CaO as dominant constituents with an average of 43.2, 28.5, 12.9, and 11.2 wt%, respectively (Table 1). Other major oxides such as K2O, TiO2, MgO, Na2O, and P2O3 are also present but in low concentrations (Table 1). The elements Si, Al, Ti, and K are mostly associated with quartz and clay minerals as identified by the XRD (Figs. 3 and 4).

SiO2 and Al2O3 showed highest concentrations in the studied samples with an average of 43.2 and 28.5 wt% (Table 1), which is consistent with the occurrence of quartz and clay minerals. The occurrence of quartz and clay minerals is confirmed by the XRD results (Figs. 3 and 4). The significant occurrence of SiO2 is considered as resultant of the detrital input due to the association of SiO2 with terrestrial detritus and coarser grained sediments in high energy environments (Ross and Bustin, 2009). In contrast, high amount of aluminum (Al2O3) is generally enriched in kaolinite (Hieronymus et al., 2001; Beckmann et al., 2005; Ratcliffe et al., 2010), while potassium (K2O) is associated with illite clay mineral (Ratcliffe et al., 2004, 2010). Therefore, the high aluminum (Al2O3) concentration in the studied claystone samples is explained by the presence of kaolinite clay mineral. The K/Al ratios in the Az Zabirah claystones are very low (0.002–0.033) and further indicate the occurrence of kaolinite mineral within studied claystones is higher than illite clay mineral as indicated by XRD analysis (Fig. 4). However, the high concentration of SiO2 and Al2O3 oxide elements could be referred to the input of detrital matter (Ross and Bustin 2009).

Iron oxide (Fe 2 O 3 ) was recorded as extraordinarily high concentrations in the claystone samples, ranging from 2.1 to 35.0 wt%. In these claystones, the high Fe2O3 is due to the presence of iron minerals like hematite and/or goethite, which likely formed under suitable Eh–pH conditions (Karadag et al., 2009). XRD analysis confirmed that high Fe concentration corresponds with the presence of goethite (Figs. 3 and 4), which is consistent with interbedded hematite and goethite associated with the bauxite zone profile of the Az Zabirah area (Fig. 2). In contrast, the low Fe is consistent with an increase of Al2O3 and clay minerals (e.g., kaolinite) and a decrease of hematite. This may be due to the dissolution of Fe under reducing conditions and to the simultaneous precipitation of clay minerals from silicic acid solution (Bardossy, 1982).

Calcium (CaO) generally showed low concentrations with highest values in some studied samples (Table 1). However, the highest concentrations of CaO in the studied samples are explained by the dominance of carbonate mineral (Fig. 3) that were developed during and after bauxitization as cement filling cavities and cracks.

Titanium oxide (TiO 2 ) is an important major oxide element in the Cretaceous claystones in the Az Zabirah with relatively high values in the range of 0.20 to 4.8 wt% (Table 1). Titanium is known to be associated with terrestrial detritus and coarser grained sediments deposited under high energy environments (Calvert et al., 1996; Ross and Bustin, 2009). Titanium and elements such as Si, Al, and K are also mostly associated with clay minerals. The high titanium in the claystones may indicate the occurrence of titanium (Ti) within clay lattices and a high input of detrital matter (Ross and Bustin, 2009). This is supported by relatively high Ti/Al ratios (0.02–0.12) and a very good positive correlation between TiO2 and Al2O3 (Fig. 5).
Fig. 5

Relationship between titanium (TiO2) and aluminum (Al2O3) in the studied claystone samples of Az Zabirah area

Certain trace elements of the Cretaceous claystones in the Az Zabirah area are also measured and listed in Table 2 along with thier several geochemical ratios. The trace element concentrations show that Sr, V, and Ba contents are prominent with average values of 254.4, 121.6, and 78.9 ppm, respectively, while Co, Ni, Th, Cu, Ga, and U have average values of 46.4, 24.2, 22.8, 19.6, 11.0, and 8.8 ppm, respectively (Table 2). These trace elements with their several geochemical ratios were used by many authors as indicators for paleo-redox and paleoclimatic conditions (e.g., Lerman, 1989; Barwise, 1990; Wang et al., 1997; Bechtel et al., 2001).

Vanadium (V) and nickel (Ni) are important indicators for the depositional environment and redox conditions during the depositional process (Barwise, 1990; Bechtel et al., 2001). In general, marine sediments have high concentration of Ni and V elements (Barwise, 1990), whereas terrestrial sediments have low metal contents (Wenger and Isaksen, 2002). The concentration of V and Ni elements in the studied claystones shows varied values, ranging from 25 to 376 and 1 to 86 ppm, respectively (Table 2). The relative proportions of V in combination with low Ni are a strongly argument for a terrestrial sedimentation under oxic conditions (Fig. 6).
Fig. 6

Cross-plot of vanadium versus nickel of the claystone samples of the Az Zabirah area (modified after Galarraga et al., 2008)

Thorium (Th) and uranium (U) were also used as sensitive indicators for paleo-redox conditions (Jones and Manning, 1994; Pattan and Pearce, 2009; Mohialdeen and Raza, 2013). Typically, U is enriched compared to Th when reducing conditions prevail (Pattan and Pearce, 2009). Values of the U greater than 10 may indicate reducing conditions, whereas a low U concentration (~ 4 ppm or less) is suggestive of oxic conditions (Pattan and Pearce, 2009). The U concentrations in the studied claystones range between 10 and less than 10 ppm (Table 2), suggesting oxic conditions, where high to moderate amount of oxygen is available during deposition of the claystones in the Az Zabirah area.

Cobalt (Co) is also an important trace element as a sensitive indicator for paleo-redox conditions (Jones and Manning, 1994). Co is usually enriched in comparison with Ni in oxic conditions (Jones and Manning, 1994). Therefore, Ni/Co ratios can be used to estimate palaeo-redox conditions, in which higher values (> 5) indicate anoxic depositional conditions and the same ratio less than 5 indicates dysoxic and oxic depositional conditions (Jones and Manning 1994). The claystones from Az Zabirah area were considered to be deposited under oxic conditions, as indicated by the Ni/Co ratio ranging from 0.10 to 2.69 (see Table 2).

Strontium (Sr) and barium (Ba) are used as indicators for seawater setting than freshwater environment (Liu et al., 1984; Deng and Qian, 1993; Wang, 1996; Reimann and de Caritat, 1998). The studied claystone samples contain Sr and Ba values in the range of 25–920 and 20–170 ppm, respectively (Table 2). Most of the claystone samples have relatively low concentration of Sr and Ba, indicating non-marine, freshwater environment. In contrast, the relatively high concentrations of the Sr and Ba in some claystone samples may be due to occurrence of high calcite mineral (CaO) which could have been replaced by these elements because of their similarity in charge and radius. This is consistent with the carbonate minerals in the claystones as indicated by the XRD analysis (Fig. 3).

Gallium (Ga) is also a useful trace element to determine the clay mineral types (e.g., Hieronymus et al., 2001; Beckmann et al., 2005). Aluminum (Al) and Ga are generally enriched in kaolinite and associated with warm and humid climate (Hieronymus et al., 2001; Beckmann et al., 2005), while potassium (K) and rubidium (Rb) are also associated with illite reflecting weak chemical weathering and related to dry and cold climatic conditions (Ratcliffe et al., 2004, 2010). Moreover, most sediments enriched in illite should have high Rb and K2O, whereas those that enrich in kaolinite will have high Ga and Al2O3. In this respect, the claystone samples in this research can be classified as kaolinitic claystone with intense chemical weathering as indicated by relatively higher Al2O3 than K2O (Table 1) and the absence of Rb compared to Ga (Table 2). This is supported by the abundance of kaolinite in the claystones of the Az Zabirah area (Figs. 3 and 4).

Paleoenvironmental conditions

In the present research, paleoenvironmental conditions were primarily examined through the use of palynoflora and geochemical compositions of the claystones in the Az Zabirah area. The occurrences of some palynomorph taxa are more common in the studied section and they are more useful indicators for the paleoenvironmental interpretation and tend to increase relatively or to be come more common in the fluvial deposits such as flood plains and inland lakes. However, the absence of phytoplankton from the studied claystones may indicate a terrestrial sedimentation. There is a large terrestrial influx that has been seen in the whole interval of the claystone. The terrestrial environment angiosperm taxa such as R. radiates and Retitriletes sp. (Jahren, 2007; Oboh-Ikuenobea et al., 2012) are delivered to the sea surface by action of winds and riverine inputs of wind indicate mixed coastal and inland subtropical environment with warm and humid climate.The terrestrial environments in this research are dominated mainly by the pollens such as Tricolpites and Triporopollenites (Nichols and Pocknall, 1994) followed by lake pollen Polyvestibulopollenites sp. (Larsson et al., 2006). This interpretation is also evidenced from the geochemistry of major and trace elements as discussed in the presence of terrestrial detritus elements (e.g., SiO2 and TiO2) with significant amounts in the claystones of Az Zabirah area (Table 1) further confirms a significant influx of terrestrial debris. Palaeo-redox conditions during the sedimentation of Az Zabirah claystones were also evaluated from the trace element data such as V, Ni, Th, U, and Co along with their ratios (Table 2). These trace elements and their ratios suggest oxic to dysoxic conditions, where high to moderate amount of oxygen was available during the deposition of the claystones in the Az Zabirah area (see Section 4.2.2). The high to moderate amount of oxygen during deposition of the claystones is also confirmed by the occurrence of relatively high Fe2O3 (Table 1) and goethite (Fig. 3).

Paleoclimatic conditions

Climatic conditions have extreme effect on the mineralogy and geochemistry of sediments (Rieu et al., 2007; Yan et al., 2010),, due to its control on theweathering process (Nesbitt et al., 1996). However, intense weathering is associated with warm and humid climate, whereas minimal weathering is associated with cold and arid climate (Nesbitt et al., 1996). In this research, the paleoclimatic conditions during sedimentation of claystones in the Az Zabirah area were evaluated based primarily on major and trace element geochemical analyses and the presence of some palynoflora in the claystone samples. The elements that were used to evaluate the paleoclimatic conditions are SiO2, Al2O3, K2O, Na2O, Sr, Cu, and Ga along with their geochemical ratios (Tables 1 and 2).

The strontium/copper ratio is an important indicator for paleoclimate conditions (Lerman, 1989; Wang et al., 1997). The concentrations of Sr and Cu have been influenced by the scale of the lake basin, the distance, and the water depth (Jia et al., 2013). However, Sr/Cu ratios more than 5.0 are suggested to reflect a hot-arid climate, while low Sr/Cu ratio in the range of 1.3–5.0 indicates a warm-humid climate (Lerman, 1989). The Sr/Cu ratio of the studied claystones shows varied values in the range of 0.7–83 with a mean value of 24 (Table 2). Therefore, the claystones could be deposited under hot-arid climate with little humidity climatic conditions. This interpretation is confirmed by the plotting of the major, trace, and rare earth elements of the discrimination diagrams proposed by several workers (e.g., Suttner and Dutta, 1986; Hieronymus et al., 2001; Beckmann et al., 2005). According to Suttner and Dutta (1986), the binary SiO2 versus (Al2O3 + K2O + Na2O) diagram reflected semiarid to warm climatic conditions with little humidity climatic conditions (Fig. 7) during deposition of the clay in the Az Zabirah. The humid-warm climatic conditions were confirmed by the enrichment of the claystones with the kaolinite (Figs. 3 and 4), which is usually associated with warm and humid climate (Hieronymus et al., 2001; Beckmann et al., 2005; Ratcliffe et al., 2010). Furthermore, the presence of the palynomorph taxa such as Retitriletes sp. and Dictyophyllidites sp. is also a strongly argument for warm and humid climate (Jahren 2007; Oboh-Ikuenobea et al., 2012).
Fig. 7

Bivariate SiO2 versus (Al2O3 + K2O + Na2O) contents, plotted on the paleoclimate discrimination diagram (After Suttner and Dutta, 1986)

Conclusions

Nine samples from the Cretaceous claystone and the bauxite zone layer in the Az Zabirah area, Northern Saudi Arabia were investigated using multi-proxies of geochemical and paleontology research. The results helped to define the paleoenvironment and paleoclimate conditions during deposition of the claystones. The palynological and geochemical data of the Cretaceous claystones suggest the following:
  1. 1.

    Az Zabirah claystones were deposited in a terrestrial environment as supported by high amounts of angiosperm taxa. The subtropical humid climate conditions are also evidenced by the presence of the microspore taxa such as Dictyophyllidites sp. and Retitriletes sp.

     
  2. 2.

    The claystones are rich in SiO2 (avg. 43.2 wt%), Al2O3 (avg. 28.5 wt%), and TiO2 (avg. 2.5 wt%), indicating a large terrestrial influx in the interval of the claystone.

     
  3. 3.

    The Al2O3 and K2O and trace elements such as Ga have revealed that the Az Zabirah claystones are enriched in kaolinite and reflected intense weathering related to warm-humid climatic conditions.

     
  4. 4.

    The trace elements such as V, Ni, Th, U, and Co and their ratios indicate a high to moderate amount of oxygen suggesting oxic conditions during deposition of the claystones from Az Zabirah area.

     
  5. 5.

    The paleoclimate conditions during deposition of the Az Zabirah claystones are hot-arid climate to warm-humid with little aridity climatic conditions as indicated from microspores taxa and geochemistry of major and trace elements.

     

Notes

Acknowledgements

The authors wish to acknowledge the financial support by the King Saud University Research Grant, Deanship of Scientific Research, College of Science Research Center. The constructive comments and suggestions by Dr. Ramadan Abu-Zied that improved the revised manuscript are gratefully acknowledged.

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Copyright information

© Saudi Society for Geosciences 2018

Authors and Affiliations

  • Madyan M.A. Yahya
    • 1
  • Mohammed H. Hakimi
    • 2
  • Mahmoud A. Galmed
    • 1
    • 3
  • Mohamed N. El-Sabrouty
    • 1
  • Yasamin K. H. Ibrahim
    • 4
  1. 1.Geology and Geophysics Department, College of ScienceKing Saud UniversityRiyadhSaudi Arabia
  2. 2.Geology Department, Faculty of Applied ScienceTaiz UniversityTaizYemen
  3. 3.Geology Department, Faculty of ScienceCairo UniversityGizaEgypt
  4. 4.Earth Science Department, Science CollegeBaghdad UniversityBaghdadIraq

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