Paleo–climatic and paleo–environment implication of clay mineral across Upper Cretaceous–Lower Eocene deposits from Gafsa Basin

doi:10.21203/rs.3.rs-1623282/v1

An integrated study of clay paragenesis has been conducted in the Gafsa Basin, southern Tunisia, during the Late Cretaceous–Lower Eocene. Six lithostratigraphic sections were logged in the Tamerza, Oued Thelja, Ong, and Chamsi. The Upper Maastrichtian Haria Formation is dominated by smectite, indicating a semi-arid climate with distinct seasons. A colder and drier climate, favoring physical alteration, is observed in the first Paleogene deposits. Danian deposits, show a decrease in smectite in favor of illite and kaolinite, indicating a period of intensified detritus under a hot and humid climate with a contrasting season. The abundance of smectite and the low percentages of kaolinite in the Thelja (Thanetian) Formation suggest a warm and arid climate. The late Thanetian–early Eocene deposits were influenced by a warm and seasonal climate, or probably, they were an alternation between dry and humid seasons and warm climatic conditions in the Lower Eocene corresponding to the Late Paleocene–early Eocene deposits outlining the Paleocene–Eocene Thermal Maximum (PETM). The consequence of this warm climate is sea level rise, which corresponds to the Paleocene– Eocene transgression.

Clays

Late cretaceous

K–Pg

Paleocene–Eocene

climate

Tethyan margin

According to the clay–mineral distribution trends in ocean sediments, the variations in the vertical clay–mineral distribution patterns in deep–sea sediment cores have been interpreted in terms of shifts in the climatic conditions prevailing in the continental source areas of the detrital clay minerals (Singer, 1984). Thiry (2000) pointed out that clay minerals in sediments can be a useful indicator of paleoclimatic conditions. Concentrations of smectite are taken (Chamley et al., 1999) as an indication for the prevalence of warm climates with fairly dry conditions and chemical weathering dominance (Singer, 1984). An abundance of illite and chlorite in the sediments indicates a cold and dry environment in the source area with dominant physical weathering (Singer, 1984). Robert & Chamely (1991) used clays in sediments to interpret climate change. More recently, Robert & Kennett (1992, 1994) used the abundance of smectite (70–100%) in the early Paleogene deposits of Antarctica to indicate seasonal changes in an arid climate. In contrast, the occurrence of kaolinite is interpreted by Robert & Kennett (1992) indicate high runoff with warm climate (Bolle et al., 1999; khozyem et al., 2013, 2015). In marine sediments, clays are inherited from continental runoff or flocculated. Their abundances provide abiotic proxy data, which may be useful to decipher climatic changes. The Upper Cretaceous–Lower Eocene interval containing the Cretaceous–Paleogene and Paleocene–Eocene boundaries was characterized by global extinction and climate change (Kennett & Stott, 1991; Zachos et al., 1993; Zachos et al., 1994, 2001, 2003). Clay fractions of this interval show different compositions (Zachos et al., 1994, 2001, 2003). The clay paragenesis of the studied deposits brings out precious information concerning climate conditions on adjacent continents and unravels the mechanisms involved in weathering, transport, and sedimentation (Robert & Chamely, 1991; Jamoussi et al., 2003; El Ayyat, 2013). In this paper, clay mineral assemblages of the sediments from the Gafsa Basin were investigated to determine paleoclimate and paleoenvironment conditions across Upper Cretaceous–Lower Eocene deposits.

Geological Setting

The Gafsa Basin is part of the southern Atlas Mountains, corresponding to a vast structural area that extends from the Gulf of Gabes in the east to the Algerian border in the west, and it corresponds to a set of relief which is located north of the Chott Jerid and Chotts chain (Burollet, 1956). The Gafsa Basin is controlled by several faults, the main ones trending E–W and NW–SE. These faults controlled Ypresian sedimentation (Zargouniet al., 1985; Zaier et al., 1998). The sections were lifted in four areas: Tamerza, Oued Thelja, Jebel Ong, and Jebel Chamsi (Figure. 1). The Tamerza region is bounded to the north and west by the Tunisian–Algerian border, to the east by the Redeyef mining sector, and to the south by Chott El Gharssa (34 ° 23 '35'' N, 7 ° 56 '45'' E). This region is located in the western part of the Gafsa chain. The city of Tamerza, which is part of the governorate of Tozeur, is located in the southwest of Tunisia. It is located about 450 km from Tunis and 70 km from Tozeur (Figure. 1). The Oued Thelja section is located 30 km west of the town of Gafsa. The typical section of the Metlaoui Formation was lifted in the gorge of Oued Thelja, which is located 5km west of the city of Metlaoui (34 ° 09 '00'' N, 8 ° 16' 59'' E ). The Jebel Ong area is found in the southern Tunisian atlas range (34 ° 19 '37'' N, 9 ° 06' 04'' E), which corresponds to a system of foreland folds and overlaps bordered in the east by the Gafsa fault oriented NW–SE (Zargouni, 1985). The study area in Jebel Chamsi was located 30 km west of the town of Gafsa. It occupies the central part of the map of El Ayacha at 1/100,000 and it is limited by the meridians 7G 40' and 7G 90' respectively to the west and the east and by the parallels 38G 20' to the north and 38G 0' to the south. The studied sections cover three formations, corresponding to Haria Formation, Thelja Formation, and Chouabine Formation (Figure. 2).

Haria Formation

Defined by Burollet (1956) and, it encompasses the transition from the Mesozoic to the Cenozoic (K/Pg). The Haria Formation corresponds to dark clays and marls with thin intercalations of marly limestone. In the Gafsa Basin, this Formation shows a particular enrichment in carbonate levels. This Formation is dated from the upper Maastrichtian–Danian (Adatte et al., 2002; Ayachi et al., 2016).

Thelja Formation

Defined by Fournié (1978), this formation overlies the Haria Formation and has been assigned a Thanetian age (Fournié, 1978; El Ayachi et al., 2016; Messadi et al., 2016, 2018). It corresponds to an evaporitic series, and its particular richness in dolomites and gypsum reflects a regressive trend (El Ayachi et al., 2016; Messadi et al., 2016, 2018).

Chouabine Formation

Defined by Fournié (1978), and assigned to the Late Paleocene–Ypresian. This unit corresponds to a phosphate series intercalating marls and limestones (El Ayachi et al., 2016; Messadi et al., 2016, 2018).

Six lithostratigraphic sections were logged in the Tamerza, Oued Thelja, Ong, and Chamsi (Messadi, 2021). Two sections were raised in the region of Tamerza and Midés, constituting the western part of the basin, including two sections: section M covers the Haria Formation (35 samples covering 100m) and two other sections cover the Thelja (Figure. 3) and Chouabine formations, Petite cluse (14 samples covering 123 m) and the Wday section (23 samples covering 149 m) (Figure. 3). In the center of the Basin, a section was measured at Oued Thelja (39 samples covering 210 m). In the eastern part of the Basin, two sections were raised, Jebel Ong (25 samples covering 275 m) and Jebel Chamsi section (36 samples covering 215 m) (Figure. 3).

The clay fractions of these samples were subjected to X–Ray diffraction analysis (XRD) (scanned between 2 and 40 2θ) to identify their clay mineral composition following the method described by Carroll (1970). Semi-quantitative determination of the identified clay minerals was undertaken based on the method adopted by Pierce & Siegel 1969; Brindley & Brown, 1980. Mineralogical analyses of the clays was carried out at four institutions: (1) Biomineralization and Sedimentary Environments (BES) in the University of Pierre and Marie Curie (Paris–France) using the diffractometer "SCINTAG XDS 2000", (2) the Faculty of Sciences of Bizerte, (3) in the company of phosphate of Gafsa, and (4) the materials laboratory of the National School of Engineers of Sfax using Philips X–ray diffractometer with CuKα radiation, 45 kV and 35 mA.

In the study area, the sampled series attributed to the Upper Cretaceous–Lower Eocene interval show variations in terms of thickness and litho–facies which can be essentially controlled by syn–sedimentary tectonism (Messadi et al., 2016, 2017, 2018, 2019, 2020; Messadi, 2021). Deposits and lithofacies on the ground made it possible to characterize the succession of the following lithostratigraphic units and formations (Table 1).

Table 1

Distributions of principal’s lithofacies and units in the studied series.
Lithostratigraphy -location		Tamerza
Haria	Unit 0	Alternation of marls, phosphates and lumachellic limestones
	Unit 1	marls
	Unit 2	Marls and micritic limestones
	Unit 3	It consists of alternating micritic limestone, and lumachellic limestones fossilizing channels and marls
Thelja and its equivalent		T1:Lumachellic limestone	T1:lumachellic limestones fossilizing channels	T1:lumachellic limestones fossilizing channels	lumachellic limestones fossilizing channels
		T2:Marls-limestones	T1:lumachellic limestones fossilizing channels
		T3:Marls-limestones-gypsum	T2:Glauconitic limestone-marls-lumachellic limestone-gypsum
		T4:Marls-limestones	T2:Glauconitic limestone-marls-lumachellic limestone-gypsum	T2:Marls-lumachellic limestone-gypsum
		T5:Marls-limestones-slumps	T3:Phosphatic limestone-marls
		T6:Marls-limestones	T3:Phosphatic limestone-marls
Chouabine and its equivalents		C1:Marls-nodular limestone	C1: Marls	C1: Marls	Marls
		C1:Marls-nodular limestone	C2: marls- lumachellic limestone-phosphate	C1: Marls	Marls
		C2:Marls-limestone-phosphate	C3: phosphate-marls- cherts- lumachellic limestone	C2: Limestones-phosphate	lumachellic limestone fossilizing channels
		C2:Marls-limestone-phosphate	C4: phosphate-marls-lumachellic limestone	C2: Limestones-phosphate	lumachellic limestone fossilizing channels

Haria Formation

Clay mineralogical analysis of Upper Cretaceous–Paleocene successions revealed the predominance of smectite, illite, and kaolinite as main clay minerals associated with calcite, quartz, and dolomite.

Midés section

The unit H0 is characterized by a particular richness in calcite 67–89% and quartz 8–23% at its lower part associate with the presence of kaolinite 1–6% and the absence of smectite. The upper part is characterized by the presence of smectite, quartz with a maximum of 17% and kaolinite at 3% (Table 2).

Table 2

Relative abundances of the identified major’s minerals in the Haria Formation
Haria Formation
Unit	Carbonates minerals	Clays minerals	Accessory minerals
H0	Calcite : 70–89% Ankerite : 2–11%	Smectite : 0–15% Kaolinite : 1–6%	Quartz : 5–23% Feldsprs : 1–4% Glauconite : 0–2%

The lowermost part of unit H1 is characterized by a relative enrichment in kaolinite (16% of the bulk rock) associated with a high percentage of quartz (54%), and the absence of calcite and smectite with the appearance of a low percentage of dolomite (5–13%). However, the lower part is characterized by the presence of smectite (10–38%), kaolinite (2–16%), and a low percentage of calcite and glauconite. In the upper part of this unit, calcite and smectite correspond to the major minerals with (0–42% and 5–42% respectively) associated with a low percentage of illite (3–9%), quartz (4–27%), and the absence of kaolinite (Table 3). Unit H2 is characterized by the dominance of opal-CT minerals (43%), a low percentage of illite (2–8%), quartz (1–2%), the absence of kaolinite, and a low appearance of smectite in the upper part. Carbonate minerals are present with a medium percentage (40%) of calcite and a low percentage of dolomite (0–4%) (Table 4). Unit H3 is characterized by a high percentage of calcite (72%) compared to the lower part (24%), a decrease in smectite (16–3%), and the appearance of gypsum (70%) (Table 5).

Table 3

Relative abundances of the identified major’s minerals in the Haria Formation
Haria Formation
Unit	Section	Carbonates minerals	Clays minerals	Accessory minerals
H1	Tamerza	Calcite : 0–80% Dolomite : 4–23% Ankerite : 0–45%	Smectite : 10–43% Kaolinite : 2–16% Illite : 2–9%	Quartz : 3–54% Feldspars : 1–4%
	Oued Thelja	Calcite : 0–47% Dolomite : 0–4% Ankerite : 2–82%	Smectite : 0% Kaolinite : 3–48% Sepiolite : 0–35%	Quartz : 2–50% Phosphate : 1–11%
	Jebel Ong	Calcite : 9–88% Ankerite : 6–88%	Smectite : 0% Kaolinite : 1–19% Illite : 0–16% Palygorskite : 0–8%	Quartz : 5–19% Phosphate : 0–12% Clinoptilolite : 0–2% Opal CT : 0–5%
	Jebel Chamsi	Calcite : 19–58% Dolomite : 0–3% Ankérite : 0–4%	Smectite : 4–20%% Kaolinite : 6–52% Illite : 0–1% Palygorskite : 0–7% Sepiolite : 0–6%	Quartz : 4–33% Phosphate : 0–17% Clinoptilolite : 0–15% Glauconie : 0–17

Table 4

Relative abundances of the identified major’s minerals in the Haria Formation
Haria Formation
Unit	Section	Carbonates minerals	Clays minerals	Accessory minerals
H2	Tamerza	Calcite : 12–40% Dolomite : 0–4% Ankerite : 0–4%	Smectite : 0% Kaolinite : 0% Illite : 2–8%	Quartz : 1–4% Opal CT : 43–59%
	Oued Thelja	Calcite : 12–94% Ankerite : 3–34%	Smectite : 0% Kaolinite : 2–6% Sepiolite : 3–40% Illite : 0–1%	Quartz : 1–7% Opal CT : 0–7% Phosphate : 0–4% Clinoptilolite : 0–4%
	Jebel Ong	Calcite : 9–62% Ankerite : 9–72%	Smectite : 0% Kaolinite : 6–11% Illite : 5–16%	Quartz : 2–10% Clinoptilolite : 0–2% Opal CT : 0–5%
	Jebel Chamsi	Calcite : 6–93% Dolomite : 2–31% Ankerite : 1–68%	Smectite : 0–29%% Kaolinite : 0–3% Illite : 0–2% Palygorskite : 0–2% Sepiolite : 0–11%	Quartz : 0–6% Clinoptilolite : 0–6% Opal CT : 0–8%

Table 5

Relative abundances of the identified major’s minerals in the Haria Formation
Haria Formation
Unit	Section	Carbonates minerals	Clays minerals	Accessory minerals
H3	Tamerza	Calcite : 24–74% Dolomite : 0–4% Ankérite : 0–11%	Smectite : 16% Kaolinite : 3%	Quartz : 7%
	Oued Thelja	Calcite : 72–94% Ankerite : 0–3% Dolomite : 0–10%	Illite : 0–1%	Quartz : 1–2% Opal CT : 0–11% Phosphate : 0–1% Clinoptilolite : 0–4% Feldspars : 0–1%
	Jebel Ong	Ankerite : 88%	Illite : 9%	Quartz : 0–2%
	Jebel Chamsi	Calcite : 72–99% Dolomite : 65–93% Ankérite : 56–92%	Smectite : 0–4%% Kaolinite : 0–1% Palygorskite : 1–11% Sepiolite : 0–1%	Quartz : 1–4% Glauconite : 0–3% Opal CT : 1–9% Feldspars : 1%

Oued Thelja section

In unit H1 smectite is absent, and kaolinite is present throughout this unit with values varying from 3–48% in the lower part and 4–11% in the upper part (Table 3). Sepiolite appears in the top part of this unit with varying percentages ranging from 28–35%. Interstratified were encountered in the middle part of this unit with percentages varying between 2–16%. Quartz is present at all levels of this unit except the basal part with values between 19 and 50% in the lower part and 2–6% in the upper part (Table 3). The various calcite ranged from 0–47% in the lower part and 43–93% in the upper part of this unit. Dolomite is observed in one level (OT93) in the middle part of the unit with a value of 4%. Ankerite is abundant in the lower part of this unit with varying percentages between 7–82% with an absence in the middle part and scanty occurrence in the uppermost part with values from 2–10%. Phosphate appears in the lower and upper parts with values ranging from 1–11% (Table 3). The clay minerals present in unit H2 are represented by kaolinite with values varying between 2–6%, illite at 1% in the upper part, and sepiolite with values ranging between 3–40% in the lower and middle parts. Quartz is detected in all levels of this unit with values varying between 1 and 7%. Calcite is present in all levels of this unit with percentages varying between 12 and 94%. Ankerite shows contents varying between 3 and 34%. The confinement minerals are represented by clinoptilolite and phosphate with values varying between 1 and 4%. The opal-CT is present with values around 7% (Table 4).

In unit H3, illite is observed with minimum percentages around 1%. Quartz is present throughout the unit with percentages in the range of 1–2%. Calcite represents the most abundant mineral with varying percentages between 72 and 94%. Dolomite is observed at the base of this unit with a content of 10%. Ankerite appears in the upper part of this unit with values of around 3%. This unit shows the presence of CT opal (11%) and feldspar (1%) in addition to the confinement minerals represented by phosphates (1%) and clinoptilolite (1–4%) (Table 5).

Jebel Ong Section

Smectite is absent in the H1 unit. Kaolinite is present throughout the unit with varying percentages between 10 and 19% in the lower part, 5 and 11% in the middle part and 1 to 9% in the top part. The illite appears in the middle and upper part with values varying between 5 and 16%. Palogyrskite is observed in two levels of the middle part of this unit with values of around 8%. Quartz is present with percentages in the range of 5–11% with a peak of 19% in the middle part. Calcite represents the most abundant mineral with values varying between 50 and 88% except in the top part with values between 9 and 19%. Ankerite is encountered in the lower and upper part of this unit with values ranging from 6–19% and 40–88% respectively. Phosphates are present in the lower part with values in the range of 5–12%. The presence of clinoptilolite at the JO 131 level is noted with a value around of 2% and the presence of opal-CT (5%) (Table 3). The clay minerals present in the H2 unit are represented by kaolinite with percentages ranging from 6–11% and illite with values varying from 5–16%. Quartz is observed throughout this unit with percentages varying between 2–10%. Carbonate minerals are represented by calcite (9–62%) and ankerite (9–72%) (Table 4). The confinement minerals are observed in the upper part with the detection of clinoptilolite (2%). With these minerals, we noticed the presence of the CT opal (5%) in the top part of this unit (Table 4). The H3 unit analysis shows the presence of illite (9%), quartz (2%), and ankerite (88%) (Table 5).

Jebel Chamsi section

The smectite shows a content varying between 4 and 20% in the lower and middle part of unit H1. Kaolinite is present throughout this whole unit with values between 6 and 52%. Illite is detected in two levels at the base (1%) and in the middle part (27%). Palygorskite is encountered in the level (JC 76) in the middle part of this unit. Sepiolite appears in the middle part of the level (JC 84) with a value of 6%. The interstratified are observed in the upper part of this unit with values varying between 5 and 32%. Quartz is present throughout this unit with values varying between 4 and 33%. Calcite characterizes all the levels of this unit with values varying between 19 and 58%. Dolomite appears in the upper part of this unit with a value of (3%). Ankerite is detected in the upper part of this unit with values of around 4%. Containment minerals are present in the lower part of this unit. They are represented by glauconite, clinoptilolite–hollandite and phosphate. These minerals are present with contents varying between 3 and 17% (Table 3).

In unit H2 Smectite is present in the upper part with percentages 18–29%. Kaolinite is detected in the lower and upper parts of this unit with values in the range of 2–3%. The illite is described in a level in the lower part of this unit with a value of around 2%. The palygorskite is also observed in the middle part of this unit with proportion of 2%. Sepiolite is present in the lower and upper parts of this unit ranging from 1–11%. Quartz is observed in the lower and upper part of this unit with values varying between 3 and 6%. Carbonate minerals are represented by calcite (6–93%), dolomite (2–31%) and ankerite (1–68%). The upper part of this unit is characterized by the appearance of clinoptilolite with values (3–6%). Note the presence of the opal CT (8%) in the upper part of this unit (Table 4). In unit H3, smectite is present with contents varying between 2 and 4%. Kaolinite appears in the middle part of this unit with a value of 1%. Palygorskite is observed in the middle and upper parts of this unit with percentages varying between 1–11%. Sepiolite occurs in the lower and upper parts of this unit with values approaching 1%. Quartz is observed along with this unit with grades varying from 1 to 4%. Carbonate minerals are represented at the base and in the middle part by the presence of calcite (72–99%) and the upper part is dominated by dolomites (65% − 93%) with the appearance of ankerite toward the top with a percentage accounting for 92%. In this unit we note the presence of glauconite (3%) in the middle part, the opal-CT (1%– 9%) in the middle and upper parts, and feldspar at the highest point (1%) (Table 5).

Thelja Formation

Tamerza section

X–ray diffraction shows two distributions. The basal part, while the enrichment in calcite is observed in Unit 1, the predominance of dolomite characterizes the other units (Table 6). The evolution of the percentages of dolomites compared to those of calcite can be related to confinement. Indeed, from the end of Unit 1, the percentages of calcite decrease to have low values in Unit T3 and the percentages of dolomite increase from those observed in Unit T2 to reach over 70% in the T4 Unit (Table 6).

Table 6

Relative abundances of the identified major’s minerals in the TheljaFormation
Thelja Formation: Tamerza section
units	Carbonates minerals	Clay minerals	Accessory minerals
TTTTT T1	Calcite:15–70% Dolomite:0–5%	Smectite:20–35% Illite: 2–7% Kaolinite: 0–10%	Clinoptilolite : 0% Quartz : 4–25%	Opal CT : 0–5% Feldspars : 0–5% Phosphate : 0–3%
T2	Calcite: 5–20% Dolomite:60–80%	Smectite: 2–5% Illite: 2–15%	Gypsum : 10% Quartz : 0–2%	Opal CT : 0–4% Feldspars : 0–5%
T3	Calcite: 5–15% Dolomite:40–65%	Smectite:20–35% Illite: 5–10%	Gypsum : 20–30% Clinoptilolite : 0% Quartz : 3–5%	Opal CT : 0–4% Feldspars : 0–5%
T4	Dolomite: 67–88 %	Smectite: 8–15% Illite: 5–12%	Gypsum : 20–30% Quartz : 2–5%	Opal CT : 2–5% Feldspars : 2–5%
T5	Calcite: 0% Dolomite:50–55%	Smectite:20–30% Illite: 5–10% Kaolinite: 0%	Gypsum : 0% Clinoptilolite : 6% Quartz : 3–5%	Opal CT : 0–4% Feldspars : 0–5% Phosphate : 0–4%
T6	Calcite:0–5% Dolomite:45–70%	Smectite:10–25% Illite: 5–10%	Gypsum : 20–30% Clinoptilolite : 0–7% Quartz : 3–10%	Opal CT : 2–15% Feldspars : 0–5% Phosphate : 0–3%

Oued Thelja section

Levels of units T2 and T3 of the Oued Thelja section are the subjects of X-ray diffraction analyses (XRD) since the T1 unit is completely formed of lumachellic limestone (Table 7). The T2 unit reveals the presence of smectite observed in the lower part of this unit with values around 23%. Kaolinite is present at all levels of this unit with contents varying between 1 and 5%. The illite is described in the middle and upper part with percentages around of 1%. Quartz is observed in at levels of this unit with contents varying between 1 and 12% with the maximum values in the middle part. Carbonate minerals are represented in the lower and middle part by calcite (2–28%) and ankerite (56–95%), and by the presence of dolomite (56–95%) in the upper part. Unit 3 shows richness in smectite (63%), kaolinite (24%) associated with quartz (8%) and phosphate (5%) (Table 7).

Table 7

Relative abundances of the identified major’s minerals in the Thelja Formation
Thelja Formation : Oued Thelja Section
Unit	Carbonates minerals	Clays minerals	Accessory minerals
Th 2	Calcite : 2–28% Dolomite : 56–95% Ankerite : 56–90%	Smectite : 15–23% Kaolinite : 1–5% Illite : 0–1%	Quartz : 1–12%
Th3	Ankerite : 0–3% Dolomite : 0–10%	Smectite : 63% Kaolinite : 24%	Quartz : 1–8% Phosphate : 0–5%

Jebel Ong section

The T1 unit is composed of illite (9%), quartz (3%), 42 dolomite and 45% ankerite.

The T2 unit shows the presence of illite (5%), quartz (2%), 91% dolomite and 2% CT opal.

The T3 unit reveals the presence of kaolinite (3%), illite (7%), quartz (3%), dolomite (83%) and 3% of CT opal (Table 8).

Table 8

Relative abundances of the identified major’s minerals in the Thelja Formation
Thelja Formation : Jebel Ong Section
Unit	Carbonates minerals	Clays minerals	Accessory minerals
Th 1	Dolomite : 42% Ankerite : 45%	Illite : 9%	Quartz : 1–3%
Th 2	Dolomite : 91%	Illite : 5%	Quartz : 1–2% Opal CT : 2%
TH 3	Calcite : 0% Dolomite : 83%	Smectite : 15–23% Kaolinite : 3% Illite : 7%	Quartz : 3% Opal CT : 3%

Chouabine Formation

Tamerza section

The C1 Unit is characterized by a particular richness in smectites at its lowermost part. Furthermore, the decrease in smectite relative abundance from the lower part (66% of the bulk rock) toward the top part (17%) of this unit. Unit C2 is characterized by a relative enrichment is smectites (25% of the bulk rock) as well as the the presence of clinoptololite (40%), sepiolite (15%), palygorskite (13%) and dolomite (7%) (Table 9).

Table 9

Relative abundances of the identified major’s minerals in the Chouabine Formation
Chouabine Formation: Tamerza Section
Unit		Carbonates minerals	Clays minerals	Associated minerals
Unit C1	Lower Part	Calcite : 0% Ankerite : 0%	Smectite : 45% Kaolinite : 6% Illite : 3% Sepiolite : 22% Palygorskite : 1%	Quartz : 4% Opal CT : 1% Feldspars :10% Clinoptilolite : 2%
Unit C1	Upper Part	Calcite : 27% Ankerite : 0%	Smectite : 5% Kaolinite : 0% Illite : 0% Palygorskite : 2%	Quartz : 1% Opal CT : 8% Feldspars : 1% Phosphate: 56%
Unit C2	Lower Part	Calcite : 7–17% Dolomite : 0–44%	Sepiolite : 31–45% Palygorskite : 5%	Quartz : 2% Opal CT : 5% Clinoptilolite : 2% Phosphate: 7%
Unit C2	Upper Part	Calcite : 4% Dolomite : 62% Ankerite : 0%	Sepiolite : 17% Palygorskite : 3%	Quartz : 1% Opal CT : 7% Phosphate: 4%
Unit C3	Lower Part	Calcite : 16% Dolomite : 44%	Palygorskite : 28% Sepiolite : 44%	Quartz : 0% Feldspars : 0% Glauconite : 0%
Unit C3	Upper Part	Calcite : 16% Dolomite : 44% Ankerite : 66%	Palygorskite : 28% Sépiolite : 44%	Quartz : 0% Feldspars : 0% Glauconite : 0%
Unit C4	Lower Part	Calcite : 2% Dolomite : 76%	Smectite : 8% Palygorskite : 4%	Quartz : 3% Feldspars : 3% Phosphate: 66%
Unit C4	Upper Part	Calcite : 12% Dolomite : 4% Ankerite : 50%	Smectite : 8% Palygorskite : 2%	Quartz : 7% Feldspars : 3% Phosphate: 7%

Oued Thelja section

Unit C1 is characterized by a richness in smectite at its base, confirming the transgressive trend of the Chouabine deposits. Furthermore, the decrease in smectite relative abundance from the lower part (45% of the bulk rock) towards the top part (5%) of this unit reflects the upward slight sea level fall (Table 10). The regressive trend is also evidenced by the drop in planktonic foraminifera and the frequent intercalation of coquina beds within the uppermost part of the afore-described unit and the lower part of the Unit 2 (Table 10).

Table 10

Relative abundances of the identified major’s minerals in the Chouabine Formation
Chouabine Formation: Oued Thelja Section
Unit		Carbonates minerals	Clays minerals	Accessory minerals
Unit C1	Lower part		Kaolinite : 6% Illite : 3% Sepiolite : 72% Palygorskite : 1%	Quartz : 4% Opal CT : 1% Feldspars :10% Clinoptilolite : 2%
Unit C1	Upper part	Calcite : 27%	Smectite : 5% Kaolinite : 0% Illite : 0% Palygorskite : 2%	Quartz : 1% Opal CT : 8% Feldspars : 1% Phosphate: 56%
Unit C2	Lower part	Calcite : 7–17% Dolomite : 0–44%	sepiolite : 31–45% Palygorskite : 5%	Quartz : 2% Opal CT : 5% Clinoptilolite : 2% Phosphate: 7%
Unit C2	Upper part	Calcite : 4% Dolomite : 62%	Palygorskite : 3% Sepiolite : 17%	Quartz : 1% Opal CT : 7% Phosphate: 4%
Unit C3	Lower part	Calcite : 16% Dolomite : 44%	Palygorskite : 28% Sepiolite : 44%
Unit C3	Upper part	Calcite : 16% Dolomite : 44% Ankerite : 66%	Palygorskite : 28% Sepiolite : 44%
Unit C4	Lower part	Calcite : 2% Dolomite : 76%	Smectite : 8% Palygorskite : 4%	Quartz : 3% Feldspaths : 3% Phosphate: 66%
Unit C4	Upper part	Calcite : 12% Dolomite : 4% Ankerite : 50%	Smectite : 8% Palygorskite : 2%	Quartz : 7% Feldspars : 3% Phosphate: 7%

Units C2 and C3 are characterized by the absence of smectite, kaolinite, and illite. The presence of sepiolite (17–45%), palygorskite (3–5%), dolomite (0–44%), and clinoptololite (2%).

Unit C4 is characterized by the presence of smectite (8%) in its upper part with a low percentage of palygorskite (2–4%) and the absence of sepiolite (Table 10).

Jebel Ong section

Unit C1 shows a richness in smectite (36%), 6% palygorskite, quartz (3%), calcite (16%), dolomite (19%), and 20% clinoptilolite (Table 11).

Table 11

Relative abundances of the identified major’s minerals in the Chouabine Formation
Chouabine Formation : Jebel Ong Section
Unit		Carbonates minerals	Clays minerals	Accessory minerals
Unit C1	Lower part		Kaolinite : 6% Illite : 3% Sepiolite : 72% Palygorskite : 1%	Quartz : 4% Opal CT : 1% Feldspars :10% Clinoptilolite : 2%
Unit C1	Upper part	Calcite : 27%	Smectite : 5% Palygorskite : 2%	Quartz : 1% Opal CT : 8% Feldspars : 1% Phosphate: 56%
Unit C2	Lower part	Calcite : 7–17% Dolomite : 0–44%	Sepiolite : 31–45% Palygorskite : 5%	Quartz : 2% Opal CT : 5% Clinoptilolite : 2% Phosphate: 7%
Unit C2	Upper part	Calcite : 4% Dolomite : 62%	Palygorskite : 3% Sepiolite : 17%	Quartz : 1% Opal CT : 7% Phosphate: 4%

The lower part of the Unit C2 is rich in phosphate (80%) in association with substantially lower proportions of calcite (6%), quartz (2%), associated with kaolinite (3%) and illite (7%) (Table 11).

The upper part is characterized by a richness in phosphate (33%), palygorskite (27%), and (22%) sepiolite is associated with kaolinite (3%), illite (7%), and quartz (5%) (Table 11).

Thelja and Chouabine equivalent at Jebel Chamsi section

Clay samples of the upper Paleocene lower Eocene argillaceous rocks demonstrate that they have different compositions. The mineralogical analysis of the samples revealed the presence of five types of clay minerals: smectite, illite, kaolinite, sepiolite, and palygorskite. The associated minerals are represented by calcite, quartz, phosphate, opal CT, clinoptilolite, feldspars, and dolomite.

The lower term shows a richness in dolomite at its base (95–97%) associated with illite (1%), kaolinite (1%), feldspars (1%) and opal-CT (1%). Its middle part shows a richness in dolomite associated with the appearance of smectite (Table 12). The upper part is characterized by the presence of 37% smectite, 38% dolomite, 9% quartz, 8% calcite, 3% kaolinite, and 1% palygorskite. However, the highest portion is rich in dolomite (95%) associated with smectite (1%), illite (1%), calcite (1%) and feldspars (1%) (Table 12).

Table 12

Relative abundances of the identified major’s minerals in the Thelja equivalent Formation
Equivalent Thelja :Lower Term: Jebel Chamsi Section
Unit	Carbonates minerals	Clays minerals	Accessory minerals
Lower part	Dolomite : 95–97%	Illite : 1%	Opal CT : 1% Feldspars : 1%
Middle part	Calcite : 8% Dolomite : 38%	Smectite : 37% Kaolinite : 3% Palygorskite : 1%	Quartz : 9% Feldspars : 1% Glauconie : 0–5%
Upper part	Calcite : 1% Dolomite : 95%	Illite : 1%	Quartz : 3% Feldspars : 1%

The middle term shows the presence of calcite at its base (40%), dolomite (21%), and phosphate (20%) associated with smectite (8%) and kaolinite (3%), quartz (8%), feldspars (4%) and opal CT (3%) suggesting a warm and arid climate (Table 13). The rest of the medium–term shows a wealth in ankerite (69–86%), smectite (2–8%), kaolinite (2–8%), palygorskite (1–4%), quartz (2–8%) associated with feldspars (0–4%) and opal CT (0–2%) (Table 13). The upper term reveals a richness in ankerite (> 70%), smectite (0–3%), kaolinite (0–2%), palygorskite (12–13%) and quartz (3–5%) (Table 13).

Table 13

Relative abundances of the identified major’s minerals in the Chouabine equivalent Formation
Equivalent Chouabine :Middle and upper Term: Jebel Chamsi Section
Unit		Carbonates minerals	Clays minerals	Accessory minerals
Middle Term	Lower part	Calcite : 40% Dolomite : 21%	Smectite : 2% Kaolinite : 3%	Quartz : 8% Opal CT : 3% Feldspars :4% Phosphate: 20%
Middle Term	Upper part	Ankerite : 69–86%	Smectite : 2–8% Kaolinite : 2–8% Palygorskite : 1–4%	Quartz : 2–8% Opal CT : 0–2% Feldspars : 0–4%
Upper Term	Lower part	Calcite : 4% Dolomie : 6%	Sepiolite : 2% Palygorskite : 3%	Quartz : 55% Phosphate: 26% Feldspars : 5%
Upper Term	Upper part	Calcite : 2% Dolomie : 88%	Palygorskite : 4% Sepiolite : 1%	Quartz : 1% Feldspars : 2% Opal CT : 2%

The clay paragenesis of the studied deposits provides information concerning climate conditions and paleoenvironment sedimentation.

Haria Formation (upper Maastrichtian–lower Paleocene deposit

The calcite contents are very important throughout all sections but seem to decrease above the K/T and toward the summit of the Haria Formation. The phyllosilicate contents show an inverse image and appear with average contents in all the units, indicating contributions of continental runoff. These contributions of clastic material can come from the approximate emerged zones. A marine regression beginning at the end of the Cretaceous (Hallam et al., 1991; Hallam, 1991) may also play a role in this increase in continental outflow. The appearance of quartz in the petrographic study in the basal part of the lifted section as well as above the K/Pg boundary of Haria Formation, is marked in the washing refusals and also noted in the mineralogical study.

The samples studied around the K/Pg boundary appear to be poor in calcite and relatively rich in quartz and phyllosilicates. Ultimately, the calcite content decreases sharply. As the main sources of this mineral are limestone, nannoplankton, and foraminifera, a biological crisis may be suggested at the K/Pg boundary, thereby reducing carbonate production (Millot, 1964; Slansky, 1980; Singer, 1984; Thiry, 2000; Jamoussi et al., 2003; El–Ayyat, 2013).

The smectite content is very high in all of the studied sections, but a fall in favor of kaolinite and illite is observed a few meters around the boundary while a slight decrease is observed in the middle part of deposits considered to be of Maastrichtian age (lower part of the Haria Formation). The smectite indicates a warm climate with contrasting seasons. Its fine, flake-like structure renders it conducive to distal transport. This clay is therefore concentrated in the center of ocean Basins and is representative of a deep depositional environment.

A slight increase in interstratified and illite contents is observed in the middle part of the Haria Formation and above the K/Pg boundary indicating paleoclimatic conditions, favoring mechanical rather than chemical alteration. The high content of these minerals therefore indicates a colder climate with less precipitation, thus promoting physical deterioration. The effect of a drop in sea level (Hallam et al., 1991; Hallam, 1992) or a rapprochement of the coasts can thus be observed across the Maastrichtian–Danian transition (Hallam et al., 1992).

Kaolinite requires more intense precipitation, favoring chemical alteration. Climate change may therefore explain the increase in the levels of this mineral in the lower part of this formation until the Cretaceous–Paleogene transition. Kaolinite seems to increase quite gradually throughout the Maastrichtian–Danian transition, suggesting increasing humidification of the climate. In summary, the first zone with a hot and humid climate with contrast seasons can be defined from the base of the Haria Formation to the K/Pg boundary.

Throughout the Maastrichtian–Danian interval, the assembly of clay minerals highlights the transition from a hot and humid climate with a marked seasonality alternating between wet and dry periods, associated with a dominance of smectite, to a drier and cooler climate, favoring mechanical alteration and kaolinite formation. A few meters above the K/Pg boundary, the simultaneous supply of illite and kaolinite in large quantities indicates significant terrigenous contributions, revealing a greater erosion of continental relief.

A colder and drier climate is established from the first centimeters of the Danian deposits (middle part of Haria Formation), favoring an increase in physical alteration. A significant increase in kaolinite and illite at the expense of smectite in the basal part of Paleogene deposits shows the possibility of significant terrigenous contributions, indicating a more significant alteration of continental relief and perhaps a decrease in distance from the coast.

The upper part of the Haria Formation shows richness in smectite and illite with little kaolinite, which seems to show a proximal and stable environment again dominated by a semi–arid climate with alternating dry and humid periods, favoring the formation of smectite.

Finally, the mineralogical assemblages generally go in the direction of a hot and humid climate with a season contrasted with the Upper Cretaceous, which becomes colder and drier at the beginning of the Paleogene.

Spatial distribution of mineralogical assemblages

The mineralogical profiles of the sections located in the center of the Gafsa Basin (OT section) generally contain less smectite than those studied in the east (JO and JC section) and west (M Tamerza section). Correlatively, the proportion of illites increases very strongly in the Jebel Ong section. The interstratified terms of the transformation from smectite to illite, are observed in eastern sectors (OJ and JC sections) while they are absent in the sections of the western region (Tamerza). This difference indicates that the transformation from smectite to illite is more complete in the eastern sectors. This succession must be compared with the increasing influence of bathymetry and depositional environment according to an east–west oriented gradient. In summary, the clay assemblages of the Haria Formation have undergone increasing diagenesis toward the east. This is marked by a clear transition from smectite to interstratified illite in the marl.

In the study area, smectite are probably of pedogenetic origin, since there are no known volcanic influences in the region during the Cretaceous and clay minerals are deposited in an open marine environment, not subject to chemical containment. Pedogenetic smectite is currently formed in hot climates with strong seasonal contrasts in humidity and the lower parts of poorly drained watersheds with little accentuated morphology (Millot, 1964; Paquet, 1970; Slansky, 1980; Singer, 1984; Thiry, 2000). The abundance of these minerals in the upper Maastrichtian reflects a warm climate with contrasting seasonal humidity as well as great stability of the continental margins allowing active pedogenesis. The relay of smectite via illite through the upper Maastrichtian–lower Danian suggests active erosion of the emerged areas since the illite characterizes deep rocks of the continental substrate. Moreover, this resumption of erosion marked by local presence of conglomerates would be linked to major tectonic movements in the internal zones.

In the Tamerza region, kaolinite is practically absent. The rarity of this mineral does not seem to be due to the diagenetic imprint, since abundant smectite is more sensitive than kaolinite to increases in pressure and temperature (Messadi et al., 2016). The very low proportions of kaolinite are most relatable to unfavorable climatic conditions at significant distance from the terrigenous sources, since this mineral is deposited preferentially near the shores and on carbonate platforms.

The deposition of marls from the upper Maastrichtian–lower Danian interval (Haria Formation) takes place in an open sea environment, in a distal marine or oceanic setting with low hydrodynamic energy and where the grains of clay are gradually deposited. The depositional environment was probably quite deep, of the circalittoral type evolving to lagoonal.

The relative abundance of smectite during the upper Maastrichtian, indicates stability of the emergent lands subjected to an active pedogenesis developed in hot climates with strong seasonal contrasts of humidity. However, the decrease of smectite in favor of illite and kaolinite in the upper Maastrichtian–lower Danian, reflects a significant resumption of erosion, coinciding with active tectonism and leading to numerous resedimentation phenomena.

The lower part of the Haria Formation “Maastrichtian” (Adatte et al., 2002) shows the presence of kaolinite in all the central sections with the eastern basin record suggestive of a hot and humid climate at that time.

The virtual absence of kaolinite in the Haria Formation in the Tamerza section suggests that the coastline was very far from this area of the Basin. The abundance of smectite in the two adjacent sections of the study area (Tamerza and JC sections) is explained by the deepening of the environment. In the other two sections (OT and JO), the presence of interstratified illite is noted, suggesting the diagenetic influence confirmed by the large percentages of ankerite (> 50%). The spatial distribution of the mineralogical assemblages shows that the depositional environment in the two sections—those of Tamerza and Jebel Chamsi are the deepest, which has already been confirmed by the study of the collected faunistic associations (Messadi et al., 2016).

In conclusion, the K/Pg boundary, the mineralogical associations show richness in kaolinite, enrichment in quartz, and the absence of other clay minerals suggestive of a hot and humid climate and a regressive trend which continues throughout the lower Danian with the presence of minerals of confinement (palygorskite and sepiolite) in the central Basin section (OT).

The upper part of Danian is characterized by the presence of kaolinite and illite which suggests a hot and humid climate with the intensification of erosion. The presence of smectite in the western part is explained by the deepening environment of deposition.

The summit of the Haria Formation (considered to be of upper Danian or Selandian) is characterized by the dominance of smectite, decrease in illite, and the appearance of kaolinite in low grades. This indicates a seasonality or possibly an alternation between dry and wet seasons.

The combination of clay minerals from upper Maastrichtian shows dominance of smectite, reflecting a semi–arid climate with contrasting seasons. A colder and drier climate, favoring physical alteration, is observed in the first deposits of the Paleogene. The Danian deposits show a decrease in smectite in favor of illite and kaolinite, which could indicate a period of intensified detritus.

Thelja Formation and its equivalent in Chamsi section

The presence of significant levels of kaolinite at the base of the Thelja Formation indicates a climatic change compared to the Haria Formation and can therefore explain the increase in the contents of this mineral in the lower part of this unit toward a wetter climate with more intense precipitation, favoring chemical alteration.

The middle part shows smectite and illite enrichment indicating a hot and arid climate. However, the presence of smectite indicates a hot climate with contrasting seasons. The presence of the smectite-kaolinite association in the uppermost part of this formation indicates the appearance of the colder and wetter seasons in the Thanetian deposits.

The spatial distribution of the mineralogical assemblages of the Thelja Formation shows the richness in smectite in the Tamerza section in comparison with the other sections, which suggests that this locality represents the deepest part of the Basin while these features may be linked to the confinement of the environment in the middle and upper part of the regional succession.

The illite is present in all sections the minimal occurrence percentage in Jebel Ong and Jebel Chamsi sections indicates a location close to the source of sediment supply. The increase in these percentages follows regressive sedimentary evolution. On the other hand, intervals particularly rich in smectite underline a tendency to toward a deepening marine setting. Its fine structure, in flakes allows distal transport. Smectite-rich clay is therefore concentrated in the center of ocean Basins and is representative of a deep depositional environment. This is also attested by a relative enrichment in planktonic organisms (Adatte et al., 2002; Messadi et al., 2016).

The study of the vertical evolution of the Thelja Formation with the preponderance of illite over smectite reveals that from the middle part to the top of this formation, illite becomes increasingly abundant. The enrichment levels in illite are accompanied by the abundance of gypsum, but also by the depletion of smectite and fossil deposits reflecting difficult conditions for the development of organisms. This clear regressive character confirms the evolution of the facies, already observed in the field. Furthermore, the presence of smectite and the absence of kaolinite, at least at the base of this unit, provides information on an arid climate (Slansky, 1980; Singer, 1984; Thiry, 2000; Jamoussi et al., 2003, ElAyyat, 2013, Messadi et al, 2016).

The enrichment of smectite within the upper levels of the Thelja Formation with smectites indicates deepening. Furthermore, the presence of clinoptilolite also suggests environmental containment conditions (Sassi, 1974). This confinement which took place in a deep environment translates into the dwarfism of the planktonic microfauna (Messadi et al, 2016). The presence of quartz indicates a detrital origin of these clays (Millot, 1964).

Chouabine Formation and its equivalent in the Jebel Chamsi

Mineralogical analysis of the samples from the upper Paleocene–lower Eocene interval from sections of the Chouabine Formation reveals the presence of five types of clay minerals: smectite, illite, kaolinite, sepiolite, and palygorskite. Associated minerals are represented by calcite, quartz, phosphate, CT opal, clinoptilolite, feldspars, and dolomite. Depending on the clay and non–clay mineral distribution, four distinct mineral zones can be defined.

Zone 1, lower part of the Chouabine Formation

The clay fraction in this zone shows dominance of smectite, a low level of illite and kaolinite. However, the absence of kaolinite in the Tamerza section and the absence of smectite in the Oued Thelja section with rates high in sepiolite, suggest to a very arid climate.

Zone 2, lower part of the Chouabine Formation (excluding basal 2 m)

This zone is marked by an increase in the smectite content but lower than at the base of the formation and the absence of kaolinite and illite except in the Tamerza section. The absence of smectite in the Oued Thelja section, and replaced by large percentages of sepiolite, suggests a hot and humid climate with contrasting seasons.

Zone, 3 middle part of the Chouabine Formation

This zone is marked by the richness in sepiolite and palyorskite and the absence of smectite and kaolinite in the Tamerza and Oued Thelja sections but with these minerals present in low concentrations in the two other sections (OJ and JC). The illite is present in Tamerza and Jebel Ong with low values indicative of a very arid climate.

Zone 4, upper part of the Chouabine Formation

Sepiolite and palygorskite are always abundant in association with illite in the Tamerza section and smectite in the Oued Thelja section as well as with kaolinite in the Jebel Ong and Chamsi sections suggest a hot and humid climate with mixed seasons. The presence of high percentages of sepiolite and palygorskite require periods of tectonic latency which are essential to avoid a supply of coarse detrital elements. However, a progressive depression of subsidence favors the confinement. The distribution of the clay fraction shows a predominance of smectite, sepiolite, and palygorskite along the sections. We note the appearance of kaolinite in the base of the Oued Thelja section and the top and basal part of the Chamsi and Jebel Ong sections at low concentrations. The associated minerals are mainly represented by calcite, quartz, phosphate, CT opal, clinoptilolite, and feldspar, and are present throughout all sections. The dolomite appears only at the top of unit C1 of the Jebel Ong section, the top of unit C2 of the Oued Thelja section, and at the top of unit C1 of the Tamerza section.

The vertical distribution shows that this formation is characterized by a particular richness in smectite at its base, indicating a significant environment deepening which confirm the major marine transgression at the base of the Chouabine Formation. In addition, we noted a paucity this mineral from the base to the top implying changes in terms of depositional environment more than hose otherwise due to climatic variance. The smectite decreased in favor of illite and palygorskite reflecting a relative decrease in the water deepening. This is also evidenced by the decrease in the percentages of benthic foraminifera and the presence of lumachellic limestone deposits toward the summit (Messadi et al., 2019). In addition, the presence of clinoptilolite reflects the slightly anoxic character of marine waters required for the genesis of phosphates (Slansky, 1980).

Laterally (west to east), the base of the Chouabine Formation is characterized by the richness of smectite with percentages that decrease and its absence in the center of the basin which is characterized by high levels of sepiolite. These two minerals are associated with illite in the Tamerza section, with kaolinite in the Oued Thelja section, Jebel Ong, and Chamsi sections with increasing in its percentages toward Jebel Chamsi. In the lower part of the Chouabine Formation, smectite and sepiolite remain dominant, but with lower percentages than at the base, which is marked by the absence of kaolinite except in the Chamsi section. The middle part shows the re–appearance of high smectite value, but it is characterized by richness in sepiolite and palygorskite with maximum values in the central part of the Basin (OT section) and, decreasing in the Tamerza section. This part of the basin wide succession is characterized by the presence of smectite associated with palygorskite in the Jebel Ong section and associated with kaolinite in Jebel Chamsi section.

The decrease in kaolinite and illite in the middle part of this formation is linked to climate change from wetter to arider conditions lending to the transformation of smectite into illite in supratidal environments following the alternation of dry and wet periods (Singer, 1984; De Coninck et al., 1985). The illite comes from recycling of the substratum, whereas the kaolinite results from the reorganization of the lands (De Coninck et al., 1985). The increase of erosion during periods of low sea level can involve an increase in illite content compared to kaolinite. The reappearance of kaolinite in the middle and top part of this formation is probably linked to arid-to-wetter climate change, and / or to the reworking of the kaolinite stored in the most proximal environments of the platform during the flooding of the second transgressive cycle of the lower Ypresian (Messadi et al., 2019). Therefore, the reworking of kaolinite stored in the most proximal depositional environments of the platform during major flooding remains the most likely solution. The increase in kaolinite is generally associated with an increase in the amount of quartz. In this case, the quantity of quartz remains low and relatively constant. Indeed, the Gafsa Basin Ypresien is characterized by a strong increase in the available space and significant carbonate production in its central portion. The upper part of the Chouabine Formation is marked by the re–appearance of smectite in the sections of Tamerza and Oued Thelja associated with palygorskite. There the two other sections show the presence of palygorskite and sepiolite, which is associated with kaolinite in the Jebel Chamsi section.

In the top part of this formation, the relative enrichment in smectite reflects a slight deepening of the marine environment. Its association with dolomite and, above all, sepiolite indicates that the environment was still slightly reduced. Kaolinite is generally characteristic of hot and humid regions, while illite indicates a temperate and arid climate (Singer, 1985; Chamley, 1989). Consequently, the increase in kaolinite in the Chamsi section is probably linked to the change in the depositional environment more than an instance of climate change from drier to wetter. In general, the mineralogical association shows the richness of the Tamerza section in smectite and associated illite and sepiolite showing an evolution in a deep marine environment in the form of two transgressive cycles. The Oued Thelja section shows the richness in smectite at the base and progressing to high values in sepiolite and palygorskite with an evolution reflecting two transgressive cycles in a confined environment representing the deepest part of the Basin (Oued Thelja section). The Jebel Ong section shows the presence of smectite in the basal and middle parts, highlighting the limits of two transgressive cycles. This mineral is associated with Kaolinite and illite. The Jebel Chamsi section shows a similar evolution to that of the Jebel Ong, but with the absence of the illite constituting the shallowest part while deeper still than at Jebel Ong.

Comparison with worldwide paleoclimate

Climatic conditions were caused by an overall change in the mode of ocean circulation reflected in patterns of clay deposition. Indeed, until the Upper Cretaceous–Lower Eocene, the Tethys had a major role in the global ocean circulation and sediment input. Global warming constitutes a potential source of deep water masses, as well as head and salinity, during the brief episode of reversal of ocean circulation. In addition, the southern Tethyan margin was located in the northern tropical zone and was subject to upwelling episodes under a warm climate (Bolle et al., 1999). Constituting a part of the southern Tethyan margin, Tunisia was under the control of synsedimentary tectonics and climatic conditions. Several authors (Salaj, 1980; Marie et al., 1982; Amiri et al., 2005) have reported that during the Paleocene interval, synsedimentary tectonics were activated since the Campanian in both central and northeastern areas, leading to complex paleotopography where horsts limit subsidence areas. These features advocate for an evident change in climate as compared to previous works carried out on the southern Tethyan margin (Scheibner and Speijer, 2008). These substantial changes were noticed overall in the world (Scheibner and Speijer, 2008). Since the pioneering work of Shackleton & Kennett (1975), the Cenozoic and more particularly the Paleogene, has been a period in which the paleoclimatic evolution has been, particular focus of study. The Paleogene experienced almost continuous cooling which, was in all environments, interrupted by only occasional warming (Tivollier & Létolle, 1968; Shackleton & Kennett, 1975; Buchardt, 1978; Miller et al., 1987; Zachos et al., 1993, 1994, 2001, 2003; Lear et al., 2000). The first climatic anomaly known in the Paleogene occurred at the Paleocene–Eocene boundary known as the PETM (Paleocene–Eocene Thermal Maximum ~ 55 Ma, Zachos et al., 2008). This occured during the warming phase initiated from the climax of the EECO (Early Eocene Climatic Optimum), which constitutes the hottest period of the Paleogene with ocean temperatures between 10 and 12°C. During this period, the ice is supposed to be absent or very reduced on Earth, and we therefore speak of the 'Greenhouse' period (Zachos et al., 2001). The temperatures were not only high, but the climatic bands, especially the tropic zones, extended to higher latitudes than today. These climatic characteristics of the Paleocene and lower Eocene were not only highlighted from studies of isotopic geochemistry (Saito & Van Donk, 1974; Barnet et al., 2019). Tropical type vegetation has been observed up to 45° N, along with assemblages of tropical planktonic Foraminifera. Alligator fossils have also been identified on Ellesmere Island in west Greenland (Estes, 1975; 78 ° N). Finally, the mineralogical assemblages also go in the direction of a hot and humid climate at the beginning of the Cenozoic with kaolinite found in the sediments around Antarctica and latitude up to 45 ° N (Robert & Chamley, 1991). The cooling that followed this climatic optimum was accompanied by a 7 ° C decrease in bottom water temperatures, which led to the glaciation of the Eocene-Oligocene boundary (~ 34 Ma), marking the start of the, Icehouse period that we still know today (Zachos et al., 2001). Between these two climatic extremes, cooling takes place is still little understood and poorly documented, even if recent studies have brought significant constraints on the climatic evolution of the middle and upper Eocene (Lear et al., 2000; Bohaty & Zachos, 2003; Tripati et al., 2005; Burgess et al., 2008; Bohaty et al., 2009).

During the Paleocene, marine limestone and shale accumulated in much of the Sahara, and the African plate was located approximately 10–20 ° N of latitude south of its modern position. The climate in the Sahara at this time is thought to have been generally hot and humid (Bellion, 1989), although studies of Paleocene strata in southern Tunisia suggest that there was variability from a warm and humid climate during the early Paleocene to a warm and arid climate during the Paleocene–Eocene transition (Keller et al., 1998; Bolle et al., 1999). Other studies cite evidence for a major transgression in the Sahara that culminated in a sea level highstand during the late Paleocene (Reyment, 1980; Bellion, 1989). This transgression would be coincident with a global warming trend that began during the late Paleocene and ended during the early Eocene (Miller et al., 1987; Zachos et al., 2001). In addition, a very abrupt and brief episode of global warming during the LPTM (Late Paleocene Thermal Maximum) occurred near the Paleocene–Eocene boundary, superimposed on the general Paleocene–Eocene warming trend (Zachos et al., 1993, 2001).

The Clay paragenesis of the studied deposits brings out valuable information about climate and paleoenvironment conditions. Six lithostratigraphic sections were logged in the areas of Tamerza, Oued Thelja, Ong and Chamsi. An initial zone showing a hot and humid climate with contrasting seasons can be defined from the base of the succession toward the K/Pg boundary generating clay sequences with mineralogical assemblages rich in smectite in the eastern part reflect the distances from the sources more than the climatic conditions. During the Maastrichtian–Danian transition, the assembly of clay minerals highlights the transition from a hot and humid climate with a marked seasonality alternating between wet and dry periods, characterized by a dominance of smectite, to a cooler climate favoring mechanical alteration and kaolinite formation. A few meters from above the K/Pg boundary, the simultaneous influx of illite and kaolinite in large quantities indicates significant terrigenous input, revealing a greater erosion of continental relief generating thick sedimentary sequences. The upper part of the Danian interval shows richness in smectite and illite, although little kaolinite. This profile seems to indicate a proximal and stable environment again dominated by a semi–arid climate with alternating dry and humid periods, favoring the formation of smectite-generating highly developed depositional sequences. Finally, the mineralogical assemblages also go point toward of a hot and humid climate with a contrasting seasonality during the Late Cretaceous, become colder and drier at the beginning of the Cenozoic.

The presence of kaolinite at the base of the Thelja Formation, dated as Thanetian indicates that climatic change can therefore explain the increase in the contents of this mineral in the lower part of this unit toward a more humid climate with more intense precipitation, favoring chemical alteration generating carbonate. The middle and top part of the Thelja Formation shows smectite and illite enrichment indicating a hot and arid climate generating evaporitic sequences. Mineralogical analysis of samples from the Paleocene/Eocene passage intervals from the section of the Chouabine Formation. Deposits of Chouabine Formation are dominated by smectite and sepiolite suggesting a hot and arid climate generating phosphatic sequences. Indeed, the abundance of clinoptilolite, sepiolite, palygorskite, and the rarity of smectites reflect a semi–confined marine environment. These analyses confirm the results obtained by microscopic examinations of the facies. Microfossil associations indicate shallow infratidal to circatidal environments.

Acknowledgements

The authors would like to thank the personnel of the Civil Engineering department at National Engineering School of Sfax (ENIS), the Physics Department of the Faculty of Science of Bizerte and the personnel of the Higher Institute of Biotechnology of Sfax for their technical support.

Data availability

This paper is written purely for academic research purposes and the author have no commercial or financial conflicts of interest. Data will be made available upon reasonable request for academic use and within the limitations of the provided informed consent by the corresponding author upon acceptance. Every request will be reviewed by the institutional review board.

AUTHORS' CONTRIBUTIONS

The authors confirm sole responsibility for the following:

Data collection, analysis and interpretation of results, and manuscript preparation

Declaration of interests

This paper is written purely for academic research purposes and the author have no commercial or financial conflicts of interest.

Adatte, T., Gerta, K., & Wolfgang, S. (2002). Late Cretaceous to early Paleocene climate and sea–level fluctuations: the Tunisian record. Palaeogeography, Palaeoclimatology, Palaeoecology, 2754, 1-32.
Amri, A., Ben Youssef, M., & Ghanmi, M. (2005). Enregistrement de phénomènes de resedimentation au cours du Maastrichtien supérieur et du Paléocène supérieur (J. Serj, Tunisie atlasique) : apport micropaléontologique et signature tectono–eustatique. Comptes rendus Geosciences, 1525-1531.
Barnet, J.S.K., Littler, K., Westerhold, T., Kroon, D., Leng, M.J., Bailey, I., Röhl, U., & Zachos, J.C. (2019). A High-Fidelity Benthic Stable Isotope Record of Late Cretaceous–Early Eocene Climate Change and Carbon-Cycling. Paleoceanography and Paleoclimatology, 34: 672-691
Bellion, Y.J.C. (1989). Histoire géodynamique post–Paléozoïque de l’Afrique de l’Ouest d’après l’étude de quelques bassins sédimentaires (Senegal, Taoudenni, Iullemmeden, Tchad). Centre International pour la Formation et les Échanges Géologiques (CIFEG), Publication Occasionnelle 1989/17. 302 p.
Bohaty, S.M., & Zachos, J.C. (2003). Significant Southern Ocean warming event in the late middle Eocene. Geology, 31, 1017-1020.
Bohaty, S.M., Zachos, J.C., Florindo, F., & Delaney, M.L. (2009). Coupled greenhouse warming and deep–sea acidification in the middle Eocene. Paleoceanography, 24, http://dx.doi.org/10.1029/2008PA001676.
Bolle, M.P., Adatte, T., Keller, G., Von Salis, K., & Burns, S. (1999). The Paleocene–Eocene
transition in the southern Tethys (Tunisia): climatic and environmental fluctuations. Bulletin de la Societe Geologique de France, 170, 661-680.
Buchardt, B. (1978). Oxygen isotope palaeotemperatures from the Tertiary period in the North Sea area. Nature, 275, 121,123.
Burgess, C.E., Pearson, P.N., Lear, C.H., Morgans, H.E.G., Handley, L., Pancost, R.D., & Schouten, S. (2008). Middle Eocene climate cyclicity in the southern Pacific: Implications for global ice volume. Geology, 36, 651-654.
Burollet, P.F. (1956). Contribution à l‟étude stratigraphique de la Tunisie centrale. Ph.D. Thesis Paris. Annales des Mines et de la Géologie, Tunis, n°18,350"p."
Brindley, G.W., & Brown, G. (1980). Crystal structures of Clay Minerals and Their X-ray Identification (first ed.), Mineralogical Society, London, 411-438
Carroll, D., (1970). Clay minerals: a guide to their X–Ray identification. Geological Society of America. Special paper (126), 80"p."
Chamley, H., De Coninck, J.F., & Millot, G. (1999). Sur l’abondance des minéraux smectitiques dans les sédiments marins communs, déposés lors des périodes de haut niveau marin du Jurassique supérieur au Paléogène, Compte Rendus Académie de Sciences. Paris, Ser. II 311, 1529-1536.
De Coninck, J., Chamley, H., Beaudoin, B., Accarie, H., & Renard, M. (1985). Paleoenvironmental and diagnostic significance of Aptian to Eocene clay mineral successions of the Umbria Marche Basin (northern Apennines, Italy). In: Abstract International Conférence. Association Internationale Pour l'Etude des Argiles, Strasbourg, 23–28 August.
EL–Ayyat, A.M. (2013). Sedimentology, sequential analysis and clay mineralogy of the lower Eocene sequence at Farafra Oasis, Western Desert of Egypt. Journal of African Earth Sciences, 78: 28-50.
El Ayachi, M.S., Zagrarni, M.F., Snoussi, A., Bahrouni, N., Gzam, M, Ben Assi, I., Hammami, K., Abdelli, H., & Ben Rhaiem, H. (2016). The Paleocene–lower Eocene series of the Gafsa Basin (South–Central Tunisia): integrated stratigraphy and paleoenvironments. Arabian Journal of Geosciences. 9. 10.1007/s12517–016–2403–0.
Estes, R., (1975). Lower vertebrates from the Fort Union Formation, late Paleocene, Big Horn
680 Basin, Wyoming: Herpetologica, v. 31, 365-385.
Fournie, D. (1978). Nomenclature lithostratigraphique des séries du crétacé supérieur au
tertiaire de Tunisie. Bulltin Centre de Recherche production Elf Aquitaine, 2, 1, 97-148.
Hallam, A. (1991). Phanerozoic sea–level changes. New York, Columbia University Press,
266 "p."
Hallam, A., Grose, J.A., & Ruffel, A.H. (1991). Palaeoclimatic significance of changes in clay mineralogy across the Jurassic–Cretaceous boundary in England and France. Palaeogeography. Palaeoclimatology. Palaeoecology. 81, 173-187.
Jamoussi, F., Bédir,M., Boukadi, N., Kharbachi, S., Zargouni, F., López–Galindo, A., & Paquet, H. (2003). Clay mineralogical distribution and tectono–eustatic control in the Tunisian margin Basins; Comptes Rendus Geoscience 335, 175-183.
Keller, G., Adatte, T., Stinnesbeck, W., Stüben, D., Kramar, U., Berner, Z., Li, L., & Salis
Perch–Nielson, K. (1998). The Cretaceous–Tertiary transition on the shallow Saharan Platform of southern Tunisia. Geobios, 30, 951-975.
Khozyem, H., Adatte, T., Spangenberg, J., Tantawy, A., & Keller, G. (2013). Paleoenvironmental and climatic changes during the PaleoceneEocene Thermal Maximum (PETM) at the Wadi Nukhul Section, Sinai, Egypt. Journal of Geology Society of London 170,341-352.
Khozyem, H., Adatte, T., Spangenberg, J. E., Keller, G., Tantawy, A. A., & Ulianov, A. (2015). New geochemical constraints on the Paleocene–Eocene thermal maximum: Dababiya GSSP, Egypt. Palaeogeography, Palaeoclimatology, Palaeoecology, 429, 117-135.
Kennett, J.P., & Stott, L. D. (1991). Abrupt deep–sea–warming, paleoceanographic changes and benthic extinctions at the end of the Paleocene. Nature, 353, 319-322.
Lear, C.H., Elderfield, H., & Wilson, P.A. (2000). Cenozoic deep–sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite. Science, 287, 269-272.
Marie, J., Trouve, P., Desforges, G., & Dufaure, P. (1982). Nouveaux éléments de la
paléogéographie du Crétacé de la Tunisie. In: Notes Mémoires. 19, CFP–total, Paris, 1982, 6-37
Messadi, A. M., Mardassi, B., Ouali, J. A., & Touir, J. (2016). Sedimentology, diagenesis, clay mineralogy and sequential analysis model of Upper Paleocene evaporite–carbonate ramp succession from Tamerza area (Gafsa Basin: Southern Tunisia), Journal of African Earth Sciences, 18, 205-230, ISSN 1464–343X.
Messadi, A. M., Mardassi, B., Ouali, J. A., & Touir, J. (2017). Sedimentology, diagenesis, and sequential analysis of a carbonate series in shallow marine environments of the Middle Eocene deposits from Gafsa basin (Southern Tunisia). In 1st Atlas georesources international congress, Hammamet-Tunisia (Vol. 3, p. 2017).
Messadi, A. M., Mardassi, B., Ouali, J. A., & Touir, J. (2018). Diagenetic process as tool to diagnose paleo–environment conditions, bathymetry and oxygenation during Late Paleocene–Early Eocene in the Gafsa Basin. Carbonates and evaporites. https://doi.org/10.1007/s13146–018–0424–3.
Messadi, A. M., Mardassi, B., Ouali, J. A., & Touir, J. (2019). Sedimentology, sequential analysis and paleoclimate associations of the upper Paleocene–lower Eocene Chouabine Formation at the Oued Thelja section, Gafsa Basin, Southern Tunisia. Stratigraphy, 16, 4, 265-277.
Messadi, A. M., Touir, J., Mardassi, B., & Ouali, J. A. (2020). Factors controlling sedimentation and sequence stratigraphy evolution in shallow marine (carbonates) platform: example of Middle Eocene deposits from Gafsa Basin. Carbonates and Evaporites, 35(2), 1-24.
Messadi, A. M. (2021). Sédimentologie et stratigraphie séquentielle des dépôts de l’intervalle Maastrichtien supérieur Eocène dans le bassin de Gafsa. Thèse de doctorat, université Sfax 278"p."
Miller, K.G., Fairbanks, R.A., & Mountain, G.S. (1987). Tertiary oxygen isotope synthesis, sea–level history and continental margin erosion. Paleoceanography, 2, 1-19.
Millot, G., (1964). Géologies des Argiles. Masson and Cie. Paris, 498p.
PAQUET, H., (1970). Evolution géochimique des minéraux argileux dans les altérations et les sols des climats méditerranéens et tropicaux ~ saisons contrastées. Mdm. Sev. Carte Gdol. Alsace Lorraine, 30, 212.
Pierce, J.W. & Siegel, F.R. (1969). Quantification in clay mineral studies of sediments and sedimentary rock. Journal Sedimentary Petrology, 39: 187-193.
Reyment, R.A. (1980). Biogeography of the Saharan Cretaceous and Paleocene epicontinental transgressions. Cretaceous Research 1, 299-327.
Robert, C. & Chamley, H. (1991). Development of early Eocene warm climates, as inferred from clay mineral variations in oceanic sediments. Global and Planetary Change, 89, 315-332.
Saito, T., & Van Donk, J. (1974). Oxygen and Carbon Isotope Measurements of Late Cretaceous and Early Tertiary Foraminifera. Micropaleontology, 20(2), 152–177.
Salaj, J. (1980). Microbiostratigraphie du Crétacé et du Paléogène de la Tunisie septentrionale et orientale (Hypostratotypes tunisiens), p. 238. Inst. Geol. Dionyz Stur, Bratislava, 1980.
Sassi, S. (1974). La sédimentation phosphatée au Paléocène dans le Sud et le Centre Ouest de la TUNISIE. Thèse d’Etat, Paris
Scheibner, C., & Speijer, R.P. (2008). Decline of Coral Reefs during Late Paleocene to Early Eocene Global Warming. Earth, 3, 19-26. http://dx.doi.org/10.5194/ee-3-19-2008
Shackleton, N.J. & Kennett, J.P. (1975). Paleotemperature history of the Cenozoic and the initiation of Antarctic glaciation: Oxygen and carbon isotope analyses in DSDP sites 277, 279 and 281. In: Initial Reports of the Deep Sea Drilling Project, 29. US Government Printing Office, Washington, DC, 743-755.
Singer, A. (1984). The paleoclimatic interpretation of clay minerals in sediments – a review. Earth Sciences Reviews. 21, 251-293.
Slansky, M. (1980). Géologie des phosphates sédimentaires–. Mémoire du B.R.G.M, n°92p
Thiry, M. (2000). Palaeoclimatic interpretation of clay minerals in marine deposits: an outlook from the continental origin. Earth–Science Reviews. 49, 201-221
Tivollier, J. & Létolle, R. (1968). Résultats et interprétation d’analyses isotopiques de faunes malacologiques du Tertiaire parisien. In: Pomerol C. (ed.) Colloque sur l’Eocène. Mémoires du Bureau de Recherches Géologiques et Minières, 58, 346-357.
Tripati, A., Backman, J., Elderfield, H., & Ferretti, P. (2005). Eocene bipolar glaciation associated with global carbon cycle changes. Nature, 436, 341-346.
Zachos, J., Lohmann, K., Walker, J.C.G., & Wise, S. (1993). Abrupt climate change and transient climates during the Paleogene: A marine perspective. Journal Geology, 101, 191-123.
Zachos, J., Stott, L., & Lohmann, K. (1994). Evolution of early Cenozoic marine temperatures. Paleoceanography, 9 (2), 353-387.
Zachos, J.C., Pagani, M., Sloan, L., Thomas, D.J., & Billups, K. (2001). Trends, rhythms, and aberrations in global climate 65 Ma to present. Science, 292, 686-693.
Zachos, J.C., Wara, M.W., Bohaty, S., Delaney, M.L., Petrizzo, M.R., Brill, A., Bralower, T.J., & Premoli–Silva, I. (2003). A transient rise in tropical sea surface temperature during the Paleocene–Eocene Thermal Maximum. Science, 302, 1551-1554.
Zachos, J.C., Dickens, G.R., & Zeebe, R.E. (2008). An early Cenozoic perspective
on greenhouse warming and carbon–cycle dynamics. Nature, 451, 279-283
Zaier, A., Beji–Sassi, A., Sassi, & S. Moody, R.T.J. (1998). Basin evolution and deposition during the Early Paleogene in Tunisia. In: Maggregor D.S., R.T.J. Moody & D.D. Clark–Lowes (Eds), and Petroleum Geology of North Africa. Geologica Society, London, Special Publication, 123, 375-393.
Zargouni. F., Laatar. S., Chaouchi. A., & Regaya, K. (1985). Carte géologique de la région de Metlaoui. Service géologique, ONM, 120 p.

No competing interests reported.

Paleo–climatic and paleo–environment implication of clay mineral across Upper Cretaceous–Lower Eocene deposits from Gafsa Basin

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Introduction

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