Paleoenvironmental reconstruction of the Pleistocene site of Oued Sarrat (Northwestern Tunisia) using mineralogical and geochemical data Текст научной статьи по специальности «Биологические науки»

VI7-

Journal of Geology, Geography and Geoecology

Journal home page: geology-dnu-dp.ua

ISSN 2617-2909 (print) ISSN 2617-2119 (online)

Journ.Geol.Geograph.

Geoecology, 27(2),316-322 doi: 10.15421/ 111855

Narjess Karoui-Yaakoub, Moncef Said Mtimet

Semeh Bejaoui, Bienvenido Martínez-Navarro Journ.Geol.Geograph.Geoecology, 27(2), 316-322

Paleoenvironmental reconstruction of the Pleistocene site of Oued Sarrat (Northwestern Tunisia) using mineralogical and geochemical data

Narjess Karoui-Yaakoub1, Moncef Said Mtimet1, Semeh Bejaoui1, Bienvenido Martínez-Navarro2'3'4

'Département des Sciences de la Terre, Faculté des Sciences de Bizerte, Université de Carthage, Jarzouna, 7021 Bizerte, Tunisia, narjess1999@yahoo.fr

2ICREA, Barcelona, Spain

3Institut Catalá de Paleoecologia Humana i Evolució Social. Campus Sescelades URV (Edifici W3), 43007 -Tarragona, Spain

4Area de Prehistoria, UniversitatRovira i Virgili (URV). Avda. Catalunya, 35. 43002 - Tarragona, Spain

Recewed 07.05.2018- Abstract. The mineralogical and geochemical analyses of Pleistocene sediments and

Recewed in fevisedform 27.07.2018; mollusks shells (gastropods and bivalves) from the archaeopaleontological site of Oued Accepted 01.06.2018 Sarrat (Tejerouine, NW Tunisia) permitted us to determine the paleoenvironmental

conditions and to reconstruct the local depositional environment during the Middle and Late Pleistocene. The mineralogical cortege of the sediments, for all the analyzed samples, records the characteristics of a mixture of silica and calcite dominance with a small fraction of gypsum and aragonite. The mineralogical analyses of all mollusk species reflect a cortege dominated by aragonite, associated with low amounts of calcite, silica, hematite and goethite. We consider that the dominance of aragonite indicates that the tests have not yet or little undergone mineralogical transformations linked to the phenomena of fossilization, as evidenced by the absence or low calcite content. On the other hand, the low percentages of silica, goethite and hematite are probably related to the existence of impurities and sediments trapped in lodges, or adhered to the shell surface. The minera-logical data confirm a composition dominated by calcium carbonates, expressed by high contents of CaO and CO2, reflecting a chemical test of organisms' development in continental environment.This kind of environment is characterized by the absence of MgO, which is usually present in the organisms' tests developed in marine environment. However, the contents of SiO2, Fe2O3, Al2O3 are related, as it was reported during the mineralogical study, to the lithological impurities trapped mainly in the lodges of helicides. Mineralogical and geochemical data tracing, carried out on sediments and tests, converge to deduce the establishment of paleoenvi-ronment attributable to fluvial deposition of sufficiently high energy where the ultrafine fractions of clay minerals are remarkably lacking. The absence of indicators of marine chemistry such as magnesium in sediments and in the tests of organisms confirms almost total contribution of the continental meteoric water without marine influence. Such environment, however, is affected by intermittent episodes of aridity as attested by the presence of evaporate minerals such as gypsumand aragonite.

Key words:Environment reconstruction, Geochemistry, Mineralogy, Pleistocene, Oued Sarrat, Tunisia

Палео-еколопчна реконструкщя плейстоценового мкцезнаходження Оуд Саррат (шв-шчно-захщний Тушс) з використанням мшералопчних та геохiмiчних даних

Нарьес Каруг-Яакуб1, Монсеф Сагд Мтiмет1, Семех Беджу1, Бенвешдо Марттез-Наварро2'3'4 1 Департамент наук в Ла-Терре, факультет наук Бгзера, Карфагенський умверситет, Ярзуна, 7021 Б1зерта, Тунк, narjess1999@yahoo.fr 2!СКЕА, Барселона, 1спатя

3 Каталонський шститут палеоекологИ людини та сощальноЧ еволюцИ. CampusSesceladesURV (EdificiW3), 43007 - Таррагона, Iспанi

4 Доiсmорична область, Умверситет Ровiра i Вергж (УРВ). Avda Каталошя, 35. 43002 - Таррагона, 1спатя

Анотащя У мшералопчному та геохiмiчному аналiзах плейстоценових осадiв та черепашок молюскв (черевоногих та двостулкових) з археопалеонтолопчного об'екта Оуд-Саррат (Тейчеруш, Швшчний Тушс) дозволили визначити палеоеко-лопчш умови навколишнього середовища та реконструювати локальне осадове середовище протягом середнього та тзньо-го плейстоцену. Мшералопчна послвдовшсть вщкладш для вах анатзованих зразюв фжсуе характеристики сум^ кремне-

зему та домшуючого кальциту 1з незначною кшьюстю гшсу та арагошту. Мшералопчний анал1з уах видш молюсюв ввдо-бражае послвдовшсть, в якш домшують арагошт, пов'язаний з низькою кшьюстю кальциту, кремнезему, гематиту та гетиту. Ми вважаемо, що домшування арагошту вказуе на те, що дослвджет зразки ще не зазнали або зазнали незначних мшерало-пчних перетворень, пов'язаних з явищами лгшфжаци, про що свщчать вщсутшсть або низький вмкт кальциту.З шшого боку, низький вмгст кремнезему, гетиту i гематиту, ймов1рно пов'язаний з юнуванням змшування i захоплення осадш у базальному шар1, або прикршлення до поверхш оболонки черепашки. Мшералопчш даш тдтвердили склад, в якому пере-важають карбонати кальщю, що ввдбиваеться високим вмктом СаО i С02 та вщображае х1м1чний склад оргашзмпв, яю розвивалися у континентальних умовах. Цей вид середовища характеризуеться вщсутшстю Mg0, який зазвичай присутнш у дооиджуваних оргашзмах, що розвивалися у морському середовищг Однак вмкт БЮ2, Ге203, А1203 е пов'язаним, як вста-новлено мшералопчними дослвдженнями, лгтолопчно неоднор1дними сумшами в норках гелщидш. Доолджеш мшералопчш 1 геоым1чш даш, яю отримаш по осадах 1 зразках, свщчать про встановлення особливостей палеосередовища у зв'язку | 1з флюв1альними потокамидостатньо високо! енерги, в яких суттево бракуе надтонких фракцш глинястих мшератв. Вщсут-шсть у осадах i зразках оргашзм1в шдикаторш утворення !х у морському середовищ^ таких як магнш, шдтверджують майже повне привнесення континентально! атмосферно! води без впливу морсько!. Втам, таки умови еколопчного середовища зумовлеш впливом перюдичних ешзодш аридизаци ктмату, про що св1дчить присутшсть такого евапоритового мшералу як гшс.

1. Introduction. The archaeopaleontological site of Oued Sarrat (Tejerouine, NW Tunisia) was discovered in 2014 and a large amount of vertebrate data was added for North Africa, with a special discovery of the aurochs Bos primigenius (Martínez-Navarro et al., 2014) and Canis othmanii fAmri et al., 2017). The Quaternary continental molluscs from this site were studied for the first time by Ka-roui-Yaakoub et al. (2016). Here we present mine-ralogical and geochemical data obtained from the Pleistocene sediments and molluscs tests (gastro-

pods and bivalves) of Oued Sarrat with the aim of reconstructing the Middle and Late Pleistocene paleoenvironments of the Oued Sarrat basin. 2. Geographical and geological setting. Oued Sarrat is located in the northwestern part of Tunisia, 10 km southwestwards from the Tajerouine (Fig.1). This region belongs to an intermediate zone between the Central and the Northern Atlas of Tunisia, with diapirs and rifts. It is dominated by folded structures interspersed with rift basins corresponding to the kalaa el Khasba and Rouhia Depression.

8°15'

9tt15'_

36= 15'

— 36c

35° 45'

Fig. 1. Geographic location of the study area

The Pleistocene series of Oued Sarrat are composed of three units (Fig. 2). At the base, there are four meters of gray-black marl (OS1 and OS2). This layer is rich on vertebrate fauna, in particular Bos primigenius and Canis othmanii. This level is dated as beginning of the Middle Pleistocene (~0.7 Ma) by magnetostratigraphy and the presence of

fossil remains of rodents (Martínez-Navarro et al., 2014; Mtimet et al., 2014). It should be noted that these marls are rich in invertebrate fossils, specifically gastropods and bivalves.

Above, a second clay level (2m) overcomes the first black level unconformably. It is less compact and dated to the Late Pleistocene (OS3). This

level is rich in invertebrate fossils - bivalves (Unio ravoisieri) and gastropods (Xerosecta cespitum, Cernuella virgata, Eobania vermiculata, Helix melanostoma, Sphincterochila baetica, Rumina

decollata) (see Amri, 2014; Bejaoui, 2014; Marti-nez-Na-varro et al., 2014; Mtimet et al., 2014; Ka-roui-Yaakoub et al., 2016; Amri et al., 2017).

Lithological description

Fine yellow sand containing gastropods

-OS4

E-OS3

Less compact gray clay containing bivalves, gastropods anc bones of vertebrates

-OS2

More oompact black day containing bivalves, gasrt'o-jeds arid *he skull of Bos prim/genius

-051

Bos primigwiius Bcnes o? vertebrates Bivalves a Gastropods Unconformity

Fig. 2. Stratigraphic synthesis of the Oued sarrat series (in Karoui-Yaakoub et al., 20116)

At the top of the section (Fig. 3), a second disconformity is registered by the deposition of the third level, yellow to slightly brownish marl about 4

m in thickness (OS4). It yielded gastropods of Ho-locene age (Martínez-Navarro et al., 2014; Karoui-Yaakoub et al., 2016).

Fig. 3. The unconformity between the Middle and Late Pleistocene and between the Late Pleistocene and Holocene (Martínez-Navarro et al., 2014)

3. Materials and methods. Shells of gastropods and bivalves were sampled following the described Middle and Late Pleistocene stratigraphic series, which is outcropped on both sides of the Oued Sarrat.

The mineralogical and geochemical studies were performed on clay sediments from three levels yielding malacofauna. Two samples (OS1 and OS2) come from the Middle Pleistocene level, one sam-

ple (OS3) - from the Late Pleistocene level, and

another one (OS4) - from Holocene marls.

4. Results of the study

4.1. Mineralogical cortege

4.1.1. Mineralogy on bivalves and gastropods

The results of mineralogical analyses of all registered mollusc species reflect a cortege dominated by mineral aragonite associated with low amounts of calcite, silica, hematite and goethite (Tab. 1, Fig. 4).

Table 1. Mineralogical composition of mollusk shells of Oued sarrat

FeO3% Hematite CaCO3% Aragonite CaCO3% Calcite FeO(oh)% Goethite SiO2% Quartz

Xerosecta cespitum 0.132% 92.90% 0 0 5.99%

Cernuella virgata 4.19% 89.57% 0 0 5.44%

Eobania vermiculata 4.70% 84.26% 0 0 9.97%

Helix melanostoma 2.34% 74.48% 10.54% 0 6.21%

Sphincterochila baetica 0 90.89% 0 7.89% 0

Rumina decollata 0.20% 82.48% 9.50% 0 0

Unio ravoisieri 0.18% 89.33% 0 0 4.13%

A*

^ y

/

#0

y

<<pv

Fig. 4. Histogram of mineralogical composition of mollusk shells of Oued sarrat

#

Fe03% Hematite CaC03 % Aragonite CaC03 % Calcite FeO(oh|% Goethite SI02 % Silice

We consider that the abundance of aragonite indicates that the shells have not yet undergone

mineralogical transformations related to fossiliza-tion phenomena as evidenced by the absence or low

content of calcite. We interpret the presence of traces of silica, goethite and hematite as due to the existence of sediment trapped in the dressing or binding to the surface of the shell. 4.1.2. Sediment mineralogy

The mineralogical cortege of the sediments, for all the analyzed samples, records a mixture of silica and calcite dominance containing a small

Table 4. Chemical composition of clays in Oued sarrat

fraction of gypsum and an aragonite fraction of 11.65% in the sample OS4 (Tab.2, Fig.5). The cal-cite-silica reflects initially the characteristics of a detrital sediment in which calcite is likely related to lithoclastic fragments with low contribution of ara-gonitic debris, as evidenced by the low content of aragonite in the sample OS4.

CaCO3% Aragonite CaCO3% Calcite Al2O3% FeO(oh)% CaSO4% SiO2%

OS1 0 40.27 1.12 7.65 3.57 36.53

OS2 0 43.31 2.94 5.54 3.66 29.05

OS3 0 51.89 2.78 7.95 0 27.20

OS4 11.65 34.12 0 6.65 0 18.98

60

50

40

30

20

10

I CaC03% Aragonite I CaC03% Calcite I AI203% i FeO{ah)% ICaS04% Si02%

OS1

OS2

OS3

OS4

Fig. 5. Histogram of mineralogical composition of marl of Oued sarrat

4.1.3. Interpretation

The absence of clear clayey minerals signals in the analyzed spectra, as well as the abundance of calcified siliceous fraction, reflects a fairly high-energy fluvial environment undergoing at times of arid conditions favorable to the formation of evapo-ritic minerals. 4.2. Geochemical tracing

4.2.1. Analysis on shells of gastropods and bivalves

The results presented in Table 3 confirm the mineralogical data with a composition dominated by calcium carbonates, expressed by high contents of CaO and CO2. This reflects a chemical test on development of organisms in a continental environment clearly confirmed by the absence of MgO, which is usually present in the organisms' tests

developed in a marine environment, with an Mg content varying from 12 to 18%. However, it should be noted that in Pleistocene tests for the species Unio ravoisieri, the Mg content is equal to zero, although the analysis of the extant species shows that this values is equal to 2.31% (Tab.3, Fig.6). This low Mg content is far from reaching the characteristic values of completely marine species. This Mg rate could be linked to a certain ability of the species to obtain this element from the fluviatile waters. This ability indicates a possible change in the behaviour of above mentioned species. On the other hand, the contents of SiO2, FeO3, Al2O3, are also comparable, as it was reported during the mineralogical study, to the lithological impurities trapped mainly in the lodges of helicides.

Narjess Karoui-Yaakoub, Moncef Said Mtimet

Semeh Bejaoui, Bienvenido Martínez-Navarro Journ.Geol.Geograph.Geoecology, 27(2), 316-322

Table 3. Chemical composition of Pleistocene mollusk shells of Oued sarrat

CaO % Al2O3 % CO2 % Fe2O3 % SiO2 % MgO%

Pleisto Pleisto Pleisto Pleisto Pleisto Pleisto

Xerosecta cespitum 53.53 3.74 37.17 0.12 5.45 0

Cemuella virgata 51.60 3.31 36.21 3.86 5.01 0

Eobania vermiculata 49.21 3.87 33.61 4.27 9.05 0

Helix melanostoma 48.84 1.07 36.95 4.79 5.73 0

Sphincterochila baetica 52.29 3.33 36.72 6.88 0.00 0

Rumina decollata 56.16 1.31 42.38 0.16 0.00 0

Unio ravoisieri 52.50 5.05 34.65 3.66 0.00 0

SO

AO -

/ /

Fig. 6. Histogram of chemical composition of Pleistocene mollusk shells of Oued sarrat

4.2.2. Sedimentological analysis

The results presented in Table 4 reflect the original sand-calcitic and detrital sediments exceeding 90% for this fraction. Coupled with very low proportions of Al2O3, about 3%, all data allow us to assume a fluvial environment where the water win-

Table 4. Chemical composition of clays in Oued sarrat

nowing seems to be unfavorable to the sedimentation of the ultrafine fraction of the clayey minerals. The continental chemistry is demonstrated by the absence of magnesium in all analyzed sediments (MgO = 0; Tab. 4, Fig. 7).

CaO % Al2O3 % CO2 % Fe2O3 % SO3 % SiO2 % MgO%

OS1 35.85 0.85 26.96 5.17 2.14 27.49 0

OS2 35.38 2.94 26.87 4.84 1.63 27.05 0

OS3 35.64 3.51 26.78 8.10 25.25 0

OS4 41.66 32.68 5.98 18.98 0

Fig.7. Histogram of chemical composition of clays in Oued sarrat

4.3. Interpretation of mineralogical and geo-chemical data

Mineralogical and geochemical data tracing, carried out on sediments and tests, allow us to conclude the establishment of a paleoenvironment attributable to fluvial deposition of sufficiently high energy where the ultrafine fraction of clayey minerals is remarkably lacking. The absence of indicators of marine chemistry, such as magnesium, in sediments and in the molluscs' tests confirms the almost total contribution of the continental meteoric waters without marine influence. Such environment, however, is affected by intermittent episodes of aridity as evidenced by the presence of evaporates such as gypsum. 5. Conclusion

Mineralogical and geochemical analyses confirm previously obtained paleoecological results (Martinez-Navarro et al., 2014; Karoui-Yaakoub et al., 2016; Amri et al., 2017). The depositional environment was definitely neither marine nor lagoonal, but rather fluvial due to continental meteoric waters in a hot climate.

The Oued Sarrat site is dated in time frame from the Middle to the Late Pleistocene, a landscape covered with swamp and forest, or even shallow freshwater lake. The latter was powered by channels and, certainly, around the lake there inhabited abundant different large mammalian species together with other small vertebrates and invertebrates that were probably consumed for human survival.

References

Amri, L., 2014..Etude paleontologique des grands mammiferes quaternaires d'Oued Sarrat (Nord-

Ouest de la Tunisie). International Master Thesis in QUATERNARY AND PREHISTORY [Unpublished], 101 p. Amri, L., Bartolini Lucenti, S., Mtimet, M.S., Karoui-Yaakoub, N., Ros-Montoya, S., Espigares, M.P., Boughdiri, M., Bel Haj Ali, N., Martínez-Navarro, B.,2017.Canis othmanii sp. nov. (Carnivora, Canidae) from the early Middle Pleistocene site of Wadi Sarrat (Tunisia). Comptes Rendus Palevol, 16(7), 774-782.

http://dx.doi.org/10.10167j.crpv.2017.05.004 Bejaoui, S., 2014.Zes mollusques continentaux d'Oued Sarrat (nord ouest de la Tunisie), paleoecologie et paleoenvironnement du Pleistocene. Mémoire de Master [Unpublished],103. Karoui-Yaakoub, N., Mtimet, M.S., Bejaoui, S., Amri, L., Khalloufi, N., Ben Aissa, L., Martínez-Navarro, B., 2016.Middle-to-Late Pleistocene malacofauna from the archeopaleontological site of Oued Sarrat (Tajerouine area, NW Tunisia). Arabian Journal of Geosciences, 9, 345. http://dx.doi.org/10.1007/s12517-016-2310-4 Martínez-Navarro, B., Karoui-Yaakoub, N., Oms, O., Amri, L., López-García, J.M., Zeräi, K., Blain, H.A., Mtimet, M.S., Espigares, M.P., Ben Haj Ali, N., Ros-Montoya, S., Boughdiri, M., Agustí, J., Khayati-Ammar, H., Maalaoui, K., Maahmou-di, O.K., Sala, R., Hawas, R., Palmqvist, P., 2014.The early Middle Pleistocene archeopaleon-tological site of Oued Sarrat (Tunisia) and the earliest record of Bos primigenius. Quaternary Science Reviews. 90, 37-46.

http://10.1016/j.quascirev.2014.02.016 Mtimet, M.S., Karoui-Yaakoub, N., López-García,

J.M.,Blain, H.A., Agustí, J.,Amri, L.,Martínez-Navarro, B.,2014.The early Middle Pleistocene microvertebrate assemblage from Wadi Sarrat (Tunisia). In: XXX (ed.), XVII World UISPP Congress 2014 Burgos, 1-7 September. Volume of abstracts, p. 100-10.