Infrared Analyzes and New U/Th Dating of Travertine (Erfoud's

INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 10, ISSUE 07, JULY 2021 ISSN 2277-8616 Infrared Analyzes And New U/Th Dating Of Travertine (Erfoud’s Radier, Morocco): Consequences On Global Climatic Variations

Samer Farkh, Soumaya Hamieh, Louis Rousseau, Bassel Ismail

Abstract: The aim of this work is to study the climate variations on a global scale by providing new radiometric data from the travertine of Erfoud’s Radier. This travertine is formed of two units, lower and upper, separated by a discontinuity surface. Our U/Th dating allowed to position the lower unit between 262 ka and 177 ka, which is contemporary with isotopic stages 8 and 6. As for the upper unit, it is between 30 ka and 11 ka, contemporary with isotopic stage 2. The even isotopic stages indicate that the climate was cold in Europe at that time while it was hot and humid in Morocco, favoring the formation of this travertine. From the obtained data, this study can rely on the climatic correspondence hypothesis described by Petit-Maire for the last two climatic extremes (18000 ± 2000 and 8000 ± 1000 ka) in the world, could be extended for a long time.

Index Terms: Travertine, Morocco, Erfoud, U/Th dating, Radier, Isotopic stages, Infrared, Paleoclimate. ——————————  —————————— 1 INTRODUCTION TRaverti nes and speleothems are calcite concretions that (Lebatardet al. [1] [2]). The method used in this work is based retain the isotopic and chemical characteristics of the water on uranium-series disequilibrium. Indeed, uranium (U) is from which they are deposited. They thus provide a record of incorporated alone in the calcic concretion at the time of its climate variations in the continental domain. Speleothems are formation while thorium (Th) is adsorbed on clay. Therefore, concretions that are deposited in caves. They can be there is a disequilibrium between uranium and thorium. stalactites, stalagmites or stalagmitic floors. The latter have the Uranium then decays to thorium, thus re-establishing the advantage that they are formed in archaeological layers, their equilibrium. Determining the U/Th ratio in a given sample dating is of great importance in Prehistory. Travertines are makes it possible to calculate its age. concretions that deposits in open air from hot springs. When rainwater mixes with atmospheric CO2, it forms the carbonic 2 TYPES OF TRAVERTINES acid H2CO3 that dissolves the carbonates CaCO3. The Travertines are formed in geodynamically very active regions reactions are summarized as follows: allowing the emergence of hot springs on the surface. They can have the shape of a dome by successive addition of + - H2O + CO2 → H2CO3 H2CO3 → H + HCO3 lamines forming lenticular units limited by convex surfaces. 2+ 2- They can also have the shape of ride by accumulation of fine CaCO → Ca + CO 3 3 carbonate precipitation lamines. This form develops along the As the compressed gases under pressure burst and formed 2+ line of a fault with symmetry in the morphology of the deposit cracks, the water becomes saturated with Ca and HCO3- on either side of this fault, giving a rided appearance to the ions as well, reaches the surface and spills on the vegetation, deposit in transverse view. Travertines can also be in terraces mixing CO2 with captured during respiration of plants, mosses, with a carbonate wall separating each terrace. When this wall algae, and cyanobacteria. The carbonate precipitation occurs is high, the travertine is called a cascade which consists of by releasing CO2 and evaporating water according to the encrustments due to a waterfall caused by a vertical surface. reaction: By comparison, limestone tuffs come from cold springs, they may be of fluviatile or lacustrine origin. The fluviatile model is 2+ - Ca + HCO3 ⇄ CaCO3 + CO2 + H2O formed by limestone deposits in oncoids forms where the river dries up. The lake model is formed by carbonate reefs on the The most known travertines are those of the Central Massif in shores of the lake colonized by cyanobacteria and algae that France, the volcanic zone in central Italy, the eastern Greece, promote their deposition. the western Turkey and the northern Africa including the Moroccan travertine studied here. 3 POSITION OF THE TRAVERTINE STUDIED The travertine outcrop studied is that of the Erfoud’s radier or Travertines have the advantage over speleothems that they Yerdi. It is located in the Errachidia region of Morocco in the are rich in uranium. The dating of travertine began a long time Anti-Atlas [11] (Figure 1). It appears on the geological map of ago [22] [24], it allowed to date the skull cap of archaic Homo Tafilalt-Taouz [14]. It is bounded to the north by the southern erectus from Kocabas in Turkey between 1 and 1.6 Ma flank of the eastern High Atlas and to the west by the northern and eastern flanks of the Anti-Atlas. ———————————————— Corresponding author: [email protected]  Samer Farkh, Soumaya Hamieh, Bassel Ismail, Lebanese University, Faculty of Sciences I, Department of Life and Earth Sciences, Beirut, Lebanon.  Louis Rousseau, University of Picardy Jules Verne, EA 7511, 80000, Amiens, France.

Drilling, targeting the sub-Cenomanian aquifer, has been towards Aoufous, 15 km to the north, in a cavity dug in the carried out at the Yerdi outcrop. The samples taken for dating Turonian cornice. and for infrared analyzes were named Irdi to avoid confusion with Yerdi. 6 U/TH DATING The dating of this travertine began with Boudad et al.[17], it continued with Rousseau et al. [18][19] then with Weisrock et al. [5] until today. They intersect with those of Rousseau et

MOROCCO al.[19], Ghaleb et al.[6] and Ouammou et al. [3]. The results are presented in Table 1. They make it possible to date the Hamada of Meski base of the unit below 262 ka and its top at 177 ka, that is to say contemporaneous with isotopic stages 8 and 6 respectively. The age of the upper unit, much more recent, is between 30 ka and 11 ka, that is to say contemporary with isotopic stage 2. Therefore, there is a chronological hiatus between the two units, which is quite remarkable in the field (Figure 2).

7 INFRARED ANALYSIS OF IRDI SAMPLES The infrared analysis was carried out on three samples, one at the bottom Irdi-1, a second in the middle Irdi-2 and a third at Quaternary carbonated formations (2:Lalla Mimouna; 3: Aït Ben Omar; 4: Tilouine; 5: M’Daghra; 6: Ferkla) Studied formations (1: Irdi; 7: Aoufous) the top Irdi-3. For irdi-1, it presents the two crystal forms of carbonates, aragonite and calcite. For Irdi-2, aragonite is Fig.1. Position of the travertine outcrop represented much more than calcite in the sample. For Irdi-3, only calcite was reported. The infrared analysis carried out on the two units allowed us to draw a conclusion: where there is

4 DESCRIPTION OF THE TRAVERTINE aragonite, in the Irdi-1 and Irdi-2 samples for example, the The Travertine, a massive deposit of 6 meters thick, is made uranium content is clearly high, in accordance with what we up of two units, lower A and upper B, separated by a surface of know about the crystallization of aragonite. major discontinuity S (Figure 2). It occupies an area of about ten square kilometers, crossed by the minor bed of the Oued 1, 2, 3, 4, 5, 6 = Irdi samples Route 21 Ziz (Figure 3). On the left bank of Oued Ziz, the layers form a set of interlocking domes covering the alluvium of the river. The work on Route 21 made it possible to clear a trench of layers 6 meters high oriented north-south.

The micromorphological analysis has highlighted the interpenetrating facies: 1- Carbonate facies with detritic elements and rectilinear or branched cavities which may be filled secondarily by calcite cement or coarser reddish sediment. These cavities correspond to locations of plants, stems and roots. Detritic elements make up 25% of the mass of the rock and include quartz and feldspar. Numerous smooth and rounded quartz grains illustrate wind shaping. 2- Travertine facies with corrugated millimeter laminates, generally arranged in convex lenses upwards, reminiscent of tipis of evaporative facies [13]. There are cavities of variable dimensions between lamines, some of which are clogged by secondary carbonate recrystallizations and others are filled with detritic sediments rich in iron oxide. Levels are particularly rich in manganese oxide. Measurements of natural remanent magnetization (NRM) show that the magnetite grains in the samples studied have been deposited since 780 ka, the magnetic period Fig. 2. Travertine outcrop of the Erfoud’s radier corresponding to the Brunhes period.

5 LOCATION OF THE SAMPLES The samples were taken from bottom to top, two from the lower unit and four from the upper unit (Figure 2). Since travertine is crystallized carbonate, the macroscopic purity of calcite was taken into account with the absence of clay beds that could affect the samples. The position of the samples is presented in figure 3. In addition, a speleothem was collected 82 IJSTR©2021 www.ijstr.org INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 10, ISSUE 07, JULY 2021 ISSN 2277-8616

Table 1. U/Th dating results

Fig. 3. Position of the travertine outcrop

n with that of the other three samples Irdi-2, Irdi-4 and Irdi-5 from the same unit. Two cases arise for Irdi-3 which can thus increase the U/Th age: either contamination by exogenous thorium or leaching of uranium. However, we cannot consider contamination by thorium for this sample because the 230Th/232Th ratio is greater than 100. On the other hand, this sample has a 234U/238U = 4.637 ratio lower than the other samples of the same unit. Consequently, uranium leaching would have aged Irdi-3 age. It should be noted that according to micromorphological analyzes, we have highlighted either a recrystallization or a detrital sediment which respectively Fig. 4. Irdi-1 spectrum reflect or a late incorporation of uranium or contamination by exogenous thorium. Therefore, our U/Th data for Irdi-3 are not consistent with micromorphological analyzes. The samples Irdi-1 and Irdi-6 from the lower unit show a very low 234U/238U ratio compared to that obtained for the samples from the upper unit. However, we cannot envisage uranium leaching for Irdi-1 and Irdi-6 because on the one hand, their 234U/238U ratio coincides with 2.7 and on the other hand, they have high uranium contents. Based on the results obtained for the upper unit, the samples have 234U/238U ratios and consistent uranium contents which hover around 2 and 5 respectively. Also for the lower unit, the samples have the same 234U/238U = 2.7 ratio and contain consistent uranium contents between 7.3 and 8.2. Therefore, our results are valid. It can be inferred that the lower unit formed under different climatic and geochemical conditions than the upper unit. This hypothesis is supported by the presence of a large Fig. 6. Irdi-3 spectrum area of discontinuity in the field, itself explained by the large

difference in age obtained between the two units. Indeed, this large difference between the ages obtained for these two units, in the absence of successive isotopic stages 5, 4 and 3 (the stages 10 and 9 are not obtained in this deposit because its basal part is rendered inaccessible by the rehabilitation of the road), is explained by: - A major erosion phase would have eliminated any deposits formed during isotopic stages 5, 4 and 3. This hypothesis is supported by previous work in which an erosion and pedogenesis phase was demonstrated around 30 ka [9] [12] [4]. In addition, the level of discontinuity is highlighted locally by decimeter pockets with detritic filling indicating a phase of erosion and alteration. However, this Fig. 5. Irdi-2 spectrum hypothesis seems weak to us because erosion could not eliminate three successive stages as for this important deposit. 8 INTERPRETATION AND DISCUSSION - A phase of stop of deposit explained by low precipitation on All the samples, from the bottom to the top, provide ages the High Atlas and thus a low water load of the aquifer of the consistent with their stratigraphic position with the exception of Infracenomanian at the origin of the formation of this deposit. the Irdi-3 sample if we consider its stratigraphic position which The latter mechanism is most likely occurring but the two gives an age in contradictio phases could probably coexist together. As for infrared analyzes, if we consider for Irdi-1 where we have 83 IJSTR©2021 www.ijstr.org INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 10, ISSUE 07, JULY 2021 ISSN 2277-8616 demonstrated calcite and aragonite (Figure 4), that there has increases. At the end of the Pleistocene or the beginning of been a passage from aragonite to calcite, we should have the Holocene, below 11.5 ka stops the deposition of travertine, obtained a loss of uranium [8]. However, the uranium content this is explained by more arid conditions slowing down its in this sample is too high, which means that the calcite is deposition and promoting its erosion. Currently only a few independent of the aragonite in this sample. In the Irdi-2 and carbonate concretions remain on the bed of Oued Ziz. Irdi-3 samples, it is either calcite or aragonite (Figures 5 and 6). On the other hand, the date obtained for the Aoufous 10 Acknowledgments speleothem is mostly consistent with the paleomagnetic data. I cordially thank François Frohlich (MNHN, Paris) for having This speleothem has a much lower uranium content than carried out the infrared analyzes. 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