The late Miocene Mediterranean-Atlantic connections through the North Rifian Corridor: New insights from the Boudinar and Arbaa Taourirt basins (northeastern Rif, Morocco)

Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

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Research paper

The late Miocene Mediterranean-Atlantic connections through the North Rifian Corridor: New insights from the Boudinar and Arbaa Taourirt basins (northeastern Rif, Morocco) Mohammed Achalhi a,b, Philippe Münch b,⁎, Jean-Jacques Cornée b, Ali Azdimousa a, Mihaela Melinte-Dobrinescu c, Frédéric Quillévéré d, Hara Drinia e, Séverine Fauquette f, Gonzalo Jiménez-Moreno g, Gilles Merzeraud b, Abdelkhalak Ben Moussa h, Younes El Kharim h, Najat Feddi i a

Laboratoire des Géosciences Appliquées LGA, Université Mohamed 1er, faculté des sciences, Oujda, Morocco UMR CNRS 5243 Géosciences Montpellier, Université de Montpellier, CC 060, Pl. Eugène Bataillon, 34095 Montpellier Cedex 05, France National Institute of Marine Geology and Geo-ecology (GeoEcoMar), Str. Dimitrie Onciul, nr 23-25, RO-024053 Bucarest, Romania d Université Lyon 1, ENS de Lyon, CNRS UMR 5276 LGL-TPE, F-69622 Villeurbanne, France e National and Kapodistrian University of Athens, Faculty of Geology and Geoenviromment, Athens, Greece f Institut des Sciences de l'Évolution, Université de Montpellier, CNRS 5554, IRD, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France g Departamento de Estratigrafía y Paleontología, Universidad de Granada, Fuenta Nueva S/N, 18002 Granada, Spain h Département de Géologie, Université Abdelmalek Esaadi, 93003 Tetuán, Morocco i Laboratoire Biodiversité et dynamique des écosystèmes, Université Cadi Ayyad, Faculté des Sciences Semlalia, Boulevard Prince-Moulay-Abdelah, Marrakech, Morocco b c

a r t i c l e

i n f o

Article history: Received 2 February 2016 Received in revised form 27 June 2016 Accepted 29 June 2016 Available online 2 July 2016 Keywords: Mediterranean-Atlantic connections Late Miocene Morocco North Rifian Corridor Chronostratigraphy Paleoenvironments

a b s t r a c t New data from the Neogene Boudinar and Arbaa Taourirt basins (northeastern Morocco) provide constraints on the late Miocene evolution of the North Rifian Corridor. The chronostratigraphy of these basins is clarified on the basis of biostratigraphic (planktonic foraminifers, calcareous nannoplankton) and radio-isotope ages. Marine sedimentation in the Boudinar Basin began during the early Tortonian at ~10 Ma and persisted until the lateearly Messinian at ~6.1 Ma. In the Arbaa Taourirt basin, it occurred between the late Tortonian and the earliest Messinian. Paleoenvironmental data (benthic foraminifera and pollen grains) record a major drowning in association with extensive tectonism in the Boudinar basin during the early Messinian (~7.2 Ma). Synchronously, there was a major sedimentological change in the Arbaa Taourirt basin with progradation of conglomerates and sandstones over late Tortonian marls. Large-scale cross-bedded sandstones indicate paleo-currents flowing from the Atlantic Ocean toward the Mediterranean Sea. During the late-early Messinian, a shallowing trend occurred, culminating with the progradation of reefal carbonates. Our findings indicate that the North Rifian Corridor opened at ~7.2 Ma ensuring Atlantic-Mediterranean connections. The Corridor was progressively restricted during the late-early Messinian with complete closure by ~6.1 Ma. The results of this study thus question existing hypotheses for the timing and nature of Atlantic-Mediterranean connections during the late Messinian. © 2016 Elsevier B.V. All rights reserved.

1. Introduction The Betic and Rif Chains started to build during the Oligocene as a result of the convergence between Africa and Europe (Jolivet et al., 2006; Chalouan et al., 2008). During the late Miocene, several marine gateway systems connected the Mediterranean Sea with the Atlantic Ocean through the Betic and Rif Chains, in southern Spain and northern Morocco, respectively (Benson et al., 1991; Krijgsman et al., 1999a; Martín et al., 2001, 2009, 2014) (Fig. 1A). The Rifian marine gateway

⁎ Corresponding author.

http://dx.doi.org/10.1016/j.palaeo.2016.06.040 0031-0182/© 2016 Elsevier B.V. All rights reserved.

comprises two corridors, the North Rifian Corridor and the South Rifian Corridor (Fig. 1A). Tectonic uplift processes caused by plate tectonics (Krijgsman et al., 1999a; Gutscher et al., 2002; Duggen et al., 2003; Garcia-Castellanos and Villaseñor, 2011), combined with climatic and eustatic changes (Krijgsman et al., 1999a; Hilgen et al., 2007; Manzi et al., 2013; Pérez-Asensio et al., 2012a; Pérèz-Asensio et al., 2012b), may have promoted the progressive restriction and the closure of these corridors. The closure of marine gateways isolated the Mediterranean Sea from the Atlantic Ocean, leading to the precipitation of thick evaporites in the Mediterranean Sea. This event, known as the Messinian Salinity Crisis (MSC, Hsü et al., 1973; Ryan et al., 1973), occurred between 5.97 Ma and 5.33 Ma (Gautier et al., 1994;

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Basement Neogene deposits

A

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Tetouan Fig. 2 Trougout Fault Al Hoceima

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ul

a rF

Melilla-Nador basin Melilla Nador

Arbaa Taourirt Boured 50 km Gharb basin

Dhar Souk

Tafrant Taounate

Internal Zones

in

as

b cif

Flysch Nappes

er

z Ta Rabat 34°

Mamora basin

Thrust Fez Saïs basin

Normal fault Strike-slip fault Post-nappe deposits Neogene-Quaternary volcanics

Intrarif External Rif

u a-G

Mesorif Rifian Nappes Prerif Rides prerifaines Foreland

Fig. 1. A) Distribution of the Tortonian-Messinian basins around the Alboran Sea (modified from Esteban, 1996). B) Structural map of the Rif Chain and location of the post-nappes basins (Tafrant, Taounate, Dhar Souk, Boured, Arbaa Taourirt and Boudinar basins). Modified from Suter (1980) and Jolivet et al. (2003).

Krijgsman et al., 1999b; Manzi et al., 2013; Roveri et al., 2014). On the Moroccan margins of the Mediterranean, the witness of the MSC is a subaerial erosional surface (Messinian Erosional Surface, MES) capped by latest Miocene to Zanclean, continental to marine deposits (e.g., Cornée et al., 2014, 2016). The timing of the different openings and closures of these corridors is still subject to significant uncertainties (Benson et al., 1991; Martín and Braga, 1994; Krijgsman et al., 1999a; Martín et al., 2001; Kouwenhoven et al., 2003; Dayja et al., 2005; Van Assen et al., 2006; Hüsing et al., 2010, 2012; Martín et al., 2014; Flecker et al., 2015). During the late Tortonian–Messinian, the Rifian Corridors were the most important passageways connecting the Mediterranean with the Atlantic (Fig. 1A). The intramontane North Rifian Corridor extended between the Boudinar and Gharb basins and the South Rifian Corridor comprised the Melilla-Nador, Taza-Guercif, Saïs and Mamora basins (Fig. 1B). Abundant data are available from the South Rifian Corridor. In the Taza-Guercif basin, the oldest marine sediments marking the opening of the corridor were deposited at ~ 8 Ma and this passageway between the Mediterranean and Atlantic restricted between 7.2 and 6.1 Ma (Krijgsman et al., 1999a). Moreover, in the Taza-Guercif basin, Nd isotope data have shown that these connections were interrupted at the eastern side of the basin at around 7.2 Ma but

persisted elsewhere (Ivanović et al., 2013). On the contrary, data from the North Rifian Corridor are scarce. Only biostratigraphic data of Wernli (1988) are available from the intramontane basins (Taounate, Dhar Souk, Boured and Arbaa Taourirt). In the Boudinar basin, finally, some information is available but contradictory (Guillemin and Houzay, 1982; Wernli, 1988; Barhoun and Wernli, 1999; Azdimousa et al., 2006). Consequently, the timing of opening and closure of the North Rifian Corridor remains unknown. In this paper, we study the evolution of the North Rifian Corridor, based on a detailed analysis of two key basins directly related to the Mediterranean Sea: the Boudinar and Arbaa Taourirt basins. We provide a refined chronostratigraphic framework of the deposits outcropping in these basins, based on biostratigraphic (planktonic foraminifera, calcareous nannoplankton) and radio-isotope ages. These new data, combined with paleoenvironmental (benthic foraminifera and pollen) and sedimentological data, allow us to reconstruct the late Miocene history of the Mediterranean-Atlantic connections through the North Rifian corridor. As the other Atlantic-Mediterranean connections in Morocco and Spain are well constrained, it is crucial to improve the knowledge of the North Rifian Corridor for establishing the timing of the isolation of the Mediterranean from the Atlantic. Indeed, it has

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Houzay, 1982; Aït Brahim, 1985, 1991; Morel, 1988). The sedimentary record of the Boudinar basin is traditionally subdivided into three main late Tortonian–early Zanclean units (Guillemin and Houzay, 1982; Aït Brahim, 1985, 1991; Morel, 1988; Wernli, 1988; El Kharim, 1991; Barhoun and Wernli, 1999; Azdimousa et al., 2006, 2011). Unit I comprises continental conglomerates and lagoonal sandy marl deposits that mainly crop out in the SW part of the basin and are considered late Tortonian (Guillemin and Houzay, 1982; Barhoun and Wernli, 1999) to latest Tortonian (Azdimousa et al., 2006). Unit II corresponds to marine deposits and comprises, from bottom to top: 1) coarse-grained conglomerates displaying marine fauna (pectinids, oysters, gastropods and barnacles) and sandstones above a marine erosional surface; 2) up to 150 m thick marine marls with several interbedded volcanic tuffs and some bryozoan-rich and red-algal limestone; 3) up to 40 m thick marl-diatomite alternation; 4) 10 m thick lenses of Porites coral boundstones topped by an erosional surface. The lowermost marine conglomerates are considered either Messinian (Guillemin and Houzay, 1982; Choubert et al., 1984; Azdimousa et al., 2006) or upper Tortonian (Barhoun and Wernli, 1999). The lowermost part of the overlying marls is considered either Messinian (Guillemin and Houzay, 1982; Choubert et al., 1984; Azdimousa et al., 2006) or upper Tortonian (Barhoun and Wernli, 1999). The marl-diatomite alternations are considered Messinian (Guillemin and Houzay, 1982; Barhoun and Wernli, 1999; Azdimousa et al., 2006). Some para-reefal

been recently proposed that marine inputs into the Mediterranean during the MSC were necessary for the deposition of the thick late Messinian evaporitic sequences (Roveri et al., 2014). This study will allow answering the following question: could the North Rifian Corridor represent the last Neogene seaway between the Atlantic Ocean and the Mediterranean? 2. Geological setting The Boudinar and Arbaa Taourirt basins are located in Morocco at the northern mouth of the North Rifian Corridor along the Nekor fault (Fig. 1B). They belong to the post-nappe Neogene basins formed after the main orogenic movements of the Rif. The Boudinar basin is infilled by Neogene sediments resting upon Cretaceous metamorphic units (Ketama and Temsamane) and the volcanic massif of Ras Tarf (13.3 Ma to 8.8 Ma; El Azzouzi et al., 2014). The basin is bounded by the post-Neogene Ras Tarf fault to the West and onlaps the Nekor fault to the South (Guillemin and Houzay, 1982; Morel, 1988) (Figs. 1B, 2). Previous studies in the Boudinar basin mainly concerned biostratigraphy (Guillemin and Houzay, 1982; Kharrim, 1987; Wernli, 1988; Barhoun and Wernli, 1999; Azdimousa et al., 2006, 2011), paleoenvironments (Benmoussa, 1991; El Kharim, 1991; El Hajjajji, 1992; El Ouahabi et al., 2007), sedimentology (El Kharim, 1991), and tectonics (Guillemin and

3° 40’ t

**

S. Haj Youssef

t d

d

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N

d

Alboran Sea

t t

Ras

ff Tar

** ** * * t Aït Abdallah

Fig. 16 A

4 km

2

t

aul

0 oû

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es

Im

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Ou

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t

d t

* **

t

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***

*

t

Late Messinian

Megziyat

continental conglomerates

Messinian

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reef

t Tortonian-Early Messinian d marl t: volcanic tuff d: Diatomite

Tortonian

marine conglomerate

t

Boudinar

Fig. 16 B

t

Beni Bou Ya’koub

Tortonian continental conglomerate

Ras Tarf volcanics Kétama unit Temsamane unit

3° 35’

Fig. 2. Simplified geological map of the Boudinar basin, modified from Guillemin and Houzay (1982).

35° 10’

t Messinian Erosional Surface Messinian reef Fault olistoliths Recent

ed

Moulay el’Arbi

Salah

t ul

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M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

(Frizon de Lamotte, 1979; Guillemin and Houzay, 1982; Wernli, 1988). The first unit consists of 5 to 10 m thick marine conglomerates. The second unit is formed by about 70 m thick Messinian marls (Guillemin and Houzay, 1982; Wernli, 1988), and is topped by an erosional surface. The third unit corresponds to up to 100 m thick undated marine sandstones and conglomerates.

to reefal carbonates occur upon the volcanic massif of Ras Tarf (up to 610 m elevation, Fig. 2) and were correlated with the Porites reef lenses from the top of Unit II (Guillemin and Houzay, 1982). Unit III begins with 100 m thick continental conglomerates covering a major erosional surface truncating late Miocene deposits. These conglomerates were considered either Pliocene (Guillemin and Houzay, 1982; Wernli, 1988; Barhoun and Wernli, 1999; Azdimousa et al., 2006) or late Messinian (Cornée et al., 2016). The erosional surface has been assigned to the MES by Azdimousa et al. (2006) and Cornée et al. (2016). It is finally covered by 150 m thick marine sandy and marly deposits assigned to the early Pliocene (Guillemin and Houzay, 1982; Barhoun and Wernli, 1999; Azdimousa et al., 2006; Cornée et al., 2016). The Arbaa Taourirt basin is a SW-NE trending elongated structure along the Nekor Fault (Fig. 1B). There, Miocene sediments were deposited upon the metamorphic basement and upon the Tortonian “Nekor olistostrome” (Frizon de Lamotte, 1981). The sedimentary record of the Arbaa Taourirt basin is traditionally subdivided into three units

3. Material and methods Our initial goal was to build a detailed chronostratigraphic framework of the Miocene deposits outcropping in the Boudinar and Arbaa Taourirt basins, based on planktonic foraminifers and calcareous nannoplankton analyses, together with the 40Ar/39Ar dating of several volcanic layers discovered in the studied sections (see below). In addition, paleobathymetric and paleoenvironmental changes were appraised on the basis of benthic foraminiferal and pollen analyses. Altogether, these analyses allow us to refine the history of the late

Irhachâmene ALBORAN SEA IRA21

Unit III

ES SY 9 SY 8 SY 7 SY 6 SY 5 SY 4 SY 3 SY 2 SY 1 SY 0

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IRA19

Sub-Unit IIb

LEGEND:

AAB3 100 m AAB2 AAB1

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MA13 MA12 MA11 MA10

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MA8

Silty marl

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Sandstone

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Calcareous sandstone

10

Marine conglomerate

Red to greyish clay Continental conglomerate

IRA6

Sub-Unit IIa

MA3 MA2 MA1

0

Black clay with microconglomerate Greyish clay

Transgressive surface

2

? Beni Bou

IRA10

MA9

Diatomite

Submarine erosional surface

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Diatomitic marl

Beni Bou Ya’koub 0

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Limestone with red algae

Substratum

Kétama

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Volcanic tuff

IRA18 IRA17

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MA17

Lithology

e

Ou

IRA16

MA19 MA18

?

m dA

Boudinar

MA21

0

e

rân

ek

Moulay el’Arbi Irhachâmene

MA22

AAB4

0

Aït Abdallah

Moulay el’Arbi

30

10 m

Ras Tarf IRA20

M

Aït Abdallah

SY10

40 m

200 m

*

S. Haj Youssef

N

S. Haj Youssef

Bivalve Bioclast

Su bSuUnit b- Ib Un it Ia

Gypsum block Porites block MES: Messinian Erosional Surface

IRA5

50

?

IRA4 IRA3 IRA2

? 50

IRA1

?

KE

T

14

-3

10

0

? 10

0

Fig. 3. Studied sections of the Miocene deposits and their location in the Boudinar basin, with lithology, sedimentary units and location of the studied samples. *: The Messinian Erosional surface following Cornée et al. (2016).

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

SW

Tortonian-early Messinian Tortonian Messinian Volcanic tuff diatomaceous marls conglomerates marls

C

B

135

NE

Late Messinian continental conglomerates

Mess

inian Erosional

Surface

A

volcanoclastic layer (sample IRA3) marine marls calcareous sandstones marine conglomerates volcanoclastic layer (sample KET14-3) continental conglomerates and red clays

?

SW

NE B

Marine conglomerates

D

C

Fig. 4. A) Field view of the Irhachâmene section. The top of the section shows the Messinian Erosional Surface. B) Detailed view of the base of the section and location of the volcanic tuffs sampled and analysed in this study. C, D) Detailed view of the marine conglomerates at the base of sub-Unit IIb.

Miocene Mediterranean-Atlantic connections through the North Rifian Corridor. In the Boudinar basin, we studied five cross-sections located in the western part of the basin (Figs. 2 and 3): from South to North, Beni Bou Ya'Koub (N35° 8′ 12″; W3° 39′ 12″), Irhachâmene (N35° 11′ 08″; W3° 40′ 18″), Moulay el'Arbi (N35° 11′ 43.5″; W3° 40′ 51.7″), Aït Abdallah (N35° 14′ 25.8″; W03° 40′ 51″) and Sidi Haj Youssef (N35° 15′ 13.1″; W3° 41′ 37.1″). The Irhachâmene, Moulay el'Arbi and Aït Abdallah sections were sampled for calcareous nannoplankton and planktonic foraminiferal analyses (43 samples). Four intercalated volcaniclastic levels were sampled for 40Ar/39Ar radiometric dating in the Irhachâmene (sample #s KET14-3, IRA-3) and Moulay el'Arbi sections, (sample #s MA-11 and MA-20). The Moulay el'Arbi and Sidi Haj Youssef sections were additionally sampled for benthic foraminiferal analyses (26 samples). Palynological analyses were finally conducted in the Irhachâmene, Moulay el'Arbi and Sidi Haj Youssef sections. In the Arbaa Taourirt basin, we sampled the North Arbaa (N34° 53′ 39″; W3° 52′ 28.80″) and the Azroû Zazîrhîne (N34° 56′ 8.50″; W3° 49′ 3.10″) sections for calcareous nannoplankton and planktonic foraminifers (9 samples).

3.1. Biostratigraphy and paleobathymetry Calcareous nannoplankton was studied in the fraction 2–30 μm and separated by decantation method using a 7% solution of H2O2. Smear-slides were mounted with Canada balsam and analysed with an Olympus transmitting light microscope at 1200 × magnification. Most of the samples yielded a poor to moderate preservation, with many upper Cretaceous and Eocene reworked taxa. Taxonomic identification followed Perch-Nielsen (1985) and Young et al. (2003). Zonal subdivision corresponds to the NN (Neogene Nannoplankton) Zonation of Martini (1971). The ages of the lowest and highest occurrences (LOs and HOs) of key nannoplankton species follow Hilgen et al. (2012). Additional calibrations from Lourens et al. (2004) and Raffi et al. (2006) were also used for the species Amaurolithus delicatus and Discoaster pentaradiatus, respectively. For planktonic foraminiferal analyses, loose sediment samples were wet-sieved (mesh sizes between 2 mm and 63 μm). Preservation was poor to moderate in most of the samples. The specimens were identified following the taxonomic concepts and nomenclature of Kennett and Srinivasan (1983). Bio-event calibrations are from Hilgen et al. (2012)

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A

NW

Late Messinian continental conglomerates

Volcanic tuff (sample MA 20)

ace

inian

Mess

Surf ional

SE

Tortonian- early Messinian marls

Eros

Volcanic tuff (sample MA 11)

C

B

continental breccia

D

marine conglomerate

metamorphic basement Fig. 5. A) Field view of the Moulay el'Arbi section showing the Tortonian-early Messinian marls with interbedded volcanic tuffs layers. B) Base of the section showing the marine conglomerates over the metamorphic basement of the Ketama Unit. C) Detailed view of a bored block. D) Detailed view of the marine conglomerates with abundant Glycimeris and other shell accumulations.

and the Zonal subdivision used in this work is from Berggren et al. (1995). Benthic foraminifers were separated from the N 125 μm size fraction. Where possible, at least 250–300 specimens were picked, identified, and counted to determine relative abundances of species. Samples with abundant foraminifera were split using a micro splitter obtaining totals close to 250 specimens. Paleodepths were determined using fossil and modern distribution patterns of certain faunas and benthic indicator taxa. Bathymetric terminology follows van Morkhoven et al. (1986): inner shelf = 0–50 m, middle shelf = 50–100 m, outer shelf = 100–200 m, upper bathyal = 200–600 m, middle bathyal = 600–1000 m, lower bathyal = 1000–2000 m, abyssal = 2000– 6000 m. Taxonomic concepts and paleodepth estimates are based on multiple references for the Miocene sections (e.g., Cuchman and Cahill, 1933; Schnitker, 1970; Gibson, 1983; Van Morkhoven et al., 1986; Olsson et al., 1987; Snyder et al., 1988; Miller et al., 1996). 3.2. Palynology For pollen analyses, clay samples were processed using a standard method allowing us to separate pollen grains from the mineral particles. This involved treatments using cold HCl and HF, to remove carbonates and silica, followed by residue enrichment procedures using ZnCl2 (density N 2). The residues were finally mixed with glycerin and mounted on microscope slides. Only 8 samples from the Irhachâmene section provided enough pollen grains for quantitative analyses (IRA4, 5, 6, 8, 9, 11, 14 and 18; Fig. 2). Around 150 pollen grains were enumerated for each analysed

sample, excluding indeterminable Pinaceae and Pinus, this latter being generally over-represented due to prolific production and overabundance in air and water transports. In coastal marine sediments, pollen floras provide reliable record of the regional vegetation altitudinal belts, as established on recent sediments (Heusser and Balsam, 1977; Heusser, 1988; Beaudouin et al., 2005, 2007). However, the proportion of Pinus pollen grains is mostly controlled by the distance from the littoral because of their high buoyancy (Heusser, 1988; Beaudouin et al., 2005). Consequently, the proportion of Pinus pollen grains may provide indication of the distance of the site from the coastline. 3.3. 40Ar/39Ar dating Biotites were separated from the volcaniclastic layers sampled in the Irhachâmene and Moulay el Arbi sections (sample #s MA-11, MA-20, IRA-3 and KET14-3). The samples were crushed and sieved and grain size for the crystals was in the order of 100–200 μm. Crystals were concentrated by using a Frantz magnetic separator. The separated crystals were cleaned in 1 N nitric acid to dissolve possible carbonate impurities, and then rinsed in successive ultrasonic baths of distilled water and pure alcohol. Finally, the grains were selected under a binocular microscope. The samples were irradiated in the core of the Triga Mark II nuclear reactor at Pavia (Italy) with several aliquots of the Taylor Creek sanidine standard (28.34 ± 0.08 Ma; Renne et al., 1998) as a flux monitor. Argon isotopic interferences on K and Ca were determined by irradiation of KF and CaF2 pure salts from which the following correction factors were

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137

NE

SW

A

Normal Faults

Diatomite

B C

Porites olistolith

Porites block

Messinian

onal Erosi

Surface

Messinian diatomaceous marls

Fig. 6. A) Field view of the Sidi Haj Youssef section showing the Messinian marls with interbedded diatomite layers. B) Messinian Erosional Surface covered by a large (up to 30 m long, 10 m wide and 2 to 4 m thick) olistolith of Porites reef. C) Detailed view of a Porites reef block.

A

NW

SE

Tortonian-early Messinian marls

continental conglomerate

marine conglomerate

B C marine conglomerate

continental conglomerate

erosional surface

Fig. 7. A) Field view of the Beni Bou Ya'koub section. B) Detailed view of the basal erosional contact between marine and continental conglomerates from the base of the Beni Bou Ya'koub section. C) Large specimen (20 × 25 cm) of pectinid from the basal part of the marine conglomerates.

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

N° samples

Irhachâmene

Unit III

Planktonic foraminifers

IRA21

indet

IRA20

Barren

Biozone Martini (1971)

Calcareous nannoplankton

40Ar/39Ar dating

Stage

late Messinian

Lithology

Reticulofenestra pseudoumbilicus Discoaster brouweri Triquetrorhabdulus rugosus Amaurolithus primus A m au rolith u s delicatu s Nicklithus amplificus Sphenolithus abies

Units

Biozone Berggren et al. (1995) Wade et al. (2011)

Neogloboquadrina acostaensis s. Neogloboquadrina acostaensis dx. Globorotalia miotumida Globoturborotalia apertura Globoquadrina dehiscens Globoturborotalia decoraperta Globoturborotalia nepenthes Globorotalia juanai Globorotalia cibaoensis Globigerinoides extremus Neogloboquadrina humerosa

138

X=6.79

NN11

7.42

NN11

early Messinian

200 m

IIb

IRA19

150

IRA18 IRA17

M13b-M14

IRA16

6.52

IRA15

Unit II

IRA14 IRA13

8.93

Barren

IRA12 IRA11 IRA10 100

IRA9 9.44

IIa

Tortonian

IRA8

IRA7

IRA6

IRA5 50

IRA4 IRA3 IRA2

M13a

9.83

M13a/M12 9.68 ± 0.08

Barren

IRA1

Unit I Ia Ib

9.69

KET 14-3

10

0

: biostratigraphic markers : reworked taxa X : Cross-over of dominance

10.76

NN8

10.46 ± 0.14

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

obtained: (40Ar/39Ar)K = 0.00969 ± 0.00038, (38Ar/39Ar)K = 0.01297 ± 0.00045, (39Ar/37Ar)Ca = 0.0007474 ± 0.000021 and (36Ar/37Ar)Ca = 0.000288 ± 0.000016. Argon analyses were performed at Géosciences Montpellier (France) with an analytical device that consists of: an IR-CO2 laser of 100 kHz used at 3–15% power to heat samples during 60 s; a lens system for beam focusing; a steel chamber, maintained at 10−8–10−9 bar, with a copper holder in which 2 mm-diameter blind holes were milled; an inlet line for purification of gases including two Zr-Al getters; and a multi-collector mass spectrometer (Argus VI from Thermo-Fisher). Mass discrimination for the spectrometer was monitored by analysing one air pipette volume and its measured values varied from 0.999037 ± 0.13% to 0.99998 ± 0.14%. Aliquots of five to ten grains of biotite were placed in holes of the copper holder and were step heated. Blank analysis was performed every three sample analyses. Raw data of each step and blank were processed and ages were calculated using the ArArCALC-software (Koppers, 2002). The criteria for defining plateau ages were: (1) plateau steps should contain at least 70% of released 39Ar, (2) there should be at least three successive steps in the plateau and (3) the integrated age of the plateau should agree with each apparent age of the plateau within a 2σ confidence interval. All the subsequent quote uncertainties are at the 2σ level including the error on the irradiation factor J. 4. Results 4.1. Boudinar basin 4.1.1. Lithostratigraphy 4.1.1.1. Irhachâmene section. At Irhachâmene, the Miocene deposits exceed 200 m thick (Figs. 3 and 4A) and record the three sedimentary Units of the Boudinar basin. At the base of Unit I, a fining-upward succession occurs with coarse breccias interbedded with decimetre thick reddish clays (sub-Unit 1a; Figs. 3 and 4B). The breccias are organized in thinning-upward metre-thick channelized beds with horizontal bedding or planar cross-bedding. Following Miall (1985), these breccias correspond to proximal alluvial fan deposits. The overlying sub-Unit Ib is mainly composed of reddish to greyish clays with rare conglomeratic lenses corresponding to floodplain deposits. A volcaniclastic layer with abundant euhedral biotite crystals (sample KET14-3; Figs. 3 and 4B) occurs within the clays. Unit I is topped by an irregular erosional surface. Unit II begins with coarse marine littoral conglomerates (sub-Unit IIa), then microconglomeratic clays or calcareous sandstones with an abundant marine fauna (pectinids, oysters, Cerithium, bryozoans, scaphopods, solitary corals). These deposits are overlain by a thin volcaniclastic layer (sample IRA3; Figs. 3 and 4B) and then by silty marls and marls. The top of sub-Unit IIa is marked by an irregular marine erosional surface. Sub-Unit IIb begins with conglomeratic submarine debris flows and then calcarenites (Figs. 3 and 4C, D) with an abundant littoral fauna (oysters, pectinids, spondylids, Veneridae, bryozoans, serpulids and red algae). These deposits are overlain by some marls containing some reworked volcanic tuffs, then by marine conglomerates and up to 1 m thick bryozoans- and red-algae-rich limestones. Above is a white volcanic tuff that represents a key stratigraphic horizon in the Boudinar basin. Sub-Unit IIb ends with marls exhibiting some diatomitic intercalations and a sandstone level with an abundant littoral marine fauna (Cardium, Glycimeris, Veneridae, scaphopods, pectinids, Porites fragments and oysters). The top of Unit II was eroded and deeply incised by the overlying continental conglomerates of Unit III (Fig. 4A). Unit III exhibits subaerial mass-flow deposits (Nemec and Steel, 1984) interpreted as subaerial fan deltas (Cornée et al., 2016).

139

4.1.1.2. Moulay el'Arbi section. In the Moulay el'Arbi section, the Neogene deposits are 130 m thick. Unit I is lacking (Figs. 3, 5A) and sedimentation begins with the marine conglomerates of sub-Unit IIa, which contain an abundant littoral fauna (oysters, pectinids, Glycimeris and Clypeaster; Fig. 5C, D), and which unconformably overlay the metamorphic basement or continental breccias (Figs. 3 and 5B). The conglomerates are capped by littoral micro-conglomeratic sandstones then by marls which contain a volcanic tuff layer in its middle part (sample MA11; Figs. 3 and 5A). Sub-Unit IIb consists of bryozoan- and red algae-rich limestones, then of a white volcanic tuff (sample MA20; Figs. 3 and 5A) and of dark marls. The top of the marls has been eroded by the continental conglomerates of Unit III. Some Porites reef olistoliths were found on the erosional surface. 4.1.1.3. Other complementary sections in the Boudinar basin. The Sidi Haj Youssef section consists of up to 45 m thick marls and diatomites of Unit IIb in which we found an intercalated volcanic tuff (Figs. 3, 6). The top of the marls is eroded and the erosional surface is capped by a decametre-sized Porites reef block from Unit III (Fig. 6B, C). At Aït Abdallah, the section begins with 30 m thick marly deposits in which outcrop a volcanic tuff and some whitish diatomaceous intercalations (sub-Unit IIb; Fig. 3). The top of the marls has been eroded by continental conglomerates and mass-flow deposits of Unit III with decimetre to metre-sized olistoliths of selenite gypsum and Porites reef fragments (Cornée et al., 2016). The Beni Bou Ya'koub section consists of 100 m thick Miocene deposits which correspond to Units I and II (Figs. 3, 7A). Unit I begins there with continental reddish, matrix-supported conglomerates resting unconformably upon the metamorphic basement and is topped by an erosional surface (Fig. 7B). Unit II begins with littoral conglomerates displaying marine fauna (Gigantopecten tournali, Gigantopecten albinus, serpulids, oysters, coral pieces; Fig. 7B, C). They change upward into calcareous sandstones and then up to 90 m thick homogeneous greyish marls. 4.1.2. Biostratigraphy 4.1.2.1. Irhachâmene section. The Irhachâmene section (Fig. 8) yielded diversified calcareous nannoplankton assemblages in which reworked taxa from the Cretaceous and the Paleogene were very important (25% to 80% of the observed species). At the base of the section, within Unit II (sample IRA1), the occurrence of Discoaster brouweri (FAD = 10.76 Ma) indicates that the lower marine clays at Irhachâmene correlate to Zone NN8 and deposited during the early Tortonian. In the middle part of the section near the base of sub-Unit IIb, sample IRA14 yielded Amaurolithus primus, whose FAD is calibrated at 7.42 Ma. Since Nicklithus amplificus (FAD = 6.91 Ma) was not found, the sample probably correlates with the middle part of Zone NN11 in the latest Tortonian. At the top of the section (sample IRA21), the co-occurrence of N. amplificus (Fig. 9E) and Triquetrorhabdulus rugosus (Fig. 9A, B) suggests that the top of sub-Unit IIb correlates with the upper part of Zone NN11 and deposited during the early Messinian (~6.79 Ma). Regarding planktonic foraminifera, the occurrence of Neogloboquadrina acostaensis (FAD = 9.83 Ma) in sample IRA4, 15 m above the base of subUnit IIa, points to Zones M13a-M12 and indicates an early Tortonian age at youngest. Sample IRA5 yielded Globorotalia juanai (FAD = 9.69 Ma), then pointing to Zone M13a in the early Tortonian. Based on the occurrence of Globorotalia cibaoensis (FAD = 9.44 Ma) and the absence of Globigerinoides extremus (FAD = 8.93 Ma), samples IRA8 and IRA9 correlate with Zone M13a in the early to middle Tortonian. Alternatively, the occurrence of G. extremus in sample IRA14, collected 10 m above the base of sub-Unit IIb, points to the upper part of Zone M13a and indicates that the lower part of sub-Unit IIb deposited during the late

Fig. 8. Stratigraphic distribution of the planktonic foraminiferal and calcareous nannoplankton taxa identified in the Irhachâmene sections. In bold and large points: biostratigraphic markers. Bio-event calibration ages by Hilgen et al. (2012).

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Tortonian at youngest. Finally, we found Globorotalia miotumida (FAD = 7.89 Ma; LAD = 6.56 Ma in the Mediterranean region) in sample IRA16. Such occurrence indicates that this part of the Irhachâmene section correlates with Zone M13b, between 7.89 Ma and 6.56 Ma in the latest Tortonian-early Messinian. 4.1.2.2. Moulay el'Arbi section. All samples from the Moulay el'Arbi section (Fig. 10) yielded an important amount (20 to 75%) of calcareous nannoplankton taxa reworked from the Cretaceous and the Paleogene. Twenty metres above the base of the section (sub-Unit IIa), sample MA5 yielded D. brouweri (FAD = 10.76 Ma; Fig. 9C), then pointing to Zone NN8 in the early Tortonian. In the middle part of the section, samples MA9, MA10 and MA13 yielded Discoaster hamatus (FAD = 10.18 Ma, LAD = 9.53 Ma in the Mediterranean region; Fig. 9I). These samples are consequently attributable to Zone NN9 in the early Tortonian. In the upper part of sub-Unit IIa, sample MA14 yielded D. pentaradiatus (Fig. 9D), whose FAD has been calibrated at 9.1 Ma (Raffi et al., 2006). This points to Zone NN10 and indicates a middle Tortonian age. Sample MA16, which yielded Discoaster berggrenii (FAD = 8.29 Ma; Fig. 9H), likely correlates with the NN10NN11 zonal transition in the late Tortonian. Within sub-Units IIb and above the volcanic tuff (sample MA11), sample MA22 yielded A. primus (FAD = 7.42 Ma; Fig. 9G). Together with the absence of N. amplificus (FAD = 6.91 Ma), this occurrence indicates that sample MA22 is probably older than 6.91 Ma. Nevertheless, the nannofossils of this sample point to the middle part of Zone NN11 and indicate a latest Tortonian-early Messinian age. The lower part of the Moulay el'Arbi section (base of sub-Unit IIa) lacks any planktonic foraminiferal biostratigraphic marker. In the middle part of the section, however, we found G. juanai (FAD = 9.69 Ma) in sample MA9, then pointing to Zone M13a in the early Tortonian. In the upper part of the section, samples MA18 and MA21 yielded G. miotumida (FAD = 7.89 Ma; and LAD = 6.52 Ma in the Mediterranean region). This occurrence points to Zone M13b, indicating a latest Tortonian-early Messinian age. Based on calcareous nannoplankton analyses, the top of the marine marls in the Moulay El Arbi section deposited during the early Messinian. 4.1.2.3. Aït Abdallah section. In the Aït Abdallah section, sample AAB3, located just above the AAB2 volcanic tuff, yielded the planktonic foraminifer G. miotumida (FAD = 7.89 Ma; LAD = 6.52 Ma in the Mediterranean region). This indicates that the lower part of sub-Unit IIb correlates with Zone M13b and was deposited during the latest Tortonian or early Messinian. 4.1.3. 40Ar/39Ar dating 4.1.3.1. Irhachâmene section. The sample #KET-14-3 displays disturbed spectra with no plateau age and a total fusion age of 11.02 ± 0.13 Ma (Fig. 11). At best a mini-plateau corresponding to an age of 10.52 ± 0.1 Ma and only to 42.89% of 39Ar released can be calculated. However, the inverse isochron (36Ar/40Ar vs. 39ArK/40Ar) for all the steps yields an age of 10.46 ± 0.14 Ma (initial 40Ar/36Ar ratio of 302.7 ± 2.2, MSWD = 2.84; Fig. 11) that is concordant with the mini-plateau age. The initial 40Ar/36Ar ratio value is close to that of air (295.5), indicating that no extraneous argon is considered in the calculated age. We retained the inverse isochrones age of 10.46 ± 0.14 Ma as the best estimate for sample #KET-14-3. However, it must be pointed out that this age is not consistent with the biostratigraphic results obtained from the overlying marine sediments. The sample #IRA-3 displays a plateau age of 9.68 ± 0.08 Ma corresponding to 100% of 39Ar released (Fig. 11). The inverse isochron for the plateau steps yields a concordant age of 9.67 ± 0.09 Ma (initial 40Ar/36Ar ratio of 304.2 ± 18.9, MSWD = 0.77; Fig. 11). The initial 40Ar/36Ar ratio value is indistinguishable from that of air (295.5), indicating that no extraneous argon is considered in the calculated age.

4.1.3.2. Moulay el Arbi section. The sample #Ma-11 displays a plateau age of 9.57 ± 0.19 Ma corresponding to 99.11% of 39Ar released (Fig. 11). The inverse isochron (36Ar/40Ar vs. 39ArK/40Ar) for the plateau steps yields a concordant age of 9.57 ± 0.19 Ma (initial 40Ar/36Ar ratio of 294.5 ± 4.6, MSWD = 0.7, Fig. 11). The initial 40Ar/36Ar ratio value is indistinguishable from that of air (295.5), indicating that no extraneous argon is considered in the calculated age. The sample #MA-20 displays a plateau age of 7.15 ± 0.15 Ma corresponding to 96% of 39Ar released (Fig. 11). The inverse isochron for the plateau steps yields a concordant age of 7.14 ± 0.15 Ma (initial 40Ar/36Ar ratio of 298.8 ± 5.6, MSWD = 1.38, Fig. 11). The initial 40Ar/36Ar ratio value is indistinguishable from that of air (295.5), indicating that no extraneous argon is considered in the calculated age. 4.1.4. Benthic foraminiferal assemblages and paleodepth estimates 4.1.4.1. Moulay el'Arbi section. Benthic foraminiferal assemblages show a low diversity. In all studied samples, Ammonia beccarii s.l. is the most abundant taxa and partially highly dominant (up to 90%), except at the top of the section (sample MA21). Agglutinated and miliolide species are absent or extremely rare. Deposits from sub-Unit IIa yielded an assemblage dominated by A. beccarii and Nonion fabum, associated with Elphidium spp., Cibicides dutemplei, Valvulineria bradyana, Bolivina sp., Bulimina sp. and Globobulimina sp. This assemblage typifies an inner shelf to middle shelf environment (0 to 100 m depth). From bottom to top, one can distinguish in sub-Unit IIa: – Samples MA1, MA2 and MA3 at the base of the section yielded A. beccarii (up to 43%), Elphidium spp. and N. fabum. All the species show their maximum concentration in the inner shelf region. Nonion fabum has been found to be abundant between 40 and 80 m in the Mediterranean Sea and in the southwestern Marmara Sea (e.g. Milker et al., 2009; Phipps et al., 2010). Therefore, the portion of the section between MA1 and MA3 is placed in the outer part of the inner shelf environment (40 to 80 m depth). – Samples MA4, MA5 and MA6 yielded A. beccarii (up to 50%) with N. fabum, C. dutemplei and V. bradyana as associated taxa. All Cibicides species (including Heterolepa dutemplei synonymous to C. dutemplei) were considered oxic indicators after Kaiho (1994, 1999) and after the morphotype analysis of Rosoff and Corliss (1992); C. dutemplei indicates an outer neritic to upper bathyal zone. This second assemblage corresponds to the middle shelf zone (75 ± 25 m depth). – Samples MA7 to MA10 yielded A. beccarii (39% to 77%), N. fabum (7% to 14%), Cibicides sp., Bolivina sp., Bulimina sp. and V. bradyana with low percentages. This assemblage characterises the outer part of the inner shelf zone (from 40 to 80 m depth).

Just above the volcanic tuff occurring in the middle part of sub-Unit IIa (sample MA11), sample MA12 yielded an oligotypic assemblage with up to 90% of A. beccarii. This species dominates the coastal shallow-water environments (depth shallower than 20 m, Jorissen, 1987). The sample MA12 is placed in the inner shelf zone (0 to 50 m depth). – Samples MA13 to MA18 yielded A. beccarii (37% to 77%), N. fabum (9% to 29%), Cibicides sp., Bolivina sp., Elphidium sp., Bulimina sp., Globobulimina sp. and V. bradyana with low percentages. Jorissen (1987) describes a minimum water depth of 40 m for V. bradyana in the Adriatic Sea. The portion of the section between MA13 and MA18 is placed in the outer part of the inner shelf zone (40 to 80 m depth).

Only one sample (sample MA21) was taken from the sub-Unit IIb. This sample yielded Cibicidoides kullenbergi (17.07%), Elphidium sp. (14.63%), A. beccarii (7.31%), V. bradyana (5.85%), Hanzawaia boueana (4.88%), C. dutemplei (4.45%), Cibicides lobatulus (4%) and Globobulimina

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

B

A

E

F

C

G

141

D

H

I

Fig. 9. Microphotographs of stratigraphically significant calcareous nannoplankton taxa, all in parallel nicols, except F in crossed nicols. A, B) Triquetrorhabdulus rugosus Bramlette & Wilcoxon; Irhachâmene section, sample IRA21. C) Discoaster brouweri Tan; Moulay el'Arbi section, sample MA5. D) Discoaster pentaradiatus Tan; Moulay el'Arbi section, sample MA14. E) Nicklithus amplificus (Bukry and Percival) Raffi, Backman & Rio; Irhachâmene section, sample IRA 21. F) Amaurolithus delicatus Gartner & Bukry; Irhachâmene section, sample IRA15. G) Amaurolithus primus (Bukry & Percival) Gartner & Bukry; Moulay el'Arbi section, sample MA22. H) Discoaster berggrenii Bukry; Moulay el'Arbi section, sample MA16. I) Discoaster hamatus Martini & Bramlette; Moulay el'Arbi section, sample MA9.

sp. (2.92%). This assemblage corresponds to outer continental shelf environments (100 to 200 m depth) often in low organic carbon areas (e.g. Lutze and Coulbourn, 1984; Fontanier et al., 2002). 4.1.4.2. Sidi Haj Youssef. In the Sidi Haj Youssef section, which correlates with sub-Unit IIb, the benthic foraminiferal assemblages are highly diversified and dominated by species indicative of deep marine environments (Fig. 12). Samples from the lower part of the section (samples SY0 to SY6) are characterized by the dominance of Bolivina spathulata, C. kullenbergi, Uvigerina peregrina, Bulimina costata, C. lobatulus, Lenticulina spp. and Elphidium spp. Most of these species are recorded from the middle shelf zone (50–70 m) to bathyal zone (b1000 m). However, C. kullenbergi is abundant in the upper-middle bathyal zone and U. peregrina becomes very abundant in bathyal muds (400–1000 m). Consequently, the portion of the section located between SY0 and SY6 was deposited in the upper bathyal zone. Sample SY7 yielded U. peregrina (26%), Bulimina aculeata (26%), Bolivina punctata (22%), C. kullenbergi (21%) and Uvigerina cylindrica gaurdrynoides and B. costata with low percentage (2%). Cibicidoides kullenbergi is abundant in the upper-middle bathyal zone and B. aculeata is common at lower bathyal depths (reported between 1800 and 5000 m; Jones, 1994). This sample thus corresponds to the middle to lower bathyal zone. At the top of the section, sample SY9 yielded B. spathulata (26%), Uvigerina cylindrica gaurdrynoides (22%), Globobulimina pupoides (20%), C. dutemplei (12.5%), B. aculeata (8%), B. costata (6%), B. punctata (4.5%), and U. peregrina (a few specimens), suggesting an outer shelf to upper bathyal depth. Sample SY10, finally, yielded C. kullenbergi, U. peregrina, Spirorutilus carinatus and Spiroplectammina carinata that is indicative of the outer shelf zone. Altogether, these assemblages suggest that the Sidi Haj Youssef section was deposited on an outer shelf to upper bathyal zone at water depths between 150 m and 400 m. 4.1.5. Pollen analyses Pollen data from the Irhachâmene section cover sub-units IIa (IRA4 to IRA11) and IIb (IRA14 and IRA18; Fig. 2). The flora is composed of 47 taxa originating from (1) megathermic plants (i.e., tropical) as Celastraceae, Buxus bahamensis type, Mussaenda type, Rutaceae, Sapotaceae; (2) mega-mesothermic plants (i.e., subtropical plants) as Arecaceae, Symplocos, Engelhardia; and (3) subdesertic plants represented by Prosopis, Acacia, Lygeum, Caesalpiniaceae, Geraniaceae and

Plumbaginaceae. The flora is dominated by herbs (mainly Asteraceae and Poaceae) and halophytes (Amaranthaceae, Ephedra), excluding Pinus, which is over-represented in marine sediments. Other than Pinus, arboreal pollen grains are mainly represented by Quercus evergreen type, Quercus deciduous type, Salix, Olea, Cupressaceae. Only one grain of Cedrus has been recorded. Pinus is very abundant in the pollen spectra with occurrences of nearly 50% of the pollen grains in most of the samples. An increasing trend in Pinus is observed throughout the studied section and in IRA14 and IRA18 it reaches ~62 and ~97%, respectively. This large increase in Pinus is accompanied by a decrease of Amaranthaceae. 4.2. Arbaa Taourirt basin 4.2.1. Lithostratigraphy The Azroû Zazîrhîne section begins with 60 m thick marls truncated by an irregular erosional surface. Although Frizon de Lamotte, 1981 reported, directly above the substratum and beneath the marls, three metre-thick azoic reddish conglomerates and then few metres of marine conglomerates, we were not able to observe such deposits. The marls are overlain by up to 100 m-thick marine mixed siliciclasticcarbonate deposits (Fig. 13A, B). In their lower part, these deposits display localized red algae-rich coarse-grained gravel beds and conglomerates (up to 200 m in lateral extent and 10 m thick) (Fig. 13B and C). They are organized into non-graded beds with a carbonate matrix and abundant remains of shallow-marine fauna (pectinids, oysters, bryozoans). The clasts are well-rounded ranging from pebble to coble displaying Lithophaga borings. The beds dip 12–20° toward the ENE to NNW and their thickness decreases in the same direction (Fig. 13C). Above these conglomerates or directly upon the erosional surface, we found 90 m thick red algae-rich sandstones with fine-grained conglomeratic lenses exhibiting large-scale cross stratification (Fig. 13A, B, C, D). The bioclastic sandstones and the conglomerates are organized into plurimetric sets (up to 10 m high and N 80 m long; Fig. 13D) of crossbeds with concave-up boundary surfaces (Fig. 13E). The internal structure of the sets is characterized by tangential, concave-up cross-beds dipping up to 15° dominantly toward the N and NNE (Fig. 13E). Perpendicular views to the main direction of progradation of these structures indicate the presence of large scale trough cross-bedded orientated NNE-SSW (Fig. 13F). As the whole, paleo-currents were dominantly directed from S-SW to N-NE.

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

Moulay el’Arbi

Unit III

120 m

Planktonic foraminifers

Biozone Martini (1971)

Calcareous nannoplankton

40Ar/39Ar stage dating

late Messinian

N° samples

Lithology

Discoaster kugleri Discoaster exilis Discoaster brouweri Discoaster hamatus Discoaster bellus gr. Discoaster pentaradiatus Discoaster berggrenii Coccolithus miopelagicus Triquetrorhabdulus rugosus Cyclicargolithus floridanus Amaurolithus primus Reticulofenestra pseudoumbilicus Sphenolithus abies

Units

Biozone Berggren et al. (1995) Wade et al. (2011)

Globoturborotalia nepenthes Globoturborotalia decoraperta Globorotalia merotumida Globorotalia juanai Globorotalia lenguaensis Neogloboquadrina acostaensis Globorotalia miotumida Globoturborotalita apertura Neogloboquadrina humerosa Globorotalia plesiotumida

142

7.42

IIb

MA21

6.52

100

7.15 ± 0.15

MA20

?

?

MA19

7.89

MA18

early Messinian

MA22

NN11

M13b

MA16

Barren

MA15

Barren

8.29

? 9.1

MA14

IIa

MA13

50

MA12 MA11 MA10

NN10

9.53

Barren

9.57 ± 0.19 9.69

M13a

10.18

NN9

10.76

NN8

?

MA9

Tortonian

Unit II

MA17

MA8 MA7 MA6

10

MA5

Barren

MA4

Barren

MA3 MA2 MA1

Barren

0

: biostratigraphic markers : reworked taxa Fig. 10. Stratigraphic distribution of the planktonic foraminiferal and calcareous nannoplankton taxa identified in the Moulay el'Arbi sections. Bio-event calibration ages by Hilgen et al. (2012).

The North Arbaa section consists of up to 100 m thick greyish marls with some thin interbedded sandstones layers and marine conglomerates in their upper part (Fig. 14B).

G. miotumida (FAD = 7.89 Ma; LAD = 6.52 Ma in the Mediterranean region) and correlate with Zone M13b. Associated with the nannoplankton data, this indicates that the samples deposited during the latest Tortonian or early Messinian.

4.2.2. Biostratigraphy 5. Discussion 4.2.2.1. Azroû Zazîrhîne section. Calcareous nannoplankton in the Azroû Zazîrhîne section (Fig. 14A) is poorly preserved and diversified. In sample NEK14-14, located about 20 m below the marine conglomerates, we found some specimens of A. primus (FAD = 7.42 Ma), then pointing to Zone NN11. Planktonic foraminifers are also rare and poorly preserved in this section. Sample NEK14-14 yielded Neogloboquadrina humerosa (FAD = 8.56 Ma), pointing to Zones M13b or M14. Associated with the occurrence of A. primus, this finding indicates that the samples deposited during the latest Tortonian or early Messinian. 4.2.2.2. North Arbaa section. As in the Azroû Zazîrhîne section, calcareous nannoplankton and planktonic foraminifers are poorly preserved and weakly diversified in the North Arbaa section (Fig. 14B). Sample NEK14-4, located in the lower part of the section, yielded A. primus (FAD = 7.42 Ma) then pointing to Zone NN11. Samples NEK14-5 and NEK14-6, located in the middle part of the section, yielded

5.1. Chronostratigraphy of the Boudinar and Arbaa Taourirt basins The combination of biostratigraphic data (calcareous nannoplankton and planktonic foraminifers) and radiometric datings allows us to calibrate a chronostratigraphic framework for the Boudinar basin (Fig. 15) and propose correlations between the deposits outcropping in the Boudinar and Arbaa Taourirt basins. 5.1.1. Boudinar basin The age of the continental deposits from the base of the Boudinar basin is estimated to be early Tortonian-late Serravalian? based on the 40Ar/39Ar age determination of 10.46 ± 0.14 Ma for the volcaniclastic layer #KET14–3 located 8 m below their top in the Irhachâmene section. The onset of continental sedimentation in this basin (Unit I) cannot be precisely dated but is estimated to be early Tortonian at youngest. This

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

15

0.0045 KET-14-3 (Biotite)

KET-14-3 (Biotite)

14

0.004 0.0035

12

36Ar / 40Ar

Age [ Ma ]

13

11 10 9

10.52 ± 0.10 Ma

0.003 0.0025 0.002 0.0015

8

0.001

7

0.0005

TFA: 11.02 ± 0.13 Ma

6

10.46 ± 0.14 Ma MSWD = 2.84 40Ar/36Ar = 302.7 ± 2.2

0 0

10

20

30

40

50

60

70

80

90

100

0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Cumulative 39Ar Released [ % ]

IRA-3 (Biotite)

0.004

16

0.0035

14

0.003

12

36Ar / 40Ar

9.68 ± 0.08 Ma

10 8 6

0.0025 0.002 0.0015

4

0.001

2

0.0005

0

9.67 ± 0.09 Ma MSWD = 0.77 40Ar/36Ar = 304.2 ± 18.9

0 0

10

20

30

40

50

60

70

80

90

100

0

0.1

0.2

0.3

0.4

0.5

0.6

12

0.8

0.9

0.0045 MA-11 (Biotite)

MA-11 (Biotite)

11.5

0.004

11

0.0035 0.003

10.5

36Ar / 40Ar

Age [ Ma ]

0.7

39Ar / 40Ar

Cumulative 39Ar Released [ % ]

9.57 ± 0.19 Ma

10 9.5 9

0.0025 0.002 0.0015 0.001

8.5

9.57 ± 0.19 Ma MSWD = 0.7 40Ar/36Ar = 294.5 ± 4.6

0.0005

8

0 0

10

20

30

40

50

60

70

80

90

0

100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

39Ar / 40Ar

Cumulative 39Ar Released [ % ] 16

0.0045

MA-20 (Biotite)

MA-20 (Biotite)

14

0.004

12

0.0035 0.003

10

7.15 ± 0.15 Ma

36Ar / 40Ar

Age [ Ma ]

1.1

0.0045 IRA-3 (Biotite)

18

8 6 4

0.0025 0.002 0.0015 0.001

2 0

1

39Ar / 40Ar

20

Age [ Ma ]

143

7.14 ± 0.15 Ma MSWD = 1.38 40Ar/36Ar = 298.8 ± 5.6

0.0005 0

10

20

30

40

50

60

70

80

Cumulative 39Ar Released [ % ]

90

100

0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

39Ar / 40Ar

Fig. 11. 40Ar/39Ar age spectra and corresponding inverse isochrons. All errors are quoted at 2σ level (plateau and isochron ages, initial intercept). In the inverse isochron diagram, open symbols correspond to steps not considered for the plateau age nor for the isochron age. MSWD = mean square of weighted deviates.

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

30 m

Van Morkhoven et al. (1986)

Inner shelf Middle shelf

Valvulineria complanata Valvulineria bradyana

Uvirgerina peregrina

Uvirgina pygmea

Nonion fabum Planulina ariminensis Pullenia bulloides Spiroplectammina carinata Spiroplectammina wrightii Spiroplectinella wright Spirorutilus carinatus Sphaeroidina bulloides Textularia soldanii Textularia conica Uvigerina cylindrical gaudrynoides

Globobulimina sp. Globobulimina pupoides Hanzawaia boueana Hoeglundina Lenticulina spp. Melonis pompiliodes

Elphidium spp.

Elphidium advenum

Cibicidoides kullenbergi

Cibicides lobatulus Criborotalia ornatissima

Bolivina dilatata Bulimina sp. Bulimina elegans Bulimina costata Bulimina aculeata Cibicides sp. Cibicides dutemplei

Bolivina punctata

Bolivina spathulata

Ammonia spp. Agglutinans Bolivina sp.

Paleobathymetry

0m

25

75 %

Sidi Haj Youssef

50

Ammonia beccarii

Benthic foraminifera

0%

late Messinian

Age Lithology

50

Outer shelf

100

200

Upper bathyal

Middle bathyal

600

lower Abyssal bathyal

1000

2000

6000

144

SY 10 SY 9 SY 7 SY 6 SY 5 SY 3 SY 2 SY 1 SY 0

early Messinian

10 0

Moulay el’Arbi

? ?

D1

MA21

100 m

?

MA18 MA17 MA16

MA14

Tortonian

MA13 MA12

50

MA10 MA9 MA8 MA7 MA6 MA5 MA4

10

MA3 MA2 MA1

0

Fig. 12. Distribution of benthic foraminiferal taxa identified in the Moulay el'Arbi and S. Haj Youssef sections with paleobathymetric interpretation. Black points: low percentage; in red, average depth curve; in blue, general trend.

result is new and discards previous proposals of a late to latest Tortonian age for the oldest continental deposits in this basin (Guillemin and Houzay, 1982; Barhoun and Wernli, 1999; Azdimousa et al., 2006). The age of the first marine deposits in the Boudinar basin can be estimated thanks to the occurrence of three volcaniclastic layers (sample #s KET14-3, IRA3 and MA11) that frame the transgressive surface. In the Irhachâmene section, the age determination of 10.46 ± 0.14 Ma for the volcaniclastic layer #KET14-3, located 8 m below the transgressive surface, also indicates that marine sedimentation in this section first occurred after the FAD of D. brouweri. 13 m above the transgressive surface, the age determination of 9.68 ± 0.08 Ma for the volcaniclastic layer #IRA3 further demonstrates that the marine invasion occurred after the FAD of N. acostaensis. Moreover, the volcaniclastic layer #IRA3 yields a concordant age with that of the volcanic tuff #MA11 (9.57 ± 0.19 Ma) located 50 m above the transgressive surface in the Moulay el'Arbi section. Consequently, we propose to correlate these two layers (#IRA3 and #MA11) and calculate a weighted mean age of 9.60 ± 0.13 Ma, which is biostratigraphically corroborated by the occurrences of G. juanai and D. hamatus, respectively found below (sample MA9) and above (sample MA13) the volcanic tuff #MA11 in the Moulay el'Arbi section. There, we can calculate a sedimentation rate of 13 cm/ky between these two markers (the thickness of the volcanic tuff is not considered as it corresponds to an instantaneous event). This rate allows estimating an early Tortonian age of ~ 10 Ma for the first marine deposits. This age, perfectly corroborated by the datations in the Irhachâmene section, appears to be much older than previously proposed (late Tortonian: Barhoun and Wernli [1999]; Messinian: Guillemin and Houzay [1982] and Azdimousa et al. [2006]). The age of the marine erosional surface occurring in the Irhachâmene section and marking the boundary between sub-units IIa and IIb can also

be estimated. In the Moulay el'Arbi section, it falls above sample MA18, which yielded G. miotumida (FAD = 7.89 Ma in the Mediterranean region), and below the volcanic tuff #MA20, dated at 7.15 ± 0.15 Ma. Therefore, in the Boudinar basin, this marine erosional surface is late Tortonian or earliest Messinian. Near the top of the marls with diatomitic interbeds, and above the volcanic tuff (sample #MA20) dated at 7.15 ± 0.15 Ma, we identified the crossover event between N. amplificus and T. rugosus, calibrated at 6.79 Ma. We therefore agree with Barhoun and Wernli (1999) that the uppermost preserved Miocene marine sediments in the Irhachâmene section were deposited at youngest during the early Messinian. However, younger Miocene deposits probably exist at Boudinar. Indeed, from the correlation with the neighbouring Melilla-nador basin we can propose younger ages for the northward prograding para-reefal limestones cropping out over the Ras Tarf volcanoe (Fig. 16) and for the oligospecific Porites reef fragments which occur above the MES in the basin (Fig. 6). 5.1.2. Correlation with the Aarba Taourirt basin In the Arbaa Taourirt basin, the marine marls resting upon the metamorphic basement were deposited during the late Tortonian-early Messinian. The youngest marls, truncated by a marine erosional surface (Figs. 13 and 14), are younger than 7.42 Ma as indicated by the occurrence of A. primus (FAD = 7.42 Ma). Similar to the Boudinar basin, this marine erosional surface is capped by red-algae rich marine conglomerates. Consequently, we consider that the marine conglomerates of the Arbaa Taourirt basin constitute a lateral equivalent of the marls with conglomerates, red-algae rich limestones and diatomitic intercalations (Sub-Unit IIb) in the Boudinar basin, and thus probably deposited during latest Tortonian or early Messinian.

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

145

SW

NE

D

Boudinar basin Nekor Fault

Late Tortonian-Early Messinian marls

A WSW

ENE

marine sandstones and microconglomerates

150 m

Marine coarse-grained conglomerates N

100

12°

10 m

C N

NE

SW

marine sandstones and microconglomerates

50

E

B D

0

N

S

E WNW

5m

ESE

Dominant paleoflow

F Fig. 13. A) Field view of the Miocene sedimentary series of the Arbaa Taourirt basin. A major erosional surface (red line) occurs at the top of the marls, overlain by prograding marine conglomerates and sandstones. B) Stratigraphic scheme of the Azroû Zazîrhîne outcrops with direction of progradation in the basal conglomeratic fans and overlying dunes. C) Detailed view of the marine conglomerates prograding toward the ENE overlain by marine sandstones and microconglomerates exhibiting large-scale trough cross-bedding. D) Field view of the sandstones/microconglomerates succession upon the late Tortonian-early Messinian marls. E) Detailed view of the prograding marine conglomerates and sandstones displaying large-scale through cross-bedding structures to the N-NNE. F) Perpendicular view to the main direction of progradation of the large-scale trough cross-beds.

5.1.3. Correlation with other Neogene marginal basins It must be stressed that in the Boudinar basin, the oldest marine sediments (~10 Ma) appear to be much older than those cropping out

in the neighbouring Neogene basins (with the exception of the “Cap des Trois Fourches” basin). In the “Cap des Trois Fourches” basin, 180 m thick shallow marine deposits were deposited during the early Tortonian,

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

A

N° samples

Azroû Zazîrhîne

Planktonic foraminifers

stage

Discoaster brouweri Triqu etrorh abdu lu s ru gosu s A m au rolith u s delicatu s Amaurolithus primus Reticulofenestra pseudoumbilicus Sphenolithus abies

Lithology

Biozone Berggren et al. Biozone (1995) Calcareous nannoplankton Martini Wade et al. (1971) (2011)

Globoturborotalia nepenthes Globoturborotalia decoraperta Globoquadrina dehiscens Globorotalia ju an ai Neogloboquadrina acostaensis Globorotalia miotumida Globoturborotalita apertura Neogloboquadrina humerosa Globorotalia plesiotumida

146

160 m

sandstones Large-scale cross-bedding

NEK 14-15

8.56 NEK 14-14

M13b-M14

7.42

NN11

40 NEK 14-13

Barren

Latest TortonianEarly Messinian

80

0

B

North Arbaa NEK 14-10

NEK 14-9 NEK 14-7

Latest TortonianEarly Messinian

80 m

NEK 14-6

7.89 NEK 14-5

40

M13b

7.42 NEK 14-4

NN11

0

Fig. 14. Planktonic foraminiferal and calcareous nannoplankton taxa in the Arbaa Taourirt basin. A) Azroû Zazîrhîne section, B) North Arbaa section.

i.e. before 9.6 ± 0.4 Ma (Azdimousa and Bourgois, 1993). The onset of the subsidence and marine sedimentation in the Boudinar and “Cap des Trois Fourches” basins were therefore synchronous during the early Tortonian. It is worth mentioning that these two basins are along NE-SW trending sinistral strike slip faults that became inactive during the Tortonian (Morel, 1988). In the other neighbouring Neogene Rifian basins, marine

sedimentation first took place during the late Tortonian, at least ca. 2 Ma later: at ~8 Ma in the Taza-Guercif basin (Krijgsman et al., 1999a) and near the Tortonian-Messinian transition in the Melilla-Nador basin (Münch et al., 2001; Cornée et al., 2002). The Melilla-Nador basin, located at the mouth of the South Rifian Corridor, constitutes one of the references for studying the stratigraphy of

Irhachamene

Aït Abdallah 30

Moulay el’Arbi

Sub-Unit IIb

Major emersion and erosion

-

Pollen

+

High subsidence

40 m

Messinian

S. Haj Youssef

X= T. rugosus6.76 N. amplificus

M ES *

?

Ages Tectonic/ Paleo1 2, 3 subsidence bathymetry

early Messinian

200 m

Azroû ? Zazîrhîne 250 m

Unit III

Boudinar basin

Arbaa Taourirt basin

This work

early Pliocene early Pliocene

Lithology / Biostratigraphy / 40Ar/39Ar dating

147

late Messinian

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

Aquatic plants Herbs Cupressaceae Meso-microthermic plants Mediterranean xerophytes Pinus Mesothermic plants Mega-mesothermic plants Megathermic plants

?

0

40

80%

150 100 MA20

7.15+/-0.15

100

D. hamatus 9.53 50

MA11

9.69

9.60 +/- 0.13

Sub-Unit IIa A. primus

10

50

late Tortonian

7.42

Tortonian

G. juanai 150

?

Low subsidence

m

0

Messinian

0

200

10 m

late

10

IRA3

10.

46+

/- 0

.14

Sub-Unit Ib

0

~10

KET14-3

10 10

Sub-Unit Ia

late Tortonian

100

?

early

0

0

Fig. 15. Biostratigraphic and radiometric dating-based correlation between the studied sections in the Boudinar and Arbaa Taourirt basins, compared with previous works: 1 — Barhoun and Wernli (1999); 2 — Guillemin and Houzay (1982); 3 — Azdimousa et al. (2006). *: Azdimousa et al. (2006); Cornée et al. (2016). To the right: tectonic regime in the Boudinar basin after Morel (1988) and Azdimousa et al. (2006), paleobathymetric evolution and pollinic diagram (this work) environmental data.

the Mediterranean Neogene basins because many magnetostratigraphic, biostratigraphic, cyclostratigraphic and tephrochronologic data have been published from there (Cunningham et al., 1994, 1997; Roger et al., 2000; Münch et al., 2001, 2006; Cornée et al., 2002, 2006; Van Assen et al., 2006). From base to top of the basin, seven sedimentary units were identified and dated between ~6.9 Ma and ~5.8 Ma (Cornée et al., 2002). Marls and diatomite interbeddings range laterally into a prograding bioclastic unit (Unit 2) dated between ~6.9 Ma and 6.5 Ma then oligospecific Porites coral reefs (Unit 3) dated between ~ 6.5 Ma and 6.1 Ma (Roger et al., 2000; Münch et al., 2001; Cornée et al., 2002). We propose that prograding para-reefal limestones and oligospecific Porites reefs in the Boudinar basin correlate with Units 2 and 3 of the Melilla-Nador basin. Marine conditions in the Boudinar basin consequently lasted until around 6.5–6.1 Ma, similar to the neighbouring Melilla-Nador basin. The history of the Boudinar basin bears similarities with that of the pre-evaporite reference succession of the Sorbas and Nijar marginal basins in SE Spain (e.g., Martín and Braga, 1994; Fortuin and Krijgsman, 2002). In these basins, the late Neogene sedimentation began with red clastic deposits during the late Serravalian-early Tortonian transition (Ott d'Estevou and Montenat, 1990), similar to the Boudinar basin. In most Spanish marginal basins, a late Tortonian regional uplift was responsible for a major unconformity occurring between middle to late Tortonian and latest Tortonian to early Messinian marine deposits. We evidenced such an unconformity between Sub-Units IIa and IIb close to the Tortonian/Messinian boundary. In Spain, the latest Tortonianearliest Messinian sediments are represented by the transgressive, mixed siliciclastic carbonate Azagador Member, overlain by the marine, marly Abab Member which was precisely dated between 7.24 Ma and 5.97 Ma (Krijgsman et al., 2001; Sierro et al., 2001; Manzi et al., 2013). Consequently, the conglomerates and limestones of the lower part of

Sub-Unit IIb at Boudinar (Fig. 15) can be correlated with the Azagador Member. The overlying marls can be correlated with the lower Abad Member which dates from ca 7.24 to ca 6.7 Ma (Krijgsman et al., 2001). Marly deposits coeval with the Upper Abad member (6.7– 5.97 Ma) are missing at Boudinar because they were eroded during the MSC (Cornée et al., 2016). However, lateral shallow water carbonates are preserved on top of the Ras Tarf and as olistoliths above the MES. 5.2. Tectonic, sedimentary and paleoenvironmental evolutions of the Boudinar and Arbaa Taourirt basins 5.2.1. Late Serravalian?-early Tortonian Previous works assigned a major role for the sinistral Nekor strikeslip fault (Fig. 1B) in the genesis of the Boudinar basin (Guillemin and Houzay, 1982; Morel, 1988). The basin should have been a graben-like structure, because of an E-W extension in association with orthogonal compression (Ait Brahim and Chotin, 1984). Based on our results, the opening of the basin began before ~10.5 Ma during the early Tortonian, while it was a continental depression opened towards the paleoAlboran Sea. At this stage, the subsidence may have been controlled by the reactivation of the Nekor strike-slip fault in an extensive context (Guillemin and Houzay, 1982; Morel, 1988). The tectonic subsidence then continued and a marine transgression took place in the Boudinar basin at around 10 Ma. The basal continental conglomerates were unconformably onlapped by early Tortonian marine clastic then marly deposits (sub-Unit IIa). Within the marls of sub-Unit IIa, the high abundances of the benthic foraminifer A. beccarii s.l. and the occurrences of Elphidium, Cibicides and Nonion indicate a wide range of environmental conditions from hyposaline to normal marine environments (Nigam and Rao, 1987; Murray, 1991; Nigam

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NW

SE

Prograding para-reefal carbonates

Ras Tarf volcanic massif

A WNW

ESE

Early Tortonian conglomerates

or ek t N faul

Early Tortonian marls

C

Early Tortonian marls

B

Sandstone beds Synsedimentary normal fault Early Tortonian conglomerates

C Fig. 16. A) Field view of the late Miocene prograding para-reefal carbonates on the Ras Tarf volcanic massif (see location in Fig. 2). B, C) Field view of the margin of the Boudinar basin in the vicinity of the Nekor fault (see location in Fig. 2). B) Serravalian?–early Tortonian conglomerates fan corresponding to the youngest Nekor fault activity in the Boudinar basin. C) Early Tortonian marls unconformably onlapping the conglomerates and sealing the Nekor fault.

and Chaturvedi, 2000). Such foraminiferal assemblages typify estuarine to inner shelf environments with shallow and restricted water conditions that may be affected by salinity variations in relation with the nearby presence of river runoff. These formations also onlap the Nekor fault (Fig. 16 B, C), indicating that it was inactive in its northeasternmost part between 10 Ma and 9.6 Ma. However, extensive tectonics along N20° synsedimentary normal faults (Azdimousa et al., 2006) were still active in the Boudinar basin as exemplified by the westward shift in subsidence after 9.6 Ma. This is indicated by higher accumulation rates at the base of the Moulay el'Arbi section than in the Irhachâmene one (i.e., before 9.6 Ma) as exemplified by the variable thickness and nature of deposits, and then by a reversal of subsidence (Fig. 15). In the Aarba Taourirt basin, despite the lack of precise biostratigraphical constraints, a similar evolution can be deduced from the basal part of the section described by Frizon de Lamotte (1981). 5.2.2. Late Tortonian During the late Tortonian, benthic foraminiferal assemblages within marls from sub-Unit IIa indicate inner-middle shelf paleoenvironments and a shallow (b 80 m) and constant paleobathymetry (Figs. 12, 15). The sediment accumulation rate roughly equalled the basin subsidence rate. These shallow-water environments are also corroborated by palynological data, with relatively low Pinus abundances indicating relative proximity to the coast and the evidence of an open vegetation type dominated by Poaceae, Asteraceae and halophytes typical of littoral environments in this region (Bachiri-Taoufiq and Barhoun, 2001; Bachiri-Taoufiq et al., 2001, 2008). Forested zones were rare and probably developed on nearby mountains and/or along the rivers. Moreover, palynological data indicate a warm and arid climate during the

Tortonian that is in agreement with previous works in the South Rifian Corridor (Bachiri-Taoufiq et al., 2001, 2008). The aridity is highlighted by the ratio between pollen percentages of Poaceae and Asteraceae that is always in favour to Asteraceae, indicating precipitation b500 mm per year (Cour and Duzer, 1978). It must also be pointed out that microthermic plants (i.e., high latitude/altitude plants) are absent (except for one grain of Cedrus). This indicates that either the drainage basin was small without high mountains, or that mountains were too far from the sedimentation point (long distance transport avoid the record of microthermic plants such as Abies), or finally that the Rif mountain was still not fully uplifted and too low to allow the development of microthermic trees. Altogether, these data suggest that during the late Tortonian, the Boudinar basin corresponded to a shallow marine gulf surrounded by low elevation mountains. Similar and constant shallow water environments (b 70 m) have been evidenced in the Aarba Taourirt basin, based on benthic foraminiferal analyses (Wernli, 1988) within marls now attributed to the late Tortonian (this study). 5.2.3. Tortonian-Messinian transition The deposits of Sub-Unit IIa are truncated by a marine erosional surface that was established during the latest Tortonian or very close to the Tortonian-Messinian transition. From the correlation with the Arbaa Taourirt basin, we can precise that this surface dates between 7.42 Ma and 7.15 Ma. Above this surface, an abrupt relative sea-level rise is recorded in the early Messinian, as indicated by upper-middle bathyal environments evidenced in the Moulay el'Arbi section (Fig. 12). The deepening of the basin continued to reach middle bathyal conditions (Fig. 12), with a depth change exceeding 500 m. This amplitude strongly exceeds the amplitude of the world's ocean sea-level changes during

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

this period (Miller et al., 2011) and indicates that the basin underwent an important tectonic subsidence during the early Messinian. Indeed, several normal faults sets affected the early Messinian marls and diatomites deposits (Azdimousa et al., 2006). These authors identified two main fault directions: E-W and NW-SE to NNW-SSE indicating two directions of extension, N-S and NE-SW respectively. Moreover, pollen data show an increase in Pinus pollen percentages and a decrease in Amaranthaceae (halophytes) in the early Messinian marls above the marine erosional surface (Fig. 15). This indicates that the sources of the sediments were then more distant than during the Tortonian, in accordance with other evidences of deepening of the basin. Palynological data also suggest that there has been no significant climatic changes since the early Tortonian in accordance with results from the South Rifian Corridor (Bachiri-Taoufiq et al., 2008). It seems that relative sea level changes are mostly controlling pollen percentage variations (i.e., Pinus) in this area. During the early Messinian, the Boudinar basin evolved into an open, deep marine basin and the shoreline was most likely relatively far. In the Arbaa Taourirt basin, localized coarse-grained conglomeratic fans and large-scale paleo-current structures within sandy to conglomeratic deposits rest upon the marine erosional surface truncating late Tortonian marine marls (Fig. 13). The basal coarse-grained conglomerates derived from the erosion of the nearby emergent land and are mainly composed of debris flows interpreted as localized submarine fan deltas (Fig. 13B) deposited in a SW-NE trending depression located along the Nekor fault. The overlying sandstones-microconglomerates with bioclastic components display giant trough cross-bedded structures. These structures, which indicate high-energy currents, are the result of the migration of submarine dunes under a strong, dominantly unidirectional current flowing toward the N-NNE. We believe that this direction is related to the flowing of Atlantic seawaters into the Mediterranean Sea since ~ 7.2 Ma. According to Anastas et al. (1997), dune height (H) is related to water depth (D) by the formula H = 0.17 D. The thickest set of through cross-beds is around 15 m thick, giving rise to an estimation of around 90 m for the paleowaterdepth. Thus, subsidence appears to have remained rather constant at Arbaa Taourirt whereas it accelerated at Boudinar during the Tortonian-Messinian transition. 5.2.4. Early Messinian In the Boudinar basin, the uppermost Messinian deposits are characterized by a shallowing upward trend from middle bathyal to outer shelf-upper bathyal environments (Fig. 12). This shallowing trend persisted during the early to late-early Messinian (6.5–6.1 Ma) as indicated by the prograding para-reefal limestones over the Ras Tarf volcanoe and the coral reef olistoliths found in the basin. We therefore conclude that Boudinar evolved into a shallow marginal basin. Deposits from this period completely lack in the Arbaa Taourirt basin. 5.3. Late Miocene Mediterranean–Atlantic connections During the early Tortonian and before 8 Ma, the Mediterranean Sea was connected to the Atlantic Ocean through the North-Betic Strait, the Granada and Guadix basins in the southern Spain (Martín et al., 2009, 2014) (Fig. 17A). Marine connections were established between 9 Ma and 8 Ma (Soria et al., 1999) and the maximum extent of the Betic seaways occurred in the late Tortonian, after 8.35 Ma (Corbi et al., 2012). On the contrary, no marine gateway between the Atlantic Ocean and the Mediterranean Sea existed before 8 Ma through the Rifian corridors. Since 10 Ma, marine ingressions were limited to shallow gulfs in the Boudinar and “Cap des Trois Fourches” areas on the Mediterranean paleo-margin (Fig. 17A). During the late Tortonian, marine Atlantic-Mediterranean connections through the South Rifian Corridor were emplaced at ~ 8 Ma (Fig. 17B). This event is marked by the onset of the marine sedimentation and the development of deep marine environments

149

(paleo-depths of ~ 600 m) in the Taza-Guercif basin (Krijgsman et al., 1999a). In the North Rifian Corridor, our results show that the Arbaa Taourirt and Boudinar basins were connected. Moreover, Atlantic sea waters may have reached the Dhar Souk, Boured basins as indicated by the occurrence of Neogloboquadrina humerosa (FAD = 8.56 Ma) or Globorotalia miotumida (FAD = 7.89 Ma in the Mediterranean region) near the base of the marine deposits in these basins (Wernli, 1988). Thus, the North Rifian Corridor was also fully opened. Roughly in the same times, the North-Betic straits suffered diachronic restrictions because of local tectonic settings between 7.9 Ma and 7.3 Ma (Corbi et al., 2012) and may have closed during the late Tortonian (Soria et al., 1999; Martín et al., 2009, 2014). During the Tortonian-Messinian transition, Krijgsman et al. (1999a, 1999b) proposed that the Atlantic-Mediterranean connections through the South Rifian Corridor were restricted as a result of a tectonic uplift combined with glacio-eustatic variations between ~ 7.2 Ma and 6.1 Ma. In the North Rifian Corridor, however, there is a major sedimentological change marked by the development of large-scale paleocurrent structures within sandy to conglomeratic deposits over a regional marine erosional surface (Fig. 13). The sedimentary structures, which indicate high-energy currents, may be related to unidirectional Atlantic water inflows into the Mediterranean Sea at around 7.2 Ma. Similar current structures have also been described in narrow corridors that connected the Mediterranean Sea and the Atlantic Ocean through the southern Spain during the late Miocene (Martín et al., 2001, 2009, 2014; Betzler et al., 2006). Different evolutions evidenced between the North and South Rifian Corridors may originate from the southward migration of the compressional front of the Rif Chain promoting tectonic uplift in the Taza-Guercif basin (Fig. 17C). During the late early Messinian, the North Rifian Corridor underwent progressive restriction and displays an evolution similar to those of the Sorbas-Nijar (Ott d'Estevou and Montenat, 1990; Sierro et al., 1997) and Guadalquivir basins (Pérez-Asensio et al., 2012a) in southern Spain. After ~ 6.1 Ma, the South Rifian Corridor may have been completely closed (Krijgsman et al., 1999a; Krijgsman and Langereis, 2000; Ivanović et al., 2013). At the same time, we propose that the North Rifian Corridor may have also been closed after 6.1 Ma (Fig. 17D), as indicated by the shallowing trend and then the development of prograding para-reefal units in the Boudinar basin. At the same time, the Guadalhorce strait (Fig. 17C) was the last Betic seaway and acted as a major outflow channel for waters flowing from the Mediterranean Sea into the Atlantic Ocean (Martín et al., 2001; Pérèz-Asensio et al., 2012b). It probably closed at ca 6.3–6.2 Ma (Corbi et al., 2012; Pérèz-Asensio et al., 2012b), roughly simultaneously with the Rifian corridors. Nevertheless, the presence of limited connections between the Atlantic and the Mediterranean cannot be definitely excluded during late Messinian. Indeed, the deposition of kilometres thick evaporitic deposits in the central parts of the Mediterranean (e.g., Lofi et al., 2011) required some sea water connections with the Atlantic at the time of the MSC (e.g., CIESM, 2008; Ryan, 2009; Roveri et al., 2014). Based on current knowledge, all the investigated marine corridors around the Alboran Sea closed during the late Tortonian-early Messinian interval. Consequently, some connections may have existed during the late Messinian through the South Rifian Corridor as suggested by Pérèz-Asensio et al. (2012b) or maybe through the Gibraltar Strait. Further investigations are necessary in these areas. 6. Conclusions By using calcareous nannoplankton, planktonic foraminifers and radioisotope dating, we built a new chronostratigraphic framework for the Miocene deposits of the Boudinar and Arbaa Taourirt basins. At Boudinar, continental deposits were emplaced during the early Tortonian or before and marine sedimentation occurred between the early Tortonian at ~ 10 Ma and the late-early Messinian at ~6.1 Ma. At

150

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

A) Early to late Tortonian

Fortuna Basin

( ? - 8 Ma)

36°

B) Late Tortonian ( 8 - 7.2 Ma) 36°

MURCIA

MURCIA

trait

c S

th

N

Nor

Beti

th

Nor

c Beti

it

Stra

Guadix Basin

N

Guadix Basin

Granada Basin Granada Basin Sorbas basin

Guadalquivir Basin

Sorbas basin

Guadalquivir Basin

ALMERIA ALMERIA

MEDITERRANEAN SEA

35°

ATLANTIC OCEAN

35°

MEDITERRANEAN SEA

ATLANTIC OCEAN

Cap des Trois Fourches Basin

Cap des Trois Fourches Basin

?

Boudinar Basin

Boudinar Basin

North Rifian Corridor Taounate Basin

Taounate Basin

Arbaa Taourirt Boured Dhar Souk

?

Gharb Basin

Gharb Basin

TAOUNATE

TAOUNATE TAZA

TAZA RABAT Mamora 34° basin

?

MELILLA

?

MELILLA

FEZ

RABAT Mamora basin 34°

?

5°

3°

FEZ

Saïs Basin

1°

5°

C) Early Messinian

D) Late Messinian

N

N

Taza-Guercif Basin

?

South Rifian Corridor

3°

1°

( > 6.1 Ma)

( 7.2 - 6.1 Ma)

Guadalquivir Basin

Guadalquivir Basin

Sorbas basin

Sorbas basin

ALMERIA

ALMERIA

Guadalhorce strait

35°

35°

MEDITERRANEAN SEA

ATLANTIC OCEAN

MEDITERRANEAN SEA

ATLANTIC OCEAN

Cap des Trois Fourches Basin

Cap des Trois Fourches Basin

Boudinar Basin

Boudinar Basin MELILLA

?

MELILLA

Emergent land Possible gateways

Arbaa Taourirt Boured

Taounate Basin

Dhar Souk Gharb Basin

TAOUNATE

Gharb Basin

?

Paleocurrents

TAOUNATE

Active tectonic front

TAZA RABAT Mamora 34° basin

FEZ

Taza-Guercif Basin

RABAT Mamora 34° basin

Saïs Basin

5°

Present-day coast

3°

FEZ

1°

5°

TAZA

3°

Inactive tectonic front

Fig. 17. Paleogeographic maps showing the changes in the Atlantic–Mediterranean connections through northern Morocco and southern Spain from the early Tortonian to the late Messinian. Modified after Martín et al. (2001, 2009, 2014) and Flecker et al. (2015).

Arbaa Taourirt, marine marls deposited from the late Tortonian to the earliest Messinian and are overlain by shallow marine, early Messinian conglomerates and sandstones. Our work allows establishing the following scenario for the Atlantic-Mediterranean connection through the North Rifian Corridor. Since 10 Ma, marine ingressions limited to shallow gulfs in the Boudinar and “Cap des Trois Fourches” areas on the Moroccan Mediterranean paleo-margin. During the late Tortonian, the North Rifian Corridor opened. Near the Tortonian-Messinian transition, the North Rifian Corridor recorded a major sedimentological event that may be related to the narrowing of the South Rifian Corridor. The North Rifian Corridor acted as a major channel for Atlantic water inflows into the

Mediterranean Sea during the early Messinian after 7.2 Ma. During the late Messinian, the Atlantic-Mediterranean connections through the North Rifian Corridor were progressively restricted and finally closed at around ~6.1 Ma, similar to the South Rifian and Betic Corridors. This raises the question of the connectivity between the Atlantic Ocean and the Mediterranean Sea during the MSC. Acknowledgements This work was funded by the French CNRS programs ActionsMargesMedOcc chantier “Alboran” and the scientific cooperation FrenchMorocco program PHC Volubilis no.: MA/12/274 and the European

M. Achalhi et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 131–152

FP7-IRSES-MEDYNA project under Grant Agreement PIRSES-GA- 2013612572. The authors are grateful to an anonymous reviewer, to J.M. Soria and Editor I.P. Montanez for their constructive comments.

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