451-R1 – REDDAD
Ital. J. Geosci., Vol. 135, No. 2 (2016), pp. 000-000, 8 figs., 3 tabs. (doi: 10.3301/IJG.2015.33) © Società Geologica Italiana, Roma 2016
Textural and compositional controls on modern fluvial and beach sands of Mediterranean coastal Rif belt (Northern Rif, Morocco) HANANE REDDAD (*), HAJAR EL TALIBI (**), FRANCESCO PERRI (***), SAID EL MOUSSAOUI (**), MOHAMED AMINE ZERDEB (**), MOHAMED NAJIB ZAGHLOUL (**) & SALVATORE CRITELLI (***)
ABSTRACT Texture and composition of beach (154 samples) and fluvial (26 samples) sands collected between the Amsa and Amter villages (Rif Thrust-Belt, Morocco) are used to characterize the hinterland petrological provinces, their drainage patterns and dispersal pathways. Multivariate analytical techniques were carried out on the textural and compositional data. The analyzed sediments are usually coarsegrained, and locally medium to fine-grained sands, varying from well sorted and graded samples (Amsa river samples) to poorly sorted and graded samples (Oued Laou, Sidi Yahia Aarab and Kanar river samples). The relationships of the coarser one percentile (C) and the median value (M) on the C-M diagram suggest that transport processes are saltation and suspension for medium to fine grained sands, and bedload-traction and rolling for coarser sand and gravels. The morphology of quartz grains, mainly characterized by angular to sub-angular shapes with V-shaped cracks and conchoidal fractures, is the result of those transport processes. Two sand petrofacies were identified and reflect the main clastic contribution of source rocks belonging to the Internal Domain Units of the Rif Belt. Sands from beaches and related fluvial systems draining Ras Akaili, Tissouka, Dhar Nesk, and Beni Mezala Mountains, have a metamorphicsedimenticlastic petrofacies (between the Amsa and Bouhmed area) and a metamorphic-ultramafic petrofacies (between the Bouhmed and Amter area), mainly derived from the Paleozoic metasedimentary rocks of the Ghomaride and Sebtide complexes.
KEY WORDS: Sand composition, Textural parameters, Fluvial and beach sands, Alboran Sea, Northern Morocco.
INTRODUCTION
In the last decade, the modern and recent sediments within the hinterland and coastal marine environments of the Circum-Mediterranean areas have been investigated to infer their relationships between the source area and the depositional basin (e.g., GARZANTI et alii, 2002, 2014; CRITELLI et alii, 2003; ZAGHLOUL et alii, 2009; PERRI et alii, 2012, 2015). The coastal areas of the northern Rif Chain, from Amsa to the Amter headland on the western part of the Alboran Sea, represent a key area for understanding provenance relations by using modern sand. The petrography, geochemistry and mineralogy of carbonatoclastic and siliciclastic sediments, can reveal the nature of parent rocks and the tectonic setting of the sedimentary basins (e.g., DICKINSON & SUCZEK, 1979; BHATIA, 1983; CULLERS,
(*) University Sultan Moulay Sliman, Beni Mellal, Morocco. (**) Department of Earth Sciences, Faculty of Sciences and Techniques, University Abdelmalek Essaadi, Tangier, Morocco. (***) Dipartimento di Biologia, Ecologia e Scienze della Terra, Università della Calabria, Italy. Corresponding author e-mail: francesco.
[email protected]
2000; GARZANTI et alii, 2007, 2014; ZAGHLOUL et alii, 2010; CARACCIOLO et alii, 2011; D’ATRI et alii, 2012; CRITELLI et alii, 2007, 2013; PERRI et alii, 2014, 2015; PERRI & OHTA, 2014; PERRI, 2014). In this work, petrographical analysis on fluvial and beach sands between Amsa and the Amter headland (northern Rif Chain, Morocco) have been carried out. This study aims to: i) characterize the hinterland petrological provinces, their drainage patterns and dispersal pathways; ii) prove how well sand composition reflects tectono-morphologic littoral provinces and source land controls on the composition of fluvial and beach sands.
GEOLOGICAL SETTING
The Rif chain is part of a poly-arcuate orogenic belt surrounding the western Mediterranean Sea and embraces the Apennines, the Calabrian Arc, the Maghrebian chains and the western Betic Cordillera (fig. 1a; DURAND DELGA, 1980; DURAND DELGA & FONTBOTE, 1980). These orogens are formed by the superposition of several nappes grouped in three main tectonic complexes: (i) the Internal Units; (ii) the Maghrebian Flysch Basin (MFB) and (iii) the External Units. The Internal Units, Internal Betic-Rifian Zone or “Alboran Domain” sensu GARCÍA-DUEÑAS et alii (1992), consist of Paleozoic continental crust, high-grade metamorphic and mantle rocks, and a Mesozoic cover characterized by different degrees of metamorphism (e.g. KORNPROBST, 1974; MICHARD et alii, 2006). The Internal Units comprise three tectonic complexes (fig. 1b): (i) the Sebtides (DURAND DELGA & KORNPROBST, 1963); (ii) the Ghomarides (DURAND-DELGA & KORNPROBST, 1963; WILDI, 1983; CHALOUAN, 1986; MICHARD & CHALOUAN, 1991) and (iii) the Dorsale Calcaire (FALLOT, 1937). The Sebtide Complex (DURANDDELGA & KORNPROBST, 1963; MICHARD et alii, 1997, 2006) consists of the sub-continental mantle peridotites of the Beni Bousera overlain by HP/HT to MP/HT granulites, gneisses and micaschists (Lower Sebtides), in turn underlying the Permo-Triassic HP/LT to LP/LT metamorphic Federico Units (Upper Sebtides). The Ghomaride Complex tectonically covers the latter units formed by low-grade Eo-Variscan and Variscan metamorphic Paleozoic rocks, passing to a Middle Triassic-Middle Miocene sedimentary cover (CHALOUAN & MICHARD, 1990; CHALOUAN et alii, 2008; ZAGHLOUL et alii, 2010 and references therein). Generally, the MFB nappes are located in front of the Internal Units; however some slices cover the Ghomaride Complex as a result of a back-thrusting stage (e.g. GUER-
2
H. REDDAD ET ALII
Fig. 1 - a) Geological map of the Alpine Chain in the central-western Mediterranean area (simplified from SUTER, 1980); b) Geological sketch maps of the Rif Chain simplified after WILDI (1983).
Fig. 2 - Schematic geological map of northern Rif (modified from CHALOUAN et alii, 2008) showing bedrock composition in the drainage regions on the western part of the Alboran Sea (Amsa-Amter province) with a detailed location of the sampling areas.
RERA et alii, 1993, 2005; HLILA, 2005; CHALOUAN et alii, 2008). The Mauretanian Units encompass two main successions: the Triassic-Cretaceous Tisirene and CretaceousLower Miocene Ben Ider sequences (DURAND DELGA & MATTAUER, 1959; ANDRIEUX, 1971; BOUILLIN et alii, 1970; THOMAS et alii, 2010). Probably these two successions formed a single stratigraphic unit successively detached along a Cretaceous level (DIDON et alii, 1973; DURANDDELGA et alii, 2000; ZAGHLOUL et alii, 2007). Finally, the External Rif Domain (Intrarif, Mesorif and Prerif Units) consists of some Mesozoic-Cenozoic platform to basin successions (e.g. GUERRERA et alii,
2005), that at places include remnants of ophiolitic rocks and/or subcontinental mantle masses and related metasedimentary covers characterized by low-grade to MP/LT metamorphism (LEBLANC, 1979; SUTER, 1980; DIDON et alii, 1973; MICHARD et alii, 2007, 2014). The external tectonic pile is unconformably covered by upper Tortonian-Messinian wedge-top basin deposits (LEBLANC, 1979; DI STASO et alii, 2010 and references therein). The investigated area from Al Hoceima to Ceuta (fig. 2) is characterized by the tectonic superposition of several thrust sheets. It has undergone multiple compressive and distensive tectonic events since Mesozoic up to
SANDS OF MEDITERRANEAN COASTAL RIF BELT (MOROCCO)
3
TABLE 1 Distribution of samples on beaches and rivers associated with the coastal strip between Amsa and Amter. Station Beach Direction Number of radial Number of samples Prepared Thin section Related River Number of samples Prepared Thin section
A
B
C
D
E
Amsa NNW-SSE 9 27 A3 O. Amsa 4 A1-A2
O.Laou- Kaa Asress NW-SE 7 6 24 19 B3 O. Laou 4 B1-B2
Stehat- Schemaala NW-SE 7 7 21 23 C3 O. Kanar 7 C1-C2
S.Y Aarab NW-SE 7 21 D3 O.S.Y Aarab 5 |D1-D2
Amter NW-SE 6 19 E3 O. Amter 6 E1-E2
late Miocene, and derived from the collision of the Iberian, African plates and a remnant continental block (“Mesomediterranean Microplate” sensu GUERRERA et alii, 1993, 2005; CRITELLI et alii, 2008; PERRI et alii, 2013) since middle Miocene (GUERRERA et alii, 1993, 2005; FRIZON DE LAMOTTE, 1985; DE CAPOA et alii, 2004, 2007; ZAGHLOUL et alii, 2005, 2007; VITALE et alii, 2014). The main neotectonic events were represented by lowand high-angle normal faults responsible for i) thinning the thickened higher and lower crusts; ii) subsequent rapid uplift of the stacked internal units and; iii) drifting of the western Mediterranean back-arc basins rifted since the Early Miocene (BENMAKHLOUF, 1990; ZAGHLOUL, 2002; OUAZANI-TOUHAMI & CHALOUAN, 1995; MICHARD et alii, 2002; ZAGHLOUL et alii, 2003; HLILA, 2005; CHALOUAN et alii, 2008).
STUDY AREA
The study area is located on the western end of the Alboran Sea (fig. 2); the Mediterranean coastline of the northern Rif chain runs from Amsa to Amter headland over a distance of about 60 Km and with a width ranging from 50 m to 150 m (EL MOUTCHOU, 1995). The western part of the Alboran Sea from the Amsa to Amter headland and principally includes Paleozoic units of the Ghomarides nappes and their sedimentary cover, locally medium to high grade metamorphic terrains of the lower Sebtides complex (CHALOUAN, 1986; MAATE, 1984, 1996; OUAZANITOUHAMI, 1994; OUAZANI-TOUHAMI & CHALOUAN, 1995; ZAGHLOUL et alii, 2003; HLILA, 2005). The coast between Amsa and Amter has distinct morphological features and sedimentary dynamics. The AmsaAmter shoreline, about 50 km long, shows mainly sandy beaches. The drainage basin is composed of a major riverbed and minor torrential streams. Sedimentary and metasedimentary rocks and medium to high grade metamorphic rocks mainly outcrop in this coastal province. The Mediterranean coastal margin of the northern Rif chain experiences the hot-humid Mediterranean-type climate. It is characterized by humid and cool winter with many extreme precipitation, and by a dry summer (BOUGHABA, 1992; EL MOUTCHOU, 1995). The relative humidity is# a result of the marine influence on the coastal stretch with average yearly values ranging from 76% to 79%. The precipitations of this region are distinctive of a Mediterranean climate, with a humid season lasting six months (EL MOUTCHOU, 1995). During the winter precipi-
tation represents 50% of the annual mean precipitation which ranges between 300 mm and 800 mm. The mean value of maximum temperature ranges between 19°C and 25°C, while the minimum mean value varies from 12°C to 17°C (EL MOUTCHOU, 1995). The drainage basins of the northern Rif include several rivers that cross the Rif mountains and are characterized by delta systems on the southern side of the Gibraltar Strait. The hydrographic network between Tetouan and Al Hoceima, is mainly controlled by the type of rocks drained including sedimentary rocks and fractured and folded metamorphic rocks (ALOUANE, 1986). The hydrography of the study area is mainly controlled by a torrential system due to the stiff dips of the young slopes, the impermeability of rocks (clay, marl, limestone or schist) and the pluviometric patterns, resulting in abundant precipitations. Both constructive and destructive processes, such as tectonic uplift, slope instability, hills erosion and chemical alteration processes have been significant in shaping the physiography of the coastal margin (LE PERA & CRITELLI, 1997).
SAMPLING AND ANALYTICAL METHODS
Samples from beach depositional systems (154 samples) and their related rivers (26 samples) have been collected and studied (tab. 1 and fig. 2). Sands were collected from five localities: (A) Amsa, (B) O. Laou-Kaa Asress, (C) Stehat-Schemaala, (D) Sidi Yahya Aarab and (E) Amter, spaced from 4 to 7 km apart along the studied area from the Ras Mazari headland to Jbeha (fig. 2). Groups of 6 first-order stream sands were sampled from small catchment basins active seasonally; they were collected from bars in the inner reaches of the channels. Three second-order sand samples were collected along the main channels of rivers. Each fluvial sand was collected about 400 m up-stream from the beach and each collected beach sample was spaced 400 m from each river mouth eastward and southward, respectively, on the western side of the Alboran Sea. All samples were prepared for grain size analysis,# they were washed using H2O2 to remove the organic matter, dried at 40°C, and then sieved (using 1-phi intervals). We selected 15 samples (10 from the main rivers and 5 from beaches, tab. 1) for petrographic analysis. The samples were sieved, the medium size fraction (0.25-0.50 mm) was used for thin section preparation. This fraction was cemented with epoxy resin, thin-sectioned, etched with HF acid and stained
4
H. REDDAD ET ALII
TABLE 2 Detrital modes of the medium sand-sized fraction of modern fluvial and beach sands. '%! (#! ($! (%!
)#!
)$!
)%!
37! 37!
38! B!
32! 6!
9! 36!
38! 4!
B!
B!
7!
3!
7!
7!
7!
3!
43!
F5! 335!
93!
F6!
63!
49!
F8!
7!
7!
3B!
37!
5!
7!
3!
B!
6!
8!
7!
7!
7!
3F!
F!
F!
7!
7!
33!
7!
8!
6!
7!
F!
9!
7!
B!
3!
F!
37!
5!
3!
3!
6!
7!
3!
3!
7!
2!
8!
7!
7!
B!
6!
7!
7!
7!
7!
7!
7!
4!
B!
7!
7!
6!
3!
B!
6!
7!
B!
8!
6!
5!
3B!
B!
B!
F!
6!
7!
3!
3!
7!
5!
3!
36!
F!
7!
7!
F!
3!
7!
7!
7!
7!
7!
B!
7!
7!
B!
4!
4!
7!
3!
8!
3!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
3!
7!
7!
K*>$!$+G!/@-=%*&.!()*+,-.!/%0)&$-1!
7!
7!
7!
7!
3!
3!
7!
B!
B!
3B!
3B!
37!
B!
F!
B!
!
K*>$!$+G!/@-=%*&.!*+!!DE!
3!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
3!
7!
!
!
K*>$!$+G!/@-=%*&.!*+!,%$+*&*>!$+G!H!,+.*))*>!DE!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
8!
7!
7!
3!
7!
!
!
K*>$!$+G!/@-=%*&.!*+!C.&$C=%!DE!
8!
B!
F!
B!
6!
6!
3!
37!
4!
39!
39!
B3!
4!
3!
6!
!
./!
L.%@*)&!DE!
7!
7!
7!
7!
7!
7!
7!
7!
7!
38!
BB!
B8!
7!
6!
F!
!
!
L.%@*)&!DE!
B7!
33!
2!
6!
BB!
67!
47! 33B! 354! F5!
39!
47!
B8!
84!
65!
!
!
L$+G)&=+.)!DE!
63!
2!
35!
B8!
37!
35!
8!
3!
7!
7!
7!
7!
6!
B!
3!
/@.%&!
!
B!
3!
3!
7!
3!
3!
3!
7!
7!
7!
7!
7!
3!
7!
7!
E*+.!,%$*+.G!L$+G)&=+.!DE!
39!
35!
5!
8!
8!
3!
3!
B!
B!
7!
7!
B!
B5!
38!
37
L*-)&=+.)!DE!
B9!
F!
2!
35!
2!
37!
8!
8!
8!
7!
7!
3B!
6B!
34!
2!
KM&$;).G*C.+&$%0!:%$,C.+&!!
9B! 3B9! 3F4! 9B!
378! BF!
B8!
5!
4!
7!
7!
7!
96!
8B!
F4!
!
!
"#! "$!
&#!
&$!
&%!
'#!
'$!
4! 7!
5! 3!
64! 36!
3! 3!
5! 4!
!
!
"#$%&'!(:*+.;,%$*+.)!%0)&$--*+.1!
B!
3!
3!
7!
7!
B!
7!
!
!
"#$%&'!*+!C.&$C=%!DE!
4B!
87!
87!
39!
B6!
5B!
32!
!
!
"#$%&'!*+!!DE!
7!
7!
7!
7!
7!
7!
7!
!
!
"#$%&'!*+!).G*C.+&$%0!DE!
BB!
F!
3B!
B!
6!
32!
6!
!
!
"#$%&'!*+!,%$+*&*>!$+G!H!,+.*))*>!DE!
7!
7!
7!
7!
7!
5!
!
+!
I;:.-G.)-$).!*+!!DE!
7!
!
!
J-$,*=>-$).!*+!).G*C.+&$%0!DE!
!
-!
!
! !
!
2! 9!
33! 7!
7!
7!
7!
7!
7!
3!
7!
33!
F!
68!
59!
64!
7!
5!
84!
!
!
N.$O0!C*+.%$-!*+!C.&$C=%!DE!
7!
7!
7!
7!
7!
7!
7!
39!
38!
84!
8B!
B4!
7!
2!
B6!
!
!
N.$O0!C*+.%$-!*+!!DE!
7!
7!
7!
7!
7!
7!
7!
7!
7!
34!
B4!
3F!
7!
3!
B7!
P=-)&=+.)!
67!
36!
3B!
F9!
B5!
39!
3B!
B!
8!
7!
7!
3!
8!
5!
B!
-*C.)&=+.)!
32!
35!
32!
99!
45!
F3!
65!
35!
37!
7!
7!
3!
37!
9!
38! 7!
#$! ! ! ! ! ! ! #%! #&!
0-! N.$O0!C*+.%$-!()*+,-.!/%0)&$-1!
3! 6!
33! 8!
"#$%&'!()*+,-.!/%0)&$-1! "#$%&'!(:*+.;,%$*+.)!%0)&$--*+.1!?*&@!&.>&=+*>ȱ:$A%*>!!
!
2! B!
"%!
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E=))*-!!!
7!
7!
7!
B!
3!
7!
7!
7!
7!
7!
7!
7!
7!
7!
E=))*-!*+!-*C.)&=+.)!Q!P=-)&=+.)!DE!
7!
7!
7!
7!
3!
7!
7!
7!
7!
7!
7!
7!
7!
7!
7!
>$->$%.=#)!$%.+*&.)!
8!
6!
5!
65!
F8!
69!
62!
3B!
4!
7!
7!
6!
39!
38!
37!
C.&$-*C.)&=+.!
7!
7!
7!
7!
7!
7!
7!
7!
7!
6!
4!
4!
7!
8!
33!
/$->*&.!()*+,-.!/%0)&$-1!
7!
7!
7!
7!
7!
8!
7!
7!
3!
7!
7!
6!
7!
7!
B!
!R*=>-$)&!
7!
7!
5!
7!
7!
7!
7!
7!
4!
7!
7!
9!
7!
7!
4!
36!
8!
F!
8!
8!
F!
B!
3!
3!
F!
7!
5!
5!
F!
B!
S-&M%*&.!
!
!
12/34!
5$%! %65! %76! %76! %8$! 59#! %59! 59%! 5%8! 5%:! 57%! 57;! %87! %8#! 5#8!
by immersion in sodium cobaltinitrite solution to allow feldspars identification. Alizarine and potassium Fe-cyanide solutions were also used for carbonate grains identification. To analyze the modal composition of the sand, about 300 points were counted on each thin section following the GAZZI-DICKINSON method (GAZZI, 1966; DICKINSON, 1970; INGERSOLL et alii, 1984; ZUFFA, 1985). A plot combining phaneritic fragments (grains having crystals >0.0625 mm) and aphanitic lithic fragments (grains having crystals
