Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)

Abstract. The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposits with condensed and erosional surfaces, whereas the syncline basins exhibit thicker and well-preserved successions. In addition, the vertical facies succession evolves from thin Silurian to Givetian deposits into thick Upper Devonian sediments. Synsedimentary structures and major unconformities are related to several tectonic events such as the Cambrian–Ordovician extension, the Ordovician–Silurian glacial rebound, the Silurian–Devonian Caledonian extension/compression, the late Devonian extension/compression, and the Hercynian compression. Locally, deformation is characterized by near-vertical planar normal faults responsible for horst and graben structuring associated with folding during the Cambrian–Ordovician–Silurian period. These structures may have been inverted or reactivated during the Devonian (i.e., Caledonian, Mid–Late Devonian) compression and the Carboniferous (i.e., pre-Hercynian to Hercynian). Additionally, basement characterization from geological and geophysics data (aeromagnetic and gravity maps), shows an interesting age-dependent zonation of the terranes which are bounded by mega-shear zones within the arches–basins framework. The old terranes are situated under arches while the young terranes are located under the basins depocenter. This structural framework results from the accretion of Archean and Proterozoic terranes inherited from former orogeny (e.g., Pan-African orogeny 900–520 Ma). Therefore, the sedimentary infilling pattern and the nature of deformation result from the repeated slow Paleozoic reactivation of Precambrian terranes bounded by subvertical lithospheric fault systems. Alternating periods of tectonic quiescence and low-rate subsidence acceleration associated with extension and local inversion tectonics correspond to a succession of Paleozoic geodynamic events (i.e., far-field orogenic belt, glaciation).



Introduction
Paleozoic deposits fill numerous intracratonic basins, which may also be referred to as "cratonic basins", "interior cratonic basins", or "intracontinental sags". Intracratonic basins are widespread around the world (Heine et al., 2008) and exploration for nonconventional petroleum has revived interest in them. They are located in "stable" lithospheric areas and share several common features (Allen and Armitage, 2011). Their geometries are large circular, elliptical, and/or saucershaped to oval. Their stratigraphy is filled with continental to shallow-water sediments. Their subsidence rate is low (5 to 50 m Ma −1 ) and long (sometimes more than 540 Myr). Their structural framework shows the reactivation of structures and emergence of arches also referred to in the literature as "ridges", "paleo-highs", "domes", and "swells". Multiple hypotheses and models have been proposed to explain how these slowly subsiding, long-lived intracratonic basins formed and evolved (see Allen andArmitage, 2011 andreferences therein or Hartley andAllen, 1994). However, their tectonic and sedimentary architectures are often poorly constrained.
The main specificities of intracratonic basins are found on the Paleozoic North Saharan Platform. The sedimentary infilling during ca. 250 Myr is relatively thin (i.e., around a few hundred to a few thousand meters), of great lateral extent (i.e., 9 million km 2 ), and is separated by major regional unconformities (Beuf et al., 1968aEschard et al., 2005Eschard et al., , 2010Fabre, 1988Fabre, , 2005Fekirine and Abdallah, 1998;Guiraud et al., 2005;Kracha, 2011;Legrand, 2003a). Depositional environments were mainly continental to shallow-marine and homogeneous. Very slow and subtle lateral variations occurred over time Fabre, 1988;Guiraud et al., 2005;Legrand, 2003a). The Paleozoic North Saharan Platform is arranged ( Fig. 1) into an association of long-lived broad synclines (i.e., basins or subbasins) and anticlines (i.e., arches) of different wavelengths (λ: 75-620 km). Burov and Cloetingh (2009) report deformation wavelengths of the order of 200-600 km when the whole lithosphere is involved and of 50-100 km when the crust is decoupled from the lithospheric mantle. This insight suggests that the inherited basement fabric influences intracratonic basin architecture at a large scale. In addition, pre-existing structures, such as shear zones and terrane suture zones, are present throughout the lithosphere, affecting the geometry and evolution of upper-crustal structural framework forming during later tectonic events (Peace et al., 2018;Phillips et al., 2018).
In this study of the Reggane, Ahnet, Mouydir, and Illizi basins, a multidisciplinary workflow involving various tools (e.g., seismic profiles, satellite images) and techniques (e.g., photogeology, seismic interpretation, well correlation, geophysics, geochronology) has enabled us to (1) make a tectono-sedimentary analysis, (2) determine the spatial arrangement of depositional environments calibrated by bios-tratigraphic zonation, (3) characterize basin geometry, and (4) ascertain the inherited architecture of the basement and its tectonic evolution. We propose a conceptual coupled model explaining the architecture of the intracratonic basins of the North Saharan Platform. This model highlights the role of basement heritage heterogeneities in an accreted mobile belt and their influence on the structure and evolution of intracratonic basins. It is a first step towards a better understanding of the factors and mechanisms that drive intracratonic basins.

Geological setting: the Paleozoic North Saharan
Platform and the Reggane, Ahnet, Mouydir, and Illizi basins The Reggane, Ahnet, Mouydir and Illizi basins (Figs. 1 and 2) are located in southwestern Algeria, north of the Hoggar Massif (Ahaggar). They are depressions filled by Paleozoic deposits. The basins are bounded to the south by the Hoggar Massif (Tuareg Shield) and they are separated one another by the Azzel Matti, the Arak-Foum Belrem, and the Amguid El Biod arches. Figure 3 synthesizes the lithostratigraphy, the large-scale sequence stratigraphic framework delimited by six main regional unconformities (A to F), and the tectonic events proposed in the literature (cf. references under Fig. 3) affecting the Paleozoic North Saharan Platform.
Synsedimentary extensional and compressional markers are characterized in this structural framework based on the analyses of satellite images (Figs. 5 and 6), seismic profiles (Fig. 7), 21 wells (W1 to W21), and 12 outcrop cross sections (O1 to O12). Wells and outcrop sections are arranged into three E-W sections (Figs. 10, 11 and 12) and one N-S section (Fig. 13). Satellite images (Figs. 5 and 6) and seismic profiles (Fig. 7) are located at key areas (i.e., near arches) illustrating the relevant structures (Fig. 2). The calibration of the key stratigraphic horizon on seismic profiles ( Fig. 7) was settled by sonic well-log data using Petrel and OpendTect software. Nine key horizons easily extendable at the regional scale are identified and essentially correspond to major depositional unconformities: near top Solid Earth, 9, 1239Earth, 9, -1275Earth, 9, , 2018 www.solid-earth.net/9/1239/2018/ Table 1. Synthesis of facies associations (AF1 to AF5), depositional environments, and electrofacies in the Devonian series compiled from internal (Eschard et al., 1999) and published studies Biju-Duval et al., 1968;Wendt et al., 2006).  (Fig. 7). The stratigraphic layers are identified by the integration of satellite images (Google Earth and Landsat USGS: https://earthexplorer.usgs.gov/, last access: 29 November 2016), digital elevation models (DEM), and the 1 : 200 000 geological maps of Algeria (Bennacef et al., 1974;Bensalah et al., 1971). Subsidence analysis characterizes the vertical displacements of a given sedimentary depositional surface by tracking its subsidence and uplift history (Van Hinte, 1978). The resulting curve details the total subsidence history for a given stratigraphic column (Allen and Allen, 2005;Van Hinte, 1978). Backstripping is also used to restore the initial thicknesses of a sedimentary column (Allen and Allen, 2005;Angevine et al., 1990). Lithologies and paleobathymetries have been defined using facies analysis or literature data. Porosity and the compaction proxy are based on experimental data from (Sclater and Christie, 1980). In this study, subsidence analyses were performed on sections using OSXBackstrip software performing 1D Airy backstripping (following Allen and Allen, 2005;Watts, 2001); available at: http://www.ux.uis.no/nestor/work/programs.html, last access: 5 January 2017).

Synsedimentary extensional markers
Extensional markers are characterized by the settlement of steeply westward or eastward-dipping basement normal faults associated with colinear syndepositional folds of several kilometers in length (e.g., Figs. 6a to e and 7a), represented by footwall anticline and hanging wall synclineshaped forced folds. They are located in the vicinity of different arches (Fig. 2) such as the Tihemboka Arch (Figs. 5b and 6a, b), Arak-Foum Belrem Arch (Figs. 5a, 6c to f and 7a, c), Azzel Matti Arch (Fig. 7b), and Bahar El Hamar area intrabasin arch (Fig. 7d). These tectonic structures can be featured by basement blind faults (e.g., fault F1 in Fig. 7a). The deformation pattern is mainly characterized by brittle faulting in Cambrian-Ordovician series down to the basement and faultdamping in Silurian series (e.g., faults F1 to F6 in Fig. 7b). The other terms of the series (i.e., Silurian to Carboniferous) are usually affected by folding except (see F1 faults in Figs. 6d, 7b, d, and c) where the brittle deformation can be propagated to the Upper Devonian (due to reactivation and/or inversion as suggested in the next paragraph).
In association with the extensional markers, thickness variations and tilted divergent onlaps of the sedimentary series (i.e., wedge-shaped units, progressive unconformities) in the hanging wall syncline of the fault escarpments are observed (Figs. 6 and 7). These are attested using photogeological analysis of satellite images (Fig. 6) and are marked by a gentler dip angle of the stratification planes away from the fault plane (i.e., fault core zone). The markers of syndepositional deformation structures are visible in the hanging-wall synclines of Precambrian to Upper Devonian series (Figs. 6 and 7).
The sinuous faults are arranged "en echelon" into several segments with relay ramps. These faults are ten to several tens of kilometers long with vertical throws of hundreds of meters that fade rapidly toward the fault tips. The sinuous geometry of normal undulated faults as well as the rapid lateral variation in fault throw are controlled by the propagation and the linkage of growing parent and tip synsedimentary normal faults (Marchal et al., 2003(Marchal et al., , 1998. We use the stratigraphic age of impacted layers (here Tamadjert Fm.) to date (re)activation of the faults.
According to Holbrook and Schumm (1999), river patterns are extremely sensitive to tectonic structure activity. Here we find that the synsedimentary activity of the extensional structures is also evidenced by the influence of the fault scarp on the distribution and orientation of sinuous channelized sand-Solid Earth, 9, 1239-1275, 2018 www.solid-earth.net/9/1239/2018/ Core description, palynological calibration, and gamma-ray signatures of well W7 modified from an internal core description report (Dokka, 1999) and an internal palynological report (Azzoune, 1999). (b) Devonian sequential stratigraphy of well-log W7. For the location of well W7 see Fig. 2a.

Synsedimentary compressional markers (inversion tectonics)
After the development of the extensional tectonism described previously, evidence of synsedimentary compressional markers can be identified. These markers are located and preferentially observable near the Arak-Foum Belrem Arch ( Fig. 6f; F2 in Fig. 7c), the Azzel Matti Arch (2 in Fig. 7v), and the Bahar El Hamar area intra-basin arch (2 in Fig. 7d). The tectonic structures take the form of inverse faulting reactivating former basement faults (F1' in Fig. 6f, F1 in Fig. 7c, F1' in Fig. 7d, F1 in Fig. 7b). The synsedimentary inverse faulting is demonstrated by the characterization of asymmetric anticlines and is especially observable in satellite images and restricted to the fault footwalls ( Fig. 5a along F1-F2).
Landsat image analysis combined with the line drawing of certain seismic lines reveals several thickness variations reflecting divergent onlaps (i.e., wedge-shaped units) which are restricted to the hanging-wall asymmetric anticlines (2 in Figs. 6f, 7b, c and d). The compressional synsedimentary markers clearly post-date extensional divergent onlaps at hanging-wall syncline-shaped forced folds (1 in Figs. 7c, c and d). This architecture is very similar to classical positive inversion structures of former inherited normal faults (Bellahsen and Daniel, 2005;Bonini et al., 2012;Buchanan and McClay, 1991;Ustaszewski et al., 2005). Tectonic transport from the paleo-graben hanging wall toward the paleo-horst footwall (F1, F2-F2', F4-F4' in Fig. 7b; F1-F1' in Fig. 7d) is evidenced. Further positive tectonic inversion architecture is identified by tectonic transport from the paleo-horst footwall to the paleo-graben hanging wall (F1-F1' in Fig. 6f; F1, F5, and F6 in Fig. 7c). This second type of tectonic inversion is very similar to the transported fault models defined by Butler (1989) and Madritsch et al. (2008). The local positive inversions of inherited normal faults occurred during Silurian-Devonian (F4' Fig. 7b) and Middle to Late Devonian times (Figs. 7b, c and d). A late significant compression event between the end of the Carboniferous and the Early Mesozoic was responsible for the exhumation and erosion of the tilted Paleozoic series. This series is related to the Hercynian angular unconformity surface (Fig. 7b).

Stratigraphy and sedimentology
The whole sedimentary series described in the literature is composed of fluviatile to braid-deltaic plain Cambrian, not only fluviatile (e.g., Brahmaputra River analogue), with a transitional facies from continental to shallow marine (Beuf et al., 1968aEschard et al., 2005Eschard et al., , 2010Sabaou et al., 2009), Upper Ordovician glaciogenic deposits (Beuf et al., 1968aEschard et al., 2005Eschard et al., , 2010, argillaceous deep marine Silurian deposits (Djouder et al., 2018;Eschard et al., 2005Eschard et al., , 2010Legrand, 1986Legrand, , 2003bLüning et al., 2000), and offshore to embayment Carboniferous deposits (Wendt et al., 2009a). In this complete sedimentary succession, we have focused on the Devonian deposits as they are very sensitive to and representative of basin dynamics. The architecture of the Devonian deposits allows us to approximate the main forcing factors controlling the sedimentary infilling of the basin and its synsedimentary deformation. Eleven facies associations organized into four depositional environments (Table 1) are defined to reconstruct the architecture and the lateral and vertical sedimentary evolution of the basins (Figs. 10, 11, 12 and 13).

Continental fluvial environments
This depositional environment features the AF1 (fluvial) and the AF2 (flood plain) facies association (Table 1). Facies association AF1 is mainly characterized by a thinning-up sequence with a basal erosional surface and trough crossbedded intraformational conglomerates with mud clast lag deposits, quartz pebbles, and imbricated grains (Table 1). It passes into medium to coarse trough cross-bedded sandstones, planar cross-bedded siltstones, and laminated shales. These deposits are associated with rare bioturbation (except at the surface of the sets), ironstones, phosphorites, corroded quartz grains, and phosphatized pebbles. Laterally, facies association AF2 is characterized by horizontally laminated and very poorly sorted silt to argillaceous fine sandstones. They contain frequent root traces, plant debris, well-developed paleosols, bioturbation, nodules, and ferruginous horizons. Current ripples and climbing ripples are associated in prograding thin sandy layers. In AF1, the basal erosional reworking and high energy processes are characteristic of channel-filling of fluvial systems (Allen, 1983;Owen, 1995). Eschard et al. (1999) identify three fluvial systems (see A, B, and C in Fig. 9) in the Tassili-N-Ajjers outcrops: braided dominant (AF1a), meandering Solid Earth, 9, 1239-1275, 2018 www.solid-earth.net/9/1239/2018/ dominant (AF1b), and straight dominant (AF1c). They differentiate them by their different sinuosity, direction of accretion (lateral or frontal), the presence of mud drapes, bioturbation, and giant epsilon cross-bedding. Gamma-ray signatures of these facies associations (A, B, and C in Fig. 9) are cylindrical with an average value of 20 gAPI. The gammaray shapes are largely representative of fluvial environments (Rider, 1996;Serra and Serra, 2003;Wagoner et al., 1990). The bottom is sharp with high value peaks and the tops are frequently fining-up, which may be associated with high values caused by argillaceous flood plain deposits and roots (Eschard et al., 1999). AF2 is interpreted as humid floodplain deposits (Allen, 1983;Owen, 1995) with crevasse splays or preserved levees of fluvial channels (Eschard et al., 1999). Gamma-ray curves of AF2 (D, Fig. 9) show a rapid succession of low to very high peak values, ranging from 50 to 120 gAPI. AF1 and AF2 are typical of the Pragian "Oued Samene" Formation (Wendt et al., 2006). In the Illizi Basin, these facies are mainly recorded in the Ajjers Formation (dated Upper Cambrian? to Ordovician, see Fabre, 2005;Vecoli, 2000;Vecoli et al., 1995Vecoli et al., , 1999Vecoli et al., , 2008Vecoli and Playford, 1997) and the Lochkovian to Pragian "Barre Moyenne" and "Barre Supérieure" formations Eschard et al., 2005).

Transitional coastal plain environments
This depositional environment comprises facies associations AF3a (delta/estuarine), AF3b (fluvial/tidal distributary channels), AF3c (tidal sand flat), and AF3d (lagoon/mudflat) (Table 1). AF3a is mainly dominated by sigmoidal cross-bedded heterolithic rocks with mud drapes. It is also characterized by fine to coarse, poorly sorted sandstones and siltstones often structured by combined flow ripples, flaser bedding, wavy bedding, and some rare planar bedding. Mud clasts, root traces, desiccation cracks, water escape features, and shale pebbles are common. The presence of epsilon bedding is attested, which is formed by lateral accretion of a river point bar (Allen, 1983). The bed surface sets are intensively bioturbated (Skolithos and Planolites) indicating a shallow marine subtidal setting (Pemberton and Frey, 1982). Faunas such as brachiopods, trilobites, tentaculites, and graptolites are present. AF3b exhibits a fining-up sequence featured by a sharp erosional surface, trough cross-bedded, very coarsegrained, poorly sorted sandstone at the base and sigmoidal cross-bedding at the top (Figs. 8 and 9). AF3c is formed by fine-grained to very coarse-grained sigmoidal cross-bedded heterolithic sandstones with multidirectional tidal bundles. They are also structured by lenticular, flaser bedding and occasional current and oscillation ripples with mud cracks. They reveal intense bioturbation composed of Skolithos (Sk), Thalassinoides (Th), and Planolites (Pl) ichnofacies indicating a shallow marine subtidal setting (Frey et al., 1990;Pemberton and Frey, 1982). AF4d is characterized by horizontally laminated mudstones associated with varicolored shales and fine-grained sandstones. They exhibit mud cracks, occasional wave ripples, and rare multidirectional current ripples. These sedimentary structures are poorly preserved because of intense bioturbation composed of Skolithos (Sk), Thalassinoides (Th), and Planolites (Pl). The fauna includes ammonoids (rare), goniatites, calymenids, pelecypod molds, and brachiopod coquinas. In AF3a, both tidal and fluvial systems in the same facies association can be interpreted as an estuarine system (Dalrymple et al., 1992;Dalrymple and Choi, 2007). The gammaray signature is characterized by a convex bell shape with rapidly alternating low to mid values (30 to 60 gAPI) due to the mud draping of the sets (see E Fig. 9). These forms of gamma ray are typical of fluvial-tidal influenced environments with upward-fining parasequences (Rider, 1996;Serra and Serra, 2003;Wagoner et al., 1990). AF3a is identified at the top of the Pragian "Oued Samene" Formation and in Famennian "Khenig" Formation (Wendt et al., 2006) in the Ahnet and Mouydir basins. In the Illizi Basin, AF3a is mostly recorded at the top Cambrian of the Ajjers Formation, in the Lochkovian "Barre Moyenne", and at the top Pragian of the "Barre Supérieure" Formation Eschard et al., 2005). The AF3b association can be characterized by a mixed fluvial and tidal dynamic based on criteria such as erosional basal contacts, fining-upward trends, or heterolythic facies (Dalrymple et al., 1992;Dalrymple and Choi, 2007). They are associated with abundant mud clasts, mud drapes, and bioturbation indicating tidal influences (Dalrymple et al., 1992(Dalrymple et al., , 2012Dalrymple and Choi, 2007). The major difference with the estuarine facies association (AF3a) is the slight lateral extent of the channels which are only visible in outcrops (Eschard et al., 1999). The gamma-ray pattern is very similar to the estuarine electrofacies (see F Fig. 9). AF3c is interpreted as a tidal sand flat laterally present near a delta (Lessa and Masselink, 1995) and associated with an estuarine environment (Leuven et al., 2016). The gamma-ray signature (see G Fig. 9) is distinguishable by its concave funnel shape with alternating low and mid peaks (25 to 60 gAPI) due to the heterogeneity of the deposits and rapid variations in the sand/shale ratio. These facies are observed in the "Talus à Tigillites" Formation of the Illizi Basin (Eschard et al., 2005). In AF4d, both ichnofacies and facies are indicative of tidal mudflat/lagoonal depositional environments (Dalrymple et al., 1992;Dalrymple and Choi, 2007;Frey et al., 1990). The gamma-ray signature has a distinctively high value (80 to 130 gAPI) and an erratic shape (see H Fig. 9). AF4d is observed in the "Atafaitafa" Formation and in the Emsian prograding shoreface sequence of the Illizi Basin (Eschard et al., 2005). It is also recorded in the Lochkovian "Oued Samene" Formation and the Famennian "Khenig" sandstones (Wendt et al., 2006).

Shoreface environments
This depositional environment is composed of AF4a (subtidal), AF4b (upper shoreface), and AF4c (lower shoreface) facies associations (Table 1). AF4a is characterized by the presence of brachiopods, crinoids, and diversified bioturbations, by the absence of emersion, and by the greater amplitude of the sets in a dominant mud lithology (Eschard et al., 1999). AF4b is heterolithic and composed of fine to mediumgrained sandstones (brownish) interbedded with argillaceous siltstones and bioclastic carbonated sandstones. Sedimentary structures include oscillation ripples, swaley cross-bedding, flaser bedding, cross-bedding, convolute bedding, wavy bedding, and low-angle planar cross-stratification. Sediments were affected by moderate to highly diversified bioturbation by Skolithos (Sk), Cruziana, Planolites, (Pl) Chondrites (Ch), Teichichnus (Te), Spirophytons (Sp) and are composed of ooids, crinoids, bryozoans, stromatoporoids, tabulate and rugose corals, pelagic styliolinids, neritic tentaculitids, and brachiopods. AF4c can be distinguished by a low sand/shale ratio, thick interbeds, abundant hummocky crossstratification (HCS), deep groove marks, slumping, and intense bioturbation (Table 1). AF4a is interpreted as a lagoonal shoreface. The gammaray pattern (see I Fig. 9) is characterized by a concave bell shape influenced by a low sand/shale ratio with values fluctuating between 100 and 200 gAPI. AF4a is identified in the "Talus à Tigillites" Formation and the Emsian sequence of the Illizi Basin (Eschard et al., 2005) and in the Lochkovian "Oued Samene" Formation (Wendt et al., 2006). AF4b is interpreted as a shoreface environment. The presence of swaley cross-bedding produced by the amalgamation of storm beds (Dumas and Arnott, 2006) and other cross-stratified beds is indicative of upper shoreface environments . The gamma-ray pattern (see J and K Fig. 9) displays concave erratic egg shapes with a very regularly decreasing-upward trend and ranging from offshore shale with mid values (80 to 60 gAPI) to clean sandstone with lower values at the top (40 to 60 gAPI). AF4b is observed in the "Atafaitafa" Formation corresponding to the "Zone de passage" Formation of the Illizi Basin (Eschard et al., 2005). AF4c is interpreted as a lower shoreface environment (Dumas and Arnott, 2006;Suter, 2006). The gamma-ray pattern displays the same features as the upper shoreface deposits with higher values (i.e., muddier facies) ranging from 100 to 80 gAPI (see J and K Fig. 9).

Offshore marine environments
This depositional environment is composed of AF5a and AF5b facies associations (Table 1). AF5a is mainly defined by wavy to planar-bedded heterolithic silty-shales interlayered with fine-grained sandstones. It also contains bundles of skeletal wackestones and calcareous mudstones. The main sedimentary structures are lenticular sandstones, HCS , mud mounds, low-angle cross-bedding, tempestite bedding, slumping, and deep groove marks. Sediments can present rare horizontal bioturbation such as Zoophycos (Z), Teichichnus (Te), and Planolites (Pl). AF5b is characterized by an association of black silty shales with occasional bituminous wackestones and packstones. It is composed of graptolites, gonitaties, orthoconic nautiloids, pelagic pelecypods, limestone nodules, tentaculitids, ostracods, and rare fish remains. Rare bioturbation such as Zoophycos (Z) is visible.
In AF5a, the occurrence of HCS, the decrease in sand thickness and grain size, and the bioturbation and the florofaunal associations indicate a deeper marine environment under the influence of storms (Aigner, 1985;Dott and Bourgeois, 1982;Reading and Collinson, 2009). AF5a is interpreted as upper offshore deposits (i.e., offshore transitional). The gamma-ray pattern is serrated and erratic with values well grouped around high values from 120 to 140 gAPI (see L Fig. 9). Positive peaks may indicate siltstone to sandstone ripple beds. AF5b is interpreted as lower offshore deposits (Aigner, 1985;Stow et al., 2001;Stow and Piper, 1984). Here again the gamma-ray signature is serrated and erratic with values well grouped around 140 gAPI (see L Fig. 9). Hot shales with anoxic conditions are characterized by gammaray peaks (> 140 gAPI). These gamma-ray patterns are typical of offshore environments dominated by shales (Rider, 1996;Serra and Serra, 2003;Wagoner et al., 1990). AF5a and AF5b are observed in the Silurian "Argiles à Graptolites" Formation and the Emsian "Orsine" Formation of the Illizi Basin Eschard et al., 2005;Legrand, 1986Legrand, , 2003b. The "Argiles de Mehden Yahia" and "Argiles de Temertasset" shales have the same facies (Wendt et al., 2006).

Sequential framework and unconformities
The high-resolution facies analysis, depositional environments, stacking patterns, and surface geometries observed in the Devonian succession reveal at least two different orders of depositional sequences (large and medium scale, Fig. 8) considered as transgressive/regressive (T/R) (Catuneanu et al., 2009). The sequential framework proposed in Fig. 8b results from the integration of the vertical evolution of the main surfaces (Fig. 8a) and the gamma-ray pattern (Fig. 9). The Devonian series under focus exhibits 9 medium-scale sequences (D1 to D9, Fig. 8; Figs. 10, 11, 12, and 13) bounded by 10 major sequence boundaries (HD0 to HD9), and 9 major flooding surfaces (MFS1 to MFS9). The correlation of the different sequences at the scale of the different basins and arches is used to build three cross sections -two E-W (Figs. 10, 11 and 12) and one N-S (Fig. 13).
The result of the analysis of the general pattern displayed by the successive sequences reveal two major patterns (Figs. 10, 12 and 13) limited by a major flooding surface MFS5. The first pattern extends from the Oued Samene to Adrar Morrat formations and is dated from the Lochkowww.solid-earth.net/9/1239/2018/ Solid Earth, 9, 1239-1275, 2018 Figure 10. SE-W cross-section between the Reggane Basin, the Azzel Matti Arch, the Ahnet Basin, the Arak-Foum Belrem Arch, the Mouydir Basin, and the Amguid El Biod Arch (well locations in Fig. 3). The well W1 biozone calibration is from Hassan (1984) and the internal report is based on the Magloire (1967)  Solid Earth, 9, 1239-1275, 2018 www.solid-earth.net/9/1239/2018/ vian to Givetian. D1 to D5 medium-scale sequences indicate a general proximal clastic depositional environment (dominated by fluvial to transitional and shoreface facies) with intensive lateral facies evolution. This first pattern is thin (from 500 m in the basin depocenter to 200 m around the basin rim) and with successive amalgamated surfaces on the edge of the arches between the "Zone de passage" and "Oued Samene" formations (e.g., Figs. 10 and 13). It is delimited at the bottom by the HD0 surface corresponding to the Silurian-Devonian boundary. D1 to D3 are composed of T/R sequences with a first deepening transgressive trend indicative of a transition from continental to marine deposits bounded by a major MFS and evolving into a second shallowing trend from deep marine to shallow marine depositional environments. D1 to D3 thin progressively toward the edge and the continental deposits, in the central part of the basin, pass laterally into a major unconformity. The amalgamation of the surfaces and lateral variations of facies between the Ahnet Basin and Azzel Matti and Arak-Foum Belrem arches demonstrate a tectonic control related to the presence of subsiding basins and paleo-highs (i.e., arches). D4 and D5 display the same T/R pattern with a reduced continental influence and upward decrease in lateral facies variations and thicknesses where the MFS4 marks the beginning of a marine-dominated regime in the entire area. It is identified as the Early Eifelian transgression defined by Wendt et al. (2006). The D5 sequence is mainly composed of shoreface carbonates. Evidence of mud mounds preferentially located along faults are well-documented in the area for that time (Wendt et al., 1993(Wendt et al., , 1997(Wendt et al., , 2006Wendt and Kaufmann, 1998). This change in the general pattern indicates reduced tectonic influence.
MFS5, at the transition between the two main patterns, represents a major flooding surface on the platform and is featured worldwide by deposition of "hot shales" during the early Frasnian (Lüning et al., 2003(Lüning et al., , 2004Wendt et al., 2006).
The second pattern extends from the "Mehden Yahia", "Temertasset" to the "Khenig" formations dated Frasnian to Lower Tournaisian. This pattern is composed of part of D5-D9 medium-scale sequences. It corresponds to homogenous offshore depositional environments with no lateral facies variations. However, local deltaic (fluvio-marine) conditions are observed during the Frasnian at the Arak Foum Belrem Arch ("Grès de Mehden Yahia" in Fig. 12). A successive alternation of shoreface and offshore deposits is organized into five medium-scale sequences (part of D5, and D6 to D9; Figs. 10, 11 and 12). They, in particular, show some regressive phases with the deposition of both "Grès de Mehden Yahia" and "Grès du Khnig" sandstones (bounded by HD6 and HD9). This pattern (i.e., part of D5 to D9) corresponds to the general maximum flooding (Lüning et al., 2003(Lüning et al., , 2004Wendt et al., 2006) under eustatic control with no tectonic influences.
6 Subsidence and tectonic history: an association of low rate extensional subsidence and positive inversion pulses The backstripping approach (Fig. 14) was applied to five wells (W1, W5, W7, W17, and W21). The morphology of the backstripped curve and subsidence rates can provide clues as to the nature of the sedimentary basin (Xie and Heller, 2009). In intracratonic basins, reconstructed tectonic subsidence curves are almost linear to gently exponential in shape, similar to those of passive margins and rifts (Xie and Heller, 2009). The compilation of tectonic backstripped curves from several wells in peri-Hoggar basins (Fig. 14a, see Fig. 1 for location) and from wells in the study area (Fig. 14b) display low rates of subsidence (from 5 to 50 m Myr −1 ) organized in subsidence patterns of: inversion of the low rate subsidence (ILRS type c, red line, Fig. 14c), deceleration of the low rate subsidence (DLRS type b, black line), and acceleration of the low rate subsidence (ALRS type a, blue line). Each period of ILRS, DLRS, and ALRS may be synchronous among the different wells studied (see B1 to J, Fig. 14b) and some wells from published data (see D to J Fig. 14a).
The Saharan Platform is marked by a rejuvenation of basement structures, around arches (Figs. 1, 2, and 3), linked to regional geodynamic pulses during Neoproterozoic to Paleozoic times (Fig. 14). A compilation of the literature shows that the main geodynamic events are associated with discriminant association of subsidence patterns: a. Late Pan-African compression and collapse (patterns a, b, and c, A Fig. 14a). The infra-Cambrian (i.e., top Neoproterozoic) is characterized by horst and graben architecture associated with wedge-shaped unit DO0 in the basement (Fig. 7). This structuring, probably related to Pan-African post-orogenic collapse, is illustrated by intracratonic basins infilled with volcanosedimentary molasses series (Ahmed and Moussine-Pouchkine, 1987;Coward and Ries, 2003;Fabre et al., 1988;Oudra et al., 2005).
d. Silurian extensional geodynamic pulse (D, Fig. 14). The Silurian post-glaciation period is featured by the reactivation and sealing of the inherited horst and graben fault system (i.e., wedge-shaped unit DO2; Figs. 6b, c, 7a and b). It is linked to an acceleration of the subsidence (ALRS of pattern b in Fig. 14). This tectonic extension is documented in seismic records (Najem et al., 2015) and is associated with the Silurian major transgression on the Saharan Platform (e.g., Eschard et al., 2005;Lüning et al., 2000).
i., j. Pre-Hercynian to Hercynian geodynamic pulses (I and J Fig. 14). This period is organized in Early Carboniferous pre-Hercynian (I, Fig. 14) to Late Carboniferous-Early Permian Hercynian compressions limited by Mid Carboniferous tectonic quiescence/extension (J, Fig. 14). The Carboniferous period is characterized by a normal reactivation and local positive inversion of the previous structural patterns involving reverse faults, overturned folds, transpressional flower structures along strike-slip fault zones (Figs. 6f, 7b, c and d). The major Carboniferous tectonic event on the Saharan Platform impacted all arches and it is mainly controlled by near-vertical basement faults with a strike-slip component (Boote et al., 1998;Caby, 2003;Carruba et al., 2014;Haddoum et al., 2001Haddoum et al., , 2013Liégeois et al., 2003;Wendt et al., 2009a;Zazoun, 2001Zazoun, , 2008. According to these authors basement fabric features exerted a very strong control on the structural evolution during the Hercynian deformation. Two major hiatuses (i.e., Mid Tournaisian to Mid Visean-Serpukhovian) are recognized (Wendt et al., 2009a).
The geodynamic pulses attest to the reactivation of the terranes and associated lithospheric fault zones. This observation questions the nature of the Precambrian basement and associated structural heritage.

Basement characterization: Precambrian structural heritage
Geochronological data show that the different terranes were reworked during several main thermo-orogenic events. The two main events deduced from geochronological data are the Neoproterozoic (i.e., Pan-African) and Paleoproterozoic (i.e., Eburnean) episodes (Bertrand and Caby, 1978). Aeromagnetic anomaly surveys are commonly used to analyze geological features such as rock types and fault zones (e.g., Turner et al., 2007). A similar study was led in the meantime showing similar interpretations (Bournas et al., 2003;Brahimi et al., 2018). In this study, these data highlight the geometries and the extension of the different terranes under the sedimentary cover. Four main domains can be identified from the aeromagnetic anomaly map, delimited by contrasted magnetic signatures and interpreted as suture zones (thick black lines, Fig. 15a). The study area is bounded to the south by the Tuareg Shield (TS), to the north by the south Atlassic Range, to the west by the West African Craton (WAC), and to the east by the East Saharan Craton (ESC) or Saharan Metacraton (Abdelsalam et al., 2002). The magnetic disturbance features (Fig. 15a) show three main magnetic trends. A major N-S sinuous fabric and two minor sinuous 130-140 • E and N45 • E trends. The major N-S lineaments coincide with terrane boundaries and mega-shear zones (e.g., 4 • 50 , 4 • 10 , WOSZ, EOSZ, 8 • 30 , RSZ shear zones; Fig. 1). Sigmoidal-shaped terranes 200 to 500 km long and 100 km wide are characterized (red lines in Fig. 15a). The whole assemblage forms a typical SC-shaped shear fabric (Choukroune et al., 1987) associated with vertical mega-shear zones and suture zones (e.g., WOSZ, EOSZ, 4 • 10 , 4 • 50 or 8 • 30 Hoggar shear zones in Fig. 1). The SC fabrics combined with subvertical lithospheric shear zones ( Fig. 16b and c) are typical features of the Paleoproterozoic accretionary orogens (Cagnard et al., 2011;Chardon et al., 2009). This architecture is concordant with the Neoproterozoic collage of the Tuareg Shield (i.e., mobile belt) between the West African Craton and the East Saharan Craton (i.e., cratonic blocks) described by (Coward and Ries, 2003;Craig et al., 2008).
The gravimetric anomaly map (Fig. 15b) shows a correlation between gravimetric anomalies and tectonic architecture (intracratonic syncline-shaped basin and neighboring arches). Positive anomalies (> 66 mGal) are mainly associated with arches, whereas negative anomalies are related to intracratonic basins (< 66 mGal). Nevertheless, negative anomaly disturbance is found in the Hoggar Massif probably due to Cenozoic volcanism and the Hoggar swell (Liégeois et al., 2005) or to Eocene Alpine intraplate lithospheric buckling (Rougier et al., 2013).
The Precambrian structural heritage is characterized by accreted lithospheric terranes limited by vertical strike-slip mega-shear zones (Fig. 16b and c). A zonation is observed between the Paleozoic basins and arches configurations and the different terranes (thermo-tectonic age). Arches are linked to Archean to Paleoproterozoic continental terranes in contrast to syncline-shaped basins which are associated with Meso-Neoproterozoic terranes (Figs. 1, 2 and 16a). (b) A conceptual model of the architecture of an intracratonic low rate subsidence basin and synthesis of the tectonic kinematics during the Paleozoic. Note that the differential subsidence between arches and basins is controlled by terrane heterogeneity (i.e., thermo-chronologic age, rheology, etc.  Allen and Armitage, 2011;Beaumont et al., 1988;Burgess, 2008;Burgess et al., 1997;Eaton and Darbyshire, 2010;Pinet et al., 2013;Potter, 2006;Sloss, 1963;Xie and Heller, 2006), South America (Allen and Armitage, 2011;de Brito Neves et al., 1984;Milani and Zalan, 1999;de Oliveira and Mohriak, 2003;Soares et al., 1978;Zalan et al., 1990), Russia (Allen and Armitage, 2011;Nikishin et al., 1996) and Australia (Harris, 1994;Lindsay and Leven, 1996;Mory et al., 2017). However, the nature of the potential driving processes (lithospheric folding, far-field stresses, local increase in the geotherm, mechanical anisotropy from lithospheric rheological heterogeneity, etc.) associated with the formation of intracratonic Paleozoic basins remains highly speculative (Allen and Armitage, 2011;Armitage and Allen, 2010;Braun et al., 2014;Burgess and Gurnis, 1995;Burov and Cloetingh, 2009;Cacace and Scheck-Wenderoth, 2016;Célérier et al., 2005;Gac et al., 2013;Heine et al., 2008;Leeder, 1991;Vauchez et al., 1998). The multiscale and multidisciplinary analysis performed in this study enable us to document a model of Paleozoic intracratonic central Saharan basins that couples basin architecture and basement structures (Fig. 17). While we do not provide any quantitative explanations for the dynamics of these basins, our synthesis highlights that their subsidence is not the result of a single process and we attempt to make a check-list here of the properties that a generic model of formation of such basins must capture: a. The association of syncline-shaped wide basins and neighboring arches (i.e., paleo-highs). The structural framework shows a close association of synclineshaped basins, interbasin principal to secondary arches, and intra-basin secondary arches (see Fig. 2).
b. By local horst and graben architecture linked to steepdipping planar normal faults and associated with normal fault-related fold structures (i.e., forced folds; a, Fig. 17a). Locally, the extensional structures are disrupted by positive inversion structures (b, Fig. 17a) or transported normal faults (c, Fig. 17a). c. A low rate of subsidence ranging between 5 to 50 m Myr −1 (Fig. 14).
e. Synsedimentary divergent onlaps and local unconformities are identified from integrated seismic data, satellite images, and borehole data (Figs. 5, 6, 7 and 10 to 13). The periods of tectonic activity are characterized by normal to reverse reactivation of border faults, emplacement of wedge-shaped units, and erosional unconformities neighboring the arches.
f. The stratigraphic architecture displays a lateral facies variation and partitioning between distal marine facies infilling the intracratonic basins (i.e., offshore deposits) and proximal amalgamated facies (i.e., fluvio-marine, shoreface) associated with prominent stratigraphic hiatus and erosional unconformities in the vicinity of the arches.
g. A close connection is evidenced between the period of tectonic deformation and the presence of erosional unconformities (i.e., 2, 3, 6, 8, 10 geodynamic events in Fig. 17b). By contrast, the periods of tectonic quiescence and extension are characterized by low lateral facies variations, thin deposits, and the absence of erosional surfaces.
h. The Precambrian heritage corresponds to Archean to Paleoproterozoic terranes identified in the Hoggar Massif and reactivated during the Meso-Neoproterozoic Pan-African cycle (Fig. 1). The Precambrian lithospheric heterogeneity illustrated by the different characteristics of Precambrian terranes (wavelength, age, nature, fault zones) spatially control the emplacement of the syncline-shaped intracratonic basins underlain by Meso-Neoproterozoic oceanic terranes and the arches underlain by Archean to Paleoproterozoic continental terranes (Figs. 1, 2 and 16). Many authors suggest control of the basement fabrics is inherited from the Pan-African orogeny in the Saharan basins (Beuf et al., 1968bBoote et al., 1998;Carruba et al., 2014;Coward and Ries, 2003;Eschard et al., 2010;Guiraud et al., 2005;Sharata et al., 2015).

Conclusions
Our integrated approach using both geophysical (seismic, gravity, aeromagnetic, etc.) and geological (well, seismic, satellite images, etc.) data has enabled us to decrypt the characteristics of the intracratonic Paleozoic Saharan basins and the control of the heterogeneous lithospheric heritage of the Solid Earth, 9, 1239-1275, 2018 www.solid-earth.net/9/1239/2018/ horst and graben architecture, low rate subsidence, and the association of long-lived broad synclines and anticlines (i.e., arches swells, domes, highs or ridges) with very different wavelengths (λ) (tens to hundreds of kilometers). A coupled basin architecture and basement structures model is proposed (Fig. 17). This study highlights a tight control of the heterogeneous lithosphere zonation over the structuring of the intracratonic central Saharan Basin. This particular type of basin is characterized by a low rate of subsidence and fault activation controlling the homogeneity of sedimentary facies and the distribution of the main unconformities. The low rate activation of vertical mega-shear zones bounding the intracratonic basin during Paleozoic times contrasts markedly with classic rift kinematics and architecture. Three different periods of tectonic compressional pulses (i.e., Caledonian, Middle to Late Devonian, and pre-Hercynian), extension, and quiescence are identified and controlled the sedimentary distribution (Fig. 17). An understanding of tectono-sedimentary interaction is key to understanding the distribution of the Paleozoic petroleum reservoirs of this first-order oil province.
Data availability. Seismic and well log data analysed in this study are part of the Neptune Energy/SONATRACH internal database. Unfortunatly, they are not publicly available. Nonetheless, satellite images and geophysical data are all available (see data and methods).
Author contributions. The strucutral seismic and photogeology interpretation as well as the basement interpretation and analyses throughout this study were mainly undertaken by PP and MG. Interpretations of the well logs, the sedimentology, and the sequence stratigraphy were primarily carried out by PP and EV. Backstripping was led by PP and controlled by IM and EP. The paper was written by PP, with additional input and scientific editing from MG and EV. All authors contributed to the technical interpretation, extensive discussions, and ideas throughout the study and the writing of the paper.