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Salt tectonics in the Cap Boujdour Area, Aaiun Basin, NW Africa
Abstract
Seismic reflection data indicate the Moroccan salt basin extends to the Cap Boujdour area in the Aaiun Basin. Two salt diapir structures have been identified and several areas of collapsed strata indicate probable salt removal at the shelf edge. The presence of salt in this area correlates to the conjugate southern George's Bank Basin and the Baltimore Canyon area, and it is suggested that the salt extends southward from the known salt diapir province in the George's Bank Basin southward to the Great Stone Dome. The paucity of salt diapirs is attributed to the thick carbonate and anhydrite sequence, which was deposited soon after salt deposition that inhibited halokinesis. The presence of salt along this large segment of the Atlantic margin should increase its hydrocarbon potential with traps created around salt diapirs and provision of migration pathways from deep potential source rocks in the early Cretaceous and Jurassic strata to shallower levels.
... Indian-Madagascar-Antarctic separation domains are from Marks and Tikku (2001) and Indian-Australia-Antarctic separation ages are from Gibbons et al. (2013). The Central Atlantic breakup age comes from Labails et al. (2010) and Davison and Dailly (2010)). In blue, oceanic fracture zones from Matthews et al., 2011. 1 includes a list of related key references. ...
... In blue, oceanic fracture zones from Matthews et al., 2011. 1 includes a list of related key references. Three figures support this description: Fig. 3, which positions each of the identified TMPs on a global breakup age map (ages from Müller et al., 2008, Müller et al., 2016a, 2016b, completed by Marks and Tikku (2001, Gibbons et al. (2013), Labails et al. (2010) and Davison and Dailly (2010)); Fig. 4, which shows detailed bathymetric views centered on each of the TMPs (labelled seafloor ages from Müller et al., 2008, Müller et al., 2016a, 2016b, completed by Marks and Tikku (2001, Gibbons et al. (2013), Labails et al. (2010) and Davison and Dailly (2010)); and Fig. 5, which presents, where available, cross-sections with crustal information (all sections are presented at the same scale and with a common legend). Supplementary file 1 shows bathymetric profiles crossing each TMP. ...
... In blue, oceanic fracture zones from Matthews et al., 2011. 1 includes a list of related key references. Three figures support this description: Fig. 3, which positions each of the identified TMPs on a global breakup age map (ages from Müller et al., 2008, Müller et al., 2016a, 2016b, completed by Marks and Tikku (2001, Gibbons et al. (2013), Labails et al. (2010) and Davison and Dailly (2010)); Fig. 4, which shows detailed bathymetric views centered on each of the TMPs (labelled seafloor ages from Müller et al., 2008, Müller et al., 2016a, 2016b, completed by Marks and Tikku (2001, Gibbons et al. (2013), Labails et al. (2010) and Davison and Dailly (2010)); and Fig. 5, which presents, where available, cross-sections with crustal information (all sections are presented at the same scale and with a common legend). Supplementary file 1 shows bathymetric profiles crossing each TMP. ...
Numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions. Due to their proximity to continents, they have been frequently labelled “marginal plateaus”, although this term has not been clearly defined or associated with a specific geology or geodynamic process. Until now, these elevations have been interpreted as submerged thinned continental fragments detached from continents, basaltic buildups formed by hotspots, volcanic margins or oceanic plateaus. Many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages.
We propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting: “Transform Marginal Plateaus” (TMPs). Based on a compilation of 20 TMPs around the world, we show that most of them have a polyphased history and have undergone at least one major volcanic phase. Our review highlights in particular a hitherto unrecognized close link between hotspots, volcanic activity and transform margins.
We also propose that, due to their polyphased history, TMPs may contain several successive basins and overlooked long-lived sedimentary archives. We finally highlight that, because these TMPs were transform plate boundaries perpendicular or oblique to surrounding rifts, many of them were close to last-contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents. Therefore, we discuss broader scientific issues, such as the interest of TMPs in recording and studying the onset and variations of oceanic currents or past biodiversity growth, bio-connectivity and lineage evolution.
... The Tarfaya-Laâyoun-Ad-Dakhla Basin (also named Boujdour or Aioun Basin) is one of a series of mature passive margin basins that lie along the Central Atlantic margins of Northwest Africa and North America (Davison and Dailly, 2010, and references therein). It extends for almost 1000 km along the African margin from the Cap Blanc Fracture Zone in northern Mauritania, north through southern Morocco to the intersection of the North Canary Island Fracture Zone and the South Atlas Fault (Fig. 1A, insert). ...
... Nevertheless, almost in the middle of Ad-Dakhla Basin along the Atlantic coast, the Paleogene Samlat Formation overlies Cretaceous outcrops (Ratschiller, 1967; Davison et Dailly (2010), modifié. Étoile : emplacement des affleurements étudiés. ...
... SAF : South Atlas Fault (accident sud-atlasique). B. Coupe NW-SE dans le Nord du bassin d'Ad-Dakhla d'après la carte géologique du Maroc au 1:1 000 000 (onshore) et Davison et Dailly (2010), offshore (avec l'aimable autorisation d'André Michard). Échelle verticale approximative. ...
Late Eocene deposits of the Samlat Formation, south of Ad-Dakhla city, southwestern Morocco, have yielded a mixed marine and terrestrial vertebrate fauna. Abundant and diversified chondrichthyans and archaeocete whales have been found, as well as the remains of sirenians and proboscideans. Here we describe the rest of this fossil assemblage which includes actinopterygians, turtles, palaeophiid snakes, crocodiles and pelagornithid seabirds. Actinopterygians are represented by at least two large-sized taxa, a scombroid probably close to the extant Acanthocybium or to the Eocene Aramichthys , and a siluriform related to the Ariidae. Turtles include at least four species represented by shell fragments. This mixed coastal and continental turtle fauna includes one littoral species of Podocnemididae, one or two deep-sea species of Dermochelyidae and one deep-sea species of Cheloniidae. Another turtle species is assigned to the terrestrial Testudinidae. Fragmentary crocodilian remains indicate the presence of undetermined eusuchians tentatively referred to Gavialidae and/or to Crocodylidae. Snake vertebrae are tentatively attributed to the genus Pterosphenus (Palaeophiidae) pending the discovery of new material. Avian remains belong to a large pseudo-toothed bird (Pelagornithidae). Pseudo-tooth morphology resembles that of the late Oligocene – Neogene genus Pelagornis . Additional bird remains are needed for a more precise taxonomic assignment. The fossil assemblage and palaeoenvironment of the upper Eocene deposits of the Samlat Formation appear closely related to those of the upper Eocene – lower Oligocene deposits of the Fayum (Egypt). The initial overview of this fauna provides an important contribution to the study of vertebrate evolution in North Africa near the Eocene–Oligocene transition.
... The Tarfaya-Laâyoun-Ad-Dakhla Basin (also named Boujdour or Aioun Basin) is one of a series of mature passive margin basins that lie along the Central Atlantic margins of Northwest Africa and North America (Davison and Dailly, 2010, and references therein). It extends for almost 1000 km along the African margin from the Cap Blanc Fracture Zone in northern Mauritania, north through southern Morocco to the intersection of the North Canary Island Fracture Zone and the South Atlas Fault (Fig. 1A, insert). ...
... Nevertheless, almost in the middle of Ad-Dakhla Basin along the Atlantic coast, the Paleogene Samlat Formation overlies Cretaceous outcrops (Ratschiller, 1967; Davison et Dailly (2010), modifié. Étoile : emplacement des affleurements étudiés. ...
... SAF : South Atlas Fault (accident sud-atlasique). B. Coupe NW-SE dans le Nord du bassin d'Ad-Dakhla d'après la carte géologique du Maroc au 1:1 000 000 (onshore) et Davison et Dailly (2010), offshore (avec l'aimable autorisation d'André Michard). Échelle verticale approximative. ...
The Samlat Formation is well exposed in coastal sections bordering the Atlantic Ocean south of Ad-Dakhla in southwestern Morocco. Here some 22 m of rhythmically-bedded, chert-rich, marine siltstones and marls are overlain by 1-1.5 m of vertebrate-bearing microconglomeratic sandstone, another 4-8 m of rhythmically-bedded siltstone and marl, and finally a second 3-6 m unit of vertebrate-bearing muddy sandstone. The microconglomeratic and muddy sandstones represent low sea stands in what is otherwise a deeper water sequence. Cetacean skeletons are rare but cetacean vertebrae are common in the lower sandstone (bed B1), where many show the effects of reworking. The cetaceans in bed B1represent a minimum of five species, from smallest to largest: cf. Saghacetus sp., cf. Stromerius sp., Dorudon atrox, cf. Dorudon sp., and Basilosaurus isis. Bed B1 yields rib fragments that may represent sirenians, but sirenians, if present, are rare. The only identifiable cetacean found in the upper sandstone (bed B2) is Basilosaurus sp. Dugongid sirenians identified as cf. Eosiren sp. are the most common mammal in bed B2. We interpret co-occurrence of the typically Early Priabonian species Dorudon atrox and Basilosaurus isis with smaller species more like Middle Priabonian genera Saghacetus osiris and Stromerius nidensis to indicate that bed B1 was deposited during low sea stand Pr-2 between the Early and Middle Priabonian (between the early and middle Late Eocene). Bed B2 is separated from B1 by an interval of deeper water sediment accumulation. Bed B2 could represent a later phase of Pr-2 or a subsequent Priabonian low sea stand (possibly Pr-3).
... On line BGR11-208 (Fig. 2), a series of anticlines are observed in deep water, which are oriented perpendicular to the coast line and have been previously interpreted to result from the inversion of pre-existing rift fabrics during the Atlas orogeny . Closer to the coast, the Jurassic to recent sedimentary record is strongly influenced by salt tectonics (Figs 1a, 3 and 4; also see Hinz et al., 1982Hinz et al., , 1984Heyman, 1989;Hafid, 2000;Hafid et al., 2000Hafid et al., , 2006Hafid et al., , 2008Tari et al., 2000Tari et al., , 2012Davison, 2005;Jabour & Tari, 2007;Tari & Jabour, 2008Davison & Dailly, 2010). Even though a variation down dip in salt tectonic style has been reported (Tari et al., 2000) and a rough regional segmentation of salt provinces has been attempted (Tari et al., 2012), the general tectonic-stratigraphic framework of the salt basin and its possible genetic relation to tectonics both onshore and farther offshore is not yet well-understood. ...
... Salt bodies of different geometries and associated deformation of surrounding sediments have been identified in the study area previously (e.g. Hinz et al., 1982Hinz et al., , 1984Heyman, 1989;Jabour & Tari, 2007;Hafid, 2000;Hafid et al., 2000Hafid et al., , 2006Hafid et al., , 2008Tari et al., 2000Tari et al., , 2012Davison, 2005;Tari & Jabour, 2008Davison & Dailly, 2010). The uppermost salt has been drilled by DSDP 546 and has been identified to consist dominantly of halite of Rhaetian to Hettangian age (Hinz et al., 1984). ...
Recently, considerable attempts have been made to compare the
sedimentary basin evolution and the associated tectonic framework on
both sides of the South-Atlantic. However, yet there are still
unresolved questions concerning the tectono-sedimentary styles of margin
basin evolution that markedly differ from north to south. Amongst the
most striking observations is that multiple phases of uplift and
subsidence are recorded after the break-up of the southern South
Atlantic margin segment on both sides of the Florianopolis-Walvis Ridge
volcanic complex, features that are regarded as atypical when compared
to published examples of other post-breakup margin successions. Adding
to the heterogeneity of the system, the northernmost segment of the
South Atlantic rift and salt basins is also characterized by a
pronounced asymmetry, with the Brazilian margin now comprising narrower
and deeper rift basins with less salt than the Congo-Gabon conjugate
margin. This project deals with a large-scale comparison of this very
different post-breakup tectono-stratigraphic development of the southern
and northern South American and African continental margins that both
record thick post-rift sedimentary successions. To gain detail of the
basin margin evolution, we focus on a regional comparison between the
post-breakup records archived in the large offshore southern Brazil
basins (Pelotas, Santos, Campos) and the post-breakup continental margin
successions of offshore Namibia (e.g. Orange Basin) and southern Angola
(e.g. Kwanza Basin). A tectonic-stratigraphic comparison of
representative geological transects provides a comprehensive
basin-to-basin documentation of key factors influencing margin
development which include the subsidence development through time, the
sediment (in-)flux and storage patterns and the respective type of basin
fill (e.g. salt vs. non-salt systems; carbonate-rich vs.
clastics-dominated systems). Data from the salt-prone areas offshore
South America and southern Africa indicate that salt-related tectonics
is amongst the key parameters controlling differential post-rift margin
development.
... Limited seismic coverage exists, but only a few wells have been drilled. Salt tectonics further complicate the understanding of the geology (Tari et al. 2000;Tari & Jabour 2008;Davison & Dailly 2010;Tari & Jabour 2013;Neumaier et al. 2016). Drilling in shallow-water and onshore domains has resulted in the discovery of several small oilfields producing from Triassic and Jurassic formations in the onshore Essaouira Basin (Clifford 1986;Broughton & Trepanier 1993;Hafid 2000). ...
... The continental part of the onshore and offshore margin carries a strong imprint from salt tectonics (e.g. Hinz et al. 1982Hinz et al. , 1984Heyman 1989;Hafid 2000;Hafid et al. 2000Hafid et al. , 2006Hafid et al. , 2008Tari et al. 2000, Tari et al. 2012aJabour & Tari 2007;Tari & Jabour 2008Davison & Dailly 2010;Neumaier et al. 2016). The nature of the crust in the outer Moroccan Atlantic margin and the location of the continent-ocean boundary transition remain under discussion (Roeser et al. 2002;Maillard et al. 2006;Jaffal et al. 2009;Klingelhoefer et al. 2009Klingelhoefer et al. , 2016Day & Hilton 2011). ...
A string of prominent structural anticlines is located in the deep offshore Atlantic Ocean c. 150 km west of Essaouira
(Morocco), possibly forming large traps. However, the basement is inferred to comprise oceanic crust, which raises concerns
for source-rock presence and sufficient subsurface temperatures for oil generation. The presented work showcases a
hydrocarbon charge assessment approach adapted to the very sparse data context and the specific geodynamic settings of the
Moroccan Atlantic margin. Regional 2D basin and petroleum systems modelling was performed to assess possible scenarios of
hydrocarbon charge of the deep-water folds, its migration style and timing. Several possible oil and gas generation drivers have
been identified for postulated Toarcian marine shale source rocks. These range from simple burial-driven heating to more
unique scenarios involving early stage oceanic ridge heating and the effect of the Canary Island hotspot. In particular, the latter
might have had a major impact on the oil and gas generation, the migration style and overall accumulated amounts.
... On line BGR11-208 (Fig. 2), a series of anticlines are observed in deep water, which are oriented perpendicular to the coast line and have been previously interpreted to result from the inversion of pre-existing rift fabrics during the Atlas orogeny . Closer to the coast, the Jurassic to recent sedimentary record is strongly influenced by salt tectonics (Figs 1a, 3 and 4; also see Hinz et al., 1982Hinz et al., , 1984Heyman, 1989;Hafid, 2000;Hafid et al., 2000Hafid et al., , 2006Hafid et al., , 2008Tari et al., 2000Tari et al., , 2012Davison, 2005;Jabour & Tari, 2007;Tari & Jabour, 2008Davison & Dailly, 2010). Even though a variation down dip in salt tectonic style has been reported (Tari et al., 2000) and a rough regional segmentation of salt provinces has been attempted (Tari et al., 2012), the general tectonic-stratigraphic framework of the salt basin and its possible genetic relation to tectonics both onshore and farther offshore is not yet well-understood. ...
... Salt bodies of different geometries and associated deformation of surrounding sediments have been identified in the study area previously (e.g. Hinz et al., 1982Hinz et al., , 1984Heyman, 1989;Jabour & Tari, 2007;Hafid, 2000;Hafid et al., 2000Hafid et al., , 2006Hafid et al., , 2008Tari et al., 2000Tari et al., , 2012Davison, 2005;Tari & Jabour, 2008Davison & Dailly, 2010). The uppermost salt has been drilled by DSDP 546 and has been identified to consist dominantly of halite of Rhaetian to Hettangian age (Hinz et al., 1984). ...
After Mesozoic rifting, the Atlantic margin of Morocco has recorded the consequences of the continental collision between Africa and Europe and the relative northward motion of the African plate over the Canary Island hotspot during Cenozoic times. Interpretation of recently acquired 2D seismic reflection data (MIRROR 2011 experiment) presents new insights into the Late Cretaceous to recent geodynamic evolution of this margin. Crustal uplift presumably started during the Late Cretaceous and triggered regional tilting in the deep-water margin west of Essaouira and the formation of the Base Tertiary Unconformity (BTU). An associated hiatus in sedimentation is interpreted to have started earlier in the north (presumably in the Cenomanian at well location DSDP 416) and propagated to the south (presumably in the Coniacian at well location DSDP 415). The difference in the total duration of this hiatus is postulated to have controlled the extrusion of Late Triassic to Early Jurassic salt during the Late Cretaceous to Early Palaeocene non-depositional period, resulting in regional differences in the preservation of salt structures: the Agadir Basin in the south of the study area is dominated by salt diapirs, whereas massive canopies characterize the Ras Tafelnay Plateau farther north and salt-poor canopies and weld structures the northernmost offshore Essaouira and Safi Basins. Accompanied by volcanic intrusions, a presumably Early Palaeogene reactivation of previously existing basement faults is interpreted to have formed a series of deep-water anticlines with associated gravity deformation of shallow-seated sediments. The orientation of the fold axes is roughly perpendicular to the present day coast and the extensional fault direction; therefore, not a coast-line parallel pattern of extensional faults, related to the rifting and break-up of the margin, but rather a coast-line perpendicular oceanic fracture zone might have caused the basement faults associated with the deep-water folds. Both the volcanic intrusions and the formation of the deep-water anticlines show a comparable age trend which gets progressively younger towards the south. A potential tempo-spatial relationship of the BTU and the reactivation of basement faults can be explained by the relative northward motion of the African plate over the Canary Island hotspot. Regional uplift producing the BTU could have been the precursor of the approaching hotspot during the Late Cretaceous, followed during the Early Palaeogene by a locally more pronounced uplift above the hotspot centre.This article is protected by copyright. All rights reserved.
... 31.5°N and 35°N, and between 16°N and 19°N off Senegal on the NWAM. New MCS data indicate local presence of salt in the Laâyoune basin (south of Canary Islands) that would extend the Moroccan salt basin as far south as 26°N (Davison and Dailly, 2010). In central parts of the CAO, there is no evidence of salt on the African margin Labails et al., 2009). ...
... Later on, numerous local biostratigraphic and sedimentologic works led to the publication of refined stratigraphic data (Wiedmann et al., 1978; Canérot et al., 1986; Rey et al., 1988; Andreu, 1989 Andreu, , 1992 Bourgeoini, 1994; Witam, 1998; Bourgeoini et al., 2002 ), sedimentary sequence successions (Canérot et al., 1986; Rey et al., 1988; Andreu, 1989; Algouti et al., 1999), detailed sedimentologic studies on the Barremian ( Chellaï, 2001, 2002) or the CenomanianeTuronian interval (Ettachfini and Andreu, 2004; Ettachfini et al., 2005; Jati et al., 2010), and paleontological or paleobiogeographic synthesis (Middlemiss, 1980; Andreu, 1992; Wippich, 2003; Masrour et al., 2004; Company et al., 2008). Meanwhile, thanks to petroleum and oceanographic explorations, the offshore part of the EAB has been explored, leading to a comprehensive understanding of this basin (Leckie, 1984; Broughton and Trepanier, 1993; Hafid et al., 2000; Herrle, 2002; Mehdi et al., 2004; Zühlke et al., 2004; Davison, 2005; Hofmann et al., 2008; Davison and Davy, 2010). The rifting phase gave way to the deposition of thick red bed deposits of Late PermianeTriassic age, overlain by a thick series of shales and evaporites intercalated with basaltic flows dated as early Liassic (Hafid et al., 2000). ...
... Figure 4 shows the distribution of salt deposits as derived from the published literature between MES-AF and Nova Scotia margins and between IB and NA on kinematic reconstructions at chrons ECMA and BSMA, respectively. The Late Triassic -Early Jurassic salt was deposited during the rifting episode on the surrounding margins of Nova Scotia, Morocco, and Iberia, and in the intracontinental basins of the Grand Banks, Morocco, Algarve, Lusitania, and Porto (Wade and MacLean 1990;Edwards et al. 2000;Sahabi et al. 2004;Matias et al. 2005;Nemcok et al. 2005;Tari and Molnar 2005;Maillard et al. 2006;Hafid et al. 2008;Albertz et al. 2010;Davison and Dailly 2010;Labails et al. 2010). ...
The kinematics of the Central and North Atlantic between North America
(NA), Africa (AF), Meseta (MES), Iberia (IB), Flemish Cap (FC) and the
Galicia Bank (GB) has been established from Late Triassic to Late
Cretaceous: AF/NA and MES/NA parameters of rotations are from Labails et
al. (2010); we have established new IB/NA, FC/NA and GB/NA parameters of
rotations for the same period of time (Late Triassic to Late
Cretaceous). Seven palaeogeographic maps, with structural elements and
magnetic lineations are presented: 1) Late Triassic - Pre-rift
configuration (Norian/Rhaetian limit, about 203 Ma), 2) Early Jurassic -
end of rifting (after CAMP and salt deposition) (ECMA,
Sinemurian/Pliensbachian limit, 190 Ma); Paleogeography of Early
Jurassic (Sinemurian-Toarcian), 3) Middle Jurassic (BSMA, Middle
Bajocian, 170 Ma); Paleogeography of Middle Jurassic
(Bajocian-Bathonian), 4) Late Jurassic (M22, Tithonian, 150 Ma);
Paleogeography of Late Jurassic (Oxfordian-Portlandian), 5) Early
Cretaceous (M11, Valanginian, 136 Ma); Paleogeography of Early
Cretaceous (Berriasian-Barremian), 6) Middle Cretaceous (M0, Late
Barremian/Early Aptian, 125 Ma); Paleogeography of Middle Cretaceous
(Aptian-Albian), 7) Late Cretaceous (C34, Santonian, 83.5 Ma);
Paleogeography of Late Cretaceous (Cenomanian-Danian). In addition, we
will present the maps of salt distributions at the
Sinemurian/Pliensbachian limit (190 Ma) (after salt deposition) and in
middle Bajocian (170 Ma). Paleo-oceanographic informations are mainly
from Gradstein et al. (1990), while the salt structure and distribution
is a compilation of numerous studies.
... Figure 4 shows the distribution of salt deposits as derived from the published literature between MES-AF and Nova Scotia margins and between IB and NA on kinematic reconstructions at chrons ECMA and BSMA, respectively. The Late Triassic -Early Jurassic salt was deposited during the rifting episode on the surrounding margins of Nova Scotia, Morocco, and Iberia, and in the intracontinental basins of the Grand Banks, Morocco, Algarve, Lusitania, and Porto ( Wade and MacLean 1990;Edwards et al. 2000;Sahabi et al. 2004;Matias et al. 2005;Nemcok et al. 2005;Tari and Molnar 2005;Maillard et al. 2006;Hafid et al. 2008;Albertz et al. 2010;Davison and Dailly 2010;Labails et al. 2010). ...
We have established a new plate kinematic model of the central and North Atlantic oceans between North America, Africa, Meseta, Iberia, Flemish Cap, and Galicia Bank from Late Triassic to Late Cretaceous to better understand the nature and timing of rifting of Nova Scotia and Morocco conjugate continental margins since Late Triassic. The maps of salt distributions at the Sinemurian–Pliensbachian limit (190 Ma; after salt deposition) and in middle Bajocian (170 Ma) show that an area of the Nova Scotia margin is devoid of allochthonous salt and that an area of similar size located oceanward of the West African Coast Magnetic Anomaly shows salt deposits, suggesting that a portion of the Nova Scotia margin with its overlying salt deposits could have been transferred onto the Moroccan side right after the formation of the conjugate East Coast Magnetic Anomaly and West African Coast Magnetic Anomaly. Seven paleogeographic maps, from Late Triassic to Late Cretaceous, are presented with structural elements and magnetic lineations. They show that the connection between the Central Atlantic and the Tethys, with an aborted rift between Iberia and North America ending in the north against the Flemish Cap – Galicia Bank dam, started to deepen at the end of the first rifting phase (190 Ma ago) after the rupture of the thinned continental crust. It is only during the Early Cretaceous, after the rupture of the Flemish Cap – Galicia Bank dam, that the deep connection around Iberia was finally established between the Central and North Atlantic, the Tethys, and the Bay of Biscay.
... At passive margins, where most of the world's salt structures are located, salt tectonics is currently interpreted by various models using geologic, geophysical, and/or modeling data (e.g. Jackson and Talbot, 1986;Koyi, 1988;Jackson et al., 1994;Jackson, 1995;Cobbold et al., 1995;Davison and Dailly, 2008). In such tectonic settings, several remarkable studies during the 1990s and 2000s (e.g. ...
We used structural, stratigraphic and sedimentologic data, together with a comparison of nearby
structures and a Bouguer gravity map, to evaluate the evolution of the Bled Dogra salt structure
(northern Tunisia) during the Cretaceous. Triassic salt sheets are recognized in the northwestern
region of the Tunisian Atlas. These salt sheets are the result of Cretaceous thick and/or thin-skinned
extension along the south Tethyan margin. The Bled Dogra salt structure is one of these submarine
allochthonous salt sheets, which was emplaced during the Early Cretaceous. The geologic framework,
during this period, produces conditions for a predominantly gravity-driven deformation: extension
has produced space for the salt to rise; vigorous differential sedimentation created differential
loading that resulted in the emplacement and extrusion of a large volume of Triassic salt and
formation of large submarine salt sheets. Geologic field data suggest an interlayered Triassic salt
sheet within Albian sequences. Salt was extruded at the sea floor during the Early-Middle Albian and
was initially buried by Middle-Late Albian strata. The Coniacian corresponds to a second
transgressive cover onto the salt sheet after the gliding of the first salt cover (Late Albian-Turonian).
In addition, this northwest Tunisian area exposes evidences for salt flow and abundant slump
features at the base of a northward facing submarine slope, which was probably dominant from the
Early Cretaceous to Santonian. Two gravity deformation processes are recognized: gravity gliding and
gravity spreading. Acting concurrently, these two processes appear indistinguishable in this geologic
context. Like the present-day salt-involved passive margins - such as the northern Gulf of Mexico, the
Atlantic margin of Morocco, the Brazilian Santos basin, the Angola margin, Cadiz in western Iberia,
and the Red Sea - the North African Cretaceous passive margin in Tunisia provides evidences that
deformation in a passive-margin salt basin is predominantly gravity-driven deformation.
... Along the passive west coast of Africa, salt tectonics has played a role in the development of the contemporary bathymetry (Davison, 2005;Davison and Dailly, 2010;Gee and Gawthorpe, 2006;Hudec and Jackson, 2007;Liu and Li, 2011). Diapiric features ranging from round to elongate in plan are well documented (cf. ...
... Dans le bassin de Tarfaya, on a identifié une roche mère effective avec des valeurs de COT qui peuvent dépasser 14 % [15,[18][19][20][21][22][23]. ...
Designed to meet the needs of oil exploration, the Rock-Eval pyrolysis is now widely used. It provides, indeed, various data on the geochemical characteristics of the rock; such as the petroleum potential, maturity and type of the source rocks in different sedimentary basins. The determination of organic carbon (TOC) by the Walkley-Black (1934) technique can be considered as an inexpensive and easy to implement alternative, compared with the Rock-Eval technique.
In the Walkley-Black (1934) technique, the determination of the Total Organic Carbon (TOC) content of the rock is made by wet oxidation (Walkley-Black). It consists of the oxidation of the organic material by an excess amount of potassium dichromate in sulfuric medium to boil. It is considered that the consumed oxygen is proportional to the carbon of the sample. Then we proceed to the titration of the excess dichromate by Mohr's salt.
This study demonstrated these two methods extracted similar organic matter levels. It suggests Walkely-black procedure could be used on most of the studied samples, especially those containing mostly between 1 and 15% organic matter.
... Geologically this is in the middle of a much larger southwest-to-northeast trending structural basin paralleling the Atlantic coast. The basin is variously called the Aaiun-Tarfaya Basin (Ranke et al., 1982), the Tarfaya-Laayoune-Dakhla Basin (Davison and Dailly, 2010), or sometimes simply the Boujdour Basin. Gueran is approximately 125 km inland from Boujdour, which is the nearest town on the coast (Fig. 2). ...
Six genera and species of archaic whales are present in a new fauna from the Aridal Formation at Gueran in the Sahara Desert of southwestern Morocco. Three of the archaeocete species represent semiaquatic Protocetidae and three species are fully aquatic Basilosauridae. Protocetids are characteristic of Lutetian lower middle Eocene strata, and basilosaurids are characteristic of Priabonian late Eocene beds. Similar representation of both families is restricted to intervening Bartonian strata and indicative of a late middle Eocene age. Archaeocetes from Gueran include (1) a small protocetid represented by a partial humerus, teeth, and vertebrae; (2) a middle-sized protocetid represented by a partial innominate and proximal femur; (3) the very large protocetid Pappocetus lugardi represented by teeth, a partial innominate, and two partial femora; (4) a new species of the small basilosaurid Chrysocetus represented by a dentary, teeth, humeri, and many vertebrae; (5) a new species of the larger basilosaurid Platyosphys (resurrected as a distinct genus) represented by a partial braincase, tympanic bulla, and many vertebrae; and (6) the large basilosaurid Eocetus schweinfurthi represented by teeth, a tympanic bulla, and lumbar vertebrae. The Gueran locality is important geologically because it constrains the age of a part of the Aridal Formation, and biologically because it includes a diversity of archaic whales represented by partial skeletons with vertebrae in sequence and by forelimb and hind limb remains. With further collecting, Gueran archaeocete skeletons promise to clarify the important evolutionary transition from foot-powered swimming in Protocetidae to the tail-powered swimming of Basilosauridae and all later Cetacea.
... Other Upper Triassic to Lower Jurassic salt basins do exist further to the south along the African margin in Senegal, the Gambia and Guinea Bissau (e.g., Tari, Molnar, & Ashton, 2003;Davison, 2005), but these basin segments will not be addressed in this chapter. Between the Moroccan and the Mauritanian salt basins there might be some isolated salt diapirs present, as reported by Davison and Dailly (2010) in the Cap Boujdour area in the Aaiun Basin. The conjugate salt basin of the Moroccan salt basin is located on the Nova Scotia margin (Chapter 13), whereas the Mauritanian salt basin finds its counterpart in the Carolina Trough, offshore United States (e.g., Post et al., 2013). ...
The salt basins of Morocco and Mauritania were developed on the NW African margin of the Central Atlantic. The age of the salt in Morocco is Upper Triassic to Liassic, as Central Atlantic Magmatic Province basalts can be found within it. The age of the Mauritanian salt is poorly constrained but it is considered analogous to that of the salt found in Morocco. The salt in both basins deposited during the synrift, or more specifically, the syn-stretching stage of continental rifting between the African and North American plates. It therefore has a patchy, discontinuous original distribution in fault-controlled extensional troughs.
... It stretches over more than 1000 km along the western margin of the Sahara and covers an area of 170,000 km 2 , both on-and offshore (Davison, 2005;Sachse et al. 2011Sachse et al. , 2014. The geological and stratigraphic structures of the basin have been investigated in detail using well and seismic data (Kolonic et al. 2002; Klingelhoefer †Author for correspondence: mbenammi@univ-poitiers.fr Davison & Dailly, 2010). The Tarfaya-Dakhla Basin is filled with Mesozoic and Cenozoic continental to shallow-marine sediments, which overlie the basement Precambrian and/or Palaeozoic rocks. ...
New Palaeogene vertebrate localities were recently reported in the southern Dakhla area (southwestern Morocco). The Eocene sediment strata crops out on cliffs along the Atlantic Ocean coast. Vertebrate remains come from five conglomeratic sandstone beds and are principally represented by isolated teeth belonging to micromammals, selachians and bony fishes, a proboscidean assigned to ?Numidotherium sp. and many remains of archaeocete whales (Basilosauridae). From fieldwork five lithostratigraphic sections were described, essentially based on the lithological characteristic of sediments. Despite the lateral variations of facies, correlations between these five sections were possible on the basis of fossil-bearing beds (A1, B1, B2, C1 and C2) and five lithological units were identified. The lower part of the section consists of rhythmically bedded, chert-rich marine siltstones and marls with thin black phosphorite with organic matter at the base. The overlying units include coarse-grained to microconglomeratic sandstones interbedded with silts, indicating deposition in a shallow-marine environment with fluvial influence. The natural remanence magnetization of a total of 50 samples was measured; the intensity of most of the samples is too weak however, before or after the first step of demagnetization. The palaeomagnetic data from the samples are very unstable, except for eight from three similar sandstone levels which show a normal polarity. Matched with biostratigraphic data on rodents, primates, the selachian, sirenian and cetacean faunas, the new carbon isotope chemostratigraphy on organics (1) refines the age of the uppermost C2 fossil-bearing bed to earliest Oligocene time and (2) confirms the Priabonian age of the B1 to C1 levels
... The marine fauna described herein comes from the Aridal Formation in the Gueran Depression (Fig. 1). Geologically, this formation belongs to the sub-basin of Boujdour, which constitutes, along with the sub-basin of Dakhla, the Atlantic basin of Tarfaya-La'Youn-Ad-Dakhla (Davison and Dailly, 2010;Ranke et al., 1982). This basin is S. Zouhri et al. / C. R. Geoscience xxx (2018) xxx-xxx 2 the onshore, proximal part of the Atlantic passive margin; the oldest, Triassic-Liassic deposits of the margin are lacking here beneath the continental Lower Cretaceous sandstones and overlying Upper Cretaceous-Cenozoic marine beds (Hafid et al., 2008). ...
The sabkha of Gueran in the Southwest Moroccan Sahara has yielded a rich and diverse fauna of late middle Eocene vertebrates that include the world's richest Bartonian age archaeocete assemblage. Archeocete remains were described previously and here we report on the rest of the vertebrate fauna. The Gueran fauna includes abundant chondrichthyan species belonging to Lamniformes, Carcharhiniformes and Rhinopristiformes, and actinopterygian assemblage consisting of Cylindracanthus, of a siluriform, and of Perciformes. Turtles are represented by at least two marine taxa referred to as Cheloniidae and Dermochelyidae. Crocodylian remains belong to at least two longirostrine species, including gavialoid remains. Snakes are represented by Pterosphenus cf. schweinfurthi (Palaeophiidae). Seabirds are represented by a pseudo-toothed bird (Pelagornithidae). The avian fossil belonged to a gigantic soaring bird and constitutes the earliest occurrence of the genus Pelagornis. The presence of proboscideans is attested by dental fragments. This fossil assemblage from Gueran shows affinities with those of the Eocene beds of Egypt and Libya. The numerous shared taxa support a close biogeographical connection between faunas from southeastern and southwestern coasts of the Mediterranean Sea.
Keywords:
Atlantic basinMorocco, Vertebrates, Middle Eocene, Palaeobiogeography
... A. Atlantic margin geomorphology and salt basins, afterBiari et al. (2017), modified. Salt basin from Tarfaya to Dakhla, afterDavison and Dailly (2010). Main geological boundaries around the WAC afterMichard et al. (2010). ...
This work concerns the northernmost limit of the West African Craton (WAC) and Variscan WAC-related terranes of NW Africa. Based on newly obtained radiometric age of an oceanic gabbro from the ‘‘Mesorif Suture Zone’’ of the External Rif Belt, we propose a revised interpretation of this puzzling lineament. We report on a 190 � 2 Ma LA–ICP–MS U–Pb zircon age of a trondhjemite vein cross-cutting the Bou Adel gabbro, which is one of the largest oceanic units of the quoted suture zone. We hypothesize that the
Mesorif suture zone corresponds to the transported trace of the West African Atlantic margin surrounding the northwestern Moroccan Meseta promontory and connecting with the ENE-trending North African Transform. The latter zone sharply bounded the
North Africa margin and connected the Central Atlantic with the Alpine Tethys. We propose that transported elements from the North African transform constitute the ‘‘Mesorif Basalt–Breccias’’ lineament parallel to and more external than the Mesorif suture zone. If correct, this new interpretation provides an opportunity to develop detailed field and laboratory studies of an exhumed segment of the up-to-now conceptual Jurassic North African transform.
... One of these structural features is the development of salt rocks and salt tectonics in the above mentioned domains. Salt tectonics is controlled by regional deformations and plays a significant role in the evolution of several sedimentary basins around the world (e.g., Koyi, 1988;Jackson et al., 1994;Davison and Dailly, 2008;Hudec and Jackson, 2002, 2004Masrouhi et al., 2013Masrouhi et al., , 2014Moragas et al., 2017, Duffy et al., 2018. Moreover, salt tectonics affected diverse evaporitic basins where these evaporites have been deposited in various settings such as cratonic basins, synrift basins, postrift passive margins and continental collusion zones and foreland basins ( Fig. 1) (Hudec and Jackson, 2007). ...
In the North African Atlas, Triassic sedimentary rocks exhibit a variety of deformation styles that are caused by the interaction between halokinesis, tectonics and sedimentation. This paper aims to present an integrated study documenting the occurrence of salt-tectonic processes in the Maknassy-Mezzouna orogenic system. The interpretation of both, field mapping and seismic data suggests the existence of a complex tectonic evolution of these
Triassic evaporites, with the occurrence of Mesozoic extensional/transtensional and Tertiary compressional/
transpressional tectonic regime accompanied by sedimentary loading. This evolution took place along three major events of either lateral or vertical migration of Triassic evaporites. The first one is tectonic-driven and is related to the extensional/transtensional tectonic regime, which occurred during the break-up of Pangea and
rifting of Neotethyan Ocean in the Early Jurassic. The second remobilization of salt Triassic rock developed during the Cretaceous. The initial mobilization of the Triassic salt was probably induced by sedimentary loading with a limited contribution of tectonic forces. During its third stage of evolution, salt Triassic rocks evolve into
salt sheets due to the shortening deformation occurred during Tertiary and Quaternary in relationship with the closure of the Neotethyan realm. Salt migration controls subsidence, generates depocenter shifts and causes thickness variation of the entire post-Triassic sedimentary sequence. The signature of salt Triassic syn-sedimentary
control is confirmed by thickness reduction and abrupt variation of structural dip that affects all the sedimentary pile in the flanks of salt sheets. In seismic sections the syn-sedimentary salt tectonic control is observed by geometries like pinching out, thickness reduction, onlap termination geometry as well as unconformities identified along the flanks of the salt sheets.
... These are associated with salt basins, which in some studies have been considered diagnostic of this type of margin Moulin et al., 2010). However, it should be noted that thick salt also covers SDRs to the south of the Red Sea (Davison and Dailly, 2010;Mohriak and Leroy, 2012). On the NW-African margin, the prominent magnetic anomaly called the West African Coast Magnetic Anomaly (WACMA) is thought to be coeval with the northern VPM-related ECMA (Fig. 3), and the ocean-continent boundary is located seaward. ...
Pre-magmatic continental extension often precedes the major magmatic expulsion of large igneous provinces (LIPs). However, the cause-and-effect relationship between pre-magmatic rifting and the extrusion of large amount of magma is controversial. It remains unclear whether magmatism arises as a consequence of passive rifting or whether it is related to active upwelling of the mantle. In addition, the relationship between the pre-magmatic stages and the final breakup, with the onset of conjugate passive margins, is ambiguous. In this study, we compiled available data from six LIPs (Central Atlantic, Karoo, Parana-Etendeka, Deccan, North Atlantic, and Afar igneous provinces) that successively occurred during the fragmentation of Pangea and found that pre-magmatic rift trends may show a high obliquity or even be orthogonal with respect to the future passive margins. We conclude that syn-magmatic rifts should not be directly correlated, both structurally and dynamically, to the ancient pre-magmatic rift phase. Furthermore, following the breakup of a supercontinent, seafloor spreading usually initiates within volcanic passive margins (VPMs) and then propagates away to create non-volcanic passive margins (NVPMs) as a consequence of the consumption and cooling of a sub-lithospheric positive thermal anomaly. Major transform faults often exist between VPMs and NVPMs, acting as a mechanical barrier to mantle melting and magmatism transportation.
We describe the structure, stratigraphy, and hydrocarbon potential of the 1000-km-long Tarfaya-Dakhla Basin (TDB) along the Atlantic rifted-passive margin Morocco. Our dataset consists of a 4885-line km grid of depth-converted industry seismic data that are tied to three DSDP wells in the deepwater area and exploratory wells on the slope and shelf. Based on mapping of this seismic grid, the tectonostratigraphic events that have affected this margin include: 1) a Late Triassic-Early Jurassic rift phase that separated the Moroccan margin from its conjugate margin in eastern Canada began during the Late Triassic-Early Jurassic; 2) early passive margin sedimentation consists of Middle Jurassic-Early Cretaceous passive margin phase consisting of a massive, 14-km-thick, reefal-carbonate platform formed above the rifted margin during the Early Jurassic and was subsequently buried by the 6-km-thick, Early Cretaceous (Berriasian) Boujdour deltaic complex. During this period continued high rates of clastic sedimentation resulted in margin steepening and gravitational collapse during the Valanginian and formed a 480-km-long and 68-km-wide passive margin fold belt characterized by a zone of updip normal faults of 480 km in length and 30 km in width and a zone of downdip folds and thrusts of 117 km in length and 15 km in width. Geochemical data from DSDP 397 and 369 wells and two pseudo-wells were used to evaluate source rock potential and hydrocarbon prospectivity of the Jurassic to Recent section. Basin modeling reveals that the Jurassic source rocks known from DSDP drilling are overmature in the study area with hydrocarbon generation beginning in the Upper Jurassic-Lower Cretaceous. The Lower Cretaceous source rocks are immature except for localized areas, and the Upper Cretaceous is immature across the study area.
Rifted margins are commonly classified as either magma-rich or magma-poor. Magma-poor margins are often implicitly related to ultraslow–slow extension. Conversely, therefore, magma-rich margins should represent more rapid extension. Although supported by numerical modelling, these relationships are based on limited data and depend on a perhaps spurious comparison between continental margins and spreading ridges. Three case studies from the Atlantic margins are therefore presented here as a local, by no means complete, examination of this concept. Extension rates for magma-poor margins are mainly derived from offshore Iberia, while the best documented rates on magma-rich margins are probably those in the NE Atlantic. Particularly for the NE Atlantic, there is a dependence on the initial oceanic spreading rate as pre-break-up rates are very difficult to quantify. Our two southerly examples, the Central Atlantic and southern South Atlantic, are both magma-rich in parts and have been described as opening during ultraslow–slow plate separation. Both would therefore seem to contradict the positive ‘rate-magmatism’ correlation. However, on closer examination, a wide range of initial extension rates are actually possible. This is largely due to poor constraints on break-up ages. The assumption that break-up is synchronous with flood basalt extrusion is flawed, and may have caused initial extension rates to have been significantly underestimated. Additionally, averaging between widely spaced oceanic magnetic anomalies allows for a wide range of extension rates. New, well-constrained ages and event chronologies from critical areas of conjugate margins are needed to determine whether this relationship has global validity. © 2018 The Author(s). Published by The Geological Society of London for GSL and EAGE. All rights reserved.
Le membre "Guerran" de la formation Samlat d'Ad-Dakhla (Périphérie sud du Bassin Tarfaya, Lâayoune et Ad-Dakhla, TLDB) est composé essentiellement d'un complexe d'alternance rythmique de chert gris et de silt marneux où s'intercalent d'importants niveaux fossilifères. Ce membre a fait objet de considérables découvertes paléontologiques et par conséquent de diverses propositions de datations: (1) Eocène-Oligocène, (2) Priabonien moyen et Priabonien supérieur; (3) base et milieu du Priabonien supérieur et (4) début Oligocène pour sa partie sommitale. Les niveaux à tendance marneuse et marno-sableuse de ce membre ont été la cible de la quête des microfossiles Datum qui peuvent enrichir et clarifier les datations préalablement proposées pour ce membre. Deux sites sur le littoral au sud d'Elargoub (Sud-Est Ad-Dakhla), ont été sélectionnés pour un échantillonnage serré: la Falaise Alaouate et le site Dafia. En dépit de l'état critique de conservation des microfossiles, une vingtaine d'espèces de Foraminifères Planctoniques ont été identifiées. Leurs répartitions s'organisent verticalement en trois assemblages. Les Datum parmi ces derniers : Acarinina topilensis s'étend de E10 à mi-E12 (Zone à Foraminifères planctoniques), entre le Lutetien supérieur et le Bartonien inferieur; Globigerinatheka semiinvoluta et Turborotalia cocoaensis dans la zone de chevauchement de E13-E14 d'âge Bartonien supérieur-Priabonien inférieur. Turborotalia cambayensi E16 (P17) et Praetenuitella insolita révèlent un âge Priabonien supérieur. Finalement, Pseudohastigerina naguewichiensis, Cassigerinella chipolensis et Tenuitella gemma s'inscrivent dans la zone O1 qui correspond au Rupélien inférieur. Deux zones équivalentes à des zones de transition sont proposées: la zone Eocène moyen-Eocène supérieur & la zone Eocène supérieur-Oligocène inférieur. Mots-clés: Foraminifère planctonique, Lutétien, Bartonien, Priabonien, Rupélien, Ad-Dakhla, Maroc. Abstract. The "Guerran" Member of the Samlat Formation near Ad-Dakhla, on the southern periphery of the Tarfaya, Laâyoune and Ad-Dakhla Basin (TLDB), is essentially a rhythmic complex of alternating gray cherts and marly silts. Important fossiliferous intervals intercalated within this have given rise to important paleontological discoveries, and consequently to various dating proposals: (1) Eocene-Oligocene; (2) middle and upper Priabonian, upper Eocene; (3) base and middle of the upper Priabonian, late Eocene and (4) lowermost Oligocene. The more marly intervals of the Guerran member were chosen for investigation of microfossils to clarify the suggested dating. Two sites on the coast south of Elargoub (Southeast of Ad-Dakhla) were selected for detailed sampling: Alaouate cliff and Dafia area. Some twenty species of planktonic Foraminifera were identified, in spite poor preservation of microfossils. Their distributions are organized into three time-successive assembages. Acarinina topilensis is distributed from E10 to mid-E12 (Planktonic Foraminiferal Zone), upper Lutetian to early Bartonian in age. Globigerinatheka semiinvoluta and Turborotalia cocoaensis overlap in zones E13-E14, which is late Bartonian to early Priabonian in age. Turborotalia cambayensi P17 (E16) and Praetenuitella insolita reveal Upper Priabonian in age. Finally, Pseudohastigerina naguewichiensis, Cassigerinella chipolensis and Tenuitella gemma overlap in O1, which is early Rupelian in age. Two zones equivalent to transition zones are proposed: Middle Eocene-Upper Eocene transition zone and Upper Eocene-Lower Oligocene transition zone.
ABSTRACT
Aptian to early Albian times were marked by various geodynamic and paleoenvironmental events such as large igneous province volcanism , perturbations of climate and the carbon cycle, and sea-level changes. The Essaouira-Agadir basin (EAB), located on the Atlantic passive margin of Morocco, offers good and fossiliferous exposures of the Aptian–Albian sedimentary series. A detailed analysis of this succession made it possible to establish a biostratigraphic framework. The identification of discontinuities allowed to define eight depositional sequences. As most of them are correlatable with depositional sequences of other Tethyan areas, they suggest that eustacy was the main parameter controlling sedimentation. The analysis of sedimentary facies and nannofossil assemblages provides information on paleoenvironmental changes. Sedimentation in the EAB evolved from a very low energy, carbonate ramp in the early Aptian to a low energy, slightly deeper, mixed carbonate-clastic ramp in the early Albian. This change occurred along with an increase of clastic input, a change from oligotrophic to mesotrophic faunal assemblages, and a decrease of sea-surface temperatures. The occurrence of current sedimentary features, sporadic dysaerobic deposits and local phosphatic and glauconitic crusts suggests that upwelling currents were significant during this period. Paleogeographic and isopach maps support a transgressive trend in the late Aptian and early Albian, and unravel subsidence anomalies suggesting mild halokinetic movements during Aptian‒early Albian times.
The Eocene–Oligocene transition was a period of high faunal and floral turnover, often correlated with climatic deterioration. Crocodyliforms are climate sensitive, and they have been often used for reconstruction of paleoclimates. The description of crocodylian material from the Bartonian of Aaiun-Tarfaya Basin (Morocco) allows the recognition of at least two longirostrine crocodylians, including a gavialoid. This identification is important, because the migration of gavialoids to South America probably occurred during the late Eocene. Close relationships between late Eocene–early Oligocene Eogavialis africanum from Egypt, Argochampsa krebsi from the Paleocene of Morocco, and the South American gavialoid clade suggests that Morocco could have had a particular place in the gavialoid dispersal route to South America. The resemblance between Moroccan material described herein and E. africanum is thus important in this context. Analysis of the distribution of longirostrine crocodylians in the Peri-Tethys area through the Eocene–Oligocene shows a strong difference in the evolution of the distribution between longirostrine crocodylians and Diplocynodon. Whereas the freshwater Diplocynodon has a continuous distribution in western Europe, the mainly marine longirostrine crocodylians have a northern maximal expansion that moves southward during the middle Eocene, being restricted to North Africa during late Eocene–early Oligocene. European freshwater Asiatosuchus-like taxa also disappear during the late Eocene. Climatic deterioration, helped by sea level oscillations, may have strongly impacted the diversity and latitudinal distribution of the crocodylians, but we highlight a possible differential tolerance in range of climatic conditions between crocodylians. This could help to refine the use of crocodylians as paleoclimatic proxies.
Une marge passive est une zone de transition non-active entre lithosphère continentale et lithosphère océanique. De nombreuses marges passives présentent un fort développement magmatique (>50%). Ces marges passives volcaniques (MPVs) marquent la rupture lithosphérique au-dessus d’un manteau en fusion (partielle) et sont typiquement caractérisées par l’intrusion et l’extrusion d’un volume significatif de produits magmatiques dans la croûte lors des périodes ante-rift, syn-rift et post-rift. A partir d’une compilation bibliographique, de données sismiques (profils de sismique réflexion ION-GXT, sismique 3D) et d’observations réalisées sur le terrain à l’Est et à l’Ouest du Groenland, les objectifs de cette thèse étaient : (1) de mieux caractériser les modes tectoniques d’accommodation des flexures de la croûte supérieure sous les SDRs (seaward dipping reflectors) et l’interprétation des SDRs externes et, (2), de placer la rupture magmatique à l’échelle de la fragmentation d’un supercontinent. Les principaux résultats obtenus sont: 1) La rupture d’un supercontinent est toujours synmagmatique. Cette rupture se propage ensuite de manière non-magmatique (article en préparation); 2) Les SDRs externes sont découplés tectoniquement d’une croûte inférieure d’origine continentale exhumée. Du matériel d’origine continental pourrait exister en profondeur de manière continue au niveau de rides asismiques transverses (comme GIFR) (article soumis); 3) La flexure crustale est aussi accommodée par du magma qui circule dans les failles de détachement sous SDRs. Un découplage existe à l’extrados des flexures accommodé par des injections de magma syn-tectoniques sous forme de laccolithes à la base des SDRs internes.
Le membre "Guerran" de la formation Samlat d'Ad-Dakhla (Périphérie sud du Bassin Tarfaya, Lâayoune et Ad-Dakhla, TLDB) est composé essentiellement d'un complexe d'alternance rythmique de chert gris et de silt marneux où s'intercalent d'importants niveaux fossilifères. Ce membre a fait objet de considérables découvertes paléontologiques et par conséquent de diverses propositions de datations: (1) Eocène-Oligocène, (2) Priabonien moyen et Priabonien supérieur; (3) base et milieu du Priabonien supérieur et (4) début Oligocène pour sa partie sommitale. Les niveaux à tendance marneuse et marno-sableuse de ce membre ont été la cible de la quête des microfossiles Datum qui peuvent enrichir et clarifier les datations préalablement proposées pour ce membre. Deux sites sur le littoral au sud d'Elargoub (Sud-Est Ad-Dakhla), ont été sélectionnés pour un échantillonnage serré: la Falaise Alaouate et le site Dafia. En dépit de l'état critique de conservation des microfossiles, une vingtaine d'espèces de Foraminifères Planctoniques ont été identifiées. Leurs répartitions s'organisent verticalement en trois assemblages. Les Datum parmi ces derniers : Acarinina topilensis s'étend de E10 à mi-E12 (Zone à Foraminifères planctoniques), entre le Lutetien supérieur et le Bartonien inferieur; Globigerinatheka semiinvoluta et Turborotalia cocoaensis dans la zone de chevauchement de E13-E14 d'âge Bartonien supérieur-Priabonien inférieur. Turborotalia cambayensi E16 (P17) et Praetenuitella insolita révèlent un âge Priabonien supérieur. Finalement, Pseudohastigerina naguewichiensis, Cassigerinella chipolensis et Tenuitella gemma s'inscrivent dans la zone O1 qui correspond au Rupélien inférieur. Deux zones équivalentes à des zones de transition sont proposées: la zone Eocène moyen-Eocène supérieur & la zone Eocène supérieur-Oligocène inférieur. Mots-clés: Foraminifère planctonique, Lutétien, Bartonien, Priabonien, Rupélien, Ad-Dakhla, Maroc. Abstract. The "Guerran" Member of the Samlat Formation near Ad-Dakhla, on the southern periphery of the Tarfaya, Laâyoune and Ad-Dakhla Basin (TLDB), is essentially a rhythmic complex of alternating gray cherts and marly silts. Important fossiliferous intervals intercalated within this have given rise to important paleontological discoveries, and consequently to various dating proposals: (1) Eocene-Oligocene; (2) middle and upper Priabonian, upper Eocene; (3) base and middle of the upper Priabonian, late Eocene and (4) lowermost Oligocene. The more marly intervals of the Guerran member were chosen for investigation of microfossils to clarify the suggested dating. Two sites on the coast south of Elargoub (Southeast of Ad-Dakhla) were selected for detailed sampling: Alaouate cliff and Dafia area. Some twenty species of planktonic Foraminifera were identified, in spite poor preservation of microfossils. Their distributions are organized into three time-successive assembages. Acarinina topilensis is distributed from E10 to mid-E12 (Planktonic Foraminiferal Zone), upper Lutetian to early Bartonian in age. Globigerinatheka semiinvoluta and Turborotalia cocoaensis overlap in zones E13-E14, which is late Bartonian to early Priabonian in age. Turborotalia cambayensi P17 (E16) and Praetenuitella insolita reveal Upper Priabonian in age. Finally, Pseudohastigerina naguewichiensis, Cassigerinella chipolensis and Tenuitella gemma overlap in O1, which is early Rupelian in age. Two zones equivalent to transition zones are proposed: Middle Eocene-Upper Eocene transition zone and Upper Eocene-Lower Oligocene transition zone.
Understanding the formation and the development of salt structures is very important especially because they are of significant economical interest. Detailed understanding of this process will help reservoir prediction and hydrocarbon recovery. In this work, we use a combination of geological observations along with the interpretation of geophysical data (seismic and Bouguer anomaly data) to better constrain the geology of the Jbel Cheid structure. The shape of Triassic body of Jbel Cheid (Northern Tunisian Atlas) structure and its geodynamic evolution have been determined by gravity analyses and 2.5D modeling, correlated with others geophysical data (seismic) and geological observations. Semi-automatic structural analysis was performed before modeling, to identify lateral gravity discontinuities. The complete Bouguer and residual gravity anomaly maps indicate a positive amplitude gravity anomaly over the Triassic evaporitic outcrop (Jbel Cheid) and prominent NE–SW-trending features associated with the boundary of the Triassic rocks and surrounded layers. The seismic profile shows a thickness variation of post-salt layers. Taking into account the 2.5D gravity model, seismic profile and surface data, geodynamic evolution of Jbel Cheid can be subdivided on three stages (reactive, active, and passive) which well correlated to the model proposed by Vendeville (2002).
Two sirenian species are present in the late Eocene Samlat Formation near Ad-Dakhla in southwestern Morocco. A well preserved mandible with left and right dentaries belongs to a new protosirenid genus and species Dakhlasiren marocensis closely related to the genus Protosiren. An early dugongid of uncertain identification (cf. Eotheroides sp.) is also present, represented by vertebrae and ribs. Protosirenids differ from dugongids in the form of the brain, size and separation of nasal bones, and conformation of the anterior mandible. Protosirenids also differ in having vertebrae with larger neural canals, in having ligamentous rib articulations, and in lacking the pachyostotic ribs characteristic of dugongids. We tentatively interpret the latter differences to be related to feeding on softer vegetation farther offshore, with a thoracic rete mirabile for counter-current heat exchange and a collapsible rib cage to enable deeper dives. Dakhlasiren seemingly carried the divergent specializations of Protosiren a step farther by reduction of tongue musculature and loss of a masticatory surface at the front of the mandible.
https://authors.elsevier.com/c/1elPL,XIvblkif
Interpretation of magnetic, gravity, seismic, and geological data shows that the curvilinear Late Paleozoic orogen affected the location of Central Atlantic syn-rift faults. While northeast-southwest striking thrust faults were perpendicular to extension, prominent curvatures, such as the Pennsylvania salient, introduced structural complexities. East-northeast/west-southwest striking, dextral, transpressional strike-slip faults of this salient became reactivated during Carnian-Toarcian rifting. They formed sinistral, transtensional strike-slip “rails” that prevented the Georges Bank–Tarfaya Central Atlantic segment from orthogonal rifting, causing formation of a pull-apart basin system. Central Atlantic segments to the south and north underwent almost orthogonal rifting. “Rails” lost their function after the continental breakup, except for minor younger reactivations. They were not kinematically linked to younger oceanic fracture zones.
Atlantic segments initiated by normal rifting differ from the segment initiated by the Georges Bank–Tarfaya strike-slip fault zone. They contain Upper Triassic-Lower Jurassic evaporites having salt-detached gravity glides, while the connecting transfer segment does not. Their structural grain is relatively simple, divided mostly by northeast-southwest striking normal faults. Northwest-southeast striking oceanic fracture zones kinematically link with continental faults in a few places, controlling the sediment transport pathways across the uplifted continental margin.
The connecting Georges Bank–Tarfaya Central Atlantic segment, initiated as a sinistral transfer-zone, has a complex structural grain, characterized by numerous small depocenters and culminations. Their boundaries are formed by east-northeast/west-southwest striking, sinistral, strike-slip, north-northeast/south-southwest, striking normal and west-northwest/east-southeast striking, dextral, strike-slip faults. Sediment transport pathways have complex trajectories, weaving through local depocenters.
The Large Triassic/Jurassic salt basin offshore Morocco is associated with the early rifting of the Central Atlantic region. The progressive deformation of the vast amount of salt during the Late Cretaceous/Tertiary period created a world-class frontier salt basin from an exploration point of view.
Exploration experience gained in specific salt basins of West Africa may not be directly applicable to other salt basins along the entire passive margin. To conduct a comparative structural analysis, regional reflection seismic transects were constructed across the salt basins of Morocco, Senegal, Guinea-Bissau, Equatorial Guinea, Gabon and Angola.
Regional-scale similarities of the salt basins include the progressive complication of salt-related structures basinward, the change from an extensional domain on the shelf to a compressional domain on the slope and the presence of a toe-thrust front at the oceanward edge of the basins. Regional-scale differences are partly attributed to the relative stratigraphic position of the salt in relation to the rift history.
In the better-known post-rift salt basins of Equatorial Guinea, Gabon, Congo and Angola updip extension is represented by a broad rafted domain balanced by downdip contraction in the form of salt tongues, canopies and a toe-thrust zone. The efficiency of this gravity sliding/spreading across the whole margin is due to the more or less uniform original distribution of Aptian salt in the post-rift succession forming a continuous detachment level.
In contrast, the typically uneven original distribution of the Late Triassic and Early Jurassic syn-rift salt in Morocco, Mauritania, Senegal, The Gambia and Guinea-Bissau is due to basement highs separating rift half-grabens and creating a different structural pattern. Individual salt structures, such as pillows and diapirs, originated from isolated patches of the autochthonous salt. In the case of syn-rift salt, updip extension may not always be the ultimate driving force for the contractional salt-deformation downdip.
The principal paleogeographic characteristics of North and Central Africa during the Paleozoic were the permanency of large exposed lands over central Africa, surrounded by northerly and northwesterly dipping pediplanes episodically flooded by epicontinental seas related to the Paleotethys Ocean. The intra-continental Congo–Zaire Basin was also a long-lived feature, as well as the Somali Basin from Late Carboniferous times, in conjunction with the development of the Karoo basins of southern Africa. This configuration, in combination with eustatic sea-level fluctuations, had a strong influence on facies distributions. Significant transgressions occurred during the Early Cambrian, Tremadocian, Llandovery, Middle to Late Devonian, Early Carboniferous, and Moscovian.
The Al Salif diapir is part of a north-south oriented diapiric wall which has caused updoming of the overburden and active extensional faulting. At the Jabal Al Milh diapir, recumbent folding and thrusting are the main deformation features observed in the siltstones and gypsum layers of the overburden. This study shows that overburden sediments above the Al Salif diapir extended to allow sediments to slide from the salt dome crest by listric faulting, whereas sediments underlying the Jabal al Milh salt glacier were sheared and shortened in the horizontal direction. -from Authors
The first oceanic crust in the central Atlantic is usually thought to have a Middle Jurassic age. The new interpretation of the two key parameters, the African homologue of the East Coast Magnetic Anomaly and the situation of the Triassic salt basin of Morocco and Novia Scotia, shows that this age was underestimated by about 20 Ma. In our kinematic reconstruction, the first oceanic crust begins at the Late Sinemurian. This difference in age is crucial for the evolution of those margins and we discuss here its consequences. To cite this article: M. Sahabi et al., C. R. Geoscience 336 (2004).
The Fuerteventura Jurassic sedimentary succession consists of oceanic and clastic de- posits, the latter derived from the southwest- ern Moroccan continental margin. Normal mid-oceanic-ridge basalt (N-MORB) flows and breccias are found at the base of the se- quence and witness sea-floor spreading events in the central Atlantic. These basalts were ex- truded in a postrift environment (post-late Pliensbachian). We propose a Toarcian age for the Atlantic oceanic floor in this region, on the basis of the presence higher up in the sequence of the Bositra buchi filament microfacies (Aalenian-Bajocian) and of clastic deposits re- flecting tectono-eustatic events (e.g., late Toar- cian to mid-Callovian erosion of the rift shoul- der). The S-1 sea-floor oceanic magnetic anomaly west of Fuerteventura is therefore at least Toarcian in age. The remaining sequence records At- lantic-Tethyan basinal facies (e.g., Callo- vian-Oxfordian red clays, Aptian-Albian black shales) alternating with clastic depos- its (e.g., Kimmeridgian-Berriasian periplat- form calciturbidites and a Lower Creta- ceous deep-sea fan system). The Fuerteventura N-MORB outcrops rep- resent the only Early Jurassic oceanic base- ment described so far in the central Atlantic. They are covered by a 1600 m, nearly contin- uous sedimentary sequence which extends to Upper Cretaceous facies.
Based mainly on published data, we attempt a synthesis of the stratigraphy, facies and tectonic evolution of the onshore Aaiun-Tarfaya Basin and its offshore extension, the West Saharan Marginal Basin. Basement rocks are Precambrian, and folded Paleozoic sediments (Mauritanides belt): they dip gently westward and are overlain by a seaward thickening wedge of Mesozoic to Cenozoic continental to shallow-marine sediments. Jurassic to Cretaceous sediments extend from the onshore basin to the present shelf and upper slope, where they are more than 12 km thick.
In the onshore basinTriassic clastic rocks, evaporites, and basalt sills and lower to middle Jurassic evaporites and carbonates are overlain by a 1–2 km thick sequence of upper Jurassic neritic carbonates (Puerto Cansado Formation). These formations document high subsidence rates (80-100 m/m.y.) which were compensated by carbonate buildup after a major transgression, that coincided with the Liassic to Oxfordian breakup of Pangaea.
The subsidence rates increased slightly (110-140 m/m.y.) during theEarly Cretaceous, when 1–4 km of regressive continental to marine-deltaic, Wealden-type sediments were deposited as part of two major delta systems (Tan Tan/Jreibichat Formation).
Restrictedmid-Cretaceous sediments (Calcaires d’ Aguidir) are overlain by up to 1.0 km of transgressiveLate Cretaceous shallow-marine carbonates Lebtaina Formation) and similar Paleogene sediments (Samlat Formation). The subsidence and accumulation rates decreased considerably during this time. Upper Cretaceous toPaleogene sediments were truncated over a wide area during several erosional cycles.
Because of uplift and erosion, theNeogene is thin or missing in the onshore coastal basin; an exception is the 1000 m thick sequence of ?deltaic to estuarine claystones in the northwestern Aaiun Basin. Sediment bypassed the present shelf and slope during this time, to accumulate in a new depocenter as gravitative and hemipelagic deposits along the uppermost continental rise.
The most importantconstructional phases of the mature passive West Saharan continental margin involved the buildup of a thick Jurassic carbonate platform, overwhelmed by up to 4 km of Early Cretaceous Wealden-type deltaic sediments. Rollover structures between antithetic growth faults produced the “lower slope anticline” and a convex Cretaceous paleoslope. We recognized no salt diapirs, but local piercement structures probably caused by mobilized Early Cretaceous prodeltaic shale. During late Cretaceous to Tertiary times the continental slope was hardly prograded. During Tertiary (especially Neogene) times the depocenter shifted to the upper rise.
Evidence from seismic profiles correlated with DSDP, commercial well, dredge, and land geological data allow the differentiation of the complex, multi-phase mid-Cretaceous to Cenozoic history ofslope destruction. At the following times slope canyons were excavated and regional unconformities formed: (1) mid-Cretaceous (upper slope; precursor valleys); (2) early Senonian; (3) Paleocene (pronounced unconformity); (4) late Eocene (local); (5) mid- to late Oligocene (major lower slope erosion; up to 100 M.Y. hiatus; major canyon cutting phase);(6) mid- to late Miocene (local); (7) Pliocene (shelf and upper slope; deeply incised Uad Craa Channel); (8) late Pleistocene (canyon reactivation, slope gullies, and incisions).
Some of these accentuated erosional phases (especially 5 and 8) can be correlated with intensified Atlantic bottom water circulation from climatic cooling during periods of exceptionally low sea level causing hiatuses on the shelf and increased mass wasting at the slope (Fig.10). A very large sediment volume (7,500 — 15,000 km3 off Cape Bojador) was removed during the mid-Tertiary sculpturing of the lower slope, probably by enhanced contour currents (pre-AABW?) and associated gravitative mass transport. In total 900 km3 of sediments were excavated by slope canyons, most of which do not extend to the shelfbreak. Both processes caused a gradual retreat of the base-of-slope line and accentuated the convex shape of the slope in this area.
During early to mid-Miocene times, massive slope failure led to thegravitative deposition of olistostromes, debris flows, turbidites and slumps on the oversteepened lowermost paleoslope, until an equilibrium gradient was achieved (Figs. 11,12). During the late Pleistocene the same processes caused giant translational slides with up to > 100 m high slide scars (Figs. 1, 8). The triggering of these massive slides at this very time and setting (passive margin, low gradient and sedimentation rates) is still enigmatic.
Interpretation of industrial seismic reflection profiles along the Atlantic Moroccan margin allows to reconstruct the geometry of the synrift basins and kinematics of the intracontinental Central Atlantic rifting. This extensive event was marked by a Triassic-Liassic horst and graben regional pattern. A first Carnian faulting phase, recorded in the eastern part of the Essaouira basin and the Souss basin, controlled deposition of coarse and sandy synrift sequences. A younger, pelitic-evaporitic synrift sequence is present over the entire margin. It registers a second, northward spreading fracturation episode developed from the Tarfaya southern basin to the Doukkala northern basin during the Norian-Hettangian times. From this structural regional point of view and at that scale, the Central Atlantic ocean opened diachronously.
The Argana rift basin of Morocco and the Fundy rift basin of the Maritime
Provinces of Eastern Canada are on the conjugate margins of the central Atlantic Ocean. In
the Late Triassic and Early Jurassic these basins lie at similar paleolatitudes within the
same great rift system. A comparison of the depositional- and tectono-stratigraphy reveal
strong similarities, much greater that those shared between the Fundy basin and other rifts
in eastern North America. Both the Argana and Fundy basins are comprised of four, mostly
unconformity-bound, tectonostratigraphic sequences (TS I-IV) probably controlled by pulses
of extension: TS I, is Permian in age and the depositional facies of the Argana basin looks
more humid than the age equivalent in the Fundy basin and the latter may not be a rift
sequence; TS II, is early Late Triassic (Carnian) in age and is the most humid looking facies
in both basins; TS Ill, is late Late Triassic (Norian and Rhaetian) in age and is much more
arid in both basins with abundant aeolianites and evaporites; TS IV, is latest Triassic and
earliest Jurassic (late Rhaetian - early Hettangian) and shows an increase in the range of
variability in climate-sensitive facies - its basal part contains the Triassic-Jurassic boundary
an overlying basalt flow sequence and additional fluvial and lacustrine strata on top. The
dramatic similarity in both facies and sequence stratigraphy between the Argana and Fundy
basins, at least during the Triassic, argues for similar tectonic control, restricted to that
latitudinal swath of Pangea, as well as similar paleoclimate.
Within the Aaiun-Tarfaya coastal basin Mesozoic to Cainozoic sediments thicken from a hinge line to the present coast. Over a lateral distance of c. 100km under the hinge line to the present shelf slope, and uppermost a sedimentary sequence of nearly constant thickness (12-14 km) overlies continental to transitional basement. This uniformly subsiding part of the margin is termed Cape Bojador marginal basin'. Seaward of the upper rise the basement rises and the sediment cover thins. During the Jurassic, the subsidence rates in the marginal basin were high (80-100m/Ma); they increased slightly during the early Cretaceous (130-140m/Ma). During the late Cretaceous and Cainozoic, subsidence slowed down more or less exponentially. -from Authors
Accreted terranes of the Appalachian Iapetan and peri-Gondwanan realms display structural trends that are mainly concordant with promontories and embayments in the Laurentian margin, indicating that during accretion, the shape of the continental margin acted as a template around which accreted terranes were molded. In North Carolina and Newfoundland, post-accretion transcurrent motion appears to be recorded by displaced outboard portions of promontories, no longer concordant with those in Laurentia. A bend in structural trends confined to the peri-Gondwanan realm at the North Carolina-South Carolina state line is interpreted to represent the dextrally displaced outboard portion of the Virginia promontory. In Newfoundland, the Hermitage flexure is interpreted as a dextrally displaced Laurentian promontory that originated along strike to the northeast. In both places, promontories were truncated and dextrally translated for similar to 220-250 km by a Devonian-Mississippian orogen-parallel transcurrent system, which may well have extended for the length of the eastern Laurentian margin. South of the nearby St. Lawrence promontory, extreme thinning of Appalachian crust beneath the Maritimes Basin is consistent with extension at a releasing stepover. Estimates of extension are consistent with those obtained from promontory offsets.
This paper summarises the stratigraphy, structure and petroleum geology of the Central Atlantic margin of NW Africa, from Morocco to Guinea. Rifting of the margin began in Late Triassic (Carnian) times and clastic red bed sequences were deposited on both sides of the Atlantic margins. Red beds were followed by early Jurassic evaporite deposition, with three separate salt basins developed. A major magmatic event with dykes, lavas and plutons occurred along the whole Central Atlantic margin at 200 Ma during salt deposition. A carbonate platform developed along the margin in Jurassic to Early Cretaceous times. This consists mainly of carbonate ramp facies, but with rimmed-shelf carbonate platforms developed in Senegal. The deepwater sections of the margin consist of predominantly deep-marine clastic sedimentation from the Jurassic to Recent. Important deltas built out at Tan Tan, Cape Boudjour (Early Cretaceous), Nouakchott (Tertiary) and Casamance (Late Cretaceous). These delta deposits are important for oil exploration, because the rich Cenomanian–Turonian source rock reaches maturity for hydrocarbon generation in these areas.
Incidences de l'e ´ volution du Haut Atlas Occidental et de son avant pays septentrional sur la dynamique meso-cé nozoique de la Marge Atlantique
- M Hafid
Hafid, M., 1999. Incidences de l'e ´ volution du Haut Atlas Occidental et de son avant
pays septentrional sur la dynamique meso-cé nozoique de la Marge Atlantique
(entre Safi et Agadir);
Les bassins ouest marocains; leur formation et leur evolution dans le cadre de l'ouverture et du developement de L'Atlantique central (marge africaine)
- Le Roy
Le Roy, P., 1997. Les bassins ouest marocains; leur formation et leur evolution dans le
cadre de l'ouverture et du developement de L'Atlantique central (marge africaine), Unpublished PhD thesis, Universite de Bretagne Occidentale, Brest, p. 326.
Incidences de l'é volution du Haut Atlas Occidental et de son avant pays septentrional sur la dynamique meso-cé nozoique de la Marge Atlantique (entre Safi et Agadir)
- M Hafid
Hafid, M., 1999. Incidences de l'é volution du Haut Atlas Occidental et de son avant
pays septentrional sur la dynamique meso-cé nozoique de la Marge Atlantique
(entre Safi et Agadir);
Incidences de l'évolution du Haut Atlas Occidental et de son avant pays septentrional sur la dynamique meso-cénozoique de la Marge Atlantique (entre Safi et Agadir); Apport de la sismique reflexion et des données de forages
- M Hafid