DOI 10.1007/s10347-004-0025-6 O R I G I N A L P A P E R
Khalil El Kadiri · Francisco Serrano · Rachid Hlila · Hoda Liemlahi · Ahmed Chalouan ·
Angel Carlos Lpez-Garrido ·
Antonio Guerra-Merchn · Carlos Sanz-de-Galdeano · Karima Kerzazi · Abdelaziz El Mrihi
Lithostratigraphy and sedimentology of the latest Cretaceous-early
Burdigalian Tamezzakht succession (Northern Rif, Morocco):
consequences for its sequence stratigraphic interpretation
Received: 4 March 2003 / Accepted: 22 July 2004 / Published online: 24 November 2004 Springer-Verlag 2004
Abstract The Tamezzakht succession (Maastrichtian–
middle Burdigalian), situated at the fringe between the Internal and the External zones, displays contrasting lithologies with abrupt facies changes, discontinuities, and/or coarse-grained calciturbidite in between. These criteria allow the definition of seven main lithostrati-graphic formations.
Depositional environments (oxygenation levels, tro-phic conditions, omission histories, among others) and/or transgressive/regressive trends are inferred from inte-grated sedimentologic data including facies change, cyclicity pattern and the textural composition of the tur-bidite facies tracts. Special emphasis is given to the ich-nological features.
Taking into account the extended time-range, the po-sition between the internal zones and the external ones, as well as the clear differentiation into several contrasting sedimentary formations, the Tamezzakht succession is expected to provide useful stratigraphic data for the re-gional correlations.
Keywords Ichnofacies · Omission surface · Sequence
stratigraphy · Cretaceous-Tertiary boundary · Eocene-Oligocene · Early Burdigalian · Morocco
Introduction
As is the rule in the Alpine Mediterranean mountains, paleogeographic reconstructions of the northwestern Rif Belt during the early-middle Jurassic show its internal domain bordered by a stable continental paleomargin (El Kadiri 1984, 1991; Olivier 1984; El Hatimi 1991; El Kadiri et al. 1992), the collapse of which during the late Jurassic-early Cretaceous times resulted in a deep flysch basin (i.e. the Maghrebian Flysch Trough, Didon et al. 1973; Raoult 1974; Bourgois 1978; Durand-Delga 1980; Chalouan et al. 2001; Michard et al. 2002). Among the issues and questions currently addressed are the origin of the clastic material and the factors controlling the calci-turbidite versus the sandstone flysch episodes, i.e., tec-tonics versus eustasy and the related environmental changes. These uncertainties are due to (i) the fact that the pioneer authors (e.g., Durand-Delga 1972, 1980; Didon et al. 1973; Raoult 1974; Bourgois 1978; Hoyez 1989) fo-cused their attention mostly on the stratigraphy of the thick sandstone bodies, and (ii) the scarcity or lack of subsequent detailed studies dealing with the sedimentol-ogy, sequence stratigraphy and environmental controlling factors of the Rifian turbidite successions.
K. El Kadiri ()) · R. Hlila · H. Liemlahi · A. El Mrihi Faculty of Sciences, Dep. Geology,
Univ. Abdelmalek Essaadi,
M’Hannech II, BP. 2121, 93003 Tetuan, Morocco e-mail: khkadiri@fst.ac.ma
F. Serrano · A. Guerra-Merchn Dep. Ecologia & Geologia, Univ. of Malaga,
Teatinos, Malaga, Spain
A. C. Lpez-Garrido · C. Sanz-de-Galdeano Facultad de Ciencias,
Dep. Geodinamica,
Av. Fuente Nueva, 18002 Granada, Spain K. Kerzazi
Ministre Energie and Mines, Div. Geology, Rabat-Institut,
Morocco A. Chalouan
Faculty of Sciences, Dep. Geology, Univ. Mohamed V,
The present paper attempts to give new insights into this second line of research in undertaking an integrated analysis embracing stratigraphy, sedimentology and ich-nology of a key stratigraphic series lying at the fringe between the internal and external Rifian domains (Fig. 1).
Purpose
The Tamezzakht succession (late Cretaceous–early Bur-digalian) displays, from the base onwards, distinct sedi-mentary units, the facies of the majority of which are clearly contrasted in the field. The sharp contact between them suggests regional events resulting in abrupt changes of the factors controlling the clastic material produced at the source area.
The purpose of this paper is to shed light on the nature of these events based upon an integrated sedimentologic description focused on four key issues, namely:
– the description and inventory of turbidite divisions building the successive facies tracts (in the sense of Mutti 1992). Precisely, the clastic composition, grain size and thickness of each of these divisions depend primarily upon the textural composition of the original parent flow, and secondarily on the downslope grain-segregation processes (Mutti 1992), which result in a facies tract composed of vertically stacked grain-seg-regated intervals (i.e., future grain divisions). Because of their distinct hydrodynamic behaviour, detachment planes may be partly or fully activated between these
intervals, so an individual bed considered separately in a stratigraphic column (i.e. a completely detached di-vision) can no longer be regarded as representing alone the original turbidite event. A facies sequence (FS) is here used in a sense slightly modified from Mutti
(1992:49, FS: “vertical expression of a facies
associ-ation”) as corresponding to a stratigraphic interval made up of successive turbidite strata deriving from parent flows of the same textural composition. Thus, a facies sequence may reflect a sedimentary episode during which the paleogeographic conditions prevail-ing at the source area remain near constant. In this context, facies sequence can have an important bearing on the tectonic and/or eustatic interpretation;
– the cyclicity pattern, which may involve the main turbidite and non-turbidite components. Hence, facies change across two distinct stratigraphic intervals may be regarded also on the scope of the change affecting the cyclicity pattern and not strictly as a consequence of the change in the lithologic composition;
– the ichnological features that help to delineate key surfaces and enable us to understand the sea-level-, climate- and/or tectonics-mediated paleoenvironmen-tal changes (sedimentation rate, omission duration, oxygen fluctuations, benthic food contents, and sub-strate consistency);
– the nature of the discontinuity surfaces between dis-tinct stratigraphic intervals. These merit a more fo-cused attention, especially in the case where they are paired with the main gravity flow events and/or the facies changes. Discontinuity surfaces classically point Fig. 1 Simplified geologic map
of the northwestern Rif belt. The Tamezzakht area is located at the boundary between the Internal zones (Sebtides, Gho-marides and Dorsale Calcaire) and the External ones (flysch nappes and the underlying para-autochthonous units, mainly)
to the role played by the tectonic, paleoenvironmental and/or eustatic controls and can serve to monitor re-gional correlations with coeval successions of the neighbouring Dorsale Calcaire and throughout the Betico-Rifian internal zones.
We will emphasize hereafter these approaches differ-ently, depending on the sedimentologic features domi-nating each formation. For convenience, some well-known interpretative comments, will be given concur-rently with the description of some sedimentological and ichnological key data, which allows us to focus the final discussion on the sequence stratigraphic and some re-gional interpretations.
Geological framework
The Tamezzakht succession is located 6 km southwest of
the city of Tetuan (Fig. 2), in an area of about 3 km2,
which is extensively quarried for building purposes. It is entirely exposed in a great quarry at the northern part of this area. It consists of a 200-m-thick calciturbidite- and marl-dominated “continuous” series that spans the late Senonian–early Burdigalian time interval.
Regionally, it belongs to the Predorsalian zone, which acted as a narrow, transitory paleogeographic zone (Di-don et al. 1973; Olivier 1984; Martin-Algarra 1987; Ben Yach et al. 1988) lying between a carbonate platform (i.e., Dorsale Calcaire) and an adjacent basinal zone (Maghrebian Flysch Trough).
Tectonically, the Tamezzakht section is overthrust by the Kobat el Keskasse olistostrome located on the northeastern side of the studied area. It includes de-cametre- to hectometre-scale blocks derived from an ex-ternal-Dorsale-type unit, probably from the neighbouring Hafat Nator unit (Fig. 2). These are embedded within the Predorsale matrix made up of the classical and wide-spread variegated marls of the late Eocene – middle Oligocene. Near the village of Dar Zkiek, thick-bedded holoquartzous sandstones of Aquitanian–early Burdi-galian age stratigraphically overlie this unit. The latter sandstones correspond to the so-called “Bliounis” sand-stones. They also occur in the uppermost part of the Tamezzakht stratigraphic succession, which indicates a certain relationship of the latter with the Predorsale do-main and/or the Tariquide Ridge units (Fig. 1; Durand-Delga 1972; Didon et al. 1973). It is noteworthy that the reworked blocks are embedded also in the Tamezzakht succession, within time-equivalent levels (precisely close to the Eocene–Oligocene transition), but the Tamezzakht ones are inherited from underlying strata of the same succession.
The Tamezzakht area, in turn, overthrusts the Tangiers unit that is represented here by its internal-type facies mainly made up of the widespread early Senonian green to grey monotonous pelites (Fig. 3). Metre- to decametre-thick slices made up of the Bni Ider sandstones may discontinuously be trapped in between.
Cartographically, a very similar succession crops out northwards in the Bni Imrane area close to the external-Dorsale/internal-Tangiers-unit fringe. It is also developed more northwards in the Andjra area upon the internal Tangiers unit (Durand-Delga and Didon 1984a, b). Along these areas, metre- to decametre-scale, Jurassic sedi-mentary blocks sparsely emerge from this succession. They strongly recall the Tariquide-Ridge units (i.e. J. Moussa Group Jurassic successions, Fig. 1), a fact that is in agreement with the presence of the above-mentioned “Bliounis”-type sandstones in the Tamezzakht succes-sion.
Stratigraphy and sedimentology
Figure 3 presents the main sedimentary formations of the Tamezzakht succession and shows the sampling levels that had yielded planktonic foraminifera and calcareous nannoplankton. Biostratigraphic data are summarized in Table 1. Bed-by-bed columns are presented in Figs. 4, 5 and 6. From the base onwards, the contrasting formations we have recognized are as follows.
Black Shale Formation (BSF, late Campanian–early Maastrichtian)
Black shales represent the basal formation of the Tamezzakht succession (5–10 m in thickness, Fig. 3). They consist of decimetre- to metre-scale mud-dominated gravity flows, which are developed in poorly graded, black, calcareous, fine-grained sandstones and black shales. They are extremely rich in wood debris, trapped as floating clasts within both sandstones and shales. This fact may indicate that the corresponding flows were ac-tive only over short distances so that no significant seg-regation within the suspension occurred. Accordingly, they cannot be interpreted in terms of the Bouma’s se-quence, but may be more or less compared to a small-scale F1 facies-type of Mutti (1992), in which no pebbles are present in their fine-grained matrix.
Glaucony-bearing, clean calciturbidites are embedded within the upper part of the black shales as centimetre- to decimetre-thick channellized beds or as metre-scale lenses and blocks. All consist mostly of large benthic-foraminifera debris (mainly Orbitoids) and testify that they were produced on a shallow-water carbonate plat-form, which episodically operated during transgressive pulses as coarse-grained basal division developed in fa-cies F3 of Mutti (1992) or in fafa-cies R1 of Lowe (1982). It may be attached to these bioclastic grainstones. They typically point to steep slopes bordering the supplying platform.
Green Pelite Formation (GPF, late Maastrichtian)
The preceding formation is followed, with an abrupt fa-cies change, by 5–10 m of carbonate-free green pelites with spaced intercalations of sandstone beds. No pro-gressive grading is observed between these two
compo-nents, so the sedimentation regime may be regarded as representing a true rhythmic alternation. Lending support to this is the common observation on the soles of
sand-stone beds of graphoglyptid (e.g., Helminthorhaphe,
Cosmorhaphe). They testify to starved deep-water set-tings experiencing both very low bottom-current and very Fig. 2 Geologic map of the Tamezzakht area (this work). A, B
Detailed geologic map for two selected sectors wherein the strati-graphic column shown in Figs. 4, 6 and 10 were established. C Structural cross section showing the stacking pattern of the main formations distinguished herein. HNUnorthernmost side of Hafat Nator unit (External Dorsale, bordering westwards the Internal domain);JM a decametric olistolite displaying a Jurassic succes-sion (Rosso-Ammonitico, radiolarite facies, etc.) of Jbel Moussa-Group type (i.e. Tariquide Ridge, Durand-Delga 1972);ITUgreen pelites of the internal Tangiers unit; BSF Black Shale Formation (late Campanian–early Maastrichtian); GPF Green Pelite
Forma-tion (late Maastrichtian);SCFSlope Calcarenite Formation (latest Maastrichtian–early Paleocene); CF Calciturbidite Formation (middle to late Paleocene); RSF Red Shale Formation (Eocene– earliest Oligocene);MSFMarlstone-and-Sandstone Formation with four members (early Oligocene–early Burdigalian). THM Transi-tional Hemipelagic Member (early Oligocene);MM Marly Mem-ber (middle Oligocene?);SMSandstone Member (late Oligocene– Aquitanian?);SMM Siliceous Marly Member (early Burdigalian); HFHoloquartzous Formation (latest early Burdigalian). Note the hidden discontinuity at the base of SCF (HD.1), CF (HD.2), RSF (HD.3) and MSF (HD.4)
low benthic-food input (Uchman 1995; Wetzel 1991; Bromley 1996; Tunis and Uchman 1996a).
The sandstone beds consist nearly exclusively of a mixture of fine-grained quartz and rare planktonic for-aminifera, within a black ferruginous carbonate matrix. These quartz grains are limpid, very angular and most of them are elongated. They recall the so-called “quartz en charde” described by Meyer (1987) as originated in the pedogenic realm.
Centimetre-sized pyrite aggregates are common and testify to oxygen-depleted conditions beneath the
sedi-ment–water interface. Both Chondrites targionii
(BRONGNIART) and Chondrites intricatus
(BRONG-NIART) may abundantly occur within the shaly laminated horizons of the sandstone beds. These trace fossils are
known to occur preferably in oxygen-poor environments (e.g., Bromley and Ekdale 1984; Olriz and Rodrguez-Tovar 1999), which is in accordance with the green colour of pelites, a result of the reduced state of iron pigments.
This formation ends with a 2.5-m-thick bed dominated by structureless yellowish mudstone rich in cm-sized, green mud clasts. They are rich in planktonic for-aminifera, which reveals that these clasts were reworked from hemipelagic deposits. The bed displays a 30-cm-thick, slightly graded, well-sorted coarse-grained basal division, in which the clasts are cm-sized and supported by the same carbonate muds. As we shall see below, this clastic mixture strongly recalls an Internal-Dorsale-type source.
Fig. 3 Stratigraphic column of the Tamezzakht succession and its possible sequence strati-graphic interpretation (see also chapter results and discussions). The transgressive–regressive cycles T1/R1–T6/R6 are not considered here in limited time-scale (see recommendations by Posamentier and James 1993, 8-9) and may fit well with Vail’s classical depositional se-quences, 3rd order, 0.5–3 my, Duval et al. 1998) or with the T/ R facies cycles, which is the case of the majority of them (2nd order, 3–30 to 50 my, Duval et al. 1998; Jacquin and De Graciansky 1998). They are recognized here based on their basal discontinuities and their lithological signal (lithologic prediction method, Posamentier and James 1993, 7; “mthode directe”, Vail et al. 1987). See Table 1 for the nannoplankton and planktonic-foraminifera dates. Abbreviations as in Fig. 2
Table 1 List of planktonic foraminifera and calcareous nannofossils (*) extracted from the studied section Forma- tions Samples Planktonic foraminifera / calcareous nannoplankton* Age HF Biostratigraphic data not available Latest early–Burdig. (?) T 8b* Helicosphaera carteri , H. kamptneri , Sphenolithus gr. abies/neoabies , Cyclicargolithus floridanus , C. abisectus , Reticulofenestra pseudoumbilica Late early–Burdigalian T 8a* Helicosphaera carteri , H. kamptneri , Sphenolithus gr. abies/neoabies , Cyclicargolithus floridanus , C. abisectus , Reticulofenestra cf. pseudoumbilica S 3832 and 3822 Globigerina venezuelana Hedberg, G. praebulloides Blow, G. woodi Jenkins, Globigerinoides altiaperturus Bolli, Neoglobo-quadrina nana (Bolli), N. siakensis (LeRoy), Globoquadrina baroemoenensis (LeRoy), Globorotaloides suteri Bolli, Catapsy-drax unicavus Bolli, Loeblich & Tappan, C. dissimilis (Cushman & Bermdez) M M T6 * Helicosphaera ampliaperta , H. scissura , Sphenolithus gr. abies/neoabies Tam 31* Helicosphaera ampliaperta (small variety), H. carteri , H. kamptneri , Sphenolithus gr. abies/neoabies , Cyclicargolithus floridanus , C. abisectus T1 * Helicosphaera ampliaperta (small variety), Discoaster druggii , D. deflandrii , Cyclicargolithus floridanus , C. abisectus, E. formosa Early Burdigalian S 4030 Planktonic Foraminifera as in sample 4049, but with N. siakensis (LeRoy) Aquitanian (?) M MM Biostratigraphic data not available Late Olig. (?) 4062 Planktonic Foraminifera as in sample 4049, but with N. siakensis (LeRoy) T 4025 Planktonic Foraminifera as in sample 4049 H 4049 Globigerina galavisi Bermdez , G. tripartita Koch, G. venezuelana Hedberg, G. euapertura Jenkins, G. ampliapertura Bolli, G. increbescens Bandy, G. eocaena G mbel , G. corpulenta Subbotina, Neogloboquadrina opima (Bolli), N. nana (Bolli), Globorotaloides suteri Bolli, Catapsydrax unicavus Bolli, Loeblich & Tappan, C. dissimilis (Cushman & Bermdez) Late middle–Oligocene M 4050 Globigerina galavisi Bermdez, G. corpulenta Subbotina 4052 Globigerina galavisi Bermdez, G. venezuelana Hedberg , G. euapertura Jenkins, G. ampliapertura Bolli, G. prebulloides Blow Early to middle Oligocene R 4053 Subbotina linaperta (Finlay), Globigerina eocaena G mbel, G. corpulenta Subbotina, G. galavisi Bermdez, Muricoglobigerina senni (Beckman), Morozovella spinulosa (Cushman), Truncorotaloides rohri (Brnniman & Bermdez), T. topilensis (Cush-man), Globigerinatheka subconglobata (Shutskaya), G. index (Finlay), Turborotalia pomeroli Tourmakine & Bolli, Catapsydrax unicavus Bolli, Loeblich & Tappan Late middle–Eocene
S F CF
3827 Eoglobigerina pseudobulloides (Plummer ), Globigerina triloculinoides (Plummer), Acarinina praeangulata (Blow), Moro-zovella angulata (White), M. cf . velascoensis (Cushman) and abundant Microcodium Late to middle Paleocene 4055 Eoglobigerina pseudobulloides (Plummer), E. inconstans ( Subbotina), E. cf . trinidadensis (Bolli) (with abundant Microcodium ) Early Paleocene S 4056 Abatomphalus mayaroensis (Bolli), A. intermedius (Bolli), Globotruncana falsostuarti Sigal , G. arca (Cushman), Globotrun-canita stuarti (de Lapparent ), G. stuartiformis (Dalbiez), Racemiguembelina fructicosa (Egger), Rugoglobigerina hexacamerata Brnniman, R. reicheli Brnniman, R. rugosa (Plummer), Archaeoglobigerina blowi Pessagno, Heterohelix cf . reussi (Cushman), Pseudotextulria elegans (Rzehak) Latest Maastrichtian C F 4058 Abatomphalus mayaroensis (Bolli), A. intermedius (Bolli), Globotruncana falsostuarti Sigal , G. aegyptiaca Nakkady, Globotruncanita stuarti (de Lapparent) , G. stuartiformis (Dalbiez), Contusotruncana contusa (Cushman), Gansserina gansseri (Bolli), Racemiguembelina fructicosa (Egger), Rugoglobigerina hexacamerata Brnniman, Heterohelix cf . reussi (Cushman), Pseudotextulria elegans (Rzehak), Pseudotextularia palpebra Brnniman & Brown Late Maastrichtian
G P F
4059 Contusotruncana contusa (Cushman), Hedbergella sp ., Globiogerinelloides sp. , Heterohelix sp. , Pseudotextulatia sp. , Rugoglobigerina sp. BSF 3826 Benthic Foraminifera: Glomospira sp., Trochamina sp., Saccamina sp., Ammodiscus sp. Early Maastr. to late Campanian
Slope Calcarenite Formation
(SCF, latest Maastrichtian–early Paleocene)
The Slope Calcarenite Formation (SCF) consists of slope to base-of-slope deposits arranged in condensed sedi-mentary packages, with numerous omission surfaces in between (see below).
The textural composition of attached facies tracts (in the sense of Mutti 1992) allows distinguishing two main members (facies tracts II and III, Fig. 4). The first one displays four distinct divisions, among which division c.3 is commonly detached and results in distinct individual beds. This may be explained by activation of lamination planes, a common feature in this division. The c.1-bearing beds occur preferentially in the lower third of the
for-mation, whereas c.4 beds are rather common in the upper part of the facies tract II interval (Fig. 4). Hence, member II fits well Mutti’s definition of a facies sequence (Mutti 1992).
The division c.1 is dominated by heavily altered do-lomite lithoclasts, the majority of which show pedogenic hematite coating. Lending support to this are the common paleosoil-derived silcrete clasts. The hematite coating is likely to have partly hindered the diagenetic cementation and also explains why the basal coarsest division easily weathers (then termed calcarenite). Other lithoclasts are inherited from white massive packstones/grainstones,
Calpionella- and/orSaccocoma-rich mudstones and from filament-rich mudstones. Albeit these lithoclasts are rep-resented in low proportions, they have an important Fig. 4 Bed-by-bed stratigraphic
column of the latest Maas-trichtian–Paleocene strata out-cropping on the northern side of the Tamezzakht area (see de-tailed geologic map, sector A, Fig. 2) and photographic illus-tration of some key surfaces (S1-S5) and key facies (see also Fig. 11). The S2 surface is ex-pected to correspond to the K/T boundary (see also Fig. 5). The majority of calciturbidites dis-play graded-bedding and well-developed Bouma-sequence di-visions. However, we prefer to use the facies-tract scheme as described by Mutti (1992, his Fig. 31) and to adopt for this an open nomenclature (e.g., c.1-c.4) in order to take into ac-count the change affecting the material delivered at the source area. Photograph legend:Zo: Zoophycos,Th: Thalassinoides, Cht: Chondrites targionii (BRONGNIART),Chi: Chon-drites intricatus (BRONG-NIART)
bearing on the paleogeographic reconstructions (see be-low).
In thin-section, the c.1 division exhibits millimetric to centimetric clasts of glaucony crusts and abundant glau-conite grains. In contrast to the lithoclasts, which had suffered alteration in paleosoils, these grains are rounded, limpid and show no sign of weathering. They are likely to be derived from adjacent shelves. Most of them may be assigned to the shallow-water, mature highly evolved– type grains (Odin and Matter 1981; Hesselbo and Hugget 2001), which are well known to develop during trans-gressive phases and under suboxic, sediment-starved en-vironments (e.g., Kitamura 1999; Hesselbo and Hugget 2001). This result is consistent with that obtained from ichnological data.
A conspicuous c.2 bed, lies just below the surface S2 (possible K/T boundary, Figs. 4, 5). This division consists exclusively of near-equigranular, red and green, centi-metric mud clasts (“kaleidoscopic” breccia, Fig. 4), which are likely derived from the underlying strata or from the same formation. Generally, muddy sediments resist cur-rent reworking due to their high shear strength, a fact that
leads us to suggest seismic instability and/or huge storm events as the possible triggering mechanisms for c.2 beds. The division c.3 is made up of parallel- to cross-lam-inated, fine-grained sandstones. It consists of a mixture of angular fine-grained quartz and lithoclasts, within a fer-ruginous carbonate matrix. The c.4 division consists of yellowish to light-coloured, structureless carbonate mud, with a more or less important amount of fine-grained quartz. Thus, it recalls the key bed 1 intercalated in the upper part of the underlying formation (GPF).
Ichnofabric features allow distinguishing four main types of surfaces (S1-S4, see Fig. 4 for their vertical distribution).
S1-type surfaces
Nearly exclusive assemblages of Chondrites isp. (both
large and small forms) dominate S1-type surfaces and
mediumZoophycosranging from 10 to 30 cm in diameter.
The former ichnotaxa occur densely in near-surface po-sition, whereas the second may extend down for about Fig. 5 Upper half of the Slope Calcarenite Formation (SCF,
com-pare with Fig. 2) showing from the base onwards: a The strati-graphic interval (rectangle) assumed to enclose the Cretaceous– Tertiary boundary (K/T). The bed K (Cretaceous) has yielded a specimen ofAbatomphalus mayaorensis(BOLLI) (in thin-section), whereas the red and greenish marls immediately underlying the bed T (Tertiary) have yielded planktonic foraminifera of early Pale-ocene in age (see Table 1 for additional dating below the bed K);b Eastward-thickening bed set (dashed lines) giving evidence of de-position in slope settings. The majority of beds consist of the three lower divisions distinguished in Fig. 3 (c1-c3, interval III);cThe key bed 3 (KB.3), which is a graded, metre-thick, turbidite event
dominated by a conspicuous red sandy division (see Fig. 3: interval III, c3 division). The top surface of the latter is of the S3-type, finely and densely bioturbated (Fig. 11,4). NumerousZoophycos subsequently penetrated this upper division (see also the corre-sponding photo in Fig. 3).BClose-up view of the interval enclosing the K/T boundary (rectangle in photo A). Hammer indicates the stratigraphic level possibly corresponding to the K/T boundary. This level is a distinctly Fe-coated hardground (S2 surface in the text) that fossilizes strange ripple-like structures originating from small-scale slumping (see photographs in Fig. 3). These strange structures allow to recognize this surface laterally along the quarry located in the northwestern part of the Tamezzakht area
10–20 cm and generally maintains a near-vertical con-nection with the bed surface. It is striking to note that
nearly all the specimens observed are Spirophyton-like
forms (as described by Gaillard and Olivero 1993; Uch-man 1998), which are believed to preferentially develop in firm substrates (Gaillard and Olivero 1993; Olivero
1996; MacEachern and Burton 2000). Chondritesisp. is
well known to colonize organic-rich sediments in oxygen-poor, quiet, deep-water environments (e.g., Ekdale and Mason 1988; Vossler and Pemberton 1988; Wetzel 1991). Otherwise, the association of these two ichnotaxa recalls the Chondrites/Zoophycos ichnoguild, which has been assigned to near-inhospitable environmental extremes (Bromley 1996). It may indicate that oxygen-poor con-ditions developed rapidly after the turbidite deposition (Wetzel and Uchman 2001:180). This satisfactorily ex-plains why forms that require fully oxygenated conditions
such as Thalassinoides are absent (e.g., Savrda et al.
1991; Ozalas et al. 1994; Savrda 1995). Bed-by-bed sur-vey shows that S1-type ichnofabric commonly occurs in the muddy upper division of the graded decimetre-thick beds (Fig. 4, division c.4 of the facies tract II), which is known to have been derived from nutrient-rich, upper slope pelagic oozes (see synthetic model developed by Wetzel and Uchman 2001). Nutrient availability in the sediment, if not pre-consumed by “bulldozing” pascichnia (see below), seems to be the most required condition for
these sessile chemichnia/fodinichnia (large Chondrites,
Zoophycos). We know also, that such a condition is met in oxygen-poor deep-water environments where no “burn-down” phenomenon occurs (Wetzel and Uchman 2001).
S2-type surface
The S2-type surface corresponds to the surface confined within the Cretaceous–Tertiary transition zone (ca 50 cm) or possibly to represent the K/T boundary itself (see Fig. 4 and biostratigraphic data in Table 1). It is light-grey co-loured and displays conspicuous synsedimentary “slump-head” structures covered with patchy, rust-coloured Fe-coating. These omission features show that the surface reached at least the firmground stage. Strikingly, it con-tains a dense, homogeneous grazing ichnocoenosis
rep-resented near-exclusively by very small Planolites in
near-surface position. They never exceed 1 mm in di-ameter and are not compacted. All tubes are unlined, with a smooth surface and a structureless filling. They are straight or gently curved and consist of the same mud-stones as the surrounding matrix. Thin-sections show no distinct internal structure, which indicates softground bioturbation that occurred immediately after turbidite
deposition. Scarce small Zoophycos are overprinted on
the Planolites, with their spreiten being sharply marked by ochre-red shales. This clearly points to a further stage of colonization. The S2-type surface also contains spaced
long tubes of Ophiomorphaisp. in sharp epichnial
posi-tion filled up with coarse grainstone, which points to a subsequent burrowing stage piping down from the
over-lying strata, since the corresponding producers are well known to commonly act as multi-layer colonizers (Uch-man 1995, 1999; Wetzel and Uch(Uch-man 1998, 2001).
According to Wignall (1991:268) small Planolites
represents the last oxygen-deficiency – resistant
ichno-coenosis occurring close to the extreme levels of O2
-de-pletion. Savrda (1998a, b) showed that the small
Plano-lites ichnocoenosis (ichnocoenosis 2 of Savrda 1998b:
142) ranges close to theChondritesichnocoenosis within
poorly oxygenated environments. Olriz and Rodrguez-Tovar (1999) have come to a similar conclusion in upper
Jurassic pelagic sediments. Planolites ichnoguild also
points to quiet water settings (Bromley and Ekdale 1986; Bromley 1996). Accordingly, the S2-type surface would record rapid oxygen depletion achieved as early as during the softground stage, like in the case of the preceding surface (S1).
S3-type surfaces
S3-type surfaces are by far the richest in trace fossils. They developed on ochre-red, shaly sandstones (top of division c.3 of facies tract III, Fig. 4), and record very dense and thin biodeformational structures with no dis-tinct outlines, probably because they were produced in a
soft substrate (Fig. 11, Pictures 1–4, 6). Cross-cutting
relationships indicate that this stage of dense churning was followed by spaced grazing trace fossils of mainly
echinoids (Scolicia). These are, in turn, commonly
cross-cut by tracemakers producing numerous simple or paired holes ranging from 0.5 up to 4 mm in diameter (probable
Arenicolitesisp.and/orDiplocraterionisp., respectively). These dwelling structures were produced after the bull-dozer effect of the churning tracemakers has ceased.
Thalassinoides isp. tunnels (probably Th. suevicus (RI-ETH) see Uchman 1995) represent the latest stage of colonization and show a muddy filling that sharply con-trasts with the surrounding sandy matrix. It gives evi-dence that subsequent colonization occurred during fir-mground conditions (see Savrda et al. 2001a, b as well as MacEachern and Burton 2000 for similar depositional
slope settings). Other epichnial Thalassinoides exhibit a
coarse-grained calcarenite filling, that commonly derive from by-passing sediment, which fill open burrows al-ready preserved in relatively stiff substrates. This fact provides additional support for the attribution of these
Thalassinoides to the Glossifungites ichnofacies (as em-phasised also by e.g., Savrda 1995; MacEachern and Burton 2000; Savrda et al. 2001a, b).
Ichnofabric of this surface type may be interpreted
based upon the presence of Thalassinoides, which
clas-sically points to well-oxygenated environments. Since oxygenation did not exert a limiting control, dense and thin bioturbation in near-surface position could be related to the competition for nutrients, probably under oligo-trophic to poorly oligo-trophic conditions, a fact that may be suggested from the ochre-red colour of the sediment.
S3-type surfaces also record a post-colonisation stage marked by Fe-coating, a feature testifying to inhospitable conditions due to extreme oxygen depletion.
S4-type surfaces
S4-type surfaces lie in the upper part of the formation (ca. 1.5 m) and terminate grey to dark-coloured, centimetre-thick beds. They display dense, small grazing trace fossils of unknown ichnotaxa, which cross-cut each other and
recall the small Planolites-dominated ichnocoenosis of
the S2 surface in being produced by the same tracemaker. Trace fossils are straight to gently curved, and correspond to dragging structures (1 to 4 mm in width and 5 to 15 cm in length) printed in a more or less firm substrate. They indicate an opportunistic colonizer rapidly invading the substrate during a specific stage of omission history.
Interpretation of these surfaces in terms of oxygen and/ or food availability seems to us difficult, owing the ab-sence of the preceding marker ichnotaxa. Nonetheless, absence of a Fe-crust suggests that they have not expe-rienced a protracted omission history, as was the case for the preceding ones.
Calciturbidite Formation (CF, middle–late Paleocene)
The CF consists of about 20 metric calciturbidite beds separated by thin intercalations of green marls. It starts with a sudden gravity-flow event reworking decimetric, red mud-pebbles (out-sized mud pebbles, Fig. 4) and a mixture of carbonate clasts. Outcrop survey shows that this first bed ravines the preceding Green Pelite Forma-tion (GPF) in the northwestern side of the Tamezzakht area, with the SCF being missing.
As in the case of the underlying strata (SCF), petro-graphic evidence shows that these clasts were inherited from the Triassic–early Jurassic, massive carbonate for-mations, mainly dolomites and white massive limestones,
as well as from late Jurassic pelagic units, namely
Cal-pionella- and/or Saccocoma-rich mudstones. The abun-dance of rust-coloured, pedogenic clasts is noteworthy. It may indicate that this clastic material was derived from an adjacent emerged area during an incipient flooding stage (i.e., “transgressive washing” concept of El Kadiri et al. 2003; “shelf sweep” process discussed by Carannante et al. 1999). Attached facies tracts show that the coarsest basal division (division Cg in the facies tract IV interval, Fig. 4) grades up into a greenish, glaucony-rich, bioclast-dominated grainstone (division c.1, facies tract IV), which in turn sharply passes upwards to black mudstones rich in
Microcodium fragments, fine-grained quartz and small planktonic foraminifera. In spite of this sharp grading, no detachment plane has been activated between divisions c.1 and c.3. Thus, they recall the F4-F5 couplet of Mutti (1992) i.e., S2-S3 couplet of Lowe (1982), and allows us to interpret this thick-bedded formation as resulting from relatively proximal gravity flows, the travelling distances
of which were too short to allow their grain populations to be laterally detached. This phenomenon may also be ex-plained with respect to the initial volume of the parent flows, since generally the greater the volume of reworked sediment, the more travelling distance is required for the detachment of the parent-flow divisions.
Bed-by-bed analysis shows that this formation can be split into four distinct bed sets with decimetre green-shale intervals in between. Surface analysis shows that each bed-set is punctuated by a heavily bioturbated omission surface (e.g., S5a and S5b, included in Fig. 4), with its internal bed surfaces being either amalgamated or non-bioturbated to poorly non-bioturbated and having experienced no significant omission history. Thus, considered sepa-rately, each of these depositional packages resulted from high frequency turbidite events. This formation displays an overall thinning-upward trend of the bed sets and the shaly intervals in between (bed sets: 5, 3, 1, 0.5 m and shaly intervals: 1, 0.25, 0.1 m, respectively).
S. 5a and S. 5b surfaces exhibit near-identical ichno-fabrics that, at first sight, recalls the preceding S3-type surfaces. Cross-cutting relationships help to recognize the following colonization suite: (1) A softground to early firmground stage with dense, thin biodeformational
structures, which are overprinted byScolicias.l. (Uchman
1995, 1999), Chondrites targionii (BRONGNIART),
Zoophycos (Spirophyton-like form), and spaced Rhizo-corallium. Spreiten of these are, in turn, partly destroyed by fine tangled fodinichnia produced by a near-surface, small tracemaker. The surface S5a lies on a centimetric
bed, on the sole of which dense Halopoa imbricata
TORELL are preserved in hypichnial semi-relief (near-identical trace fossils are presented by Uchman 1998:115, his Fig. 9A). (2) A firmground stage with numerous single
or paired holes (probable Arenicolites) and spaced
Tha-lassinoides suevicus(RIETH) in epichnial positive semi-relief. Some of the latter trace fossils show a coarse-grained filling sharply contrasting with the surrounding shaly matrix. (3) Small patches of Fe-coating indepen-dently cover the previous traces, a feature that give ad-ditional evidence that these surfaces attained at least the firmground stage (incipient hard-ground of Kennedy and Garrison 1975).
As stressed above for S3-type surfaces, S5a-b
ichno-fabrics may be assigned to theGlossifungitesichnofacies,
which is pointing here to a more or less prolonged omission phase immediately following minor transgres-sive pulses. Thus, it may be assumed that such calcitur-bidite events might be tied to the transgressive-induced export (e.g., Savrda et al. 2001b). Lending support to this is the concomitant reworking of glaucony-bearing bio-clastic material (division c.3, facies tract interval IV, Fig. 4), which is well known to be produced by healthy platforms, in which the carbonate production is com-monly favoured during the transgressive regime (many authors, e.g., Swift 1968; Droxler and Schlager 1985; Nummedal and Swift 1987; Baum and Vail 1988; Plint 1988; F rsich et al. 1991, 1992; Glaser and Droxler 1991; Schlager 1991; El Kadiri 2002a, b). Such an assumption
may also be extended to certain gravity-flows at the re-gional scale, since they may act as the basal conglomerate of transgressive marine formations, a phenomenon that might be interpreted in terms of the “shelf sweep” process as discussed by Carannante et al. (1999) or the trans-gressive washing concept presented by El Kadiri et al. (2003).
Ochre green, carbonate-free siliceous shales, of about 3 metres in thickness, overlie the CF. They contain three spaced centimetric black sandstone intercalations. These
show denseChondrites intricatus(BRONGNIART) close
to the bed surfaces, a position that points to an oxygen-poor to -deficient environment. This shaly interval strongly recalls the above-described late Maastrichtian GPF, which occurred during a regressive regime.
Red Shale Formation (RSF, Eocene–earliest Oligocene)
The Calciturbidite-Intercalated Red Shale Formation (RSF) starts with five decimetric, amalgamated, calcare-ous sandstone beds, which indicates high-frequency tur-bidite events. By contrast to the preceding formations (BSF and GPF), wherein the quartz grains corresponded
to the angular and very fine pedogenic “
quartz-en-charde” (as witnessed by the paleo-silcrete fragments observed in thin-sections), the present sandy facies con-sists of the filonian-type quartz, whose appearance is here the first in the studied succession. These are millimetre-sized, rounded and may be red, white, or black in colour and correspond to the quartz grains classically derived from crystalline basements.
Lending support to this distinction is the common observation that this basement-rock-derived quartz is classically accompanied by a mixture of clasts derived from other older strata, namely carbonates and/or the schists (see below). Petrographic evidence shows that the majority of the reworked lithoclasts were inherited from Liassic strata, particularly from white massive grainstones and light-coloured pelagic mudstones, whereas lithoclasts in the underlying formations were represented chiefly by the Triassic dolomites.
Both the quartz grains and the reworked lithoclasts clearly show that the onset of this formation coincided with an important change in the source area (see inter-pretation below). Outcrop survey and detailed mapping reveal that this thick-bedded sandy interval as well as the underlying green shales may laterally be missing so that the overlying ochre-red shales rest directly onto the pre-ceding Calciturbidite Formation (CF). A low angle in between delineates this unconformity, which is likely to be generated by slope failure processes.
Attached facies-tracts from the downslope grain-seg-regation processes exhibit four divisions (see details in Fig. 6, facies tract interval V), with the coarse-grained basal one (division Cg) being poorly graded and generally small (1–10 cm in thickness), and the sandy one (division Q.2, 30–70 cm in thickness) being structureless to faintly laminated. This contrasts with the overlying c.3 division
that is wavy to parallel laminated. Twenty to 50-cm-thick parallel-laminated green marls represent the uppermost division (c.4).
A decimetre-thick, pink marlstone bed overlies the fifth sandy bed and immediately precedes the first level of the ochre-red, carbonate-free shales. Identical pink marl-stones (background sedimentation b.3, Fig. 6) reappear throughout the lower half of this formation, onto the calciturbidite intercalations. They may also rhythmically alternate with decimetric-scale intervals dominated by the ochre-red, carbonate-free shales, without calciturbidite flows (Fig. 7, i.e., interval between the Fe-crust and bed Kb4a). Additionally, these red intervals may in turn contain, at a smaller-scale, millimetric- to centimetric-scale horizons of pelagic green marls (background sedi-mentation b.4).
Analysis of the ichnological signature within these components and at levels in between helps elucidate the stacking pattern of this alternation:
– The pelagic green marly horizons lie with sharp con-tact onto the ochre-red shales. The sole of the former
commonly records well-preserved predepositional
graphoglyptids, namely Paleodictyon isp. and
Spir-orhaphe involuta (DE STEFANI) (see Uchman
1998:182, his Fig. 88; see also Fig. 12, Picture 4).
Interestingly, these trace fossils, preserved thanks to delicate scouring and casting, testify to very low sed-imentation episodes punctuating deposition of the red shales. In addition, they are well known to colonize
oligotrophic to super-oligotrophic sediments in
starved, quiet deep-water settings (e.g., Wetzel 1991; Uchman 1995; Bromley 1996; Tunis and Uchman 1996a). Internally, the green marly horizons show varve-like laminations and exhibit rare trace fossils. They are opportunistic colonizers favoured by food flux related to short “eutrophic” periods (Fig. 12,
Pictures 1, 2 ). These green horizons progressively
pass upwards into the ochre-red shales. Thus, these two components are likely to have originated during a similar sedimentary event.
– The pink marlstone beds are homogeneous, non-lam-inated hemipelagite deposits. They are heavily
bio-turbated by mm- to cm-sized Phycosiphon hamatum
(FISCHER-OOSTER) and Phycosiphon geniculatum
(STERNBERG) (noPh. incertumis observed; Fig. 12,
Picture 3). Spaced Chondrites intricatus
(BRONG-NIART) cross-cut the former during a subsequent
stage probably of oxygen-depleted conditions.
Phy-cosiphon is randomly inclined and its density pro-gressively decreases downwards. As emphasized by Wetzel and Uchman (2001) this vertical pattern indi-cates sediments, which are both fully oxygenated and rich in food material. Such a condition is met when hemipelagic mud-flows originating from the conti-nental slope undergo both mixing with the oxygenated water-column and deposition sudden enough to trap oxygen and food material. The homogeneous aspect of the present facies duly confirms this phenomenon.
These dense occurrences of Phycosiphonare likely to reflect an opportunistic behaviour by virtue of which the tracemaker rapidly colonized the sediment during the pre-omission stage.
Diverse intercalations of this facies within the lower half of this formation (background sedimentation b.3, Fig. 6), show that it constantly bears this same ichnofabric and might be originated from specific pelagic, carbonate-mud flows independent of that carrying the calciturbidite ones and the green horizons/red shales couplets.
– The calciturbidite flows exhibit centimetre-scale, well-sorted, nummulite-rich arenites (division c.1, facies-sequence intervals VI and VII, Fig. 6) passing upwards
into faintly laminated green marlstones (division c.4, 1–2 cm in thickness). These commonly exhibit dense biodeformational structures (i.e., dense bioturbation with no distinguishable trace fossils) that may be
overprinted by spaced Scolicia and Chondrites
intri-catus (BRONGNIART) during a subsequent soft-ground stage. The soles of these arenites commonly exhibits both: (i) predepositional graphoglyptids (e.g.,
Desmograpton alternum (KSIA˛ Z˙ KIEWICZ), which
are cross-cut by Protovirgularia vagans(KSIA˛ Z˙
KIE-WICZ), and (ii) post-depositional Thalassinoides and
Planolites. At the sole of many arenite beds, Tha-lassinoides has a sharp contact with the surrounding arenite matrix, and is filled with the overlying
ochre-red shales (Fig. 12, Picture 5). This is a firmground
Fig. 6 Bed-by-bed stratigraphic column of the Eocene strata outcropping on the northern side of the Tamezzakht area (see detailed geologic map, sector A, Fig. 2) and photo-graphic illustration of the cyclicity pattern and of some key facies (see also Figs. 12, 13). Facies tracts and facies se-quences as mentioned for Fig. 4. KB4a-c: Key Beds 4a-c; FS (V-IX)/FTD: facies se-quences (V-IX) and facies tract divisions Cg, c.1-c.4
signature that points to the Glossifungitesichnofacies. Fe encrusting may subsequently occur.
– The ochre-red shales are free of carbonate, structure-less and generally lack bioturbation (except some rare
clusters of Chondrites intricatus (BRONGNIART),
Fig. 12, Picture6). This indicates that they were barren
of organic matter (as indicated by graphoglyptid at omission surfaces within these shales). They show no evidence of transportation as gravity mud flows, which points to deposition from suspension. It may be as-sumed that they originated from wind-blown dusts. Commonly such environmental conditions are known to trigger nutrient-bearing upwelling currents and hence eutrophic conditions, which in turn would result
in the deposition of green marls. The green
hemipelagic marly horizons lying at the base of the majority of the red-shale–dominated cycles are con-sistent with this assumption, since they may reflect the short period during which the minor amount of avail-able organic matter was rapidly consumed.
Within the upper third of the present formation three conspicuous, channelled and normally graded calcitur-bidite beds occur (ca. 100–70 cm in thickness, Fig. 7, beds
KB4 a, b, c). The two lower ones consist of five distinct divisions (see attached-facies tract-interval VIII, Fig. 6). Unsorted, poorly graded, grain-supported conglomerates dominate their lower half (division Cg) that abruptly passes up into a nummulite-rich grainstone division (c.2). A similar sharp contact (potential detachment plane) ex-ists between divisions c.2 and c.3, which consist of nummulite-rich, structureless arenites and finely lami-nated mudstones, respectively.
The first bed ends with a very thin green marly division (1 – 3 cm in thickness). This displays dense
biodeforma-tional structures overprinted by spacedScolicia priscaDE
QUATREFAGES, before being covered with a thin Fe-crust. The second ends with near-planar, laminated shaly horizons, the topmost of which shows patchily distributed
Phycosiphon incertum FISCHER-OOSTER and spaced
cylinders of Thalassinoides suevicus (RIETH). The
un-derlying horizons are dominated byChondrites intricatus
(BRONGNIART) that were preceded by large circular
Rotundusichnium zumayaensis(GOMEZ DE LLARENA).
In some cases, Naviculichnium marginatum KSIA˛ Z˙
KIE-WICZ may cross cut the latter trace fossil. No Fe crust occurs.
These ichnological features show that the first surface underwent a more rapid oxygen-depletion than the second (and probably also a more prolonged one as witnessed by the Fe-crust). This exhibits a progressive ichnological
evolution between two end-members, namely
Phy-cosiphon, the most demanding in terms of both food and
oxygen, andChondrites, which resists restricted ones.
The third bed is a remarkable debris flow with out-sized, ochre-red mud clasts, derived certainly from un-derlying strata of the same formation. This bed contrasts with the two preceding clean grain-flows in being free of coarse-grained carbonate lithoclasts, but recalls them by the texture of c.1 and c.2 divisions. Outcrop survey of this key level shows that it may laterally be coarser and
transform into an olistostrome-like gravity event
(Fig. 8B), precisely in the southern part of the Tamez-zakht area, where it contains meter-sized boulders inher-ited from the Calciturbidite Formation (CF). Here, the overlying ochre-red shales may independently rest onto the Green Pelite Formation (GPF) or the Black Shales one (BSF). Both the low-angle and the important hiatus in between (RSF/GPF-CF-BSF) led us to assign such an unconformity to the “hidden discontinuity” in the sense of Clari et al. (1995:108), the genesis of which is linked to slope-failure processes. At some localities where no de-bris flow delineates it, this discontinuity passes unnoticed between the monotonous ochre-red shales and the Calci-turbidite Formation (CF).
Marlstone-and-Sandstone Formation (MSF, early Oligocene–early Burdigalian)
The Marlstone-and-Sandstone Formation (MSF) overlies the RSF with an abrupt change in colour, well delineated in the field (Fig. 8A). It consists of well-developed Fig. 7 General view of the Red Shale Formation (RSF) along a N/
S-oriented quarry (compare with Fig. 4). The “double-bed” on the lower left corresponds to the top of the underlying formation (CF). It is covered by siliceous green shales, which are completely eroded on the lower right (south) by the early Eocene amalgamated sandstone-beds. These may unconformably rest onto the Calcitur-bidite Formation (CF) through a hidden discontinuity (HD). The red-shale – dominated middle interval (interval VII, Fig. 6) is preceded by a well-delineated Fe-horizon (Fe-crust) resulting from the iron-staining of the upper half of a decimetre-thick calcitur-bidite bed. Three channelled, coarse-grained calciturcalcitur-bidite events occur in the upper part of this formation (interval VIII, Fig. 6): KB4a, KB4b and KB4c, with the latter being poorly contrasted in the field due to the red colour of its coarse-grained mud-clast-reworking division (MCg, Fig. 6). Total height of the quarry: 30 m
rhythmic alternations of fine-grained sandstones, yellow marls and light-green marlstones (ca. 80 m in thickness). While the thickness of these alternating facies remains vertically thoroughly constant, it undergoes a significant change within individual cycles. In addition, the stacking pattern of the latter allows three main members to be distinguished (Fig. 9, cyclicity pattern change throughout the MSF).
Transitional Hemipelagic Member (THM, early Oligocene)
The Transitional Hemipelagic Member (THM) consists of centimetric- to decimetric-scale (mainly) cycles domi-nated by homogeneous to faintly lamidomi-nated, light-green marlstones. Each of these cycles starts with a centimetric sandstone bed, which is immediately followed by a yel-low, marly millimetric horizon (Fig. 9). The lower cycles Fig. 8 General view of the distinct facies change across the
boundary between the Red Shale Formation (RSF, Eocene–early Oligocene) and the yellowish Marl-Sandstone Formation (MSF, middle Oligocene–early Burdigalian), with the Transitional Hemipelagic Member (THM) at the base of the latter. Along the southwest side of this same outcrop the MSF unconformably rests on distinct levels of the RSF and then on the two basal formations (GPF, BSF, see also Fig. 1A).BExample of a chaotic-breccia lens
derived from the underlying CF (late Paleocene) and embedded within the upper part of the RSF (late Eocene levels). This resed-imentation event may be correlated with coeval coarse-grained debris-flows occurring in the Dorsale Calcaire and in equivalent successions in the Predorsale domain close to the Eocene–Oligo-cene boundary. It also may be correlated with the turbidite event KB4c (see Fig. 7)
Fig. 9 Evolution of the cyclicity pattern throughout the main for-mations of the Tamezzakht succession and possible facies-corre-lation between their components. Change affecting the cyclicity pattern might be an alternative useful tool of interpreting facies changes and the factors controlling the material delivered at the source area, especially in the case of hemipelagite-dominated
successions wherein the reduced volume of the turbidite flows do not allow the facies sequence/facies tract concept to be fully used as a predictive method. RS-1: lower half of the Red Shale Formation; RS-2: upper half of the Red Shale Formation (other abbreviations as in Fig. 2)
still show patchy red-coloured levels resulting in a var-iegated, purple colour at the outcrop scale. This fact suggests that these green marlstones derived from the preceding ochre-red shales via “discolouration” (partly, due to Fe-pigment–reduction). By comparison with the cyclicity pattern in the underlying formation, it may be assumed that the ochre green shales would correspond precisely to the expansion of the green hemipelagic horizons lying at the base of the ochre-red shales.
Surface analysis shows scarce trace fossils, represented
by rare post-depositional Planolites on the sole of
sand-stone beds and rare Phycosiphon incertum
FISCHER-OOSTER on or near their top. Both do not record sig-nificant omission surfaces, but may indicate that the sandstone-bed events were punctuating the marly ones. A possible interpretation of this marl/sandstone cyclicity pattern is proposed hereafter based on much more com-plete ichnological data (see below the Siliceous Marly Member). The yellow/green marl boundary is either dif-fuse or planar and shows no trace fossils. The absence or scarcity of trace fossils within the marly intervals and between them are likely to be linked to the following controlling factors:
(i) The negative impact of the abrupt increase of sed-iment input on the benthic food resources (Savrda et al. 2001b: 54) and/or, (ii) the muddy substrate that is here too thick to favour sandy-substrate burrowers (as stressed by Tunis and Uchman 1996b: 185), and/or (iii) the relative shortage of dissolved oxygen, which is a common feature in “eutrophic” green shales.
Marly Member (MM, Middle Oligocene?)
The Marly Member (MM, ca. 25 m in thickness) develop from the underlying one through a rapid decrease in thickness of the green-marlstone, with a slight increase in the thickness of the yellow one, which results in a yel-lowish centimetric-scale, sandstone/marl alternation. This facies change coincides with the onset of a second type of dark green shales that are randomly interlayered as
decimetre- to metre-spaced, dm-thick intercalations
within the whole of this member. Contrary to the former shales, the dark green shales are highly laminated and show a slight grading from their very base. This is thor-oughly planar and strongly suggests that the dark lami-nated shales were detached from a different kind of par-ent-flow, whose textural composition is independent of that resulting in the general marl/sandstone-alternation regime.
As was the case for the preceding member, no trace fossils are preserved within the homogeneous marly in-tervals, whereas the sandstone beds commonly display on their sole pre-depositional trace fossils corresponding to
either Scolicia strozzi (SAVI & MENEGHINI) or
Planolites isp. The corresponding bed surfaces may be
sparsely colonized by Phycosiphon incertum
FISCHER-OOSTER. In comparison with the underlying member, such an ichnological signature points to a relatively more
lowered sedimentation rate, a fact that may otherwise be witnessed by the marked thinning of the marl/sandstone
cycles. Importantly, the presence of Ph. incertum
indi-cates a certain tendency towards better bottom-water oxygenation (e.g., Tunis and Uchman 1996b: 184).
Sandstone Member (SM, late Oligocene Aquitanian?)
Five-m-thick couplets of micaceous sandstone/shale split into four intervals the background marl/sandstone alter-nation (Fig. 10 presenting the bed-by-bed column of the last interval). These are 5 to 10 m in thickness and differ from the underlying member by the sandstone beds, which become thicker (Fig. 9). Strikingly, the majority of the sandstone beds are not graded to poorly graded, ho-mogeneous to faintly laminated. The lack of the parallel-to cross-laminated structures (the classical “Tc” and “Td” Bouma divisions) that typify the outer fan deposits, does not allow us to consider them as detached from the upper part of low-density turbidity currents. Wood debris is frequently trapped within the sandy matrix, which re-quired moderate to weak suspension-segregation. Such a type of fine-grained sandy deposits likely derives from bed loads that underwent a mechanism of deposition similar to grain-flow frictional-freezing (Lowe 1982). They should be distinguished from the classical base-missing Bouma’s sequences that originate from low-density turbidite flows (i.e., suspension loads). Ichnolog-ical features presented below lend support to this inter-pretation (see bed-types 2 and 3).
Bed surfaces exhibit a more pronounced ichnological record, which provides evidence for very low sedimen-tation regime occurring both before and just after the sandstone turbidite events. Ichnological signature on both the top surface and on the sole of the successive sandstone beds, allows the comparison of the pre- and post-depo-sitional ichnological record. This leads to the recognition of six main types of beds within each sandstone/marl interval. Depending upon their relative occurrence from the base onwards, these bed types are as follows:
1. The first type corresponds precisely to those beds that directly overlie the metric-scale micaceous shales. Their sole casts giant winding, semi-relief structures
(ichnotaxon indet. A, Fig. 14, Picture 5), which are
about 12 cm in diameter and 5 cm in height. A well-developed Fe-coating on these trace fossils shows that there was a notable omission phase after deposition of the micaceous sandstones. The corresponding bed top appears relatively smooth with rare or no trace fossils. 2. The second type dominates the two lower marl/sand-stone intervals and occurs in the lower half of the two
last sandstone/marl intervals (Fig. 14, Picture 1). Bed
surfaces show densePhycosiphon incertum
FISCHER-OOSTER, which may be subsequently cross-cut by
spaced Nereites irregularis (SCHAFHUTL). Later,
Ophiomorpha rectus (FISCHER-OOSTER) and/or
independently the two former trace fossils. NoScolicia
are found here. The corresponding soles are dominated
by other post-depositionalOphiomorphaisp.
Phycosiphon (produced by a single-layer colonizer) is known to require both well-oxygenated and nutrient-rich sediments; a double condition met when the original gravity flow undergoes deposition sudden enough to trap nutrient particles and dissolved oxygen (see references
above). Additionally, Ophiomorpha is a bulldozing
(Uchman 1999:160), multi-layer colonizer that prefers plant detritus and survives moderate- to high-frequency turbidite events. It occurs in unstable, moderate to rela-tively high sedimentation-rate environments (Uchman 1995, 1999).
3. The third type is common in the upper half of the four
sandstone/marl intervals (Fig. 14, Pictures 3, 6). It is
also typified by near-surface, dense Phycosiphon
in-certumFISCHER-OOSTER that are commonly
cross-cut by Nereites irregularis (SCHAFHUTL) and
during a subsequent stage of colonization by Scolicia
vertebralis KSIA˛ Z˙ KIEWICZ. The soles of the same beds are dominated by pre-depositional domichnia represented by numerous mm-sized mound structures,
that may be either paired (Saerichnites ? isp.) or
clustered traces (Parahaentzschelinia ? isp., Uchman
1995; Tunis and Uchman 1996a). They testify to rel-atively quiet deep-water before the onset of a turbidite event.
Producers of Scolicia vertebralis (solely epichnial;
Uchman 1995, 1999) are known as single-layer colonizers that also preferred plant detritus, but may have been able to survive oxygen-poor conditions. Likely, this is the
cause behind the disappearance of Ophiomorpha (as
pointed out by Uchman 1995, onset of low oxygenation conditions generally results in the replacement of
OphiomorphabyScolicia).
4. The fourth type of bed occurs near the topmost of the
two last sandstone/marl intervals (Fig. 13, Pictures 3,
Fig. 10 Bed-by-bed column of the last marl-sandstone interval of the Sandstone Member (SM) and the lower part of the Siliceous Marly Member (SMM). Between two given micaceous-sandstone intercalations, hemipelagic marls and rust-coloured sandstones
make up a metre-scale interval, that considered alone, records a depositional regime during which both omission duration and oxygen-depleted conditions progressively increase upwards (see text for additional explanation)
Fig. 11 1–3Example of S3-type surfaces of the Slope Calcarenite Formation. Cross-cutting relationships allow distinguishing three main stages of colonization: 1 Surficial dense churning (fine biodeformational structures) produced during an early stage of probably good oxygenation. It reflects a competition for the food flux. Later, this diffuse bioturbation is “peacefully” cross cut by echinoid grazers (the winding trace fossil: Scolicia (Sc.) in the sense of Uchman 1998:153). 2 Small vertical tubes produced by domichnia tracemakers (Arenicolitesand/orDiplocraterion) during a further stage of colonization when the bulldozing effect of the grazers ceased, probably because the substrate entered the firm-ground stage (i.e. Arenicolites and Diplocraterion are common components of the Glossifungites ichnofacies, e.g.; MacEachern and Burton 2000). Note the small holes penetrating previous pas-cichnia.3The preceding domichnia become so dense as to produce new diffuse bioturbation.1–3shows that this colonization suite is only the first step of a protracted omission history. This step was followed by a post-colonization stage marked by Fe-coated, rust-coloured, large areas, a fact that testifies to inhospitable conditions due probably to lethal levels of oxygen depletion (e.g., El Kadiri
2002a, b).4Example of S3-type surface of the Slope Calcarenite Formation, showing a filled tunnel of Thalassinoides suevicus (RIETH) (Th.s.), another domichnion that followed the first stage of dense churning. Note its distinct muddy filling, sharply contrasting with the ochre-red “ background ” facies.5Horizontal U-tube of a Rhizocoralliumisp. (Rh) on a S1-type surface, which is markedly less bioturbated than the preceding ones. Rhizocorallium crosses clusters of small Chondrites (scarcely visible in the photograph) and is in turn cross-cut by spaced small domichnia (simple holes). The S1-type surface is interpreted as undergoing relatively rapid oxygen-depletion preventing intense bioturbation as early as at the softground stage. This is in accordance with the presence of both Rhizocorallium and Chondrites. 6 Another example of S3-type surface (typified by fine biodeformational structures + perforating domichnia) showing a tunnel ofThalassinoides suevicus(RIETH) (Th.s.), subsequently filled with coarse grainstones piped down from the basal coarse division of the overlying stratum. This dis-tinct burrow fill testifies that the corresponding excavator was ca-pable of penetrating firm substrates
Fig. 12 1–2Sole of a thin horizon of hemipelagic green marls (see Fig. 6, term b4) interlayered within the carbonate-free ochre-red shales of the middle interval of the RSF (Eocene). Contrary to the “oligotrophic” ochre-red shales, the green horizons point to short “eutrophic” periods resulting in phases of abrupt food flux. These favoured rapid colonization by opportunists, which are represented here byThalassinoides suevicus(RIETH) and/orPlanolites. In1, the green cylinders show that the corresponding tracemaker piped down into the underlying red shales without reworking them. In-terestingly, this gives evidence that the ochre-red shale deposition was punctuated by omission plus consolidation before being cov-ered by an “eutrophic” marly horizon. This also may be evidenced by the mud-crack – like structures, which are commonly printed on the sole of the green marly horizons.2Close-up view of a similar green surface (sole of a green marly horizon) showing a smooth, branched cylinder ofThalassinoides suevicus(RIETH).3Another example of the “eutrophic” marls punctuating the “oligotrophic” red shale deposition: pink marlstones, which are characteristically
colonized byPhycosiphon incertumFISCHER-OOSTER (arrows, see also a similar photograph in Fig. 6, interval VI). 4 The graphoglyptidSpirorhaphe involuta(DE STEPHANI) on the sole of a centimetre to millimetre green shale horizons interlayered within the middle part of the Red Shale Formation. Such highly patterned traces are known to require stable conditions and to resist long-lasting food-shortage episodes. It gives additional evidence that the red shale deposition was punctuated by omission histories. 5Light-coloured sole of a calciturbidite bed lying near the upper-most level of the Red Shale Formation (above the three turbidite events, see Fig. 7 in the text). It shows post-depositional Tha-lassinoides isp. and/or Ophiomorpha tunnels, both produced by crustaceans that require good benthic oxygenation. Their contrast-ing muddy infillcontrast-ing points to colonization durcontrast-ing firmground con-ditions.6Sole of a thin horizon of green marls (on the upper right) with sparsely visible burrowing, and a cluster ofChondrites intri-catus(BRONGNIART) in the basal levels of a decimetric red shale interval
Fig. 13 1 Paleogene cover of the Internal Dorsale outcropping along the road to television aerial. The yellow sandstones (Middle (?)–late Oligocene to Aquitanian (?) on the left side, correspond to the so-called “Grs Roux”. They sharply overlie green and pink hemipelagic marls of the early to middle Oligocene (Maat et al. 1993). This sandstone event may tentatively be correlated with the onset of near-identical sandstones from middle Oligocene levels (MM) of the Tamezzakht succession.2Close-up view of d to m-sized synsedimentary faults affecting the base levels of the “Grs Roux”, a fact showing that the onset of this facies coincided with a tectonic collapse event.3General view of the last marl/sandstone interval at the uppermost part of the SM (just below the Siliceous Marly Member, SMM). Note the thickening-upward trend of the sandstone beds and their rhythmic alternation with yellowish and green marls. From the base onwards, each cycle is made up of: (i) yellow soft marls (YSM), which rest on a sandstone bed via an omission surface (OS), (ii) Viuela-like Siliceous Marls (VLM), (iii) “Grs Roux”-type sandstone bed (GR) (see also Fig. 9 for
comparison with the cyclicity pattern in the underlying members). The thickest brown bed (BB) capping this interval is the first at the base of the overlying member (Siliceous Marly Member). The latter is typified by both the abrupt change of bed colour and the increase of thickness of the bed sandstones and green marlstone interval.4 example of aScoliciasurface, which typifies the last rust-coloured sandstone beds of the Sandstone Member. This meandering form is a post-depositional variant of the echinoid-produced trace fossil: Scolicia vertebralisKSIA˛ Z˙ KIEWICZ (Sc.v) (e.g., Uchman 1998, p. 155, his Fig. 58B). For another example see Fig. 14 (4).5–7 Examples of trace fossils observed on top surfaces of the light grey-coloured beds of the Siliceous Marly Member. They are poorly to moderately bioturbated. 5: cluster of Phycosiphon incertum FI-SCHER-OOSTER; 6 Ophiomorpha isp. tube with casting of its pelletal wall structure (Ophiomorphais commonly lined with very small muddy pellets); 7 Tube ofPalaeophycus(?)tubulariswith lining consisting of the material of the host rock itself
4; Fig. 14, Picture 4). It is entirely dominated by
abundant pre-depositional bulldozing pascichnia
recorded on the bed sole, namely Scolicia plana
(KSIA˛ Z˙ KIEWICZ) (mainly), Scolicia strozzii (SAVI
& MENEGHINI) andPlanolites isp. The
correspond-ing bed surfaces display other bulldozcorrespond-ing
echinoid-produced trace fossils, namely post-depositional
Scol-icia vertebralis KSIA˛ Z˙ KIEWICZ. Fe-coating
com-monly covers such a type of Scolicia-dominated bed.
5. The fifth type is found only in the topmost of the second and the third sandstone/marl interval (insofar as observed). The beds are rust-coloured and topped with a Fe-coating. They show near-surface, dense colonies of Chondrites intricatus(BRONGNIART), which can
be ascribed to both oxygen-poor (e.g., Bromley and
Ekdale 1984; Olriz and Rodrguez-Tovar 1999) and nutrient-rich sediments (Vossler and Pemberton 1988). 6. The sixth type corresponds to centimetric micaceous-sandstone beds, which are interlayered with yellow
marlstones. They occur in the top of this member, precisely just after the deposition of the last and the greatest micaceous sandstone event (4 m thick). Their upper surface is smooth and shows no trace fossils. In contrast, their sole casts dense, strange centimetric
mound structures (Fig. 14,2). This bed type strongly
suggests that the preceding ecologic niche became liberated after the preceding oxygen-depletion peak and the subsequent onset of an important turbidite event (i.e., the 2-m-thick, micaceous sandstone bed, immediately underlying the stratigraphical top of this member). The latter is known to kill the majority of the single-layer colonizers (Uchman 1995:65). Important-ly, this ichnological event coincides with the facies change resulting in the deposition of the following member.
Fig. 14 (All the beds are from the Sandstone Member, SM).1, 3Top surface of centimetre type-2 and type-3 beds, respec-tively. They are intensely colo-nized byPhycosiphon incertum FISCHER-OOSTER (Phy), which is subsequently cross-cut byOphiomorpha(Oph) and/or Thalassinoides(1) or by Nere-ites irregularis (SCHAF-HUTL) (3).2Strange mound structures on the sole of a mi-caceous, centimetric type-6 bed at the uppermost part of the Sandstone Member (biogenic origin?).4 Scolicia vertebralis KSIA˛ Z˙ KIEWICZ (Sc.v) on the top surface of a type-4 bed at the upper part of the Sandstone Member (see also Fig. 13,3).5 Giant biodeformational struc-tures (ichnotaxon indet. A) on the sole of the basal bed of the last sandstone interval, which directly overlies a 3-m-thick micaceous sandstone turbidite event. These giant structures are cast from the stratigraphic top of the micaceous shales (this is also true for the strange mound structures shown in2above).6 Scolicia vertebralisKSIA˛ Z˙ -KIEWICZ (Sc.v) crossing Ophiomorphaand/or Thalassi-noides(type-3 bed) probably during a subsequent stage of relative oxygen depletion
