1. Introduction
Ichnology is the science of describing traces produced by the life processes of organisms in either ancient (trace fossils) or modern (neoichnology) systems. In recent years, it has become an important tool in the analysis of sedimentary basins, providing valuable information on ecological and depositional parameters active in a depositional setting (e.g. Wetzel, Reference Wetzel1991; Cummings & Hodgson, Reference Cummings and Hodgson2011; Phillips et al. Reference Phillips, McIlroy and Elliott2011; Uchman & Wetzel, Reference Uchman, Wetzel, Hüneke and Mulder2011, p. 518, 533; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014; Riahi et al. Reference Riahi, Uchman, Stow, Soussi and Lattrache2014; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010, Rodríguez-Tovar, Reference Rodríguez-Tovar2022; Cabrera-Ortiz et al. Reference Cabrera-Ortiz, Dorador and Rodríguez-Tovar2023). Trace fossil investigation can thus enhance facies characterisation and the interpretation of both paleoenvironments and paleoenvironmental evolution in a variety of depositional environments (e.g. marine coastal and slope-channel/submarine fan systems or fluvial-lacustrine systems) (Buatois & Mángano, Reference Buatois, Mángano and McIlroy2004, p. 327; Kane et al. Reference Kane, Kneller, Dykstra, Kassem and McCaffrey2007; Hovikoski et al. Reference Hovikoski, Lemiski, Gingras, Pemberton and MacEachern2008; Heard & Pickering, Reference Heard and Pickering2008; Knaust, Reference Knaust2009; Cummings & Hodgson, Reference Cummings and Hodgson2011; Pearson et al. Reference Pearson, Mángano, Buatois, Casadío and Raising2012; Callow et al. Reference Callow, McIlroy, Kneller and Dykstra2013; Knaust et al. Reference Knaust, Warchoł and Kane2014; Buatois et al. Reference Buatois, Mángano and Pattison2019, Reference Buatois, Wetzel and Mángano2020). This enhanced characterisation is due to the recognition that trace fossil producers react and change according to prevalent biotic and abiotic characteristics within a depositional environment (Uchman, Reference Uchman2003; Löwemark et al. Reference Löwemark, Schönfeld, Werner and Schäfer2004; Miller & White, Reference Miller, White and Miller2007, p. 532 ff.; Buatois & Mángano, Reference Buatois and Mángano2011, p. 99, 206; Rodríguez-Tovar, Reference Rodríguez-Tovar2022). Such influencing factors include sedimentation rates, nutrient supply, hydrodynamic energy/water turbidity, oxygenation/salinity of water, topography and substrate type/consolidation, as well as bulldozing or symbiosis (e.g. Wetzel, Reference Wetzel1991; Kane et al. Reference Kane, Kneller, Dykstra, Kassem and McCaffrey2007; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010; Giannetti & McCann, Reference Giannetti and McCann2010; Buatois & Mángano, Reference Buatois and Mángano2011, p.121; Cummings & Hodgson, Reference Cummings and Hodgson2011; Uchman & Wetzel, Reference Uchman, Wetzel, Hüneke and Mulder2011, p. 519; Phillips et al. Reference Phillips, McIlroy and Elliott2011; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014; Buatois et al., Reference Buatois, Almond, Mángano, Jensen and Germs2018, Reference Buatois, Mángano and Pattison2019).
In post-Ordovician turbidites, the preservation of trace fossils belonging to the Nereites ichnofacies is characteristic and generally gives rise to the preservation of pre-depositional (before the emplacement of the next sediment gravity flow) graphoglyptids – intricate nets, spirals and meanders – and post-depositional traces from opportunistic settlers (Fuchs, Reference Fuchs1895; Książkiewicz, Reference Książkiewicz1954; Seilacher, Reference Seilacher1962, Reference Seilacher and Hallam1977a ; Wetzel, Reference Wetzel1991; Uchman, Reference Uchman2003; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014). Extensive research on such traces has enabled the differentiation of subichnofacies, describing three broad settings in deep marine sediments: (i) channels and proximal lobes (Ophiomorpha rudis subichnofacies), (ii) sandy turbidites in the channel periphery/fan fringe (Paleodictyon subichnofacies), and (iii) mud-rich distal turbiditic fan fringe/basin plain settings (Nereites subichnofacies), although other subdivisions based on ichnofabrics have also been frequently used (Seilacher, Reference Seilacher1974; Uchman, Reference Uchman2001, Reference Uchman2009; Heard & Pickering, Reference Heard and Pickering2008; Bayet-Goll et al. Reference Bayet-Goll, De Carvalho, Moussavi-Harami, Mahboubi and Nasiri2014, Reference Bayet-Goll, Monaco, Jalili and Mahmudy-Gharaie2016; Heard et al. Reference Heard, Pickering and Clark2014; Knaust et al. Reference Knaust, Warchoł and Kane2014; Buatois et al. Reference Buatois, Mángano and Pattison2019; Rodríguez-Tovar, Reference Rodríguez-Tovar2022). Variability, however, can be even greater, with trace fossils originally characteristic of other settings found across a broader range of environments depending on ecological preferences, variability/opportunity and transport or trace fossil assemblages changing over geological time periods depending on producer proliferation, existence and behaviour (Kane et al. Reference Kane, Kneller, Dykstra, Kassem and McCaffrey2007; Buatois et al. Reference Buatois, Mángano, Brussa, Benedetto and Pompei2009; Uchman, Reference Uchman2009; Cummings & Hodgson, Reference Cummings and Hodgson2011; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014; Fan & Gong, Reference Fan and Gong2016). Apart from the characterisation of the deep marine depositional setting itself, the depositional media (e.g. deposits derived from bottom currents, or pelagic and gravitational processes) can also be further characterised by the study of trace fossils (Rodríguez-Tovar, Reference Rodríguez-Tovar2022) and exert a direct influence on trace fossil distribution (e.g. Buatois et al. Reference Buatois, Mángano and Pattison2019; Bayet-Goll et al. Reference Bayet-Goll, Sharafi, Daraei and Nasiri2023).
The Beni Ider Unit crops out across the NW part of Morocco in an area extending from the W of Tanger to Tétouan in the E, while the Talaa Lakrah Unit crops out in two small areas, one E of Tanger and the second to the NW of the town of Beni Ider. The ages of the successions extend from the Late Cretaceous to the Early Miocene period (e.g. Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Chalouan et al. Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008). While a variety of studies have examined these units comprising a rich ichnofauna, gathering sedimentological, petrographic and biostratigraphic, as well as geochemical data (e.g. Franchi & Vannucci, Reference Franchi, Vannucci, Chiocchini, Franchi, Guerrera, Ryan and Vannucci1978, p. 51-53; Puglisi et al. Reference Puglisi, Zaghloul and Maate2001; Zaghloul et al. Reference Zaghloul, Guerrera, Loiacono, Maiorano and Puglisi2002; El Kadiri et al. Reference El Kadiri, El Kadiri and Rahouti2003, Reference El Kadiri, El Kadiri, Chalouan, Bahmad, Salhi, Liemlahi and Hlila2006; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007), no detailed systematic ichnological analysis has been – to date – undertaken. This is comparable with the prior absence of detailed descriptions of trace fossils in the corresponding Algeciras and Bolonia units of Spain, which has only recently changed (Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; McCann, Reference McCann2021, Reference McCann2023).
The present study focused on those locations containing particularly rich ichnofossil assemblages and compared and linked these ichnological data to important depositional parameters, such as lithology and depositional setting, in order to enable a detailed paleoenvironmental reconstruction for this part of the Maghrebian Flysch Basin. The data gathered were subsequently compared with the coeval Spanish successions to produce a broader stratigraphic and basin developmental overview within the Maghrebian Flysch Basin.
2. Regional geology
The Maghrebian Flysch Basin forming the Intermediate Domain (i.e. Flysch Domain) of the neo-Alpine Orogenic system (Guerrera et al. Reference Guerrera, Martín-Algarra and Perrone1993, Reference Guerrera, Martín-Martín and Tramontana2020, Reference Guerrera, Martín-Martín and Tramontana2021; Martín-Algarra et al. Reference Martín-Algarra, Messina, Perrone, Russo, Maate and Martín-Martín2000; Chalouan et al. Reference Chalouan, El Mrihi, El Kadiri, Bahmad, Salhi, Hlila, Moratti and Chalouan2006, p. 161; Puglisi, Reference Puglisi2014; Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020, Reference Martín-Martín, Perri and Critelli2023b ) was a NW-SE trending deep-marine trough, extending from modern-day Spain and Morocco to Italy (Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020) (Fig. 1). The deposits of the basin comprise a range of generally Cretaceous- to Miocene-age calcareous and siliciclastic sediments (Critelli & Martín-Martín, Reference Critelli and Martín-Martín2022). These sediments are derived from either the external or internal domains, located to the South and North of the basin, respectively. The internal domain comprises three superimposed structural complexes (Negro et al. Reference Negro, Beyssac, Goffé, Saddiqi and Bouybaouène2006; Zaghloul et al. Reference Zaghloul, Critelli, Perri, Mongelli, Perrone, Sonnino, Tucker, Aiello and Ventimiglia2010; Vitale et al. Reference Vitale, Zaghloul, D’Assisi Tramparulo and El Ouaragli2014, Perri et al. Reference Perri, Martín-Martín, Maaté, Hlila, Maaté, Criniti, Capobianco and Critelli2022), composed of deeper crustal rocks, rocks of differing metamorphic grade and Mesozoic to Cenozoic sedimentary cover (Durand-Delga & Kornprobst, Reference Durand-Delga and Kornprobst1963; Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Chalouan & Michard, Reference Chalouan and Michard1990; Maaté et al. Reference Maaté, Martín-Algarra, Martín-Martín and Serra-Kiel2000; Martín-Algarra et al. Reference Martín-Algarra, Messina, Perrone, Russo, Maate and Martín-Martín2000; Chalouan et al. Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 206, 209; Zaghloul et al. Reference Zaghloul, Critelli, Perri, Mongelli, Perrone, Sonnino, Tucker, Aiello and Ventimiglia2010; Martín-Martín et al. Reference Martín-Martín, Tosquella, Guerrera, Maaté, Hlila, Maaté, Tramontana and Le Breton2023a). Units of the internal domain are most often associated with an intermediate microplate (Mesomediterranean Microplate, MM) (Guerrera et al. Reference Guerrera, Martín-Algarra and Perrone1993, Reference Guerrera, Martín-Martín, Perrone and Tramontana2005, Reference Guerrera, Martín-Martín and Tramontana2020, Reference Guerrera, Martín-Martín and Tramontana2021), implying multiple oceanic branches of the western Tethys (i.e. the Nevado-Filabríde and Maghrebian-Lucanian oceanic branches) (Guerrera et al. Reference Guerrera, Martín-Algarra and Perrone1993, Reference Guerrera, Martín-Martín, Perrone and Tramontana2005, Reference Guerrera, Martín-Martín and Tramontana2021; Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014, Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020, Reference Martín-Martín, Perri and Critelli2023b ).
Figure 1. Overview of the structural/geological units in southernmost Spain and Northern Morocco. (a) Structural context of the Betic-Rif chain (modified after Vergés & Fernàndez, Reference Vergés and Fernández2012). (b) Major geological units of southernmost Spain and Northern Morocco (Didon, Reference Didon, Saadi, Bensaïd and Dahmani1984, modified) with outcrop locations marked by numbered stars: 1) Spirada quarry, 2) Spirada (N2) road section, 3) Spirada riverbed section, 4) RP4702 road section & 5) SW of Beni Harchan section.
The external domain, in contrast, represents former continental margins that delimited the various sectors of the Neo-Tethys (i.e. Mesozoic to Miocene units of the deformed African NW margin in the Spanish-Moroccan sector of the Maghrebian Flysch Basin) (Lonergan & White, Reference Lonergan and White1997; Martín-Algarra et al. Reference Martín-Algarra, Messina, Perrone, Russo, Maate and Martín-Martín2000; Zaghloul et al. Reference Zaghloul, Critelli, Perri, Mongelli, Perrone, Sonnino, Tucker, Aiello and Ventimiglia2010; Critelli, Reference Critelli2018; Critelli & Martín-Martín, Reference Critelli and Martín-Martín2022; Martín-Martín et al. Reference Martín-Martín, Perri and Critelli2023b).
Sedimentation within the Maghrebian Flysch Basin was mainly controlled by changes in the type and degree of tectonic activity (Guerrera, Reference Guerrera, Chiocchini, Franchi, Guerrera, Ryan and Vannucci1978, p. 45; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020), while the evolution of internal depositional environments depended on both autogenic and allogenic forcing and included ocean and climate dynamics, as well as basin paleotopography and depositional environment-specific processes (Guerrera, Reference Guerrera1981-1982; Thomas et al. Reference Thomas, Bodin, Redfern and Irving2010; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; Abbassi et al. Reference Abbassi, Cipollari, Zaghloul and Cosentino2021; Koch & McCann, Reference Koch and McCann2024).
The Maghrebian Flysch Basin has traditionally been subdivided into an internal (Mauretanian) and external (Massylian) subdomain, with their deposits being supplied from the northern (MM) and southern basin margins (African continent), respectively (Bouillin et al. Reference Bouillin, Durand-Delga, Gélard, Leikine, Raoult, Tefiani and Vila1970; de Capoa et al. Reference de Capoa, Di Staso, Guerrera, Perrone and Tramontana2003; Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Thomas et al. Reference Thomas, Bodin, Redfern and Irving2010; Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014; Fornelli et al. Reference Fornelli, Micheletti, Langone and Perrone2015; Jabaloy Sánchez et al. Reference Jabaloy Sánchez, Martín-Algarra, Padrón-Navarta, Martín-Martín, Gómez-Pugnaire, López Sánchez-Vizcaíno, Garrido, Quesada and Oliveira2019, p. 394; Abbassi et al. Reference Abbassi, Cipollari, Fellin, Zaghloul, Guillong, El Mourabet and Cosentino2022; Koch & McCann, Reference Koch and McCann2023). While Early Cretaceous to Oligocene-age deposits were broadly similar, comprising various clays, marls and calcareous, as well as siliciclastic turbidites (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Puglisi, Reference Puglisi2009; de Capoa et al. Reference de Capoa, D’Errico, Di Staso, Morabito, Perrone and Perrotta2014; Fornelli et al. Reference Fornelli, Micheletti, Langone and Perrone2015), specifically Miocene deposits show diverging characteristics related to the source they are derived from. The Massylian subdomain comprises notably quartzarenitic (polycyclic) sediments (i.e. Numidian Formation in Morocco) supplied from Africa and delivered into the Maghrebian Flysch Basin in a time span ranging from 20 – 19 Ma (Lancelot et al. Reference Lancelot, Reille and Wezel1977; Guerrera et al. Reference Guerrera, Loiacono, Puglisi and Moretti1992, Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; de Capoa et al. Reference de Capoa, Di Staso, Guerrera, Perrone and Tramontana2003; Thomas et al. Reference Thomas, Bodin, Redfern and Irving2010; Fornelli et al. Reference Fornelli, Micheletti, Langone and Perrone2015; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020; Abbassi et al. Reference Abbassi, Cipollari, Fellin, Zaghloul, Guillong, El Mourabet and Cosentino2022; Belayouni et al. Reference Belayouni, Guerrera, Martin-Martin, Le Breton and Tramontana2023). However, since the Numidian unit has recently been described as being in stratigraphic continuity with the Tanger unit (which is part of the (Moroccan) external domain), this would imply that the Numidian unit would similarly belong to this zone and not to the Massylian subdomain (cf. Abbassi et al. Reference Abbassi, Cipollari, Zaghloul and Cosentino2021, Reference Abbassi, Cipollari, Fellin, Zaghloul, Guillong, El Mourabet and Cosentino2022).
The Mauretanian subdomain, in contrast, was supplied from the MM with immature siliciclastics of the Internal Zone (i.e. Morocco: Beni Ider Unit, Spain: Algeciras Unit; comprising Hercynian crystalline basement and (carbonate) Meso-Cenozoic sedimentary cover sediments) (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020).
Source mixing is documented within an intermediate (mixed) sector/zone (i.e. Morocco: Talaa Lakrah Unit, Spain: Bolonia Unit; mixed succession), demonstrating the lateral (palaeogeographic) relationships of internal and external deposits and their depositional systems (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Didon & Hoyez, Reference Didon and Hoyez1978b; Guerrera, Reference Guerrera1981-1982; Hoyez, Reference Hoyez1989; Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014).
The current contribution is focused on the Moroccan deposits of the Mauretanian subdomain (i.e. Beni Ider Unit) and the Moroccan mixed succession referred to as Talaa Lakrah Unit.
3. Stratigraphy of the Beni Ider succession and mixed succession turbidites
The present study examines outcrops from the Beni Ider and Talaa Lakrah units and connects sedimentary environments and processes to the observed trace fossil assemblages. A more detailed account of the stratigraphy of the Beni Ider Unit of the Mauretanian subdomain, as well as the Talaa Lakrah Unit (representing the mixed succession), is provided below (Fig. 2).
Figure 2. Stratigraphic columns of the Jbel Tisirène, Beni Ider and Talaa Lakrah units, as well as the Numidian Formation (Fm). 1: basalts, 2: calcilutites (marls) and radiolarites, 3: marly limestones, grey marls (A: Aptychus; C: Calpionella, N: Nannoconus), 4: turbiditic sandstones and greyish pelites (marl/clay), 5: calciturbidites, marls and breccias (B), 6: sandy and calcareous turbidites with pelites (marl/clay), including Microcodium (M) or larger foraminifers (Fo), 7: varicoloured pelites and siltites with turbiditic sandstones, marly limestones; chaotic breccias (cB) at Eocene-Oligocene transition, 8: sandy and pelitic turbidites (micaceous and lithic-rich), rare calciturbidites and conglomerates, 9: varicoloured or brownish pelites with thin quartz- and calcarenites, rare Tubotomaculum sp. (T), silicified marker-bed (’silexite’) (S), 10: quartzarenites and varicoloured or brownish pelites; Numidian sandstones (Nu). Based on data from Didon et al. (Reference Didon, Durand-Delga and Kornprobst1973), Didon & Hoyez (Reference Didon and Hoyez1978b ), Durand-Delga et al. (Reference Durand-Delga, Gardin and Olivier1999), Guerrera et al. (Reference Guerrera, Martín-Martín, Perrone and Tramontana2005, Reference Guerrera, Martín-Algarra and Martín-Martín2012), Chalouan et al. (Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008), Abbassi et al. (Reference Abbassi, Cipollari, Zaghloul and Cosentino2021, Reference Abbassi, Cipollari, Fellin, Zaghloul, Guillong, El Mourabet and Cosentino2022), Belayouni et al. (Reference Belayouni, Guerrera, Martin-Martin, Le Breton and Tramontana2023).
Figure 3. (a) Arenituba isp. preserved in convex hyporelief, Spirada road. (b) Belorhaphe zickzack preserved in convex hyporelief, Spirada quarry. (c) Chondrites affinis preserved in epirelief, Spirada quarry. (d) Chondrites intricatus preserved exichnially, Spirada road. (e) Chondrites recurvus preserved in epirelief, RP4702 road. (f) Chondrites targionii preserved in epirelief, Spirada road. (g) Circulichnis montanus preserved in convex hyporelief, Spirada quarry. (h) Cochlichnus anguineus preserved in hypichnial relief, Spirada quarry. (i) Cosmorhaphe helminthopsoidea preserved in concave hyporelief, Spirada road. (j) Cosmorhaphe isp. preserved in convex hyporelief, Spirada riverbed. (k) Cosmorhaphe lobata preserved in hypichnial relief, RP4702 road. (l) Desmograpton dertonensis preserved in convex hyporelief, SW of Beni Harchan. Scale bar is 1 cm.
Figure 4. (a) Desmograpton ichthyforme preserved in convex hyporelief, Spirada quarry. (b) Gordia marina preserved in hypichnial relief, Spirada quarry. (c) Halopoa annulata preserved in convex hyporelief, Spirada road. (d) Halopoa imbricata preserved in convex hyporelief, Spirada road. (e) Helminthopsis isp. preserved in convex hyporelief, SW of Beni Harchan. (f) Helminthopsis hieroglyphica preserved in convex hyporelief, Spirada quarry. (g) Lorenzinia carpathica preserved in hyporelief, Spirada quarry. (h) Imponoglyphus isp. preserved in convex hyporelief, Spirada quarry. (i) Lockeia isp. preserved in hypichnial relief, Spirada road. (j) Megagrapton submontanum preserved in hypichnial relief, Spirada quarry. (k) Nereites irregularis preserved in epirelief, Spirada quarry. (l) Ophiomorpha nodosa preserved in convex hyporelief, Spirada quarry. (m) Palaeophycus tubularis preserved in hypichnial relief, Spirada quarry. Scale bar is 1 cm.
3. a. Mauretanian subdomain
This subdomain (in Morocco) comprises the Tisiren Nappe series and the Beni Ider nappe series (Zaghloul et al. Reference Zaghloul, Guerrera, Loiacono, Maiorano and Puglisi2002, Reference Zaghloul, Di Staso, de Capoa and Perrone2007; de Capoa et al. Reference de Capoa, Di Staso, Guerrera, Perrone and Tramontana2003; Durand-Delga, Reference Durand-Delga2006). The Tisiren Nappe series (Jebel Tisirène Unit) shows a range of deposits including Upper Jurassic basalts and radiolarites (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Chalouan et al. Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 235), and Lower Cretaceous calcareous/siliciclastic sediments (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Durand-Delga et al. Reference Durand-Delga, Gardin and Olivier1999; Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Durand-Delga, Reference Durand-Delga2006; Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007; Chalouan et al. Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 235), which are separated from the upper Mauretanian basin fill (i.e. Beni Ider nappe series) by a décollement (Chalouan et al. Reference Chalouan, El Mrihi, El Kadiri, Bahmad, Salhi, Hlila, Moratti and Chalouan2006, p.163, Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 235).
The Beni Ider nappe series (herein Beni Ider Unit) comprises Upper Cretaceous to Aquitanian/Burdigalian-age deposits (Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007). Upper Cretaceous units comprise mainly calcareous sediments, including calciturbidites (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; El Kadiri et al. Reference El Kadiri, El Kadiri, Chalouan, Bahmad, Salhi, Liemlahi and Hlila2006, p. 177). These Upper Cretaceous deposits are overlain by Palaeocene to Eocene variegated clays with intercalated fine-grained arenitic/calcareous turbidites (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005), showing a range of structures/bioclasts (i.e. Palaeocene deposits: reworked Microcodium; Eocene deposits: Nummulites) (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Didon & Hoyez, Reference Didon and Hoyez1978a; Chalouan et al. Reference Chalouan, El Mrihi, El Kadiri, Bahmad, Salhi, Hlila, Moratti and Chalouan2006, p.163, 2008, p. 235). Oligocene units broadly comprise sandy-calcareous and clayey-calcareous turbiditic successions with greenish to reddish pelites (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Chalouan et al. Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 235) that are overlain by varicoloured pelites and siltites with occasionally intercalated turbidites (Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007).
The most characteristic sediments of the Beni Ider Unit are the Late Oligocene to Late Burdigalian deposits referred to as the ‘Beni Ider Flysch Fm’ or ‘Flysch gréso-micacé’ (=Algeciras Flysch Fm in Spain) (Didon, Reference Didon1960; Didon & Hoyez, Reference Didon and Hoyez1978b; Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007, Reference de Capoa, D’Errico, Di Staso, Morabito, Perrone and Perrotta2014; Chalouan et al. Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 235). They chiefly comprise a thick succession (2000-2300 m) of silty-pelitic (marly) and silty-arenaceous turbidites (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Zaghloul et al. Reference Zaghloul, Guerrera, Loiacono, Maiorano and Puglisi2002, Reference Zaghloul, Di Staso, de Capoa and Perrone2007; Guerrera et al. Reference Guerrera, Martín-Martín, Perrone and Tramontana2005; Chalouan et al. Reference Chalouan, El Mrihi, El Kadiri, Bahmad, Salhi, Hlila, Moratti and Chalouan2006, p. 163; Durand-Delga, Reference Durand-Delga2006; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007). According to Zaghloul et al. (Reference Zaghloul, Di Staso, de Capoa and Perrone2007), the Beni Ider Flysch Fm in Late Oligocene times (Chattian) shows primarily alternating marls/mudstones and siltstones intercalated with calcareous sandstones. These deposits evolve into massive or nodular greenish marls and thick-bedded arenitic/pelitic turbidites (comprising feldspathic litharenites) (Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007). The transition from the Late Oligocene to the Early Miocene is marked by an olistostrome deposit (Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007). Aquitanian-Early Burdigalian-age deposits comprise arenitic (mica-rich quartzo-feldspathic litharenitic)/pelitic turbidites with very thick individual beds (up to 8–10 m) of mudstones and siltstones (=’Flysch gréso-micacé’, cf. Didon, Reference Didon1960) (Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007; de Capoa et al. Reference de Capoa, Di Staso, Perrone and Zaghloul2007). These sediments are overlain by Late Burdigalian intercalated amalgamated sub-litharenites (centimetre to decimetre thick) and nodular/massive marls evolving into marl/clay-rich deposits with intercalations of sandstone, siltstone or volcaniclastic beds (‘silexites’) (Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007). These deposits are overlain by more pronounced ‘silexite’ beds interbedded with grey/greenish massive marls (nodular), the latter of which thicken up section (Zaghloul et al. Reference Zaghloul, Di Staso, de Capoa and Perrone2007). Chalouan et al. (Reference Chalouan, Michard, El Kadiri, Negro, Frizon de Lamotte, Soto, Saddiqi, Michard, Sadiqqi, Chalouan and Frizon de Lamotte2008, p. 235, their Fig. 5.23), in contrast, describe this final depositional interval of the Beni Ider Unit to comprise brown pelites, breccias with schist elements and silicious tuffs.
Figure 5. (a) Paleodictyon strozzi preserved in convex hyporelief, Spirada quarry. (b) Parahaentzschelinia isp. preserved in epirelief, RP4702 road. (c) Phycodes bilix preserved in hypichnial relief, SW of Beni Harchan. (d) Phycosiphon preserved in epirelief, RP4702 road. (e) Planolites beverleyensis preserved exichnially, Spirada quarry. (f) Scolicia plana preserved in epirelief, RP4702 road. (g) Protopaleodictyon spinata preserved in convex hyporelief, Spirada quarry. (h) Rhizocorallium jenense preserved in epirelief, Spirada quarry. (i) Skolithos linearis preserved endichnially, Spirada quarry. Scale bar is 1 cm.
Figure 6. (a) Scolicia strozzi preserved in epirelief, Spirada quarry. (b) Spirophycus bicornis preserved in hypichnial relief, SW of Beni Harchan. (c) Taenidium barretti preserved in epirelief, RP4702 road. (d) Urohelminthoida isp. preserved in convex hyporelief, Spirada quarry. (e) Thalassinoides suevicus preserved in convex hyporelief, Spirada riverbed. (f) Zoophycos brianteus preserved exichnially, Spirada quarry. (g) Zoophycos insignis preserved in partial convex epirelief, Spirada riverbed. Scale bar is 1 cm.
3. b. Mixed succession
Deposits of this type are herein referred to as the Talaa Lakrah Unit, after their Moroccan type section, which is also often used as a term when comparing mixed successions deposits of other countries with Moroccan deposits (e.g. Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Thomas et al. Reference Thomas, Bodin, Redfern and Irving2010; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020; Belayouni et al. Reference Belayouni, Guerrera, Martin-Martin, Le Breton and Tramontana2023). Structurally, they form part of the Numidian Nappe (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973) and have been integrated into its stratigraphy (i.e. they are known as ‘Lateral Succession (Type C) of the Numidian Formation’) (Guerrera et al. Reference Guerrera, Martín-Algarra and Martín-Martín2012; Belayouni et al. Reference Belayouni, Guerrera, Martin-Martin, Le Breton and Tramontana2023).
The Talaa Lakrah Unit generally comprises Senonian-age marls, Lower to Middle Eocene marly-calcareous deep-marine sediments and Upper Eocene sediments, which are comparable to those described from the coeval Beni Ider Unit deposits (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973). These deposits are overlain by successions of Oligocene- to Burdigalian-age marls and micaceous sandstones with several intercalated Numidian sandstone beds or generally pass into Numidian Flysch sediments (brownish shales and quartzarenitic turbidites) up section (Didon et al. Reference Didon, Durand-Delga and Kornprobst1973; Didon & Hoyez, Reference Didon and Hoyez1978a; Abbassi et al. Reference Abbassi, Cipollari, Fellin, Zaghloul, Guillong, El Mourabet and Cosentino2022). In the western sector of the Maghrebian Flysch Basin, Talaa Lakrah Unit deposits are mainly of a Chattian to Burdigalian age, while their deposition extends up to the Langhian/Serravalian in the eastern sector of the Maghrebian Flysch Basin (i.e. Southern Apennines) (Guerrera & Martín-Martín, Reference Guerrera and Martín-Martín2014).
4. Depositional setting
The deep-marine sediments of the Maghrebian Flysch Basin were deposited across a range of depositional settings. The turbidites of the Beni Ider (=Algeciras) Unit were deposited in a submarine plain to submarine lobe/fan setting (Guerrera, Reference Guerrera, Chiocchini, Franchi, Guerrera, Ryan and Vannucci1978; Pendón, Reference Pendón1987; Zaghloul et al. Reference Zaghloul, Guerrera, Loiacono, Maiorano and Puglisi2002; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; McCann, Reference McCann2023; Koch & McCann, Reference Koch and McCann2024), with the coarser-grained sediments deposited in a slope or base of slope setting (Zaghloul et al. Reference Zaghloul, Guerrera, Loiacono, Maiorano and Puglisi2002). The mixed succession (i.e. Talaa Lakrah & Bolonia units) sediments were deposited in more distal (or lateral) settings, relative to the Beni Ider Unit (Didon & Hoyez, Reference Didon and Hoyez1978b; Guerrera, Reference Guerrera1981-1982), with material being supplied from the two opposing basin margins (Guerrera, Reference Guerrera, Chiocchini, Franchi, Guerrera, Ryan and Vannucci1978, Reference Guerrera1981-1982; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) and deposited as lobes/fan or submarine plain settings (Guerrera, Reference Guerrera, Chiocchini, Franchi, Guerrera, Ryan and Vannucci1978, p. 47; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; Koch & McCann, Reference Koch and McCann2024). More recently, Koch & McCann (Reference Koch and McCann2024) recognised four specific lobe-related subenvironments (facies associations) in the sediments of the Beni Ider and Talaa Lakrah units, namely, lobe axis, lobe off-axis, lobe fringe and distal fringe settings. The various settings crop out as stacked successions, which can be interpreted in terms of particular phases of lobe development (e.g. lateral lobe migration or aggradation). Table 1 below relates these subenvironments to the outcrops investigated in the present study. Furthermore, trace fossils present in situ are assigned to specific subenvironments. However, since many trace fossils were found in the scree of the outcrops, they could not be assigned to a particular subenvironment.
Table 1. Distribution and characterisation of lobe subenvironments in the Beni Ider and Talaa Lakrah units. Based on data from Koch & McCann (Reference Koch and McCann2024)
Sedimentation within the Maghrebian Flysch Basin was primarily influenced by variations in the type and degree of tectonic activity, related to the various stages of basin evolution. Activity was initially extensional (Cretaceous), prior to passing into the pre-orogenic (Paleocene to Early Oligocene) and synorogenic (Late Oligocene to Early Miocene) phases (Guerrera, Reference Guerrera, Chiocchini, Franchi, Guerrera, Ryan and Vannucci1978, p. 45; Martín-Martín et al. Reference Martín-Martín, Guerrera and Miclăuş2020). Autogenic and allogenic controls (e.g. ocean and climate dynamics) (Thomas et al. Reference Thomas, Bodin, Redfern and Irving2010; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; Abbassi et al. Reference Abbassi, Cipollari, Zaghloul and Cosentino2021; McCann, Reference McCann2023) also played an important role, with submarine lobe switching being primarily controlled by autogenic forcing (Koch & McCann, Reference Koch and McCann2024).
5. Systematic ichnology
The following section provides an overview of all the ichnofossils recorded from the Beni Ider and Talaa Lakrah units in Morocco, with both descriptions and assignments being presented in Table 2. Ichnofossil preservational terminology follows Häntzschel (Reference Häntzschel and Teichert1975) and Ekdale et al. (Reference Ekdale, Bromley and Pemberton1984), whereby traces may be preserved epichnially (bed top) or hypichnially (bed base). More rarely, ichnofossils may be preserved within mudstone (exichnial) or sandstone (endichnial). Distributional information is presented in Table 3 (note: the fossils were left in the field).
Table 2. Systematic ichnology of the Beni Ider and Talaa Lakrah units
Table 3. Ichnogenera from the Beni Ider and Talaa Lakrah units (this paper) and the Spanish equivalent units of the Maghrebian Flysch Basin, showing the ichnogenera distribution across specific outcrops
Footnotes: *Data of the Spanish equivalent units.
Table 4. Ichnogenera from the Beni Ider/ Algeciras and Talaa Lakrah/ Bolonia units of the Maghrebian Flysch Basin, listing their ethological, depositional and morphological characteristics, as well as their abundance in Moroccan outcrops
* Footnotes: Ichnogenera not present in the Moroccan outcrops. Data from Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) and McCann (Reference McCann2023).
‡ Ichnogenera only showing this occurrence in the Beni Ider Unit.
†Key to the occurrence of ichnogenera: abundant = >10, common = 5–10, scarce = 3–5, rare = <3; na = not present in Moroccan outcrops.
6. Discussion
A total of 31 ichnogenera (41 ichnospecies) were recorded from the Beni Ider and Talaa Lakrah units in NW Morocco (Table 2). Of these, the majority are post-depositional, non-graphoglyptid ichnofossils (22 ichnogenera) and are mainly feeding-type traces (fodinichnia, pascichnia) (Table 4). The pre-depositional graphoglyptids comprise 9 ichnogenera and are of particular importance since they belong to the deep-marine Nereites ichnofacies (e.g. Uchman, Reference Uchman2003, Lehane & Ekdale, Reference Lehane and Ekdale2016, Fan et al. Reference Fan, Gong and Uchman2016; although rare shallow-water occurrences have been noted, e.g. Olivero et al. Reference Olivero, Lopez Cabrera, Malumian and Torres Carbonell2010). The graphoglyptid-producing organisms occur across a range of ethologies, including agrichnia, fodinichnia and domichnia (with some authors favouring the former, e.g. Cummings & Hodgson, Reference Cummings and Hodgson2011; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016).
6. a. The Nereites ichnofacies
The various traces recorded from the Moroccan succession range from the ichnogenus Palaeodictyon (typically deep marine) through to facies-crossing ichnogenera (e.g. Helminthopsis, Palaeophycus). The entire assemblage can be considered as belonging to the Nereites ichnofacies, which is typically found in bathyal to abyssal, (well-) oxygenated, very low-energy (with occasional higher energy turbiditic events) marine environments (Wetzel, Reference Wetzel1991; Uchman, Reference Uchman and Miller2007; Buatois & Mángano, Reference Buatois and Mángano2011; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010; MacEachern et al. Reference MacEachern, Bann, Gingras, Zonneveld, Dashtgard, Pemberton, Knaust and Bromley2012).
The post-depositional traces are generally recorded within turbiditic or other sediment density flow deposits (Bromley, Reference Bromley1996, p. 251; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010) and mostly represent r-selected ichnotaxa. Such forms include low-diversity opportunistic settlers, with generalised feeding strategies, that can tolerate high environmental stresses and unstable conditions (Wetzel, Reference Wetzel1991; Pemberton et al. Reference Pemberton, Zhou and MacEachern2001; Rodríguez-Tovar, Reference Rodríguez-Tovar2022).
In contrast, the pre-depositional trace-making organisms are well adapted to living in the oligotrophic, fine-grained sediments (cf. Wetzel & Uchman, Reference Wetzel and Uchman1998; Uchman, Reference Uchman2001, Reference Uchman2003) where they develop their highly specialised feeding strategies (Miller, Reference Miller1991; Buatois & Mángano, Reference Buatois and Mángano2011). These K-selected forms generally comprise high-diversity assemblages (Wetzel, Reference Wetzel1991; Tunis & Uchman, Reference Tunis and Uchman1996; Uchman, Reference Uchman and Miller2007; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012, p. 652; Rodríguez-Tovar, Reference Rodríguez-Tovar2022).
The Nereites ichnofacies is one of the archetypal marine ichnofacies (Seilacher, Reference Seilacher1964, Reference Seilacher1967; Knaust & Bromley, Reference Knaust and Bromley2012, and references therein). The ichnofacies comprises a range of ichnofossils, with the highly patterned graphoglyptids being considered diagnostic. Seilacher (Reference Seilacher1974) noted the presence of two different subichnofacies within the Nereites ichnofacies, namely the Nereites subichnofacies representing a mud-rich fan fringe to basin plain environment (Uchman, Reference Uchman2009), and the Paleodictyon subichnofacies characteristic of thin- to medium-bedded, sand-rich turbidite lobe settings (Buatois & Mángano, Reference Buatois and Mángano2011; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014; Rodríguez-Tovar, Reference Rodríguez-Tovar2022). Subsequently, Uchman (Reference Uchman2001) included a third subichnofacies, the Ophiomorpha rudis subichnofacies, found in medium- to thick-bedded channel deposits as well as proximal lobe and lobe fringe facies (Uchman, Reference Uchman2009; Buatois & Mángano, Reference Buatois and Mángano2011). All three subichnofacies were originally described from submarine fan settings along proximal-distal transects, although variations have been noted (e.g. Heard & Pickering, Reference Heard and Pickering2008, Olivero et al. Reference Olivero, Lopez Cabrera, Malumian and Torres Carbonell2010, Olivero & López Cabrera, Reference Olivero and López Cabrera2023).
6. b. Environmental conditions
Thin-bedded turbidite-rich units often contain ichnocoenoses rich in pre-event graphoglyptids, particularly in Late Cretaceous to Paleogene successions (e.g. Książkiewicz, Reference Książkiewicz1977; McCann, Reference McCann1990; Olivero & López Cabrera, Reference Olivero and López Cabrera2023). The graphoglyptids are usually associated with a range of post-depositional traces, including Nereites, Scolicia and Phycosiphon (e.g. Wetzel & Uchman, Reference Wetzel and Uchman1997; Uchman, Reference Uchman2001, Reference Uchman2003; López Cabrera et al. Reference López Cabrera, Olivero, Carmona and Ponce2008, Olivero et al. Reference Olivero, Lopez Cabrera, Malumian and Torres Carbonell2010, Callow et al. Reference Callow, McIlroy, Kneller and Dykstra2013, McCann, Reference McCann2023). The close association of both pre- and post-depositional traces is indicative of the range of ecological, evolutionary and sedimentary factors, which influence the development of particular ichnoassemblages (Olivero & López Cabrera, Reference Olivero and López Cabrera2023). Typical environmental factors include substrate and substrate consistency, nutrient sources (i.e. benthic food supply), hydrodynamic regime and oxygenation, as well as the frequency and type of depositional events (e.g. Wetzel, Reference Wetzel1991; Leszczyński, Reference Leszczyński1991, Reference Leszczyński1993; Kane et al. Reference Kane, Kneller, Dykstra, Kassem and McCaffrey2007; Giannetti & McCann, Reference Giannetti and McCann2010; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010; Cummings & Hodgson, Reference Cummings and Hodgson2011; Phillips et al. Reference Phillips, McIlroy and Elliott2011; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014, Starek & Šimo, Reference Starek and Šimo2015; Buatois et al. Reference Buatois, Mángano and Pattison2019). Both the invertebrate fauna as well as their behavioural patterns are related to these various factors (e.g. Buatois & Mángano, Reference Buatois and Mángano2011, Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012).
6. b.1. Hydrodynamic regime & turbidite events
As noted in Table 1, the abundance of trace fossils is highest in areas of mixed sandstone-mudstone deposition (i.e. Lobe Off-Axis and Lobe Fringe). While these numbers reflect only the ichnofossils observed directly in the measured sections (as opposed to the material collected from the scree slopes, which could not be directly attributed to a particular facies association), they do indicate that the Lobe Off-Axis and Lobe Fringe settings contained particularly abundant ichnoassemblages. Both environments were marginal to the lobes and, thus, somewhat distant from the main sediment transport routes (i.e. Lobe Axis). These relatively distal locations were presumably characterised by more stable conditions, with a longer colonisation window (sensu Pollard et al. Reference Pollard, Goldring and Buck1993) between the deposition of individual turbidites, as well as generally lower rates of sedimentation. In such settings, gradual decreases in pore water oxygen and food flux would have led to an upward migration of the redox boundary within the sediments, reducing the frequency and activity of large mobile deposit feeders or large bulldozing organisms (where present). Such conditions would have favoured the development of epifaunal grazing trails and trapping or farming graphoglyptid traces, albeit to a lesser degree than might be anticipated from other deep-marine turbiditic environments (cf. Cummings & Hodgson, Reference Cummings and Hodgson2011; Bayet-Goll et al. Reference Bayet-Goll, Monaco, Jalili and Mahmudy-Gharaie2016, Reference Bayet-Goll, Sharafi, Daraei and Nasiri2023; Sharafi et al. Reference Sharafi, Rodríguez-Tovar, Janočko, Bayet-Goll, Mohammadi and Khanehbad2021). A study by Olivero & López Cabrera (Reference Olivero and López Cabrera2023) on a deep-marine channel-levee complex in Argentina also noted a marked paucity of graphoglyptids while post-depositional forms predominated. They interpreted this as being related to the presence of microbial mats and low oxygen conditions within the succession (Olivero & López Cabrera, Reference Olivero and López Cabrera2023). While microbial mats and biofilms are common in a wide range of modern-day sedimentary environments, they have rarely been described from deep-marine successions. Leonowicz et al. (Reference Leonowicz, Bienkowska-Wasiluk and Ochmanski2021) have noted the presence of such mats in a mixed carbonate-clastic deep-marine succession based on the presence of irregular laminae as well as erosional and torn fragments of laminated layers. Such features, however, were not noted from the sediments of the present study, suggesting that conditions differed from those described by Olivero & López Cabrera (Reference Olivero and López Cabrera2023).
6. b.2. Substrate
Substrate is a significant factor both in the preservation and occurrence of ichnofossils (Giannetti & McCann, Reference Giannetti and McCann2010; Buatois et al. Reference Buatois, Mángano and Pattison2019), with both substrate type and consistency being important (Bromley, Reference Bromley1990, Reference Bromley1996; Ekdale et al. Reference Ekdale, Bromley and Pemberton1984; Lewis & Ekdale, Reference Lewis and Ekdale1992; Rodríguez-Tovar & Delgado, Reference Rodriguez-Tovar and Delgado2006). The present succession contained both marls and mudstones, as well as bioclast-rich and siliciclastic sandstones (cf. Table 1 & Fig. 8). In marl-rich turbidites, post-depositional forms (e.g., Chondrites, Nereites, Phycosiphon, Planolites and Scolicia) are generally more prevalent (Uchman, Reference Uchman and Miller2007; Uchman & Wetzel, Reference Uchman, Wetzel, Hüneke and Mulder2011; Rodríguez-Tovar, Reference Rodríguez-Tovar2022). Indeed, marl-rich turbidites have been noted to inhibit preservation, since the turbidity flows are not sufficiently erosive to adequately expose pre-depositional traces for casting.
In terms of the substrate itself, Uchman & Wetzel (Reference Uchman, Wetzel, Davies and Shillito2025) noted that true substrates are difficult to recognise in turbidites. The presence of pre-lithification deformation features in turbidite successions may occur during the emplacement of turbidity currents as a result of shear acting on the syn-depositional seabed (e.g. Collinson, Reference Collinson and Maltman1994; Butler & Tavarnelli, Reference Butler and Tavarnelli2006; Eggenhuisen et al. Reference Eggenhuisen, McCaffrey, Haughton and Butler2010) and the presence (or, indeed, absence) of such features may provide clues with regard to both the rheology of the submarine flows themselves, and more importantly for this study, the rheology of the substrate during deposition (Butler et al. Reference Butler, Eggenhuisen, Haughton and McCaffrey2016). In the present study, kinematic structures (e.g. convolute lamination) within the turbidite beds were common, suggesting that the shearing of the substrate by the passage of erosive and depositional turbidity flows (related to the proximal-distal variations in internal organisation within the turbidity current, Postma et al. Reference Postma, Cartigny and Klevelaan2009) affected the rheology of the substrate. Thus, the substrate in the present setting was most probably a softground or firmground. The relatively isolated distribution of ichnofossils across the various beds would also suggest that there were variations in substrate properties (although the lateral segregation of graphoglyptids may also have been controlled by feeding strategies (i.e. feeding-type amensalism (Boucot, Reference Boucot1981) or trophic-group amensalism (Rhoads & Young, Reference Rhoads and Young1970)) (Leszczynski & Seilacher, Reference Leszczyński and Seilacher1991)).
Substrate instability, as indicated by the presence of kinematic/soft-sediment deformation structures, would have limited the proliferation of trace makers (e.g. Menzoul et al. Reference Menzoul, Uchman, Adaci and Bensalah2022). In addition, the lack of detailed morphological features on the observed traces (e.g. scratch marks) would support the idea of wetter substrates. In contrast, the strategies used by the organisms in the environment (e.g. agrichnia, pascichnia) would suggest firmer substrates. These two contrasting aspects would also support the idea of laterally, and temporally (in the short term), variable substrate consistencies.
6. b.3. Oxygen content
Benthic oxygenation is a significant control on the character of infaunal communities and the ichnofabrics produced (Savrda, Reference Savrda and Miller2007), with intense bioturbation generally indicating O2-rich pore waters while reduced or absent bioturbation suggests O2 depletion or even anoxia (e.g. Bromley & Ekdale, Reference Bromley and Ekdale1984; Savrda & Bottjer, Reference Savrda and Bottjer1986; Savrda, Reference Savrda1992, Reference Savrda and Miller2007; Uchman et al. Reference Uchman, Hanken, Nielsen, Grundvåg and Piasecki2016). Sediment colour has been used as a proxy for O2 content, suggesting that grey-coloured sediments had higher levels of O2. This would correlate with the present study, where such (greenish) grey sediments contained the highest ichnodiversities (with the lowest in black or red sediments), suggesting that O2 levels were higher in the former.
The situation, however, is not always straightforward. For example, bioturbation density and burrow size tend to decrease with decreasing levels of oxygen (Buatois & Mángano, Reference Buatois and Mángano2011; although such conclusions have also been called into question e.g. Smith et al. Reference Smith, A. Levin, Hoover, McMurtry and Gage2000; Levin et al. Reference Levin, Rathburn, Gutiérrez, Muñoz and Shankle2003). In the Moroccan successions, the majority of the recorded ichnofossils were simple (and often smaller) forms, particularly Paleophycus and Planolites, which, according to Casanova-Arenillas et al. (Reference Casanova-Arenillas, Rodríguez-Tovar and Martínez-Ruiz2022), are more tolerant with respect to O2 levels (from dysoxic to oxic). Furthermore, there was little evidence of infaunal burrowing (suggesting low levels in porewater O2). Indeed, ichnofossil preservation in the Moroccan outcrops of the Maghrebian Flysch Basin tended to be mainly epichnial and hypichnial, most probably related to the fact that incoming turbidity currents produced localised oxygenation events (e.g. Giannetti & McCann, Reference Giannetti and McCann2010; Zheng & Cao, Reference Zheng and Cao2024).
6. b.4. Nutrient content
Organic matter within marine environments can be present in different forms – refractory or non-refractory – both of which are derived from different sources and can be variable in the case of specific trophic regimes (e.g., eutrophic vs. oligotrophic ecosystems) (Baudin et al. Reference Baudin, Disnar and Martinez2010; Callow et al. Reference Callow, Kneller, Dykstra and McIlroy2014; Nomaki et al. Reference Nomaki, Rastelli, Alves, Suga, Ramos, Kitahashi, Tsuchiya, Ogawa, Matsui, Seike, Miyamoto, Corinaldesi, Manea, Ohkouchi, Danovaro, Nunoura and Amaro2021). Generally, benthic food content is considered to be a controlling factor on the bioturbation density, with the latter increasing in relation to the greater availability of nutrients (e.g., Leszczyński, Reference Leszczyński1991; Wetzel, Reference Wetzel1991; Leszczyński & Uchman, Reference Leszczyński and Uchman1993; Wetzel & Uchman, Reference Wetzel and Uchman1998; Rodríguez-Tovar, Reference Rodríguez-Tovar2022). Within the study area, bioturbation density is generally very low, with only rare beds containing a range of ichnofossils.
The low density of bioturbation within the succession is also indicative of the sporadic nature of nutrient distribution. The depositional settings are mainly distal lobe environments, and the sediments were generally deposited from low- or high-concentrated flows (Koch & McCann, Reference Koch and McCann2024). However, related units in Spain (cf. McCann, Reference McCann2023) were possibly derived from hyperpycnal flows with the deposits containing concentrations of organic (plant) matter. Plant material is generally rich in refractory organic material and is not considered to be a valuable food source (Giannetti & McCann, Reference Giannetti and McCann2010; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010). Despite this, some ichnofossils (e.g. Ophiomorpha) may be abundant where plant material is present (Uchman et al. Reference Uchman, Janbu and Nemec2004; Uchman, Reference Uchman2009; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010). However, the lack of plant material in the sediments of the present study area, as well as the characteristic ichnofossils representative of the O. rudis subichnofacies, is in marked contrast to the Spanish outcrops (cf. Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; McCann, Reference McCann2023). Clearly, although the general influences on the environments within the basin were similar, the interaction of the various factors affecting ichnoassemblages changed both spatially (potentially related to intrabasinal division, i.e. sub-basins) and also over time.
Of note here is the fact that the levels of organic matter were probably low and heterogeneously distributed across the environment. In general, the presence of graphoglyptids with their specialised feeding strategies can be related to low organic input and nutrient-poor substrates. However, the percentage of graphoglyptids present in the Moroccan succession is low, suggesting that other mechanisms must have played an important role in their distribution.
6. b.5. Basin and lobe development
In addition to the environmental factors (as discussed above) which influenced both the presence of the various trace makers and their activities, the general evolution of the basin into a foreland basin adjacent to a growing orogen may have appreciably influenced both the development and the variety of habitats present, as well as their temporal stability. Indeed, within different basins, tectonic processes have been noted to have affected trace fossil assemblages. Smelror et al. (Reference Smelror, Grenne, Gasser and Bøe2023) in their study of deep-water trace fossils in two Norwegian coeval formations noted significant differences in the ichnoassemblages between the two (one graphoglytid rich, the other with none), which they attributed to possible active tectonic processes (resulting in unstable depositional conditions) (Smelror et al. Reference Smelror, Grenne, Gasser and Bøe2023). More frequent, high volume turbidity currents would have resulted in lower preservation rates and/or proliferation potential for graphoglyptid traces (Miller, Reference Miller1991; Phillips et al. Reference Phillips, McIlroy and Elliott2011) or indeed a limited colonisation window.
The degree of confinement within a basin is one of the most important influences on lobe development (e.g. Zhang et al. Reference Zhang, Wu, Fan, Fan, Jiang, Chen, Wu and Lin2016; Spychala et al. Reference Spychala, Hodgson, Prélat, Kane, Flint and Mountney2017a; Cumberpatch et al. Reference Cumberpatch, Kane, Soutter, Hodgson, Jackson, Kilhams and Poprawski2021; Rohais et al. Reference Rohais, Bailleul, Brocheray, Schmitz, Paron, Kezirian and Barrier2021) and the stacking pattern of lobes (Spychala et al. Reference Spychala, Hodgson, Stevenson and Flint2017b). Basin confinement may thereby result in variations in aggradation and lateral migration due to, for example, lateral-to-downstream gradient or topographic compensation (Gervais et al. Reference Gervais, Savoye, Mulder and Gonthier2006; Prélat et al. Reference Prélat, Covault, Hodgson, Fildani and Flint2010; Zhang et al. Reference Zhang, Wu, Fan, Fan, Jiang, Chen, Wu and Lin2016). The Mauretanian Zone, as well as the Mixed Zone turbidite successions (including the Beni Ider and Talaa Lakrah units), was suggested to have been deposited in structurally restricted sub-basins (Guerrera, Reference Guerrera1981-1982), with both lobe aggradation and lateral migration being important processes (Koch & McCann, Reference Koch and McCann2024). This could have affected benthic communities by limiting the development of particular habitats or contributing to habitat instability. An example of the former would be the marked reduction in distal (fringe) deposits due to flow ponding in restricted settings, thus favouring the predominance of post-depositional tracemaking (e.g. Phillips et al. Reference Phillips, McIlroy and Elliott2011; Knaust et al. Reference Knaust, Warchoł and Kane2014). Instability would increase due to the reduction in nutrients/oxygen due to lobe switching. Such factors (i.e. instability, higher frequency and/or greater volume of sediment delivery) would have been important within the Maghrebian Flysch Basin, specifically in Oligocene to Early Miocene times. While it would appear that these factors contrast with those introduced above (i.e. more sporadic turbiditic events), it is, however, clear that the environment was a very dynamic one and also one which was variable. The degree of variability in terms of turbidity current activity vis-à-vis basin development would have increased the complexity of the system, contributing to the observed differences within the ichnoassemblages present.
6. c. Comparing the ichnofossil records of the Spanish and Moroccan successions within the Maghrebian Flysch Basin
In the Spanish sector of the Maghrebian Flysch Basin, Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) and McCann (Reference McCann2023) examined the ichnoassemblages from the Algeciras (=Beni Ider) and Bolonia (=Talaa Lakrah) units. For the Algeciras Unit, they described 12 or 34 ichnogenera, respectively, while Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) identified 24 ichnogenera within the Bolonia Unit. The present study, investigating the Moroccan equivalent units (i.e. the Beni Ider and Talaa Lakrah units), identified 31 ichnogenera in the Beni Ider and 12 ichnogenera in the Talaa Lakrah Unit. The general percentage of graphoglyptids in both the Moroccan and Spanish sectors is comparable for the Beni Ider and Algeciras units (i.e. about 30%), while the Talaa Lakrah and Bolonia units show some divergence (Talaa Lakrah Unit: 17%, Bolonia Unit: 42%). Similarly, the general distributions of pre- and post-depositional ichnofossils are more variable (i.e. Fig. 7: pre: 0%–30%, post: 38%–67%).
Figure 7. Distribution of pre- and post-depositional ichnofossils within the Beni Ider/ Algeciras and Talaa Lakrah/ Bolonia units of the Maghrebian Flysch Basin. ntotal refers to the total number of ichnogenera present within the various units. Data for the Spanish sector are from Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) and McCann (Reference McCann2023).
To better compare the data from the different studies, Figure 8 shows the various outcrops with their stratigraphic assignations (following Morocco Service Géologique. (1984), Didon (Reference Didon2004) and IGME (2008)), the total number of ichnogenera (pre- vs. post-depositional forms and graphoglyptids), the main associated depositional environments, lithologies and the distribution of the various ethological types. Previous studies in (partly coeval) deep-marine basins (i.e. the Middle Eocene Ainsa-Jaca and Cretaceous-Eocene-age Basque basins) have shown that ichnodiversity tends to increase from the axial lobe area towards the fan fringe. Additionally, lobe fringe deposits show the most diverse assemblages, followed by fan fringe deposits. Ichnodiversity is also lower in areas where thicker, amalgamated sandstones predominate (cf. Heard & Pickering, Reference Heard and Pickering2008; Cummings & Hodgson, Reference Cummings and Hodgson2011).
Figure 8. Stratigraphic and paleoenvironmental distribution of the various ichnofossil groups (pre- and post-depositional) from the Beni Ider/Algeciras and Talaa Lakrah/Bolonia units. The detailed distribution of the various ichnogenera according to the ethology is also shown. Data for the Spanish sector are from Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) and McCann (Reference McCann2023).
These same trends would also seem to be applicable in the case of the Maghrebian Flysch Basin. The outcrops of the Algeciras and Bolonia units described by Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) comprise a channel/channel margin within a lobe deposit (Algeciras Unit) and a lobe fringe environment (Bolonia Unit). The latter environment contains more pre-depositional and graphoglyptid trace fossils (and associated ethological types such as agrichnia) than the former.
McCann (Reference McCann2023), in contrast, investigated a series of outcrops from the Algeciras Unit, interpreted as lobe fringe, channel/channel margin (the same as those investigated by Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) and a combined lobe fringe and lobe off-axis setting. Ichnodiversities vary across the outcrops, as do ethological types. This variability may, in part, be caused by the presence of more than one depositional subenvironment (i.e. axial and more distal environments) within one profile and the fact that traces were not always found in situ. Indeed, in the present study, both of these problems also occurred (see above). Particularly, in the case of material being found in scree, it cannot always be assigned to a specific subenvironment.
Despite these issues, clear ichnodiversity trends can be recognised when comparing the Spanish and Moroccan data, in particular for Eocene-age units. Additional outcrops, broadly Eocene to Upper Oligocene in age, may also show similar trends, if outcrops such as Sierra Cabrito and Cala Arenas represent Eocene deposits (although this is not known due to the difficulty of precisely dating the turbiditic sections).
Deep-marine ichnofossil diversity in the Eocene period is considered to be at a maximum (Uchman, Reference Uchman2003, Reference Uchman and McIlroy2004). Similarly, graphoglyptids are especially diverse and abundant in Paleocene and Eocene times, with a marked decline noted in the Oligocene period (Uchman, Reference Uchman2003; Uchman, Reference Uchman and Miller2007, p. 260; Uchman & Wetzel, Reference Uchman, Wetzel, Knaust and Bromley2012). This phenomenon has been associated with oceanic oligotrophy (Tunis & Uchman, Reference Tunis and Uchman1996; Uchman, Reference Uchman2003) and has been observed in many coeval successions (e.g., Tunis & Uchman, Reference Tunis and Uchman1996; Uchman, Reference Uchman2001; Heard & Pickering, Reference Heard and Pickering2008; Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010), although different trends – related to local conditions – have also been noted (e.g., López Cabrera et al. Reference López Cabrera, Olivero, Carmona and Ponce2008; Knaust et al. Reference Knaust, Warchoł and Kane2014). The phase of oligotrophy has been related to global warming commencing in the Late Paleocene, the effects of which also extended to the deeper ocean (e.g., Shackelton, Reference Shackleton1986; Boersma & Premoli Silva, Reference Boersma and Premoli Silva1991). From late Middle Eocene to Oligocene times, in contrast, oceanic eutrophication connected to cooling water temperatures was noted (Boersma & Premoli Silva, Reference Boersma and Premoli Silva1991). This cooling and related eutrophication would have inhibited the spread of graphoglyptids (i.e. reducing their diversity, cf. Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Uchman, Payros, Orue-Etxebarria, Apellaniz and Molina2010). Such a diversity trend may also be reflected in the Bolonia Unit (Sierra Cabrito) and Talaa Lakrah Unit (SW of Beni Harchan) outcrops (cf. Fig. 7 & 8).
Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016), in contrast, suggested that the increased diversity and abundance of graphoglyptids within the Bolonia Unit may be related to the fact that nutrients were being supplied from two separate source areas, namely to the N and S of the Maghrebian Flysch Basin – this, however, cannot be confirmed for the Moroccan trace fossil data.
Trace fossil proliferation and ichnodiversity may also, as discussed in the previous section, have been influenced by the evolution of the Maghrebian Flysch Basin and its northern basin margin. This would have affected trace makers specifically in Oligocene to Early Miocene times. Indeed, both climatic and tectonic processes may have impacted habitats within the basin, with allogenic processes acting in concert with autogenic processes as discussed above.
In terms of specific ichnofacies within the Nereites ichnofacies, Rodríguez-Tovar et al. (Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016) suggested that the Algeciras Unit represented the Nereites subichnofacies with minor contributions from the Paleodictyon and Ophiomorpha rudis subichnofacies. McCann (Reference McCann2023) suggested that both the Nereites and Paleodictyon subichnofacies were present in the Tarifa-Algeciras area (= Algeciras Unit). The Moroccan Beni Ider Unit succession mainly comprises the Nereites and Paleodictyon subichnofacies.
In contrast, the Bolonia Unit ichnoassemblages contain greater amounts of graphoglyptids (associated with the Paleodictyon subichnofacies) as well as Ophiomorpha (= Ophiomorpha rudis subichnofacies?) (Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016). The Talaa Lakrah Unit outcrop in Morocco, in contrast, shows an ichnoassemblage more similar to the Nereites subichnofacies. While, as noted above, trace fossil diversity is dependent on a range of local and regional factors, there is broad agreement between the assemblages from Spain and Morocco, with both belonging clearly to the Nereites ichnofacies, with a higher degree of overlap in the Algeciras/Beni Ider Unit – broadly reflective of the greater amount of outcrop available (particularly in Spain).
7. Conclusion
Ichnological analysis of the deep-marine ichnofossils from the Beni Ider and Talaa Lakrah turbidite successions of the Maghrebian Flysch Basin has revealed a rich ichnoassemblage of 31 ichnogenera (41 ichnospecies). While the majority of the assemblage comprised post-depositional ichnofossils, 9 ichnogenera represented graphoglyptids. The Beni Ider Unit comprises both the Nereites and Paleodictyon subichnofacies of the Nereites ichnofacies as its main ichnoassemblages, while the Talaa Lakrah Unit showed a predominantly Nereites subichnofacies. This is generally comparable to ichnological data from equivalent units of the Spanish sector of the Maghrebian Flysch Basin (cf. Rodríguez-Tovar et al. Reference Rodríguez-Tovar, Pinuela and Garcia-Ramos2016; McCann, Reference McCann2023), although some ichnofaunal elements (e.g. from the Ophiomorpha rudis subichnofacies) were more common in the Spanish deposits.
Investigating the various ecological parameters within the basin in relation to the observed ichnoassemblages showed that ichnofossil distribution was influenced by the location on the lobe (i.e. away from the main sedimentary transport channels). In these locations, the ambient energy level was lower and the colonisation window time was extended. Furthermore, sedimentation rates were lower, while nutrient and oxygenation levels were suited to organism proliferation.
Environmental influences within the various parts (subbasins) of the basin were broadly similar, with local variations playing a role in the composition of the ichnoassemblages. Viewed stratigraphically, pre- and post-Eocene ichnofossil assemblages tend to be less diverse, while Eocene successions showed higher ichnodiversity (specifically the graphoglyptids). A post-Eocene period decline in ichnodiversity correlates well with changes in global oceanographic and climatic conditions at the transition from the Eocene to the Oligocene period, which involved a general cooling (also in deeper waters) and a concomitant change from an oligotrophic to an eutrophic regime.
Acknowledgements
D. Beißel is thanked for his support during the fieldwork in North Morocco and for many of the great pictures of ichnofossils within this publication. The authors are furthermore extremely grateful for the help of J. Eddine in procuring additional geological maps, which were of great use, as well as his valued support in obtaining fieldwork permissions. Lastly, the helpful suggestions and comments of the reviewers were greatly appreciated as they greatly improved the manuscript.
Financial support
This work was financed by DFG Grant MC 10/17-1 awarded to the second author.
Competing interests
The authors declare none.
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