Adaptative strategies of the Toarcian benthic foraminiferal assemblages from the Middle Atlas (Morocco): Palaeoecological implications

Reolid, Matías; Chakiri, Saïd; Bejjaji, Zohra

doi:10.1016/j.jafrearsci.2013.03.008

Cited by 40 publications

(12 citation statements)

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“…Such an assemblage is typical of this time interval in the basins of the Western Tethys (e.g. Reolid et al, 2013Reolid et al, , 2014bRita et al, 2016). The forms are mainly uniserial (MG-J1), like Dentalina and Nodosaria, as occurs in the studied section (Fig.…”

Section: Prebiotic Crisissupporting

confidence: 59%

Microfossil assemblages and geochemistry for interpreting the incidence of the Jenkyns Event (early Toarcian) in the south-eastern Iberian Palaeomargin (External Subbetic, SE Spain)

Reolid¹

2020

J. Micropalaeontol.

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Abstract. By studying the facies, geochemistry, and microfossil assemblages of the uppermost Pliensbachian and lower Toarcian of the Cueva del Agua section, I was able to appraise the impact of the Jenkyns Event in the eastern part of the South Iberian Palaeomargin (Western Tethys). Depleted oxygen conditions are envisaged for the Polymorphum–Serpentinum Zone boundary (lower Toarcian), represented by dark marls, precisely in a laminated interval. The decrease in the α diversity of foraminifera and ostracods, along with greater proportions of opportunists such as Lenticulina, Eoguttulina, and Cytherella just before the negative carbon isotopic excursion (CIE), would indicate a disturbance of the environmental conditions during the initial phase of the biotic crisis. The peak of the biotic crisis is characterized by an absence of trace fossils, increased organic matter content, an increased Mo∕Al ratio, and negative CIE and δ18O, as well as fewer specialist forms and more opportunists. This biotic crisis peak is related to oxygen-depleted conditions in the bottom waters and in the sediment pore water, while warming negatively affected microfauna – to the point of leaving a barren benthic horizon in the record. Recovery is evidenced by the occurrence of carbonate layers with hummocky cross-stratification and a decrease in organic matter content, the Mo∕Al ratio, and the trace fossil record. In terms of microfauna, the first phase of recovery shows highly abundant foraminifera, ostracods, and microgastropods, mainly opportunist forms. After the proliferation of opportunist forms, a second phase of recovery is marked by a progressive increase in α diversity.

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Section: Prebiotic Crisissupporting

confidence: 59%

Microfossil assemblages and geochemistry for interpreting the incidence of the Jenkyns Event (early Toarcian) in the south-eastern Iberian Palaeomargin (External Subbetic, SE Spain)

Reolid¹

2020

J. Micropalaeontol.

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“…3,4). The Toarcian deposits are generally hemipelagic and correspond to basin environments (Reolid et al, 2013). The biostratigraphic framework of the Issouka section and the Middle Atlas has been established with ammonites (Benshili, 1989;Sabaoui, 1998;El Hammichi et al, 2008) and benthic foraminifera (Bejjaji, 2007;Bejjaji et al, 2010).…”

Section: Lithology and Stratigraphymentioning

confidence: 99%

“…In order to further document these palaeoenvironmental changes, the Late Pliensbachian-Early Toarcian of the Middle Atlas rift basin of Morocco, was investigated. Previous investigations in the region have mainly focused on the platform drowning event observed in the Middle Atlas Basin at the Pliensbachian-Toarcian boundary (Benshili, 1989;Ruget and Nicollin, 1997;Blomeier and Reijmer, 1999;Lachkar et al, 2009;Dera et al, 2009), and a few studies have characterized palaeoenvironmental change using benthic foraminiferal assemblages (Bejjaji, 2007, Bejjaji et al, 2010Reolid et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Bulk-carbonate and belemnite carbon-isotope records across the Pliensbachian-Toarcian boundary on the northern margin of Gondwana (Issouka, Middle Atlas, Morocco)

Ait-Itto

Price

Addi

et al. 2017

Palaeogeography, Palaeoclimatology, Palaeoecology

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The data presented here provide the first high resolution investigation of carbon isotope and geochemical analyses derived from the Pliensbachian-Toarcian boundary, of Issouka, Middle Atlas, Morocco. The isotope data recorded in micrite reveal a stepwise negative carbon isotope excursion with values dropping to-1.8 ‰ within the Polymorphum Zone. This excursion coincides with major marine biological changes and extinctions and corresponds with European records supporting the assertion that the excursion is global in origin. The Issouka section is relatively expanded compared to other well-studied European sections. The excursion at the Pliensbachian-Toarcian boundary also shows several similarities with the negative Early Toarcian event. In contrast, carbon isotope values derived from coeval belemnites show positive values. The belemnite δ 13 C data presented here suggests spatial heterogeneity in the Early Jurassic ocean. Overturning or upwelling of a stratified water mass, is inconsistent with our data, as it requires the belemnites to have lived elsewhere and only later migrated into the Middle Atlas area where they became fossilized. The oxygen isotope values from belemnite calcite show no distinct trend across the event, indicative of either no significant change in temperatures or change in seawater δ 18 O. We suggest the introduction of any light carbon (e.g. a volcanogenic) source must have resulted in spatial variability in the δ 13 C of the dissolved inorganic carbon of seawater. Alternatively, a regional change in the source of the carbonate carrying the isotope signal, could lead to a negative shift in the δ 13 Cmicrite signature without any relation to variations in the global carbon isotope trend.

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“…Studies carried out in different sections in the upper Toarcian-lower Aalenian of the Lusitanian Basin, located in the distal, middle and inner part of the platform (Canales andHenriques, 2008, 2013;Canales et al, 2010Canales et al, , 2014Figueiredo et al, 2010a;Henriques and Canales, 2013), confirm this fact, as to this genus corresponds the higher values of relative abundance in almost all the analyzed assemblages. The high values of this genus, corresponding to a lenticular morphogroup (Nagy, 1992;Tyszka, 1994a;Reolid et al, 2008Reolid et al, , 2012Reolid et al, , 2013, indicate that the studied assemblages developed in oxic environmental conditions. This reinforces previous interpretations supported by the taxonomical composition analysis at suborder level.…”

Section: Taxonomical Composition Of the Assemblagesmentioning

confidence: 91%

Foraminifera of the Toarcian-Aalenian boundary from the Lusitanian Basin (Portugal): a paleoecological analysis

Figueiredo

Canales

Henriques

2014

Journal of Iberian Geology

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A detailed study carried out on 37 well preserved benthic foraminiferal assemblages sampled throughout the upper Toarcian-middle Aalenian in two well calibrated sections representing different facies within the Lusitanian Basin (Portugal) -the Maria Pares and the Zambujal de Alcaria sections -allows interpreting the past environmental conditions. Several mathematical indexes related to diversity, which enable establishing the particular conditions to which the assemblages were submitted, were applied. All the studied assemblages are characteristic of the Jurassic carbonate platforms of the Boreal Realm, in which the genus Lenticulina usually dominates. The suborder Lagenina is the most abundant, but taking the second more abundant suborder into account, the comparison between coeval sections in the Lusitanian Basin allows the recognition of a regional gradient ranging from the distal part of the platform (Murtinheira) towards the transitional and proximal parts of the shelf (sections of Maria Pares and Zambujal de Alcaria respectively). The relative abundance values, as well as the obtained data from the diversity indexes indicate that the studied assemblages are relatively abundant and diverse, reflecting general appropriate paleoenvironmental conditions for their development. The detailed analysis of the data allows the identification in both sections of three different episodes, traducing particular environmental conditions: unstable (Mactra Subzone-lower part of the Opalinum Subzone), favorable and stable (lower part of the Opalinum Subzone-upper part of the Comptum Subzone), and unfavorable (upper part of the Comptum Subzone-lower Bradfordensis Subzone). These data are consistent with previous results obtained in the sections of Murtinheira and São Gião, located in the Northern Lusitanian Basin and corresponding to the distal and transitional parts of the platform respectively, and they aimed at contributing to a better understanding of the paleoecological conditions prevailing within the Lusitanian Basin during the Early-Middle Jurassic times.Keywords: Benthic foraminifera, Lower-Middle Jurassic boundary, Portugal, paleoecology, diversity index, Paleoenvironmental gradient Resumen Se ha realizado el estudio detallado de 37 asociaciones de foraminíferos bentónicos bien preservados, registradas en materiales del intervalo estratigráfico Toarciense superior-Aaleniense medio en dos secciones bien calibradas que representan diferentes facies dentro de la Cuenca Lusitánica (Portugal) -Maria Pares y Zambujal de Alcaria -permitiendo realizar interpretaciones de las condiciones paleoambientales. Para ello, se han aplicado varios índices matemáticos relacionados con la diversidad, que permiten establecer las condiciones ambientales concretas en las que se desarrollaron dichas asociaciones. Todas las asociaciones estudiadas son características de las plataformas carbonatadas jurásicas del Dominio Boreal, en las que predominan los representantes del género Lenticulina. El suborden Lagenina es el más abundante,...

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Adaptative strategies of the Toarcian benthic foraminiferal assemblages from the Middle Atlas (Morocco): Palaeoecological implications

Cited by 40 publications

References 53 publications

Microfossil assemblages and geochemistry for interpreting the incidence of the Jenkyns Event (early Toarcian) in the south-eastern Iberian Palaeomargin (External Subbetic, SE Spain)

Microfossil assemblages and geochemistry for interpreting the incidence of the Jenkyns Event (early Toarcian) in the south-eastern Iberian Palaeomargin (External Subbetic, SE Spain)

Bulk-carbonate and belemnite carbon-isotope records across the Pliensbachian-Toarcian boundary on the northern margin of Gondwana (Issouka, Middle Atlas, Morocco)

Foraminifera of the Toarcian-Aalenian boundary from the Lusitanian Basin (Portugal): a paleoecological analysis

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