The Westernmost Tethys Blog Geology mapping, basin analysis and 3D modeling

02/17/2021

Tectono-sedimentary Cenozoic evolution of the El Habt and Ouezzane Tectonic Units (External Rif, Morocco)

Filed under: geodynamic evolution,Morocco — Tags: , , — messinianalicante @ 7:41 AM

An interdisciplinary study based on lithostratigraphic, biostratigraphic, petrographic and mineralogical analyses has been performed in order to stablish the Cenozoic tectono-sedimentary evolution of the El Habt and Ouezzane Tectonic Units (Intrarif Subzone, External Rif, Morocco). The reconstructed record allowed identification of the depositional architecture and related sedimentary processes of the considered units. The Cenozoic successions were bio-chronologically defined allowing, at the same time, identification of unconformities and associated stratigraphic gaps.

Stratigraphic architecture of the Cenozoic of the El Habt and Ouezzane Units. The arrangement of the studied Logs and correlation with the timetable reflects the supposed paleogeographic position from proximal to distal. In addition, depositional sequences, unconformities, gaps (erosive and depositional), sedimentary realms and tectonic phases are shown.

The presence of five unconformities allowed to define the main stratigraphic units arranged in a regressive trend: (1) lower Paleocene interval (Danian p.p.) assigned to a deep basin; (2) Eocene interval (lower Ypresian-lower Bartonian p.p.) from a deep basin to an external carbonate-siliceous platform; (3) lower Rupelian-upper Chattian p.p. interval deposited on unstable slope with turbidite channels passing upward to an external siliciclastic platform; (4) Burdigalian p.p. interval from a slope; (5) Langhian-Serravallian p.p. interval from slope to external platform realms. The petrography of the arenites and calcarenites allowed to identify supplies derived from erosion of a recycled orogen (transitional and quartzose sub-types).

 

Qm/F/Lt + CE ternary diagram indicating a discrimination of the sandstones’ provenance. Qm: monocrystalline quartz; F: feldspars (plagioclase and K-feldspars); Lt + CE: lithic fragments including carbonate extrabasinal clasts.

 

The clay-mineralogy analysis indicates an unroofing (first erosion of Cretaceous terrains followed by upper Jurassic rocks) always accomplished by erosion of Cenozoic terrains. Several tectofacies checked in some stratigraphic intervals seems to indicate the beginning of deformation of the basement generating gentle folds and first activation of blind thrusts, mainly during the Paleogene. A pre-orogenic tectonic framework is considered as risponse to the generalized tectonic inversion (from extension to compression) as frequently registered in the central-western peri-Mediterranean areas. The large volumes of reworked terrigeneous supply during the latest Oligocene-Miocene p.p. indicates the beginnigs of the syn-orogenic sedimentation (foredeep stage of the basins) controlled by active tectonics.

Cites as: Martín-Martín, M., Guerrera, F., Hlila, R., Maaté, A., Maaté, S., Tramontana, M., Serrano, F., Cañaveras, J.C., Alcalá, F.J., Paton, D., 2020. Tectono-Sedimentary Cenozoic Evolution of the El Habt and Ouezzane Tectonic Units (External Rif, Morocco). Geosciences. 2020; 10(12):487.. https://doi.org/10.3390/geosciences10120487

02/15/2021

Middle Eocene carbonate platforms of the westernmost Tethys

A study of the paleoenvironmental evolution of the middle Eocene platforms recognized in the westernmost Tethys has been carried out in the well exposed middle Eocene succession from Sierra Espuña-Mula basin (Betic Cordillera, S Spain). Eight microfacies (Mf1 to Mf8) have been recognized, based mainly on fossil assemblages (principally larger benthic foraminifera), and rock texture and fabric.

Environmental microfacies distribution for the Middle Eocene marine Depositional Sequence 2 (Malvariche andCánovas fms) in Sierra Espuña, arranged from proximal to distal depositional environments: Mf3, Inner ramp lagoon, upper subtidal environment; Mf5, Inner ramp seagrass, euphotic subtidal environment; Mf6 – Mf7, Inner ramp, euphotic lower subtidal environment; Mf2, Proximal middle ramp LBF accumulations (nummulitids), mesophotic environment; Mf1, Proximal middle ramp maërl, mesophotic environment; Mf8, Distal middle ramp LBF accumulations (orthophragminids), mesophotic environment; Mf4, Outer ramp lacking Large Bethic Foraminifera (LBF), oligophotic environment. Ramp subdivision is based on Burchette and Wright (1992), and photic zones are analogous to those described by Pomar et al. (2017), with a ‘mesophotic zone’ comprised between lower limit of occurrence of marine vegetation and the storm wave base (swb).

 

The fossiliferous assemblage can be asigned to the ‘subtropical’ heterozoan association or to the low-latitude ‘foralgal facies’ , which are dominated by non-framework building, light-dependent biota such as perforate larger benthic foraminifera, coralline algae, and sometimes green algae and solitary corals. Larger benthic foraminifer assemblages, corresponding from euphotic to oligophotic conditions and the large surface showed, suggest a progressive marine ramp under essentially oligotrophic conditions. Eventually, supply of detrital sediments from the continent and/or upwelling currents increasse the nutrients of marine waters. Comparision with other Tethyan sectors allows stating that coral-reef buildups (z-corals) were widespread on shallow platforms of the central and eastern Tethys Ocean, but that these were neither of great dimensions nor dominant because of the much more dominant presence of larger benthic foraminifera. Moreover, these coral constructions were completely absents in the westernmost Tethys. The dominance of larger benthic foraminifera and the absence of z-corals in the westernmost Tethys is explained by particular paleogeographic features due to the occurrence of a narrow and deep oceanic branch (i.e., the Maghrebian Flysch Basin) connecting the Tethys with the Atlantic Ocean.

Biochronostratigraphic chart with numerical time scale, magnetochrons, magnetic polarity, planktonic foraminifera and calcareous nannoplankton zones based on GTS 2012 (Gradstein and Ogg, 2012), correlated with shallow benthic zones (SBZ). Interpretations of main climatic events, trophic resources continuum, LBF specific diversity and coral events in the Tethyan domain are also represented. A synthetic column with the stratigraphic formations and the main trophic conditions and Large Bethic Foraminifera (LBF) and coral (*) events of the Sierra Espuña-Mula Basins are also included.

The various issues regarding the morphological characters and evolution of larger benthic foraminifera in the study area, such as sizes of tests, specific diversity and/or intraspecific variability, number of appearances and last occurrences during the middle Eocene are analyzed and compared with those appearing in other Tethyan sectors. In addition, the early to late Bartonian boundary is recognized in the study area as critical for the biological change as in other shallow-marine environments along the Tethys margins.

Cite as: Martín-Martín, M., Guerrera, F., Tosquella, J., Tramontana, M., 2021. Middle Eocene carbonate platforms of the westernmost Tethys. Sediment. Geol. 415, 105861. doi:10.1016/j.sedgeo.2021.105861

 

02/01/2021

Sedimentary History and Palaeogeography of the Cenozoic clastic wedges of the Malaguide Complex, Internal Betic Cordillera, Southern Spain

Filed under: Betics,geodynamic evolution — Tags: , , , , , — messinianalicante @ 8:59 PM

The Cenozoic sedimentary cover of the Malaguide Complex (Internal Betic Cordillera, Spain), in the Almería and Málaga areas, consists of a suite of sedimentary successions from continental and shallow-marine to deep-marine environments. Structural and stratigraphic relations, and petrological and geochemical signatures reveal the sedimentary evolution of the Cenozoic Malaguide Complex (CMC) from pre-orogenic (Palocene-Eocene) to syn-orogenic (Oligocene-Early Miocene) stages.

Figure 1. A, Geological sketch map of the Betic Cordillera. B, Paleogeographic reconstruction of the central-western Mediterranean area showing the position of the Mesomediterranean Microplate. C, The Internal Zones of others alpine chains of the Circum-Mediterranean belts (i.e. Rif, Tell, Calabria-Peloritani and Apennine chains). Modified from Martín-Algarra (1987), Guerrera et al. (1993, 2005), Perrone et al. (2006), Critelli et al. (2008), Perri et al. (2013).

Sandstones detrital modes of the overall succession are heterogeneous testifying to a multi-source area, marked by exhumation of the Malaguide basement terranes and of the Internal Betic Zone (Alpujárride Complex) in lower position. Pre-orogenic and syn-orogenic strata consist of four main depositional sequences: the Mula Group (Paleocene), the Xiquena Group (Eocene) for the preorogenic successions; and Ciudad Granada Group (Oligocene-Aquitanian) and Viñuela Group (Burdigalian) for the synorogenic successions. Pre-orogenic strata evolve from intra-arenite to hybrid arenites to progressive increase of sandstones in abundance of detrital supply from sedimentary cover of the internal Betic units. The unroofing history of the internal Betic Units, predominantly in the Malaguide Complex, is clearly testified in strata of the synorogenic clastic units, where detrital supply is coming from the Malaguide Complex. Sedimentary lithic fragments were derived from the Mesozoic strata of the Malaguide Complex while metamorphic detritus is related to the Internal Betic Zone basement that was exhumed starting from the Oligocene. Pre-orogenic mudrocks mainly show abundance of calcite and dolomite over quartz and phyllosilicates. Syn-orogenic mudrocks, record an abrupt decrease in calcite and dolomite and an increase of phyllosilicate, quartz and feldspars mainly in the Malaga section. The geochemical signatures attest to a compositional variation of the samples from pre-to-synorogenic successions, with palaeoweathering indices showing moderate values and a weak up-section decrease. The Cenozoic Malaguide Complex played a key role in the geodynamic evolution of the Betic Cordillera, representing the key tectonic element of the western Mesomediterranean domains.

 

Figure 2 Mineralogical variations along the studied stratigraphic formations.

Cite as: Critelli, S., Martín-Martín, M., Capobianco, W., Perri, F., 2021. Sedimentary history and palaeogeography of the Cenozoic clastic wedges of the Malaguide Complex, Internal Betic Cordillera, southern Spain. Mar. Pet. Geol. 124, 104775. https://doi.org/https://doi.org/10.1016/j.marpetgeo.2020.104775

 

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