The Sidi El Hemissi region, Souk-Ahras, is part of the Tellian Atlas where the Triassic sediments tectonically outcrop under the Tellian nappes of the Maghrebide chain. Mafic rocks, mainly gabbros ...and dolerites, called “ophites,” are interbedded as a ~ 200 × 30-m lenticular body within the Triassic gypsum-rich formation. These rocks show granular, microgranular, and microlithic textures and are composed of plagioclase, amphibole, pyroxene, and scarce olivine crystals. Albitization is the main alteration process, though chloritization, calcitization, and epidotization of ferromagnesian minerals can also be occasionally observed. The major, trace, and rare earth element studies show that these mafic rocks display relatively low P
2
O
5
(less than 0.2 wt%) and moderate to low TiO
2
contents (less than 2 wt%) and exhibit low-Ti continental tholeiitic basalt affinity. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) compared with high field strength elements (HFSE) and heavy rare earth elements (HREE). This, along with the observed weak Nb and Ce anomalies and the low-Ti contents, suggests an enriched mantle source for the generation of the magma, which likely underwent crustal contamination before emplacement within the Triassic sediments.
The petrological and geochemical features of the Sidi El Hemissi ophites show many similarities with the basaltic rocks emplaced during the Late Triassic–Early Jurassic times, now cropping out in north-western Africa, south-western Europe, north-eastern, and south-eastern America. This large magmatic activity is believed to be related to the continental rifting associated with the early stages of the Pangea breakup.
The late Quaternary sequences of north-eastern Algeria composed of alternating dark and light layers, which are rich in molluscan fauna, could correspond to synchronous environmental phases. The ...facies variations of the Morsott Region deposits were systematically sampled as part of a sedimentological and malacological study in order to establish a palaeoenvironmental and climatic reconstruction of the late Quaternary. The alternation of sandy clayey silts levels, which contain abundant molluscan hygrophilous organisms, indicates an isostasis cycle followed, at the top, by a succession of rhexistasis and biostasis cycles. The molluscan record shows a dominant succession of xerophilous organisms in relation to the hygrophilous organisms. The faunistic richness in the fine levels is linked to sub-humid periods where the region has suffered numerous floods. The reduction in the number of species in the coarse levels comes is likely due to desiccation when the climate was semi-arid. This study is new in Algeria and will provide an insight into climatic changes. Further research will be required in order to understand the fluvial dynamics during the Quaternary.
In the northern Aurès Range near Batna, Algeria, the Cenomanian Smail Marls Formation consists of fossiliferous deposits rich in diverse benthic macrofauna, mostly dominated by bivalves, among them ...the carditid Maghrebella forgemoli (Coquand, 1862). Almost exclusively Cenomanian, the abundance zone of Maghrebella forgemoli is in the higher levels of Lower Cenomanian, extending from the Sharpeiceras schlueteri zone to the Mantelliceras dixoni zone and corresponds to a limited circalittoral interval with relatively low energy, soft substrata, and relatively cold temperatures. The distribution of Maghrebella forgemoli in Mountains of Batna evidences bathymetric variation controlled by the tectonic activity affecting the ante-Triassic and the Upper Cretaceous substrata and generating a system of tilted blocks, at the beginning of the uppermost Albian-Cenomanian and Turonian, in the eastern Atlasic domain that extends to central Tunisia.
Les niveaux inférieurs du Cénomanien de la région de Batna (NE, Algérie) constituent la partie du Cénomanien la plus riche et la plus diversifiée en matière de macro-invertébrés, essentiellement ...dominés par le groupe des bivalves en termes de spécimens et de taxons. Parmi les bivalves, les Crassatellidae sont exclusivement présents dans les niveaux inférieurs du Cénomanien et représentés par la seule espèce Crassatella baudeti. Cette dernière, facilement identifiable par sa forme d’ancre, et ses lamelles commarginales assez fortes, s’avère très abondante. Elle est présente dans les niveaux compris depuis la sous-zone à Sharpeiceras schlueteri jusqu’à la zone à Cunningtoniceras inerme. Cette espèce est, par conséquent, un bon marqueur des derniers niveaux du Cénomanien inférieur et le début du Cénomanien moyen. Une description paléontologique et une discussion environnementale précises ont été réalisées. Ainsi, Cr. baudeti serait révélatrice d’un environnement peu profond, avec des eaux froides mais calmes, une salinité normale et un substrat modérément mou. Retrouvée uniquement dans quelques sites téthysiens, la présence exclusive de Cr. baudeti dans le Cénomanien reflète un gradient thermique et une zonation climatique spécifiques.
The lower Cenomanian strata from the Batna region (NE Algeria) constitute the richest and most diversified deposits in terms of macro-invertebrates, mainly dominated by bivalves both in terms of specimens and taxa. Among them, Crassatellidae are restricted to the lower Cenomanian stratigraphical levels. They are represented by the single species Crassatella baudeti. The species is easily distinguished by its flattened boat anchor shape and quite strong commarginal lamellae, and is very abundant. It is present in levels ranging from Sharpeiceras schlueteri Subzone to Cunningtoniceras inerme Zone. The species is, therefore, a good marker of the last levels of the lower Cenomanian and the beginning of the midlle Cenomanian. A precise palaeontological description and an environmental discussion were conducted. Thus, Cr. baudeti would be indicative of a shallow environment, with cold but calm waters, normal salinity and moderately soft substrate. Recorded exclusively from the Cenomanian of a few Tethys localities, the exclusive presence of Cr. baudeti reflects a specific thermal gradient and climatic zonation.
Rare earth element (REE) analyses are reported on glauconite-bearing phosphorites from northeastern Algeria. These rocks of Paleocene-Eocene age are located in the Eastern part of the Saharan Atlas, ...where two localities were investigated: the Djebel El Kouif in the north and the Kef Essenoun in the south. The latter belongs to the world-class Djebel Onk mining deposit. Petrographic examination indicates that phosphorite from the main layer of the Kef Essenoun deposit has a significant abundance in glauconite grains, while their occurrence in the Djebel El Kouif is restricted to the basal levels. In both deposits, glauconite grains are richer in REEs than other co-existing particles (pellets, coprolites, enameloid and dentine of marine fish teeth), but the glauconites of the Kef Essenoun deposit exhibit significantly higher REE concentration (min = 654 ppm, max = 1760 ppm, average = 1146 ppm) than those of Djebel El Kouif deposit (min = 543 ppm, max = 623 ppm, average = 584 ppm). The whole-rock REE concentrations also show substantial differences between the two deposits and the REE enrichment in the Kef Essenoun main sub-layer is more likely the result of the high glauconite content. PAAS normalized-REE patterns of the glauconite grains display similar patterns between the northern and southern localities with weak negative Ce anomalies and slight middle REE enrichments. On the other hand, the pellets and whole phosphorite grains from the northern deposit indicate a REE source from oxic-suboxic seawater, whereas those from the Kef Essenoun deposit exhibit slight middle REE enriched patterns with weak negative Ce anomaly suggesting a different environment of deposition (i.e. a tendency to reduced conditions). These geochemical results along with previous petrographic studies confirm the allochthonous character of the main phosphorite sub-layer in Kef Essenoun, where winnowing, transport and re-deposition of previously deposited phosphorites resulted in high accumulation and formation of glauconite grains. The glauconitization process of fecal pellets happened in two stages and was controlled by semi-confined micro-environments. This can explain the abundance of glauconite grains in the phosphorites from Kef Essenoun deposit and their restricted occurrence in the basal levels of the Djebel El Kouif outcrop.
•Evidence of substantial REE enrichments in glauconite grains comparing to coexisting particles (∑REE > 1000 ppm).•Glauconite grains show high Ca, P, Fe, Al, K and Si contents indicating the glauconitization of preexisting pellets.•REE-signature of glauconite grains emphasizes their allochthonous character (remobilization and re-worked grains).•The higher REE content in whole rock of the southern phosphorites is linked to the abundance of glauconite grains.
In the Batna area of Algeria, the Cenomanian is represented by the Smail Marls Formation, a highly fossiliferous unit with a diverse benthic macrofauna (mainly of ostreid bivalves). A total of 1090 ...specimens belonging to 65 macrobenthic species were identified from 19 stratigraphic samples. The macrofaunal communities were quantitively analyzed using the hierarchical clustering (HC), nonmetric multidimensional scaling (NMDS), and permutational analysis of variance (PERMANOVA). Five distinct associations are recognized: 1) Costagyra olisiponensis, 2) Rhynchostreon suborbiculatum, 3) Aspidiscus cristatus, 4) Rhynchostreon suborbiculatum-Mecaster ameliae, and 5) Pycnodonte vesicularis. Data suggests that during the Cenomanian, the dominance of high-energy opportunistic oyster species within the soft marly sediments are related to their adaptive strategies. The changes noted in the community structure are attributed to sea-level fluctuations, rate of sedimentation and the prevailing hydrodynamics. Towards the uppermost Cenomanian and the Cenomanian–Turonian boundary, the oysters become rare due to eustatic sea-level rise and this decline coincides with increasing predation intensity on oysters and the destruction of their shallower habitats.
In the Batna Mountains, the Cenomanian Marnes de Smail Formation yield fossiliferous deposits mostly dominated by bivalves. Thirty-five bivalve species were identified, belonging to nine orders, 19 ...families and 26 genera. Five of them are mentioned for the first time from the Cenomanian of the study area (i.e., Nucula ? cf. margaritifera Douvillé, Barbatia (Barbatia) aegyptiaca Fourtau, Cucullaea trigona Seguenza, Arctica inornata d’Orbigny, and A. cordata Sharpe). Their distribution provided interesting insights on the marine paleoenvironment of the Cenomanian times. The paleobiogeographic distribution of the studied bivalves corresponds to the Tethys Realm. Keywords: Bivalvia, Cretaceous, Cenomanian, Algeria, Batna, Tethys
The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as ...subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian–Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ∼110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained simply by the evaporation of seawater to halite saturation and requires a dilution of more than two times by meteoric water. The higher K/Na values in fluid inclusions from barite suggest that the brines interacted with K-rich rocks in the basement or siliciclastic sediments in the basin. Carbonate gangue minerals (ankerite and calcite) have δ
13
C and δ
18
O values that are close to the carbonate host rock and indicate fluid equilibrium between carbonate host rocks and hydrothermal brines. The δ
34
S values for sphalerite and galena fall within a narrow range (1 to 10 ‰) with a bulk value of 7.5 ‰, indicating a homogeneous source of sulfur. The δ
34
S values of barite are also relatively homogeneous (22 ‰), with 6 ‰ higher than the δ
34
S of local and regional Triassic evaporites (15 ‰). The latter are believed to be the source of sulfate. Temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of Triassic sulfate via hydrocarbons produced probably from Late Cretaceous source rocks. The
87
Sr/
86
Sr ratio in the Bou Jaber barite (0.709821 to 0.711408) together with the lead isotope values of Bou Jaber galena (
206
Pb/
204
Pb = 18.699 to 18.737;
207
Pb/
204
Pb = 15.635 to 15.708 and
208
Pb/
204
Pb = 38.321 to 38.947) show that metals were extracted from homogeneous crustal source(s). The tectonic setting of the Bou Jaber ore deposit, the carbonate nature of the host rocks, the epigenetic style of the mineralization and the mineral associations, together with sulfur and oxygen isotope data and fluid inclusion data show that the Bou Jaber lead-zinc mineralization has the major characteristics of a salt diapir-related Mississippi Valley-type (MVT) deposit with superimposed events of fluorite and of barite deposition. Field relations are consistent with mineral deposition during the Eocene–Miocene Alpine orogeny from multiple hydrothermal events: (1) Zn-Pb sulfides formed by mixing of two fluids: one fluid metal-rich but reduced sulfur-poor and a second fluid reduced sulfur-rich; (2) barite precipitation involved the influx of a meteoric water component that mixed with a barium-rich fluid; and (3) fluorite precipitated from a highly saline fluid with higher temperatures.
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