Calcareous Series Research Articles

A c. 1710 Ma mafic sill emplaced into a quartzite and calcareous series from Ighrem, Anti-Atlas – Morocco: Evidence that the Taghdout passive margin sedimentary group is nearly 1 Ga older than previously thought

The Taghdout Group is a passive margin sequence deposited during rifting and break-up of the northern margin of the West African craton (WAC), culminating with the creation of an oceanic basin between the northern edge of the WAC and an unknown terrane. However, the age of this passive margin has been poorly constrained. It was previously thought to be c. 800–1000 Ma on the basis of age of the contact metamorphosed host rocks of the associated mafic dykes (Rb/Sr, 789 ± 10 Ma). However, with the U-Pb dating of numerous dyke swarms in the Anti-Atlas Inliers, at c. 870, 1416-1380, 1650, 1750, and 2040 Ma, it was suggested by Youbi et al. (2013) that the Taghdout Group could be Mesoproterozoic in age, with a preference for an age of 1750 Ma. In order to test this idea, a mafic sill within the Taghdout Group has been dated by the ID-TIMS U-Pb method on baddeleyite, yielding an approximate age of c. 1710 Ma. This preliminary age confirms that the Taghdout Group is much older than previously thought. Further geochronology work is required to determine whether this c. 1710 Ma age represents a new intraplate event in the WAC or whether more concordant data could yield an age closer to the known WAC LIP event of c. 1750 Ma. With this result we propose a new lithostratigraphic framework for the Proterorozoic in the Anti-Atlas.

Hidrogeología del Karst de Pico Frentes (Cordillera Ibérica, España)

The karst system of Pico Frentes has developed within an Upper Cretaceous calcareous series whose well-defined folded geometry determines that its aquifer reserves are held mainly in three hydraulically-connected synclines, with a groundwater capacity of between 5 and 7 hm 3 . The recharge to this unconfined peneplain aquifer is autogenous and diffuse. On a large scale, groundwater flow is directed by the base of the synclines, while on a small scale, it flows along groundwater conduits towards the Fuentetoba Spring (210 l/s) and source of the River Mazos (50 l/s), following a highly variable flow regime of low inertia, with other smaller discharges emanating during periods of high water. Analysis of hydrographs of these springs indicates a very variable rate system and little power regulating natural, characteristic of a typical karstic aquifer, with great capacity for renewal and low residence time. Using hydrogram simulations of these upwellings using a mathematical rainfall-runoff model, a detailed quantification of the average water balance was made for a twenty-year time series. This water balance consists of 16,86 hm 3 rainfall (100%); natural recharge, 8,35 hm 3 (49,53%); EVT 8,50 hm 3 (50,41%); pumped groundwater abstractions, 0,01hm 3 (0,06%); surface runoff, 0 hm 3 , groundwater transfers to other aquifer, 0 hm 3 .

Miocene diagenetic and epigenetic strontium mineralization in calcareous series from Cyprus and the Arabian Gulf: Metallogenic perspective on sub- and suprasalt redox-controlled base metal deposits

During the Neogene, celestite deposits evolved in the Neo-Tethys basins, in what is today called the Mediterranean Sea and the Arabian Gulf. Two evaporite deposits, in Cyprus and in Qatar have been investigated from the sedimentological and mineralogical point of view with emphasis placed on Sr, S and Ca isotopes of carbonate, gypsum and celestite. During the early Miocene shallow marine environments occurred in the Gulf region and in Cyprus both of which are abundant in syndiagenetic sulphate minerals. The calcareous environments had a strong impact on the fluid migration leading to the Sr mineralization. In the Gulf region algal biostromes favored the lateral migration of fluids but had a sealing effect so that any epigenetic mineralization based on vertical fluid flow was hampered. In contrast, the Cypriot depocentre overlying the Troodos ophiolite is dominated by patch and knoll reefs (bioherms) which provide enough porosity and permeability to be favorable for the circulation of fluids with a strong vertical component. Owing to these changes in the calcareous host series, epigenetic sulphate mineralization evolved in Cyprus during the late Miocene. This occurred as the Mediterranean Sea gradually became isolated from the open ocean and, as a precursor to the “Messinian salinity crisis” evaporitic brines circulated deep into the Meso-Cenozoic platform sediments and the underlying Troodos ophiolite where these fluids leached some base metals and sulphur for the celestite mineralization. The Red Sea Rifting was at full swing during the Late Miocene and its northern propagation into the Mediterranean Sea is assumed to have had a structural control on the positioning of the Sr deposits in Cyprus. In the Gulf area, the final closure of the Neo-Tethys and Zagros folding terminated deposition of marine calcareous rocks and alluvial-fluvial siliciclastic rocks were deposited across an unconformity. Missing circulation of highly saline brines was responsible for the absence of an epigenetic Sr mineralization of Cyprus-type in the Gulf area. Assemblages of light (e.g. zeolites) and heavy minerals (e.g. rutile, zoisite, clinopyroxene) and Ca isotope analyses support basic igneous rocks as the source for the detrital and dissolved matter in the depositional environments in Cyprus and the Arabian Gulf. The Ca isotope data imply formation of the sulphate and carbonate minerals in a marine environment without significant contributions of more radiogenic 40Ca coming from old continental crust, e.g., the Kyrenia Range or Mamonia Complex, both of which containing rocks as old as Permian. Cyprus-type (bioherm-type) and Gulf-type (biostrome-type) evaporites are potential progenitors of sediment-hosted mineral deposits (SHSCD) or base metal vein-type deposits. Syndiagenetic celestite-bearing evaporites of the Gulf-type are a model source and progenitor of base metal deposits of stratigraphically-controlled fixed or mobile reductants such as Kupferschiefer-type deposits. Is the Arabian Gulf a Kupferschiefer basin in the making? The epigenetic celestite-bearing mineralization of the Cyprus-type reflects an advanced stage of fluid migration relative to the celestite deposits along the Trucial coast but this brine mobilization failed to create a base metal deposit of its own mainly due to the absence of fixed or mobile reductants. These reductants were present in the western Mediterranean regions in Tunisia and Algeria, where evaporite-associated base metal deposits are going to be mined and in the Mesozoic through Cenozoic platform sediments in central Europe, where numerous suprasalt unconformity-related metal deposits were mined in the past.

Les series du Toarcien-Aalenien du SW du Moyen-Atlas (Maroc); precisions stratigraphiques et signification paleogeographique

Abstract Toarcian and Aalenian deposits from south west of the Middle Atlas named "Couches du Seloum", were classically considered as a "border facies" of the Middle Atlas trough, which was extensively developed in the northern part of the folded Middle Atlas. Both studies realized on the border of the Bekrit-Timahdite syncline and the Iguer Awragh-Afennourir syncline, allow to specify the stratigraphy, the spatial distribution of deposits and to reconsider the paleogeographic organization of this "border" in the integral context of the northern Middle Atlas trough during the Toarcian and the lower Bajocian interval. A lithostratigraphic succession of the "Couches du Selloum" raised in the western part of Bekrit-Timahdite syncline shows the superposition of three units. Unit 1 is made of clay, reddish and gray marl, locally gypseous, assigned to the lower Toarcian. Unit 2 is essentially composed of a subnodular calcareous series, which consists of discontinuous, wavy and upward-thickening beds. The upper offshore is the most frequent environment. It is mainly made of crinoidal calcarenites, yielding some ammonites and brachiopods rich levels. The Middle Toarcian (Bifrons zone and Gradata zone) was identified in the lower part of this unit. Most of the upper Toarcian zones were distinguished (Speciosum zone, Meneghinii zone and Aalensis zone), they are represented in the upper part by brachiopods (Stroudithyris) and ammonites (Hammatoceras, Dumortieria and Catulloceras) rich set. On several lateral sections, the uppermost part of these pseudo nodular limestones is dated from Opalinum zone (levels with Leioceras and Tmetoceras). Unit 3 shows several facies: bioclastic calcarenites arranged in decimetrics beds, showing cross stratifications; microsparitic limestones in thick beds with silexites. The macrofauna is scarce, often represented by some crinoidal and mollusks fragments; some Zoophycos appear in the top bed of the set. The following deposits illustrate the evolution from the shoreface to the upper offshore. This unit is overlain by a sedimentary discontinuity, materialized by a boring surface, some pockets of accumulations with belemnites and a cover of ferruginous nodules. Ammonites drowned on the discontinuity surface or in the basis of the first interbedded marls which overlies this surface sign the Aalenian-Bajocian transition (top of the Concavum zone and the basis of Discites zone). Immediately above we found some index fauna of the Laeviuscula zone. The series overlaying the "Couches du Selloum" comprises thinning up alternations of limestone/marl, passing progressively to the "Marnes de Boulmane" Formation. Lateral variations and interpretations; SW to NE variations: The thickness and facies variations observed in the Bekrit-Timahdite syncline (C1 to C9), denote the existence of marine intervals generally more dilated, with some marly deposits developed towards the SW; on the contrary towards the NE, series are exclusively calcareous, reduced in thickness, and often condensed in their upper part. The same evolution is observed between the deposits of the Iguer Awragh syncline to the SW and those of Afennourir in the NE [Benshili et al., 1999]. SE to NW variations: Some observations realized in a Toarcian-Aalenian outcrop recently discovered in the sector of Outghalline (C11), shows that an uplifted area separates the marly basin of Bekrit from the Iguer Awragh one. Such variations denote a partition of the Toarcian Selloum basin, located in south west of the Middle Atlas trough, into several entities which are regrouped under the denomination of "Blocks of Selloum"; two NE-SW trending notably subsiding gutters are recognized, the Iguer Awragh-Afennourir and the Bekrit-Timahdite, separated by a shoal (ridge of Ijadrane). Paleogeographic framework of the SW border of the Middle Atlas trough: A synthesis of the geometry of the "Blocks of Selloum" and some paleogeographic and structural features of the NW border of the Middle Atlas trough, as they appear in a recent synthesis [Benshili, 1989; Elmi et al., 1989; Benshili et Elmi, 1994; Charriere, 1990; Fedan, 1993; Laadila, 1996; Sabaoui, 1998; El Arabi et al., 1999], is shown in 3 episodes from Toarcian to Aalenian. The southwestern part of the Middle Atlas studied here, does not appear in any case as a coastal area surrounding the Middle Atlas trough, but like a gulf occupied by marine deposits which is isolated from the Middle Atlas trough by the shoal areas called the "Haut-fond de Boulmane". In the Middle Atlas trough, the sequences prograde in a NE direction and show blocks tilting generally towards the same direction. On the other hand, in the "Blocks of Selloum" the tilting acts toward the SW, against the direction of the global Tethyan polarity.

Characteristics of magmatic rocks and tectonic setting of Mazhuangshan area, East Tianshan, China

The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate-acid rocks, which were formed in the Middle-Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calcareous series. All values of ACNK(1.03–2.12), ANK (1.67–2.93), SI(4.1–33), δ(0.71–4.82), La/ΣREE(0.09–0.26) ΣLREE/ΣHREE(1.76–11.01), (La/Sm)N(l.60–6.35), (Sm/Nd)N(0.33–0.58), (La/Yb)N(4.7–12.1), LaN/LuX(5.9–11.8), (Ce/Yb)N(3.14–6.64), δEu(0.38–1.06), RbN/SrN(42–120) and Sr* (0.02–0.2) demonstrate they vary with D_ I(45–90). S-B diagram also shows that the lithophile elements are abundant in acidic magmatic rocks. Moreover, it is concluded that the primitive magma originated from a subduction zone at the continental edge, and underwent fractional crystallization and contamination, then generated the magmatic rocks. The multi-cation index (R1: 3055–3993, R2: 286–438) shows that the primitive magma originated from the mantle. All these conclusions are beneficial for exploring gold deposits in the area.

The Geology of the Northern Border of Dartmoor between Whiddon Down and Butterdon Down

In this paper the Lower Carboniferous formation bordering the granite of Dartmoor for a length of about 4½ miles, between Whiddon Down on the west and Butterdon Down towards the east, are the only stratified rocks dealt with; but the nature of, and variations found in the granite south of the Carboniferous rocks are also considered. The area examined includes part of the deep gorge of the River Teign, known as Fingle Glen, between Hunter's Tor and about a mile east of Fingle Bridge, or rather more than two-thirds of the length of the gorge. The area described is covered by the 6-inch Ordnance Survey quarter-sheets of Devon:—LXXVII, S.E.; LXXVIII, S.W.; LXXVIII, S.E.; XC, N.W.; and XC, N.E. Of these quarter-sheets only the whole of LXXVIII, S.W. is covered; but portions of the other sheets are required to describe the area in a comprehensive manner. In the area dealt with, the Lower Carboniferous, or Culm Measures, may, as found by Mr. R. H. Worth (10) in the granite-border south-west of Okehampton, be divided into two groups: the Lower Aluminous Series and the overlying Calcareous Series. Both these series of rocks have been affected by contact-meta-morphism from the granite. The Lower Aluminous Series in this district can be divided into zones: the lower zone characterized by the occurrence of much segregated or disseminated iron-pyrites, and the upper zone in which chiastolite is found. The Lower Aluminous Series passes upwards by gradual change, and without any physical feature, from black slates into

Societies and Academies

LONDON. Geological Society, December5.—Prof. A. C. Seward, president; and, afterwards, Dr. G. T. Prior, in the chair.—The following communications were read: C. W. Osman: The geology of the northern border of Dartmoor, between Whiddon Down and Butterdon Down. The Lower Carboniferous rocks may be divided into a Lower Aluminous and a Calcareous Series. The latter commences with grey shales above the Lower Aluminous series, without any physical feature, and contains a volcanic band, generally in a fragmentary condition, mixed with ash, slate, and other fragments, and impregnated with chert; but, at East Underdown, the rock is more solid, and is a quartzless keratophyre. The corresponding mixed igneous rocks of the north-western Dartmoor border, which have been variously described, are altered keratophyres. Above the volcanic band are two limestone-areas: one on the west, near Whiddon Down, and, separated by quartzose rocks, another limestone-area at Drewsteignton. Throughout the length of border considered, the top of the Calcareous Series is formed of grey shales, with hard rock-bands which pass upwards into the Upper Aluminous Series. The granite south of the Carboniferous border-rocks shows three separate intrusions, all from the same magma, but showing sufficient differences to separate them.—D. J. Farquharson: The geology of southern Guernsey. With the possible exception of some dykes of doubtful Palaeozoic age, the whole of Guernsey consists of pre-Cambrian rocks-gneisses and schists in the south; unfossiliferous shales and grits at Pleinmont; and a series of intrusions in the north, which range from hornblende-gabbro through diorites and tonalites to granites with their accompanying dykes. These dykes not only pierce the last-named suite, but also the gneisses and grits of the south.

Geological Notes on the North-West Provinces (Himalayan) of India

Abstract ‘The country examined extends in a north-westerly direction across the line of strike, from ... South-eastern Kumaon to north of the Alaknunda River.’ The foothills consist of Tertiary clays and sandstones, the snowy ranges of gneissose, granitic, and metamorphic rocks of various descriptions. ‘Between the snowy ranges, or rather the more southerly range of the Himalaya chain, a band of hills extends, for nearly 50 miles on an average, to the foothills. The whole area is rich in minerals.’ The Author refers to the occurrence of various rocks, met with mainly in this third belt. They include slates with vein-quartz; mica- and graphitc-schists; dykes of dolerite; granites; clay-slates, sandstones, and schists, with copper, lead, and tin; limestones, serpentines, and hornblendic rocks, with tale, steatite, etc.; various schists, quartzites, and limestones. The summary of the Author9s observations leads him to ‘suppose that there are at least three distinct limestone or calcareous series in Kumaon and Garhwal, and that schists and quartzites, with several isolated patches of granitic rock, form a large part of the remaining formations.’

Petrological Notes on the Vicinity of the Upper Part of Loch Maree

The relations of the rocks on the western border of Ross and Sutherland have long been a subject of controversy. Into the details of this it is needless to enter on the present occasion, as they have been recently recapitulated to the Geologists′ Association and published in their Proceedings*. The materials for this sketch are mainly contained in our own Journal; and the last contribution to the subject was a paper read by Dr. Hicks on May 22, 1878†. After listening to the ingenious theory put forward by that author, it occurred to me that the question was one on which the testimony of the microscope ought to be especially valuable. According I spent some days last summer at Kinlochewe, in order to examine the rocks in the field and to obtain specimens for microscopic work. I have now the honour of laying before the Society the results of these investigations. (1) Syenite of Glen Laggan. Previous writers on the above section have agreed in stating that a mass of igneous rock makes its appearance on the floor of Glen Laggan, about two miles from Kinlochewe, and extends for some distance up the bed of the stream, apparently cutting off the quartzite from the newer group. This rock is called diorite by Nicol, syenite by Murchison, Geikie, and Hicks; it is shown by the last author upon a section‡ as intrusive among the calcareous series which overlies the quartzites. Almost immediately on reaching the spot where the “syenite” first appears