Nodular Limestones Research Articles

Early Wuchiapingian (Lopingian, late Permian) drowning event in the South China block suggests a late eruptive phase of Emeishan large Igneous Province

Abstract Although the precise age and magnitude of the end-Guadalupian biodiversity crisis is still debated, this “mass” extinction has been customarily linked with the onset of massive volcanism in the Emeishan Large Igneous Province (ELIP) in south China. The onset of ELIP eruptive activity at least partly coincides in time with episodes of regional subsidence interrupting the predominant regime of carbonate platforms during Capitanian times. Here, we present a strikingly similar but younger (early Wuchiapingian) subsidence episode from the Pingtang syncline in southern Guizhou, termed the Mapojiao Event. Shallow-marine, light-grey, thick-bedded bioclastic limestone of the Wuchiaping Formation (Unit A) are overlain by deep-marine radiolarian-sponge spicule, thin-bedded black limestone (Unit B). The latter is followed by volcaniclastic distal turbidites (Unit C). The base of the next overlying unit consists of cherty, nodular limestone (Unit D) rich in radiolarians and sponge spicules, whose respective abundances decline up-ward within a few meters. Concomitant replacement by a shallow marine benthic fauna documents the uplift that terminates the event. A total of five index species of Clarkina conodonts indicating an early Wuchiapingian age were obtained from Units A and B. Brachiopods of Wuchiapingian age were also documented in units A, B and D. Compilation of drowning events in the Guadalupian-Lopingian (G-L) interval suggests clustering into three episodes; 1: middle Capitanian, 2: possibly latest Capitanian, 3: early Wuchiapingian. The first drowning event is overlain by ELIP volcanics in sections near the center of the volcanic province. In peripheral areas, the first drowning is intercalated within carbonate platforms (e.g. Maoershan). A second drowning event cannot be excluded close to G-L boundary but it is obscured by the unconformity associated with an eustatic regression and by ambiguous conodont age control. Overlying this unconformity, the Wangpo Shale, which contains ELIP-derived volcanic materials, rests on the first (e.g. in Chaotian) drowning event. The striking similarities of the facies architecture shared by the first and third drowning events suggest a similar driving mechanism. Hence, we propose that the Mapojiao Event represents the youngest, early Wuchiapingian, burst of ELIP eruptive activity. There is no one-to-one correlation between these episodes related to ELIP eruptive activity and extinction phases of marine clades. Only the end-Guadalupian extinction has been correlated with the first eruptive episode. In marked contrast, the newly discovered Mapojiao drowning episode occurred within a diversification phase, which undermines any causal relations between the younger phases of ELIP volcanism and additional extinctions.

Carbon-isotope stratigraphy and pelagic biofacies of the Middle–Upper Jurassic transition in the Tethys–Central Atlantic connection

A bulk carbon-isotope stratigraphy, based on high-resolution sampling of five stratigraphic ammonite-dated sections from pelagic swells of the Subbetic basin (External Zones of the Betic Cordillera, southern Spain) is presented. The studied sections are characterized by Callovian–Oxfordian stratigraphic successions located in the South Iberian palaeomargin, a key area connecting the Central Atlantic to the Tethys oceans. The rocks are mainly nodular limestones with common extreme condensation (rosso ammonitico facies). Discontinuities with hiatuses of variable duration, submarine “hardgrounds”, Fe-Mn ooids, limonite crusts, and neptunian dykes are observed around the Callovian/Oxfordian boundary. The stratigraphic record, although very time-averaged, allows for a consistent and accurate ammonite chronostratigraphy. The carbon isotopes of marine carbonates show a marked trend towards high δ13C values from Lower Oxfordian to the Middle Oxfordian (~4.3‰, near the Plicatilis/Transversarium boundary). The isotopic values stand between 2.7 and 3.0‰ at the Upper Oxfordian (Bifurcatus and Hypselum Zones) and lowermost Kimmeridgian (Bimammatum Zone); afterward δ13C values decrease and reach a relative minimum (~2.3–2.5‰) in the Lower Kimmeridgian (Bimammatum/Planula boundary). Finally, isotopic values increase again (~2.6–2.7‰) in the lower Kimmeridgian (mid part of the Planula Zone). Comparison of carbon-isotope stratigraphy between Subbetic and other Tethyan areas shows similar trends. The replacement of thin-shelled bivalves by planktonic foraminifers and radiolarians that took place in the Callovian/Oxfordian boundary can be associated to the widening of the trans-Pangaean seaway. This, in turn, triggered the global warming which increased nutrients concentration in upper water column due to intensified nutrient input by river plumes. These phenomena are concomitant with the major Oxfordian δ13C positive excursion and with a transgressive cycle.

A Reappraisal of Stratigraphy of Bagh Group of Rocks in Dhar District, Madhya Pradesh with an Outline of Origin of Nodularity of Nodular Limestone Formation

Abstract Upper Cretaceous Bagh Group of rocks in M.P. have been studied by many workers. Several stratigraphic successions have been proposed. It has resulted in controversies in terms of applicability, absence of characterization of contact surfaces, no mention of locality names where characteristic features are well visible. Hence a new stratigraphic succession has been proposed. Besides, the entire area is characterized by different types of nodularity at least in the lower part of carbonates. This worldwide unique characteristic has not been resolved earlier. The present authors have tried to explain the origin of this nodularity on the basis of adequate field evidences and came to the conclusion that overburden mechanical compaction produced by Lametas and Deccan Trap and subsequent chemical compaction are the ultimate cause of nodularity in the carbonates. Later entire area was reactivated and churned by Thallassinoid burrow producing organism, the presence of which bears testimony.

A Study of Bioerosion of Belemnites and Taphonomy of Cephalopods from Kuldhar Member of Jurassic Jaisalmer Formation from Jaisalmer, Rajasthan

ABSTRACT The Callovian-Oxfordian Kuldhar Member of Middle-Upper Jurassic Jaisalmer Formation, Rajasthan is characterized by a rich cephalopod (ammonites and belemnites) fauna along with other invertebrates. They are embedded in oolitic limestone, at places in nodular limestone, grey shale and occasional red mud. The belemnite rostra bear bioerosions in the form of borings of circular or elliptical type. The present study identified those as Trypanites isp. and Rogerella isp. and characterized the hitherto unnoticed bioerosions of these belemnite rostra to be post-mortal. Different dispositions of major diameter of belemnite rostra has been interpreted to represent churning effect of ichnofossil producing organisms which put evidences of several generations of omission surfaces. Vertical and horizontal orientations of stephanoceratid ammonites side by side have been critically analysed in the light of lithology and prevailing environmental condition and inferred to be an artifact of gravity and thixotropic property of clay. Ammonites like Stephanoceratids and Macrocephalitids inhabit within 110m depth which is also permissible depth of belemnites as well as probable depth of formation of oolites, carbonate mud and aluminosilicate mud. Considering the lithology of the rocks like oolites, carbonate mud, aluminosilicate, the habitat of stephanoceratid and habitat of acrothoracid barnacles (organisms responsible for Rogerella isp.), the environment has been delineated to be sublittoral which was previously designated as shoreface zone to offshore transition zone.

New data on the age and stratigraphic relationships of the Czajakowa Radiolarite Formation in the Pieniny Klippen Belt (Carpathians) based on the radiolarian biostratigraphy in the stratotype section

The radiolarian biostratigraphy of the Middle–Upper Jurassic pelagic siliceous sediments (Czajakowa Radiolarite Formation) in the Niedzica succession of the Pieniny Klippen Belt (Carpathians) is interpreted in terms of their age in a stratotype section, and facies equivalents in other tectonic-facies units of this region. The siliceous sediments are represented by radiolarian cherts and silicified limestones which are underlain and overlain by red nodular limestones, equivalents of the Rosso Ammonitico facies. The radiolarian association includes thirty-seven taxa belonging to twenty one genera which represent the Northern Tethyan Palaeogeographic Province. Key radiolarians recorded provide a means of correlation with zonation schemes based on Unitary Associations defined for the Jurassic Tethyan sediments. The age of the Czajakowa Radiolarite Formation in the stratotype section is determined as U.A.Z.9 to U.A.Z.11 corresponding to middle Oxfordian up to Kimmeridgian. Comparison of radiolarian biozones from the stratotype section with other facial equivalent sections in the Pieniny Klippen Belt reveals a significant diachronism for both the lower and the upper limits of the Jurassic pelagic siliceous facies.

Facies characteristics and depositional environments of the middle Eocene (Lutetian) Harudi Formation, Kachchh, Western India

The 8.5 m thick, 1.4 km long and 0.35 km wide, ESE–WNW oriented cliff section (N 23°31′32″ E 68°41′00″) exposed across Harudi–Baranda road is extensively studied for its facies characteristics and based on that depositional environments of the middle Eocene (Lutetian) Harudi Formation are deciphered in the present study. Two cycles of grey mudstone alongwith nodular limestone–coquina limestone-gypsiferous mudstone facies in the lower part of the succession suggest sedimentation in coastal quiet-water lagoonal to tidal flat environments, while glauconitic shale, bioclastic packstone and gypsiferous foraminiferal packstone facies in the upper part suggest sedimentation on middle- to inner-shelf and tidal flat depositional environments. In all, three shallowing upward cycles have been identified in the studied outcrops and based on that lagoonal-middle shelf-inner shelf-tidal flat depositional environments are suggested for the middle Eocene Harudi Formation.

Erratum to: Genesis of Paleocene and Lower Eocene shallow-water nodular limestone of South Tibet (China)

Erratum to: Genesis of Paleocene and Lower Eocene shallow-water nodular limestone of South Tibet (China)

Uppermost Famennian stratigraphy and facies development of the Reigern Quarry near Hachen (northern Rhenish Massif, Germany)

As a contribution to the ongoing international revision of the Devonian/Carboniferous boundary, we present a bed-by-bed study of the Reigern Quarry in the northern Sauerland (Rhenish Massif, Germany), which is famous as an uppermost Famennian ammonoid locality. Currently exposed are ca. 2.5 m of strongly cyclic Wocklum Limestone, conformably overlain, but with a long hiatus (topmost Famennian to upper Tournaisian), by laminated radiolarites and a thin metabentonite of the Lower Carboniferous Hardt Formation. The nodular limestones are pelagic mud-wackestones with some sporadic occurrences of cephalopod float-rudstones. The exposed part of the Wocklum Limestone falls in the successive Bispathodus ultimus ultimus and Siphonodella (Eosiphonodella) praesulcata (s.l.) zones. It yielded two new Siphonodella (Eosiphonodella) species left in open nomenclature, Neopolygnathus communis aff. dentatus and the possibly stratigraphically relevant Bispathodus ultimus corradinii ssp. nov. The upper range of Palmatolepis gracilis semisigmoidalis is significantly expanded. The conodont faunas mostly belong to variants of the pelagic Palmatolepis-Bispathodus biofacies; but in the lower part of the succession, there is a new Neopolygnathus biofacies that previously has not been recorded from deeper-water, pre-Hangenberg Crisis strata. Neopolygnathus is interpreted as a palaeoecological generalist that variably blossomed in outer or inner shelf facies and after other conodont groups declined. The mostly loose ammonoid faunas comprise almost 30 taxa and fall mostly in the lower Wocklumian Kalloclymenia subarmata and Muessenbiaergia bisulcata zones (Upper Devonian = UD VI-A1/A2), which agrees with previous ammonoid-conodont correlations.

Genesis of Paleocene and Lower Eocene shallow-water nodular limestone of South Tibet (China)

This paper examines the genesis of the Paleocene to Lower Eocene shallow-water nodular limestones in South Tibet. The negative carbon isotope excursion representative for the Paleocene–Eocene boundary is located in one nodular limestone bed of the Zhepure Shan Formation showing an extraordinary thickness of about 9 m, inspiring the question under which conditions these nodular limestones were formed. Based on field appearance, the shallow-water nodular limestones of Tingri and Gamba can be classified into five nodular limestone categories (Stylonodular Rock I, Nodular Rock I, Nodular Rock II, stylobedded rock and stylomottled rock) and some transitional members (stylobedded rock transitional to Stylobedded Rock II). Clay variations are assumed to be responsible for these various types of nodular limestones within the sediments. Observations of nodular limestones in South Tibet suggest that those sediments were mostly formed due to autochthonous rather than allochthonous processes. Differential diagenesis resulted in an early selective cementation of limestone nodules due to carbonate supply, while the marls were not cemented but provide the carbonate for the nodule cementation. Additionally, cemented and carbonate-rich nodules are resistant to chemical compaction, while the uncemented and clay-rich marl layers are affected by pressure solution processes due to an overburden of sediments. Additionally, a model is presented, illustrating the origin of different nodular limestones described here.

Anatomy of a mountain: The Thebes Limestone Formation (Lower Eocene) at Gebel Gurnah, Luxor, Nile Valley, Upper Egypt

We present a detailed geologic study of the Thebes Formation at Gebel Gurnah in its locus typicus on the West Bank (opposite Luxor) of the Nile River in the Upper Nile Valley, Egypt. This is the first detailed measurement and lithologic description of the ∼340 m thick (predominantly) carbonate section. The Thebes Formation is divided into thirteen major lithic units (A to M). We interpret data on the lithologic succession and variations, whole rock/clay mineralogy, and macro/micropaleontology in terms of deposition on a shallow carbonate platform episodically influenced by continental runoff, and describe six depositional sequences that we place in the global framework of Lower Eocene (Ypresian) sequence stratigraphy. We note however significant incompatibilities between the Thebes depositional sequences and the global sequences. We emend the definition of the Thebes Formation by defining its top as corresponding to level 326 m at the top of Nodular Limestone ‘L’ (NLL), and assigning the overlying beds to the Minia Limestone Formation. New biostratigraphic data and revision of previous studies establish the direct assignment of the Thebes Formation to planktonic foraminiferal Zones E4/P6b (upper part), E5/P7 and (indirectly) Zone E6/P8, and (probably, indirectly) Zone E7a/”P9”, and to calcareous nannofossil Zone NP12 and lower Zone NP13 of the Lower Eocene (Ypresian) and provide a temporal framework spanning ∼ 2.8 Myr from <52.45 to ∼49.6 Ma for the deposition of the Thebes Formation prior to the prominent sea level fall (∼49.6 Ma) towards the end of the Early Eocene. Dominantly carbonate deposition, with a strongly reduced detrital influx, occurred on a very wide shelf (probably) at least ∼ 100 km from the coastline. The thick sedimentary succession and the marked vertical lithologic variations are interpreted as resulting from sea level fluctuations imprinted on a long-term decrease in sea-level associated with rapid subsidence reflecting tectonic relaxation after the major Late Paleocene tectonic reorganization of the Syrian Arc.

Selective incidence of the toarcian oceanic anoxic event on macroinvertebrate marine communities: a case from the Lusitanian basin, Portugal

A macroinvertebrate assemblage has been studied from the Thin Nodular Limestones Member (TNL) of the Fonte Coberta section (Lusitanian Basin, Portugal), giving special attention to its trace fossils. The assemblage was studied to analyse the influence of the Toarcian Oceanic Anoxic Event (T-OAE) on the macroinvertebrate community. The TNL consists of thin alternations of marl/limestone and nodular limestone beds, showing clear differentiations from bottom to top. Integrative analysis of the macrofossil assemblage for the studied interval, conducted for the first time in the Lusitanian Basin, reveals three major features: (1) abundant trace fossils with dominance or near exclusiveness of Thalassinoides, and a local record of Spongeliomorpha; (2) scarcity, but not extinction, of ammonoids; and (3) the absence of previously abundant brachiopods. The findings reveal a selective incidence of the T-OAE on the macrobenthic community, with a major influence (extinction) of brachiopods, severe changes (diminution in abundance and diversity) on ammonoids and a minor effect on macrobenthic tracemakers. A complex relationship between different palaeoenvironmental conditions during the T-OAE can be interpreted, discarding anoxic conditions in the seafloor, although low oxygen conditions in the water column are a possibility. The increase in seawater temperature and availability of nutrients on the seafloor would have played an influential role.

Trans-Tethyan correlation of the Lower–Middle Cenomanian boundary interval; southern England (Southerham, near Lewes, Sussex) and Douar el Khiana, northeastern Algeria

Abstract A 480 m section of marls with widely separated levels of nodular limestone in the Fahdene Formation north of Bou Khadra in Tebessa Province, northeastern Algeria, spans the Lower/Middle Cenomanian boundary. A total of 30 ammonite species are present, of which two: Forbesiceras reversum and Calycoceras (Newboldiceras) algeriense are new. The fauna allows recognition of the Northwest European upper Lower Cenomanian Mantelliceras dixoni Zone, the succeeding lower Middle Cenomanian Cunningtoniceras inerme Zone, the Acanthoceras rhotomagense Zone and its subzones of Turrilites costatus and Turrilites acutus. The sequence of index species occurs in the same order in both north-eastern Tunisia and the Southerham Grey Pit in Sussex (and indeed elsewhere in Northwest Europe), indicating these to be robust assemblage zones and subzones that can be recognised on both the north and south sides of the Tethys. Other occurrences of taxa that are common in both sections and regions are markedly different, and include the co-occurrence of Cunningtoniceras inerme (Pervinquière, 1907) with Acanthoceras rhotomagense (Brongniart, 1822) in the costatus Subzone in north-eastern Algeria and central Tunisia, the extension of Acompsoceras renevieri (Sharpe, 1857) into the lower Middle Cenomanian in north-eastern Tunisia, whilst the acme of Turrilites scheuchzerianus Bosc, 1801, is in the dixoni Zone in Northwest Europe, and in the inerme Zone in northeasten Algeria and adjacent parts of Central Tunisia. These differences are not a result of collection failure or non-preservation, but must rather reflect environmental controls on occurrence and abundance.

Microfacies and Diagenetic Analysis of Lockhart Limestone, Shah Alla Ditta Area Islamabad, Pakistan

The Larger Foraminifera made a major contribution to Paleocene and Eocene biota. The microfacies and diagenetic setting of the Paleocene Lockhart Formation were analyzed in Shah Alla Ditta area, Islamabad. The Lockhart Formation is highly fossiliferous, comprising of thin nodular limestone with interbedded shale/marl. The lower contact is unconformable with Jurassic Samansuk formation while the upper contact is conformable with Margalla Hill Limestone. Rock samples were collected from the field and thin sections were prepared and analyzed under the microscope and on the basis of detailed petrographic study three types of microfacies were identified and interpreted based on Dunham’s textural classification, allochem type, fossil content and sedimentary structures. The microfacies include: LH-MF 1: Foraminiferal Wackestone/Biomicrite Microfacies, LH-MF 2: Algal Foraminiferal Wackestone Microfacies, LH-MF 3: Mixed Bioclastic Mudstone Microfacies. A number of larger benthic foraminifera, and the lack of Planktonic foraminifera in the Lockhart Limestone, indicate shallow to deep water of restricted inner to middle shelf environment of deposition. Larger foraminifera and dasycladacena algae are the two major fossil contents present in the Lockhart Formation. Larger foraminiferal species like Lockhartia hameii and Lockhartia conditi present in the formation confirm the age of Lockhart Limestone as Paleocene. The main diagenetic fabric recognized in the limestone reveals mechanical and chemical compaction, deep burial water pressure, pressure solution and tectonics-related fracturing. The nodularity in the limestone is credited to pressure solution.

The Grajcarek Succession (Lower Jurassic–mid Paleocene) in the Pieniny Klippen Belt, West Carpathians, Poland: a stratigraphic synthesis

A concise stratigraphic synthesis of the Grajcarek Succession of the Pieniny Klippen Belt (West Carpathians,Poland) is presented. This succession consists of 12 lithostratigraphic units with the rank of formation, and two with the rank of member, spanning the geological time from middle Toarcian (late Early Jurassic) to Maastrichtian (Late Cretaceous) and mid Paleocene. The stratigraphical column starts with deep-water flysch (the Szlachtowa Fm; Toarcian–Aalenian through Bajocian–?lower Bathonian), followed by dysoxic shales, marls and limestones (the Opaleniec Fm; Bajocian–Bathonian). The previously distinguished Krzonowe and Stembrow formations, are downgraded to members. Late Bathonian–Oxfordian times were characterized by the widely occurring deposition of abyssal radiolarites and shales, which is represented by the Sokolica Radiolarite Fm and the Czajakowa Radiolarite Fm, common to both the Grajcarek and Klippen successions. Red nodular limestones and aptychus marls (the Czorsztyn Limestone Fm; Kimmeridgian–lower Tithonian) overlie the radiolarites. Above, pelagic cherty limestones occur (the Pieniny Limestone Fm; Tithonian–Aptian). These are followed by Lower Cretaceous predominantly dark shales and marls (the Kapuśnica Fm; Aptian–Albian, the Wronine Fm; Albian, and the Hulina Fm; Albian–Cenomanian), succeeded by abyssal, red shales (the Malinowa Shale Fm; upper Cenomanian–Campanian), and these in turn by grey, marly, flyschoid strata (the Haluszowa Fm; ?Campanian). The Grajcarek Succession terminates with the Jarmuta Fm (Maastrichtian–mid Paleocene). It consists of sedimentary breccias, often with large olistoliths of Jurassic–Cretaceous rocks, and conglomerates and sandstones in a southern zone, giving way to proximal flysch and distal flysch facies further north. This was the time of orogenic Laramian folding events, associated with subaerial and submarine erosion. A sedimentary hiatus separates the Jarmuta Fm flysch (Maastrichtian) from the Szczawnica Fm (Upper Paleocene–Eocene) in both the Klippen and Grajcarek successions. This hiatus seems to diminish and finally close in a northward direction, in the Magura Nappe succession.

Jurassic red nodular limestone from NE Slovakia used as the Ľubovňa “marble” during the Renaissance in Slovakia and Poland

The Ľubovňa “marble” is red nodular limestone of Oxfordian to Tithonian age, which used to be extracted in several quarries near the town of Stara Ľubovňa in NE Slovakia. It replaced the Hungarian Gerecse “marble” which was extensively used in the Kingdom of Hungary and surrounding countries from the end of the 12th to the first third of the 16th century when its use was interrupted by the Turkish occupation of the area. The Ľubovňa “marble” was used as a substitution especially for Renaissance tombstones in today’s Slovakia and Poland and it was found also in Hungary. It reached the top of its popularity between the mid-16th and mid-17th century. To a smaller extent it was still used in the surrounding territories during the other styles in the 18th and 19th centuries. The “marble” production was probably affected by the political situation and wars. It is possible to distinguish the Ľubovňa “marble” from the Gerecse “marble” and the Adnet “marble” from Austria macroscopically on the basis of its distinct cleavage, and microscopically on the basis of microfacies with Saccocoma , Globuligerina and calcareous dinoflagellates. According to the stable isotopes of 18 O and 13 C, it is approximately similar to the Adnet “marble”.

Taphocoenoses and diversification patterns of calcimicrobes and calcareous algae, Ordovician, Tarim Basin, China

Despite the crucial role of epibenthic primary producers (cyanobacteria, green and red algae), no diversity curves for calcimicrobes and calcareous algae are available to assess the pyramiding paleoecology characterizing the Ordovician biodiversification episode. A total of 24 taxa of calcimicrobes and calcareous algae are identified from a Dapingian to lower Katian succession of carbonate sedimentary rocks exposed at the Leyayilitag ridge, Bachu Uplift, Tarim Basin, northwest China. Calcimicrobes (14 taxa), Dasycladales (seven taxa), Bryopsidales (one taxon), and Cyclocrinales (two taxa) contribute to five distinct taphocoenoses characterizing a suite of carbonate mounds. In stratigraphic order, these are calathid sponge mounds, algal calcimicrobial mounds, algal mounds, algal reefs, and calcimicrobial mounds. Within the lower Katian Belodina confluens Zone, the diversity increases substantially from around 5 to more than 20 taxa per 2 Ma. This increase in diversity is based on new calcimicrobes (Bija, Ortonella, Garwoodia, Hedstroemia, Rothpletzella, Phacelophyton, Rauserina) and the diversification of Dasycladales and Cyclocrinales. By comparison, the global diversity of calcimicrobes and calcareous algae (derived from literature data) started to increase earlier, namely within the late Darriwilian Pygodus serra Zone (offset of about 4 Ma). This offset might be due to the peculiar lithology of the Sandbian Tumuxiuke Formation (condensed section of red nodular limestones bounded by disconformities). However, a similar temporal offset is recorded for calathid sponge mounds; therefore, the Tarim tectonic microplate (Tarim Block) might display an endemic–anachronistic character. The diversity curves of Ordovician benthic primary producers (calcimicrobes, calcareous algae) are similar to those recorded by some fossil groups, in particular eleutherozoan echinoderms.

Multiple proxies indicating methane seepage as the origin of Devonian large barite deposit in Zhenning-Ziyun, Guizhou, SW China

Bedded barite deposits are found in Cambrian and Devonian strata in China. In this paper, we report the occurrence of Late Paleozoic methane seeps from bedded barite in one of the largest barite deposits in China. The ore bodies are stratiform and lenticular in shape and are hosted within Upper Devonian cherts. The barite deposits usually have laminar, banded, fragmental, massive and rosette textures, and radial and spheroidal structures were observed in the barite ores. Nodular limestones are associated with the barite deposits; they consist of clotted micrites and framboidal pyrites. The internal structure of framboidal pyrite is simple, in which the sun-flower structure has been observed, similar to modern seep carbonates. The δ13CV-PDB values range from −8.82‰ to −10.27‰, and δ18OV-PDB ranges from −8.10‰ to −8.20‰ in Xiyahe and from +0.03‰ to −3.31‰ in Luocheng. The 13C depletion suggests that these carbonates formed in a methane seep through the anaerobic oxidation of methane (AOM). This evidence lends strong support to the interpretation that methane hydrate contributed to the barite deposition. In addition, the δ13CV-PDB values decrease gradually from Xiyahe to Luocheng, which indicates the gradually weakening strength of the methane seep activities. The δ30SiNBS-28 values of the cherts range from −0.3‰ to +0.5‰, except for two samples (LJ-24: δ30SiNBS-28 values=+0.9‰; ZL18: δ30SiNBS-28 values=+1.1‰). The lowest δ30SiNBS-28 values reflect silicon derived from hydrothermal fluids ascribed to intense tectonic activity, which consequently caused the rapid maturity of hydrocarbons. The 87Sr/86Sr values (87Sr/86Sr=0.70863–0.70898, avg. 0.70877; n=11) of barite are higher than the average value of contemporary seawater, showing that hydrothermal processes played a minor role in barite mineralization.

Ammonite assemblages and chronostratigraphy of the uppermost Bajocian–Callovian (Middle Jurassic) of the Murcia Region (Betic Cordillera, south-eastern Spain)

In this paper the stratigraphy and biostratigraphy of the Bathonian–Callovian rocks of the Murcia Region, based on high-resolution sampling yielding good ammonite dating, is reported. All the ammonites analysed are from four sections located on a pelagic swell (External Subbetic palaeogeographic domain) of the External Zones of the Betic Cordillera, Murcia Region, southern Spain. These represent characteristic Bathonian–Callovian sections of the Subbetic epipelagic swells in the Betic Cordillera. The lithology consists mainly of both nodular limestones and marly limestones. Discontinuities with hiatuses of variable duration, submarine hardgrounds, Fe–Mn macrooncoids, limonite crusts, neptunian dykes, etc., occur in the Middle Bathonian–Callovian interval. Extreme condensation episodes are common, but abundant ammonite faunal records have enabled a consistent and accurate chronostratigraphy. The Parkinsoni Zone, Daubenyi and Dimorphus subzones (uppermost Bajocian), the Zigzag and Aurigerus zones (Lower Bathonian), the Sofanus and Costatus zones (Middle Bathonian), the Orbis Zone (Upper Bathonian), and the Bullatus and Gracilis Zones (Lower Callovian) are recognised and characterised. The ammonite fauna shows a typical Mediterranean character. Phylloceratina and Lytoceratina are the predominant elements within the ammonite fauna, but Lytoceratina is dominant in the Lower Bathonian whereas Phylloceratina predominates in the rest of the Bathonian and in the Callovian. Other ammonites, such as Oppeliidae, Lissoceratidae, Stephanoceratidae, Perisphinctidae, Tulitidae, and Reineckeiidae, are also common throughout the uppermost Bajocian to Lower Callovian interval. Strigoceratidae are present, but scarce.

Geochemical Assessment of Limestone for Cement Manufacturing

The El Mashar Unit of Triassic-Quaternary successions from limestone deposit of Cement Lafarge quarry (North, Morocco) is characterized by the occurrence of several sedimentary rocks. This study, based on chemical composition of more than 1600 samples of drill cuttings provides insight into the chemical parameters controlling the use of limestone in cement making. El Mashar formation can subdivided into twelve facies based on the chemical composition and geological position of different lithostratigraphic successions, being: dolomite Triassic limestone, Rhaetian limestone marl, Hettangian nodular limestone, Hettangian limestone with low magnesium, Hettangian limestone with silica, Hettangian limestone with high magnesium, Sinemurian brecciated limestone, basal Sinemurian limestone, central Sinemurian limestone, sommital Sinemurian limestone, Eocene marl and Quaternary topsoil. This study documents the importance of geochemical assessment of limestone for cement manufacturing.

Toarcian ammonitico rosso facies from the South Iberian Paleomargin (Betic Cordillera, southern Spain): paleoenvironmental reconstruction

The Toarcian ammonitico rosso facies were widespread in the Mediterranean Tethys (between 15 and 30°N latitude) in the North Gondwana Paleomargin (Apulian promontory and North African Margin) and southern Iberian Paleomargin (Betic Cordillera). These facies were associated with epi-oceanic slopes of a sedimentary swell-trough system related to the extensional phase of continental rifting. In the Median Subbetic (southern Iberian Paleomargin), ammonitico rosso facies show a progressive change through the Toarcian on the hemipelagic swells after the fragmentation of a carbonate platform. During the latest Pliensbachian to the Bifrons Zone (middle Toarcian), sedimentation was dominated by epi-oceanic limestone and marl with a high influence of neighboring shallow-water environments represented by common turbidite–tempestite beds (with foraminifera and ooids). Microfossils and trace fossils provide no evidence of oxygen-restricted conditions. In the Gradata Zone (middle Toarcian), the ammonitico rosso facies appear (red nodular limestone and marly-limestone rich in the trace fossils Phycodes, Planolites, Thalassinoides, and Chondrites). Progressively more pelagic conditions and a restricted influence of emergent lands and carbonate platforms are reflected by the reduced input of turbidite–tempestite beds and increase of ammonitellas and radiolaria. A sea-level fall affected the hemipelagic swell during the middle–late Toarcian and favored sediment-winnowing by currents, with subsequent nodulation. The combined action of burrowing, compaction, and dissolution controlled nodulation, which ranges from diffuse nodules to sharp-edged nodules. The sedimentation rate conditioned the time available for nodule growth, the migration of the Ca2+ and HCO3 − precipitation horizon, and the degree of nodulation (from horizons with diffuse-edged nodules to semi-continuous to continuous layers formed by the coalescence of sharp-edged nodules).