Pedro Cózar

Late Asbian to Brigantian (Mississippian) foraminifera from southeast Ireland: comparison with northern England assemblages

Foraminiferal assemblages from platform carbonates in the Carlow district (SE Ireland) are analysed. This platform contains a near-continuous succession of Upper Asbian to lower Upper Brigantian strata. Detailed sampling of several quarry and borehole sections allows characterization of foraminiferal assemblages throughout the succession. Assemblages typifying the Late Asbian, Early Brigantian and Late Brigantian are described, with the most common genera and species, as well as the guides for the recognition of these substages. In addition, three successive faunal events are recognized within the Early Brigantian. A comparison with northern England foraminiferal assemblages from the Asbian and Brigantian stratotype sections shows a great similarity in the recorded taxa. Furthermore, these taxa have closely comparable stratigraphical ranges, demonstrating the biostratigraphic utility of these foraminifera throughout Ireland and Britain. Taxa proposed here as guides for the basal Brigantian are potentially an alternative to the previously published taxa (which are either unrecorded, or recorded at higher stratigraphic levels in the Brigantian).

New Foraminifers in the Visean/Serpukhovian Boundary Interval of the Lower Limestone Formation, Midland Valley, Scotland

Abstract The biostratigraphy of the upper part of the Mississippian Lower Limestone Formation in the Midland Valley, Scotland is revised using foraminiferal assemblages. This formation was previously assigned exclusively to the upper part of the Brigantian Substage (upper Cf6δ, P2 or latest Visean), whereas the succeeding Limestone Coal Formation (barren of foraminifers and conodonts) was assigned to the Pendleian Substage (lower Cf7, E1 or early Serpukhovian). The foraminifers, in particular those recorded from the Second Hosie and Top Hosie limestones and their lateral equivalents (Anvil and MacDonald limestones), are comparable to Serpukhovian assemblages from the Ukraine and Russia. Consequently, the Visean/Serpukhovian stage boundary is repositioned at the base of the Second Hosie Limestone. This assignment of the Second Hosie Limestone to the Pendleian is reinforced by the first occurrence of the ammonoid Emstites (Cravenoceras), although it occurs 1 m below the Top Hosie Limestone. Pendleian foraminiferal assemblages from northern England, its geographically closest equivalent, are similar but not well enough known for a detailed comparison. A few similarities are found between the foraminiferal assemblages from the Midland Valley and those from southwest Spain and North African basins. Faunas from the Second and Top Hosie limestones and their lateral equivalents allow us to propose an assemblage zone, valid for regional correlations within the British Isles, and the faunas can be potentially used as Serpukhovian markers for western Paleotethyan basins. Two new genera and species are described, Praeplectostaffella anvilensis n. gen. n. sp. and Praeostaffellina macdonaldensis n. gen. n. sp., and two new species, Tubispirodiscus hosiensis n. sp. and Euxinita pendleiensis n. sp.

Potential foraminiferal markers for the Visean–Serpukhovian and Serpukhovian–Bashkirian boundaries—a case-study from Central Morocco

Abstract The Carboniferous succession in Adarouch (Central Morocco, north of the Atlas Transform Fault) contains thick carbonate beds including upper Visean, Serpukhovian and basal Bashkirian rocks. Foraminifers enable precise recognition of the Visean/Serpukhovian (V/S), early/late Serpukhovian (eS/lS) and Serpukhovian/Bashkirian (S/B) boundaries. Insolentitheca horrida, Loeblichia ukrainica, “Millerella” spp. and Endostaffella? sp. 2 are regarded as regionally useful indices to the V/S boundary, whereas Eostaffellina spp., Eostaffella pseudostruvei and some evolved species of Archaediscus exhibit greater reliability for worldwide correlation of this level. Similarly, the eS/lS boundary is marked locally by Brenckleina rugosa, Eosigmoilina sp., and Monotaxinoides spp. and globally by Loeblichia minima, Bradyina cribrostomata, Plectostaffella spp., Eostaffellina “protvae” and “Turrispiroides”, and the S/B boundary is marked locally by Globivalulina bulloides and globally by Seminovella elegantula, and Novella?. Occurrences of these taxa in Morocco allow correlations with the Moscow Basin, the Urals, the Donetz Basin and North America. The Moroccan assemblages share few taxa in common with Saharan basins south of the Atlas Transform Fault. Correlations with western European basins are difficult because of the paucity in the latter of foraminiferal-bearing carbonate strata.

The Carboniferous Archerbeck Borehole, near Canonbie (Dumfriesshire, southern Scotland): biostratigraphic revision of the late Asbian to early Pendleian succession using foraminiferans and regional correlations

The upper half of the Archerbeck Borehole contains a continuous Mississippian succession from the late Asbian (late Visean) to the Pendleian (early Serpukhovian), with numerous limestone horizons. The borehole sequence lies within the Solway Basin (western end of the Northumberland Trough) and bridges the successions between the Midland Valley of Scotland and the Pennines (northern England). The rich foraminiferal and algal assemblages are compared to those described by previous authors, and genera as well as species are updated as far as is possible. In addition, some other overlooked or underestimated taxa have been identified and illustrated, which improve notably the biostratigraphic resolution of the Archerbeck Borehole succession. Within the abundant foraminiferal assemblages can be highlighted the richness and diversity of representatives of the family Archaediscidae. In general, the succession developed in the Archerbeck Borehole is closely comparable with that in the Alston Block of northern England. The Asbian/Brigantian transition mimics that observed in the Janny Wood boundary stratotype section, with clear late Asbian horizons (lower part of the Archerbeck Beds), transitional beds (middle and upper parts of the Archerbeck Beds), and Brigantian limestones (from the Cornet Limestone upwards). The base of the early Brigantian is placed at the base of the Cornet Limestone (equivalent to the Lower Peghorn Limestone in the Alston Block). The base of the late Brigantian is placed at the base of the Gastropod Limestone (equivalent to the Scar Limestone Member in northern England), and the base of the Pendleian is repositioned at the base of the Under Limestone (equivalent to the Four Fathom Limestone Member in northern England). Throughout, the borehole, protista and microfloral elements are abundant, which allows the recognition of Assemblages 4 to 10, previously recognised in northern England and the Midland Valley of Scotland. Furthermore, other local assemblages are recognised and related to palaeoecological controls, although they do not represent any improvement in biostratigraphical resolution.

Foraminiferal, calcareous algal and problematica assemblages from the Mississippian Lower Limestone Formation in the Midland Valley, Scotland

Foraminiferal, algal and problematica assemblages from the Mississippian (late Visean and early Serpukhovian) Lower Limestone Formation have been studied in order to validate lithostratigraphical correlations of limestones within the central and western parts of the Midland Valley of Scotland. Analysis of more than 100 outcrops allows recognition of four calcareous microfossil assemblages, which span the late Brigantian and early Pendleian, and enables a detailed correlation to be made within the Central Coalfield (north Lanarkshire) and with the thinner sequences to the west (north Ayrshire), to the south (Douglas area, south Lanarkshire), and to the east (Bathgate area, West Lothian). The age of the Lower Limestone Formation is modified because the upper part of this formation is now assigned to the Pendleian (due to the first occurrences of new foraminiferans and the co-occurrence with the Namurian goniatites), and some individual limestone horizons within the formation are repositioned, or their precise correlation with other limestones is established. A refined stratigraphical framework is proposed for the above noted areas, and a correlation between them and the Pennine region in northern England is proposed, passing through the Archerbeck Borehole sequence in the Scottish Borders.

Palaeobiogeographical constraints on the distribution of foraminifers and rugose corals in the Carboniferous Tindouf Basin, South Morocco

Abstract The northern flank of the Tindouf Syncline in southern Morocco exhibits a continuous, well exposed Carboniferous succession with limestones of Late Asbian to Early Bashkirian age containing rich and diverse foraminiferal and rugose coral assemblages. Analysis of these assemblages provides new data on the relatively poorly known Saharan basins. The palaeobiogeographical relationship of the Tindouf Basin with other Palaeotethyan basins is complex. Although there is a predominance of cosmopolitan taxa for the Palaeotethys, it is recognized that there was an influence of basins from NW Europe, such as the UK and Ireland. Some taxa are recorded in both NW Europe and Tindouf without any characteristic contributions from intermediate basins in northern Morocco. The neighbouring Bechar Basin in Algeria presents distinct assemblages. The bulk of the data analyzed suggest that this sector of the western Palaeotethys can be subdivided into four palaeobiogeographical subprovinces: the Atlantic Subprovince (UK, Ireland, N France and Belgium), the Mediterranean Subprovince (Pyrenees, Montagne Noire, Betic Cordillera, Rif (N Morocco) and Balearic Islands), and the Saharan Subprovince (Bechar, Reggan, Ahnet-Mouydir and Tindouf). In between, mobile belts of mixed faunal assemblage characteristics are observed ( e.g. , SW Spain and Central Meseta) forming the West peri-Gondwanan Subprovince. Analysis of the Tindouf Basin faunas shows that, as in other Saharan basins, there is a high diversity and abundance of foraminiferal taxa, with a higher proportion of survivors and longer stratigraphic ranges; these features also are mirrored by rugose corals. This emphasizes the longevity of the carbonate platform in a tropical setting, where periodic transgressions introduced new assemblages, and oceanic currents are interpreted as one of the main controlling factors for the distribution of the taxa in these subprovinces. Moreover, not only were water temperatures on the platform higher, but also tectonic stability greater. It is considered that the effects of the first phases of the Gondwanan glaciation were minimal on the Tindouf faunas.

The palaeoecological distribution of the endothyroids (foraminifera) in the Guadiato area (SW Spain, Mississippian)

Abstract This paper focusses on the distribution and methodological problems that are observed in the palaeoecological analyses of the endothyroids from the Guadiato area, in the southwestern part of the Iberian Peninsula. In spite of a long history of taxonomical and biostratigraphical studies on endothyroids, there have been few investigations of their palaeoecology and taphonomy. The Guadiato area contains a sequence of upper Visean to Pendleian marine carbonates. The upper Visean units were deposited in a storm-dominated ramp. The Pendleian strata were deposited in a tectonically controlled shelf, with narrow platform facies (supra-, inter- and subtidal) and a wide area of slope deposits. Some of the foraminiferal assemblages of this succession typify intertidal facies and incipient shoals, and are regarded as para-autochthonous. Other assemblages, such as the endothyroids in the higher part of the Pendleian slope, are of doubtful allochthony. It is likely that endothyroids did not live in slope facies (it was too deep), but the extent of their transportation cannot be determined since their tests do not show signs of abrasion. Several factors controlled the endothyroid distribution, such as salinity and depth. Deposits formed in high-energy environments such as shoals and tidal flats were not favourable for the endothyroids. Particular palaeoecological factors also determine the distribution of certain families, subfamilies or genera. One of these factors is relative environmental stability; for example, some endothyroids that lack secondary deposits (the Archaediscinae and ‘ Endothyra ’= Priscella ) were more abundant in stable environments. In contrast, other genera with secondary deposits (the Asteroarchaediscinae, Omphalotis and the evolved Endothyra ) were more abundant in unstable or fluctuating microfacies. This factor, however, did not control the distribution of every genus, because this difference is not observed in some species of genera with or without secondary deposits (e.g. Globoendothyra ).

Environmental parameters of a coral assemblage from the Akerchi Formation (Carboniferous), Adarouch Area, central Morocco

Rich assemblages of rugose corals occur in the Tizra, Akerchi and Idmarrach formations (Mississippian) near El-Hajeb City. The Akerchi Formation, approximately 140 m thick, is divided into two members. The upper part of the lower member contains a biostrome 2 to 5 m thick, composed mainly of rugose corals and gigantoproductid brachiopods embedded in marly limestone. Its local thickness increases from southwest to northeast in an outcrop extending for more than one kilometre. The Akerchi biostrome is mostly composed of rugose corals. Brachiopods, bryozoans, porifera (chaetetids, sponges), and molluscs are conspicuous elements of the biostrome, but none of them constitutes a significant component. Other common fossil taxa in thin sections are foraminifers, algae and cyanobacteria, ostracods, trilobites and echinoderms. The coral assemblage in the biostrome is regarded as a paleocommunity, because the biostrome is not composed of distinct coral bearing beds in different time slices, but rather, it is a mass of corals which in many instances show their original relationships and continuous colonial growth. The assemblage is diverse, including 12 genera and 20 species. Micro- and macrofacies analyses of corals and surrounding rock allowed some environmental inferences: a high level of energy is suggested by the degree of fragmentation of branches in fasciculate colonies and other features of the rocks. However, the energy was not high enough to destroy the colonies, and the presence of abundant micrite indicates that the energy level was discontinuous. Other environmental factors inferred from paleoecological and taphonomical evidences are shallow water with normal marine salinity and a hard substrate provided by quick cementation of oolite bar and by abundant bioclasts. Massive coral colonies and gigantoproductids are attached directly to the oolite bar which in turn provided a hard susbstrate for attachment of fasciculate corals that are dominant in the biostrome.

AN UPPER VISÉAN (ASBIAN-BRIGANTIAN) AND SERPUKHOVIAN CORAL SUCCESSION AT DJEBEL OUARKZIZ (NORTHERN TINDOUF BASIN, SOUTHERN MOROCCO)

The Djebel Ouarkziz Formation, located in the northern part of the Tindouf Basin, in western Algeria and southern Morocco, is composed mainly of shales with interbedded limestones, dolostones and sandstones. The limestone beds are relatively thin, but are laterally persistent, and can be followed along strike for tens of kilometres. We have identified 19 limestone beds in three main sections; one logged along the road from Assa to Zag, a second in the Tinguiz-Remz Valley, 15 km to the east, and a third section 10 km west of the Assa-Zag road section. Rugose coral assemblages are recorded in most limestone beds, but the stratigraphically higher beds become more diverse However, many rugose genera and species are persistent throughout much of the succession. The oldest coral assemblages are Asbian in age and the youngest coral assemblages indicate a Serpukhovian age, as confirmed by foraminiferal biostratigraphy. The first appearance of rugose corals shows a different pattern than that in northern Moroccan basins; some common genera that first appear in the Asbian and lower Brigantian in northern Morocco and Europe, appear much later, in the upper Brigantian or Serpukhovian in the Djebel Ouarkziz. The genus Kizilia , which is rare in the Upper Visean in northern Moroccan basins, is, however, abundant in the Tindouf Basin. Interestingly, the occurrence of the genus Lonsdaleia in the Serpukhovian from Djebel Ouarkziz poses a palaeogeographic problem because of its absence in northern Moroccan basins (except as transported elements in Serpukhovian conglomerates). Similarly, Actinocyathus in the Serpukhovian in the Tindouf Basin is not present north of the Anti-Atlas Mountains. A possible coral migration route to the Tindouf Basin may be from the northeast via the Bechar Basin in Algeria, similar to that already inferred for foraminifers and calcareous algae.

Stratigraphic succession, facies and depositional environment of Emsian reefal carbonates in the Ossa-Morena Zone (SW Spain)

The Devonian succession between the Guadiana and Guadalquivir valleys in the Obejo- Valsequillo Domain comprises more than 600 m of shale and sandstone with some interbedded limestone and marl. The most complete reefal sequences of the region are exposed in the Guadamez-2 section, which is located on the western bank of the Guadamez River, near Zalamea de la Serena. It consists mainly of shale and calcareous shale in its lower part and shaly, skeletal and reefal limestone in its upper part. Conodont and brachiopod data indicate that this section spans the interval from the Lochkovian to at least the upper Emsian. Eight microfacies types have been identified in the calcareous facies: A, brachiopod-echinoderm wackestone/packstone; B1, echinoderm grainstone; B2, echinoderm-bryozoan grainstone/packstone; C, echinoderm packstone; D, tabulate coral rudstone; E, brachiopod wackestone/packstone; F, brachiopod grainstone/packstone; and G, stromatoporoid and tabulate coral boundstone/rudstone. Microfacies A, B1, C, E and F represent a sequence of environments from middle platform (A) to tidal flat (F), including shoals (B1) and shallow platform facies. Microfacies B2, D and G represent the development of patch-reefs super - imposed on the shoals.