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Table VII Stratigraphical Nomenclature and correlation in the Carboniferous of Western Europe, U.S.S.R. and U.S.A. The Series names for Western Europe are those recognized by the International Subcommission on Carboniferous Stratigraphy. The Stage names for the Dinantian are those recently proposed by George et al. (1976).

Table VII Stratigraphical Nomenclature and correlation in the Carboniferous of Western Europe, U.S.S.R. and U.S.A. The Series names for Western Europe are those recognized by the International Subcommission on Carboniferous Stratigraphy. The Stage names for the Dinantian are those recently proposed by George et al. (1976).

Figs. 39 and 40 are described by Dr. M. R. Feeder.

Fig. 39 Tidal-flat Community A 39 Tidal-flat Community A a stromatolite domes (Algae)

Stromatolitic limestones are developed by the blue-green algae and are believed to be for the most part accretions formed by the trapping of sediment. The algal filaments themselves are usually not calcified. These algae are prolific in extremely shallow coastal waters and are tolerant of hyper-salinity, and here they often form the only colonisers. The structural details of the fossil algal domes may be obscured by dolomitisation, which was partly contemporary, and at times by silification as well. The size and shape of the particular growth forms seems to have depended largely on the degree of turbulence of the waters and upon the growth of the algae over initial irregularities of the substrate. Dome-like growths are commonest in low energy environments, and they may be single isolated domes or laterally-linked domes forming a continuous substrate cover.

The laterally linked stromatolite domes illustrated probably accreted in an intertidal, or sheltered shallow subtidal environment.

40 Tidal-flat Community B

Many nearshore facies in the Lower Carboniferous contain well developed algal stromatolites. Those illustrated here are based on examples from the Lower Border Group (Lower Visean) in southern Scotland, and represent actual in situ assemblages (Leeder, 1975). The isolation of pillars was probably the result of tidal action where scouring by currents prevented all but temporary lateral linkage between adjacent pillars. The pillars grew together upon a carbonate sand deposit made up of molluscan fragments (Polidevcia attenuata), pellets, ooids and eroded algae. The crinkled algal mat crept over the pillars because of the regression of the shoreline. The mat probably accreted in the high intertidal zone. Spirorbid worms sometimes colonised the partly Iithified protruding pillars and crinkles.

In areas of slightly deeper water the blue-green algae occurred as rounded nodules with the form of the genus Osagia.

mmm mmm

Fig. 40 Tidal-flat Community B

a stromatolite pillar (Algae) b Polidevcia attenuata (Mollusca: Bivalvia: Palaeotaxodonta) c Spirorbis (Annelida:

Serpulid) d temporary bridging laminae between pillars e carbonate sand f sediment-rich laminae

(in inset) g algal-rich laminae (in inset)

Fig. 40 Tidal-flat Community B

a stromatolite pillar (Algae) b Polidevcia attenuata (Mollusca: Bivalvia: Palaeotaxodonta) c Spirorbis (Annelida:

Serpulid) d temporary bridging laminae between pillars e carbonate sand f sediment-rich laminae

(in inset) g algal-rich laminae (in inset)

Mollusks Pictures

Modiolus Community

Modiolus latus (Mollusca: Bivalvia: Mytiloida)

Sanguinolites (Mollusca: Bivalvia: Anomalodesmata) turreted snail (Mollusca: Gastropoda) d worm burrows (Annelida) e ostracodes (Arthropoda:

Crustacea) f seaweed (Algae) d worm burrows (Annelida) e ostracodes (Arthropoda:

Crustacea) f seaweed (Algae)

Modiolus Community

Modiolus latus (Mollusca: Bivalvia: Mytiloida)

Sanguinolites (Mollusca: Bivalvia: Anomalodesmata) turreted snail (Mollusca: Gastropoda) d worm burrows (Annelida) e ostracodes (Arthropoda:

Crustacea) f seaweed (Algae) d worm burrows (Annelida) e ostracodes (Arthropoda:

Crustacea) f seaweed (Algae)

41 Modiolus Community

Dolomitic calcite mudstones are often present with very restricted faunas. These beds are believed to have been hypersaline because of the extreme shallowness of the water and its high temperature, accounting for the chemical deposition of calcium carbonate and its contemporaneous dolomitization (Ramsbottom, 1973). Under such conditions life must have been harsh, and it is not surprising that the fauna is highly specialized and by no means abundant. The community living in these areas has been called the "Modio^a

Phase by Dixon and Vaughan (1911). The bivalve Modiolus is the most characteristic member and was perhaps a burrower, though it may also have been byssally attached to seaweed (as shown). Another, less common burrowing bivalve is Sanguinolites. A few small turreted gastropods also occur, and there are traces of burrows believed to have been made by worms, though some of them may be of crustacean origin. Some bedding planes are covered with abundant smooth-shelled ostracodes, though only two or three species are represented, and the low diversity indicates the hypersalinity deduced from other evidence. There are a few rare traces of stromatolitic algae in these beds.

Beds of this type occur in the shallowest parts of the regressive phases (Ramsbottom, 1973) of the British Carboniferous.

42 Composita Community

This community is well developed in calcite mudstones, which typically occur in cycles (1 to 4m thick) showing alternations of fine and slightly coarser-grained limestones. The finer beds of calcite mudstones are perhaps of chemical origin, the calcium carbonate being deposited from the warm water in the same manner as is the "fur" in a kettle. In each cycle the grain size decreases upwards into calcite mudstones often with small rounded algal nodules; sometimes thin stromatolitic beds are present at the top of each cycle.

Fossils occur in the middle part of these cycles; the community consisting almost entirely of the smooth-shelled spiriferide Composita (usually C. ficoides) together with a few gastropods. The Composita often form shell beds, with the shells crowded together; both valves are usually preserved together in place, indicating that conditions were quiet. Occasionally a few rhynchonellids ("Camarotoechia") and Linoprotonia are found, but corals are virtually absent. Such a restricted and specialised fauna is taken to indicate a slightly hypersaline environment, with shallow, warm water.

Camarotoechia

Fig. 42 Composita Community a Composita (Brachiopoda: Articulata: Spiriferida) b 'Camarotoechia' (Brachiopoda: Articulata: Rhynchonellida) c Linoprotonia (Brachiopoda: Articulata: Strophomenida) d turreted gastropod (Mollusca: Gastropoda) e Straparollus (Mollusca: Gastropoda: Archaeogastropoda)

Fig. 42 Composita Community a Composita (Brachiopoda: Articulata: Spiriferida) b 'Camarotoechia' (Brachiopoda: Articulata: Rhynchonellida) c Linoprotonia (Brachiopoda: Articulata: Strophomenida) d turreted gastropod (Mollusca: Gastropoda) e Straparollus (Mollusca: Gastropoda: Archaeogastropoda)

43 Oolitic Limestone Community

The fauna of the oolites in the Carboniferous tends to be rather sparse. The repeated shifting of the bottom material, through current and possibly tidal action in water probably no more than a metre or two deep, seems to have prevented all but the larger species becoming established: most of these forms are fairly massive, presumably to give them abetter hold on the mobile sea floor.

Gastropod Microfossil

Fig. 43 Oolitic Limestone Community a Palaeosmilia (Coelenterata: Anthozoa: Rugosa) b Megachonetes (Brachiopoda: Articulata: Strophomenida) c Linoprotonia (Brachiopoda: Articulata: Strophomenida) d Koninckophyllum (Coelenterata: Anthozoa: Rugosa)

Fig. 43 Oolitic Limestone Community a Palaeosmilia (Coelenterata: Anthozoa: Rugosa) b Megachonetes (Brachiopoda: Articulata: Strophomenida) c Linoprotonia (Brachiopoda: Articulata: Strophomenida) d Koninckophyllum (Coelenterata: Anthozoa: Rugosa)

Large simple corals [Palaeosmilia, Koninckophyllum) and large brachiopods [Megachonetes, Linoprotonia) are the commonest fossils, and many of these appear to have been carried by currents and damaged to some extent. Microfossils are scarce, though small foraminiferida often form the central core round which oolite grains have developed. The community shown here is typical of that found in the Gully Oolite of Somerset and Avon, (the equivalent of the Caninia Oolite of south Wales); this oolite is found in the regressive period near the close of Major Cycle 2 (Ramsbottom, 1973), and is of Chadian age. It can be traced as far east as Aachen in West Germany. Because of their very shallow water origin, oolite limestones are useful in delineating palaeogeography.

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