摘要:

Attachment surfaces of ostreids preserve the (negative) imprint of the substrate morphology while the right (upper, free) valve may reflect its positive form (xenomorphism or xenomorphic sculpture). The substrate may be an invertebrate skeleton which is dissolved during diagenesis. The imprint of such skeletons on ostreid valves has often a greater biostratigraphic significance than the ostreid itself. Fossil examples are described.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1972.tb00865.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1972.tb00866.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Stromatolitic structures from the Late Precambrian Visingö Beds are described. The mode of development of these sedimentary‐biogenic structures and the problems related to their characterization in a system of formulas are discussed. The study of the stromatolitic structures and their associated sediments proved that the stromatolitic structures LLH (vertically arranged, lateral‐linked hemispher‐oids) and SH (discrete, vertically stacked hemispheroids) could develop together on the same stromatolite dome, depending on different degrees of exposure to the action of water currents in an intertidal environment. Superimposed LLH and SH structures in the Visingsö Beds may indicate periodical changes in current activity depending on repeated periodic events such as tidal and/or stor

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1972.tb00867.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Similarities of the extinct strornatoporoids to the sponges of the recently established order Sclerospongia have strengthened arguments that these fossils are closer to the Porifera than to the Coelenterata. Major features favouring the affinity of the stromatoporoids to the sclerosponges include: (1) lack of evidence of colonialism in the strornatoporoids, (2) similarity of gross structure of some stromatoporoids to that of one sclerosponge (Astrosclera), (3) fibrous microstruc‐ture of sclerosponges, Mesozoic stromatoporoids, and some Paleozoic stromatoporoids, (4) similarity of stromatoporoid astrorhizae to the excurrent canals of sclerosponges. Points of dissimilarity include: (1) the solid aragonitic skeletons of most sclerosponges, (2) the presence of dissepiments, laminae, and latilaminae in stromatoporoids, (3) the absence of siliceous spicules in stromatoporoids.These comparisons suggest that the stromatoporoids were basically encrusting filter feeders like the sclerosponges but had progressed by loss of spicules and periodic introduction of dissepirnents and laminae toward a secretion of a skeleton of the coelenterate type. They cannot be placed with confidence in either the sclerosponges or the hydrozoans and should be recognized us a separate subphylum of the Porifer

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1972.tb00868.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Pliensbachian and Toarcian molluscs and brachiopods of Morocco, Iberia, England, and Greenland are analysed in terms of diversity and density. With regard to local variations, Substrate and food supply are thought to be the major factors controlling the predominance of suspension‐feeding bivalves in shallow water deposits while the greater physical stability of deeper water favoured the ammonites; high diversity of the gastropods relates to firm substrates. On a regional scale, both bivalve density and diversity tend to increase from the Tethyan to the Boreal redm, while there is a Variable tendency for a northward diversity reduction in other groups. The bivalve data are incompatible with either temperature or salinity control of faunal provinciality. To provide a better account of this, a model is developed which lays emphasis on the physical instability of a boreal inland sea as compared with the Tethys. Some broader implications for endemism in Jurassic faunas are briefly discusse

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1972.tb00869.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1972.tb00864.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY