Le genre Paraspirifer Wedekind, R., 1926 dans le Dévonien moyen de la partie orientale de l’Amerique du Nord

The authors describe seven species of the genus Paraspirifer WEDEKIND, R., 1926 on the basis of more than one hundred specimens from twenty-three localities in North America. Three of these species are new: P. conradi n. sp., P. halli n. sp. and P. clarkei n. sp. Two others are provisionally named P. cf. halli and P. sp. A. A Neotype is proposed for P. acuminatus (CONRAD, T.A., 1839) and the Lectotype of P. brownockeri (STEWART, G.A., 1927) is designated. The problems concerning the species Terebratula acuminatissima DE CASTELNAU, F., 1843 and Delthyris prora CONRAD, T.A., 1842 are briefly discussed. The genus Paraspirifer is confined to an area of ± 6.500.000 km2 in eastern North America. In New York, the biostratigraphic range-zone for the genus is from the upper Onondaga Limestone (Moorehouse Member) to the middle Marcellus Shale (Solsville Member) and, in Ohio and Ontario, from the upper part of the Columbus Limestone (Zones F — H) to the Silica Shale. In Indiana and Kentucky, the genus occurs in the upper Jeffersonville Limestone (P. acuminatus sensu lato Zone) and, in Illinois and Missouri, in the Grand Tower Limestone

Cretaceous history of Pacific basin guyot reefs : a reappraisal based on geothermal endo-upwelling

The mid-cretaceous histories (origin, growth, death) of algal-rudist-stromatoporoid reef communities located on many Pacific basin guyots are complex and controversial. These shallow water, tropical communities originated on volcanic edifices extruded during the Barremian-Albian, grew upward during edifice subsidence/trangression throughout the Aptian, Albian and Cenomanian and several of them died almost synchronously near the Cenomanian-Turonian boundary. During their periods of origin and growth, we postulate that the reef ecosystem received dissolved oxygen by wave surge and nutrients by geothermal endo-upwelling. By this process oceanic waters of intermediate depth (approx. 500-1500m) were : (a) drown into the weathered and fractured volcanic summit and lower part of the older reef and driven upward through the porous framework bythe remnant geothermal gradient of the volcanic foundation and (b) emerged atthe reef surface to support the high metabolism of the living community. (D'après résumé d'auteur

Geothermal endo-upwelling : a solution to the reef nutrient paradox ?

Les écosystèmes algo-coralliens sont paradoxaux du fait de leurs fortes biomasses et productivités au sein d'eaux océaniques oligotrophes. De plus, ils emportent dans l'océan (perte) une partie de leur biomasse ce qui implique un apport en nutriants neufs pour rétablir leur balance énergétique. Le fonctionnement par endo upwelling géothermique permet de résoudre ce paradoxe nutritif, en particulier au sein du gyre oligotrophe du Pacifique central (Polynésie). (Résumé d'auteur

Interpretation of the origin of massive replacive dolomite within atolls and submerged carbonate platforms : strontium isotopic signature ODP hole 866A, resolution Guyot, mid-Pacific mountains

Endo-upwelling is a geothermally driven convective process operating within the upper part of the volcanic foundation and overlying carbonate pile, in atolls and guyots. By this process deep oceanic water, rich in CO2, and dissolved nitrates, phosphates and silicates is drawn into the pile, circulates slowly upward through the porous-permeable carbonate interior and emerges at either the reef crest or lagoon on atolls to support the primary productivity of the surficial communities, or towards the interior of the platform surface on guyots. Continuous operation of the endo-upwelling process requires : (a) heat from the volcanic foundation; (b) an external impermeable apron on the submerged flanks to confine the convective flow within the pile; and (c) a porous cap from which water exiting the plumbing system returns to the ocean. (D'après résumé d'auteur

Palaeobiology, ecology, and distribution of stromatoporoid faunas in biostromes of the mid-Ludlow of Gotland

Six well exposed mid−Ludlow stromatoporoid−dominated reef biostromes in four localities from the Hemse Group in southeastern Gotland, Sweden comprise a stromatoporoid assemblage dominated by four species; Clathrodictyon mohicanum, “Stromatopora” bekkeri, Plectostroma scaniense, and Lophiostroma schmidtii. All biostromes investigated in this area (of approximately 30 km2) are interpreted to belong to a single faunal assemblage forming a dense accumulation of fossils that is probably the best exposed stromatoporoid−rich deposit of the Silurian. The results from this comprehensive study strengthen earlier interpretations of a combination of genetic and environmental control on growth−forms of the stromatoporoids. Growth styles are similar for stromatoporoids in all six biostromes. Differences in biostrome fabric are due to variations in the degree of disturbance by storms. The uniformity of facies and the widespread low−diversity fauna support the view that palaeoenvironmental conditions were similar across the area where these biostromes crop out, and promoted the extraordinary growth of stromatoporoids in this shallow shelf area

Interpretation of the origin of massive replacive dolomite within atolls and submerged carbonate platforms : strontium isotopic signature ODP hole 866A, resolution Guyot, mid-Pacific mountains

Endo-upwelling is a geothermally driven convective process operating within the upper part of the volcanic foundation and overlying carbonate pile, in atolls and guyots. By this process deep oceanic water, rich in CO2, and dissolved nitrates, phosphates and silicates is drawn into the pile, circulates slowly upward through the porous-permeable carbonate interior and emerges at either the reef crest or lagoon on atolls to support the primary productivity of the surficial communities, or towards the interior of the platform surface on guyots. Continuous operation of the endo-upwelling process requires : (a) heat from the volcanic foundation; (b) an external impermeable apron on the submerged flanks to confine the convective flow within the pile; and (c) a porous cap from which water exiting the plumbing system returns to the ocean. (D'après résumé d'auteur