Impulsive Excitation as The New Horizons of Geophysical Studies, The Future of High-Productivity Ultra-High-Density Seismic in The Shallow Water

The benthic communities of fringing and mushroom-shaped shallow-water reefs of the Abrolhos region (southern coast of Bahia) were surveyed. Line transects were used to estimate coral and algal percentage cover. Mussismilia braziliensis is the most conspicuous coral species in the majority of the communities surveyed, but turf algal make up the dominant cover in all but one studied reef. In general, communities on mushroom-shaped reefs have higher diversity and higher coral cover than on fringing reefs. For both reef morphologies, the coral to alga cover ratio does. not show marked differences between annual surveys, despite the high productivity characteristic of the dominant algal species.

Download Full-text

Neoproterozoic sedimentation on the northeast margin of Laurentia and the opening of Iapetus

Geological Magazine ◽

10.1017/s0016756800011067 ◽

1994 ◽

Vol 131 (3) ◽

pp. 291-299 ◽

Cited By ~ 50

Author(s):

N. J. Soper

Keyword(s):

Shallow Water ◽

Strain Hardening ◽

East Greenland ◽

Eastern Margin ◽

Sedimentary Sequences ◽

Pan African ◽

Hardening Effect ◽

The Pacific ◽

The Future ◽

Cordilleran Margin

AbstractVery thick shallow water sedimentary sequences were deposited in Neoproterozoic time along the future margins of Laurentia. On the eastern margin these include the Eleonore Bay and Hecla Hoek sequences of Greenland and Svalbard; these are described and their geotectonic context briefly reviewed. They present both geotectonic and geodynamic problems: why did subsidence continue for some 300 Ma prior to the opening of Iapetus, and how could 15–20 km of sediment be accommodated in an ensialic environment?Prolonged slow stretching appears to have affected the eastern margin of Laurentia while the western (Cordilleran) margin progressed through the rift-drift transition as the Pacific opened. It is proposed that expansion of the Pacific was associated with both the convergence of Proto-Gondwanan continental terranes during the Pan-African orogeny (the extended SWEAT hypothesis) and also the maintenance of very slow extension rates on the future Iapetus margin. The strain-hardening effect of slow stretching may have been inhibited by a continuous basin-fill of juvenile heat-producing Grenville detritus. The onset of subduction in the Pacific freed up this margin; major rifting took place between East Greenland and possibly the Tornquist margin of Baltica in Vendian time, followed by the opening of northern Iapetus.

Download Full-text