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Re: Purbeck Beds
On Fri, 6 Feb 2004, Donna Braginetz wrote:
> The Ananova article reads:
> ** Bone from 20-tonne dinosaur found in quarry
> The fossil has come from rocks known as the Purbeck Beds, in Portland,
> Dorset, formed in an arid lagoon about 130 million years ago.
> What, exactly, is an "arid lagoon"? This is a contradiction in terms,
> no? Can someone more fully describe what the environment that produced
> the Purbeck Beds was like?
Huh. Well, that got me curious, did the google routine. Three hits and two
of them are the article. The other is
Some sort of wetlands project.
The objectives of the project are to document the changes in the
hydrological properties of mangrove wetlands as a response to landscape
freshwater diversions towards a river-dominated, arid lagoon-delta
ecosystem ( Cienaga Grande de Santa Marta, extension ~ 1280 km2) and
determine the productivity and structural changes of mangrove wetlands
during the rehabilatation process.
Looking up "Cienaga Grande de Santa Marta", several hits. This link
seemed to exlpain a bit:
The Cienaga Grande de Santa Marta (CGSM) is a lagoon-delta ecosystem
which forms the exterior delta of the Magdalena River. [...] This system
can be classified as a type I setting (river-dominated, arid, with low
tidal amplitude) containing fringe, basin, and riverine mangroves (Thom
1982). [...] The coastal climate zone is arid tropical, with 6-7
dry-months a year and an annual deficit of 1,031 mm because
evapotranspiration (1,431 mm year-1) largely exceeds precipitation (400
mm year-1). [...] Freshwater diversion from the lagoon-delta complex in
this arid coastal region has resulted in hypersalinization of mangrove
Hmmm. A lagoon that apparently gets a little dry seasonally.