Geology of the Gulf of Cadiz

 
Geological Facts enabling the Catastrophe of Atlantis II

By seismic examination of the sea floor in the Gulf of Cadiz was found, that there is a zone of geological instability. It is caused by a through and on top of each other of solid masses , layers of salt and clay and other not solid sediments, which partly give methane and prevent a consolidation of the ground.

The layers of salt and clay sedimented between have the effect of lubricant to the solid masses, which are dammed in the coast area at strong obstacles forming zones of compression which cause upward and downward movement. Further outside they form extended slopes of gliding, upon which masses of the coast can slip as far as 400 Km slowly or suddenly into the ocean.

When the movement happens suddenly it can cause a tsunami (a big wave in the sea ) which can grow to several meters in the coast area and create considerable destruction. In the area of compression at the coast can happen long-term or, in the case of sudden release of dammed tensions, caused by earthquakes of extern origin or by getting out of hand of own tensions, raising or lowering at short notice of separate regions of the coast.

Altogether proves the examination made in the 90th of the past century that raising and lowering of the land as catastrophic waves can happen in this area suddenly or in long-term. At long -term change they appear as raising or lowering of the level of the sea.

With this the geological precondition for the possible validity of the Atlantis-story of Platon is given for the Bay of Cadiz.

In the following the geological report:

The Betic-Rifian accretionary prism

Mass wasting, from blocks to turbidites, has occurred along the Atlantic-facing Iberian and Moroccan continental margins over a down-dip distance up to 300 km. Salt and clays within the migration blocks and stacked thrusts serve as lubricants. The juxtaposition of varying lithologies due to mass wasting tectonics could provide boundaries for complex compartments.

"The Cadiz Salt Nappe"

 
Salt-floored gravity-driven ramps along low-angle detachments link extensional structures (roll-over anticlines, listric growth faults and counter-regional growth faults) in the shelf to downdip folding , thrusting and salt sheets along the outer slope and upper slope of the Gulf of Cadiz. Salt-withdrawal growth fault basins developed on the shelf reflect two stages of high subsidence rates from the Late Tortonian to Late Messinian (200 to 400 m/Ma) and from Early Pliocene to Late Pliocene (100 to 150 m/Ma). These migrating allochthons apparently may have travelled up to 400 km down slope , originating along the Iberian and Moroccan continental margins.

The term "Olistostrome":
Mediterranean mega allochthons towards the oceanic crust


The westward Gibraltar arc migration oversteepened the Atlantic facing Iberian-Moroccan continental margins (Fig. 1) , which initiated farther westward migration of gravity-driven continental and salt-floored blocks whose ultimate emplacement was over oceanic crust as the continental blocks migrated, normal listric faulting along the present continental shelf of the Gulf of Cadiz developed, providing accomodation space for upper Miocene (past 19 Ma) tectonics and deposition.

Advancing salt sheets along the frontal imbricate thrusting of the Betic-Rifian accretionary wedge (Iberian-Moroccan Atlantic continental margin) trigger down-slope movement of giant allochthonous masses (Fig.1) . These are detached from the front of accretionary wedge by extensional low-angle normal faults (Fig. 2). These faults initiate salt tectonics, including diapirism and withdrawal, and large mass-wasting from the shelf and upper slope as far west as to the Eastern Horseshoe and Seine abyssal plains.

Mega submarine slumps, earthquakes and tsunamis?

A tsunami is a series of very long wavelength ocean waves caused by the sudden displacement of water by earthquakes, landslides, or submarine slumps. Ordinarily, tsunamis are produced only by earthquakes exceeding magnitude 7.5. In the open ocean, tsunami waves travel at speeds of 600-800 kilometers per hour, but their wave heights are usually only a few centimeters. As they approach shallow water near a coast, tsunami waves travel more slowly, but their wave heights may increase to many meters, and thus they can become very destructive.

From: Noson, Qamar, and Thorsen, Washington State Earthquake Hazards, 1988, Washington Division of Geology and Earth Resources Information Circular 85, p. 11, p.66.

High-resolution stratigraphy of the shelf wedges

The stratal architecture of the Gulf of Cadiz continental margin (SW Spain) has been analyzed by using single-channel, very high-resolution seismic reflection profiles. An evolutionary scheme of asymmetrical depositional sequences is proposed that was governed by the Late Pleistocene-Holocene sea-level fluctuations. Stratigraphic analysisdefined 14 seismic units, that are configured into two major type-1depositional sequences related to 4th-order eustatic sea level changes(100-110 ka). Within these sequences, minor asymmetrical depositional sequences have been recognized related to 5th-order eustatic cycles (22-23ka) superimposed and modulated by the regressive trends of 4th-ordercycles. In 5th-order depositional sequences, the forced regressive andlowstand deposits are Volumetrically dominant. They cause the main progradation of the margin in such a way that they form the margin structure almost entirely.
From Somoza. L. et al. 1997. Continental-Shelf Architecture and Sea-Level Cycles - Late Quaternary High-Resolution Stratigraphy of the Gulf-of-Cadiz,
Spain.
Full source: GEO-MARINE LETTERS 1997, Vol 17, Iss 2, pp 133-139

All information from:
http://tierra.rediris.es/TASYO/area.html

With these geological facts the Atlantian catastrophe, described by Platon and others, seems to be really possible for the area of Cadiz and Puerto de Santa Maria.

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