Newsgroup: it.scienza.geologia
Titolo: Domande:La Pianura padana

 
 
In questi giorni di terremoto, si parla di pianura padana.
 
In tempi geologici era un mare?
Quanto era profondo?  da che cosa e composto il sottosuolo?
 
Se una scossa di terremoto si sente a 200km, il sotto suolo da cosa
e composto di roccia/granito' :-)
 
 
 
 
Ciao 
 
 


Scusa ma sono tutte domande prive di significato.
 
I tempi geologici sono gli ultimi 5 miliardi di anni
 
 
 

 Quanto era profondo?  da che cosa e composto il sottosuolo?
 
qui c'è qualcosa
 
http://it.wikipedia.org/wiki/Val_padana#Geologia
 


> Ciao
 
Ciao
 
 
 

 Avevo già guardato su Wiki, ma non mi ha soddisfatto! :-)
 
Più interessante quello che dice la Wikipedia anglosassone:
 
 
http://en.wikipedia.org/wiki/Po_Valley#Geology
 
 
  The Po Valley and the Adriatic overlay a system of deeply buried
  ancient canyons surviving from the tectonic collision of an offshore
  land mass, Tyrrhenis, with the mainland, an incident within the
  collision of the African and Eurasian plates. Since the Messinian
  (7-5 mya) the system has been filling with sediment mainly from
  the older Apennines but also from the Alps. The shoreline of the
  Adriatic depends on a balance between the sedimentation rate and
  isostatic factors. Until about 1950 the Po delta was prograding
  into the Adriatic. After that time due to human alteration of
  geologic factors, such as the sedimentation rate, the delta
  has been degrading and the coastline subsiding, resulting in
  ongoing contemporaneous crises in the city of Venice, where
  much irreplaceable art and architecture is likely to be lost
  due to soaring sea level in the next centuries. Where the land
  surface now dips below sea level the river must run at a relative
  elevation between dikes.
 
 
http://en.wikipedia.org/wiki/Po_River#Geology
 
 
  The Mediterranean Basin is a depression in the Earth's crust caused
  by the African Plate slipping under the Eurasian Plate. Typically
  in geologic history the depression is filled with sea water under
  various geologic names such as Tethys Sea. In the last period of
  the Miocene Epoch, the Messinian (7-5 mya), the Messinian salinity
  crisis, a near drying of the Mediterranean, was caused by the sea level
  dropping below the sill at the Strait of Gibraltar and the equilibrium
  between evaporation and replenishment shifting in favor of evaporation.
  At that time the Po Valley and the Adriatic depression were a single
  canyon system thousands of feet deep. On the southwest the Apennine
  Mountains bordered a land mass termed Tyrrhenis geologically.
  Their orogeny was just being completed in the Miocene. On the north
  the Alpine Orogeny had already created the Alps.
 
  At the end of the Messinian the ocean broke through the sill and
  the Mediterranean refilled. The Adriatic transgressed into all of
  northern Italy. In the subsequent Pliocene sedimentary outwash
  primarily from the Apennines filled the valley and the central
  Adriatic generally to a depth of 1,000 m (3,300 ft) to 2,000 m
  (6,600 ft) but from 2,000 m (6,600 ft) to 3,000 m (9,800 ft)
  off the current mouth of the Po, with pockets as deep as 6,000 m
  (20,000 ft). At the start of the Pleistocene the valley was full.
  Cycles of transgression and regression are detectable in the valley
  and the Adriatic as far as its centre and in the southern Adriatic.
 
  From the Pleistocene alternation of maritime and alluvial sediments
  occur as far west as Piacenza. The exact sequences at various locations
  have been studied extensively. Apparently the sea advanced and receded
  over the valley in conformance to an equilibrium between sedimentation
  and glacial advance or recession at 100,000-year intervals and 100 m
  (330 ft) to 120 m (390 ft) fluctuation of sea level. An advance began
  after the Last Glacial Maximum around 20,000 years ago, which brought
  the Adriatic to a high point at about 5500 years ago.
 
  Since then the Po delta had been prograding. The rate of coastal zone
  progradation between 1000 BC and 1200 AD was 4 m/yr. Human factors,
  however, brought about a change in the equilibrium in the mid-20th
  century with the result that the entire coastline of the northern
  Adriatic is now degrading. Venice, which was originally built on
  islands off the coast, is most at risk due to subsidence, but the
  effect is realized in the Po delta as well. The causes are first
  a decrease in the sedimentation rate due to the locking of sediment
  behind hydroelectric dams and the deliberate excavation of sand
  from rivers for industrial purposes. Second, agricultural use
  of the river is heavy; during peak consumption the flow in places
  nearly dries up, causing local contention. As a result of decreased
  flow salt water is intruding into the aquifers and coastal ground
  water. Eutrophication in standing waters and streams of low flow
  is on the increase. The valley is subsiding due to the removal
  of ground water.
 
Bye,
 
  *GB* 
 

 
quello che mi interessava, era sapere la profondità di questo mare, che era
prima la pianura padana! dai 2000mt ai 6000mt, da quello che leggo!
 
Ciao