GRANITES_V3

PSEUDOKARST IN GRANITES

Juan Ramón Vidal-Romaní, IUX Marcos Vaqueiro-Rodriguez, CEM

Presentation for Vercors 2008

TYPES OF GRANITE CAVES • Caves developed along major fracture planes. Weathering is essentially due to mineral washing, leading to further widening of the fracture. • Caves associated with residual blockfields. Here the finer fractions of the granite regolith, if exist, have been washed away, leaving the coarse fractions - blocks and boulders- in situ. Voids between these residuals have become linked in some places, giving rise to caves of irregular shape • Tafone caves: The term refers to a cavern or hollow developed inside a fracture-defined block. The inside wall or vault may develop alveoles (honeycomb structure), mamillated (convex relief) or scalloped (concave relief) forms and also negative exfoliation forms.

Caves developed along major fracture planes

O Forno Cave, Castelo da Furna (Valença, Portugal) and A Cunchosa System, Aldán (Pontevedra, Spain).

O Folón Cave – Passages developed along the main fault plane. (Pontevedra, Spain)

Caves developed along major fracture planes O Folón System (Vigo, Pontevedra-Spain) has been developed taking advantage of the discontinuity system of the granite rock massif. The water circulation in the area is underground at present. The formation of this cave is older than Quaternary and would start after the development of the surface +120 m.a.s.l., whose chronology we may assign to the Pliocene approximately. The cavity has a vertical development of 34 m from the terrain surface. The total length of the galleries is 905 m of which about 235 m are normally occupied by water.

To the left: O Folón Cave: Evolution model from Plio-Pleistocene to the present. Pictures: Passage morphomolgies in Portugal (at the top), and fossil phreatic conduits in O Folon (at the bottom).

Regressive sequence fot the evolution of cave: O Folón System

Present stage

From 1,8 kyr B.P.

When different paleo-flow levels have been determined, they can be related to the structure. A complete and complex geomorphological work and the use of different methods for datation (C14, luminiscence,…), permit us to approach a regressive sequence for the evolution of cave.


Paleolevel L4

5,5 kyr B.P.


Paleolevel L3


Paleolevel L2


Paleolevel L1


Paleolevel L0

At the end of the PlioQuaternary

Caves associated with residual blockfields

Cova da Becha Cave (Dragon's Cave), Serra do Galiñeiro (Pontevedra, Spain) and Coto dos Namorados Cave, Ponteareas (Pontevedra, Spain).

Tafone caves

Prehistoric pictures located inside a tafone cave, Los Barruecos de Malpartida (Cáceres, Spain)

Coto da Moura: Tafone cave, Serra do Galiñeiro (Pontevedra, Spain)

Tafone, O Pindo (A Coruña, Spain)

Tafone, Outeiro das Campanas (Pontevedra, Spain)

Tafone caves, type “lapa”. A Touba do Brión Cave, Serra do Galiñeiro (Pontevedra, Spain)

Neolithic mills and millstone inside a tafone cave, Serra do Galiñeiro (Pontevedra, Spain)

NATURAL, ARCHAEOLOGICAL AND GEOLOGICAL HERITAGE RELATED TO GRANITE CAVES

Natural heritage * Root stalagmites * Chioglossa lusitanica * Alites obstetricans * Schistostega pennata

Chioglossa lusitanica, protected by Directive 92/43/CEE.

Opal-A Speleothemes

Biogenical opal stalactites. O Forno, Castelo da Furna (Valença, Portugal)

Opal-A Speleothemes

Biogenical opal stalactites. O Forno, Castelo da Furna (Valença, Portugal)

Opal-A Speleothemes

Different Opal-A morphologies To the left: O Cebro System, Pindo (A Coruña, Spain); and to the right: O Forno, Castelo da Furna (Valença, Portugal)

FOSIL D.N.A. INSIDE BIOGENICAL OPAL SPELEOTHEMES

Fotos: J.R.Vidal-Romaní, Instituto Universitario de Xeoloxía “Isidro Parga Pondal”, Universidade de A Coruña

Pigotite Speleothemes

Gours located in Coral Roxo Cave, O Folón System, Vigo (Pontevedra, Spain)


Flowstone and dripstone located in Pozo da Rá Cave, O Folón System, Vigo (Pontevedra, Spain)


Flowstone located in Coral Roxo Cave, O Folón System, Vigo (Pontevedra, Spain)


Flowstone located in A Trapa System, Ribadelouro (Pontevedra, Spain)

Archaeological heritage

Findings are mainly from Neolithic Age, Coper and Bronze Age. In O Folón System there is about 56 beds with archaeological remains.

Archaeological heritage

To the left, prehistoric and Medieval engraved pictures. To the right, at the top, a Copper Age ceramic piece from O Folón System. To the right, at the bottom a Medieval buckle from Portugal.

Troglodite chapels

Many troglodite chapel have been built inside granite caves. At the top Capilla de la Asunción built in the XX century. To the left, two pictures from San Pedro de Rocas, Esgos (Ourense, Spain): First it was an hermitage cave, transformed in a chapel and monastery during the Low Medieval Age.

Thank you for your attention!

GRANITES_V3

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