Splendour of geoforms at Lajedo de Pai Mateus in Paraíba, Brazil

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“Pedra do Capacete”, in Lajedo de Pai Mateus, which represents an elaborate tafone in granite rock

The Lajedo de Pai Mateus is an archaeological site that has a rocky elevation of 1.5 km², with numerous other stone blocks. It stands out for its beauty, and attracts tourists from various parts of the country.

In the northern northeast of Brazil, in the sectors where there is an outcropping crystalline embayment (composed of igneous and/or metamorphic rocks), such as granites and rocks, it is possible to see the rock blocks; and gneisses), the occurrence of forms of saprolitic relief is common – that is, reliefs originating from rocks deeply altered by chemical action, due to the penetration of water.

These features result from the formation of a mantle of chemical alteration in the subsurface, which is removed by subsequent erosive action, leaving blocks that have not been completely altered or that are larger than the removal/transport capacity (Twidale, 2002).

These forms are associated with the past occurrence of wetter tropical climates, or more precisely, with the alternation between wetter and drier climates (Maia and Nascimento, 2018).

Video about Lajedo de Pai Mateus in Paraíba

Wetter climates allow for chemical alteration of the rock in the subsurface (dissolution, rotting of the rock, facilitated by the set of fractures that the surface crystalline rocks <nbsp;commonly present), and drier climates imply the removal of the altered material, leaving large rocky blocks protruding in the landscape (Twidale, 2002).

The main result of rock alteration is the loss of granular cohesion, thus allowing the evacuation of the unconsolidated debris (friable: Vidal Romaní and Temiño, 2004).

Thus, the removal of friable debris resulting from the alternations between erosional cycles (wet and dry climates) will originate saprolitic reliefs through the inability of erosional systems to remove the larger calibre granitic blocks (Vidal Romaní and Twidale, 1998) (Figure 1).

Stages of evolution of the saprolitic relief. 1. initial stage, facilitated by fractures and alternation of high and lower temperatures that imply expansion and contraction of the rock (thermoclasty); 2. exfoliation of the rock by the action of the climate; 3. altered rock; 4. formation of an alteration mantle; 5. removal of the alteration mantle; 6. formation of the saprolitic relief (exhumation of the rock blocks not completely altered).
FIgura 1. stages of evolution of the saprolitic relief. 1. initial stage, facilitated by fractures and alternation of high and lower temperatures that imply expansion and contraction of the rock (thermoclasis); 2. exfoliation of the rock by the action of the climate; 3. altered rock; 4. formation of an alteration mantle; 5. removal of the alteration mantle; 6. formation of the saprolitic relief (exhumation of the rock blocks not completely altered).

.A great example of the evolution of this type of geoform is the Lajedo de Pai Mateus. The Lajedo de Pai Mateus is a granite cliff located in the city of Cabaceiras, in the centre of the state of Paraiba, 180 km from the capital João Pessoa.

It is approximately 1.5 km² in area and has about one hundred large rounded rocky blocks weighing up to tonnes, which stand out amidst the flattened surface that characterises the Paraiba Caririo.

In its interior, the granite modelling in Lajedo de Pai Mateus presents a great diversity of forms, such as lajedos (flat and lowered granite surfaces), matacões (rock fragments) and matoons; (rock fragments of metric size), granite balls  and tors (rock outcrop that rises abruptly in the middle of a flatter surface) (Figures 2 and 3).

Lajedo de Pai Mateus PB
Figure 2 – Lajedo de Pai Mateus, PB, showing granitic relief of the saprolitic type, with granite slabs, matacões and balls.
Geoform of the tor type (castle koopies), in Lajedo de Pai Mateus, formed when the process of removal of the mantle of alteration occurs before the complete weathering (exfoliation) in the subsurface of the rock blocks (saprolites).
Figure 3. castle koopies geoform, in Lajedo de Pai Mateus, formed when the process of removal of the mantle of alteration occurs before the complete weathering (exfoliation) in the subsurface of the rocky blocks (saprolites).

Another type of feature present in Lajedo de Pai Mateus are the basal cavities that form in the large granite blocks, called “tafoni”. These are concave features that expand upwards from the base of the granite block until they consume its interior.

This expansion expands to the point of breaking the side of the block, thus generating an access to the internal part of the material. Inside the rock block, the expansion of the cavity occurs by the progressive flaking of the internal surfaces accompanied by granular disintegration (Maia and Nascimento, 2018) (Figure 4).

Figure 4 – “Pedra do Capacete”, in Lajedo de Pai Mateus, which represents a tafone made of granite rock

Another smaller feature that occurs in the area are the channels, which represent shallow vertical furrows produced by chemical erosion (dissolution).

When they occur in profusion, they are called “karrens”, being characterised by well-marked channels, arranged parallel to the top to the base of the granite block (Maia and Nascimento, 2018). (Figure 5).

Karrens (agglomeration of flutings) at Lajedo de Pai Mateus.
Figure 5 – Karrens (agglomeration of flutings) at Lajedo de Pai Mateus.

In summary, it is posited that the development of the saprolitic granitic morphology, in Lajedo de Pai Mateus and in other localities of the Northeast and the world, occurs in two stages. In the first, there is a chemical change in the soil base, and in the second, there is the gradual exposure of saprolites through erosion (Roque et al., 2013).

The rock formation would thus be the result of the wear and tear of the Earth’s surface over millions of years, due to the existence of natural cracks (which allow water to penetrate) and variations between clasts; variations between wetter and drier climates, with chemical alteration occurring in wet climates and in dry climates, the removal of the mantle of alteration and the exhumation of saprolites. This is the secret of the origin of these geoforms!

In some blocks of the Lajedo de Pai Mateus, rock paintings are found, attributed to the Cariris Indians, who inhabited the region since the early Holocene (10,000 years ago).

The local name, however, has another origin: legend has it that Father Matthew was a hermit healer who lived in the region around the 18th century and was much sought after by pilgrims from the region. The historical name of this geomorphological site is due to him.

The Lajedo de Pai Mateus is located on private property, and access is by dirt road from the centre of Cabeceiras.

The geosite represents a set of spectacular granitic geoforms, whose knowledge is expanding today, and has been the object of increasing visitation. After the visit of the area, it only remains to vibrate with the following greetings: long live the geomorphodiversity of Lajedo de Pai Mateus! Long live the geomorphic richness of the Brazilian Northeast!

How to get there

The tourist spot is 25 km away from the centre of Cabaceiras, a municipality known throughout the country as “Roliúde Nordestina”, for having been the stage of several film productions, among them the film O Auto da Compadecida, from 2000.

Curiosity

The Lajedo de Pai Mateus was used as a “Ceremonial Centre or Sacred Site” by the prehistoric indigenous peoples who inhabited the region for at least 10,000 years, and for this reason many people today find a “mysticism” in its stones.

Its “positive energy” does not go unnoticed by visitors with some sensitivity or “open” to this kind of mystical experience.

But regardless of this side, the lajedo is indeed a special region with a unique and beautiful look, in a region marked by the harshness of nature and the sweetness of its natives.

Paraíba and Northeast Tourism Guide – Lajedo de Pai Mateus in Paraíba

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