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Passo Valles: an open-air geological museum EarthCache

Hidden : 07/06/2009
Difficulty:
2 out of 5
Terrain:
2 out of 5

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Geocache Description:

Passo Valles: an open-air geological museum

This earthcache was created to celebrate the inclusion of the Dolomites in the World Heritage List by the United Nations Educational Scientific and Cultural Organization (UNESCO). This announcement refers to the beauty of these mountains, their diversity on landforms, the importance of dynamic processes and fossil records. The purpose of this earthcache is to introduce the geocacher to the geology of the Dolomites, showing some types of rocks present in this area. For this purpose, I select one of the most interesting places in the Dolomites from a geological point of view: Passo Valles (2032 m).

The Dolomites comprise a mountain range in the northeastern Italian Alps, covering about 142,000 ha, and relatively well confined from the physiographic point of view (Figure 1). They feature some of the most wonderful mountains anywhere, with typical sheer cliffs and narrow, deep and long valleys. The Dolomites are also characterized by a great variety of environments and a great variety of different habitats. This fact allows a great richness in animal and vegetal forms, some of which are endemic species, rare species, or species with a great biological value.


Figure 1. Location of the Dolomites in the Eastern Alps (Source: Wikipedia, http://en.wikipedia.org/wiki/Dolomites).



The Dolomites are also very important from a geological point of view, because composed by several different rocks originated in various geologic periods and forming complex and interesting stratigraphic series. With this earthcache, I would to take the geocacher for a walk through the geological history of the Dolomites. The cache is composed of 6 waypoints. You can visit 4 waypoints (1, 2, 5 and 6) with your car and 2 waypoints (3 and 4) with a little walk near Passo Valles (approx 500 m return). This cache take about 1 hour. See the map on Figure 2. Reading the following text and looking for the waypoints, you can see some rocks and you can learn the information to reply to some questions, absolutely mandatory to log this cache. Remember the ethics "leave no trace"... please respect the nature and don't remove the rocks!


Figure 2. The earthcache location with the WPs.

Waypoint 1 - Porphyries (N 46°20.464; E 11°48.890). During the Early Permian (299-271 million years ago), a great volcanic system originated a great amount of ashes. The deposit of the pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, created the oldest rock you can see at Passo Valles: the ignimbrite, the most common type of Porphyry on Earth's crust, an extrusive igneous rocks. The accumulation of volcanic ashes resulted in the formation of a thick volcanic package covering over 2000 km2, with a thicknesses locally exceeding 2000 m. Ignimbrite has a dark red color, and it is primarily composed of a matrix of volcanic ashes with fragments of volcanic glass, pumice fragments, and crystals (Figure 3).


Figure 3. Ignimbrites at waypoint 1.

Waypoint 2 - Gardena Sandstone (N 46°20.417; E 11°48.229). During the Late Permian (260-251 million years ago), the ending of the volcanic processes allowed the erosion of the porphyries and then the transport and deposition of fragments by rivers. A red beds of sediments deposited in a semi-arid setting of alluvial fans and formed the Gardena Sandstone, a sedimentary rock composed mainly of sand-size mineral or porphyry grains. Due to their origin, this sandstone has the same color as the ignimbrites (Figure 4).

Figure 4. Gardena Sandstone at waypoint 2.

Waypoint 3 – Gypsum, Bellerophon Formation (N 46°20.226; E 11°48.087). Approx 255-260 million years ago, the sea invaded the mainland (marine transgression process) leading to the formation of depositional environments, as coastal sabkha, lagoons, saline deposits and shallow shelves. In this way, shallow marine evaporites and carbonates were originated, the so-called Bellerophon Formation. Now, you need to park your car at the original earthcache coordinates: The next two waypoints are accessible only by foot. At waypoint 3, you can see the gypsum (Figure 5), probably originated in a lagoon from the evaporation of surficial water.

Waypoint 4 – Grey Marlstone, Bellerophon Formation (N 46°20.132; E 11°48.131). At waypoint 4 you can see some grey marlstone, a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays (Figure 6).



Figure 5. Gypsum at waypoint 3.


Figure 6. Grey marlstone at waypoint 4.

Waypoint 5 – Werfen Formation and Sciliar Dolomite (N 46°20.473; E 11°47.445). During the Lower Triassic (approx 251 million years ago), a thick sequence of shallow-water carbonates and terrigenous deposits overlies the Bellerophon Formation. This very complex and heterogeneous sequence of grey dune limestone, grey-red siltstones and sandstones is called Werfen Formation. To reach this waypoint you need to return at Passo Valles and take your car. From waypoint 5, near the Malga Vallazza, look to SE to see the Cima Valles (2305 m). In the lower part, you can see some badlands, a type of geomorphologic feature where softer Bellerophon Formation have been extensively eroded by rain water. Do you see the complex stratigraphic texture? Moreover, in the upper part you can see some rock of the Werfen Formation (Figure 7).
During the Late Anisian period (approx 235 million years ago) a regional drowning due to the subsidence processes, created shallow-water environments, with several small isolated islands. This downing process was slowly sinking islands, where start to live some organisms forming a primitive coral reef. This subsidence caused relative sea level changes sufficient to drown coral reefs. However, these organisms have been able to grow fast enough to avoid drowning by subsidence. The growing of the colony rapidly reached a thickness of 800–900 m. This material created some of the most famous Dolomite Mountains, such as Sciliar, Latemàr, Marmolada, Catinaccio, Pale di S. Martino, Odle, Putia and the lower part of Civetta. The Dolomite is a sedimentary carbonate rock composed of calcium magnesium carbonate (CaMg(CO3)2). From this waypoint you can see the Pale di San Martino looking at SSE (Figure 8).


Figure 7. Cima Valles from Malga Vallazza, waypoints 5 and 6.

Your little tour in the history of the Dolomites is terminated. Now, you can reply to some questions. Therefore, the Dolomites history continue… see the additional information.

To log this EarthCache you must first email me via the profile or directly to mauro78.geocaching@gmail.com, with the answer to the following questions:
1) Near waypoint 1, you can see a road sign (Figure 3, yellow covered area): how many kilometers?
2) How many flagpoles you can see near the Passo Valles parking (at original earthcache coordinates)?
3) Which rocks originated during the Late Permian period?
4) Which rock formations are visible in the badlands on waypoint 6?
5) What is the chemical formula of the Dolomite?
When you receive a confirmatory email, log this earthcache uploading a photograph of any rock or any geological feature you found interesting. I appreciate if you also include the waypoint and a brief explanation in your log. Good luck!

Mauro



Additional information

The Dolomites history continue… Approx 230 million years ago, two new volcanoes arise from the ocean (one near Predazzo and one near the Velle S. Niccolò) originating a great amount of lava and tuffs and pouring down the sea basins and onlapping the platform slopes. Some mountains are totally or partially formed by these volcanic rocks, e.g., Mt Padon, Mt Pore and Col di Lana. Most of the coral reefs was killed (e.g., Latemàr, Marmolada) being close to the volcanoes and were even buried to the volcanic materials.

At the ending of the magmatic activity (237-228 million years ago), a new coral reef production started, causing the widespread progradation of several generations of carbonate platforms, called as Cassian Dolomites. These formations are much less developed in height due to reduced subsidence. These rocks formed the Settsass, Lastoi di Formìn, Picco di Vallandro/Dürrenstein and the lower part of Sella.
During the Early Carnian period (224 million years ago), a new fast subsidence process results in the end of the development of the reefs, and the sedimentation of new material on the basins. This is the Raibl Formation, with a red-green color forming the base of the Tofana di Rozes and Five Towers. About 223 million years ago, the previous platform/basin systems were replaced by a variety of shallow-water environments, and a powerful succession of laminated dolomite, the so-called Dolomia Principale was made. Their thickness is well 1000 meters, and today it represents some of the most famous Mountains (e.g., Tre Cime di Lavaredo/Dreizinnen, Cristlallo, Pomagagnon, Croda da Lago, Five Towers, the upper part of Civetta).

Some additional information were available reading the Italian geological maps on these links, sheet 11 (Marmolada) and 22 (Feltre), or reading this interesting scientific text (link).

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