English version
Any Earth cache consists of an earth science lesson that requires a visit to a unique geological feature and does not have a container with logbook.
This Earth cache is located in a publicly accessible part of Ben Aknoun Park in Algiers and will provide you with information about the geology and geomorphology of the area.
Geology is a branch of natural science concerned with Earth, the rocks of which it is composed, and the processes by which they change over time.
Geomorphology is scientific discipline concerned with the description and classification of the Earth’s topographic features.
Geological and geomorphological situation
The northern part of Algeria is dominated by the Atlas Mountain. The coastal plain around Algiers is relatively narrow, with the sea to the north and the Atlas Mountains to the south.
During the Quaternary period, which began about 2.6 million years ago, the climate of the region changed several times, with periods of wetter and drier conditions. The rivers flowing through the area in wetter periods carried large quantities of materials downstream. Materials were formed by weathering and erosion of the rocks. These were eventually deposited to form sediments called alluvial deposits. They usually consist of a mixture of soil particles of varying sizes, including clay, silt, sand and gravel.
- Clay: particles smaller than 0.002 millimeters in diameter
- Silt: particles between 0.002 and 0.05 mm
- Sand: particles between 0.05 and 2 mm
- Gravel: particles larger than 2 mm
Stratification
Alluvial deposits can exhibit various types of stratification, including horizontal layers as well as inclined, tilted, or even folded layers. This is because the deposition of alluvial sediments is often influenced by dynamic processes such as flowing water, sediment transport, erosion, and tectonic activity.
Ben Aknoun Park
Ben Aknoun Park is located in the south-west of the Alger city, specifically on the wooded plateau between Hydra and El Achour. The park was opened in 1982. This large green space is popular with locals and tourists. It includes jogging and walking trails, relaxing zones, a ZOO, shops, restaurants and hotels. Two cable cars and small train line were available to visitors.
Observable layers
In the area between WP2 and WP3 the train used to run through the terrain notch. The rock walls on the sides consist of sedimentary rocks of the grain size of sandstones to conglomerate sandstones (at the bottom of the profile), respectively conglomerates (at the top of the profile). These are not typical sandstones and conglomerates consisting mainly of quartz grains and pebbles, but of finer limestone fragment rocks, so-called calcarenities (up to 2 mm) and calcirudity (over 2 mm in diameter). Alluvial layers are clearly visible in the profile.
Questions and task
If you head eastwards from WP2 along the disused rails, you can see in the middle part of the left wall (i.e. towards the north) alluvial deposits with distinctive oblique parallel stratification.
Questions:
1. Are the layers rising or falling from left to right?
2. What is the height of the wall at this point (m)?
3. What color is this wall?
Task:
1. Attach a photo of yourself or a photo of the subject with your nickname that proves you were at that location and that does not reveal the answers to the above questions.
To log a find, answer the above questions and send the answers to the owner via GC profile (message center or e-mail). Attach the required photo to your log. You can log right away, if your answers are wrong, the owner will contact you. If you do not send any answers or your log does not contain the photo as requested, the log will not be accepted and will be removed.
Source: Wikipedia, Britannica, National Library of France, Czech Geological Survey.
Résumé en français
Tout cache de terre se compose d'une leçon de science de la Terre qui nécessite une visite à une caractéristique géologique unique et n'a pas de conteneur avec un journal de bord.
Questions et tâche
Si vous vous dirigez vers l'est de WP2 le long des rails désaffectés, vous pouvez voir dans la partie médiane de la paroi gauche (c'est-à-dire vers le nord) des dépôts alluviaux avec une stratification parallèle oblique distinctive.
Des questions:
1. Les couches montent-elles ("rising ") ou diminuent-elles ("falling") de gauche à droite?
2. Quelle est la hauteur du mur à cet endroit (en mètres)?
3. De quelle couleur est ce mur?
Tâche:
1. Joignez une photo de vous-même ou une photo du sujet avec votre surnom qui prouve que vous étiez à cet endroit et qui ne révèle pas les réponses aux questions ci-dessus.
Pour enregistrer une recherche, répondez aux questions ci-dessus et envoyez les réponses au propriétaire via le profil GC (Centre de messages ou e-mail). Joignez la photo requise à votre journal. Vous pouvez vous connecter immédiatement, si vos réponses sont fausses, le propriétaire vous contactera. Si vous n'envoyez aucune réponse ou si votre journal ne contient pas la photo comme demandé, le journal ne sera pas accepté et sera supprimé.