The Tagoudite Formation (also known as the "Upper Tamadout Formation") is a geological formation of Toarcian (Lower Jurassic) age in the Béni-Mellal, Imilchil, Tinerhir, Tinejdad and Errachidia areas of the High Atlas (reaching areas near Rich in the Middle Atlas) of Morocco.
Description
The Tagoudite Formation marks a major shift in Liassic sedimentation, replacing the carbonate turbidites of the Ouchbis Formation with mostly siliciclastic layers. These layers alternate between gray and green sandstone, sandy marls, and siltstones, forming sequences up to 20 meters thick. They show a decrease in grain size and an increase in marl content from bottom to top, with features like ripple marks and laminations. Microscopically, the turbidites are mainly fine silt, with varying amounts of quartz, feldspar, and carbonate detritus, and occasional pyrite. This formation suggests an open marine environment with sediment interruptions and materials coming from distant areas. It is widespread in the Central High Atlas, with thicknesses reaching up to 320 meters, and varies across different regions like Tounfite and Beni Mellal. In the Central Middle Atlas, sedimentation was interrupted by emersion before the formation's deposition. The deposits of the Tagoudite Formation are mostly restricted to the central High Atlas, with a thickness of approx. 200 m in the northwest vs at 30–70 m in the southeast, but retaining around 200 m at center areas like Foum Tillicht. More at the E it starts to disappear like at the Cirque de Jaafar, SW of Midelt or more at the E at Bou Redine Gorges, were the Agoudim Formation directly overlies the Pliensbachian. Small (-1 cm) rounded ridges and troughs wrinkle structures occur on the tops of fine-grained turbidite beds deposited rapidly in deep, low-light conditions, too deep for photosynthetic mats. The wrinkles were likely formed by chemosynthetic microbial mats, sulfur-oxidizing bacteria (Beggiatoaceae, Thioploca spp., and similar Gammaproteobacteria) that thrive in dark, organic-rich sediments where chemical gradients provide energy. Frequent turbidity currents, high organic content (including woody debris), and sulfide-rich pore waters created ideal conditions for these mats to grow and for their textures to be preserved. Low animal activity due to toxic sulfide levels further enhanced preservation.
Biota Phytoplankton marks oscillations of negative carbon isotope excursions at T-OAE and Pliensbachian-Toarcian (Pl-To) transition, dominated by open marine haptophytan or incertade sedis coccoliths like Biscutum, Carinolithus (including the index C. superbus, marker of the Polymorphum biozone), Calcivascularis, Calyculus, Lotharingius, Mitrolithus, Parhabdolithus or Schizosphaerella, measured in the Tagoudite Fm in areas like Amellago or Talghemt. Dinoflagellates are rare and limited to taxa such as Luehndea, Mancodinium and Mendicodinium.
Foraminifera
Ichnofossils
Brachiopoda
Mollusks
Arthropoda
Echinodermata Rare Ophiuroid impressions can be observed.
Actinopteri
Viridiplantae Phytoclasts, spores, pollen and Tasmanites & Botryococcus algae indicate that the palaeoenvironment of the lower Toarcian Amellago area was likely proximal continental shelf with a high terrestrial input, and notorious influence of brackish water in the depositional environment. This interval is numerically dominated by Classopollis, which usually accounts for more than 60.95% of the palynomorphs present.
See also Toarcian turnover Toarcian formations Tafraout Formation, SISTER UNIT, Morocco Azilal Formation, SISTER UNIT, Morocco Aganane Formation, Morocco Calcaires du Bou Dahar, Morocco Marne di Monte Serrone, Italy Podpeč Limestone, Slovenia El Pedregal Formation, Spain Mizur Formation, North Caucasus Sachrang Formation, Austria Posidonia Shale, Lagerstätte in Germany Irlbach Sandstone, Germany Ciechocinek Formation, Germany and Poland Krempachy Marl Formation, Poland and Slovakia Djupadal Formation, Central Skane Lava Formation, Lithuania Whitby Mudstone, England Fernie Formation, Alberta and British Columbia Poker Chip Shale Whiteaves Formation, British Columbia Navajo Sandstone, Utah Los Molles Formation, Argentina Mawson Formation, Antarctica Kandreho Formation, Madagascar Kota Formation, India Cattamarra Coal Measures, Australia
References
