Summary
The high-plateau of the Jbel Bou Dahar, situated in the Central and Eastern High Atlas of Morocco, represents a Lower Jurassic carbonate platform that drowned at the beginning of the Toarcian. Three phases of platform evolution can be distinguished:
During thepre-drowning phase (upper Sinemurian— upper Pliensbachian) the platform interior facies reflects a restricted-marine lagoonal environment, protected by scattered buildups and cemented debris at the platform margin. Upper and mid-slope are dominated by coarse-grained, poorly sorted limestones, deposited through debris flows during sea-level lowstands. Sea-level highstand deposits occur at the toe of slope and are formed by an alternation of fine-grained litho- and bioclastic pack- to grainstones (turbidites), marls and mud- to wackestones (hemipelagic oozes).
A condensed section, reflecting an abrupt and fundamental environmental change along the entire platform, characterises thedrowning phase (upper Pliensbachian— lower Toarcian). Within the platform interior densely packed biosparites represent the switch to high-energy environments, causing erosion of the former pre-drowning lagoonal sediments. These erosional products were redeposited on the platform slope, leading to the formation of coarse-grained non-skeletal sparites and micrites. Both platform interior and slope successions show a series of cyclic variations in sediment composition that could have been triggered by small-scale sea-level fluctuations.
In contrast to the abrupt facies change at the pre-drowning —drowning boundary, the transition to thepost-drowning phase (lower Toarcian—Aalenian) is gradual. During this phase, biopelmicrites and pure micrites were deposited in all platform sections, followed by the deposition of calcistiltites. The facies point to quiet-water conditions below storm-wave base and display a uniform deep-marine sedimentation.
This analysis shows that the drowning of the Jbel Bou Dahar carbonate platform was caused by abrupt and fundamental changes in the shallow-water realm. After exposure of the platform, these changes prevented the carbonate factory from re-establishing itself and made it impossible for the platform to keep up with the subsequent rise in sea level. These local changes were probably triggered by high-frequency sealevel variations in combination with regional or even worldwide changes in ocean circulation patterns.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Agard, J. &du Dresnay, R. (1965): La region minéralisée du Jebel Bou-Dahar, près de Beni-Tajjite (Haut-Atlas oriental), Etude géologique et métallogénique.—Not. Mém. Serv. géol. Maroc,181, 135–166. Rabat
Blomeier, D. (1997): Evolution of a Lower Jurassic carbonate platform, Sequence stratigraphy and depositional processes at the Jbel Bou Dahar (High Atlas, Morocco)—unpubl. Ph.D. Thesis, Univ. Kiel, 164 p., Kiel
Bosscher, H. &Southam, J. (1992): CARBPLAT—A computer model to simulate the development of carbonate platforms.— Geology,20, 235–238, Boulder
Brechbühler, Y.A., Bernasconi, R. &Schaer, J.P. (1988): Jurassic sediments in the Central High Atlas of Marocco: Deposition, burial and erosion history.—In:Jacobshagen, V.H. (ed.): The Atlas System of Morocco, 15, 201–215, Berlin (Springer)
Campbell, A.E. (1992): Unconformities in seismic records and outcrop.—Ph.D. Thesis, Univ. Amsterdam, 187 p., Amsterdam
Campbell, A.E. &Stafleu, J. (1992): Seismic modeling of an Early Jurassic, drowned carbonate platform: Djebel Bou Dahar, High Atlas, Morocco.—Amer. Ass. Petrol. Geol. Bull.,76/11, 1760–1777, Tulsa
Conti, M.A. &Monari, S. (1992): Thin-shelled bivalves from the Jurassic Rosso Ammonitico and Calcari a Posidonia.— Paleopelagos,2, 193–213, Roma
Crevello, P.D. (1990): Stratigraphic evolution of Lower Jurassic carbonate platforms, Record of rift tectonics and eustasy, Central and Eastern High Atlas, Morocco.—Ph.D. Thesis, Colorado School of Mines, Golden, 456 p., Golden
Dominguez, L.L., Mullins, H.T. &Hine, A.C. (1988): Cat Island platform, Bahamas: an incipiently drowned Holocene carbonate shelf.—Sedimentology,35, 805–819, Oxford
Drzewiecki, P.A. &Simo, J.A. (1997): Carbonate platform drowning and oceanic anoxic events on a Mid-Cretaceous carbonate platform, South-central Pyrenees, Spain.—J. Sed. Res.,67/4, 698–714, Amsterdam
Dubar, G. (1948): La faune domérienne du Jebel Bou-Dahar, près de Béni-Tajjite.—Not. Mém. Serv. géol. Maroc.,68, 1–250, Rabat
— (1950): Sur des faunes de brachiopodes du Lias inferieur dans les fentes du Domérien supérieur au Jebel Bou-Dahar (Haut-Atlas macrocain).—A. Soc. géol. du Nord.,70, 205–230, Paris
— (1962): Notes sur la paléogéographie du Lias marocain (Domaine atlasique).—Livre à la mémoire de Pault Fallot, 1, 531–544, Paris
du Dresnay, R. (1971): Extension et développement des phénomènes récifaux jurassiques dans le domaine atlasique marocain, particulièrement au Lias moyen.—Bull. Soc. Géol. France,13/7, 46–56, Paris
— (1979): Sediments Jurassiques du domaine des chaines Atlasiques du Maroc.—Symposium “Sédimentation Jurassique W. Européen”, Ass. Sed. Fr. Spec. Publ.1, 345–365, Paris
Dunham, R.J. (1962): Classification of carbonate rocks according to depositional texture.—Amer. Ass. Petrol. Geol. Memoir,1, 108–121, Tulsa
Einsele, G. (1991): Submarine Mass Flow Deposits and Turbidites. —In:Einsele, G., Ricken, W. &Seilacher, A. (eds.): Cycles and Events in Stratigraphy, 314–339, Berlin (Springer)
Flügel, E. (1982): Microfacies analysis of limestones.—633 p., Berlin (Springer)
Folk, R.L. (1959): Practical petrographic classification of limestones. —Amer. Ass. Petrol. Geol. Bull.,43/1, 1–38, Tulsa
— (1962): Spectral subdivision of limestone types.—Amer. Ass. Petrol. Geol. Memoir,1, 62–84, Tulsa
Föllmi, K.B., Weissert, H., Bisping, M. &Funk, H. (1994): Phosphogenesis, carbon-isotope stratigraphy, and carbonate-platform evolution along the Lower Cretaceous northern Tethyan margin.—Geol. Soc. Am. Bull.,106, 729–746, Boulder
Frakes, L.A., Francis, J.E. &Syktus, J.I. (1992): Climate Modes of the Phanerozoic, The history of Earth’s climate over the past 600 million years—274 p., Cambridge (Cambridge University Press)
Ghissassi, S.E.A., Saadi, M., Skalli, T., Hilali, E.A. &Boudda, A. (1976): Carte géologique du Haut Atlas d’Anoual-Bou Anane (Haut Atlas Oriental); 1,200.000.—Ministère du Commerce, de l’Industrie, des Mines et de la Géologique et de l’Energie, Rabat
Glaser, K.S. &Droxler, A.W. (1991): High production and highstand shedding from deeply submerged carbonate banks, northern Nicaragua Rise.—J. Sediment. Petrol.,61/1, 128–142, Tulsa
Hallock, P. &Schlager, W. (1986): Nutrient excess and the demise of coral reefs and carbonate platforms.—Palaios,1, 389–398, Tulsa
Hallock, P., Hine, A.C., Vargo, G.A., Elrod, J.A. &Jaap, W.C. (1988): Platforms of the Nicaraguan Rise, Examples of the sensitivity of carbonate sedimentation to excess trophic resources. —Geology,16, 1104–1107, Boulder
Haq, B.U., Hardenbol, J. & Vail, P.R. (1988): Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change.— In:Wilgus, C.K., Hastings, B.S., Kendall, C.G.S.C., Posamentier, H.W., Ross, C.A. & Van Wagoner, J.C. (eds.): Sea-level changes: an integrated approach,—Soc. Econ. Paleont. Min., Spec. Publ.,42, 71–108, Tulsa
Jenkyns, H.C., Géczy, B. &Marshall, J.D. (1991): Jurassic manganese carbonates of Central Europe and the Early Toarcian anoxic event.—J. Geol.,99, 137–149, Chicago
Kenter, J.A.M. (1990): Geometry and declivity of submarine slopes.—Ph.D. Thesis, Univ. Amsterdam, 128 p., Amsterdam
Kenter, J.A.M. &Campbell, A.E. (1991): Sedimentation on a Lower Jurassic carbonate platform flank: geometry, sediment fabric and related depositional structures (Djebel Bou Dahar, High Atlas, Morocco).—Sed. Geol.,72, 1–34, Amsterdam
Laville, E. (1988): A multiple releasing and restraining stepover model for the Jurassic strike-slip basin of the Central High Atlas (Morocco).—In:Manspeizer, W. (ed.): Triassic-Jurassic Rifting, Continental Breakup and the Origin of the Atlantic Ocean and Passive Margins, Part A..—Develop.-Geotect.,22, 499–523, Amsterdam (Elsevier)
Lee, C.W. &Burgess, C.J. (1978): Sedimentation and tectonic controls in the Early Jurassic Central High Atlas trough, Morocco.—Geol. Soc. Am. Bull.,89, 1199–1204, Boulder
Loeblich jr., A.R. &Tappan, H. (1988): Foraminiferal genera and their classification.—970 p., New York (Van Nostrand)
Richter, M. (1970): Das Atlas-System in Nordafrika.—Z. deutsch. geol. Ges.,120, 68–84, Hannover
Scheibner, C. (1995): Geologische Großkartierung des mittleren Teils des Djebel Bou Dahar, Hoher Atlas (Marokko) mit Beiträgen zum Übergangsbereich Hang—Innere Plattform einer Karbonatplattform und Beiträgen zur Mikrofazies (Geographisches Blatt Bni Tajjit).—M.Sci. Thesis, Univ., 154 p., Kiel
Scheibner & Reijmer, J.J.G. (this volume): Facies patterns within a Lower Jurassic upper slope to inner platform transect (Jbel Bou Dahar, Morocco).—Facies,41, Erlangen
Schlager, W. (1981): The paradox of drowned reefs and carbonate platforms.—Geol. Soc. Am. Bull.,92/1, 197–211, Boulder
Schlager, W. (1989): Drowning unconfomities on carbonate platforms.—In:Crevello, P.D., Wilson, J.L., Sarg, J.F. & Read, J.F. (eds.): Controls on Carbonate Platform and Basin Development.—Soc. Econ. Paleont. Min., Spec. Publ.,44, 15–26, Tulsa
— (1998): Exposure, drowning and sequence boundaries on carbonate platforms.—Spec. Publ. Int. Ass. Sediment.,25, 3–21, Oxford
Schlager, W. &Camber, O. (1986): Submarine slope angles, drowning unconformities and self-erosion of limestone escarpments. —Geology,14, 762–765, Boulder
Stafleu, J. (1994): Seismic models of outcrops as an aid in seismic interpretation.—Ph.D. Thesis, Univ. Amsterdam, 223 p., Amsterdam
Stafleu, J. &Schlager, W. (1995): Pseudo-unconformities in seismic models of large outcrops.—Geol. Rundsch.,84, 761–769, Berlin
Warme, J.E. (1988): Jurassic carbonate facies of the Central and Eastern High Atlas Rift, Morocco.—In:Jacobshagen, V.H. (ed.): The Atlas System of Morocco, 15, 169–199, Berlin (Springer)
Wilson, J.L. (1975): Carbonate Facies in Geologic History.—471 p., Berlin (Springer)
Wilson, P.A., Jenkyns, H.C., Elderfield, H. &Larson, R.L. (1998): The paradox of drowned carbonate platforms and the origin of Cretaceous Pacific guyots.—Nature,392, 889–894, London
Zempolich, W.G. (1993): The Drowning Succession in Jurassic Carbonates of the Venetian Alps, Italy, A Record of Supercontinent Breakup, Gradual Eustatic Rise, and Eutrophication of Shallow-Water Environments.—In:Loucks, R.G. and Sarg, J.F. (eds.), Carbonate-Sequence Stratigraphy— Recent Developments and Applications.—Amer. Ass. Petrol. Geol. Memoir,57, 63–105, Tulsa
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Blomeier, D.P.G., Reijmer, J.J.G. Drowning of a Lower Jurassic carbonate platform: Jbel Bou Dahar, High Atlas, Morocco. Facies 41, 81–110 (1999). https://doi.org/10.1007/BF02537461
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/BF02537461