Influence de la densité et du type de peuplement sur le dépérissement du Cèdre à Sidi M'Guild (Moyen Atlas marocain)

Cet article sur le Cèdre au Maroc surprendra, sans doute, quelques "vieux forestiers", qui ont connu l'époque où le sylviculteur prenait le temps d'aller "écouter les arbres pousser dans sa forêt"! Les plus caustiques penseront, peut-être, qu'on "réinvente l'eau tiède" Ils auront tort ! Cette étude présente deux qualités majeures à notre époque : on ose y reprendre les précis de sylviculture d'auteurs du siècle dernier, pour guider cette étude du dépérissement du Cèdre ; on y démontre, de façon indubitable, en utilisant un dispositif statistique rigoureux et les techniques modernes d'analyse de données, qu'au Maroc, cette essence autochtone obéit aux mêmes lois sylvicoles que nos essences européennes : l'élimination naturelle des arbres dominés, la nécessité des éclaircies raisonnées et - moins classique et à confirmer - l'effet positif du mélange des essences (cèdre-chêne vert)

Influence de la densité et du type de peuplement sur le dépérissement du Cèdre à Sidi M'Guild (Moyen Atlas marocain)

International audienceCet article sur le Cèdre au Maroc surprendra, sans doute, quelques "vieux forestiers", qui ont connu l'époque où le sylviculteur prenait le temps d'aller "écouter les arbres pousser dans sa forêt"! Les plus caustiques penseront, peut-être, qu'on "réinvente l'eau tiède" Ils auront tort ! Cette étude présente deux qualités majeures à notre époque : on ose y reprendre les précis de sylviculture d'auteurs du siècle dernier, pour guider cette étude du dépérissement du Cèdre ; on y démontre, de façon indubitable, en utilisant un dispositif statistique rigoureux et les techniques modernes d'analyse de données, qu'au Maroc, cette essence autochtone obéit aux mêmes lois sylvicoles que nos essences européennes : l'élimination naturelle des arbres dominés, la nécessité des éclaircies raisonnées et - moins classique et à confirmer - l'effet positif du mélange des essences (cèdre-chêne vert)

Depositional sequences of carbonate ramp in the Eastern edge of Maastrichtian-Paleogene Atlantic Gulf (Atlas of Marrakech)

Chellaï El Hassane, Marzoqi M., Mouflih M., Pascal André. Depositional sequences of carbonate ramp in the Eastern edge of Maastrichtian-Paleogene Atlantic Gulf (Atlas of Marrakech). In: Géologie Méditerranéenne. Tome 21, numéro 3-4, 1994. Perimediterranean carbonate platforms. First International Meeting. Marseille – France (5-8 septembre 1994) sous la direction de Jean-Pierre Masse. p. 39

Geochemical investigation of the taphonomy, stratigraphy, and palaeoecology of the mammals from the Ouled Abdoun Basin (Paleocene-Eocene of Morocco)

International audienceWe performed different geochemical analyses of Paleogene terrestrial mammal remains to establish their taphonomy, stratigraphic provenance, and palaeoenvironmental conditions. Rare earth element (REE) results indicate a similar diagenetic history to that of previously investigated marine taxa from these beds. Therefore, the mammal remains were initially deposited in a marine setting, and probably not long after the death of the animals their bodies were washed into the sea. The Ce/Ce* and Pr/Pr* ratios for the mammal fossils were compared with the background dataset from the phosphate mines, which varies with time. This allowed us to characterize the stratigraphic levels bearing the fossils. The provenances of fossils with known origins were confirmed, while remains with unknown origins could be assigned to certain stratigraphic horizons that are compatible with previously proposed phylogenic relationships. Marine diagenesis affected the various skeletal tissues differently, with the largest alteration in the bone and the least or none in the enamel. This is mostly demonstrated by the high F concentration, high Ca/P, and seawater related 87 Sr/ 86 Sr in the bone/dentine samples. Enamel shows the opposite, and retained the most pristine terrestrial values. The δ 18 O PO4 and δ C results from mammal enamel revealed warm (>20°C mean annual temperature-MAT) and dry (<500mm mean annual precipitation) conditions for Paleocene-Eocene period in the region. From the early to mid-Ypresian about +5°C ∆MAT is recorded that might be linked to the Early Eocene Climatic Optimum. Furthermore, the 87 Sr/ 86 Sr ratios derived from shark tooth enameloid fit the global open ocean Sr-isotope record during the latest Paleocene and early Eocene providing further evidence for the age of these phosphate beds in the Ouled Abdoun Basin. However, older marine fossils yielded higher ratios than the global Sr-isotope curve, reflecting an alteration and/or somewhat restricted conditions in the Moroccan coastal basins, possibly triggered by global sea-level changes

Comprehensive stable isotope investigation of marine biogenic apatite from the late Cretaceous-early Eocene phosphate series of Morocco

International audienceFossil biogenic apatites were studied for their geochemical composition across the late Cretaceous–early Eocene Moroccan phosphate series in the Ouled Abdoun and Ganntour basins in Morocco in order to characterize paleoenvironmental conditions and to improve stratigraphy. The vertebrate remains show particularly good structural, mineralogical and chemical preservations, which relate to the favorable depositional environment of the phosphorite. The main studied fossils – shark tooth enameloid and dentine, and coprolites – show large range in δ13C values from − 14 to + 6‰, which can be coupled to different carbon sources. Enameloid yielded mostly positive δ13C isotopic compositions that are comparable with values reported from modern teeth. Coprolites have the lowest δ13C values that reflect burial conditions with intensive organic matter recycling.The large variation in δ18OPO4 values of the shark teeth can be related to ecological differences. However, the mean δ18OPO4 data reflect important temporal variation along the series, together with the corresponding average δ13C values. Comparisons with the global isotope records allow identifying the Early Eocene Climatic Optimum in the top of the Ouled Abdoun series (above Bed 0′). The isotope data further suggest a sedimentary gap during the latest Thanetian and the Paleocene Eocene Thermal Maximum. The top of the Paleocene series (Bed IIa) can be dated to late Selandian–early Thanetian, with the recognition of the Early Late Paleocene Event (ELPE). The Eritherium Bone Bed, that yielded the earliest known placental mammals from Africa, would be located below the ELPE and therefore, cannot be younger than late Selandian.The isotope data from the older Paleocene (Bed IIb) and Cretaceous (upper Bed III) beds in the Ouled Abdoun Basin can be correlated with the latest Danian–early Selandian and the latest Maastrichtian global isotope record, respectively. Based on the δ18OPO4 data, the Cretaceous layers of the Ganntour Basin cover most of the Maastrichtian period except the very early part. All these early Paleogene and Cretaceous chemostratigraphic ages, however, need further confirmations from other proxies. Yet, the interpretations are in general agreement with the biostratigraphy derived from the selachian fauna

First carbon isotope chemostratigraphy of the Ouled Abdoun phosphate Basin, Morocco; implications for dating and evolution of earliest African placental mammals

The well-known Maastrichtian-Ypresian vertebrate-bearing phosphate series, in the Ouled Abdoun Basin, Morocco, is classically dated using regional selachian biostratigraphic zonation. These marine sediments yielded Paleocene and Eocene mammals comprising the earliest known placentals from Africa. This study provides the first insight into the organic carbon isotope chemostratigraphy (δ13Corg) of the Moroccan phosphate series and a refined dating of its vertebrate-bearing levels. Four Paleocene-Eocene sections in the NE Ouled Abdoun quarries show consistent δ13Corg long term evolutions, from the base to the top: 1) positive trend in phosphorite Bed IIa, beginning with the lower Bone Bed yielding mammals such as Eritherium, Ocepeia, Abdounodus, Lahimia, of early Thanetian and Selandian age; 2) transitional negative trend in the Intercalary phosphorite Beds II/I that includes the Otodus obliquus and Phosphatherium escuilliei Bone Bed of earliest Ypresian age; 3) negative trend to the lowermost δ13Corg values that are correlative to the early-middle Ypresian interval including ETM 2 and ETM 3 hyperthermal events in the global record; 4) positive trend in chert-enriched facies containing the middle Ypresian EECO global climatic event. Our chemostratigraphic study of the Ouled Abdoun phosphate series provides a new chronostratigraphic framework for calibrating the beginning of the evolution of placental mammals in Africa. The lower Bone Bed level from the Paleocene phosphorite Bed IIa yielding Eritherium is not younger than early Thanetian, and is most likely Selandian. The Phosphatherium Bone Bed in the Intercalary Beds II/I is earliest Ypresian. The phosphorite Bed 0, from which Daouitherium probably came, is early-middle Ypresian, just below the EECO. This suggests that the first large proboscideans evolved after the PETM, during mid-Ypresian warming events. The δ13Corg study does not support the presence of Lutetian in the NE Ouled Abdoun phosphate series and suggests that a noticeable part of the upper Thanetian is absent. © 2013 International Association for Gondwana Research