Les bassins sédimentaires d'Hamakoussou et du Mayo Oulo-Léré sont des bassins à sédiments continentaux. Ils se situent en territoire camerounais, dans le prolongement de la branche de Yola de direction Est-Ouest du Fossé de la Bénoué dont la mise en place est liée à l'ouverture de l'Atlantique Sud à partir de la dislocation du Gondwana. L'âge de ces bassins est basé sur des études biochronologiques les situant dans le Crétacé inférieur. La série sédimentaire est sensiblement la même dans les deux bassins, elle est constituée de dépôts fluviatiles à fluviolacustres montrant une alternance de grés, de siltite et d'argilite.Des prélèvements paléomagnétiques ont été effectués sur des niveaux fins situés dans la partie supérieure de la série sédimentaire de chaque section. Dans le bassin sédimentaire d'Hamakoussou, 50 échantillons sur 11 sites d'épaisseur égale à 69 m, ont été prélevés dans la localité de Djallou et 78 échantillons sur 20 sites d'une épaisseur de 511 m dans la localité d'Ourokessoum. Dans le bassin du Mayo Oulo-Léré, 116 échantillons sur 45 sites sur une épaisseur de 478 m ont été prélevés dans la localité de Tchontchi.La désaimantation progressive au champ alternatif et à la température de ces échantillons montre que les séries sédimentaires de ces bassins portent une aimantation primaire. Les directions d'aimantation ont permis de déceler une tectonique régionale marquée par un mouvement de rotation autour de l'axe vertical et un mouvement de translation des blocs. Les minéraux magnétiques porteurs de cette aimantation sont de faible, moyenne et de forte coercivité. Une séquence de trois polarités a été déterminée le long de chaque section du bassin d'Hamakoussou : une polarité inverse et deux polarités normales. Dans le bassin du Mayo Oulo-Léré, la section Mayo a livré deux polarités dont une normale et une, inverse. La séquence de polarités obtenue pour chaque coupe a été corrélée avec l'échelle de temps de polarités magnétiques. Les trois polarités des coupes du bassin d'Hamakoussou ont été corrélées avec les chrones M1 et M3 avec un âge compris entre 125 Ma et 128,11 Ma. La séquence d'inversions de la coupe du Mayo Oulo-Léré a été corrélée avec le chrone M1 avec un âge compris entre 125 Ma et 127,61 Ma. Le taux de sédimentation des dépôts du bassin d'Hamakoussou varie entre 5,5 cm/ma et 40,5 cm/ma et est de 38 cm/ma dans la section du Mayo Oulo-Léré. / Hamakoussou and Mayo Oulo-Léré sedimentary basins are extension of the executive branch of East-West Yola Benue Trough, whose formation is related to the opening of the South Atlantic from the dislocation of Gondwana, in the Cameroonian territory. An age range of lower Cretaceous to Barremian-Hauterivian limit has been assigned based on biochronological studies. The sedimentary sequence in both basins is composed upward finnings fluivial to fluviolacustrine deposits. The deposits present an alternation of fine grained sandstone, siltstone and mudstone overlying coarse sandstone which is underlain by micro-conglomerate to conglomerate facies at the base.A magnetostratigraphic study has been carried out on a fine sediments in the upper part of each sections. 50 samples from about 69.03 m thickness, were collected from 11 sites at Djallou and 78 samples, about 511.03 m thickness, were collected from 20 sites at Ourokessoum localities in the Hamakoussou basin ; and 116 samples, about 478.19 m thickness, collected from 45 sites at Tchontchi locality in the Mayo Oulo-Lere basin.Specimens subjected to progressive alternating field and thermal demagnetization show that the sedimentary sequences have a primary magnetization. The directions of magnetization indicate a regional tectonic marked by a rotation and translation block. Rock magnetic investigations reveal the presence of both high and low coercivity minerals. A sequence of three polarities was determined along each section of the Hamakoussou basin: one reversal polarity and two normal polarities, whereas two polarities: (normal and a reversal) were determined along Mayo section in the Mayo Oulo-Lere basin The three polarities sequences from the two sections from Hamakoussou basin are correlated with M1 and M3 Chrons and suggest an age between 125 and 128, 11 My. While the two polarities sequences from the Mayo Oulo-Lere basin are correlated with M1 Chron, and suggest an age between 125 and 127.61 My. The sedimentation rates of Hamakoussou basin deposits vary between 5.5 cm/kyr and 40.88 cm/kyr and 38.26 cm/kyr in the section of Mayo Oulo-Lere basin.

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Lake Tanganyika is a complex, tropical ecosystem in East Africa, harboring an estimated 2,100 species. Extensive watershed deforestation threatens the biodiversity and ecological integrity of the lake. In this dissertation, ecological and paleoecological methods were employed to study the distribution of invertebrate biodiversity through space and time, with particular emphasis on linkages between biodiversity and land –use patterns. Ecological surveys of fish, mollusc, and ostracod crustacean diversity at sites in northern Lake Tanganyika representing different levels of watershed disturbance revealed a negative correlation between biodiversity and intensity of watershed disturbance. To elucidate the long -term relationship between disturbance and biodiversity, paleoecological records of invertebrates offshore from watersheds experiencing different degrees of anthropogenic disturbance were examined. Life, death, and fossil assemblages of ostracod valves were compared to assess the reliability and natural variability inherent to the paleoecological record. These comparisons indicated that paleoecological (i.e. death and fossil) assemblages reliably preserve information on species richness, abundance, and occurrence frequency at comparable -to- annual resolution. Unlike life assemblages, species composition of paleoecological assemblages reflects input of species from multiple habitat types. Ostracod paleoecological assemblages are characterized by spatiotemporal averaging that renders them representative of larger areas and longer time spans than life assemblages. Thus, paleoecological assemblages provide an efficient means of characterizing longer -term, site -average conditions. Natural variability in ostracod fossil assemblages from a sediment core representing the Late Glacial to the present indicates that abundance of individual ostracod species is highly variable. Ostracod assemblages were preserved in only the most recent 2,500 years of sediment. Species composition of ostracod assemblages reflects lake water depth. Core geochemical data indicate that the coring site may have been below the oxycline for ~2,000 years, inhibiting ostracod survival and preservation. Paleoecological, sedimentological, and stable isotope data revealed differences in biodiversity and watershed disturbance through time offshore from a pair of sites. The protected site is offshore from Gombe Stream National Park (Tanzania), the other offshore from a deforested watershed outside the park. Offshore from the deforested watershed, sedimentation rates increased, and turnover in ostracod species composition occurred during the past 50 years. Comparable changes were not observed offshore from the park.

From the Proceedings of the 1978 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 14-15, 1978, Flagstaff, Arizona / Sediment is widely recognized as a significant pollutant affecting water quality. To assess the impact of land use and management practices upon sediment yield from upland areas, it is necessary to predict erosion and sediment yield as functions of runoff, soil characteristics such as erodibility, and watershed characteristics. The combined runoff-erosion process on upland areas was modeled as overland flow on a plane, with rill and interrill erosion. Solutions to the model were previously obtained for sediment concentration in overland flow, and the combined runoff-erosion model was tested using observed runoff and sediment data. In this paper, the equations are integrated to produce a relationship between volume of runoff and total sediment yield for a given storm. The sediment yield equation is linear in runoff volume, but nonlinear in distance and, thus, watershed area. Parameters of the sediment yield equation include the hydraulic resistance parameter, rill and interrill erodibility terms, and flow depth-detachment coefficient and exponent.

This study uses the storm surge sediment beds deposited by Hurricanes Audrey (1957), Carla (1961), Rita (2005) and Ike (2008) to investigate spatial and temporal changes in sedimentation rates on the McFaddin National Wildlife Refuge in Southeast Texas. Fourteen sediment cores were collected along a transect extending from 90 to 1230 meters inland from the Gulf Coast. Storm-surge-deposited sediment beds were identified by texture, organic content, carbonate content, the presence of marine microfossils, and Cesium-137 dating. The hurricane-derived sediment beds are marker horizons that facilitate assessment of marsh sedimentation rates from nearshore to inland locations as well as over decadal to annual timescales. Near the shore, on a Hurricane Ike washover fan, where hurricane-derived sedimentation has increased elevation by up to 0.68 m since 2005, there was no measurable marsh sedimentation in the period 2008-2014. Farther inland, at lower elevations, sedimentation for the period 2008-2014 averaged 0.36 cm per year. The reduction in sedimentation in the period 2008-2014 on the nearshore part of the marsh is likely due to reduced flooding in response to increased elevation from hurricane storm surge sediment deposition. These results provide valuable knowledge about the sedimentary response of coastal marshes subject to storm surge deposition and useful guidance to public policy aimed at combating the effects of sea level rise on coastal marshes along the Gulf of Mexico.

From the Proceedings of the 1974 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 19-20, 1974, Flagstaff, Arizona / An erosion prediction method that has recently received wide attention in the United States is the universal soil loss equation which is given as: a=rklscp. Where a = estimated soil loss (tons/acre/year), r = a rainfall factor, k = a soil erodibility factor, l = a slope length factor, s = a slope gradient factor, c = a cropping-management factor, and p = an erosion control practice factor. Data collected on the walnut gulch experimental watershed in southeastern Arizona were used to estimate these factors for semiarid rangeland conditions. The equation was then tested with data from watersheds of 108 and 372 acres. The predicted value of annual sediment yield was 1.29 tons/acre/year as compared with an average 1.64 tons/acre/year for 4 years of data for the 108-acre watershed, and a sediment yield of 0.39 tons/acre/year was predicted for the 372-acre watershed as compared with the measured value of 0.52 tons/acre/year. Although good agreement was noted between predicted and actual sediment yield, additional work is needed before the equation can be applied to other areas of the southwest.

From the Proceedings of the 1974 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 19-20, 1974, Flagstaff, Arizona / A stochastic model is presented for the prediction of sediment yield in a semi-arid watershed based on rainfall data and watershed characteristics. Random variables which lead to uncertainty in the model are rainfall amount, storm duration, runoff, and peak flow. Soil conservation service formulas are used to compute the runoff and peak flow components of the universal soil loss equation, and a transformation of random variables is used to obtain the distribution function of sediment yield from the joint distribution of rainfall amount and storm duration. Applications of the model are in the planning of reservoirs and dams where the effective lifetime of the facility may be evaluated in terms of storage capacity as well as the effects of land management of the watershed. In order to calibrate the model and to evaluate the uncertainties involved, experimental data from the Atterbury watershed near Tucson, Arizona were used.