Mexico’s coasts: Half-way to sustainability

Sustainability was estimated through a Sustainable Capacity Index defined as the combination of three aspects (state of the environment, quality of life of the human population, and pressure applied by human activities), used as a guideline for the differentiation of sustainability situations. We identified five different municipality groups, in terms of sustainability, as well as two thresholds, beyond which sustainable capacity was not present: below the sustainable capacity lower threshold, close to the sustainable capacity threshold, optimum situation, close to the sustainable capacity higher threshold, and above the sustainable capacity higher threshold. In general Mexico was found to be in an apparent balanced situation, in the sense that it is not overweighed around extreme values, the majority of the coastal municipalities falling in the optimum sustainable situation, within the cross comparison, characterized by medium coastal cities. We can conclude that Mexico has reached a critical point where it has to decide about the direction its coastal development has to take, since our results suggest that Mexican’s municipalities are half way to sustainability. The ideal situation would be that the optimum situation would maintain its actual low pressure with high state, but could increase its quality of life. This work provided a rapid monitoring and cross comparison tool for an estimation of the sustainable situation of Mexico’s coasts, repeatable in time, and in phase with the recent national coastal zone management principles and strategies.     

Hydrological and geotechnical investigations of mass movements in an equatorial city (Yaoundé, Cameroon)

In the present study, mass movements (landslide and mudslide) bound to a gully located at Mendong, a suburb of Yaoundé in Cameroon were examined using hydrological, geotechnical and geomorphological observations. The data indicate that water is an important causative factor of mass movements in the area studied. In fact, the water flow (waste water and runoff) provokes the saturation of materials at the slope foot. These materials lose their mechanical qualities and some deep ruptures generate landslide. During the rainy season, when the cumulative rainfall is more than 200 mm, these landslides are accompanied by mudslides that generate disturbances on the infrastructure situated around the gully and farther downstream. The economic and environmental damages resulting from the Mendong mass movements are considerable, such as degradation of the topography, losses in farm land, transportation and downstream sedimentation in a pond situated at the slope foot, loss of life and damage to the economy. All this calls for a multidisciplinary and integrated approach to hazard assessment and risk mitigation, which included data collection and interpretation, growing public and authority awareness, and preventing or reducing runoff and waste water flows by proper management and drainage.     

Trace elements in magnetite as petrogenetic indicators

We have characterized the distribution of 25 trace elements in magnetite (Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb), using laser ablation ICP-MS and electron microprobe, from a variety of magmatic and hydrothermal ore-forming environments and compared them with data from the literature. We propose a new multielement diagram, normalized to bulk continental crust, designed to emphasize the partitioning behavior of trace elements between magnetite, the melt/fluid, and co-crystallizing phases. The normalized pattern of magnetite reflects the composition of the melt/fluid, which in both magmatic and hydrothermal systems varies with temperature. Thus, it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts. The crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in Ti or Cu, respectively. The chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite (e.g., Si and Ca). Magnetite formed from low-temperature fluids has the lowest overall abundance of trace elements due to their lower solubility. Chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning, which records the changing conditions and composition of the fluid during magnetite growth. This new way of plotting all 25 trace elements on 1 diagram, normalized to bulk continental crust and elements in order of compatibility into magnetite, provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments. It has applications in both petrogenetic and provenance studies, such as in the exploration of ore deposits and in sedimentology.     

Accretion and tectono-sedimentary progradation: The Taranto Gulf (Southern Italy)

The geological structures of the eastern Calabrian Apenninic front within the Gulf of Taranto, southern Italy, are compared to those of a convergent margin, using simple criteria such as the origin and volume of the sediment supply, and the relative ratio between sediments carried by the sinking plate and those directly supplied by the overriding margin. Based on this criteria we distinguish four main types of sedimentary accretion occurring at convergent continental margins: (a) Pacific type, (b) Indonesian type, (c) Caribbean type, and (d) Apenninic type.     

Factor analysis: How it copes with complex geological problems

Factor analysis utilizing textural data from 81 bottom samples was used to analyze the surficial sediments covering a 40,000-sq km area, which is one input data point per 500 km. On the other hand, the surficial geology of the area studied is complex as some map units are only 1 km wide in places. Under these circumstances it is interesting to determine that factor analysis nonetheless aims toward a reasonable geological solution. If the premise is accepted that factor analysis provides a solution best-fitted to the data, the geologist has carried his research one step further and is left with the problem of interpreting the results of factor analysis correctly. In this experiment, the interpretation of the factors representing the gravel and the mud is relatively simple, although the two factors representing sands are more difficult to explain. The proper interpretation of factors leads naturally to an inquiry on the optimum number of factors to use, but this problem can be solved objectively by considering the factor loadings.     

Genesis of the Assif El Mal Zn–Pb (Cu,Ag) vein deposit. An extension-related Mesozoic vein system in the High Atlas of Morocco. Structural,mineralogical, and geochemical evidence

The Assif El Mal Zn–Pb (Cu–Ag) vein system, located in the northern flank of the High Atlas of Marrakech (Morocco), is hosted in a Cambro-Ordovician volcaniclastic and metasedimentary sequence composed of graywacke, siltstone, pelite, and shale interlayered with minor tuff and mudstone. Intrusion of synorogenic to postorogenic Late Hercynian peraluminous granitoids has contact metamorphosed the host rocks giving rise to a metamorphic assemblage of quartz, plagioclase, biotite, muscovite, chlorite, amphibole, chloritoid, and garnet. The Assif El Mal Zn–Pb (Cu–Ag) mineralization forms subvertical veins with ribbon, fault breccia, cockade, comb, and crack and seal textures. Two-phase liquid–vapor fluid inclusions that were trapped during several stages occur in quartz and sphalerite. Primary inclusion fluids exhibit T _h mean values ranging from 104°C to 198°C. Final ice-melting temperatures range from −8.1°C to −12.8°C, corresponding to salinities of ∼15 wt.% NaCl equiv. Halogen data suggest that the salinity of the ore fluids was largely due to evaporation of seawater. Late secondary fluid inclusions have either Ca-rich, saline (26 wt.% NaCl equiv.), or very dilute (3.5 wt.% NaCl equiv.) compositions and homogenization temperatures ranging from 75°C to 150°C. The δ¹⁸O and δD fluid values suggest an isotopically heterogeneous fluid source involving mixing between connate seawater and black-shale-derived organic waters. Low δ¹³C_VPDB values ranging from −7.5‰ to −7.7‰ indicate a homogeneous carbon source, possibly organic matter disseminated in black shale hosting the Zn–Pb (Cu–Ag) veins. The calculated δ³⁴S_H2S values for reduced sulfur (22.5‰ to 24.3‰) are most likely from reduction of SO₄ ²⁻ in trapped seawater sulfate or evaporite in the host rocks. Reduction of sulfate probably occurred through thermochemical sulfate reduction in which organic matter was oxidized to produce CO₂ which ultimately led to precipitation of saddle dolomite with isotopically light carbon. Lead isotope compositions are consistent with fluid–rock interaction that leached metals from the immediate Cambro-Ordovician volcaniclastic and metasedimentary sequence or from the underlying Paleo-Neoproterozoic crustal basement. Geological constraints suggest that the vein system of Assif El Mal formed during the Jurassic opening of the central Atlantic Ocean.     

30 and 43 months period cycles found in air temperature time series using the Morlet wavelet method

A wavelet-based methodology is applied to relevant climatic indices and air temperature records and allow to detect the existence of unexpected cycles. The scale spectrum shows the presence of two cycles of about 30 and 43 months, respectively, in the air–temperature time series, in addition to the well-known cycles of 1 day and 1 year. The two cycles do not affect the globe uniformly: some regions seem to be more influenced by the period of 30 months (e.g. Europe), while other areas are affected by the period of 43 months (e.g. North-West of the USA). Similar cycles are found in the indices and the regions influenced by these indices: the NAO index and the Western Europe display a cycle of 30 months, while the cycle of 43 months can be found in the ENSO index and in regions where it is known to have an impact.