Mexico Margin Research Articles

Impact of the National Crusade against Hunger (CNCH) on anemia and dietary diversity among Mexican children

The National Crusade against Hunger (CNCH by its initials in Spanish) is a social inclusion and wellbeing strategy aimed at combating poverty, social marginalization and malnutrition in Mexico. The CNCH intervention was launched in Mexico during the current presidential term (2013 – 2018).ObjectiveTo assess the impact exerted by CNCH food assistance programs on the dietary diversity and nutritional status of children at one‐year follow‐up.MethodsA comparative study was conducted with two cohorts of children under five years of age: 1. CNCH intervention group (n=1500) and 2. Control group (n=800). Assessment was performed in two stages: at baseline (2014) and at one‐year follow‐up (2015). The study used a randomized, probabilistic design based on a nationally representative sample. The children in both cohorts were residents of highly and very highly marginalized localities. A differences‐in‐differences estimator was combined with generalized linear models to estimate CNCH impact on anemia and dietary diversity indicators.ResultsThe probability of suffering from anemia was lower in the CNCH than in the control group children (p=0.021). Furthermore, those in the CNCH group were more likely to consume cereals (p=0.022), leguminous vegetables (p<0.001), and fruit and vegetables (p=0.006) than were those in the control group (p=0.001).ConclusionThe CNCH social food assistance programs contribute to [U1] dietary diversity and anemia reduction in children under five. It is recommended to monitor the care strategies in each program and to improve targeting in the most socially deprived households.

“Santísima Muerte, Vístete de Negro, Santísima Muerte, Vístete de Blanco”: La Santa Muerte’s Illegal Marginalizations

La Santísima Muerte, the death saint patron of the marginalized and dispossessed in Mexico, the United States, and beyond, is especially favored by devotees who identify with her duality between dark and light, and good and evil. Most of Santa Muerte’s devotees understand that good and evil coexist in her, and they often simultaneously appeal to both. At the same time, illegality and marginalization, which are generally associated with the saint’s “dark” or “evil” sides, take on multiple, diverse forms, encompassing criminalized activity such as narcotrafficking, religious transgressions that reflect unorthodox spiritual practices such as witchcraft, and most contentiously of all, the very conditions of poverty and racialization in Mexico. Nevertheless, cultural representations of Santa Muerte often resist such diversity and persist in opposing her dark and light sides. Films such as Eva Aridjis’s La Santa Muerte and Pável Valenzuela Arámburo’s La Santísima Muerte aim to represent all Santa Muerte in all of her multiplicity and to correct stereotypical representations of the death saint in general. But perhaps inadvertently, Aridjis’s film reinforces the contrast, rather than the intersections, between “light” and “dark”. However, in La Santísima Muerte, Valenzuela Arámburo deliberately embraces the saint’s contradictory duality to provide a different perspective on illegality and criminality, simultaneously accepting such illegality as a dark menace in the vein of Santa Muerte’s typical detractors, and rearticulating it as a necessary aspect of the saint’s holy works. Valenzuela Arámburo’s film not only emphasizes that the very same devotees invoke Santa Muerte for her powers of “good” as well as for those of “evil”, it demonstrates that these devotees incorporate the saint’s dark side as they see fit not as a consequence of their marginalized status, but as a means to resist it. Thus, while both films underscore that marginalized populations are just as nuanced and contradictory as their patroness of death is, Valenzuela Arámburo’s film grounds itself in Santa Muerte’s duality in order to demonstrate how her seemingly contradictory aspects construct and shape each other. As such, the film combats the representation of marginalization and criminality in Mexico and beyond, highlighting the extent to which her devotees appeal to both her dark and light sides precisely because they are simultaneously victims of marginalization and agents of resistance.

Mesozoic tectono-magmatic evolution of Mexico: An overview

The Geological Framework of Mexico is formed by a mosaic of tectono-stratigraphic terranes that were assembled during the Paleozoic and Mesozoic as the result of the complex interaction between Laurentia, Gondwana, and the paleo-Pacific plate. Even though the Mexican tectono-magmatic evolution is still object of study, some main representative stages can be recognized. Determining the time span and regional distribution of magmatism throughout the geological history of Mexico is crucial for the exploration of mineral resources. This paper contains a brief description of the terranes and is focused on summarizing the main Mesozoic tectono-magmatic events, from the assembling of Pangea in Late Paleozoic time to the end of the Mesozoic. These main events are: 1) Permo-Triassic continental (submarine) arc that developed along eastern Oaxaquia and was related to a subduction zone developed along the paleo-pacific margin. 2) Magmatic activity ceased in central and southern Mexico, during Middle to Late Triassic time, and a wide submarine fan was formed along the western margin of Pangea, which apparently acted like a passive margin. Evidence of a contemporaneous intra-oceanic arc is found at Baja California. 3) Inland Early Jurassic volcanism is found in northeast and central Mexico. Whether this magmatic event evolved in a rift or arc (Nazas) tectonic setting is still undetermined. 4) By Late Jurassic, magmatism was widespread. It is the time of the breakup of Pangea, leading to the opening of the Gulf of Mexico and the Arperos Basin. Therefore, volcanism was mostly related to subduction and supra-subduction rifting. 5) The Gulf of Mexico and Arperos basins were formed by Early Cretaceous time. Igneous rocks of that age have a wide range of composition (arc, continental rift, strike slip, and oceanic rift, within plate), and are geographically widespread. 6) At the end of Early Cretaceous, volcanism moved to a more localized belt along the paleo Pacific margin; it is also the time of formation of major carbonate platforms along east Mexico. 7) Coeval to Sevier-Laramide orogeny of North America, a large fold and thrust belt developed throughout Mexico, during Late Cretaceous time. It was accompanied by arc magmatism along the pacific margin of Mexico (Tarahumara Arc). It is the first continental arc that evolved after accretion and consolidation of Guerrero and Alisitos terranes to Continental Mexico. These Mesozoic tectonic processes originated westward-eastward migrations of arc-related and rift-related volcanism, which in turn lead to the present distribution of Mesozoic mineral deposits.

Early Miocene continental-scale sediment supply to the Gulf of Mexico Basin based on detrital zircon analysis

The early Miocene was a period of major continental margin progradation in the Gulf of Mexico Basin that accompanied prominent tectonic and climatic changes in North America. However, sediment pathways from continental upland sources to deep basinal sinks remain poorly constrained. This study presents 2192 new detrital zircon U-Pb analyses from 19 Lower Miocene samples spanning the entire northern Gulf of Mexico margin to elucidate early Miocene sediment provenance and paleodrainage systems. The U-Pb age patterns indicate that the Great Plains, southern Rocky Mountains, and mid-Cenozoic volcanic field were the major source terranes for the western-central Gulf of Mexico coast, whereas the Appalachian foreland basin and Appalachian Mountains mainly contributed sediment to the eastern Gulf of Mexico coast. Local source terranes included the Llano uplift and Edwards Plateau in central Texas and the Ouachita Mountains and foreland basin in Oklahoma and Arkansas. A comparison to previous detrital zircon studies around the Gulf of Mexico indicates that sediment recycling was important during the early Miocene. Sediment associated with major paleorivers, including the Rio Bravo, Rio Grande, Houston-Brazos, Red, Mississippi, Tombigbee, and Apalachicola Rivers, can be differentiated using the detrital zircon U-Pb analyses. These data help to better define the early Miocene source-to-sink system in the northern Gulf of Mexico, by relating the basin fill to hinterland tectonic and geological evolution. In comparison to the Paleocene−Eocene Wilcox drainage system, the early Miocene drainage system of the northern Gulf of Mexico was smaller and received less input from western Mexico arc terranes and Archean basement in Wyoming. This drainage area reduction, related to regional thermal uplift and Basin and Range−Rio Grande rifting, likely explains the reduced sediment volume of the Lower Miocene strata in the Gulf of Mexico relative to the Paleocene−Eocene Wilcox Group.

Multichannel Seismic Imaging of the Rivera Plate Subduction at the Seismogenic Jalisco Block Area (Western Mexican Margin)

During the TSUJAL marine geophysical survey, conducted in February and March 2014, Spanish, Mexican and British scientists and technicians explored the western margin of Mexico, considered one of the most active seismic zones in America. This work aims to characterize the internal structure of the subduction zone of the Rivera plate beneath the North American plate in the offshore part of the Jalisco Block, to link the geodynamic and the recent tectonic deformation occurring there with the possible generation of tsunamis and earthquakes. For this purpose, it has been carried out acquisition, processing and geological interpretation of a multichannel seismic reflection profile running perpendicular to the margin. Crustal images show an oceanic domain, dominated by subduction–accretion along the lower slope of the margin with a subparallel sediment thickness of up to 1.6 s two-way travel time (approx. 2 km) in the Middle American Trench. Further, from these data the region appears to be prone to giant earthquake production. The top of the oceanic crust (intraplate reflector) is very well imaged. It is almost continuous along the profile with a gentle dip (<10°); however, it is disrupted by normal faulting resulting from the bending of the plate during subduction. The continental crust presents a well-developed accretionary prism consisting of highly deformed sediments with prominent slumping towards the trench that may be the result of past tsunamis. Also, a bottom simulating reflector (BSR) is identified in the first half a second (twtt) of the section. High amplitude reflections at around 7–8 s twtt clearly image a discontinuous Moho, defining a very gentle dipping subduction plane.

The Lower Cretaceous Atzompa Formation In South-Central Mexico: Record of Evolution From Extensional Backarc Basin Margin To Carbonate Platform

Abstract: Lower Cretaceous depositional systems of southwestern Oaxaquia, in south-central Mexico, were influenced by initiation of a continental arc on mainland Mexico and subsequent accretion of the Guerrero composite arc terrane to mainland Mexico. The Atzompa Formation, defined herein, which crops out in the Sierra de Tentzo, constitutes a succession of conglomerate, sandstone, siltstone, and limestone with Early Cretaceous fauna and detrital zircon maximum depositional ages that range 126–123 Ma (late Barremian to early Aptian). The lower part of the Atzompa records a transition from alluvial to deep lacustrine depositional environments, suggesting the early stages of an extensional basin; overlying deposits of anabranching axial fluvial systems that flowed to the NE–SE accumulated after a period of rapid subsidence in the Tentzo basin, also formerly undescribed. Fluvial facies grade up-section to tidal deposits overlain in turn by a carbonate ramp succession that contains late Barremian to early Aptian fossils. The ramp deposits of the uppermost Atzompa Formation are overlain on a sharp contact by basinal carbonates of early Albian age.The Tentzo basin, formed due to crustal extension of the overriding plate in a backarc setting, was characterized by very high rates of sedimentation (3.6 mm/yr) during the early stages of basin formation (rift initiation and rift climax), and slower rates during the development of tidal systems and the carbonate ramp (post-rift stage). Regional and local subsidence took place in the backarc region of the Zicapa magmatic arc, which was established in the western margin of Mexico by Hauterivian time. Abrupt deepening following Atzompa Formation deposition is attributed to flexural subsidence related to collision of the Guerrero composite volcanic terrane with the western margin of Mexico. Following late Aptian accretion of the Guerrero terrane to Oaxaquia, the carbonate basin eventually shallowed to become a carbonate platform that faced the Gulf of Mexico.

The informational life of the poor: A study of digital access in three Mexican towns

This paper seeks to contribute to the debate on the impact of the adoption of information technologies (ICT) in poverty reduction by understanding how the poor obtain, share and use ICT on their everyday life – what we call the informational lives of the poor. It identifies the opportunities and challenges regarding ICT adoption in three rural communities with different levels of marginalization and connectivity in Mexico. Using “before and after” studies we attempt to identify and understand mechanisms through which ICT (and broadband, in particular), may have an impact on poverty alleviation.Using a combination of the Capabilities Approach and Livelihoods Perspective, this research shows that mobile broadband access (as opposed to fixed shared access) and effective training through the role of infomediaries enables low-income communities to develop new skills, to engage in new practices and to find useful applications for old and new abilities, needs and interests. A specific finding that has not received attention in the literature is the productive role of immediate family members as infomediaries; the weight of family networks plays a crucial role in learning about ICTs. These networks fuel a sense of confidence required to handle knowledge and practices that are initially alien in this sector.We found that ICT adoption changes the pattern of information seeking and enhances informational capabilities and existing assets of low-income communities. Through our control case, that did not have any connectivity, we identified the high transaction cost people face as well as the business opportunities the digitally excluded forego.

Gravity and magnetic constraints on the Jurassic opening of the oceanic Gulf of Mexico and the location and tectonic history of the Western Main transform fault along the eastern continental margin of Mexico

Although the Gulf of Mexico (GOM) has been the subject of geophysical and geologic studies for several decades, its crustal structures and opening kinematics remain poorly understood largely because of the difficulty in imaging the deeper basinal structure beneath its thick sedimentary and evaporitic layers. We have used gravity and magnetic data combined with seismic reflection and refraction data to better understand the crustal structure and basin opening kinematics. We have focused on the 700-km-long Jurassic continent/ocean transform fault that accommodated counterclockwise rotation of the Yucatan Block along the eastern continental margin of Mexico. We have used recent satellite-derived gravity data to reveal the pattern of spreading ridge-transform segments in the center of the basin. We then derived on a pole of rotation that revealed the kinematics of early opening of the GOM basin and the tectonic control the continent-ocean transform fault, the Western Main Transform fault (WMTF), that defined the continent-ocean boundary (COB) between continental rocks in the eastern Mexico and Jurassic oceanic crust in the western GOM. Regional magnetic anomaly data along with seismic reflection and refraction data were used to further constrain the location of the WMTF. Three 2D gravity models revealed the location of the WMTF approximately 100 km offshore eastern Mexico at its furthest point and extending onshore in southern Mexico. The gravity models found that the contact between continental and oceanic crust is marked by an abrupt increase from 6.5 to 10 km in crustal thickness. To the west of the WMTF, the eastern Mexico margin is underlain by a 60-km-wide zone of stretched continental crust. We also determined a COB for the entire GOM that was consistent with the plate reconstruction, values of crustal thickness based on seismic refraction, and fracture zone azimuths related to the Jurassic spreading system.

The metallogenic evolution in Mexico during the Mesozoic, and its bearing in the Cordillera of Western North America

The Mesozoic ore and industrial mineral deposits in Mexico can be classified into four supergroups of deposits or ‘realms’: oceanic magmatic, continental magmatic, sedimentary-diagenetic, and orogenic-metamorphic. The oceanic magmatic realm comprises volcanogenic massive sulfide and sulfate deposits (VMS) and mineral deposits in ultramafic–mafic massifs that formed in oceanic arcs, largely between the Upper Jurassic and the early Upper Cretaceous. The continental magmatic realm comprises porphyry-type, non-iron oxide skarns, and magmatic-hydrothermal iron oxide deposits (MHIO) that formed in continental arcs, basically between the late Lower Cretaceous onward into the Cenozoic. Both magmatic realms are dominant along the Pacific margin of Mexico and extended up to several hundreds of km inland. The sedimentary-diagenetic realm comprises Mississippi Valley-type (MVT) and associated deposits, sedimentary-exhalative (SEDEX), red-bed or Kupferschiefer-type, and sedimentary phosphorite deposits that started forming in the basins of eastern Mexico since the latest Middle Jurassic, and formed mostly between the late Lower Cretaceous and the Eocene, although their ages remain largely undetermined. The orogenic-metamorphic realm is known only to comprise orogenic gold deposits, which formed between the Upper Cretaceous and the Eocene in western and southwestern Mexico.Three main metallogenic epochs for the Mesozoic are recognized in Mexico: (I) Triassic to Middle Jurassic, (II) Upper Jurassic to Lower Cretaceous, or Oxfordian to Albian-Cenomanian, and (III) Upper Cretaceous to the Cretaceous-Cenozoic limit, or Albian-Cenomanian to Maastrichtian, which connects with the Cenozoic epochs. The Triassic to Middle Jurassic epoch basically comprises deposits in ultramafic–mafic complexes and VMS deposits in the Vizcaíno terrane. The metallogenic belts or provinces for Upper Jurassic to Lower Cretaceous epoch occur mostly in the Guerrero composite terrane (GCT) and in the Baja California Peninsula. These are: (1) Late Jurassic to earliest Cretaceous province of sedimentary and sedimentary-exhalative deposits in the domain of the Gulf of Mexico, (2) Late Jurassic to earliest Cretaceous province of VMS deposits in the southern GCT, (3) Early Cretaceous province of VMS deposits in the Alisitos arc terrane, (4) Early Cretaceous province of deposits in ultramafic–mafic complexes on the southeastern border of the GCT, (5) Early Cretaceous province of generic MHIO deposits, and other deposits associated with calc-alkaline magmatism in the Peninsular Range batholithic belt (Baja California), along with (6) a few similar deposits in the coastal GCT, and (7) Cretaceous province of deposits in ultramafic–mafic complexes in the northern GCT. The Upper Cretaceous provinces are: (a) orogenic gold belts in NW Sonora and the southern Baja California Peninsula, which possibly constitute different belts, (b) the beginning of the metallogeny associated with the Sierra Madre Occidental silicic large igneous province (SLIP) during the Late Cretaceous to the Paleocene with generic MHIO deposits and deposits associated with calc-alkaline magmatism in Sonora and Chihuahua, (c) a trail of Late Cretaceous non-iron oxide skarn deposits along the northeastern and eastern (?) terrane boundaries of the GCT, (d) Late Cretaceous to Cenozoic province of magmatic-hydrothermal iron oxide deposits in the southern portion of the Pacific coast of Mexico, and (e) Late Cretaceous to Paleocene province of generic MHIO deposits and non-iron oxide skarn deposits in northern Baja California.The above configuration of metallogenic events and provinces occurred in response to drastic changes in the general tectonomagmatic regime: from magmatism associated with Jurassic to Albian synvolcanic extensional unroofing (magmatic oceanic realm for ore deposits) to a contractional continental volcanic arc thereafter (magmatic continental-subaerial realm for ore deposits). The transition from these metallogenic magmatic realms occurred between the mid-Aptian and mid-Cenomanian, and Mexico represents the last region in the Cordillera of western North America in which such transition occurred—it was predated by similar processes in Alaska and Canada between the Lower Jurassic and the Middle-Upper Jurassic, and in the southwestern USA between the Middle-Upper Jurassic and the Lower Cretaceous. Such southward and cratonward (eastward) progression was accompanied by orogenic pulses, which overlap in NE Mexico as thin-skinned Sevier structures were followed by thick-skinned Laramide structures, and were largely controlled by flattening of the subducted slabs. Laramide orogenic pulses played a key role in the formation of orogenic gold deposits, but are also responsible for the mobilization of basinal brines that ultimately led to the formation of MVT and red-bed deposits, although several of such deposits might have formed earlier, and others are post-orogenic.

Deposits associated with ultramafic–mafic complexes in Mexico: the Loma Baya case

Several ultramafic–mafic complexes of assumed ophiolitic affinity that contain ore deposits occur mostly along the Pacific margin of Mexico and the boundaries of the Guerrero composite terrane, which have been described in association with various tectonomagmatic settings. These are (1) roots of volcanic arcs, (2) ophiolites, (3) oceanic basins, (4) continental fragments underlying a magmatic arc, and (5) subduction complexes or rift-transform magmatic suites. However, the petrogenesis of such ultramafic–mafic complexes and the associated ore deposits remains ill defined to date, as their comprehensive study virtually lacks an appropriate geochemical approach. Ultramafic–mafic complexes with known or estimated ages in Mexico are mostly of Paleozoic and Mesozoic ages, and very few of them formed once the crustal dynamics of the Mexican Pacific margin switched from generally extensional to compressional tectonic settings during the Late Cretaceous. A few deposits, aged Late Cretaceous to Paleocene, were interpreted to have formed in association with tectonomagmatic settings different from most deposits in the Guerrero composite terrane. To move forward in the understanding on how these mafic–ultramafic complexes and their associated ore deposits formed, the genesis of the chromitite deposits within the Loma Baya ultramafic–mafic complex (southernmost Guerrero composite terrane) is hereby endeavored. The combination of the geochemical study of both major and trace elements in chromite (including platinum-group elements; PGE), the mineralogy, PGE geochemistry and radiogenic isotopes (i.e., Re–Os) in platinum-group minerals (PGM), provides new assessment on the genesis of this ultramafic–mafic complex. From the obtained results it stems that the Loma Baya complex and the chromitite deposits associated with it are closely related with the formation of a back-arc basin in an active supra-subduction zone during the Lower Cretaceous, and the parental melts resulted from re-melting of an ultramafic protolith of Paleozoic (or older) age. The melts that originated in such back-arc basin were of tholeiitic affinity and produced Al-rich chromitites with a moderate enrichment in PGE, associated with rates of partial melting of a depleted mantle source of at least 20%. Such geological framework is in frank disagreement with previous work, thus highlighting the necessity of further research in other Mexican ultramafic–mafic complexes to better constrain their geodynamic setting of formation. The obtained Re–Os model ages in PGM of the Loma Baya chromitite deposits (ca. 300 and 130Ma) suggest a possible correlation between these deposits and those in the Californias, in the sense that both areas record similar geological processes (mantle rock melting, re-melting, and chromitite emplacement) within similar tectonomagmatic environments and time frame for their occurrence. Such possibility further highlights the necessity to carry on similar studies in chromitite deposits elsewhere along the Pacific margin in Mexico and southwestern USA, in order to better reconstruct its tectonomagmatic evolution during the Mesozoic.

Paleoceanographic insights on recent oxygen minimum zone expansion: lessons for modern oceanography.

Climate-driven Oxygen Minimum Zone (OMZ) expansions in the geologic record provide an opportunity to characterize the spatial and temporal scales of OMZ change. Here we investigate OMZ expansion through the global-scale warming event of the most recent deglaciation (18-11 ka), an event with clear relevance to understanding modern anthropogenic climate change. Deglacial marine sediment records were compiled to quantify the vertical extent, intensity, surface area and volume impingements of hypoxic waters upon continental margins. By integrating sediment records (183-2,309 meters below sea level; mbsl) containing one or more geochemical, sedimentary or microfossil oxygenation proxies integrated with analyses of eustatic sea level rise, we reconstruct the timing, depth and intensity of seafloor hypoxia. The maximum vertical OMZ extent during the deglaciation was variable by region: Subarctic Pacific (~600-2,900 mbsl), California Current (~330-1,500 mbsl), Mexico Margin (~330-830 mbsl), and the Humboldt Current and Equatorial Pacific (~110-3,100 mbsl). The timing of OMZ expansion is regionally coherent but not globally synchronous. Subarctic Pacific and California Current continental margins exhibit tight correlation to the oscillations of Northern Hemisphere deglacial events (Termination IA, Bølling-Allerød, Younger Dryas and Termination IB). Southern regions (Mexico Margin and the Equatorial Pacific and Humboldt Current) exhibit hypoxia expansion prior to Termination IA (~14.7 ka), and no regional oxygenation oscillations. Our analyses provide new evidence for the geographically and vertically extensive expansion of OMZs, and the extreme compression of upper-ocean oxygenated ecosystems during the geologically recent deglaciation.

Tephrochronology and geochemistry of Eocene and Oligocene volcanic ashes of east and central Texas

New single-crystal sanidine 40 Ar/ 39 Ar dates of 12 middle Eocene to Oligocene rhyolitic volcanic ash beds of the Texas coastal plains range from 30.64 ± 0.03 Ma (lower Catahoula Formation) to 41.841 ± 0.016 Ma (lower Crockett Formation). These dates are from Texas coastal plains strata in the Crockett marine transgression and the Yegua and Jackson depositional wedges. Radiometric dating of sanidine and electron microprobe analysis of volcanic apatite phenocrysts validate previous regional correlation of the Upper Alabama Ferry volcanic ash from Brazos County to Houston County, Texas, and provide support for correlation of this bed with the St. Johns bentonite deposit in Louisiana. Middle Eocene ash beds are distinguished by differences in apatite phenocryst composition. The wide distribution of the thick Alabama Ferry volcanic ashes points to an early age (41.841 ± 0.016 Ma) for the start of major explosive rhyolitic volcanism in western North America. Volcanic ash bed samples have subalkaline rhyolite composition with geochemical characteristics consistent with derivation from volcanic arc rocks. Trace-element data show a temporal change in volcanic ashes: Middle Eocene ashes are depleted in heavy rare earth elements compared to late Eocene and Oligocene units. This change in ash composition coincides with the time of transition from subduction compression to arc-rifting on the western margin of Mexico, and compositional data are consistent with the Sierra Madre Occidental being the source for the volcanic ash. Volcanic units of the eastern portion of the Trans-Pecos of Texas and Mogollon-Datil area of New Mexico overlap temporally, but geochemical characteristics and K/Ca ratios in sanidine indicate they are geochemically unlikely to be sources for the Texas coastal plains middle Eocene to Oligocene volcanic ash beds.

Identifying the Confounders of Marginalization and Mortality in Mexico, 2003–2007

Confounders alter any predicted outcome by modifying the relationship between cause and consequence. Confounders can appear in different proportions inside a population and their effect might not be the same for different geographic regions. This paper focuses on establishing the impact of the marginalization index and confounders like migration and percentage of indigenous population on a municipality’s mortality rate. Data come from the 2003–2007 Instituto Nacional de Estadistica y Geografia death records and the 2005 Marginalization Index from the Consejo Nacional de Poblacion. WLS regressions of age-adjusted mortality rates on the index as a whole and on seven of its nine components are calculated to measure the impact of these confounders. Overall, results were mixed for municipalities with a higher level of marginalization. Percentage of indigenous population is the most consistent confounder throughout the analysis. The results show the difficulty of quantifying confounders accurately but open the door for further refinement.

Citizenship from below: Hñähñu heritage in a transnational world

This article illustrates the need to redefine notions of citizenship to take into account the articulations and negotiations of difference (that is, class, ethnicity) through active community participation at the local/community level – below the levels of governance of nation-states (a “citizenship from below”). The research focuses on the indigenous Hnahnu's sense of cultural identity and notions of citizenship, constructed as a response to social and political challenges presented by centuries of conquest and marginalization in Mexico. Once in the United States, these understandings of citizenship are broadened to include their communities of destination in their transnational spaces. This fluidity of borders challenges rigid definitions of citizenship that function below the levels of governance of the nation-state and requires the development of a new migratory geometry that allows for simultaneous membership in both host and home communities.

Wilson Cycles, Tectonic Inheritance, and Rifting of the North American Gulf of Mexico Continental Margin

The tectonic evolution of the North American Gulf of Mexico continental margin is characterized by two Wilson cycles, i.e., repeated episodes of opening and closing of ocean basins along the same structural trend. This evolution includes (1) the Precambrian Grenville orogeny; (2) formation of a rift-transform margin during late Precambrian opening of the Iapetus Ocean; (3) the late Paleozoic Ouachita orogeny during assembly of Pangea; and (4) Mesozoic rifting during opening of the Gulf of Mexico. Unlike the Atlantic margins, where Wilson cycles were first recognized, breakup in the Gulf of Mexico did not initially focus within the orogen, but was instead accommodated within a diffuse region adjacent to the orogen. This variation in location of rifting is a consequence of variations in the prerift architecture of the orogens. The Appalachian-Caledonian orogeny involved substantial crustal shortening and formation of a thick crustal root. In contrast, the Ouachita orogeny resulted in minimal crustal shortening and thickening. In addition, rather than a crustal root, the Ouachita orogen was underlain by the lower plate of a relatively pristine Paleozoic subduction system that is characterized by a shallow mantle. A finite element model simulating extension on the margin demonstrates that this preexisting structure exerted fundamental controls on the style of Mesozoic rifting. The shallow mantle created a strong lithosphere beneath the orogen, causing extension to initiate adjacent to, rather than within, the orogen. On the Atlantic margins, the thick crustal root resulted in a weak lithosphere and initiation of extension within the interior of the orogen. Major features of the modern Gulf of Mexico margin, including the Interior Salt Basin, outboard unextended Wiggins arch, and an unusually broad region of extension beneath the coastal plain and continental shelf, are direct consequences of the prerift structure of the margin.

Petrogenesis and thermobarometry of the ∼50 Ma rapakivi granite-syenite Acapulco intrusive: Implications for post-Laramide magmatism in southern Mexico

The Acapulco intrusion is a composite pluton that belongs to the coastal batholithic belt of southern Mexico, intruding the Xolapa metamorphic complex and cropping out in the neighboring area of Acapulco city. The Acapulco intrusion has been considered as an anomaly based on its age, which contrasts with the surrounding plutons and the general age trend from the coastal batholithic belt and corresponds to an Eocene–Oligocene age. It ranges in composition from granite (sensu stricto) to syenite and diorite. The most distinctive characteristic of the Acapulco intrusion is the rapakivi texture developed in the granites, which are characterized by biotite, amphibole, allanite, and fl uorite as distinctive minerals, plus titanite, zircon, and apatite as accessory phases. Geochemically, the Acapulco intrusion varies from metaluminous to peraluminous, and displays the distinctive signatures of arc-related magmas. The studied rocks show strong negative Sr, Ba, and Eu anomalies, coupled with incompatible element enrichments and high Ga/Al ratios, which are typical characteristics of A-type granites that underwent strong plagioclase fractionation from a formerly metaluminous magma. Initial isotopic ratios ( 87 Sr/ 86 Sr from 0.7035 to 0.7100, and eNd from +5.50 to +1.78) indicate a range from depleted mantle compositions to compositions consistent with crustal contamination by continental crust, particularly from the surrounding Xolapa Complex. U-Pb geochronology in zircons by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) established crystallization ages of 49.40 ± 0.40 Ma, 50.20 ± 1.0 Ma, 50.42 ± 0.39 Ma, and 50.56 ± 0.39 Ma for different lithologies of the Acapulco intrusion. These geochronological data, together with previous published works, confi rm that post-Laramide plutonism between 50 and 60 Ma is widespread in the southern continental margin of Mexico as a major magmatic event. Finally, new thermobarometric determinations established emplacement conditions of ~700 °C at 8–10 km depth (2.08–2.8 kbar), indicating an exhumation rate of ~0.21 km/m.y. between 50 and 20 Ma, which is slower than the previous estimated rate of 0.44 km/m.y. These results call for a review on models suggesting fast and/or slow exhumation of the southern Mexico coastal batholitic belt.

Evolution of the Guerrero composite terrane along the Mexican margin, from extensional fringing arc to contractional continental arc

The western margin of Mexico is ideally suited for testing two opposing models for the growth of continents along convergent margins: accretion of exotic island arcs by the consumption of entire ocean basins versus accretion of fringing terranes produced by protracted extensional processes in the upper plate of a single subduction zone. We present geologic and detrital zircon evidence that the Zihuatanejo terrane of the Guerrero composite terrane originated from the latter mechanism. The evolution of the Zihuatanejo terrane can be explained by extensional and compressional processes operating entirely within the upper plate of a long-lived subduction zone that dipped east under the Mexican margin. This process controlled crustal growth by continental margin rifting and addition of new igneous and volcaniclastic material during extension, followed by accretion and thickening of the crust during contraction. Prior to this study, all Mesozoic rocks in the western part of the Guerrero composite terrane were considered to be part of a single arc. However, we divide it into four distinctive tectonostratigraphic assemblages: (1) a Triassic–Early Jurassic accretionary complex (Arteaga complex); (2) a Jurassic to earliest Cretaceous extensional volcanic arc assemblage; (3) an Early Cretaceous extensional arc assemblage; and (4) a Santonian–Maastrichtian compressional arc assemblage. (1) The Arteaga subduction complex forms the basement to the Zihuatanejo terrane and includes Grenville, Pan-African, and Permian detrital zircon suites that match the Potosi fan of the Mexican mainland. (2) The Jurassic to earliest Cretaceous extensional volcanic arc assemblage shows a Callovian–Tithonian (ca. 163–145 Ma) peak in magmatism; extensional unroofing began in this time frame and continued into through the next. (3) The Early Cretaceous extensional arc assemblage has two magmatic peaks: one in the Barremian-Aptian (ca. 129–123 Ma), and the other in the Albian (ca. 109 Ma). In some localities, rapid subsidence produced thick, mainly shallow-marine volcano-sedimentary sections, while at other localities, extensional unroofing of all older assemblages resulted in recycling of zircon from all older units (1, 2, 3). (4) For the Santonian–Maastrichtian compressional arc assemblage, our new detrital zircon dates show for the first time that arc volcanic rocks of this age are present in the coastal Zihuatanejo terrane. The contractional arc developed atop assemblages 1–3, which were shortened between Turonian and Santonian time (ca. 93 and 84 Ma). Taken together, the western Zihuatanejo terrane records a more protracted history of arc magmatism than has yet been dated in other terranes of western Mexico, but it closely matches the history of Baja California to the northwest

Paleoseismic Sand Blows in North Louisiana and South Arkansas

Aerial photography from the 1940s through 1950s of the Wisconsinan and Holocene portion of the lower Mississippi alluvial valley from 32°N to 34.6°N identifies three previously unrecognized areas that have circular to elliptical tonal anomalies similar in size, shape, and spacing to the aerial photography signature of sand blows previously documented in this region by trenching. Coring, ground conductivity surveying, trenching, sedimentological/soil analysis, and age analysis by 14C and luminescence techniques demonstrate that these three areas are fields of seismically induced sand blows of late Holocene age. The sand blows have a “popcorn” pattern indicative of hydraulic fracturing of surficial clay and a local seismic source. We found evidence for one sand-blow episode in Richland Parish, Louisiana, between 300 and 5,900 yr B.P., for two episodes in Morehouse Parish, Louisiana, that both occurred between 650 and 3900 yr B.P., and for two in Bradley County, Arkansas circa 1400 to 1760 yr B.P. and circa 1050 to 1400 yr B.P. The older buried blow in Morehouse Parish has a large vent several meters wide, which we attribute to lateral spreading rather than hydraulic fracturing, perhaps triggered by a large earthquake. Thus at least three (probably more) paleoearthquakes between 700 and 8,000 years ago caused the sand blows in south Arkansas and north Louisiana, but more data is needed to establish a clear chronology. Based on spatial and temporal relationships, we speculate that the paleoearthquakes that triggered these sand venting episodes accompanied reactivation of the Triassic Saline River fault zone or related faults of the rifted Gulf of Mexico margin.

Carbon, nitrogen, oxygen and sulfide budgets in the Black Sea: A biogeochemical model of the whole water column coupling the oxic and anoxic parts

Carbon, nitrogen, oxygen and sulfide budgets are derived for the Black Sea water column from a coupled physical–biogeochemical model. The model is applied in the deep part of the sea and simulates processes over the whole water column including the anoxic layer that extends from ≃ 115 m to the bottom ( ≃ 2000 m). The biogeochemical model involves a refined representation of the Black Sea foodweb from bacteria to gelatinous carnivores. It includes notably a series of biogeochemical processes typical for oxygen deficient conditions with, for instance, bacterial respiration using different types of oxidants (i.e denitrification, sulfate reduction), the lower efficiency of detritus degradation, the ANAMMOX (ANaerobic AMMonium OXidation) process and the occurrence of particular redox reactions. The model has been calibrated and validated against all available data gathered in the Black Sea TU Ocean Base and this exercise is described in Gregoire et al. (2008). In the present paper, we focus on the biogeochemical flows produced by the model and we compare model estimations with the measurements performed during the R.V. KNORR expedition conducted in the Black Sea from April to July 1988 ( Murray and the Black Sea Knorr Expedition, 1991). Model estimations of hydrogen sulfide oxidation, metal sulfide precipitation, hydrogen sulfide formation in the sediments and water column, export flux to the anoxic layer and to the sediments, denitrification, primary and bacterial production are in the range of field observations. With a simulated Gross Primary Production (GPP) of 7.9 mol C m −2 year −1 and a Community Respiration (CR) of 6.3 mol C m −2 year −1, the system is net autotrophic with a Net Community Production (NCP) of 1.6 mol C m −2 year −1. This NCP corresponds to 20% of the GPP and is exported to the anoxic layer. In order to model Particulate Organic Matter (POM) fluxes to the bottom and hydrogen sulfide profiles in agreement with in situ observations, we have to consider that the degradation of POM in anoxic conditions is less efficient that in oxygenated waters as it has often been observed (see discussion in Hedges et al., 1999). The vertical POM profile produced by the model can be fitted to the classic power function describing the oceanic carbon rate ( C R = Z − α ) using an attenuation coefficient α of 0.36 which is the value proposed for another anoxic environment (i.e. the Mexico Margin) by Devol and Hartnett (2001). Due to the lower efficiency of detritus degradation in anoxic conditions and to the aggregation of particles that enhanced the sinking, an important part of the export to the anoxic layer (i.e. 33%, 0.52 mol C m −2 year −1) escapes remineralization in the water column and reaches the sediments. Therefore, sediments are active sites of sulfide production contributing to 26% of the total sulfide production. In the upper layer, the oxygen dynamics is mainly governed by photosynthesis and respiration processes as well as by air–sea exchanges. ≃ 71% of the oxygen produced by phytoplankton (photosynthesis+nitrate reduction) is lost through respiration, ≃ 21% by outgasing to the atmosphere, ≃ 5% through nitrification and only ≃ 2% in the oxidation of reduced components (e.g. Mn 2+, Fe 2+, H 2S). The model estimates the amount of nitrogen lost through denitrification at 307 mmol N m −2 year −1 that can be partitioned into a loss of ≃ 55% through the use of nitrate for the oxidation of detritus in low oxygen conditions, ≃ 40% in the ANAMMOX process and the remaining ≃ 5% in the oxidation of reduced substances by nitrate. In agreement with data analysis performed on long time series collected since the 1960s ( Konovalov and Murray, 2001), the sulfide and nitrogen budgets established for the anoxic layer are not balanced in response to the enhanced particle fluxes induced by eutrophication: the NH 4 and H 2S concentrations increase.

Culturable prokaryotic diversity of deep, gas hydrate sediments: first use of a continuous high‐pressure, anaerobic, enrichment and isolation system for subseafloor sediments (DeepIsoBUG)

Deep subseafloor sediments may contain depressurization-sensitive, anaerobic, piezophilic prokaryotes. To test this we developed the DeepIsoBUG system, which when coupled with the HYACINTH pressure-retaining drilling and core storage system and the PRESS core cutting and processing system, enables deep sediments to be handled without depressurization (up to 25 MPa) and anaerobic prokaryotic enrichments and isolation to be conducted up to 100 MPa. Here, we describe the system and its first use with subsurface gas hydrate sediments from the Indian Continental Shelf, Cascadia Margin and Gulf of Mexico. Generally, highest cell concentrations in enrichments occurred close to in situ pressures (14 MPa) in a variety of media, although growth continued up to at least 80 MPa. Predominant sequences in enrichments were Carnobacterium, Clostridium, Marinilactibacillus and Pseudomonas, plus Acetobacterium and Bacteroidetes in Indian samples, largely independent of media and pressures. Related 16S rRNA gene sequences for all of these Bacteria have been detected in deep, subsurface environments, although isolated strains were piezotolerant, being able to grow at atmospheric pressure. Only the Clostridium and Acetobacterium were obligate anaerobes. No Archaea were enriched. It may be that these sediment samples were not deep enough (total depth 1126–1527 m) to obtain obligate piezophiles.