Characterization of distal turbidites in marine sedimentary sequences using magnetic mineral data and factor analysis of microfossils assemblages

Results of a study of turbiditic deposits in a sequence of middle to late Holocene marine sediments from Alfonso Basin in the southern Gulf of California are presented. Turbidites are identified from analyses of core sections, X-ray images, texture and granulometry. Characterization of distal turbidites could be difficult, particularly for thin fine-grained deposits with little contrast in grain size, mineralogy and texture. We have here included analyses of microfossil and magnetic mineral data. Turbiditic currents transport material from various depths in the continental slope into the basin and it can be expected that turbiditic deposits are characterized by re-worked material, lack of microfossils or mixed assemblages with no content of paleoceanographic and paleoclimatic record. This may show in lack of internal coherence as quantified by factor analysis of microfossil assemblages. Turbidites in some cases may also show distinct magnetic properties as compared with those in the sediment sequence. In Alfonso Basin, turbidites show increased contents of detrital magnetic minerals volcanic-derived and transported from the basin slope. We identify twelve turbiditic layers through the sequence that present high magnetic susceptibility and low communalities from factor model to the microfossils data providing characterization of the turbidites.     

Insights from experimental economics on local cooperation in a small-scale fishery management system

Cooperation is central to collective management of small-scale fisheries management, including marine protected areas. Thus an understanding of the factors influencing stakeholders’ propensity to cooperate to achieve shared benefits is essential to accomplishing successful collective fisheries management. In this paper we study stakeholders’ cooperative behavioral disposition and elucidate the role of various socio-economic factors in influencing it in the Roviana Lagoon, Western Solomon Islands. We employed a Public Goods Game from experimental economics tailored to mimic the problem of common pool fisheries management to elucidate peoples’ cooperative behavior. Using Ostrom's framework for analyzing social-ecological systems to guide our analysis, we examined how individual-scale variables (e.g., age, education, family size, ethnicity, occupational status, personal norms), in the context of village-scale variables (e.g., village, governance institutions, group coercive action), influence cooperative behavior, as indexed by game contribution. Ostrom's framework provides an effective window for conceptually peeling back the various socio-economic and governance layers which influence cooperation within these communities. The results of our research show that the most important resource user characteristics influencing cooperative behavior were age, occupation and beliefs about giving access to others to fish for commercial gain. Through elucidating the factors affecting stakeholders’ propensity to cooperate to achieve shared benefits, our analysis provides guidance in understanding cooperation in relation to collective management of marine resources.     

Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism

The IODP‐ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well‐preserved peak ring. The borehole penetrated a sequence of post‐impact carbonates and a unit of suevites and clast‐poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre‐impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long‐distance transport of weakened material during collapse of the transient cavity and final crater formation.     

Reconstruction of a complex late Quaternary glacial landscape in the Cordillera de Cochabamba (Bolivia) based on a morphostratigraphic and multiple dating approach

Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations in the Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results from detailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulated luminescence (OSL), and radiocarbon dating (¹⁴C) from the Huara Loma Valley, Cordillera de Cochabamba (Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solid geomorphic framework. We identified two major glaciations. The older is not well constrained by the available data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regarding the latter, a first advance dated to ~ 29-25 ka occurred roughly contemporaneous with the onset of the global last glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20-18 ka. The local last glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~ 17-16 ka, followed by several smaller readvances until ~ 10-11 ka, and complete deglaciation at the end of the Early Holocene.     

Fluid inclusion study of the Plomositas–Los Arcos polymetallic epithermal vein tract, Plomosas district, Sinaloa, Mexico

The most important deposit in the Plomosas–Rosario district, Sinaloa, is the vein tract named Plomositas–Plomosas–Los Arcos. These are NNW–SSE striking veins hosted in rocks of the Lower Volcanic Supergroup (LVS), and also in rocks at the bottom of the Upper Volcanic Supergroup (UVS). Both supergroups belong to the Sierra Madre Occidental. These veins evolved from an early intermediate sulfidation stage (1), rich in base metal sulfides, to a low sulfidation stage (2), rich in silver sulfides and sulfosalts. There is also a 45 m-wide stockwork with native silver and gold. Stage 1 is found in the deeper portion of the veins whereas stage 2 is found in the most shallow portion of the deposit. These stages record fluid inclusion salinities ranging from 7 to 12 wt.% NaCl equiv., and from 0.2 to 3.5 wt.% NaCl equiv., respectively. Homogenization temperatures range from 120 °C for surface samples to 200 °C at a depth of 320 m. The low homogenization temperatures recorded, and the dispersion of veins within host rocks as veinlets, suggest that this deposit formed at shallow depths and was probably blind.     

Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact

Discovery of the Chicxulub multi-ring impact crater came as a result of oil exploration surveys in the southern Gulf of Mexico. Subsequent studies on the Chicxulub impact and the Cretaceous/Palaeogene (K/Pg) boundary have revealed links between the impact and hydrocarbons, with implications for the K/Pg global environmental and climatic effects, as well as for oil exploration in the Gulf.     

Magnetic properties of lake sediments from Lake Chalco,central Mexico,and their palaeoenvironmental implications

Lake Chalco (99.0°W, 19.5°N) in the Basin of Mexico, was formed during the Pleistocene after the emplacement of the Chichinautzin volcanic field that closed the former drainage system. The lake sediment record has been influenced by a number of factors, including glacial–interglacial cycles, local volcanism, erosion of soils and anthropogenic disturbances. The magnetic properties of the lake sediments and the associated tephra layers of the last 16500 yr have been studied. It is found that the magnetic properties of the Lake Chalco sediments are very distinctive. Magnetic concentration varies by a factor of 1000 and magnetic stability also varies over an extremely wide range. The predominant magnetic mineral is titanomagnetite in addition to an imperfect antiferromagnetic phase, possibly goethite. An unusually large range of coercivities is found in certain of the tephras. Down‐core variations in magnetic properties closely follow climatic/environmental changes previously established by other proxy methods. The late Pleistocene and late Holocene lake sediments display a higher concentration of magnetic minerals than the early–middle Holocene sediments. In the non‐volcanic sediments, fluctuations in the magnetic concentration reflect changes in both the intensity of erosion, as represented by ferrimagnetic and paramagnetic minerals, and by the maturing of soils, as represented by geothite. Copyright © 2000 John Wiley & Sons, Ltd.     

Episodic wood loading in a mountainous neotropical watershed

The Upper Rio Chagres drains 414 km² of steep, mountainous terrain in central Panama. A tropical air mass thunderstorm on 10 July 2007 produced a flood across the basin that peaked at 720 m³ s^− 1 at a headwaters gage draining 17.5 km² and 1710 m³ s^− 1 at a downstream gage draining 414 km². The storm also triggered numerous landslides in the upper basin, which facilitated the formation of large logjams along portions of the channel where transport capacity of wood was reduced by a change in channel geometry such as a bend or channel expansion. During field work in February 2008, we characterized three jams with surface areas of 400–2450 m²; two of these jams resulted in storage of substantial (1100–8200 m³) sediment wedges upstream. We returned to these sites in March 2009 to document changes in the logjams and sediment storage. Drawing on observations made in the basin since 2002, and site visits during 2008 and 2009, we suggest that jams such as these last two years or less. We propose that wood dynamics in the Upper Chagres alternate between brief periods of moderate wood load in the form of large logjams and much longer periods of essentially no wood load, a situation that contrasts with the more consistent wood loads in catchments of similar size in temperate environments and with limited studies of more consistent wood load in tropical catchments with no landslides.     

Middle Eocene deformation–sedimentation in the Luracatao Valley: Tracking the beginning of the foreland basin of northwestern Argentina

The Andean foreland basin overlaps the Cretaceous-Paleogene Salta rift basin in northwestern Argentina. Knowledge of the relationship between rift and foreland basins is key to understanding the initial stages of foreland basin development related to Andean shortening. We present a new stratigraphic scheme for the Luracatao Valley, revealing that the Quebrada de los Colorados Formation (Payogastilla Group) lies over the Santa Bárbara Subgroup (Salta Group) through an erosional unconformity that turns into an angular unconformity close to folds and faults recorded in the Santa Bárbara Subgroup. The base of the Quebrada de los Colorados Formation shows growth strata along the west frontal limb of an anticline with Santa Bárbara units in its core. The finding of a mammalian fossil at the base of the Quebrada de los Colorados Formation allows us to assign a Middle-Upper Eocene age to the sedimentation; therefore, the time elapsed between the deposition of the final postrift strata and the beginning of Andean sedimentation was brief and constrained to the Lower-Middle Eocene. This data indicates that the Eocene deformation phase described in other portions of the Puna-Cordillera Oriental transition (e.g., the northern Calchaquí Valley and Aguilar range) is also present in the Luracatao Valley, offering new tools for interpreting the ages and distributions of the initial episodes of sedimentation and deformation related to the Andean shortening. Thus, the Luracatao Valley provides new evidence for tracking the distribution of the Paleogene deformation in northwestern Argentina.