Criação de zonas de alta permeabilidade em fraturas: modelagem numérica do Lajedo de Soledade, Formação Jandaíra, Bacia Potiguar

The fracturing in carbonate rocks has been attracting increasingly attention due to new oil discoveries in carbonate reservoirs. This study investigates how the fractures (faults and joints) behave when subjected to different stress fields and how their behavior may be associated with the generation of karst and consequently to increased secondary porosity in these rocks. In this study I used satellite imagery and unmanned aerial vehicle UAV images and field data to identify and map faults and joints in a carbonate outcrop, which I consider a good analogue of carbonate reservoir. The outcrop comprises rocks of the Jandaíra Formation, Potiguar Basin. Field data were modeled using the TECTOS software, which uses finite element analysis for 2D fracture modeling. I identified three sets of fractures were identified: NS, EW and NW-SE. They correspond to faults that reactivate joint sets. The Ratio of Failure by Stress (RFS) represents stress concentration and how close the rock is to failure and reach the Mohr-Coulomb envelopment. The results indicate that the tectonic stresses are concentrated in preferred structural zones, which are ideal places for carbonate dissolution. Dissolution was observed along sedimentary bedding and fractures throughout the outcrop. However, I observed that the highest values of RFS occur in fracture intersections and terminations. These are site of karst concentration. I finally suggest that there is a relationship between stress concentration and location of karst dissolution in carbonate rocks.

Criação de zonas de alta permeabilidade em fraturas: modelagem numérica do Lajedo de Soledade, Formação Jandaíra, Bacia Potiguar

The fracturing in carbonate rocks has been attracting increasingly attention due to new oil discoveries in carbonate reservoirs. This study investigates how the fractures (faults and joints) behave when subjected to different stress fields and how their behavior may be associated with the generation of karst and consequently to increased secondary porosity in these rocks. In this study I used satellite imagery and unmanned aerial vehicle UAV images and field data to identify and map faults and joints in a carbonate outcrop, which I consider a good analogue of carbonate reservoir. The outcrop comprises rocks of the Jandaíra Formation, Potiguar Basin. Field data were modeled using the TECTOS software, which uses finite element analysis for 2D fracture modeling. I identified three sets of fractures were identified: NS, EW and NW-SE. They correspond to faults that reactivate joint sets. The Ratio of Failure by Stress (RFS) represents stress concentration and how close the rock is to failure and reach the Mohr-Coulomb envelopment. The results indicate that the tectonic stresses are concentrated in preferred structural zones, which are ideal places for carbonate dissolution. Dissolution was observed along sedimentary bedding and fractures throughout the outcrop. However, I observed that the highest values of RFS occur in fracture intersections and terminations. These are site of karst concentration. I finally suggest that there is a relationship between stress concentration and location of karst dissolution in carbonate rocks.

Grain size distribution of the lagoonal deposits within the South Malé Atoll, Maldives, Indian Ocean

Seismic and multibeam data, as well as sediment samples were acquired in the South Malé Atoll in the Maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits. Multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15-20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea-level lowstand. Such depocenters are located in current-protected areas flanking the reef rim of the atoll or in infillings of karst dolinas. Much of the 50 m deep sea floor in the lagoon interior is current swept, and has no or very minor sediment cover. Erosive current moats line drowned patch reefs, whereas other areas are characterized by nondeposition. Karst sink holes, blue holes and karst valleys occur throughout the lagoon, from its rim to its center. Lagoonal sediments are mostly carbonate rubble and coarse-grained carbonate sands with frequent large benthic foraminifers, Halimeda flakes, red algal nodules, mollusks, bioclasts, and intraclasts, some of them glauconitic, as well as very minor ooids. Finer-grained deposits locally are deposited in current-protected areas behind elongated faros, i.e., small atolls which are part of the rim of South Malé Atoll. The South Malé Atoll is a current-flushed atoll, where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim. With an elevated reef rim and tower-like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record.

Upper-Pleistocene terrace deposits in Mediterranean climate: geomorphological and source-rock control on mineral and geochemical signatures (Betic Cordillera, SE Spain)

Mineral and chemical composition of alluvial Upper-Pleistocene deposits from the Alto Guadalquivir Basin (SE Spain) were studied as a tool to identify sedimentary and geomorphological processes controlling its formation. Sediments located upstream, in the north-eastern sector of the basin, are rich in dolomite, illite, MgO and KB2BO. Downstream, sediments at the sequence base are enriched in calcite, smectite and CaO, whereas the upper sediments have similar features to those from upstream. Elevated rare-earth elements (REE) values can be related to low carbonate content in the sediments and the increase of silicate material produced and concentrated during soil formation processes in the neighbouring source areas. Two mineralogical and geochemical signatures related to different sediment source areas were identified. Basal levels were deposited during a predominantly erosive initial stage, and are mainly composed of calcite and smectite materials enriched in REE coming from Neogene marls and limestones. Then the deposition of the upper levels of the alluvial sequences, made of dolomite and illitic materials depleted in REE coming from the surrounding Sierra de Cazorla area took place during a less erosive later stage of the fluvial system. Such modification was responsible of the change in the mineralogical and geochemical composition of the alluvial sediments.

Incisión fluvial del río Darro durante el periodo 1890-2010 en el sector urbano de Granada (Alambra-Valparaíso, España) determinada a partir de fotografías históricas

En este trabajo se calcula la tasa media de incisión fluvial del río Darro (Granada, España) durante el periodo 1890-2010 en su tramo urbano (sector Alhambra-Valparaíso). Para ello se han utilizado fotografías históricas en las que aparece dicho río, a partir de las cuales se ha podido determinar la posición del cauce en el momento en el que se realizaron las fotografías. La comparación con los escenarios actuales de tales imágenes ha permitido determinar la diferencia de altura del cauce a través de medidas de cotas absolutas realizadas mediante teodolito. Esta metodología ha permitido estimar de modo cuantitativo un índice de encajamiento vertical medio del río de 1,05 cm/año para el periodo histórico considerado.

The Neolithic of El Niño cave (Ayna, Albacete) in the Sierra del Segura context

Since its excavation in the summer of 1973, El Niño cave has been considered a key site to understand the process of production economy and pottery technology introduction in South-eastern Iberian Peninsula, and especially to approach how such process could have affected people already settled in the Segura mountains. However, data from El Niño cave was very fragmentary, due to the lack of a broad study of Neolithic occupations of the site. In this paper, we present the analysis of pottery, lithic industry and faunal remains, as well as the existing dates from the site´s Holocene levels. The review of different evidence from the site allows suggesting that El Niño cave would have probably acted as a hunting and shepherding station, being a logistical site of larger places. However, limitations due to the fact that we are dealing with a 40- year-old excavation, prevent specifying how the process of Neolithic introduction in the Segura Mountains occurred.

Tropical limestone forest resilience and late Pleistocene foraging during MIS-2 in the Tràng An massif, Vietnam

In this paper we present a multi-proxy study of tropical limestone forest and its utilization by human groups during the major climatic and environmental upheavals of MIS-2 (29-11.7 kBP). Our data are drawn from new field research within the Tràng An World Heritage property on the edge of the Red River Delta, northern Vietnam. Key findings from this study include 1) that limestone forest formations were resilient to the large-scale landscape transformation of the Sunda continent at the end of the last glaciation; 2) that prehistoric human groups were probably present in this habitat through-out MIS-2; and 3) that the forested, insular, karst of Tràng An provided foragers with a stable resource-base in a wider changing landscape. These results have implications for our understanding of the prehistoric utilization of karst environments, and resonance for their conservation in the face of climate and environmental change today.

Contribuição para a valorização, geoconservação e gestão da jazida fossilífera de Cacela (Parque Natural da Ria Formosa, Algarve, Portugal)

Dissertação de mest. em Gestão e Conservação da Natureza, Faculdade de Ciências do Mar e do Ambiente, Univ. do Algarve, 2004

The Amplifier - v. 13, no. 1

In this issue...Homecoming, Intramural Football, Cheerleaders, Poetry, Yellowstone Park, Snowflake-Springs, Karst Ranch, Butte Symphony, Surveying

Hydrogeophysical Characterization of Anisotropy in the Biscayne Aquifer Using Geophysical Methods

The anisotropy of the Biscayne Aquifer which serves as the source of potable water for Miami-Dade County was investigated by applying geophysical methods. Electrical resistivity imaging, self potential and ground penetration radar techniques were employed in both regional and site specific studies. In the regional study, electrical anisotropy and resistivity variation with depth were investigated with azimuthal square array measurements at 13 sites. The observed coefficient of electrical anisotropy ranged from 1.01 to 1.36. The general direction of measured anisotropy is uniform for most sites and trends W-E or SE-NW irrespective of depth. Measured electrical properties were used to estimate anisotropic component of the secondary porosity and hydraulic anisotropy which ranged from 1 to 11% and 1.18 to 2.83 respectively. 1-D sounding analysis was used to models the variation of formation resistivity with depth. Resistivities decreased from NW (close to the margins of the everglades) to SE on the shores of Biscayne Bay. Porosity calculated from Archie's law, ranged from 18 to 61% with higher values found along the ridge. Higher anisotropy, porosities and hydraulic conductivities were on the Atlantic Coastal Ridge and lower values at low lying areas west of the ridge. The cause of higher anisotropy and porosity is attributed to higher dissolution rates of the oolitic facies of the Miami Formation composing the ridge. The direction of minimum resistivity from this study is similar to the predevelopment groundwater flow direction indicated in published modeling studies. Detailed investigations were carried out to evaluate higher anisotropy at West Perrine Park located on the ridge and Snapper Creek Municipal well field where the anisotropy trend changes with depth. The higher anisotropy is attributed to the presence of solution cavities oriented in the E-SE direction on the ridge. Similarly, the change in hydraulic anisotropy at the well field might be related to solution cavities, the surface canal and groundwater extraction wells.

The taxonomy, zoogeography and ecology of amphibians and reptiles of Hin Nam No National Protected Area (Laos) in comparison with data from Phong Nha – Ke Bang National Park (Vietnam).

In this thesis the mostly unknown herpetofauna in Hin Nam No National Protected Area Laos in the northern Truong Son Range was for the first time intensively investigated, and its diversity was compared to the bordering, and well-investigated Phong Nha - Ke Bang National Park in Vietnam. Twelve new vertebrate species were described comprising 11 geckonids (Cyrtodactylus bansocensis, C. calamei, C. hinnamnoensis, C. jaegeri, C. rufford, C. sommerladi, C. soudthichaki, Gekko boehmei, G. bonkowskii, G. sengchanthavongi, G. thakhekensis, Lycodon banksi and one colubrid snake (Lycodon banksi). Seven species were discovered for the first time in Laos including three frogs (Gracixalus quyeti, G. supercornutus, Rhacophorus maximus), two geckos (Cyrtodactylus cryptus, C. pseudoquadrivirgatus) and two snakes (Lycodon futsingensis, L. ruhstrati abditus). The main hypothesis that the Truong Son Range acted as a biogeographic barrier for the distribution of amphibians and reptiles could be confirmed at least for karst adapted gekkonids. Compared to other herpetofaunal groups the number of gekkonids in karst formations was particularly high (seven bent-toed geckos, four true geckos). By comparing the relative amounts of shared species in Hin Nam No and Phong Nha - Ke Bang, it is interesting to note that fewer reptile species (38%) than amphibian species (66%) were shared between both regions. This might indicate that the Truong Son Range acts as a stronger biogeographical barrier for reptiles than for amphibians. Two pairs of karst-adapted cryptic gecko species (i.e. species with distinct genetic differences, but a similar phenotype) occurred on both sides of the Truong Son Range. Only in one case these were sibling species (Crytodactylus sommerladi in Laos versus C. roesleri in Vietnam), but not in the other (C. hinnamnoensis in Laos versus C. phongnhakebangensis in Vietnam). On the Laotian side, nine gecko species (Cyrtodactylus bansocensis, C. calamei, C. darevskii, C. hinnamnoensis, C. khammouanensis, C. multiporus, C. sommerladi, G. boehmei, G. sengchanthavongi) currently have to be regarded as endemic to the Hin Nam No region. On the Vietnamese side, seven species including two bent-toed geckos (Cyrtodactylus phongnhakebangensis and C. roesleri), three skinks (Lygosoma boehmei, Sphenomorphus tetradactylus and Tropidophorus noggei), and two snakes (Hebius andreae and Boiga bourreti) are currently only known from Phong Nha - Ke Bang and adjacent regions. These high numbers of potential endemic species together with the cryptic species complex in Cyrtodactylus provide strong evidence that the karst formations in the northern Truong Son Range represent a hot spot of reptile diversity and of speciation in Crytodactylus in particular. Correct species identification is a fundamental requirement for conservation measures. The discovery of cryptic species complexes poses a challenge for alpha taxonomy and species conservation, because the true distribution ranges of the species are in fact much smaller than previously assumed. Species conservation in this area of Laos is facing a number of further problems. New and potentially endemic species were discovered in highly populated and disturbed areas. Conversion of the Ho Chi Minh Trail into a highway provided easy access for farmers and still continues to accelerate the destruction of remote forest areas. Southern Hin Nam No with its high diversity of endemic species was identified as the first priority area for conservation. Also Ban Soc, an area isolated from Hin Nam No, should be among the conservation priorities because this region houses a so far overlooked population of the critically endangered Siamese crocodile. Efforts to establish a legal conservation status for this habitat are in progress.

Seasonal dynamics and operational monitoring of hedgerow olive tree transpiration in response to applied water

We used 2012 sap flow measurements to assess the seasonal dynamics of daily plant transpiration (ETc) in a high-density olive orchard (Olea europaea L. cv. ‘Arbequina’) with a well-watered (HI) control treatment A to supply 100 % of the crop water needs, and a moderately (MI) watered treatment B that replaced 70% of crop needs. To assure that treatment A was well-watered, we compared field daily ETc values against ETc obtained with the Penman-Monteith (PM) combination equation incorporating the Orgaz et al. (2007) bulk daily canopy conductance (gc) model, validated for our non-limiting conditions. We then tested the hypothesis of indirectly monitoring olive ETc from readily available vegetation index (VI) and ground-based plant water stress indicator. In the process we used the FAO56 dual crop coefficient (Kc) approach. For the HI olive trees we defined Kcb as the basal transpiration coefficient, and we related Kcb to remotely sensed Soil Adjusted Vegetation Index (SAVI) through a Kcb-SAVI functional relationship. For the MI treatment, we defined the actual transpiration ETc as the product of Kcb and the stress reduction coefficient Ks obtained as the ratio of actual to crop ETc, and we correlated Ks with MI midday stem water potential (ψst) values through a Ks-ψ functional relationship. Operational monitoring of ETc was then implemented with the ETc = Kcb(SAVI)Ks(ψ)ETo relationship stemmed from the FAO56 approach and validated taking as inputs collected SAVI and ψst data reporting to year 2011. Low validation error (6%) and high goodness-of-fit of prediction were observed (R2 = 0.94, RSME = 0.2 mm day-1, P = 0.0015), allowing to consider that under field conditions it is possible to predict ETc values for our hedgerow olive orchards if SAVI and water potential (ψst) values are known.