玻利维亚Chaco盆地油气地质特征及勘探方向

玻利维亚Chaco盆地是安第斯山前陆盆地之一,盆地发现以天然气为主。结合该盆地的勘探历史与勘探现状,对相关钻井、地震及地化等资料进行综合分析,评价了该盆地的石油地质条件及其勘探潜力。Chaco盆地发育泥盆系Los Monos组与志留系Kirusillas组2套主力烃源岩,并分别于石炭纪与三叠纪开始成熟生烃,新近纪进入生气高峰期。2套主力烃源岩生成的天然气分别向下注入下伏储层Huamampamba组与Santa Rosa组,仅少部分向上注入其他储层聚集成藏。盆地内圈闭以逆冲背斜、背斜、断背斜为主。Chaco盆地西部褶皱冲断带(Subandean带)西部与山前带(Foothill带)为该盆地的2个重要勘探潜力区域。

Morphological Diversity of Populations of the Genus <i>Prosopis</i>in the Semiarid Chaco of Northern Cordoba and Southern Santiago Del Estero

The objective of this study consisted in the characterization of morphological variability presented in the Prosopis population in the corridor that unites the semiarid with the arid region in Argentina. In this region, four species of Prosopis get in contact (P. chilensis, P. flexuosa, P. alba and P. nigra). Due to the fact that these species make fertile hybrids, this corridor has an enormous diversity. The mother’s allowed the differentiation of five morphologic groups, which from the point of view of classic taxonomy have been classified in 16 taxa. Only groups 3 and 4 presented intermediate characteristics. The morphologic study of the descendants showed that the regrouping of the intermediate groups had a high error rate. This fact reaffirms the condition of intermediate groups. The canonical correlation analysis between the morphologic variables of the mothers and the seedlings revealed that each morphologic group had its own association of canonical variables between mothers and their seedlings, and that the variability observed in the set of the mothers and their seedlings follows a certain order. The enormous existing morphologic diversity in the Prosopis populations of the semi-arid Chaco of the north of Córdoba and southeast of Santiago del Estero was ordered in five morphologic groups. The descendant’s morphologic studies confirmed the existence of the defined morphologic-genetic groups.

南美玻利维亚重点盆地油气地质特征和勘探潜力评价

基于对玻利维亚区域构造演化与沉积充填特征的分析,研究盆地烃源岩、储集层及盖层等油气成藏地质条件的差异,分析盆地勘探潜力。玻利维亚境内发育查科、贝尼和马德雷德迪奥斯等3个重点盆地,均是在前寒武系基底基础上发育起来的叠合盆地,盆内依次充填了古生代克拉通边缘海相沉积层序、三叠纪-白垩纪裂谷期海相-海陆过渡沉积层序和晚白垩世至今前陆陆相沉积层序。油气成藏地质条件综合对比分析认为,3个盆地均发育泥盆系主力烃源岩,储集层以泥盆系-石炭系和白垩系砂岩为主,发育古生界泥岩和碳酸盐岩及古近系泥岩等多套区域盖层。成熟烃源岩主要分布在冲断带和前渊区,油气必须通过垂向和侧向运移才能聚集成藏,具有晚期生烃、晚期成藏的特点。马德雷德迪奥斯盆地前渊-斜坡带低幅构造圈闭和地层圈闭、查科盆地和贝尼盆地逆冲褶皱带构造圈闭是主要的勘探目标。

Symbolism of the Shadows in Son of Man by Roa Bastos

In his novel Son of Man, Augusto Roa Bastos uses images and symbols of shadows to represent the ramifications ofthe Paraguayan Dr. Jose Rodriguez de Francia＇s dictatorship. Rodriguez de Francia＇s legacy, which begins duringthe postcolonial years and extends well into the 20th century, resonates in the novel in soeio-political structures andcharacters＇ ideologies and behaviors. It allows for plantation owners to enslave workers and their families; itconfines and oppresses people through unfounded legends and myths; and among other things, it creates a falseidea of purpose and patriotism in the Chaco War （1932-1935）, which in the end lets down the soldiers. Tocounteract these deleterious social conditions, Roa Bastos creates surreal characters, such as a fantastic helper whoaids plantation workers to escape dehumanizing situations. Roa Bastos also narrates how the people in Itapr, asmall town, make an idol of a Christ statue carved by one of their own. However, when the two Goiburfl brothersreplace the statue by crucifying their sister＇s rapist, the people＇s myth is destroyed. Likewise, Roa Bastos availshimself of Christian and Catholic concepts and symbols to transpose them into a humanistic ideology so as toconvey hope to his people through a new perspective. In this way, a new Annunciation takes place when the son ofa raped woman is born. In the end, Roa Bastos lets the course of these warped transpositions take their logicaldenouement： In the absence of a purpose beyond an earthly existence, death becomes the narrator＇s option.

Small-Scale Spatial Patterns of <i>Copernicia alba</i>Morong near Bahia Negra, Paraguay

We assessed the spatial distribution of Copernicia alba Morong. In the study area, a lowland palm savanna floodplain, C. alba is the only overstory species. We hypothesized C. alba would be randomly distributed within natural stands. Palms were tallied in six randomly located 0.25 haplots and analyzed using a first-order, Ripley’s K function to assess the distribution of juvenile, adult, and total palm populations. While the total population had either aggregated or random distributions, when analyzing juvenile and adult population separately, we found juveniles were consistently more aggregated than the adults.

南美前陆盆地古生界天然气成藏特征及勘探潜力分析

基于对Chaco盆地的详细解剖,通过分析其古生界天然气的成藏条件和成藏特征,总结其成藏主控因素,进而类比和分析南美前陆盆地古生界天然气的成藏特征和勘探潜力。Chaco盆地天然气资源丰富,为南美天然气储量最大的盆地,且天然气资源主要集中在古生界;其古生界天然气成藏模式优越,成藏具有优生、多储、圈闭规模大、新生古储、多期成藏、近源成藏及集中分布的特征,天然气成藏受主力成藏组合和断裂的双重控制。由于构造演化的差异,南美前陆盆地古生界有效储层仅在中部3个盆地发育;除Chaco盆地外,其他2个前陆盆地古生界与Chaco盆地具有相似的天然气成藏条件,成藏背景有利,具有一定的勘探潜力。研究指出Chaco盆地古生界天然气勘探程度较高,下一步勘探仍以次安第斯带和前渊带泥盆系为主要目的层系,兼探深层和斜坡带浅层非构造圈闭。Beni盆地和Madre de Dios盆地古生界勘探程度非常低,下一步应加强断裂最为发育的次安第斯带和前渊带的勘探力度,以构造圈闭为最有利勘探目标。

Arthropods on plants in a fragmented Neotropical dry forest： A functional analysis of area loss and edge effects

Loss and fragmentation of natural ecosystems are widely recognized as the most important threats to biodiversity conservation, with Neotropical dry forests among the most endangered ecosystems. Area and edge effects are major factors in fragmented landscapes. Here, we examine area and edge effects and their interaction, on ensembles of arthropods associated to native vegetation in a fragmented Chaco Serrano forest. We analyzed family richness and community composition of herbivores, predators, and parasitoids on three native plant species in 12 fragments of varying size and at edge/interior positions. We also looked for indicator families by using Indicator Species Analysis. Loss of family richness with the reduction of forest fragment area was observed for the three functional groups, with sirnilar magnitude. Herbivores were richer at the edges without interaction between edge and area effects, whereas predators were not affected by edge/interior position and parasitoid richness showed an interaction between area and position, with a steeper area slope at the edges. Family composition of herbivore, predator, and parasitoid assemblages was also affected by forest area and/or edge/interior situation. We found three indicator families for large remnants and five for edges. Our results support the key role of forest area for conservation of arthropods taxonomic and functional diversity in a highly threatened region, and emphasize the need to understand the interactions between area and edge effects on such diversity.

Natural vegetation cover in the landscape and edge effects： differential responses of insect orders in a fragmented forest

Human activities have led to global simplification of ecosystems, among which Neotropical dry forests are some of the most threatened. Habitat loss as well as edge effects may affect insect communities. Here, we analyzed insects sampled with pan traps in 9 landscapes （at 5 scales, in 100-500 m diameter circles） comprising cultivated fields and Chaco Serrano forests, at overall community and taxonomic order level. In total 7043 specimens and 456 species of hexapods were captured, with abundance and richness being directly related to forest cover at 500 m and higher at edges in comparison with forest interior. Community composition also varied with forest cover and edge^interior location. Different responses were detected among the 8 dominant orders. Collembola, Hemiptera, and Orthoptera richness and^or abundance were positively related to forest cover at the larger scale, while Thysanoptera abundance increased with forest cover only at the edge. Hymenoptera abundance and richness were negatively related to forest cover at 100 m. Coleoptera, Diptera, and Hymenoptera were more diverse and abundant at the forest edge. The generally negative influence of forest loss on insect communities could have functional consequences for both natural and cultivated systems, and highlights the relevance of forest conservation. Higher diversity at the edges could result from the simultaneous presence of forest and matrix species, although ＂resource mapping＂ might be involved for orders that were richer and more abundant at edges. Adjacent crops could benefit from forest proximity since natural enemies and pollinators are well represented in the orders showing nositive edge effects.

Functional strategies and distribution of climbing plant communities in different vegetation patches in a subtropical dry forest, central Argentina

Aims In the context of global change,the impacts of forest structure alter-ation on climbing plants in extra-tropical ecosystems are poorly understood.It also remains little explored,the functional strategies among climbing plant species and its relationship with the local-scale distribution of climbing plant communities.Here,we aimed at three goals:(i)we studied how climbing plant community com-position responds to the modification of the original forest structure in a subtropical dry forest;(ii)we characterized climbing plant spe-cies according to functional traits related to the acquisition and use of resources;and(iii)we examined whether functional strategies at the community level are also responding to vegetation structure change,a much less addressed topic in the ecology of climbing plants.Methods The study was carried out in the Chaco forest of Córdoba Mountains,central Argentina.We selected 18 patches of‘native forests’,‘shrublands’and‘Ligustrum lucidum forests’.We counted and identified climbing plant individuals in each patch,including woody and herbaceous species.For each spe-cies,we measured 10 functional traits:leaf area,leaf area ratio,leaf dry matter content,leaf tensile strength,specific leaf area,stem density,wood saturated water content,inter-node length,petiole length and plant cover.We compared climbing plant composition,richness and abundance among the three vegeta-tion types.Then,we assessed trends of functional variation of climbing plant species by performing a principal component analysis.Finally,we investigated whether simple mean,weighted mean and Functional Richness index of principal component analysis(PCA)axes differed among the climbing plant communi-ties of the three vegetation types.Important Findings Multivariate analysis revealed that climbing plant composition of native forests significantly differed from that of shrublands and L.lucidum forests.Also,L.lucidum forests had the lowest climb-ing plant species richness.Functional variation of climbers was explained by three PCA axes:axis 1 represented the resource-use strategy,axis 2 was associated with light-foraging strategy,and axis 3 related to plant size.The most abundant species in native forests presented a more acquisitive functional strategy and larger sizes than those of shrublands and L.lucidum forest.Furthermore,the most abundant species in shrublands had shorter internodes and petioles than the most abundant climbers of the other vegeta-tion types.Finally,the climbing plant community in the native forests had the highest Functional Richness index regarding the resource-use and the size strategies.Here,we demonstrated that there are floristic and functional differences among climb-ing plant communities in patches of three vegetation types in a subtropical dry forest biome.Particularly,we found climbers spreading along three functional axes which were directly related to climbing plant community distribution among the different patches,highlighting their ecological importance and the need of further research.