Challenges of forest governance in Madagascar

There has been a huge surge in interest in the preservation of Madagascar's forests in the past two decades, but despite the investment of hundreds of millions of dollars, the goal remains elusive. Recent legislation has given the government the authority to enter into contractual arrangements with communities for the management of the country's public forests, so it has become crucial to grapple with the significant challenges involved. This paper explores the enormity of the challenge of forest governance in Madagascar in an era of decentralization. By examining several forests in one part of the country, it reveals a dizzying range of forest types and forms of use and governance within a fairly small portion of the country. These examples make it apparent that the history of forest management in Madagascar constitutes a broad-ranging experiment with forest governance. Simply monitoring the dynamics of the forest canopy is a significant technical challenge. However, this pales in comparison to the difficulties inherent in explaining those dynamics and assessing the sustainability and equity of different management regimes. Of the forests considered in the study, those where the Malagasy state has partnered with international conservation and development organizations seem to stand out, both in terms of stabilized, or even growing, forest cover, as well as a balance of interests among users.     

Geochemistry and Petrogenesis of Central Lebombo Basalts of the Karoo Igneous Province

Three distinet basaltic rock types are recognized on the basisof detailed new analyses in the eastern zone (central Lebombo)of the Karoo Igneous Province. The high titanium and zirconiumgroup is composed of low-Fe (henceforth called simply high Ti-Zrbasalts) and high-Fe (henceforth called ‘high-Fe’)varieties and distinguished from the low titanium and zirconiumgroup by 2–4 times greater abundances of Ti, P, Zr, Nb,Y, La, Ce, and Nd (high field strength elements; HFSE), as wellas higher but more variable abundances of K, Rb, Ba, and Sr,All rock types are interbedded to some degree, although thehigh Ti-Zr type (low-Fe) predominates at the base of the sectionand the ‘high-Fe’ type occurs mostly at the topof the section. Stratigraphic relationships show that the highTi-Zr basalts to the south within a distance of 60 km. Eruptionof each rock type from replenished, tapped, and fractionatedmagma chambers can account for much of the major and trace elementvariation within each suite, with the notable exceptions ofthe large ion lithophile elements (LILE; K, Rb, and Ba) andSr. Neither crystal fractionation nor contamination with graniticcrust can produce the variations between the basalt types anddoes not appear to affect significantly the geochemistry withinany basalt type. The North Lebombo high Ti-Zr picrites are themost likely parent magmas to the high Ti-Zr low-MgO group. Considerationof previous studies of the picrites suggested that the highTi-Zr picrite geochemistry requires a mixed source or the mixingof two picrite endmember magmas discriminated on the basis ofdegree of incompatible element enrichment. At least one of theendmembers must be within, or derived from, sub-continentallithospheric mantle. The low-MgO high Ti-Zr basalt geochemistryis consistent with evolution from a picritic parent with abouta 30–44 wt. % mantle lithospheric component. In contrast,the low Ti-Zr basalt group parental composition is outside thecompositional range suggested for the high Ti-Zr picrite endmembers,being more depleted in incompatible elements (e.g., Ti, P, Zr,Nb, LREE, and LILE). Again, by analogy with possible picriticparents, this group may segregate from a source more depletedin incompatible elements than a mid-ocean ridge basalt (MORB)source, leaving a harzburgitic residue. The ‘high-Fe’basalt group is very evolved (e.g., MgO <5%) but may stillbe constrained by Nd-isotope and Zr/Y ratios to have a mantlesource geochemically similar to that from which the Walvis Ridgebasalts were derived. If a mantle plume contributed to basaltgeochemistry significantly, then the late-stage ‘high-Fe’basalts represent this component most closely.     

The Marl Slate: a model for the precipitation of calcite, dolomite and sulphides in a newly formed anoxic sea

Detailed studies of a new, complete Marl Slate core in South Yorkshire have provided information on isotopic (δ¹³C, δ¹⁸O, δ³⁴S) and geochemical variations (trace elements and C/S ratio) which enable the formulation of a model for carbonate and sulphide precipitation in the Late Permian Zechstein Sea. Calcite and dolomite are intimately associated; the fine lamination, organic character and absence of benthos in the sediments are indicative of anoxic conditions. Lithologically the core can be divided into a lower, predominantly sapropelic Marl Slate (2 m) and an upper Transition Zone (0·65 m) of alternating sapropel and calcite-rich and dolomite-rich carbonates. C/S ratios are 2·22 for the Marl Slate and 1·72 for the Transition Zone respectively, both characteristic of anoxic environments. δ¹⁸O in the carbonates shows a large and systematic variation closely mirrored by variations in calcite/dolomite ratio. The results suggest a fractionation factor equivalent to a depletion of 3·8% for ¹⁸O and 1·5% for ¹³C in calcite. The δ³⁴S values of pyrite are isotopically light (mean value = - 32·7%) suggesting a fractionation factor for the Marl Slate of almost 44%, typical of anoxic basins. The results are related to stratification in the early Zechstein Sea. Calcite was precipitated in oxic upper layers above the halocline. Below the oxic/anoxic boundary framboidal pyrite was precipitated, resulting in lower sulphate concentration and elevated Mg/Ca ratio (due to calcite precipitation). As a result of this, dolomite formation occurred below the oxic/anoxic interface, within the anoxic water column and in bottom sediments. Variations in calcite/dolomite ratios, and isotopic variations, are thus explained by fluctuations in the relative level of the oxic/anoxic boundary in the Zechstein Sea.     

Textural constraints on the formation of impact spherules: A case study from the Dales Gorge BIF,Paleoproterozoic Hamersley Group of Western Australia

Abstract— Impact ejecta (about 2.5 Gyr old) in the DS4 layer of the Dales Gorge BIF (Hamersley Group, Western Australia) are so well preserved that many original textures such as vesicles and microlites are faithfully preserved. About 65% of the particles in the layer originated as impact ejecta, of which 81% are splash forms. The remaining 19% are angular, but the splash forms and angular particles have the same composition (mainly diagenetic stilpnomelane and K‐feldspar) and share a common suite of internal textures. Some particles contain randomly oriented microlites texturally identical to plagioclase in basalts. Most splash forms have rims of inward‐growing crystals that may have formed from the melt (perhaps nucleated by impinging dust) or via thermal devitrification. The rims clearly formed in flight because in broken particles (which make up about 13% of the splash forms) they are generally not present on broken surfaces. The origin of the angular particles is uncertain, but they may represent solid ejecta. Given the large sizes and variable shapes of the splash forms, they are probably droplets of impact melt emplaced ballistically. This is largely by analogy to the K‐T boundary layer, but DS4 splash forms differ from K‐T spherules in important ways suggesting the K‐T model is not universal. The occurrence of basaltic ejecta from a large impact highlights its scarcity in the stratigraphic record despite the areal abundance of oceanic crust. The diverse textures formed via in‐flight crystallization suggest particle paths in the plume are more complex than is generally appreciated.