Geological Survey of Denmark and Greenland Bulletin 26 ... - Geus

More documents

Recommendations

Info

Bach Long Vi 5 km Bach Long Vi 20°14Ń 20°13Ń A dense net of seismic data cover the area offshore Bach Long Vi and reveals a N–S to NE–SW-trending, inverted Eocene–Oligocene graben. The graben fill sub-crops at and closely beneath the seafloor and forms the core of Bach Long Vi (Fig. 3A). The graben is part of a larger rift system that actively subsided during Palaeogene time (Fig. 3B). The deposits, including the sampled source rocks on and around Bach Long Vi, therefore form part of a regional syn-rift system, which is directly continuous with the syn-rift kitchen areas sourcing the recent oil and condensate discoveries in the region (Fig. 3). The preliminary results suggest that rich source-rock intervals could be present throughout much of the syn-rift succession in the basin, highly encouraging for further exploration. 500 m 107°72Ń 107°74Ń Acknowledgements The ENRECA project is funded by the Danish Ministry of Foreign Affairs via Danida. PetroVietnam co-funded the ENRECA 3 well and is thanked for providing data and for permitting publication of this paper. Fig. 4. Map of the island of Bach Long Vi. Red dots show sites of sourcerock samples. The inset map shows the nearest industrial seismic lines in the area. For location see Figs 1 and 3. the Palaeogene syn-rift succession. Sampled source-rock intervals are studied through general source rock screening and biomarker analysis combined with more advanced analysis of selected source-rock intervals. Situated at the intersection of the Beibuwan and the Song Hong Basin, Bach Long Vi occurs in the centre of a newly discovered petroleum province offshore Vietnam (Fig. 3). Bach Long Vi sits at the top of a prominent structure associated with inversion of a Palaeogene graben. The island therefore provides a window into the nature of the Palaeogene syn-rift succession of the area. Highly oil-prone lacustrine mudstones with an organic content ranging from c. 2 to 7 wt.% total organic carbon were sampled from scattered outcrops on Bach Long Vi and from sub-sea outcrops around the island (Fig. 4). ENRECA analyses of these excellent source rocks confirm that petroleum-prone mudstones occur at various stratigraphic levels that crop out over the entire area (e.g. Petersen et al. 2004 and new unpublished data). References Fyhn, M.B.W., Boldreel, L.O. & Nielsen, L.H. 2009: Geological development of the central and south Vietnamese margin: Implications for the establishment of the South China Sea, Indochinese escape tectonics and Cenozoic volcanism. Tectonophysics 478, 184–214. Hall, R. & Morley, C.K. 2004: Sundaland Basins. In: Clift, P. et al. (eds): Continent–ocean interactions within the East Asian marginal seas. Geophysical Monograph Series 149, 55–85. Washington D.C.: American Geophysical Union.Leloup, P.H., Arnaud, N., Lacassin, R., Kienast, J.R., Harrison, T.M., Trong, T.T.P., Replumaz, A. & Tapponnier, P. 2001: New constraints on the structure, thermochronology and timing of the Ailao Shan-Red River shear zone, SE Asia. Journal of Geophysical Research 106, B4, 6683–6732. Petersen, H.I., Nytoft, H.P. & Nielsen, L.H. 2004: Characterisation of oil and potential source rocks in the northeastern Song Hong Basin, Vietnam: indications of a lacustrine–coal sourced petroleum system. Organic Geochemistry 35, 493–515. Sladen, C. 1997: Exploring the lake basins of east and Southeast Asia. In: Fraser, A.J., Matthews, S.J. & Murphy, R.W. (eds): Petroleum geology of Southeast Asia. Geological Society Special Publications (London) 126, 49–76. Authors’ addresses M.B.W.F., H.I.P., L.H.N. & I.A., Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: mbwf@geus.dk T.C.G. & L.H.Ng., Vietnam Petroleum Institute, 173 Trung Kinh Str., Yen Hoa Wrd., Cau Giay Dist., Hanoi, Vietnam. N.T.M.H., Hanoi University of Mining and Geology, Dong Ngac, Tu Liem, Hanoi, Vietnam. N.D.N., Hanoi University of Science, 334 Nguyen Trai-Thanh Xuan-Hanoi, Vietnam. 84
I Rock phosphate and lime for small-scale farming in Tanzania, East Africa Per Kalvig, Niels Fold, Jesper Bosse Jønsson and Elisante Elisaimon Mshiu Poor soils are a major cause of poverty in sub-Saharan Africa, and thus restoration of soil fertility is a significant challenge for sustainable agriculture. Some of the main resources required, e.g. phosphate and lime, are present in many African countries and can be used by smallholder farmers in a relatively unprocessed form instead of expensive commercial fertilisers. Here we present a small study of the Mbeya region in Tanzania, which locally has both phosphate and lime. Most soils in sub-Saharan Africa are losing nutrients necessary for sustainable agriculture. This is mainly due to intensive farming and the fact that the nutrients are not replaced adequately. Further reasons for nutrient losses are leaching, soil erosion and fixation by iron and aluminium oxides. Vast areas experience moderate to acute phosphorus deficiency (Vanlauwe & Giller 2006). The Mbeya region in south-western Tanzania (Fig. 1) is characterised by intensive smallholder plots along with several local sources of phosphate-bearing rocks and limestone. The former were examined in the 1980s (Chesworth et al. 1988, 1989), but have never been utilised (Kalvig et al. 2010). Phosphates and lime – opportunities and constraints Soils may become acid for many reasons and high rainfall may lead to washing out the nutrients needed for healthy plant growth. Thus phosphorus and calcium deficiencies are common factors that restrict plant growth in highly leached tropical soils. The majority of smallholders cannot afford to use adequate quantities of commercial fertilisers and lime, resulting in low yields. An alternative is to use local sources, which can improve agricultural productivity by slowly releasing essential elements and raising the pH value of the soil. Phosphates, lime, potassium-rich minerals, clay, zeolite and mica are common locally, but lacking awareness of their effects, very few smallholders use them. If such an awareness could be fostered and local resources made available at affordable prices, it would give farmers an opportunity to improve their crop yields (van Straaten 2002; Mitchell 2005). The phosphate potential in Tanzania was outlined twenty years ago by Mchihiyo (1991). The study presented here shows that local phosphate can be made available at affordable costs. Phosphate minerals. Natural fertilisers are available and can be used untreated. They comprise organic fertilisers such as manure, leaf litter and sludge, and rock fertilisers such as marl, rock phosphate, volcanic rock and mica. In contrast to natural fertilisers, artificial fertilisers are readily soluble and contain guaranteed total, active nutrient concentrations. The practical challenges and potential benefits involved in the use of rock phosphate have been widely discussed (Mchihiyo 1991; Appleton 2002; van Straaten 2002, 2006; Vanaluwe & Giller 2006). The general view is that the use of rock phosphate for local agriculture is justified, provided its addition is managed in accordance with the type of crop and the conditions of the soil. Usually, crop yields only show a slow response over 2–3 years after the addition of rock phosphates, which makes it difficult to generate interest among local farmers. The solubility of phosphate-bearing rocks differs widely depending on the mineralogy and chemistry of the rock 9°S Rukwa Rift Lake Rukwa I I I I I I Major road Minor road Railway River Regional capital District capital International boundary Prospects 33°E 33°E Kenya Njelenje Sukumavera Songwe Scarp Muvwa Mbeya Nanyala I I I I I I I I I Mbalizi Panda Hills 25 km I 400 km I I I I Tanzania I I I Lake Nyasa Fig. 1. Map of south-western Tanzania showing the Mbeya region with its main towns, roads and railway. The prospects indicated are known carbonatite occurrences which were considered potential phosphate resources by previous studies. I I 9°S © 2012 GEUS. Geological Survey of Denmark and Greenland Bulletin 26, 85–88. Open access: www.geus.dk/publications/bull 85
Page 1 and 2:
GEOLOGICAL SURVEY OF DENMARK AND GR
Page 4 and 5:
Greenland Denmark Mexico Nigeria Gh
Page 7 and 8:
Review of Survey activities 2011 Fl
Page 9 and 10:
Nano-quartz in North Sea Danian cha
Page 11 and 12:
Dispersed in distilled water Disper
Page 13 and 14:
Geology of the Femern Bælt area be
Page 15 and 16:
Biostratigraphic marker fossils: Di
Page 17 and 18:
Rock-cored drumlins on Bornholm, De
Page 19 and 20:
N 50 km Pre-Quaternary geology Gran
Page 21 and 22:
Methane distribution in Holocene ma
Page 23 and 24:
Baltic Sea. Such a map shows only t
Page 25 and 26:
Natura 2000 habitat mapping in Katt
Page 27 and 28:
Interpretation of the side-scan ima
Page 29 and 30:
Early Holocene sea-level changes in
Page 31 and 32:
Depth (cm) 0 50 Lithology Terrestri
Page 33 and 34: Cliff collapse at Stevns Klint, sou
Page 35 and 36: Fig. 4. Aerial photograph of the cl
Page 37 and 38: Mean annual temperature Shallow geo
Page 39 and 40: Table 1. Thermal conductivity of di
Page 41 and 42: Efforts to include geological and g
Page 43 and 44: Fig. 3. Tilt of shorelines on Læs
Page 45 and 46: Results of monitoring groundwater a
Page 47 and 48: C 1 /(C 2 +C 3 ) 10 5 remained at t
Page 49 and 50: Groundwater protection in Denmark a
Page 51 and 52: Before Water Sector Law Water suppl
Page 53 and 54: Anorthosites in Greenland: a possib
Page 55 and 56: A B Fig. 3. A: The anorthosite at I
Page 57 and 58: From 3D mapping to 3D modelling: a
Page 59 and 60: points and polylines (Fig. 2C). In
Page 61 and 62: Geological assessment of the East G
Page 63 and 64: Two-way travel time (sec) 0 1 2 3 4
Page 65 and 66: New evidence for possible generatio
Page 67 and 68: source rocks. In the Ilímaussaq in
Page 69 and 70: Methane and possible gas hydrates i
Page 71 and 72: cal analyses, including measurement
Page 73 and 74: Ablation observations for 2008-2011
Page 75 and 76: the ice. During a single melt seaso
Page 77 and 78: Testing of an automatic earthquake
Page 79 and 80: A spectrogram produced by short-tim
Page 81 and 82: The Cenozoic Song Hong and Beibuwan
Page 83: I I I I I I I I I I I I I I I I I I
Page 87 and 88: Fig. 3. Landscape around the villag
show all

Geological Survey of Denmark and Greenland Bulletin 26 ... - Geus

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?