An incomplete correlation between pre-salt topography, top reservoir erosion, and salt deformation in deep-water Santos Basin (SE Brazil)

In deep-water Santos Basin, SE Brazil, hypersaline conditions during the Aptian resulted in the accumulation of halite and carnallite over which stratified evaporites, carbonates and shales were folded, translated downslope and thrusted above syn-rift structures. As a result, high-quality 3D seismic data reveal an incomplete relationship between pre-salt topography and the development of folds and thrusts in Aptian salt and younger units. In the study area, three characteristics contrast with known postulates on passive margins’ fold-and-thrust belts: a) the largest thrusts do not necessarily occur where the salt is thicker, b) synthetic-to-antithetic fault ratios are atypically high on the distal margin, and c) regions of intense folding do not necessarily coincide with the position of the larger syn-rift horsts and ramps below the salt. Regions marked by important erosion and truncation of pre-salt strata, uplifted and exposed sub-aerially before the deposition of Aptian salt, can form structural lows at present or be part of horsts uplifted after the Aptian. This is an observation that suggests significant intra-salt shear drag above pre-salt structural highs during Aptian-Late Cretaceous gravitational gliding, but not on younger horsts and ramps reactivated after the main phase of salt movement. Either formed by drag or sub-aerial erosion, strata truncation below the Aptian salt does not correlate with the present-day pre-salt structure in terms of its magnitude and distribution. In addition, there is a marked increase in deformation towards the distal margin, where low-angle thrusts are ubiquitous on seismic data. The geometry and large synthetic-to-antithetic fault ratios of post-salt strata on the distal margin lead us to consider a combination of gravitational gliding of salt from the northwest and ridge push from the east as responsible for the observed styles of salt deformation

Fertilizer minerals in Asia and the Pacific

This publication is volume one of Mineral Concentrations and Hydrocarbon Accumulations in the ESCAP Region Series with this collection of papers from its Workshop on the Occurrence, Exploration, and Development of Fertilizer Minerals of the Asia and Pacific region. The Workshop on Occurrence, Exploration and Development of Fertilizer Minerals was organized jointly by the Mineral Resources Section of the Natural Resources Division of ESCAP, the Regional Mineral Resources Development Centre (RMRDC), and the Department of Mineral Resources (DMR) of the Government of Thailand on 26-30 August 1986. These collected papers are the documents which flowed from that Workshop. They include 15 papers presented by resource persons and 13 papers by experts of developing countries of the region.Report........................................................................................................................................................................................ 1 Part One Papers of Resource Persons 1. Fertilizer Sector Development in Asia and the Pacific ................................................................................................. 1 by L.M. Maene 2. Global Outlook for the Supply and Demand of Mineral Raw Materials for Fertilizer............................................... by P.L. Louis 3. Potash Deposits of the Khorat Plateau, Thailand ........................................................................................................... 51 by Robert J. Hite 4. Phosphate Rock Production and Exploration in the ESCAP Region: A Review of Progress..................................... 74 by Arthur J.G. Notholt 5. Geology of Sulphur Deposits ......................................................................................................................................... 84 by Marek Niec 6. Phosphate Resources of the World and Models for Exploration with Special Reference to Southeast Asia............ 93 by James B. Cathcart 7. Geology and Agriculture ................................................................................................................................................ 104 by Robert J. Hite 8. The Potential of the Thai Potash Deposit in the Light of a Future World Potash Fertilizer Supply......................... 108 by Gustav-A. Burghardt 9. Phosphate and Sulphur Market Prospects for the Development of Indigenous Fertilizer Industries in the ESCAP Region...................................................................................................................................................................... 119 by Igor Kotlarevsky 10. The Mineral Economics of Potash in the Asian Region................................................................................................. 126 by Paul Acher 11. Mining of Sulphur Deposits ........................................................................................................................................... 143 by Marek Niec 12. End Uses and Applications of Potash Salts..................................................................................................................... 147 by Stephen F. Dowdle 13. Measures on the Soil Amelioration Potential of Rock Phosphates in Oxisols and Ultisols........................................ 157 by H.W. Müller 14. Exploration and Evaluation of Offshore Phosphate Deposits — A review................................................................... 165 by J. Robert Woolsey 15. Methodologies and Techniques for the Exploration of Offshore Phosphate ................................................. 170 by J. Robert Woolsey Part Two Country Papers 1. Brief Information about the Development of Fertilizer Production in the Democratic Republic of Afghanistan . . 179 by Abdul Rahman Qazikhani 2. The Geological Characteristics of the Potash Deposit of the Qarhan Inland Salt Lake in Qaidam Basin, China .... 181 by Yang Qian 3. Phosphate Deposits in Indonesia................................................................................................................................ 191 by Sarno Harjanto 4. Hong-Cheon Apatite Deposit, Republic of Korea ...................................................................................................... 198 by Jang-Han Yoo 5. Present Status of Phosphorites of Nepal .................................................................................................................... 203 by U.B. Pradhananga 6. Production and Imports of Fertilizers in Malaysia...................................................................................................... 209 by Yusoff Bin Ismail 7. Exploration and Assessment of Fertilizer Mineral Deposits in the Philippines.......................................................... 212 by Bassanio S. Vargas and Pablito P. Escalada 8. The Assessment of Igneous Apatite Deposits in Sri Lanka for Manufacture of High Analysis Water Soluble Phos phate Fertilizer ................................................................................................................................................... 234 by D.E. de S. Jayawardena 9. An Overview of Potash Development in Thailand...................................................................................................... 243 by Anant Suwanapal 10. Structural Geology of Potash and Rock Salt in Nachuak Area, Khorat Plateau, Thailand ....................................... 255 by Parkorn Suwanich 11. Use of the Computer in Potash and Rock Salt Post-Depositional Structural Models at Bamnet Narong Area, Northeastern Thailand........................................................................................................................................ 261 by Sombat Yumuang 12. The Discovery of Devonian Marine Phosphate Rocks in Thailand.............................................................................. 275 by Sangad Bunopas, Somkiet Maranate and Aphichart Lamchuan 13. Mineral Deposits for Fertilizers in Viet Nam ............................................................................................................. 280 by Hoang Nga Dinh</p

Impact du climat et de la tectonique sur la dynamique des systèmes sédimentaires pendant l'ouverture de l'Atlantique Sud

Mémoire de Géosciences-Rennes n°147. ISBN : 2-914375-89-1The opening of the South Atlantic was initiated by a rifting phase during the Early Cretaceous. During this period a large salt sequence develops in the Central segment. The presence of evaporites, commonly associated to an arid climate, suggests the possibility of having, during the Cretaceous, arid zones close to the equator. This observation raises majors questions: what was the incidence of the rifting on the climate ? And what were the roles of these two processes on the sedimentary dynamic and particularly during the salt deposit? In this purpose a numerical modeling approach was chosen and three major steps were followed: (1) paleogeographic synthesis, (2) climate modeling, and (3) stratigraphic modeling. The paleogeographic synthesis has highlighted, in a first time, a diachronous evolution of rift activity, early in the northern part of the Central segment before spreading in the southern part, and secondly to clarify the chronology of two phases of extension, rift and sag. Climate models have shown the existence of a humid climatic belt northern to the study area, and a strong seasonality. Finally, stratigraphic modeling revealed the importance of taking into account (1) of this seasonality pattern and (2) of the paleogeography of the Central segment. The interaction between the three thematic has clarified the importance of the control factors for the formation of evaporites. Thus, (1) the climate played a major role in providing favorable climatic conditions due to the seasonnality, but (2) the rift has been the primary control factor by allowing a subsidence for marine connection and income of salt for deposition of evaporites in a restricted basin.L'ouverture de l'Atlantique Sud s'est initiée par une phase de rifting au Crétacé inférieur. Pendant cette période, une épaisse série salifère s'est développée dans tout le segment Central. La présence contemporaine d'évaporites, communément associées à un climat aride, suggère donc la possibilité d'avoir eu, au Crétacé inférieur, des zones arides à proximité de l'Equateur. Cette observation soulève alors des questions majeures: quelle a été l'incidence du rifting sur le climat? Et quels rôles ont pu jouer ces deux processus, climat et tectonique, dans la dynamique sédimentaire et entre autre sur la dynamique des dépôts du sel? Dans ce but, une approche par modélisation numérique a été choisie et trois grandes étapes ont été suivies, (1) une synthèse paléogéographique, (2), une modélisation climatique, et (3) une modélisation stratigraphique. La synthèse paléogéographique a permis, dans un premier temps, de mettre en évidence une évolution diachrone de l'activité du rift, précoce au Nord du segment Central avant de se propager dans la partie Sud, et d'autre part de préciser la chronologie des deux phases d'extension, rift et sag. Les modélisations climatiques ont montré l'existence d'une ceinture climatique humide au Nord de la zone d'étude, ainsi qu'une forte saisonnalité. Enfin, les modélisations stratigraphiques ont révélé l'importance de la prise en compte (1) de cette saisonnalité dans les modèles et (2) de la paléogéographie du segment Central. L'interaction entre les trois thématiques a permis de préciser l'importance des paramètres de contrôle pour la formation des évaporites. Ainsi, (1) le climat a joué un rôle majeur en offrant des conditions climatiques favorables grâce à la saisonnalité du climat dans la mise en place des évaporites, mais (2) le rift a éxercé un contrôle primordial puisqu'il a généré un régime de subsidence permettant la connexion marine et l'apport de sel nécéssaire au dépôt des évaporites dans un bassin encore protégé

Climate in Earth history

Complex atmosphere-ocean-land interactions govern the climate system and its variations. During the course of Earth history, nature has performed a large number of experiments involving climatic change; the geologic record contains much information regarding these experiments. This information should result in an increased understanding of the climate system, including climatic stability and factors that perturb climate. In addition, the paleoclimatic record has been demonstrated to be useful in interpreting the origin of important resources-petroleum, natural gas, coal, phosphate deposits, and many others

Geochemistry and Petrology of Evaporites Cored from a Deep-Sea Diapir at Site 546 offshore Morocco

These evaporites are in the potash facies. The S isotope ratio suggests that the anhydrite was derived from sea-water of Permian to Scythian age.-K.A.R

Experimental investigation of calcium carbonate mineralogy in past and future oceans

Inorganic marine calcium carbonate formation and mineralogy varies significantly concurrent with the solution composition. During the Phanerozoic, due to oscillations in the seawater composition, this resulted in the formation of either dominantly calcite or aragonite. Variations in seawater composition also appear to have influenced the evolution of biomineralizing organisms. Additionally, many organisms utilize amorphous calcium carbonate (ACC) during biomineralization. The occurrence of calcite and aragonite throughout the Phanerozoic and calcium carbonate biomineralization were investigated. This was done by determining the influence of solution chemistry (SO4 and Mg) on calcium carbonate formation, mineralogy and stability via a variety of laboratory and synchrotron based synthesis experiments. During the formation of aragonite and calcite, aqueous SO4 and the Mg/Ca ratio both affect the formation of calcite and aragonite. An increase in aqueous SO4 decreases the Mg/Ca ratio at which calcite is destabilized and aragonite becomes dominant. These results suggest that the models relating seawater chemistry to calcium carbonate formation needs re-evaluation. Abiotic ACC crystallization to vaterite occurs in three stages. In the first stage, ACC crystallizes to vaterite via a spherulitic growth mechanism. The second stage is characterized by surface particle growth at the expense of ACC. Finally, particle growth via Ostwald ripening is the only remaining process. This process can be described as the inorganic analogue to biological ACC crystallization, which is adjusted by organisms to produce their preferred calcium carbonate polymorph and morphology. An increase in SO4 concentration only decreases the spherulitic growth rate and Ostwald ripening, even when rapidcreekite (as an intermediate) and gypsum crystallizes. Finally, SO4 promotes the formation of vaterite. Depending on the formation process this is caused by either the stabilization of vaterite and destabilization of calcite (slow heterogeneous formation), or by the destabilization and inhibition of calcite formation (spherulitic growth)