Effects of Rice Straw Silicification and Characters of Extraction Biogenic Silicon on the Degradation of Fibrous Components in Rice Straw

Straw of seven rice varieties with early-, middle- and late maturity was collected from Huazhong Agricultural University in Hubei. A study was carried out for rice straw in the aspects of the characters of straw silicification and extraction biogenic silica (EBSi), the relationship between characters of EBSi and kinetic characteristics of degradation of fibrous components in fistulated cows, as well as the effect of urea treatment on rice straw desilicification. Although total silica content (ADISi) in rice straw was similar, the efficiency of extraction biogenic silica (EEBSi) and cellulose in early varieties were significantly higher than those in middle (18.9% and 9.1 %) and late ones (26.1% and 11.2%). The degradability of EBSi and cellulose of early varieties were higher than those of middle by 70.0% and 17.5%, and of late varieties by 47.8% and 23.7% , respectively. The in sacco degradability and in vitro VFA production of early varieties were also higher than those of middle by 14.5% and 19.0%, and late by 12.9% and 14.8%. Comparing the morphological fractions of the rice straws, EEBSi, cellulose content, and in vitro VFA production were different with the order of blade < sheath < stem. A significant correlation was found between the contents of EBSi and cellulose (r= 0.86), and the two contents were remarkably correlated with the potential straw degradability (a + b) by r = 0.90 and 0.84 respectively. Therefore, EBSi in rice straw was a main factor affecting the potential degradability of rice straw, rather than the ADISi of straw. Urea treatment improved rice straw degradability, degradation rate and potential degradability by 10.8% , 27.9% , and 10.1% respectively, compared to untreated straws.

Silicification in Mississippian Lodgepole Formation,Northeastern Flank of Williston Basin,Manitoba,Canada

Five types of replacement silica are recognized in the Lower Mississippian Virden Member carbonates on the northeastern flank of Williston basin： microcrystalline quartz, chalcedonic quartz, anhedral megaquartz, euhedral megaquartz, and stringy megaquartz. Silica tends to replace various bioclasts, and all except the stringy megaquartz also occur as non-replacive void-filling cement or as silica forming chert nodules and silicified limestone. Although crinoids, brachiopods, corals, bryozoans, molluscs, trilobites, forams, and ostracodes are present in the sediments studied, only the first three show evidence of silicification. Crinoids are commonly replaced by microcrystalline quartz whereas brachiopods typically by spherules of length slow chalcedony. Coalesced spherules, often in concentric rings （beekite rings）, may form sheet-like masses on the surface of corals and brachiopods. Although bryozoans are common in the Virden Member, none showed any evidence of silicification. The difference in the susceptibility to silicification may be related to the shell microstructure, biological group, size of organism, skeletal mineralogy, and organic content of the bioclasts. Biogenic silica derived from the dissolution of siliceous sponge spicules is considered to be the most likely silica source for silicification. Most silica is believed to be released during early diagenesis before the sediments were deeply buried. The Virden Member carbonate may have experienced two episodes of replacement, the first affecting the bioclasts, the second producing silicified limestone and chert nodules.

Silicification and mineralization in hydrothermal deposits

In hydrothermal deposits there are many types of alteration, including potassic alteration (altered minerals are potassic feldspar and biotite), sericitization, silicification, argillazation,chloritization, carbonification and propylitization, but most of them belong to post-or premineralization alteration except silicification formed during the mineralization period. Silicifation occurred in hydrothermal deposit formation from high, moderate temperature to low temperature and can be divided into early, middle and middle-late stages. The early stage is featured by formation under high temperature and accompanied by mineralization of Sn, W and Mo, while the middle stage was formed under moderate temperature and related to mineralization of Cu.The middle-late stage is characterized by moderate-low ternperature and varied mineralization of Cu,Au,Zn,Ag, Pb and U.

Hydrothermal Origin of Early Permian Chert Nodules in the Central North China Craton Linked to Northern Margin Cratonic Activation

Sedimentary chert phases from the Archean to the present are widely used to trace sedimentary environments and tectonic settings.Recently,chert nodules occurring within carbonates have been the subject of possible hydrothermal or biogenic origin,in lieu of a diagenetic origin.However,chert nodules from a vast cratonic basin represent extremely rich silica accumulations but less noted is how they respond to submarine hydrothermal activity(and/or surface siliceous organism productivity).The links between the cratonic-type chert depositions and environmental changes regarding cratonic evolution need to be revisited at a large temporal-spatial scale.The chert nodules are widespread throughout the Lower Permian Taiyuan Formation in the North China Craton(NCC).Several Taiyuan chert-rich successions across the NCC have been selected to study possible links between chert deposition and cratonic evolution in scenario of partial cratonic activation of the northern NCC margin during the Late Paleozoic.Based on stratigraphic correlation,the chert nodules are ubiquitously,evenly distributed throughout the Taiyuan Formation at a large craton-basin scale from the northern to southern interior NCC.Petrological results,elemental abundances,together with silicon and oxygen isotopic compositions of chert samples infer significant hydrothermal contributions for the silica accumulations.Therefore,the cratonic-scale chert depositions of hydrothermal origin infer a giant and remote silica reservoir,linking to the large igneous province and magmatism in the NCC northern margins.The Taiyuan chert nodules could be unique marine sedimentary archives recording the Late Paleozoic NCC partial activation,which also generated continental records of igneous rocks,bauxites and tuffs.The strong tectonics of the northern margin,south-dipping topography and northward transgression of the Early Permian NCC facilitated the chert deposition on the shallow marine platform in the cratonic interior.

Geochemical Siliceous and Silicified Facies of Phosphate Series of Ouled Abdoun Basin (Morocco)

Syn-sedimentary post-diagenetic phenomena are remarkable in Moroccan phosphates. Indeed they are reference deposits for geological study, where important interests are given of determination and identification of these geochemical phenomena. Silicification is one of the phenomena that we have studied to determine the diagenetic processes that control the new-formation of silica in phosphate series of Ouled Abdoun. This study was performed on deposit EL Halassa, which belongs to the Ouled Abdoun Basin;they spread out the Maastrichtian to Lutetian. At first, petrographic approach was applied on different terms composing the phosphate series. In a second step, a geochemical approach on the same silica and silicified facies of phosphate series Ouled Abdoun Basin for characterizing silicification deduced the probable links between this diagenetic phenomenon and facies and forms’ affect. Ten major trace elements were measured. According to the phases’ petrographic relationship, the results were presented and discussed: silicate phase, the carbonate phase and clay phase.

Petrography and Mineralography of Emarat Lead and Zinc Deposit (South Arak)

Iran is host to more than 285 zinc and lead carbonated host deposits including world-class deposits such as Mehdi Abad and Irankouh. Emarat deposit is located in Sanandaj-Sirjan zone and Malayer-Isfahan metallogenic province (northwestern part of Sanandaj-Sirjan tectonic zone). In the area, the mineralization has stratabound shape and restricted to Early Cretaceous limestones and dolomites. With investigation of the optical properties in microscopic survey and evaluation results of analysis, sphalerite, galena, pyrite and chalcopyrite were recognized as the main minerals, covellite, tennantite-tetrahydrite and serosities, quartz and barite as the secondary minerals and gyps, smithsonite were recognized as the minorminerals in the samples. Silicification alteration acted as major process in studied deposit and dolomitization, pyritization and hematitization also were observed in the deposit. Evidences show that mineralization has occurred in post diagenetic stage (epigenetic type) and after tectonic influence.

Polycyclic Evolution of Paleoproterozoic Rocks in the Southwestern Part of the Mako Group(Eastern Senegal,West Africa)

After an extensional stage giving rise to tholeiitic basalts and gabbros, the south western part of Kédougou Kéniéba Inlier (KKI) was affected by three phases of compressionnal deformation. The first phase (D1) was related to NE-SW stress that led to northeastward thrusting. Early granitoids would be implemented during this tectonic event. The second phase (D2) was due to East-West compressional stress that created combined strike sleep faults: NNW-SSE and NNE-SSW respectively sinistral and dextral. During this phase, some volcanic rocks and gabbros were mylonitized, hydrothermalized and transformed into quartzites. These quartzites were considered as sedimentary rocks in previous studies. Granitic plutons and andesites took place during this tectonic phase. D3 deformation occurred towards the end of the Eburnean orogeny. It would be held in two episodes. In the first episode, WNW-ESE stresses created conjugate shears: sinistral NNW-SSE and dextral NE-SW. In the second episode, stresses moved toward the NE-SW direction and made the resulting brittle structures arranged in NS dextral corridors.