Interest in mineral–microbe interaction has grown enormously over recent decades, providing information in a puzzle-like manner which points towards an ever increasingly intimate relationship between the two; a relationship that can be truly termed co-evolution. Clay minerals play a very central role in this co-evolving system. Some 20 years ago, clay scientists looked at clay mineral–microbe studies as a peripheral interest only. Now, can clay scientists think that they understand the formation of clay minerals throughout geological history if they do not include life in their models? The answer is probably no, but we do not yet know the relative weight of biological and inorganic factors involved in driving clay-mineral formation and transformation. Similarly, microbiologists are missing out important information if they do not investigate the influence and modifications that minerals, particularly clay minerals, have on microbial activity and evolution. This review attempts to describe the several points relating clay minerals and microorganisms that have been discovered so far. The information obtained is still very incomplete and many opportunities exist for clay scientists to help to write the real history of the biosphere.

/pdf/clay-minerals-interaction-with-microorganisms-a-review-2sfh67ilmk.pdf

Clay minerals interaction with microorganisms: a review

X-Ray Diffraction by Disordered Lamellar Structures

ABSTRACT The diagenetic history of the Neogene clastic sediments of the Bengal Basin is described based on petrological analysis of samples from four boreholes. In the shales evidence has been found of progressive illitization of the mixed-layer illite-smectite with increasing depth of burial. Unlike other studies, notably of the Tertiary Gulf Coast sediments, there is no evidence of the illite-smectite changing from a random to a regular mixed-layer phase during diagenesis. Other diagenetic changes in the shales include the decrease in the proportions of kaolinite and calcite with increasing burial. Diagenesis in the sandstones principally involves the progressive development of various types of cements in the following order: chlorite authigenesis, siderite crystallization, illite rim formation, quartz overgrowths, and late Fe calcite cements. After the formation of the cementation phases, there was a dissolution phase creating secondary porosity via the dissolution of carbonate and feldspars, and this was accompanied by the generation of a late kaolinite-cementing phase. The latter processes are thought to arise from the generation of acidic pore waters generated by the maturation of organic matter in the Neogene and Paleogene shales. In some of the sandstones, an early poikilotopic Fe calcite cement formed and halted further diagenesis beyond the formation of the chlorite and early siderite crystallization.

Diagenesis in the neogene clastic sediments of the Bengal basin, Bangladesh

The Main Glauconite Bed (MGB) is a pelleted greensand located at Stone City Bluff on the south bank of the Brazos River in Burleson County, Texas. It was deposited during the Middle Eocene regional transgression on the Texas Gulf Coastal Plain. Stratigraphically it lies in the upper Stone City Member, Crockett Formation, Claiborne Group. Its mineralogy and geochemistry were examined in detail, and verdine facies minerals, predominantly odinite, were identified. Few glauconitic minerals were found in the green pelleted sediments of the MGB. Without detailed mineralogical work, glaucony facies minerals and verdine facies minerals are easily mistaken for one another. Their distinction has value in assessing paleoenvironments. In this study, several analytical techniques were employed to assess the mineralogy. X-ray diffraction of oriented and un-oriented clay samples indicated a clay mixture dominated by 7 and 14A diffraction peaks. Unit cell calculations from XRD data for MGB pellets match the odinite-1M data base. Electron microprobe analyses (EMPA) from the average of 31 data points from clay pellets accompanied with Mossbauer analyses were used to calculate the structural formula which is that of odinite: Fe3+0.89 Mg0.45 Al0.67 Fe2+0.30 Ti0.01 Mn0.01) Σ = 2.33 (Si1.77 Al0.23) O5.00 (OH)4.00. QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) data provided mineral maps of quantitative proportions of the constituent clays. The verdine facies is a clay mineral facies associated with shallow marine shelf and lagoonal environments at tropical latitudes with iron influx from nearby runoff. Its depositional environment is well documented in modern nearshore locations. Recognition of verdine facies clays as the dominant constituent of the MGB clay pellets, rather than glaucony facies clays, allows for a more precise assessment of paleoenvironmental conditions.

/pdf/mineralogy-and-geochemistry-of-the-main-glauconite-bed-in-3f37g1u0za.pdf

Mineralogy and Geochemistry of the Main Glauconite Bed in the Middle Eocene of Texas: Paleoenvironmental Implications for the Verdine Facies

Reservoir sandstones in the Mid- and South Tapti gas fields in the Surat Depression (Mumbai Offshore Basin, western India) have been investigated using a range of petrographic techniques, isotope geochemistry and basin modelling. Authigenic chlorite is abundant in the shallow-marine sandstones of the Miocene Mahim Formation, a major reservoir rock in the Mid- and South Tapti fields, which are described here in terms of their quality and diagenetic characteristics. The sandstones are currently at burial depths of between ∼1500 and 2800m. The authigenic chlorite has had a significant impact on the resulting reservoir quality of the sandstones and is interpreted to have originated as odinite clay of the verdine facies that replaced faecal or pseudo-faecal pellets, together with volumetrically small but abundant grain coatings and grain rims, and formed at the site of major riverine iron influx onto the shallow-marine shelf during periods of relatively low sea level. Pellets have been variably compacted to form pseudomatrix. Reservoir sandstones from similar depositional settings on the west coast of India or other sub-tropical settings are likely to exhibit comparable diagenetic effects on reservoir quality.

Compositionally, the chlorite is the iron-rich form known as chamosite. The chemistry of all the chlorite morphologies is the same in all studied samples. Oxygen isotope analyses of carbonate cements in the Mahim Formation sandstones have provided an approximate temperature framework for diagenesis of the non-carbonate cements. Oxygen isotope results for the chlorite, however, suggest much higher temperatures than its position in the paragenetic sequence would warrant. These results suggest that the clay formed first as 1:1 layer clays, in this case odinite, which were then transformed to Fe-chlorite as burial depths and temperatures increased.

Reservoirs in the Mahim, Daman and Mahuva Formation sandstones are thus greatly influenced by the diagenesis of authigenic chlorite and locally by the precipitation of carbonate cements. Reservoir quality is good where thick, continuous chlorite rim cements are present and where chlorite pellets are sufficiently indurated for them not to be compacted. Chlorite rim cements have reduced the extent of quartz overgrowth cementation in the sandstones.

The nature and origin of authigenic chlorite and related cements in oligo–miocene reservoir sandstones, tapti gas fields, surat depression, offshore western india

The Weches Formation of the Claiborne Group (Eocene) in northeast Texas consists of clayey sandstones and mudrocks, both with variable proportions of dark green to brown clay peloids deposited in a marginal to open marine setting on the Gulf Coast margin. The composition of the dark green peloids, from two localities, has been investigated using X-ray diffraction, back-scattered electron microscopy with X-ray analysis, electron energy-loss spectroscopy (EELS), Mossbauer spectroscopy, chemical analysis and Fourier transform infrared spectroscopy. These peloids were previously described on the basis of their color as glauconite (Yancey and Davidoff, 1994); our results, however, show that the dark green indurated pellets are predominantly composed of mixed-layer clays with a high proportion of Fe-rich 7 A serpentine layers coexisting with a mixed-layer phase containing glauconite, nontronite and vermiculite layers, in addition to discrete illite and kaolinte. Analyses by EELS of single particles with a chemical composition consistent with them being the Fe-rich clay indicate that the Fe is >95% ferric, while Mossbauer analyses of the bulk magnetically separated fraction for the same samples indicates a ferric iron content of ~60–70%, despite the variable relative proportions of expandable and 7 A layers. Taking into account that there is a significant amount of 2:1 layers containing ferric Fe, we interpret these data as indicating that the Fe in the 7 A layers has a significant amount of Fe2+ even taking into account the high ferric Fe ratio from the EELS analysis when the coexisting 2:1 layers are considered. Thus, these 1:1 layers are closer to berthierine in composition than to odinite. The vermiculite layers in the Texas clay may indicate partial ‘verdinization’ of expandable 2:1 clay. A possible reaction is smectite → vermiculite → berthierine-like phase. We estimate a temperature of 20°C for the seawater in which the Texas clay formed, the lower end of the range for modern occurrences of odinite.

http://petroclays.com/publications/Huggett-et_al-CandCM-2006.pdf

C. C. Calvert

Papers

Serpentine-nontronite-vermiculite mixed-layer clay from the weches formation, claiborne group, middle eocene, northeast texas