Diagenesis in shales from a partly overpressured sequence in the Gulf Coast, Texas, USA

Shaw, H. F.; Primmer, T. J.

doi:10.1016/0264-8172(89)90015-9

Cited by 16 publications

(10 citation statements)

References 7 publications

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“…Furthermore, the error envelope for the illite composition plots in a similar fashion to the cluster of AEM data for the Bothamsall data (Fig. 2b) and the data populations for illite-smectites (Velde & Nicot, 1985;Shaw & Primmer, 1989;Huff et al, 1988) and micas (Dudoignon et al, 1988). Note that the error envelopes capture only 67, 95 and 97% of calculated data points, and outliers in real data sets will fall outside the Table 1 represented on the three standard clay diagrams: (a) Si-AI-K, (b) Velde (1977) coordinates, (c) MCP.…”

Section: Calculated Analytical Errorssupporting

confidence: 57%

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The Influence of analytical error upon the interpretation of chemical variations in clay minerals

Warren¹,

Ransom²

1992

Clay miner.

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Understanding the chemical variability of clay minerals depends on the analytical reliability of the techniques used. Uncertainties in clay mineral compositions were computed for common sources of analytical error such as those that arise from contaminant phases present in clay size-fractions in concentrations below the detection limit of routine XRD screening techniques, and the analytical limits of precision for TEM/AEM analysis. When plotted on standard diagrams used to represent clay mineral compositions, the calculated error envelopes were found to be of significant size, such that analyses of pure illites and pure smectites straddled the field for mixed-layered illite-smectites. In addition, on some diagrams random analytical errors resulted in linear trends identical to those caused by mixtures of two or more clay minerals. It follows that variations in the compositions of clay minerals reported in the literaure do not always necessarily represent the actual chemical variation of the minerals. As a result, current interpretations of clay compositional variations may not be as definitive as hoped.

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Section: Calculated Analytical Errorssupporting

confidence: 57%

“…2b) form a distinct linear trend. Similar trends have been interpreted as representing mixtures of pure illite and a mixed-layer illite-smectite, smectite or kaolinite (Velde, 1984;Velde & Nicot, 1985;Dudoignon et al, 1988;Huff et al, 1988;Shaw & Primmer, 1989). Similarly, on the MCP diagram (Fig.…”

Section: Apparent Compositional Variation Of Clay Mineralssupporting

confidence: 52%

The Influence of analytical error upon the interpretation of chemical variations in clay minerals

Warren¹,

Ransom²

1992

Clay miner.

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“…They noted evidence for this reaction in the XRD results of Hower et al (1976), in which the total of illite plus smectite decreases as illitization proceeds. Other evidence for this Al-conserving reaction is provided by microprobe determinations of clay compositions in shales from the Frio formation (Shaw and Primmer 1989). These analyses found that deeper, illitic, mixed-layer clays actually contained slightly less A1 than shallower, more smectitic mixed-layer clays.…”

Section: Introductionmentioning

confidence: 92%

Smectite Illitization in Pliocene-Age Gulf of Mexico Mudrocks

Rask

Bryndzia

Braunsdorf

et al. 1997

Clays and clay miner.

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Abstract--Utilizing high-resolution transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques, we have studied the transition from shallower smectite-rich mudrocks to deeper illite-rich mudrocks in Pliocene-age turbidite sediments from the northern Gulf of Mexico (GOM). Our objective in this work was to better understand how the smectite-illite transition may affect the onset of geopressuring in GOM sediments. The samples studied were sidewall cores from an offshore Louisiana well. In previous studies of GOM sediments, the smectite-to-illite reaction has mainly been documented in considerably older, Miocene-age sediments.The results of this study elucidate the reaction mechanisms entailed in the transformation of clays in this sediment from smectitic to illitic. We found that illite formed at the expense of smectite in 2 ways: 1) growth of preexisting discrete illite flakes, and 2) creation of new illite layers within mixed-layer illitesmectite. Also, illitization apparently proceeded via a dissolution/precipitation, Al-conserving reaction rather than a solid-state, layer-conserving reaction. Smectite illitization is commonly believed to require input of K from feldspar dissolution. Our XRD results found little correlation between decreases in K-feldspar and increases of illite. However, in 1 instance TEM/EDS analyses indicated the presence of high-charge smectite, which suggests that insufficient K was available for illitization. TEM images also show small packets of authigenic chlorite in illite-rich mudrock. This chlorite may act as a sink for Fe liberated upon smectite illitization.

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“…Similarly, it is pointed out here that such great detail was given to mineralogy and chemistry of specific parts (individual size fractions) in the study by Hower et al (1976), that little consideration was given to the whole (the bulk shale). Moreover, although subsequent studies of the smectite-toillite reaction documenting changes with depth in one or more specific size fractions have monitored corresponding mineralogical changes in the bulk rock (e.g., Boles and Franks, 1979;Pollastro, 1985;Jennings and Thompson, 1986;Awwiller, 1993), others have not (e.g., Shaw and Primmer, 1989). Boles and Franks (1979) first related bulk-shale composition in CWRU6, in part, to smectite illitization by calculating the weight percent of 1/S in the bulk rock for the five samples of cuttings analyzed for particle size distribution by Hower et al (1976).…”

mentioning

confidence: 99%

Clay Diagenesis and Mass Balance—The Forest and the Trees

Pollastro

1994

Clays and clay miner.

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Diagenesis in shales from a partly overpressured sequence in the Gulf Coast, Texas, USA

Cited by 16 publications

References 7 publications

The Influence of analytical error upon the interpretation of chemical variations in clay minerals

The Influence of analytical error upon the interpretation of chemical variations in clay minerals

Smectite Illitization in Pliocene-Age Gulf of Mexico Mudrocks

Clay Diagenesis and Mass Balance—The Forest and the Trees

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