Open-system chemical behavior in deep Wilcox Group mudstones,Texas Gulf Coast,USA
Ruarri J.Day-Stirrat a ,*,Kitty https://www.doczj.com/doc/f43069007.html,liken a ,Shirley P.Dutton a ,Robert G.Loucks a ,Stephen Hillier b ,Andrew C.Aplin c ,Anja M.Schleicher d
a
Bureau of Economic Geology,Jackson School of Geosciences,The University of Texas at Austin,University Station,Box X,Austin,TX 78713,USA b
Macaulay Institute,Craigiebuckler,Aberdeen,AB158QH,UK c
School of Civil Engineering and Geosciences,Drummond Building,Newcastle University,Newcastle upon Tyne,NE17RU,UK d
Department of Geological Sciences,University of Michigan,C.C.Little Building,425E.University Ave.,Ann Arbor,MI 48109,USA
a r t i c l e i n f o
Article history:
Received 27April 2010Received in revised form 4August 2010
Accepted 21August 2010
Available online 27August 2010Keywords:Mudstone Wilcox Group Illite e smectite Element mobility
a b s t r a c t
Wilcox Group mudstones have been mechanically and geochemically transformed over a temperature range of 20e 200 C.Our research controlled for provenance and age by sampling from ?ve wells,parallel to the paleodepositional axis,all within the Houston delta system.Across the sampled depths,mudstone porosity has been reduced from w 25to <10%and bulk mineralogical change as documented by quan-titative X-ray diffraction includes decreases in quartz,K-feldspar and kaolinite content whereas illite tillite àsmectite,chlorite,and plagioclase increase.These mineral transformations transfer elements at a scale of less than 1mm from one mineralogical form to another,however,X-ray ?uo-rescence data suggest that among major elements only Al 2O 3and TiO 2are fully conserved within the system (trace-element ZrO 2is also conserved).K 2O has been added to and SiO 2released from the Wilcox Group mudstones.Cathodoluminescence and secondary electron imaging did not ?nd this SiO 2locally precipitated.We,therefore,document an open-system geochemical behavior.
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1.Introduction
Consolidation of mud into mudstone during burial involves both mechanical (Athy,1930;Hedberg,1936;Bj?rlykke,1999;Mondol et al.,2007,2008)and chemical processes (e.g.Burst,1959;Boles and Franks,1979;Awwiller,1993;Eberl,1993;Land et al.,1997;Lynch et al.,1997;Srodon et al.,2006)causing profound alterations of mudstone physical properties (Katsube et al.,1991;Aplin et al.,2006;Day-Stirrat et al.,2008;Peltonen et al.,2008).The processes that governporosity reduction in shallow buried sediments have been described by a variety of consolidation trends controlled by lithology (see Mondol et al.,2007for curves).At temperatures above w 80 C (<2km)consolidation processes move from solely mechanical means into a mix of mechanical and mineralogical transformations (Bj?rlykke and Hoeg,1997),the chemical processes being governed principally by dissolution and precipitation reactions.The smectite-to-illite transformation is the best documented reaction (Burst,1959;Hower et al.,1976;Boles and Franks,1979;Awwiller,1993;Berger
et al.,1997;Lynch et al.,1997)and its role in permeability decrease (Nadeau et al.,1985,2002;Freed and Peacor,1989,1992)and mudstone anisotropy (Ho et al.,1999;Aplin et al.,2006;Day-Stirrat et al.,2008;Haines et al.,2009)is well studied.Kaolinite loss (Lanson et al.,2002;Milliken,2004;Meunier,2005)and K-feldspar dissolution (Hower et al.,1976;Boles and Franks,1979;Awwiller,1993;Milliken,2004)with increasing temperature are signi ?cant reactions in many basins.The latter is often cited as the potassium source for the smectite-to-illite transformation.It is well established that smectite dissolution in the presence of a potassium source precipitates illite and releases silica but where this quartz precipitates is still an open question.Proponents of a system open to elemental transport between mudstones and sandstones interpret quartz being transported from mudstones and precipitated into adjacent sand-stones (Boles and Franks,1979;Land et al.,1987;Awwiller,1993;Lynch et al.,1997;Land and Milliken,2000).A discussion of global silica/alumina in mudstones appears to de ?ne silica release rather than local precipitation (van de Kamp,2008).However,new data point to silica remaining in the mudstone system (Peltonen et al.,2008;Thyberg et al.,2010)as micro-quartz cements.
Perhaps the key to untangling whether silica remains in mudstones or is exported to adjacent sandstones is to return to
*Corresponding author.Tel.:t151********.
E-mail address:Ruarri.Day-Stirrat@https://www.doczj.com/doc/f43069007.html, (R.J.
Day-Stirrat).Contents lists available at ScienceDirect
Marine and Petroleum Geology
journal ho mep age:www.elsevier.co m/lo cate/marp
etgeo
0264-8172/$e see front matter ó2010Elsevier Ltd.All rights reserved.doi:10.1016/j.marpetgeo.2010.08.006
Marine and Petroleum Geology 27(2010)1804e 1818
studies of elemental transport and,speci?cally,the role of potas-sium and aluminum in mudstones.Therefore,we use geochemical, mineralogical and petrographical information from a series of mudrock samples buried to temperatures between20and200t C to examine element transport.Although variation in the initial composition of sediments is inevitable,we attempted to minimize compositional variation by selecting samples from wells that are distributed parallel to the paleodepositional axis.The dataset is source-and age-equivalent,and we employ a quartz-normalizing procedure to whole-rock X-ray?uorescence data that allows documentation of element trends in clay minerals and feldspars free of the heterogeneity of detrital quartz.Although this approach sheds light on the openness of the system,relative timing is less clear and establishing it requires petrographic data.Most clay minerals are below the resolution of thin-section petrography,but we present some petrographic and electron-microscope images and X-ray maps to further illuminate the mineralogical and elemental system.
2.Samples and geological setting
The Upper Paleocene and Lower Eocene Wilcox Group repre-sents the?rst major regional siliciclastic wedge built over and beyond the Cretaceous carbonate shelf of the Texas Gulf Coast in the Cenozoic(Galloway et al.,2000).In Texas,the Wilcox Group produces hydrocarbons along a strip paralleling the coastline from the Louisiana-Texas state line to the Mexican border;the lower Wilcox outcrop parallels this farther inland.Wilcox Group sand-stones are currently exploration targets at depths of4e9tkm onshore,on the shelf,and in deep waters of the Gulf of Mexico basin.Wilcox Group thicknesses range from w300m in outcrop (Bebout et al.,1992)to>3000m in the deep subsurface under the current position of the Gulf of Mexico coastline.Regional well log correlations suggest that mudstones form the bulk(w70%)of the group(Dodge and Posey,1981).Siliciclastic deposition occurred on a broad,?at,low-lying coastal plain with drainage axes approxi-mately comparable to the modern day drainage pattern(e.g. Galloway and McGilvery,1995;Galloway et al.,2000;Galloway, 2005and references therein).Laramide uplands and source areas from the Rocky Mountains provided the source material to the updip?uvio-deltaic depositional environments interpreted in the Houston delta system and slope e fan complexes downdip(Dutton and Loucks,2010).
Uplift and erosion of the Wilcox Group inland from the present coastline of the Gulf of Mexico were discussed by Dutton and Loucks(2010)and references therein.In the updip part of the study area,they inferred,on the basis of huminite re?ectance(Ro) data and thickness of younger sediments farther downdip that
Table1
Well name,API number,operator,county,present-day burial depth,and modeled temperature.
Well Name API No.Operator County Depth[m]Temp C
TOH-2AO Hydrologic Test Well e Law Engineering
Testing Company
Leon297e71222e23 Selected Lands#7e e Grimes2724e2728102e102 #48Lake Creek Unit423393085700Mobil Montgomery3487e3535118e119 M.D.Hallson422010787700Texaco Harris4266e5066168e190
#1W.L.Crews420393129200ARCO Brazoria5777e6596187e
210
Fig.1.Locations of the Wilcox Group mudstone samples in the Houston delta system.Location of the Wilcox group outcrop is depicted.A)Law Engineering Testing Company TOH-2AO hydrologic test well,Leon County;B)#7Selected Lands,Grimes County;C)Mobil#48Lake Creek Unit,Montgomery County;D)Texaco M.D.Hallson NTC-1,Harris County;E)ARCO#1W.L.Crews well,Brazoria County,Texas(See Table1).
R.J.Day-Stirrat et al./Marine and Petroleum Geology27(2010)1804e18181805
w300m of Wilcox Group sediments may have been removed. Closer to the coast the Wilcox Group is assumed to be at its maximum burial depth(Fisher and Land,1986).Burial histories, therefore,are simple subsidence pro?les.Calculated geothermal gradients in wells used by Dutton and Loucks(2010)in their study of Wilcox Group sandstones range from28to42 C/km,and,as a consequence,these workers opted to discuss diagenesis in terms of temperature rather than depth.We apply corrected bottom-hole temperatures using a time-since-circulation method(Corrigan,2003)and a commercially available1-D thermal model to constrain temperature for each sample depth.The result is only a small,insigni?cant difference between the temperature data presented here and that of Dutton and Loucks(2010),who calcu-lated temperature on the basis of geothermal gradients that had been calculated from corrected bottom-hole temperatures (Corrigan,2003)from the appropriate logging run.The basinwide geothermal gradient as mapped by DeFord et al.(1976),Nagihara and Jones(2005),and Forrest et al.(2007)shows an increase
in
Fig.2.BSE images and associated X-ray maps for potassium,iron,magnesium and sodium for samples Cr08at187 C(Fig.2a)and Cr10at187 C(Fig.2b)from ARCO#1W.L.Crews well,well E in Fig.1.Figure modi?ed from Day-Stirrat et al.(2010)and temperature based on present-day corrected bottom-hole temperatures.
R.J.Day-Stirrat et al./Marine and Petroleum Geology27(2010)1804e1818
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temperature westward along the Louisiana coast and a continual increase down the Texas coast to the South Texas onshore study area of Bodner et al.(1985)and Bodner and Sharpe (1988).Addi-tionally,geothermal gradient increases progressively onshore and decreases offshore.Discussion of our data in terms of temperature is appropriate.
Core material was sampled from ?ve wells (Table 1)on a tran-sect (Fig.1)perpendicular to the coastline and parallel to the paleodepositional axis (Galloway et al.,2000),with geothermal gradient increasing updip.Samples are from the Houston delta system (Fisher and McGowen,1967;Galloway et al.,2000)and are ?uvio-deltaic updip and marine slope fan in the downdip age equivalents.Wilcox Group samples are,therefore,source and age equivalents.Cores were half slabs of conventional core (4.5inches in diameter),and material was collected from the mudstone and siltstone horizons.Mudstone core samples (2?4?4cm)were
taken for X-ray powder diffraction (XRPD),as well as,optical microscopy,backscattered electron microscopy,X-ray mapping,and cathodoluminescence.The subsample for XRPD separation was used for X-ray ?uorescence,and a further 1-cm 3plug was used for mercury porosimetry.In hand specimens,core material shows signs of soft-sediment deformation (slump structures).Samples are well indurated and non ?ssile.3.Methods
3.1.Mercury porosimetry
Porosities and pore size distributions were determined on a 1g block of sample that was freeze dried (Delage and Lefebvre,1984)for 24h,then dried in an oven at 105 C for a further 24h.Freeze drying processes manipulate temperature and pressure conditions and effectively eliminate surface tension forces and,therefore,no shrinkage of the sample by the dehydration of illite e smectite is expected (Romero and Simms,2008).Porosities were calculated from dry bulk density (r d )and grain density (G s ):
f ?1à
r d
G s
Grain density was measured on samples dried at 105 C using the “Small Pyknometer Method ”.Dry bulk density was calculated from the bulk volume of the known mass of sample used in the process of measurement of pore size distribution using the mercury intrusion technique.Pore size distributions were determined on a Micromeritics óAutopore P 9220.Pore diameters were calculated from the mercury intrusion data.The analysis used the assumption that the surface tension of mercury was 0.48N/m and the contact angle between mercury and the particle surface was 141 .Pore radius,r ,is given by
r ?
746;000
p
where r is the pore throat radius (nm)and p is the pressure in kPa.3.2.Backscattered electron microscopy and X-ray mapping
Thin sections for backscattered electron microscopy (BSE)observations were prepared perpendicular to bedding.Thin sections for BSE were polished to a microprobe ?nish following
surface
Fig.3.Top,annotated backscattered image of Wilcox Group sandstone (6594.7m/210 C)adjacent to mudstone sample.Lower four images are X-ray maps of potassium,magnesium,sodium and iron.Samples from well E,Fig.1.
10203040
Plagioclase composition (An%)
Fig.4.Plagioclase composition of shallow (well A in Fig.1)and more deeply buried (well E in Fig.1)Wilcox Group mudstones.
R.J.Day-Stirrat et al./Marine and Petroleum Geology 27(2010)1804e 18181807
Fig.5.Cathodoluminescence of variable color and intensity in detrital quartz grains in Wilcox mudrock.Non-quartz grains are labeled:d ?dolomite,f ?feldspar,L ?lithic grain.Rare instances of overgrowth-like textures (white arrows),are variable in color and highly discontinuous distribution on grain surfaces.Circular spots,bright or dark,are beam damage created by a ?xed beam.Cathodoluminescence/secondary electron images.Samples from well E,Fig.1.
R.J.Day-Stirrat et al./Marine and Petroleum Geology 27(2010)1804e 1818
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impregnation with a low-viscosity medium.We used a JEOL8200
Microprobe equipped with an energy dispersive detector(EDS)and
a backscattered electron detector.The machine was operated at
15kV and12e15nA,with a spot size of1m m and a working distance of w11mm in backscattered mode.X-ray maps were collected for
sodium,magnesium,iron,and potassium.A focused1-m m spot with a15-kV accelerating voltage and a30-nAmp current on brass was
used for mapping.Elements were mapped using wavelength
dispersive spectra over a1024-?1024-pixel grid,with1pix-
el?1m m.The X-ray maps were rendered as false color images,and consistent levels were used from sample to sample so that qualita-
tive assessments of abundance could be made.
3.3.Cathodoluminescence
Cathodoluminescence(CL)and secondary electron(SE)imaging
were performed on polished carbon-coated thin sections using
a Gatan Chroma CL detector mounted on an FEI Nova Nano?eld-
emission SEM.In thin sections of this type,silt particles of quartz,
feldspar,and dolomite display more highly polished surfaces than
surrounding clay-sized particles that are dominated by micas and
clay minerals,and grain boundaries can be seen most clearly in SE
images.CL imaging data for small quartz crystals in this type of
sample,imaged on this type of system,contain a substantial
background component(i.e.,they are‘noisy’and lack sharpness).
By combining CL and SE data(inherently less noisy)into a multi-
channel image,variations of CL with respect to grain boundaries
can be seen with greater clarity.Multichannel images presented in
this paper contain an approximately equal component of CL and SE
and have been enhanced for contrast and saturation but not color
balance.A variety of factors affect color in images of this type,
including carbon-coat thickness and scan speed;colors in these
images should be considered close to true but are not exact
renditions of what would be seen in direct visual observation.
3.4.Electron microprobe analysis
Detrital feldspars in four samples were analyzed using wave-
length dispersive spectrometry on a JEOL8200microprobe in the
electron microbeam laboratory of the Department of Geological
Sciences at the University of Texas at Austin.Accelerating voltage
was15KV,sample current was12nA(measured on brass),beam
diameter was10m m,and count times were20s for all elements. Standards used Amelia albite(Na),orthoclase(K,Si),and anorthite
glass(Ca,Al).
3.5.X-ray powder diffraction(XRPD)
Mineralogical analyses by X-ray powder diffraction(XRPD)
methods were performed on the whole-rock bulk samples and on <2-m m clay-sized fractions obtained by gentle crushing,disaggre-gation,dispersion,and timed sedimentation.For the whole-rock
analysis,samples were prepared by McCrone milling of3g of
sample in water,followed by spray drying of the resulting slurry to
obtain random powder specimens,as described by Hillier(1999,
2002).Clay-sized fractions were prepared by mounting the clay
onto glass slides using a?lter-peel-transfer method to obtain
highly oriented specimens(Moore and Reynolds,1997;Hillier,
2003).All XRPD patterns were recorded on a Siemens D5000X-
ray diffractometer using Co K a radiation,which was selected by a diffracted-beam graphite monochromator.Whole-rock samples were scanned from2to75 2Q,counting for2s per0.02 step.Clay fractions were scanned from2to45 2Q,counting for1s per0.02 step in the air-dried state,following glycolation by an overnight vapor pressure method,as well as heating to350 C for1h.Quantitative mineralogical analysis of the whole-rock data was made by a full-pattern?tting,using the normalized reference-intensity-ratio method,as described in Omotoso et al.(2006). Uncertainty for quartz determination by XRD at95%con?dence is given by X^0.35where X is the measured concentration(wt%)see Hillier(2003)for further details of the RIR method.Potassium feldspar(K-feldspar)lower limit of detection,by the RIR method (Hillier,2003),is estimated at0.5to0.7wt%at95%con?dence in measured patterns.Detailed identi?cation of clay minerals in the clay-sized fraction was made according to procedures given in Moore and Reynolds(1997)and Hillier(2003).
3.6.X-ray?uorescence analysis
X-ray?uorescence was analyzed for major and trace elements by a single-bead(2:1tetraborate beads),low-dilution-fusion technique as outlined in Johnson et al.(1999).All analyses were run at Washington State University GeoAnalytical Laboratory on a Rigaku XRF Spectrometer.A rhodium(Rh)target was run at50kV/ 50mA,with full vacuum and a25-mm mask for all elements. Concentrations of elements in the samples were measured in a comparison between X-ray intensity for each element and intensity for the sample element in two of nine USGS standard samples and two pure-vein-quartz beads as blanks.Intensities of each element were corrected automatically for line interference and absorption effects owing to all the other elements using the fundamental parameter method(Johnson et al.,1999).Precision was checked between every28unknown samples following two internal standards.Oxidation state of iron is not measured in the Washington State University GeoAnalytical Laboratory protocol, and,therefore,all iron is expressed as FeO and normalized to100%. Loss on ignition(LOI)was measured and normalized out of the dataset.Volatiles are independent of X-ray analysis,and all
results
Fig.6.Possible quartz overgrowth cement(Qc)on quartz grains(Qg)within a silt-rich lamina in a Wilcox mudrock.Yellow ovals indicate regions where the spatial rela-tionship of the cement and the pyrite framboids(white spheres)can be examined. Cathodoluminescence/secondary electron image.Samples from well E,Fig.1.(For interpretation of the references to colour in this?gure legend,the reader is referred to the web version of this article).
R.J.Day-Stirrat et al./Marine and Petroleum Geology27(2010)1804e18181809
are on a volatile-free basis (Johnson et al.,1999).Estimates of the accuracy of SiO 2in X-ray analysis are between 0.02and 0.67wt%with accuracy increasing with increasing SiO 2(Johnson et al.,1999).3.7.Quartz-normalization procedure
Because volatile-free,major-element geochemistry in mudstones is dominated by silicon (e.g.Mumme et al.,1996;Rowe et al.,2008),all elemental trends are in ?uenced by the two largest silicon-bearing mineral groups,quartz and clay minerals.In order to extract elemental tends in samples in which detrital quartz is
a dominant component,we employed a quartz-normalization procedure in which XRPD-quanti ?ed quartz (assumed to be 100%SiO 2)is removed from the XRF data,which are then renormalized to 100%.Silicon that remains is in clay minerals,and minor amounts are in feldspars.In normalizing for quartz,we make the assumption that all quartz in our dataset is detrital in origin,while conceding that this assumption is controversial (e.g.see Peltonen et al.,2008).However,four mudstone samples from temperatures of w 50 C and 190 C (well A and E Fig.1)were viewed using cath-odoluminescence at The University of Texas at Austin in order to image quartz overgrowths.No quartz overgrowths were found,possibly because (1)there was an image resolution issue or (2)there were no quartz overgrowths to be observed in Wilcox Group mudstones.We assume that no quartz overgrowths are present and assert that all quartz is detrital and may be normalized out of a discussion of element trends within our dataset.4.Results 4.1.Petrology
BSE images presented in Fig.2document the range of textures found in samples from the hottest Wilcox Group mudstones.Potassium maps act as a proxy for the distribution of potassium-bearing clays (illite and mica),as well as K-feldspar.Differentiation between feldspars and sheet silicates is based on shape;illite and mica are platy,whereas K-feldspar is more equant.Platy phyllosi-licates are seen to be oriented perpendicular to maximum vertical effective stress (Fig.2),with this relationship becoming less de ?ned at the contact with the coarser,quartz-rich truncation.Iron maps delineate the distribution of large,presumably detrital,chlorite grains.Smaller platy iron-bearing grains are possibly authigenic chlorite.Fe-rich crystals of equant form are pyrite.Chlorite in the matrix of the ?ne-grained fraction is also picked out by magnesium maps,along with isolated dolomite crystals.In the silt-rich zone (Fig.2B),iron also describes the distribution of Fe-dolomite cement.Fe-dolomite is visible only between coarse grains in the silt-rich zone and is not present in the ?nest-fraction.Sodium,present in albite,decreases in abundance with decreasing grain size and cannot be imaged in clay-sized material.
The mineralogy of adjacent sandstones is largely similar to the mudstones of the Wilcox group.A signi ?cant difference lies in the abundance of chlorite and Fe-dolomite,where Fe-dolomite commonly replaces albite in sandstones.The ‘reaction front ’between albite and ankerite forms a euhedral ankerite crystal face,and X-ray maps for iron and magnesium highlight this growth pattern (arrow in Fig.3).
Table 2
Clay percentage based on total clay mineral wt%from XRD data (X denotes no information).Total porosity calculated from MICP.R mean ?mean pore-sized diameter in nanometers.Sample TOH2TOH14TOH20TOH21TOH24SL8SL10Depth (m)300.2410.4455.4472481.22728.12728.6Clay (%)
33.240.539.9X 41.735.134.8Total porosity 292125202676r _mean (nm)43434820273726Sample LC4LC13LC17LC24LC31HA5HA7HA19HA30Depth (m)3488.13491.33494.8
3504.23517.94274.54970.14876.55065.6Clay (%)
64.849.16474.5X X 53.943.9Total porosity 432335675r _mean (nm)41075151215914Sample CR10CR17CR21CR26CR28CR29CR31CR36CR37Depth (m)5780.35788.55794.26357.66358.86361.56585.66594.16594.7Clay (%)
X X X X X X X X X Total porosity 9879891069r _mean (nm)
11
7
10
11
13
12
15
11
10
Fig.7.Porosity from volume and bulk density.
R.J.Day-Stirrat et al./Marine and Petroleum Geology 27(2010)1804e 1818
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Microprobe analysis (Fig.4and Table 3)reveals a detrital feld-spar assemblage in the shallower portion of the Wilcox Group that includes a substantial amount of plagioclase that ranges in composition from the pure Na-end-member to Na-rich andesine (Table 3).Grains in the compositional range of authigenic albite make up around 10percent of the plagioclase https://www.doczj.com/doc/f43069007.html,position of the detrital feldspar assemblage in these shallower samples is consistent with the dominantly metamorphic and older sedimen-tary provenance that is indicated by the lithic grain types in the associated sandstones (Dutton et al.,2009).
In the deeper samples,at temperatures approaching 200 C,the detrital feldspar assemblage within the Wilcox Group mudstones is prominently altered,again consistent with ?ndings for associated sandstones (Dutton et al.,2009).K-feldspar and the more Ca-plagioclase grains have been lost from the population.Around 40percent of the remaining grains are within the compositional range of authigenic albite,and the remainder has an average composition of approximately An 5,ranging as high as An 15.
CL images reveal quartz silt particles having a variety of colors,CL intensities,and CL fabrics (Fig.5).The most common color is uniform red-brown.Other common color/intensity combinations are bright-light-blue,darker-blue,and bright-mauve.CL variations within individual grains range from uniform to highly mottled.Apparent fracture ?lls are common and typically appear as dark-reddish quartz within blue or mauve grains.A minority of grains have discontinuous external zones of darker,luminescing quartz,which in some cases is blue and in others red or red-brown.
To determine the character of any quartz cement that is poten-tially associated with these mudrocks,a silt-rich lamina was examined closely.This silt-rich zone (see Fig.2B,sample at w 200 C)is very thin (<1mm)and still generally clay rich,although it contains silt in greater abundance and of larger size than that of the surrounding mud.A few occurrences of possible quartz cement were located (Fig.6)on the basis of intergrowth relationships between cement crystals nucleated on adjacent grains.4.2.Porosity
Total porosity in Wilcox Group mudstones calculated from mercury-injection data generally decreases with increasing temperature (Fig.7and see Table 2for depths).Porosities in the lowest temperature samples average 25%,consistent with samples buried to w 400m (see Mondol et al.,2007their Fig.3).The deeper mudstone samples have <10%porosity,with samples from moderate temperatures having the lowest porosity (w 3%),which correlates to the highest clay-mineral content (according to XRPD analysis).Marginally higher porosities are recorded in the hottest samples,correlating with increased quartz contents in these
samples.
Fig.8.Whole rock mineralogical compositions (XRD)as a function of maximum burial temperature for the Wilcox Group mudstones.
Table 3
Feldspar chemistry.Sample T ( C)n P/(P tK)1x Or 2Ab/F 3x An 4x (An-Ab)5UTB 1839550.5393.20.119.411.7UTB 1233510.4589.50.0814.317.0CR 0818748 1.00e 0.38 1.7 3.5CR 20
187
44
1.00
e
0.42
2.1
6.6
a Plagioclase/total feldspar.
b Average Orthoclse content in K-feldspar.
c Albite (>Ab 98)/total feldspar.
d Averag
e anorthite content.
e
Average anorthite content excluding albite.
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4.3.Mineralogy
Quartz is relatively abundant in most samples of Wilcox Group mudstones(30e40%).In whole-rock quanti?cation,it generally decreases from35to60%at w50 C to20e35%at w190 C with overall increasing temperature(Fig.8),although its content is quite hetero-geneous.Similar levels of quartz heterogeneity are prevalent in adja-cent sandstones at similar temperatures(Dutton and Loucks,2010).
Plagioclase is the dominant feldspar(range of w6wt%),and there is a small increase in plagioclase volume with depth/temperature (Fig.8),although values spread at a given temperature point toward the heterogeneity of plagioclase within Wilcox Group mudstones. Potassium feldspar(K-feldspar)decreases from w5.5wt%in the lowest temperature samples to<1.1wt%in the hottest(Fig.8).This measurement contrasts with complete depletion of K-feldspar within adjacent sandstones at temperatures>150 C(Dutton and Loucks,2010).Total carbonate accounts for<2wt%of the whole rock,with only marginal increases in dolomite and decreases in calcite with increasing temperature.Minor amounts of pyrite are noted in isolated samples.Mica,illite,and illite e smectite are undifferentiated in whole-rock quanti?cation;the patterns, however,suggest that illite e smectite is the main component,and it increases from w30to50wt%with increasing temperature. Kaolinite decreases rapidly(w20e0%)with increasing temperature, but chlorite is variably present(1e8%)with perhaps a modest increase with increasing temperature.
The<2-m m fraction is dominated by illite and illite e smectite (Fig.9).At any given temperature there is considerable heteroge-neity,but illite e smectite increases with depth.Expandability is 90e75%at low temperature and decreases rapidly to10e20%at high temperatures;further heating does not change expandability. Discrete illite increases from w8%at40 C to w18%at200 C. Kaolinite,by contrast,decreases rapidly.Chlorite is present throughout the depth pro?le(1e10%)and decreases with increasing temperature,contrasting with whole-rock analysis.
4.4.Bulk-rock geochemistry
By compensating for a major component of the primary compositional heterogeneity,application of a
quartz-normalizing
Fig.9.Relative percentage of<2m m fraction.Illite and illite e smectite are combined.
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methodology allows for a better sense of element ?ux in the Wilcox Group mudstone system.This can be best emphasized by looking at the K 2O trend in the whole-rock and quartz-normalized data (Fig.10A and B,respectively).By removing the quartz content the K 2O trend in the reacting phases becomes clearer.
The volatile-free quartz-normalized data describe Al 2O 3trends that are constant with increasing temperature (Fig.11).TiO 2,CaO,and Na 2O,likewise,are constant with temperature,but their relative proportions within the whole-rock geochemical system are much lower than that of Al 2O 3(Fig.11).SiO 2decreases by w 5wt%in clays and feldspars with increasing temperature and is the only major element to do so.FeO and MgO both increase by w 2wt%.The largest increase with temperature is in K 2O,which increases from 4to w 8wt%over the temperature range of this study.
ZrO 2is commonly assumed to be an immobile element within siliciclastic geochemical systems (e.g.Wilkinson et al.,2003)
and,
Fig.10.K 2O from whole-rock XRF data (a)and quartz-normalized data
(b).
Fig.11.Bulk rock geochemical trends (XRF).Volatile free major element data normalized to be free of quartz.The non-quartz system has its Al 2O 3concentration remaining constant with temperature increase and SiO 2increasing.Marginal increases in FeO,MgO and a notable increase in K 2O are noted.
R.J.Day-Stirrat et al./Marine and Petroleum Geology 27(2010)1804e 18181813
indeed,it neither varies with increasing temperature (Fig.12)nor correlates with Al 2O 3,which we document to be constant with increasing temperature.The increase in K 2O with increasing temperature is clearly seen in the decreasing trend of ZrO 2/K 2O (Fig.12).SiO 2/Al 2O 3and K 2O/Al 2O 3are two commonly used geochemical trends in mudstone systems (e.g.Awwiller,1993;Land et al.,1997),and within Wilcox Group mudstones,SiO 2/Al 2O 3marginally decreases with temperature,and K 2O/Al 2O 3increases (Fig.13).5.Discussion
5.1.Origin of quartz in Wilcox Group mudstones
The goal of this study was to examine physical and chemical changes that occur with increasing temperature in similarly aged and sourced mudstones.The dataset was designed to control variations caused by provenance differences by sampling similarly aged Wilcox Group mudstones from wells parallel to the well-de ?ned paleo-depositional axis (e.g.Galloway and McGilvery,1995;Galloway et al.,2000;Galloway,2005and references therein)as opposed to applying a down-hole approach (e.g.Day-Stirrat et al.,2008;Peltonen et al.,2008).The temperature range over which the dataset is spread is suf ?cient to cover the range of the volumetrically signi ?cant diage-netic mineral reactions typical in most siliciclastic sedimentary basins,e.g.,smectite-to-illite transformation (e.g.Burst,1959;Hower and Mowatt,1966;Hower et al.,1976;Boles and Franks,1979),kaolinite loss (https://www.doczj.com/doc/f43069007.html,nson et al.,1996;Milliken,2004;Meunier,2005),K-feldspar depletion (Land and Milliken,1981;Milliken,1992a;Thyne et al.,2001;Wilkinson et al.,2001;Milliken,2004),and albitization (Milliken,1992a ).Unavoidable heterogeneity of the mudrock system results in mineral and element trends that are dif ?cult to discriminate within the noise of primary compositional variation (sorting)at any given temperature (Land et al.,1997).To partially compensate for this primary heterogeneity,where we have matching X-ray diffraction and X-ray ?uorescence data we employ a quartz-normalizing tech-nique to remove some of this noise (Fig.10)so that we can assess reactions related to the most reactive components,the clay minerals and feldspars,without resorting to sample preparation by disaggre-gation and size fractionation.Extracting size fractions from well-lithi ?ed rocks may break particles during disaggregation and contaminate ?ner fractions with material derived from coarser fractions.
In mudrocks of the Gulf of Mexico sedimentary basin primary detrital variation in the ratio of silt-size (dominantly quartz)and clay-size (dominantly clay minerals)is large and complicates efforts to document smaller variations in composition related to diagenesis (Land et al.,1997).It is not possible,across a broad temperature range in available cores,to obtain a sample set that has a suf ?ciently uniform composition (invariant silt/clay ratio)to avoid this problem.In this normalization procedure only Si that is related to quartz is removed.A key assumption is that the quartz
(as
Fig.12.Volatile free quartz-normalized XRF data for Al 2O 3and volatile free ZrO 2.Al 2O 3and ZrO 2concentrations remain relatively constant with temperature.K 2O increases in concentration with temperature (compare with Fig.11).
R.J.Day-Stirrat et al./Marine and Petroleum Geology 27(2010)1804e 1818
1814
determined by XRPD)is detrital and not authigenic.Based on observations in sandstones,quartz overgrowths are not expected to be abundant in mudrocks because of the strong role of nucleation substrate in controlling the nucleation and growth of quartz cement and the tendency of clay coating to inhibit the growth of quartz (e.g.,Heald and Larese,1974;Pittman et al.,1992;Ehrenberg,1993;Bloch et al.,2002).Cathodoluminescence imaging was per-formed to test this assumption.Two deep samples Cr08(187 C)and Cr20(187 C)were used because the higher temperatures to which these samples have been exposed are conducive to quartz precipitation (Walderhaug,1994).
Quartz cement is abundant within Wilcox sandstones (Loucks et al.,1984;Fisher and Land,1986;Dutton and Loucks,2010)and so it is reasonable to search carefully for such overgrowths in the associated mudrocks because mudrocks and associated sandstones often contain similar diagenetic phases (Milliken,1992b,2004).It is clear from the CL images in Fig.5that the greater bulk of quartz in these mudrocks is indeed detrital.Quartz grains manifest variation in CL color,intensity,and fabric that are typical for quartz grain populations (Zinkernagel,1978;Owen,1991;Milliken,1994;Seyedolali et al.,1997;Bernet and Bassett,2005).Rare cases in which grains manifest small,dark-luminescing zones (arrows in Fig.5)on their outer edges are best interpreted as either reworked overgrowths or as CL-mottled grains that simply happen to have a portion of dark-luminescing material on the outer edge.Several lines of evidence support the interpretation that the features illustrated by the arrows in Fig.6are not quartz overgrowths formed in situ :1.Colors of these outer dark zones are variable,whereas quartz overgrowths in sandstones tend to have a uniform color or a uniform range of colors with a distinct zoning pattern.2.These dark-luminescing regions are suf ?ciently large that it is dif ?cult to envision pores of suf ?cient size to accommodate these overgrowths within the matrix of clay-size particles that surrounds the quartz silt,especially at burial depths where temperatures are conducive to quartz cementation.Overgrowths in this situation could potentially grow as clay-engul ?ng poikilotopes but there is no evidence of such clay inclusions within the quartz.3.Alterna-tively,the quartz could grow as a replacement of the surrounding clays (force of crystallization replacement;see Maliva and Siever,1988)but the euhedral terminations characteristic of this style of replacement are absent. 4.These dark-luminescing zones are present on a small minority of grains whereas quartz cement when present in sandstones tends to develop pervasively on all amenable surfaces.5.Where present,these zones are highly discontinuous and entirely anhedral,more consistent with abraded features inherited from the source rocks than with cements.
A likely case of quartz cement was located in the silt-rich lamina shown in Fig.6.Most of the silt particles within this lamina are completely surrounded by clay-size particles and show no evidence of overgrowths.In the case illustrated in Fig.6however several quartz grains in close proximity to one another appear to have preserved a pocket of clay-free intergranular pore space into which an overgrowth of blue-luminescing quartz has grown.It is inter-esting to note these overgrowths appear to pre-date the abundant pyrite framboids that are present in the lamina.Framboids are generally interpreted as the products of near-sea ?oor diagenesis (e.g.,Wilkin et al.,1996;Wilkin and Barnes,1997;Wignall and Newton,1998)and thus,an early-diagenetic interpretation of these quartz-cemented grains must be considered.An alternative to a late diagenetic origin would be that these quartz-cemented grains are fragments of the test of an agglutinated foraminifer (Milliken et al.,2007).
In summary,with the petrographic methods applied in this study (combined CL and SE imaging at magni ?cations of 900?to 2400?),no strong evidence for a component of authigenic quartz in Wilcox mudrock analogous to the quartz cement component in associated sandstones can be observed.Our observations cannot rule out the presence of a component of very small (sub-micron)authigenic quartz crystals,but the abundance of these cannot be large as the total quartz content (much of which may also be detrital)in clay-size material extracted from Wilcox mudrocks is <1%(Awwiller,1993his Table 1,p.503)
Our conclusion about the lack of authigenic quartz in Wilcox mudrocks may not extend to mudrocks with lower sediment accumulation rates that contain a substantial component of highly reactive siliceous biogenic debris,for example the Barnett Shale (Papazis and Milliken,2005)and the Cretaceous of the Norwegian Continental Margin (Peltonen et al.,2008;Thyberg et al.,2010).In the case of the Wilcox however,with its high sedimentation rates (see cross-sections in Dodge and Posey,1981),quartz silt of domi-nantly detrital derivation,and clay-rich composition there appears to be little or no authigenic quartz.Quartz-normalization proce-dures for examining depth trends in elemental composition can be applied with some con ?dence.
5.2.Mineralogical change Wilcox Group mudstones
Based on our whole-rock mineralogical analysis,dissolution of detrital smectite,kaolinite,K-feldspar,and Ca-plagioclase are the potentially important sources for the constituent elements in the authigenic clays (illite and chlorite)and albite that develop progressively with increasing temperature (Fig.8).The
smectite-to-
Fig.13.Whole rock SiO 2/Al 2O 3and K 2O/Al 2O 3wt%on a volatile free and quartz free basis.
R.J.Day-Stirrat et al./Marine and Petroleum Geology 27(2010)1804e 18181815
illite transformation(Fig.9)and the various elemental losses and gains with respect to detrital smectite dissolution and illite precipitation are well-documented(Hower et al.,1976;Awwiller, 1993;Land et al.,1997;Lynch et al.,1997).
Potassium release from K-feldspar dissolution(https://www.doczj.com/doc/f43069007.html,liken, 2004)is a key reaction as it is the sole detrital source of the K that is required for the illite e smectite transformation,as well as for any additional illite that may form authigenically as cement or other grain replacements.Our mudstone XRD data appear to show K-feldspar dissolving more slowly(Fig.8)than in adjacent sandstones (Dutton and Loucks,2010)where it is completely removed by w175 C;however petrographic examination of the deepest mudrocks during microprobe analysis failed to locate even a trace of K-feldspar in the deepest samples at a temperature of w190e210 C.
In a closed system potassium would simply move from dissolving K-feldspar into neoforming potassium-bearing clays and there would be no change in K2O or any increase in clay-mineral content with increasing temperature.Such K2O trends are recorded in other basins around the world,the Norwegian Continental Margin (Peltonen et al.,2008)and the Podhale Basin of southern Poland (Srodon et al.,2006)for example.The K2O trend observed in this study(Fig.11)entails an approximately three-fold increase in potassium over the depth range studied.Across the studied transect there are no discernible shifts in provenance that could account for a primary detrital assemblage that is enriched in potassium in the more offshore(and now deeper)parts of the section.The addition of potassium to the system could result from dissolution and albitiza-tion of K-feldspar that is observed in the in adjacent sandstones. Notable amounts of K-feldspar dissolution have formed secondary porosity in these sandstones and much primary porosity is occluded by quartz overgrowths,the silica for which cannot be internal to the sandstones(Dutton and Loucks,2010).A similar scenario dominates the stratigraphically younger Frio Formation(Wilkinson et al., 2003),with the additional complication that there can be more feldspars dissolved from the sandstone than is indicated by primary porosity occlusion(Harris,1989;Milliken et al.,1989).We,however, reach broadly the same conclusions as Awwiller(1993)with regard to the source of potassium in the Wilcox Group as our Fig.13is remarkably similar to his Fig.9.Potassium must be derived from elsewhere within the basin although its exact source is still https://www.doczj.com/doc/f43069007.html,rge-scale advection appears required to transfer K from the underlying Mesozoic,although this appears to be precluded by low mudstone permeabilities(e.g.Dewhurst et al.,1999)and there exists extensive literature citing the contrary(Hower et al.,1976;Jennings and Thompson,1986;Bj?rlykke et al.,1989;Bj?rlykke,1993,1999; Bj?rlykke and Egeberg,1993).
Mass balances of Al and Si are more complex than for K and necessarily involve the dissolution and precipitation of multiple detrital and authigenic silicate phases.Illite-forming reactions involving kaolinite have been proposed previously by Bjorlykke and Aagaard(1992),Bjorlykke(1998),Chuhan et al.(2001)and Awwiller (1993).
In the case of the Wilcox,chlorite precipitation also needs to be considered in the overall balance of Al and Si over the temperature range of illite precipitation,thus bringing substantial amounts of Fe and Mg in the overall elemental balance for these clay reactions as well.In addition to chlorite,previously documented Wilcox Group illite e smectite chemistries(Ahn and Peacor,1985,1986;Awwiller, 1993)describe octahedral sites slightly enriched in Fe and Mg. Minor Fe-dolomite replacement of detrital feldspar adds to the overall amount of Mg and Fe added to the authigenic fraction in the mudrocks.Our whole-rock XRF data may suggest that a?ux of Fe and Mg into the system accompanies burial diagenesis.
Aluminum conservation as suggested by our data(Figs.11and 12)is not a new?nding for the Gulf of Mexico basin in general (Wintsch and Kvale,1994;Land et al.,1997).Indeed,other elements af?liated with detrital components appear conserved within the Wilcox Group.ZrO2for example,is commonly assumed to be immobile within mudstone systems(Wilkinson et al.,2003)and ZrO2does not vary systematically with temperature(Fig.12).
If the Wilcox Group mudstones are a perfectly closed system quartz precipitation would potentially result from either illite formation from kaolinite and K-feldspar or as a product of smectite illitization(Boles and Franks,1979),yet we are unable to petro-graphically discern this.Our Si/Al trend(Fig.13)strongly agrees with the global Si/Al trend documented by van de Kamp(2008).We are,therefore,forced to accept silica release from mudstones(Figs. 5,6and13)regardless of depositional heterogeneity.
6.Conclusions
Mineralogical trends in Wilcox Group mudstones with increasing temperature show decreases in quartz,kaolinite and K-feldspar and increases in chlorite,illitetilliteàsmectite,and albite. The mixed-layer phase illite e smectite has become more illitic with increasing burial temperature but has not approached R3ordering even though there is abundant potassium in the system.
This mineralogical and elemental study of the Wilcox Group mudstones describes an open system in which K2O is enriched in the deeper/higher temperature parts of the system.This conclusion supports the previous work of Awwiller(1993)but applies aquartz-normalization procedure thereby reducing noise in the system created by quartz heterogeneity and allowing bulk rock geochem-ical trends to be discussed.The system behaves conservatively with respect to Al2O3and ZrO2.This study supports the conclusion of Land and Fisher(1987)and Awwiller(1993)that potassium enrichment in the Wilcox Group mudstones is derived from K-feldspar dissolution in adjacent sandstone and underlying Meso-zoic sections.
Acknowledgements
We thank the Jackson School of Geosciences at The University of Texas at Austin for providing postdoctoral funding to RJDS,which facilitated this study,along with sponsor companies of the Deep Shelf Gas consortium at the Bureau.Publication authorized by the Director,Bureau of Economic Geology.Cathy Brown and Lana Dieterich are thanked for graphics and editing support.Drs.Richard Lahann and David Awwiller,and associate editor Dr.Nicholas Harris provided constructive and rigorous reviews that greatly improved this article.
References
Ahn,J.H.,Peacor,D.R.,1985.Transmission electron-microscopic study of diagenetic chlorite in Gulf-coast argillaceous sediments.Clays and Clay Minerals33(3), 228e236.
Ahn,J.H.,Peacor,D.R.,1986.Transmission and analytical electron microscopy of the smectite to illite transition.Clays and Clay Minerals34,165e179.
Aplin,A.C.,Matenaar,I.F.,McCarty,D.K.,van der Pluijm,B.A.,2006.In?uence of mechanical compaction and clay mineral diagenesis on the microfabric and pore-scale properties of deep-water Gulf of Mexico mudstones.Clays and Clay Minerals54(4),500e514.
Athy,A.F.,1930.Density,porosity and compaction of sedimentary rocks.Bulletin of the American Association of Petroleum Geologists14,1e24.
Awwiller,D.N.,1993.Illite smectite formation and potassium mass-transfer during burial diagenesis of mudrocks e a study from the Texas Gulf-coast Paleocene-Eocene.Journal of Sedimentary Petrology63(3),501e512.
Bebout,D.G.,White,W.A.,Garrett Jr.,C.M.,Hentz,T.F.,1992.Atlas of Major Central and Eastern Gulf Coast Gas Reservoirs.The University of Texas at Austin,Bureau of Economic Geology,88pp.
Berger,G.,Lacharpagne,J.C.,Velde, B.,Beaufort, D.,Lanson, B.,1997.Kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone/shale sequences.Applied Geochemistry12(1),23e35.
R.J.Day-Stirrat et al./Marine and Petroleum Geology27(2010)1804e1818 1816
Bernet,M.,Bassett,K.,2005.Provenance analysis by single-Quartz-Grain SEM-CL/ Optical microscopy.Journal of Sedimentary Research75(3),492e500. Bjorlykke,K.,Aagaard,P.,1992.Clay minerals in North Sea sandstones.In: Houseknecht,D.W.,Pittman,E.D.(Eds.),Origin,Diagenesis,and Petrophysicas of Clay Minerals in Sandstones.SEPM Special Publication,pp.65e80.
Bj?rlykke,K.,Egeberg,P.K.,1993.Quartz cementation in sedimentary basins.
Bulletin of the American Association of Petroleum Geologists77,1538e1548. Bj?rlykke,K.,Hoeg,K.,1997.Effects of burial diagenesis on stresses,compaction and ?uid?ow in sedimentary basins.Marine and Petroleum Geology14(3),267e276. Bj?rlykke,K.,Ramm,M.,Saigal,G.C.,1989.Sandstone diagenesis and porosity modi?cation during basin evolution.Geologische Rundschau78,243e268.
Bj?rlykke,K.,1993.Fluid-?ow in sedimentary basins.Sedimentary Geology86, 137e158.
Bjorlykke,K.,1998.Clay mineral diagenesis in sedimentary basins e a key to the prediction of rock properties.Examples from the North Sea Basin.Clay Minerals33, 15e34.
Bj?rlykke,K.,1999.Principal Aspects of Compaction and Fluid Flow in Mudstones.
In:Geological Society,London,Special Publications,vol.158(1)pp.73e78. Bloch,S.,Lander,R.H.,Bonnell,L.,2002.Anomalously high porosity and perme-ability in deeply buried sandstone reservoirs:origin and predictability.Amer-ican Association of Petroleum Geologists Bulletin86,301e328.
Bodner,D.P.,Sharpe,J.M.,1988.Temperature variations in south Texas subsurface.
Bulletin of the American Association of Petroleum Geologists72(1),21e32. Bodner,D.P.,Blanchard,P.E.,Sharp,J.M.,1985.Variations in Gulf-coast heat-?ow created by Groundwater-Flow.Bulletin of the American Association of Petro-leum Geologists69(9),1418.
Boles,J.R.,Franks,S.G.,1979.Clay diagenesis in Wilcox sandstones of southwest Texas.Journal of Sedimentary Petrology49,55e70.
Burst,J.F.,1959.Postdiagenetic clay mineral environmental relationships in the Gulf Coast Eocene.Clays and Clay Minerals6,327e341.
Chuhan,F.A.,Bjorlykke,K.,Lowrey,C.J.,2001.Closed-system burial diagenesis in reservoir sandstones:examples from the Garn formation at Haltenbanken area, offshore Mid-Norway.Journal of Sedimentary Research71(1),15e26. Corrigan,J.,2003.Correcting bottom hole temperature data.http://www.zetaware.
com/utilities/bht/default.html.
Day-Stirrat,R.J.,Aplin,A.C.,Srodon,J.,van der Pluijm,B.A.,2008.Diagenetic reor-ientation of phyllosilicate minerals in Paleogene mudstones of the Podhale Basin,southern Poland.Clays and Clay Minerals56(1),100e111.
Day-Stirrat,R.J.,Dutton,S.P.,Milliken,K.L.,Loucks,R.G.,Aplin,A.C.,Hillier,S.,van der Pluijm,B.A.,2010.Fabric anisotropy induced by primary depositional variations in the silt:clay ratio in two?ne-grained slope fan complexes:Texas Gulf Coast and northern North Sea.Sedimentary Geology226(1e4),42e53.
DeFord,R.K.,Kehle,R.O.,Connolly,E.T.,1976.Geothermal Gradient Map of North America.American Association of Petroleum Geologists and U.S.Geological Survey,Reston,Virginia.Scale1:5,000,000.
Delage,P.,Lefebvre,G.,1984.Study of the structure of a sensitive Champlain clay and of its evolution during consolidation.Canadian Geotechnical Journal21(1),21e35. Dewhurst,D.N.,Yang,Yunlai,Aplin, A.C.,1999.Permeability and Fluid Flow in Natural Mudstones.In:Aplin,A.C.,Fleet,A.J.,MacQuaker,J.H.S.(Eds.),Muds and Mudstones:Physical and Fluid Flow Properties.Geological Society,London, Special Publication,vol.158,London,pp.23e43.
Dodge,M.M.,Posey,J.S.,1981.Structural cross sections Tertiary formations Texas Gulf coast.Bureau of Economic Geology,6p.2?gs.32pls.1981;reprinted1987.
CS0002.
Dutton,S.P.,Loucks,R.G.,2010.Diagenetic controls on evolution of porosity and permeability in lower Tertiary Wilcox sandstones from shallow to ultradeep (200e6700m)burial,Gulf of Mexico Basin,USA.Marine and Petroleum Geology27(1),69e81.
Eberl,D.D.,1993.Three-zones for illite formation during burial diagenesis and metamorphism.Clays and Clay Minerals41(1),26e37.
Ehrenberg,S.N.,1993.Preservation of anomalously high porosity in deeply buried sandstones by grain-coating chlorite:examples from the Norwegian continental shelf.American Association of Petroleum Geologists Bulletin77, 1260e1286.
Fisher,R.S.,Land,S.L.,1986.Diagenetic history of Eocene Wilcox sandstones,south-central Texas.Geochemica et Cosmochimica Acta50,551e561.
Fisher,R.S.,McGowen,J.H.,1967.Depositional systems in the Wilcox Group of Texas and their relationship to occurrence of oil and gas.Gulf Coast Association of Geological Societies Transactions17,105e125.
Forrest,J.,Marcucci, E.,Scott,P.,2007.Geothermal gradients and subsurface temperatures in the northern Gulf of Mexico.Gulf coast Association of Geo-logica;Societies Transactions55,233e248.
Freed,R.L.,Peacor, D.R.,1989.Variability in temperature of the smectite/illite reaction in Gulf coast sediments.Clay Minerals24,171e180.
Freed,R.L.,Peacor,D.R.,1992.Diagenesis and the formation of authigenic illite-rich I/S crystals in Gulf-coast shales e TEM study of clay separates.Journal of Sedimentary Petrology62(2),220e234.
Galloway,W.E.,McGilvery,T.A.,1995.Facies of a Submarine Canyon Fill Reservoir Complex,Lower Wilcox Group(Paleocene),Central Texas Coastal Plain,SEPM core Workshop.Society of Economic Paleontologists and Mineralogists,United States,p.1.
Galloway,W.E.,Ganey-Curry,P.E.,Li,X.,Buf?er,R.,2000.Cenozoic depositional history of the Gulf of Mexico basin.Bulletin of the American Association of Petroleum Geologists84(11),1743e1774.Galloway,W.E.,2005.Gulf of Mexico Basin Depositional Record of Cenozoic North American Drainage Basin Evolution.In:Special Publication of the International Association of Sedimentologists.Blackwell,Oxford,International,pp.409e423. Haines,S.H.,van der Pluijm,B.A.,Ikari,M.J.,Saffer,D.M.,Marone,C.,2009.Clay fabric intensity in natural and arti?cial fault gouges:Implications for brittle fault zone processes and sedimentary basin clay fabric evolution.Journal of Geophysical Research-Solid Earth114.
Harris,N.B.,1989.Diagenetic Quartzarentite and destruction of secondary porosity-an example from the Middle Jurassic Brent sandstone of Northwest Europe.
Geology17(4),361e364.
Heald,M.T.,Larese,R.E.,1974.In?uence of coatings on quartz cementation.Journal of Sedimentary Petrology44,1269e1274.
Hedberg,H.D.,1936.Gravitational compaction of clays and shales.American Journal of Sciences31,241e287.
Hillier,S.,https://www.doczj.com/doc/f43069007.html,e of an air brush to spray dry samples for X-ray powder diffraction.Clay Minerals34(1),127e135.
Hillier,S.,2002.Spray drying for X-ray powder diffraction preparation.IUCR Commission on Powder Diffraction Newsletter27(27),7e9.
Hillier,S.,2003.Quantitative analysis of clay and other minerals in sandstones by X-ray Powder Diffraction(XRPD).In:Worden,R.H.,Morad,S.(Eds.),International Association of Sedimentologists Special Publication34:Clays and Clay Cements in Sandstones.Blackwell,Oxford,pp.213e251.
Ho,N.C.,Peacor,D.R.,van der Pluijm,B.A.,1999.Preferred Orientation of phyllosi-licates in Gulf coast mudstones and Relation to the smectite e illite transition.
Clays and Clay Minerals47(4),495e504.
Hower,J.,Mowatt,T.C.,1966.The mineralogy of illites and mixed-layer illite-montmorillonites.American Mineralogist51,825e854.
Hower,J.,Eslinger,E.V.,Hower,M.E.,Perry,E.A.,1976.Mechanism of burial meta-morphism of argillaceous sediment1.Mineralogical and chemical evidence.
Geological Society of America Bulletin87(5),725e737.
Jennings,S.,Thompson,G.R.,1986.Diagenesis of pliopleistocene sediments of the Colorado river-delta,southern-California.Journal of Sedimentary Petrology56
(1),89e98.
Johnson,D.M.,Hooper,P.R.,Conrey,R.M.,1999.XRF analysis of rocks and minerals for major and trace elements on a single low dilution Li-tetraborate Fused bead.
Advances in X-ray Analysis41,843e867.
Katsube,T.J.,Mudford,B.S.,Best,M.E.,1991.Petrophysical characteristics of shales from the Scotian shelf.Geophysics56(10),1681e1689.
Land,L.S.,Fisher,R.S.,1987.Wilcox sandstone diagenesis,Texas Gulf Coast:
a regional isotopic comparison with the Frio Formation.In:Marshall,J.D.(Ed.),
Diagenesis of Sedimentary Sequences:Geological Society Special Publication 36,pp.219e235.
Land,L.S.,Milliken,K.L.,1981.Feldspar diagenesis in the Frio formation,Brazoria county,Texas GUlf coast.Geology9,314e318.
Land,L.S.,Milliken,K.L.,2000.Regional loss of SiO2,and gain of K2O during burial diagenesis of Gulf coast mudrocks,USA.In:Worden,R.H.,Morad,S.(Eds.), Quartz cementation in sandstones.International Association of Sedimentolo-gists,pp.183e197.
Land,L.S.,Milliken,K.L.,McBride,E.F.,1987.Diagenetic evolution of the Cenozoic sandstones,Gulf of Mexico sedimentary basin.Sedimentary Geology50, 195e225.
Land,L.S.,Mack,L.E.,Milliken,K.L.,Lynch,F.L.,1997.Burial diagenesis of argillaceous sediment,south Texas Gulf of Mexico sedimentary basin:a reexamination.
Geological Society of America Bulletin109(1),2e15.
Lanson,B.,Beaufort,D.,Berger,G.,Baradat,J.,Lacharpagne,J.-C.,1996.Illitization of diagenetic kaolinite-to-dickite conversion series;late-stage diagenesis of the Lower Permian Rotliegend Sandstone reservoir,offshore of the Netherlands.
Journal of Sedimentary Research66(3),501e518.
Lanson, B.,et al.,2002.Authigenic kaolin and illitic minerals during burial diagenesis of sandstones:a review.Clay Minerals37(1),1e22.
Loucks,R.G.,Dodge,M.M.,Galloway,W.E.,1984.Regional controls on diagenesis and reservoir quality in lower Tertiary sandstones along the Texas Gulf Coast.Clastic Diagenesis.American Association of Petroleum Geologists Memoir37,15e45. Lynch,F.L.,Mack,L.E.,Land,L.S.,1997.Burial diagenesis of illite/smectite in shales and the origins of authigenic quartz and secondary porosity in sandstones.
Geochimica Et Cosmochimica Acta61(10),1995e2006.
Maliva,R.G.,Siever,R.,1988.Diagenetic replacement controlled by force of crys-tallization.Geology16,688e691.
Meunier,A.,2005.Clays.Springer-Verlag,Berlin Heidelberg.
Milliken,K.L.,McBride,E.F.,Land,L.S.,1989.Numerical assessment of dissolution versus replacement in the subsurface destruction of detrital feldspars, Oligocene Frio formation,South Texas.Journal of Sedimentary Petrology59
(5),740e757.
Milliken,K.,Choh,S.-J.,Papazis,P.,Schieber,J.,2007.“Cherty”stringers in the Barnett Shale are agglutinated Foraminifera.Sedimentary Geology198(3e4),221e232. Milliken,K.L.,1992a.Chemical behavior of detrital feldspars in mudrocks versus sandstones,Frio formation(Oligocene),South Texas.Journal of Sedimentary Petrology62(5),790e801.
Milliken,K.L.,1992b.Chemical behavior of detrital feldspars in mudrocks versus sandstones,Frio Formation(Oligocene),South Texas.Journal of Sedimentary Petrology62,790e801.
Milliken,K.L.,1994.Cathodoluminescent textures and the origin of quartz silt in Oligocene mudrocks,South Texas.Journal of Sedimentary Research64A, 567e571.
R.J.Day-Stirrat et al./Marine and Petroleum Geology27(2010)1804e18181817
Milliken,K.L.,https://www.doczj.com/doc/f43069007.html,te Diagenesis and Mass Transfer in Sandstone-shale Sequences Treatise on Geochemistry.Elsevier Pergamon,Oxford,United Kingdom,United Kingdom.
Mondol,N.H.,Bjorlykke,K.,Jahren,J.,Hoeg,K.,2007.Experimental mechanical compaction of clay mineral aggregates e changes in physical properties of mudstones during burial.Marine and Petroleum Geology24(5),289e311. Mondol,N.H.,Bjorlykke,K.,Jahren,J.,2008.Experimental compaction of clays: relationship between permeability and petrophysical properties in mudstones.
Petroleum Geoscience14(4),319e337.
Moore,D.M.,Reynolds,R.C.J.,1997.X-Ray Diffraction and the Identi?cation and Analysis of Clay Minerals.Oxford University Press,Oxford,New York. Mumme,W.G.,Tsambourakis,G.,Madsen,I.C.,Hill,R.J.,1996.Improved petrological modal analyses from X-ray powder diffraction data by use of the Rietveld method.Part2Selected sedimentary rocks.Journal of Sedimentary Research66
(1),132e138.
Nadeau,P.H.,Wilson,M.J.,McHardy,W.J.,Tait,J.M.,1985.The conversion of smectite to illite during diagenesis e evidence from some illitic clays from Bentonites and sandstones.Mineralogical Magazine49(352),393e400.
Nadeau,P.H.,Peacor,D.R.,Yan,J.,Hillier,S.,2002.I-S precipitation in pore space as the cause of geopressuring in Mesozoic mudstones,Egersund Basin,Norwegian Continental Shelf.American Mineralogist87(11e12),1580e1589.
Nagihara,S.,Jones,K.O.,2005.Geothermal heat?ow in the northeast margin of the Gulf of Mexico.Bulletin of the American Association of Petroleum Geologists89
(6),821e831.
Omotoso,O.,McCarty, D.K.,Hillier,S.,Kleeberg,R.,2006.Some successful approaches to quantitative mineral analysis as revealed by the3rd Reynolds Cup contest.Clays and Clay Minerals54(6),748e760.
Owen,M.R.,1991.Application of cathodoluminescence to sandstone provenance.In: Barker, C.E.,Kopp,O.C.(Eds.),Luminescence Microscopy and Spectroscopy: Quantitative and Qualitative Applications.SEPM,pp.67e75.
Papazis,P.K.,Milliken,K.L.,2005.Cathodoluminescent Textures and the Origin of Quartz in the Mississippian Barnett Shale,Fort Worth Basin,Texas,Annual Meeting.
In:American Association of Petroleum Geologists,Calgary,Alberta,pp.A105. Peltonen,C.,Marcussen,O.,Bjorlykke,K.,Jahren,J.,2008.Mineralogical control on mudstone compaction:a studyof late Cretaceous to early Tertiary mudstones of the Voring and more basins,Norwegian Sea.Petroleum Geoscience14(2),127e138. Pittman,E.D.,Larese,R.E.,Heald,M.T.,1992.Clay coats:occurrence and relevance to preservation of porosity in sandstones.In:Houseknecht,D.W.,Pittman,E.D.
(Eds.),Origin,Diagenesis,and Petrophysics of Clay Minerals in Sandstones.
Special Publication.SEPM(Society for Sedimentary Geology),Tulsa,Oklahoma, pp.241e256.
Romero, E.,Simms,P.,2008.Microstructure investigation in unsaturated soils:
a review with special attention to contribution of mercury intrusion
porosimetry and environmental scanning electron microscopy.Geotechnical and Geological Engineering26(6),705e727.
Rowe,H.D.,Loucks,R.G.,Ruppel,S.C.,Rimmer,S.M.,2008.Mississippian Barnett formation,Fort Worth basin,Texas:bulk geochemical inferences and Mo-TOC constraints on the severity of hydrographic restriction.Chemical Geology257 (1e2),16e25.
Seyedolali,A.,et al.,1997.Provenance interpretation of quartz by scanning electron microscope e cathodoluminescence fabric analysis.Geology25,787e790. Srodon,J.,et al.,2006.Diagenetic history of the Podhale-Orava Basin and the underlying Tatra sedimentary structural units(Western Carpathians):evidence from XRD and K-Ar of illite e smectite.Clay Minerals41,751e774.
Thyberg,B.,Jahren,J.,Winje,T.,Bj?rlykke,K.,Faleide,J.I.,Marcussen,?.,2010.
Quartz cementation in Late Cretaceous mudstones,northern North Sea: Changes in rock properties due to dissolution of smectite and precipitation of micro-quartz crystals.Marine and Petroleum Geology27(8),1752e1764. Thyne,G.,Boudreau,B.P.,Ramm,M.,Midtbo,R.E.,2001.Simulation of potassium feldspar dissolution and illitization in the Statfjord Formation,North Sea.The American Association of Petroleum Geologists Bulletin85(4),621e635.
van de Kamp,P.C.,2008.Smectite e Illite e Muscovite transformation,quartz disso-lution,and silica release in shales.Clays and Clay Minerals56(1),66e81. Walderhaug,O.,1994.Temperatures of quartz cementation in Jurassic sandstones from the Norwegian continental-shelf-evidence from?uid inclusions.Journal of Sedimentary Research Section A-Sedimentary Petrology and Processes64(2), 311e323.
Wignall,P.B.,Newton,R.,1998.Pyrite framboid diameter as a measure of oxygen de?ciency in ancient mudrocks.American Journal of Science298,537e552. Wilkin,R.T.,Barnes,H.L.,1997.Formation processes of framboidal pyrite.Geo-chimica et Cosmochimica Acta61,323e339.
Wilkin,R.T.,Barnes,H.L.,Brantley,S.L.,1996.The size distribution of framboidal pyrite in modern sediments:an indicator of redox conditions.Geochimica et Cosmochimica Acta60,3897e3912.
Wilkinson,M.,Milliken,K.L.,Haszeldine,R.S.,2001.Systematic Destruction of K-Feldspar in Deeply Buried Rift and Passive Margin Sandstones.In:Journal of the Geological Society,London,vol.158675e683.
Wilkinson,M.,Haszeldine,R.S.,Milliken,K.L.,2003.Cross-formation?ux of aluminium and potassium in Gulf Coast(USA)sediments.In:Worden,R.H.,Morad,S.(Eds.), Clay Mineral Cements in Oil Field Sandstones.International Association of Sedi-mentologists,Special Publication.Blackwells,Oxford,pp.43e61.
Wintsch,R.P.,Kvale,C.M.,1994.Differential mobility of elements in burial diagen-esis of siliciclastic rocks.Journal of Sedimentary Research64,349e361. Zinkernagel,U.,1978.Cathodoluminescence of Quartz and Its Application to Sandstone Petrology.In:Contributions to Sedimentology,vol.8.E.Schwei-zerbart’sche Verlagsbuchandlung(N?gele und Obermiller),Stuttgart,69pp.
R.J.Day-Stirrat et al./Marine and Petroleum Geology27(2010)1804e1818 1818