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Quartz-cementation-in-Late-Cretaceous-mudstones-northern-North-Sea-Changes-in-rock-properties-due

Quartz cementation in Late Cretaceous mudstones,northern North Sea:Changes in rock properties due to dissolution of smectite and precipitation of micro-quartz crystals

Brit Thyberg *,Jens Jahren,Turid Winje,Knut Bj?rlykke,Jan Inge Faleide,?yvind Marcussen

Department of Geosciences,University of Oslo,P.O.Box 1047,Blindern,NO0316Oslo,Norway

a r t i c l e i n f o

Article history:

Received 3November 2008Accepted 9July 2009

Available online 28July 2009Keywords:Opal-A/CT

Cathode luminescence Clay diagenesis Compaction Mudstone North Sea

Quartz cement

a b s t r a c t

Late Cretaceous mudstones from two wells located in the northern North Sea and the Norwegian Sea have been examined with respect to quartz cement.Two different types of quartz cement (Type 1and Type 2)have been identi?ed using SEM/EDS/CL-analysis of drill-bit cuttings at depths 2370–2670m (80–85 C).Type 1appears as relatively large aggregates (30–100m m)of depth/temperature related crypto-or microcrystalline to macrocrystalline irregular quartz cement formed by local re-crystallization of biogenic silica.The CL-responses of Type 1quartz cement give a clear indication of an authigenic origin.Type 2quartz cement represents relatively high amounts of extremely ?ne-grained micro-sized (1–3m m)crystals embedded as discrete,short chains or small clusters/nests within the illitized clay matrix.The CL-responses of micro-quartz crystals indicate an authigenic origin.The micro-quartz is most probably sourced from silica released during the smectite to illite dissolution–precipitation reaction.The petrographic evidence indicates that most of the silica released by the smectite to illite reaction has not been exported out of the mudstones.The silica released produce a subtle inter-connected micro-quartz network interlocked with aggregates of micro-quartz and authigenic clay crystals.This micro-quartz cementation process causes a signi?cant and sharp change in the mudstone stiffness at the onset of the chemical compaction regime.This is indicated by an abrupt increase in well log velocity (Vp)and change in seismic facies close to 2500m (80/85 C).

1.Introduction

Compaction of soft muds to hard shales during progressive burial involves both mechanical and chemical processes (e.g.,Bj?rlykke,1999)causing signi?cant changes of the physical mudstone rock properties (e.g.,Magara,1980;Baldvin and Butler,1985;Bayer and Wetzel,1989;Katsube et al.,1991;Kim et al.,1998,1999;Chuhan et al.,2003;Worden et al.,2005;Aplin et al.,2006;Peltonen et al.,2009).

Mechanical compaction,starting immediately after deposition,is mainly governed by increasing effective stress resulting in volume reduction due to rearrangements or breaking of grains (e.g.,Bj?rlykke,1999).In the shallow parts of sedimentary basins,(<2km/60–80 C)siliceous sediments compact mostly mechan-ically.Precipitation of carbonate cement may however cause lithi-?cation and stiffening of sediments at a relatively shallow depth (e.g.,Bj?rlykke and H?eg,1997;Bj?rlykke,1999;Nyg?rd et al.,

2004).It has been documented that different mudstone lithologies show different mechanical compaction trends (Chilingar and Knight,1960;Jordt et al.,2000;Thyberg et al.,2000;Storvoll et al.,2005;Mondol et al.,2007;Marcussen et al.,2009).Compaction curves based on well data show that below about 2km (<60–80 C)most mudstones compact more than experimentally compacted mud at the equivalent effective stresses (Peltonen et al.,2009).At these temperatures,the compaction of siliceous sediments is mostly chemical and controlled by temperature resulting in stiffer and mechanically pseudo-over-consolidated sediments (Bj?rlykke and H?eg,1997;Storvoll et al.,2005;Bj?rlykke,2006;Marcussen et al.,2009;Peltonen et al.,2009).

Chemical compaction involves dissolution and precipitation of solids changing petrophysical and seismic properties,and is a function of mineral stability and kinetics of precipitation (e.g.,Bj?rlykke,1998,1999;Bj?rkum et al.,1998;Lander and Walder-haug,1999).Well-documented example of chemical compaction processes in mudstones includes the clay mineral reaction smectite to illite through a mixed layer illite–smectite (IS)taking place between about 60and 100 C (depending also on time)during progressive burial (e.g.,Perry and Hower,1970:Hower et al.,1976;

*Corresponding author.

E-mail address:b.i.thyberg@geo.uio.no (B.

Thyberg).

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Marine and Petroleum Geology 27(2010)1752–1764

Yeh and Savin,1977;Boles and Franks,1979;Hoffman and Hower, 1979;Pearson and Small,1988;Glasman et al.,1989;Bj?rlykke and Aagaard,1992;Bj?rkum and Nadeau,1998;Bj?rlykke,1998;Pear-son,1990;Lindgren et al.,1991;Nadeau et al.,2002;Strixrude and Peacor,2002;Peltonen et al.,2009).

The illitization of smectite results in formation of smaller and stiffer crystals in?uencing mudstone physical properties(e.g.,Chi-lingar and Knight,1960;Bj?rlykke,1998).This process may also reduce the permeability in mudstones leading to overpressure formation(e.g.,Nadeau et al.,1985,2002;Freed and Peacor,1989; Bj?rkum and Nadeau,1998;Kim et al.,1999).During illitization,an increased alignment is also recorded increasing the mudstone anisotropy resulting in changes in rock properties(Ho et al.,1999; Kim et al.,1999;Charpentier et al.,2003;Worden et al.,2005). These studies have discussed the effect of the clay mineral trans-formation during progressive burial on petrophysical properties. However,the changes in physical properties and the stiffening and strengthening of mudstones associated with the smectite to illite transformation in mudstones are not yet completely understood.

It has been known for a long time that smectite releases signi?cant amounts of silica when it is dissolved and replaced by illite(e.g.,Weaver,1959;Towe,1962;Hower et al.,1976;Yeh and Savin,1977;Boles and Franks,1979;Foster and Custard,1980; Abercrombie et al.,1994;Bj?rlykke,1998;Srodon,1999;Van der Kamp,2008;Peltonen et al.,2009).The released silica must be precipitated as quartz for the clay mineral reaction to proceed (Egeberg and Aagaard,1989;Bj?rlykke and Aagaard,1992;Aber-crombie et al.,1994).Despite this,petrographic evidence of?nely dispersed quartz cement in mudstones is sparse from previous studies of mudstones(Foster and Custard,1980;Hower et al.,1976; Yeh and Savin,1977;Small,1994;Peltonen et al.,2009).This could be because many authors have concluded that silica released as a result of clay mineral reactions in mudstones and shales is transported and precipitated as quartz cement in associated sandstones(e.g.,Towe,1962;Boles and Franks,1979;Lynch et al., 1997;Land and Milliken,2000;Van der Kamp,2008).In the present study we have undertaken detailed high resolution petrographic examination of mudstones at depth/temperatures corresponding to the smectite–illite transformation to identify the reaction product quartz.

2.Data and analytical methods

The bulk(whole-rock)and clay mineralogy data obtained from

washed drill-bit cuttings of well33/5-2(Fig.1),presented in this study,were mainly obtained during a regional provenance study that was part of the Integrated Basin Study Project(e.g.,N?ttvedt, 2000).The sample material was collected from the Norwegian Petroleum Directorate(NPD).22samples from Late Cretaceous to early Cenozoic from well33/5-2with a sampling interval of approximately100m were analyzed for whole-bulk and clay fraction(<2m m)mineralogy by using XRD.The preparation,anal-ysis and interpretation procedures are based on information from Moore and Reynolds(1997).Both unoriented powders of bulk samples and oriented samples of the clay fraction(<2m m)were run on a Phillips PMI1700/1710diffractometer with CaK a radiation (1.54060?)connected to a PDP11753computer system with Phillips ADP software.In addition,some samples were more recently analyzed on a Phillips X’Pert Data Collector.

The semi-quanti?cation was based on calculations of the inte-grated area of the respective mineral phases,multiplied by in-house calibrated and/or published weight factors(Pearson and Small,1988;Pearson,1990;Ramm,1991).Semi-quanti?cation of the minerals is based on calculations of the integrated area of clay minerals using the Phillips X-Pert HighScore software.The diffractions diagrams of the whole-rock analysis were collected from2to50 2q.In addition,slow scans(26–28.5 2q)were com-plemented for more accurate feldspar determination.The clay fraction(<2m m)was separated by suspension settling,following dispersal by ultrasonic disaggregation.The oriented samples were prepared by?ltering the samples through a0.45m m Millipore?lter and then transferring the material to a silica slide.Analysis of the clay fraction was done by multiple treatments2–50 2q,35 3q and 30 2q(0.06 2q/4times per second),obtained after the following treatment;samples were Mg saturated and air-dried,then ethylene glycolated and heated to550 C for2h.Slow-scan diagrams between24and26 2q(0.01 2q/4times per second)on air-dried specimens were obtained to separate the d(002)kaolinite and d(004)chlorite re?ections.The‘‘expandable clays’’were catego-rized as smectitetI/S(illite–smectite),determined by the inte-grated area of the expanded17?peak with ethylene glycol treatment.The7?(chlorite002/kaolinite001)peak was used to quantify the sum of chlorite and kaolinite.The ratio between the two was determined by the peak heights of kaolinite002(3.58?) and chlorite004(3.53?)obtained from the slow-scan run.Illite was determined by the integrated areas of the10?peak,which also

Fig.1.Base map of the M?re and V?ring Basin–Norwegian Sea and Northern North Sea,with locations of North Sea well33/5-2and the revisited Norwegian Sea well 6505/10-1.MNSH,Mid North Sea High;RFH,Ringk?bing-Fyn High;STZ,Sorgenfrei-Tornquist Zone;OG,Oslo Graben;CG,Central Graben;MF,Moray Firth;SP,Shetland Platform;VG,Viking Graben;HP,Horda Platform;MB,M?re Basin;HT,Halten Terrace; TP,Tr?ndelag Platform;VB,V?ring Basin;MMH,M?re Marginal High;VMH,V?ring Marginal High;EJMFZ,Eastern Jan Mayen Fracture Zone.

B.Thyberg et al./Marine and Petroleum Geology27(2010)1752–17641753

may represent mica,muscovite,and glauconite(Moore and Rey-nolds,1997).With the aim of integrating the clay mineral amounts in the whole-rock data,the clay fraction XRD quanti?cation result for each clay mineral was multiplied by the total clay content determined from the4.5?peak from the bulk run.

In order to establish a relationship between changes in miner-alogical data and physical properties,well logs of gamma ray, resistivity,p-wave velocity and bulk density were acquired from the Norwegian data repository for petroleum data(NPD DISKOS–PetroBank).Data points from5m depth intervals were averaged in order to reduce the amount of data and to extract representative depth trends.The sample depths used in this study are all close to vertical,and are given as true vertical depths in meters below sea bottom.

8selected samples in the sample depth interval2370–2870m corresponding to approximately80–90 C from the North Sea well 33/5-2,as well as6samples below2520m/85 C(Peltonen et al., 2009)from the revisited Norwegian Sea well6505/10-1(Fig.1) were studied.The temperatures have been estimated by applying bottom hole temperatures taken from NPD(2009).Both dried material from the clay fraction(<2m m)and polished thin-sections were examined to identify and document authigenic quartz in mudstones and its textural relationships to illite/smectite and illite.

The dried material of the clay fraction(<2m m)mixed with ethanol was disintegrated in an ultrasonic bath for a few minutes. The?nest fraction of the disintegrated clay fraction material was taken out by a pipette and transferred to a polished carbon-slab, dried,carbon coated and then examined.The slab and thin-sections were coated with a thin carbon layer to prevent any build-up of electrical charge during the SEM/EDS/CL operation.Authigenic quartz cement found in these samples were investigated petro-graphically by Scanning electron microscopy(JEOL JSM6460LV) and secondary electron imaging(SEI)linked with energy dispersive X-ray spectroscopy(EDS)and equipped with monochromatic wavelength dispersive cathode luminescence system(Gatan MonoCL).CL-analysis was carried out in the wavelength area of 350–850nm with dwell time2.0and step size5.0.

The SEM/CL-technique is well known and commonly used on sandstones to differentiate authigenic quartz cement overgrowths from the original detrital grains and to determine provenance of detrital quartz(e.g.,see references in Go¨tze et al.,2001),but more seldom used on quartz cement in mudstones.No reports of CL on1–2m m small authigenic quartz grains in mudstones have been found in the literature.

https://www.wendangku.net/doc/1a858357.html,te Cretaceous to early Cenozoic seismic sequence stratigraphic framework

The mineralogical,petrological and petrophysical well log data with estimated temperatures from well33/5-2located in the northern North Sea(Fig.1)are presented in relation to a Late Cretaceous to early Cenozoic seismic sequence stratigraphic framework(Fig.2,Jordt et al.,1995,2000;Gabrielsen et al.,2001; Kyrkjeb?et al.,2001;Faleide et al.,2002).The Cretaceous succes-sion in the North Sea has been subdivided into six main seismic sequences;K-1–K-6(Fig.2;Gabrielsen et al.,2001;Kyrkjeb?et al., 2001).The Late Cretaceous Shetland Group comprises four sequences(K-3–K-6),the K-3of Cenomanian age,the K-4of late Cenomanian to Turonian age,K-5of Coniacian to Campanian age and the K-6of Maastrichtian age(Fig.2;Gabrielsen et al.,2001; Kyrkjeb?et al.,2001).These sequences are dominated by mudstones interbedded with limestones and calcareous claystones (Isaksen and Tonstad,1989).The approximately time-equivalent Shetland Group sediments in the Norwegian Sea well6505/10-1 (Fig.1),corresponding to K-5and K-6in the North Sea,are composed primarily of mudstones(F?rseth and Lien,2002).These mudstones have only occasional thin layers of silty sandstones and carbonates(Peltonen et al.,2009)and a minor component of deep marine sandstones(e.g.,Brekke et al.,1999).

The Cenozoic succession is subdivided into ten major seismic stratigraphic sequences;CSS-1–CSS-10(Fig.2)(Jordt et al.,1995, 2000;Faleide et al.,2002).The CSS-1is of Late Paleocene–earliest Eocene age and the top CSS-2is dated to the Eocene–Oligocene transition(Fig.2,Jordt et al.,1995,2000;Faleide et al.,2002).These sequences correlate to the Rogaland Group in the North Sea(Fig.2) as well as in the Norwegian Sea(e.g.,F?rseth and Lien,2002).The top CSS-1corresponds to top of the Balder formation in the North Sea which is equivalent to the Tare formation in the Norwegian Sea. Marine sedimentation sourced from the Shetland Platform in the northern North Sea and volcanic activity in the northwest related to the break-up of the NE Atlantic was dominant in the Norwegian Sea (Brekke et al.,1999),throughout early Cenozoic time(Jordt et al., 1995,2000;Faleide et al.,2002

Fig.2.The Cretaceous–Cenozoic seismic sequence stratigraphic framework corre-lated to the formal stratigraphical nomenclature(Isaksen and Tonstad,1989),modi?ed from Gabrielsen et al.(2001).The time scale is based on Gradstein et al.(2004).The notations for the sequences of Late Cretaceous K-3–K-6(Gabrielsen et al.,2001; Kyrkjeb?et al.,2001)and the early Cenozoic CSS-1and CSS-2(Jordt et al.,1995;Faleide et al.,2002)are used in the present study.

B.Thyberg et al./Marine and Petroleum Geology27(2010)1752–1764 1754

4.Results

4.1.Bulk and clay mineralogy

The whole-rock mineralogical(bulk and clay fraction(<2m m)) composition based on XRD analysis of the mudstone succession of the North Sea well33/5-2is presented within the Late Cretaceous to early Cenozoic seismic sequence stratigraphic framework in Fig.3.The XRD results from the Late Cretaceous K-3–K-6sequences reveal a relative similar mineralogical composition throughout the entire mudstone succession.There is a general high relative uniform quartz,plagioclase,kaolinite and chlorite content in the sediments.Nevertheless,there are some noteworthy important exceptions from this pattern delineating Late Cretaceous seismic sequences and depth/temperature related changes in the miner-alogy(Fig.3).A rather signi?cant smectitetI/S decreases down-wards within the K-5and K-4sequences compared to the20–25% smectitetI/S bulk content found in the K-6and uppermost part of the K-5sequences.SmectitetI/S are absent in the lowermost part of the K-4sequence and the entire K-3sequence.An increase in the illite and chlorite content is associated with the decrease in smectitetI/S with burial.Close to the K-2/K-3sequence boundary (base Shetland Group,Fig.2)chlorite also suddenly disappears. Slightly higher content of the carbonate minerals calcite,ankerite/ dolomite and siderite in the depth interval(z1900–2350m,upper part of the K-5sequence)compared to the underlying sediments of the Late Cretaceous mudstone succession is also noteworthy.Trace amounts of K-feldspar are detected in the upper part of the K-5and K-6sequences disappearing with increasing depth/temperature within the K-5sequence and upwards close to the K-6/CSS-1 sequence boundary.The most marked mineralogical changes in well33/5-2can be observed close to this sequence boundary (Fig.3).The highest bulk smectite content correlates with CSS-1, which is also low in chlorite,carbonate and quartz content and has no detectable K-feldspar.

Bulk and clay mineralogy data of the Late Cretaceous and early Cenozoic mudstone succession from well6505/10-1in the Norwe-gian Sea have been recently published by Peltonen et al.,(2008), and display similar mineralogical composition and depth/temper-ature trends as well33/5-2located in the Northern North Sea.

4.2.Petrophysical well log data

Relationships between gamma ray,resistivity,p-wave velocity (Vp)and bulk density as a function of depth/temperature of well 33/5-2are presented within the context of the Late Cretaceous to early Cenozoic seismic sequence stratigraphic framework(Fig.3). The estimated temperatures have been subdivided into40–80 C and80–110 C intervals.

The early Cenozoic smectite-rich CSS-1(and uppermost part of K-6)mudstone sequence displays the highest gamma ray readings, the lowest resistivity,velocity(Vp)and bulk density measure-ments.The petrophysical well log data of the Late Cretaceous K-3to lower part of the K-6sequences differ from the CSS-1and the upper part of the K-6sequences(Fig.3).

Based on the gamma ray readings the Late Cretaceous mudstone section appears to be a relatively homogeneous mudstone succes-sion,but the resistivity and p-wave velocity data display signi?cant ?uctuations with progressive burial depth.A detailed discussion of the sequences and petrophysical related mineralogical changes (Fig.3)found in the entire northern North Sea Late Cretaceous mudstone succession will be presented in a forthcoming paper. However,the velocity/depth increases near2250m(annotated Vp1 in Fig.3)is associated with an increase in resistivity readings consistent with the high carbonate content con?rmed by XRD data in the interval1900–2350m.The velocity peak close to2900m (annotated Vp3in Fig.3)is most probably due to biogenic silica that has been enriched and re-crystallized to quartz during progressive burial.In this paper,we will however lay emphasis on the interval close to and below the velocity/depth contrast(annotated Vp2in Fig.3)at2500m(80 C).This is the depth/temperature interval (2370–2870m, 80 C,Fig.3)where smectite has been trans-formed to illite-smectite and illite(and chlorite).The gamma ray and resistivity measurements as well as XRD data re?ect that these mudstones are relatively homogeneous with respect to clay mineral content and low in carbonate content(Fig.3).Close to 2500m(80 C)abrupt increase in p-wave velocity with a corre-sponding shift in seismic facies is clearly seen,marked Vp2in Fig.3. The Late Cretaceous mudstones section in well6505/10-1display similar mineralogical trends and petrophysical well log readings, including the smectite to illite thermal transformation associated with abrupt increase in velocity close to2500m(2430m/85 C; Peltonen et al.,2009;Thyberg et al.,2009).A close-up and comparison of well log data of p-wave velocity(Vp)and bulk density(RHOB)in the1800–2800m depth interval of well33/5-2 and6505/10-1display also similar trends showing the abrupt velocity change close to2500m(85 C;Fig.4).Note also that well 6505/10-1close to and below2500m display slightly higher velocities(Vp)values than well33/5-2.The density/depth trend of the Late Cretaceous mudstone succession in both wells shows

a general progressive increase in density with depth(Figs.3and4).

4.3.Petrographic evidence of quartz cement in mudstones

The homogeneous mudstone interval with low constant carbonate content2370–2870m( 80 C)of well33/5-2and the mudstone section below2500m( 85 C)in well6505/10-1where an abrupt increase in velocity is documented(Figs.3and4and Peltonen et al.,2009),were chosen for high resolution petrographic investigation of quartz cement in mudstones.The samples where investigated by SEM/EDS/CL techniques to identify possible authi-genic quartz cement potentially important for the physical rock property development seen in the chemical compaction regime of Late Cretaceous mudstone sequences.

4.3.1.Scanning electron microscopy images

Two different types of quartz cement(Type1and2)have been identi?ed by SEM/EDS(Figs.5–7)in the Late Cretaceous K-4and K-5mudstones sequences from well33/5-2and from the K-5 sequence from well6505/10-1.Type1quartz cement occurs as relatively large aggregates of crypto-or microcrystalline(Fig.5a) and macrocrystalline(Fig.5b)irregular quartz cement approxi-mately30–100m m in size.In the shallowest sample studied (2370m),macrocrystalline quartz is observed towards the edges of the irregular crypto-to microcrystalline quartz cement aggregates (Fig.5a and b).In the deepest sample studied(2670m),only fragments of patchy macrocrystalline quartz cement are present (Fig.5c and d).This type of quartz cement is consistent with the ?ndings of Peltonen et al.(2008).

The?ne-grained quartz cement of Type2is found within the micro-pores of the?ne-grained clay matrix consisting mainly of illite and illite–smectite mixed layer minerals(Figs.6and7).The micro-quartz mainly occurs as sub-micron to approximately 1–3m m in size(Figs.6and7).The crystals are found as:i)subhedral to euhedral isolated grains(Fig.6a)but most often identi?ed as ii) more spherical occurring discrete grains or identi?ed as short chains or clusters/nests of several micro-sized grains(Figs.6b,c and7).This type of quartz cement in consistent with the?ndings of Thyberg et al.(2009).The micro-sized neoformed quartz crystals appear to have inter-grown with the mixed layered minerals and

B.Thyberg et al./Marine and Petroleum Geology27(2010)1752–17641755

illite.To further investigate the subtle interlocking relationships of micro-quartz networks and clay crystals,dried material of the clay fraction (<2m m)mixed with ethanol was disintegrated ultrasoni-cally and examined in SEM.The main ?ndings were aggregates of inter-connected micro-sized quartz cement and clay (illite–smec-tite and illite)crystals that were still preserved after ultrasonic treatment (Fig.7c and d).Fine-grained clay minerals (illite–smec-tite and illite)also appear to be partly embedded in quartz cement,con?rming the interlocking cementing relationships between clay and micro-quartz crystals.As expected,the smectite-rich mudstones buried at shallow depth/temperature corresponding to the smectite-rich CSS-1sequence in well 33/5-2(sample 1380m and 1470m exposed to temperatures below about 60–70 C,Fig.3)showed no evidence of micro-quartz formation.

4.3.2.CL-responses of the quartz cement

Typical examples of the CL-responses of the two different types of quartz cement (Type 1and 2)identi?ed in the Late Cretaceous mudstones from well 33/5-2are presented in Figs.5–7.The CL-responses of Type 1quartz cement,categorized as silt-sized irreg-ular aggregates of quartz,display two major different categories of broad luminescence emission bands during the monochromatic CL-analysis (Fig.5:CLa–d).A characteristic broad ‘‘bell-shaped’’or Gaussian shaped luminescence peak between 580nm and 620nm are detected in all the CL-responses of Type 1quartz cements.In addition,the occurrence of a broad luminescence emission band centered at approximately 420nm is frequently obtained (Fig.5:CLa,CLb and CLd).Thus,the characteristic CL-response of Type 1quartz cement constitutes either two broad symmetric ‘‘bell-sha-ped’’/Gaussian shaped luminescence peaks close to 390–430nm and 580–620nm or one broad peak centered at approximately 580–620nm (Fig.5).

Type 2quartz cement categorized as micro-sized quartz crystals embedded in the ?ne-grained clay matrix typically displays a CL-response within the wavelengths of about 580nm and 620nm (Figs.6and 7).The luminescence peak close to 390–430,frequently obtained for Type 1quartz aggregates,has not been detected during monochromatic cathode luminescence analysis of the micro-sized quartz crystals.In addition,the characteristic broad symmetric ‘‘bell-shaped’’/Gaussian shaped CL-response found for Type 1quartz cement (Fig.5)is not so frequently detected,although examples of Type 1quartz cement CL-response (Fig.5:CLc)similar to micro-quartz crystals (Type 2)have been obtained (Fig.6:CLa).Examples of the most common CL-response of the micro-sized quartz crystals are presented in Fig.6(CLb–d)and Fig.7(CLa).They typically display a more irregular and less ‘‘bell-shaped’’/Gaussian shaped with a smaller luminescence emission band centered close to 600nm.There is also a tendency that the luminescence peak with the maximum wavelength of about 620nm has a higher intensity (counts)than the peak close to 580nm (Fig.6:CLb and CLc).In some CL-spectra the peak close to 580nm are not detected (Fig.6:CLd and Fig.7:CLa).More typically a ‘‘shoulder’’of background ‘‘noise’’from the ?ne-grained clay matrix has been emitted in the wavelength range between about 350and 580nm (Fig.7:CLa),probably due to an additional signal from the surrounding clay matrix since very small grains (1–2m m)quartz crystals have been analyzed.Fig.7(CLb)displays an example of the CL-properties of the ?ne-grained clay matrix showing simi-larities to the ‘‘shoulder’’of the CL-response found during the analysis of the micro-quartz crystals,seen in Fig.7(CLa).

2000 3000 4000 2, 22 ,4 2, 62

Vp (m/s)

RHOB (g/cm)

D e p t h (m )

C o

80 C o

Well 33/5-2 Well 6505/10-1 Well 6505/10-1

Well 33/5-2 https://www.wendangku.net/doc/1a858357.html,parison of well log data of p-wave velocity (Vp)and bulk density (RHOB)depth relationships,re?ecting the changes in physical properties during progressive burial,of

well 33/5-2(green dots)and well 6505/10-1(red dots)in the burial depth interval 1800–2800m.This interval is approximately corresponding to the K-5sequence (refer to Fig.2).Close to the 80/85 C temperature (marked by black lines with arrows)a distinct velocity increase but not a corresponding change in bulk density is present in both wells.Location of sample 2470m shown in yellow (well 33/5-2,refer to Fig.6a)and 2620m shown in blue (well 6505/10-1,refer to Fig.6b).(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this article.)

B.Thyberg et al./Marine and Petroleum Geology 27(2010)1752–17641757

5.Discussion

Based on the CL-wavelength responses of both the two different quartz cement types(Type1and2)found in the Late Cretaceous mudstones from well33/5-2and well6505/10-1(Figs.5–7and Peltonen et al.,2009),they have been identi?ed as authigenic. Although low temperature authigenic quartz generally generates less intense CL than quartz formed at high temperature(e.g.,Sipple, 1968;Zinkernagel,1978;Walker and Burley,1991;Milliken,1994), they typically display characteristic CL-peaks close to wavelengths of about600nm(e.g.,Mu¨ller,2000;Go¨tze et al.,2001).The CL-emission of low temperature authigenic quartz may be due to intrinsic effects related to a combination of lattice defects of oxygen vacancies around580nm and/or from non-bridging oxygen hole centers around620nm(e.g.,Mu¨ller,2000;Go¨tze et al.,2001).These intrinsic effects are giving rise to the typical broad‘‘bell-shaped’’/ Gaussian shaped CL-emission spectra of Type1quartz cement(e.g., Fig.5:CLa–CLd)close to600nm.By comparison,the CL-spectrum from a typical detrital silt grain found in mudstones(Fig.7:CLc), shows a different CL-response which displays,among others, a characteristic peak of high intensity close to700nm.The Fig.7 (CLc)is taken from Peltonen et al.(2008),because no clastic quartz grains were found in the Lower Cretaceous mudstones succession of well33/5-2.

The CL-response of some of the Type1quartz cement shows in addition a high intensity(counts)peak in the wavelength range of 390–430nm(Fig.5:CLa,CLb and CLd).This peak cannot be systematically related to the depth/temperature dependent crypto-to microcrystalline or macrocrystalline appearance of the irregular quartz cement,as illustrated in Fig.5.Type1quartz cement is interpreted to have been re-crystallized locally during progressive burial from a biogenic precursor most likely of pelagic organisms like radiolarians and sponge spiculus(opal-A)directly or from recycled siliceous sediments from uplifted adjacent areas.The reworked biogenic sediments of Type1quartz cement have been identi?ed as chert in optical light microscopy.Amorphous silica will,due to slow quartz formation kinetics,re-crystallize in steps forming several unstable/metastable silica phases before the stable end product quartz is formed(Williams et al.,1985).Opal-A is transformed diagenetically to better ordered opal-CT(cristobalite–tridymite),to cryptocrystalline or microcrystalline quartz and ?nally to macro-quartz mainly as a function of time and/or temperature(e.g.,Riech and Von Rad,1979;Williams et al.,1985). Nodular and bedded chert formation has an opal-CT precursor(e.g., Maliva and Siever,1988).

The change of the CL-response during the re-crystallization to quartz from diagenetically altered siliceous biogenic components has not been investigated in detail(Richter et al.,2003).However, according to Marshall(1988),opal-CT shows blue CL with an emission maximum at450nm.In addition,very preliminary results (Richter et al.,2003),indicate that biogenic opal-A without visible CL,or ultra-violet to violet CL according to Mu¨ller(2000,p.61), changes to opal-CT with greenish to greenish-blue CL(around 500nm,see references in Mu¨ller,2000,p.61).Further CL-research on silica phases should help to clarify the changes in CL-properties during the diagenetic pathway opal-A-opal-CT-quartz.The CL-peak centered close to390–430nm is interpreted as being remnants of the CL-properties of opal-A/opal-CT inheritance from the biogenic precursor material to the re-crystallized irregular Type2quartz cement.The presence of these inheritance/remnants at2370–2670m(Fig.5)indicates that the metastable opal-A/CT silica phases may be present at much greater depths than previously thought(e.g.,Bj?rlykke,1998).This is possible due to incorporation or isolation of metastable opal-A/CT in quartz cement during the local re-crystallization process.

Quartz cement in shales from re-crystallization of amorphous silica has been well-documented(e.g.,Murata and Larson,1975; Williams et al.,1985;Schieber et al.,2000;Peltonen et al.,2009).On the other hand,the origin,authigenic or detrital,of silt-sized quartz (Blatt and Schultz,1976;Milliken,1994;Schieber et al.,2000; Williams et al.,2001)not identi?able as biogenically derived has been an issue of long-standing controversy(e.g.,Milliken,1994). Consistent with the?ndings of this study,silt-sized quartz veri?ed by SEM/CL as authigenic,has been interpreted as re-crystallized siliceous planktonic organisms(Milliken,1994;Schieber et al., 2000;Peltonen et al.,2009).Quartz cement sourced by dissolved smectite has been harder to identify in mudstones,due to the extremely?ne-grained nature of the quartz precipitated(Hower et al.,1976;Foster and Custard,1980;Small,1994:Peltonen et al., 2009).

CL-work on micro-quartz crystals is dif?cult due to the small grains analyzed(1–2m m).The‘‘noise’’from the background clay minerals(Fig.7:CLa and CLb)and instrument resolution limitations (e.g.,Mu¨ller,2000;Go¨tze et al.,2001),can make an authigenic veri?cation based on the CL-response of the micro-sized quartz crystals(Type2)somewhat more uncertain.The authigenic nature of Type2quartz cement can however be identi?ed with a relatively high level of con?dence.The fact that typical,or close to,‘‘bell-shaped’’CL-response centered at600nm found in Type1quartz also commonly exist in larger grains of Type2micro-quartz crystals (Fig.6:CLa and CLb),strengthens the interpreted authigenic nature of micro-quartz crystals.Moreover,the lower intensity(counts)of the580nm peak(Fig.6:CLb and CLd)and in fact that the580nm peak is frequently missing(Fig.5:CLd and Fig.6:CLa)giving rise to a more irregular shape of the CL-response from the micro-quartz crystals.The reasons why the580nm peak is lacking or has less intensity may be due to completely or partly‘‘healing’’of the oxygen vacancy lattice defects during the electron exposure. Alternatively,the irregular CL-response found in most Type2 quartz cement may represent differences in CL-properties between authigenic quartz sourced from a biogenic precursor(Type1)and micro-quartz crystals(Type2)formed away from the parent material.

The authigenic micro-pore-?lling micro-quartz is found at burial depths between2370and2870m corresponding to the depth/ temperature interval were smectite has been transformed to illite–smectite,illite and chlorite(Fig.3and Peltonen et al.,2009;Thyberg et al.,2009).The authigenic micro-quartz crystals identi?ed in this study are interpreted to be sourced from local release of Si from the dissolution of smectite and precipitation of illite.The simpli?ed reaction equation below taken from Boles and Franks(1979)illus-trates the process:

Smectite D K D[Illite D Silica D H20

The smectite to illite reaction results in the release of signif-icant amounts of silica(e.g.,Weaver,1959;Towe,1962;Hower et al.,1976;Boles and Franks,1979;Abercrombie et al.,1994; Srodon,1999;Van der Kamp,2008;Peltonen et al.,2009).The presence of micro-sized quartz crystals sourced from the smec-tite to illite reaction documented by this study con?rm results from laboratory mineral growth experiments showing an increase in the bulk quartz content after smectite to illite trans-formation(Small,1994).The amount of Si released in the smec-tite to illite reaction will depend on the composition of smectite present(e.g.,trioctahedral or dioctahedral)(Peltonen et al.,2009; see discussion therein).As can be seen from the reaction equa-tion presented above,a potassium source must be available, (most likely from dissolution of K-feldspar)for the reaction to proceed.

B.Thyberg et al./Marine and Petroleum Geology27(2010)1752–17641761

The smectite to illite reaction has been described as a dissolu-tion–precipitation reaction(e.g.,Nadeau et al.,1985,2002;Inoue et al.,1987;Yau et al.,1987;Boles and Franks,1979;Strixrude and Peacor,2002).This implies that the smectite particle dissolves and authigenic illite particle nucleates and grows(e.g.,Nadeau et al., 1985;Srodon,1999).The excess silica(aq)will quickly precipitate as quartz near together with the neoformed illite–smectite and illite crystals(e.g.,Abercrombie et al.,1994),implying that the authigenic micro-quartz sourced from smectite do not inherit CL-properties from the precursor material.

Dissolution of metastable smectite minerals(and opal-CT)at temperatures between60and80 C create a high silica concen-tration relative to quartz saturation in the pore water(e.g.,Egeberg and Aagaard,1989;Bj?rlykke and Egeberg,1992;Bj?rlykke and Aagaard,1992;Abercrombie et al.,1994).The high silica concen-trations result in the formation of small quartz crystals(micro-sized quartz).This is the only possible form of quartz cement formation in a high silica supersaturation system,since the growth rate of quartz is very low at these low temperatures(around60–80 C) (e.g.,Williams et al.,1985;Bj?rlykke and Egeberg,1992;Jahren and Ramm,2000).

Dissolution of smectite(and opal-A/CT)produces silica super-saturation estimated to be5–10times higher than quartz saturation (e.g.,Bj?rlykke and Aagaard,1992).Most of the re-crystallization of amorphous silica to Type1quartz cement was probably?nished before substantial amounts of smectite became illitized because the high silica saturation produced by amorphous silica stabilizes the smectite.The illitization reaction requires a silica saturation approaching quartz solubility(e.g.,Egeberg and Aagaard,1989; Bj?rlykke and Aagaard,1992)indicating that the Type1quartz cement most likely(except for the preserved remnants of opal-A/CT due to incorporation)pre-dates the micro-quartz crystal formation sourced from the smectite to illite reaction.Precipitation of authi-genic micro-quartz sourced from opal-CT will gradually reduce the silica concentration in the pore water.Smectite then becomes unstable and is gradually replaced by mixed layer minerals(illite–smectite or chlorite–smectite)and discrete illite(or chlorite),while the excess silica is precipitated as micro-quartz.Mudstone samples with a high content of smectite(CSS-1and CSS-2,Fig.3)found at shallower depths(1380m and1470m,exposed to temperatures below about60–70 C only(Fig.3)),did not show evidence of micro-quartz formation.This is because the high silica saturation produced by opal-CT stabilizes the smectite at these temperatures(Egeberg and Aagaard,1989;Bj?rlykke and Aagaard,1992;Abercrombie et al.,1994).

Due to the presence of relatively high amounts of micro-pore-?lling micro-sized quartz cement in the illitized smectitic Late Cretaceous mudstones(K-4&K-5sequences)it is unlikely that the smectite to illite reaction have lead to the export of signi?cant volumes of silica to adjacent sandstones.The low permeability and diffusion coef?cient in mud will strongly reduce the potential for transport of silica(e.g.,Bj?rlykke,1994;Bj?rlykke et al.,1995).The local formation of micro-sized quartz networks,precipitated as discrete grains,short chains and small clusters or nests in the?ne-grained clay matrix(Figs.6and7),is also consistent with closed system diagenesis and a low mobility of silica in mudstones.The growth rate of quartz and diffusion of silica is not high enough even in sandstones to prevent micro-quartz formation(Jahren and Ramm,2000).

In a low temperature closed system like the one studied herein the combination of slow quartz growth(e.g.,Williams et al.,1985; Bj?rkum and Nadeau,1998;Bj?rlykke,1998)and high silica satu-ration creates conditions favoring continuous nucleation and growth of many micro-quartz crystals within the micro-pores of the mudstones.The micro-quartz crystals nucleate on suitable substrates like earlier formed micro-quartz crystals and on illite–smectite and authigenic illite leading to formation of micro-quartz networks.Parts of these quartz networks have been cemented together with illite and illite–smectite crystals.These cementing processes probably result in connections between smaller indi-vidual micro-quartz networks/chains forming larger aggregates. Formation of larger aggregates is re?ected in the interlocking cementing micro-textural relationships found between the authi-genic micro-quartz and clay crystals,potentially extending and reinforcing the micro-quartz networks identi?ed.The micro-quartz precipitation and nucleation process,documented in this study to take place close to and at temperatures exceeding80/ 85 C in well33/5-2and6505/10-1respectively,can be described by formation of inter-connected micro-pore-?lling micro-quartz cement.This micro-quartz nucleation and precipitation process in mudstones is similar to what is found in sandstones(Jahren,1993; Hendry and Trewin,1995;Aase et al.,1998;Jahren and Ramm, 2000;Aase and Walderhaug,2005),where also micro-quartz has been documented to grow on both quartz(e.g.,Jahren and Ramm, 2000)and on authigenic illite–smectite clay?bres(Hendry and Trewin,1995).

The micro-quartz cementing process stiffens the mudstone framework and affects the petrophysical properties of the mudstones.Associated with the depth/temperature interval where smectite transforms to illite–smectite,illite(chlorite)and forma-tion of micro-quartz cementing networks and aggregates,a signif-icant increase in rock stiffness is recorded.This is re?ected by abrupt increase in velocity and a shift in seismic facies close to80 C in well33/5-2(Vp1in Fig.3).This intra K-5seismic re?ector at approximately2800stwt corresponds to the velocity contrast close to2500m burial depth.A similar velocity contrast at85 C has been documented in well6505/10-1(Fig.4and Peltonen et al.,2009; Thyberg et al.,2009).

Quartz will for kinetic reasons not precipitate in sediments before a temperature of60–80 C is reached(e.g.,Bj?rkum and Nadeau,1998;Bj?rlykke,1998).At this‘‘stage’’the crystals may be precipitated as discrete or not-connected quartz crystals in the micro-pores of the mudstones.The gradual increase in density within the chemical compaction regime in both wells(Figs.3and4) could be due to gradually increasing quartz cementation.Forma-tion of aggregates and connected small networks forming longer range stiffening micro-quartz cement complexes can explain the sharp increase in Vp seen around80/85 C.The instant change in velocity(Vp1;Figs.3and4)at the onset of the chemical compac-tion regime(80/85 C)may be related to the degree of connectivity between the micro-quartz crystals and the aggregate formation(as nodes?).Hence,a‘‘critical mass’’of inter-connected micro-quartz and clay crystals may be needed to produce such a signi?cant increase in velocity.In well6505/10-1(Fig.7b,2620m corre-sponding to approximately90 C;Peltonen et al.,2009),a more pervasive inter-connected network of micro-quartz crystals are identi?ed resulting in a stiffer mudstone with higher velocity compared to what is found in well33/5-2(Figs.4and7a,2370m close to80 C).

The distribution of micro-quartz,degree of stiffness and thereby petrophysical properties can be related to the primary content/ distribution of the precursors such as smectite and opal-A.This is ultimately linked to provenance,facies and depositional processes determining the seismic properties/facies of mudstones and shales in sedimentary basins,as illustrated in Fig.3.The mineralogical and petrophysical changes are expressed in the Late Cretaceous to early Cenozoic seismic stratigraphic framework.This provides informa-tion about provenance(primary composition),facies,clay mineral diagenesis and the corresponding changes in physical properties of the mudstones.

B.Thyberg et al./Marine and Petroleum Geology27(2010)1752–1764 1762

6.Conclusions

1.Relatively large aggregates(30–100m m)crypto-to microcrys-

talline and macrocrystalline irregular quartz cement(Type1) replacing biogenic siliceous precursors have been found in Late Cretaceous mudstones of the northern North Sea well33/5-2.

The CL-responses indicate an authigenic origin and is charac-teristic of quartz re-crystallized from opal-A and opal-CT.

2.For the?rst time,direct petrographic evidence of?ne-grained

micro-quartz crystals(1–3m m)as micro-pore-?lling cement (Type2)in mudstones has been detected in the Late Cretaceous (K-4and K-5)mudstone sequences in well33/5-2and well 6505/10-1.

3.The CL-responses of the micro-quartz crystals indicate an

authigenic origin interpreted to be sourced locally from the silica released during the smectite to illlite clay mineral reac-tion.This indicates that silica is not exported but precipitated locally as micro-quartz in a continuous nucleation-precipita-tion process during high silica saturation produced by dis-solving smectite(and opal-A).

4.The micro-quartz crystals have been found as discrete grains,

short chains and small nests/clusters interpreted to be parts of larger inter-connected micro-quartz networks and interlocking aggregates of micro-quartz and clay crystals at the critical depth for pervasive micro-quartz formation(2500m/80–

85 C).

5.The formation of micro-quartz networks(quartz skeletons)and

aggregates increase the rock density and strength.This is re?ec-ted by the gradual increase in well log density and a sudden velocity increase at about2500m(80–85 C).A change in seismic facies can be observed at the same depth.

Acknowledgements

This study is part of the PETROMAKS(Programme for the Optimal Management of Petroleum Resources)project title ‘‘Quantifying the Effects of Sediment Deposition,Compaction and Pore Fluid on Rock Properties and Seismic Signature’’funded by the Norwegian Research Council(NFR).We also thank Berit L?ken Berg at the Department of Geosciences,University of Oslo for help with XRD preparation and analysis.

References

Aase,N.E.,Bj?rkum,P.A.,Nadeau,P.H.,1998.The effect of grain-coating microquartz on preservation of reservoir porosity.APPG Bulletin80(10),1654–1673. Aase,N.E.,Walderhaug,O.,2005.The effect of hydrocarbons on quartz cementation: diagenesis in the Upper Jurassic sandstones of the Miller Field,North Sea, revisited.Petroleum Geoscience11,215–223.

Abercrombie,H.J.,Hutcheon,I.E.,Bloch,J.D.,de Caritat,P.,1994.Silica activity and the smectite–illite reaction.Geology22(6),539–542.

Aplin, A.,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),500–514.

Baldvin,B.,Butler,C.O.,https://www.wendangku.net/doc/1a858357.html,paction curves.APPG Bulletin69(4),622–626. Bayer,U.,Wetzel, A.,https://www.wendangku.net/doc/1a858357.html,pactional behavior of?ne-grained sediments;

examples from Deep Sea Drilling Project cores.Geologische Rundschau78(3), 807–819.

Bj?rlykke,K.,1994.Pore-water?ow and mass transfer of solids in solution in sedimentary basins.In:Parker,A.,Sellwood,B.W.(Eds.),Quantitative Diagen-esis:Recent Developments and Applications to Reservoir Geology,pp.189–221. Bj?rlykke,K.,1998.Clay Mineral Diagenesis in Sedimentary Basins;a Key to the Prediction of Rock Properties;Examples from the North Sea Basin.In:Clay Minerals in the Modern Society,vol.33(1).Mineralogical Society of London, London,United Kingdom,pp.15–34.

Bj?rlykke,K.,1999.Principal aspects of compaction and?uid?ow in mudstones.In: Aplin,A.C.,Fleet,A.J.,Macquaker,J.H.S.(Eds.),Muds and Mudstone;Physical and Fluid Flow Properties.Geological Society of London,London,United Kingdom,Special Publications,vol.158,pp.73–78.Bj?rlykke,K.,2006.Effects of compaction processes on stresses,faults,and?uid ?ow in sedimentary basins:examples from the Norwegian margin.In: Buiter,S.J.H.,Schreurs,G.(Eds.),Analogue and Numerical Modelling of Crustal-Scale Processes.Geological Society,London,London,United Kingdom,Special Publications,vol.253,pp.359–379.

Bj?rlykke,K.,Aagaard,P.,1992.Clay Minerals in North Sea Sandstones.In: Houseknecht,D.W.,Pittman,E.D.(Eds.),Origin,diagenesis,and petrophysics of clay minerals in sandstones,vol.47.Society for Sedimentary Geology(SEPM), Tulsa,OK,United States,pp.65–80.

Bj?rlykke,K.,Aagaard,P.,Egeberg,P.K.,Simmons,S.P.,1995.Geochemical constraints from formation water analyses from the North Sea and the Gulf Coast Basins on quartz,feldspar and illite precipitation in reservoir rocks.In: England,W.A.,Cubitt,J.M.(Eds.),The Geochemistry of Reservoirs.The Geological Society of London,London,United Kingdom,Special Publications, vol.86,pp.33–50.

Bj?rlykke,K.,Egeberg,P.K.,1992.Quartz cementation in sedimentary basins.AAPG Bulletin77(9),1538–1548.

Bj?rlykke,K.,H?eg,K.,1997.Effects of burial diagenesis on stresses,compaction and?uid?ow in sedimentary basins.Marine and Petroleum Geology14(3), 267–276.

Bj?rkum,P.A.,Nadeau,P.H.,1998.Temperature controlled porosity/permeability reduction,?uid migration,and petroleum exploration in sedimentary basins.

Australian Petroleum Production&Exploration Association Journal38,453–464. Bj?rkum,P.A.,Oelkers,E.H.,Nadeau,P.H.,Walderhaug,O.,Murphy,W.M.,1998.

Porosity prediction in quartzose sandstones as a function of time,temperature, depth,stylilite frequency,and hydrocarbon saturation.AAPG Bulletin82, 637–648.

Blatt,H.,Schultz,D.J.,1976.Size distribution of quartz in mudrocks.Sedimentology 23,857–866.

Boles,J.R.,Franks,S.G.,1979.Clay diagenesis in Wilcox sandstones of Southwest Texas;implications of smectite diagenesis on sandstone cementation.Journal of Sedimentary Petrology49(1),55–70.

Brekke,H.,Dahlgren,S.,Nyland,B.,Magnus,C.,1999.The prospectivity of the V?ring and M?re basins on the Norwegian Sea continental margin.In:Fleet, A., Boldy,S.(Eds.),Petroleum Geology of Northwest Europe;Proceeding of the5th Conference.The Geological Society of London,London,United Kingdom, pp.261–274.

Charpentier,D.,Worden,R.H.,Dillon,C.G.,Aplin,A.C.,2003.Fabric development and the smectite to illite transition in Gulf of Mexico mudstones:an image analysis approach.Journal of Geochemical Exploration78–79,459–463.

Chilingar,G.V.,Knight,L.,1960.Relationship between pressure and moisture content of kaolinite,illite,and montmorillonite clays.American Association of Petroleum Geologists Bulletin44(1),101–106.

Chuhan,F.A.,Kjeldstad,A.,Bj?rlykke,K.,Hoeg,K.,2003.Experimental compression of loose sands;relevance to porosity reduction during burial in sedimentary basins.Canadian Geotechnical Journal40(5),995–1011.

Egeberg,P.K.,Aagaard,P.,1989.Origin and evolution of formation water from oil ?elds on the Norwegian shelf.Applied Geochemistry4,131–142.

Faleide,J.I.,Kyrkjeb?,R.,Kjennerud,T.,Gabrielsen,R.H.,Jordt,H.,Fanavoll,S., Bjerke,M.D.,2002.Tectonic impact on sedimentary processes during Cenozoic evolution of the northern North Sea and surrounding areas.In:Dore′,A.G., Cartwright,J.A.,Stoker,S.J.,Turner,J.P.,White,N.(Eds.),Exhumation of the North Atlantic Margin;Timing,Mechanisms and Implications for Petroleum Exploration.The Geological Society of London,London,United Kingdom Special Publications,vol.196,pp.235–269.

Foster,W.R.,Custard,H.C.,1980.Smectite–illite transformation-role in generating and maintaining geopressure.AAPG Bulletin64(5),708.

Freed,R.L.,Peacor,D.R.,1989.Geopressure shale and sealing effect of smectite to illite transition.AAPG Bulletin73(10),1223–1232.

F?rseth,R.B.,Lien,T.,2002.Cretaceous evolution of the Norwegian Sea–a period characterized by tectonic quiescence.Marine and Petroleum Geology19, 1005–1027.

Gabrielsen,R.H.,Kyrkjeb?,R.,Faleide,J.I.,Fjeldskaar,W.,Kjennerud,T.,2001.The Cretaceous post-rift basin con?guration of the northern North Sea.Petroleum Geoscience7,137–154.

Glasman,J.R.,Larter,S.,Briedis,N.A.,1989.Shale diagenesis in the Bergen High area, North Sea.Clay and Clay Minerals37(2),97–112.

Go¨tze,J.,Plo¨tze,M.,Habermann, D.,2001.Origin,spectral characteristics and practical applications of the cathodoluminescence(CL)of quartz–a review.

Mineralogy and Petrology71,225–250.

Gradstein,F.M.,Ogg,J.,Smith,A.(Eds.),2004.A Geologic Time Scale2004.Cam-bridge University Press,589pp.

Hendry,J.P.,Trewin,N.H.,1995.Authigenic quartz microfabrics in Cretaceous turbidites:evidence for silica transformation processes in sandstones.Journal of Sedimentary Research A65(2),380–392.

Ho,N.-C.,Peacor,D.R.,Van der Plujim,B.,1999.Preferred orientation of phyllosili-cates in Gulf Coast mudstones and relation to the smectite–illite transition.Clay and Clay Minerals47,495–504.

Hoffman,J.,Hower,J.,1979.Clay mineral assemblages as low grade metamorphic geothermometers:application to the thrust faulted disturbed belt of Montana, USA.In:Scholle,P.A.,Schluger,P.R.(Eds.),Aspects of Diagenesis.Society for Sedimentary Geology,Special Publication,Tulsa,Ok,United States,pp.55–79. Hower,J.,Eslinger,E.,Hower,M.E.,Perry,E.A.,1976.Mechanism of burial meta-morphism of argillaceous sediment;1,mineralogical and chemical evidence.

Geological Society of American Bulletin87(5),725–737.

B.Thyberg et al./Marine and Petroleum Geology27(2010)1752–17641763

Inoue,A.,Kohyama,N.,Kitagawa,R.,Waranabe,T.,1987.Chemical and morpho-logical evidence for the conversion of smectite to illite.Clays and Clay Minerals 35(2),111–120.

Isaksen,D.,Tonstad,K.,1989.A revised Cretaceous and Tertiary lithostratigraphi nomenclature for the Norwegian North Sea.Norwegian Petroleum Directorate Bulletin5,1–59.

Jahren,J.,1993.Microcrystalline quartz coatings in sandstones.A scanning electron microscopy study.In:Karlson,G.(Ed.),Extended Abstracts from the45th Annual Meeting of the Scandinavian Society for Electron Microscopy, pp.111–112.

Jahren,J.,Ramm,M.,2000.The porosity-preserving effects of microcrystalline quartz coating in arenitic sandstones;examples from the Norwegian conti-nental shelf.In:Worden,R.H.,Morad,S.(Eds.),Quartz Cementation in Sand-stones.Special Publication No29of the International Association of Sedimentologists.Blackwell,Oxford,International,pp.271–280.

Jordt,H.,Faleide,J.I.,Bj?rlykke,K.,Ibrahim,M.T.,1995.Cenozoic sequence stratig-raphy of the central and northern North Sea basin;tectonic development, sediment distribution and provenance areas.Marine and Petroleum Geology12

(8),845–879.

Jordt,H.,Thyberg,B.I.,N?ttvedt,A.,2000.Cenozoic evolution of the central and northern North Sea with focus on differential vertical movements of the basin ?oor and surrounding clastic source areas.In:N?ttvedt,A.,Larsen,B.T.(Eds.), Dynamics of the Norwegian Margin.The Geological Society of London,London, United Kingdom,Special Publications,vol.167,pp.219–243.

Katsube,T.J.,Mudford,B.S.,Best,M.E.,1991.Petrophysical characteristics of shales from the Scotian shelf.Geophysics56,1681–1689.

Kim,J.-W.,Bryant,W.R.,Watkins,J.S.,Tieh,T.T.,1998.Mineralogical and fabric changes of shale during burial diagenesis and their effects on petrophysical properties.Gulf Coast Association of Geological Societies Transactions vXLVIII, 139–150.

Kim,J.-W.,Kim,J.-W.,Bryant,W.R.,Watkins,J.S.,Tieh,T.T.,1999.Electron micro-scopic observations of shale diagenesis,offshore Louisiana,USA,Gulf of Mexico.

Geo Marine Letters18,234–240.

Kyrkjeb?,R.,Kjennerud,T.,Gillmore,G.K.,Faleide,J.I.,Gabrielsen,R.H.,2001.

Cretaceous–Tertiary palaeobathymetry in the northern North Sea;integration of palaeo-water depth estimates obtained by structural restoration and micropalaentological analysis.In:Martinsen,O.J.,Dreyer,T.(Eds.),Sedimentary Environments Offshore Norway–Palaeozoic to Recent.Norwegian Petroleum Society Special Publication,vol.10,pp.321–345.

Land,L.S.,Milliken,K.L.,2000.Regional loss of SiO2and CaCO3,and gain of K2O during burial diagenesis of Gulf Coast Mudrocks,USA.In:Worden,R.H., Morad,S.(Eds.),Quartz Cementation in Sandstones.Special Publication No29 of the International Association of Sedimentologists.Blackwell,Oxford,Inter-national,pp.271–280.

Lander,R.H.,Walderhaug,O.,1999.Predicting porosity through simulating sandstone compaction and quartz cementation.AAPG Bulletin83(3),433–449. Lindgren,H.,Jacobsen,H.,Jakobsen,H.J.,1991.Diagenetic structural transformations in North Sea Jurassic illite/smectite.Clay and Clay Minerals39(1),54–69. 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),1995–2006.

Magara,K.,https://www.wendangku.net/doc/1a858357.html,parison of porosity–depth relationships of shale and sand-stone.Journal of Petroleum Geology3(2),175–185.

Maliva,R.G.,Siever,R.,1988.Pre-Cenozoic nodular cherts:evidence for opal-CT precursors and direct quartz replacement.American Journal of Science288, 798–809.

Marcussen?.,Thyberg, B.I.,Peltonen, C.,Jahren,K.,Bj?rlykke,K.,Faleide,J.I., 2009.Physical properties of Cenozoic mudstones from the northern North Sea:impact of clay mineralogy on compaction trends.AAPG Bulletin93(1), 127–150.

Marshall,J.D.,1988.Cathodoluminescence of Geological Materials.Unwin Hyman, Boston,146pp.

Milliken,K.L.,1994.Cathodoluminescent textures and the origin of quartz silt in Oligocene mudrocks,South Texas.Journal of Sedimentary Research A64(3), 567–571.

Mondol,N.H.,Bj?rlykke,K.,Jahren,J.,Hoeg,K.,2007.Experimental mechanical compaction of clay mineral aggregates–changes in physical properties of mudstones during burial.Marine and Petroleum Geology24(5),289–311. Moore, D.M.,Reynolds,R.C.,1997.X-ray Diffraction and the Identi?cation and Analysis of Clay Minerals.Oxford University Press,Oxford,378pp.

Mu¨ller,A.,2000.Cathodoluminescence and Characterization of Defect Structures in Quartz with Applications to the Study of Granitic Rocks.der Georg-August-Universita¨t zu Go¨ttingen,Go¨ttingen,229pp.

Murata,K.J.,Larson,R.R.,1975.Diagenesis of Miocene siliceous shales,Temblor Range,California.Journal of Research of the US Geological Survey3,553–566. Nadeau,P.H.,Wilson,M.J.,McHardy,W.J.,Tait,J.M.,1985.The Conversion of Smectite to Illite During Diagenesis:Evidence from Some Illitic Clays from Bentonites and Sandstones,Diagenesis and Low-temperature Metamorphism.

Mineralogical Society of London,United Kingdom,pp.393–400.

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 Mineralogist87,1580–1589.NPD,2009.http://www.npd.no/engelsk/cwi/pbl/en/index.htm.Norwegian Petro-leum Directorate Fact-pages.

Nyg?rd,R.,Gutierrez,M.,H?eg,K.,Bj?rlykke,K.,2004.In?uence of burial history on microstructure and compaction behaviour of Kimmeridge clay.Petroleum Geoscience10,259–270.

N?ttvedt,A.,2000.Integrated basin studies–dynamics of the Norwegian margin: an introduction.In:N?ttvedt,A.,Larsen,B.T.(Eds.),Dynamics of the Norwegian Margin.The Geological Society of London,London,United Kingdom,Special Publications,vol.167,pp.1–14.

Pearson,M.J.,1990.Clay mineral distribution and provenance in Mesozoic and Tertiary mudrocks of Moray Firth and northern North Sea.Clay Minerals25(4), 519–541.

Pearson,M.J.,Small,J.S.,1988.Illite–Smectite diagenesis and palaeotemperatures in northern North Sea Quaternary to Mesozoic shale sequences.Clay Minerals23

(2),109–132.

Peltonen,C.,Marcussen,?.,Bj?rlykke,K.,Jahren,J.,2009.Clay mineral diagenesis and quartz cementation in mudstones:the effects of smectite to illite reaction on rock properties.Marine and Petroleum Geology26(6),887–898.

Perry,E.,Hower,J.,1970.Burial diagenesis in Gulf Coast politic sediments.Clays and Clay Minerals18(3),165–177.

Ramm,M.,1991.On Quantitative Mineral Analysis of Sandstones Using XRD.In: Department of Geology,University of Oslo,Internal Series,vol.62,28pp. Richter,D.K.,Go¨tte,Th.,Plo¨tze,M.,Neuser,R.D.,2003.Progress in application of cathodoluminescence(CL)in sedimentary petrology.Mineralogy and Petrology 79,127–166.

Riech,V.,Von Rad,U.,1979.Silica diagenesis in the Atlantic Ocean:diagenetic potential and transformation.In:Talwani,M.,Hay,W.,Ryan,W.B.F.(Eds.),Deep Drilling Results in the Atlantic Ocean,Continental Margins and Paleoenviron-ments.Maurice Ewing Ser 3.American Geophysical Union,Washington, pp.315–340.

Schieber,J.,Krinsley, D.,Riciputi,L.,2000.Diagenetic origin of quartz silt in mudstones and implications for silica cycling.Nature(London)406,981–985. Sipple,R.F.,1968.Sandstone petrology,evidence from luminescence petrography.

Journal of Sedimentary Petrology38,530–554.

Small,J.S.,1994.Fluid Composition,Mineralogy and Morphological Changes Asso-ciated with the Smectite-to-Illite Reaction;an Experimental Investigation of the Effect of Organic Acid Anions.Issue Devoted to Papers Read at a Conference on Diagenesis,Overpressure and Reservoir Quality.Mineralogical Society,London, United Kingdom,pp.539–554.

Srodon,J.,1999.Nature of mixed-layer clays and mechanism of their formation and alteration.Annual Review of Earth and Planetary Sciences27,19–53. Storvoll,V.,Bj?rlykke,K.,Mondol,N.H.,2005.Velocity–depth trends in Mesozoic and Cenozoic sediments from the Norwegian shelf.AAPG Bulletin89(3), 359–381.

Strixrude,L.,Peacor,D.R.,2002.First-principles study of illite–smectite and impli-cations for clay mineral systems.Nature(London)420(6912),165–168. Thyberg, B.I.,Jordt,H.,Bj?rlykke,K.,Faleide,J.I.,2000.Relationships between sequence stratigraphy,mineralogy and geochemistry in Cenozoic sediments of the northern North Sea.In:N?ttvedt,A.,Larsen,B.T.(Eds.),Dynamics of the Norwegian Margin.The Geological Society of London,London,United Kingdom, Special Publications,vol.167,pp.245–272.

Thyberg,B.,Jahren,J.,Winje,T.,Bj?rlykke,K.,Faleide,J.I.,2009.From mud to shale: rock stiffening by micro-quartz cementation.First Break27,27–33.

Towe,K.M.,1962.Clay mineral diagenesis as a possible source of silica cement in sedimentary rocks.Journal of Sedimentary Petrology32(1),26–28.

Van der Kamp,P.C.,2008.Smectite–illite–muscovite transformations,quartz dissolution,and silica release in shales.Clays and Clay Minerals56(1),66–81. Walker,G.,Burley,S.,1991.Luminescence petrography and spectroscopic studies of diagenetic minerals.In:Barker,C.E.,Kopp,O.C.(Eds.),Luminescence Microscopy and Spectroscopy:Quantitative and Qualitative Application:SEPM Short Course 25,pp.83–96.

Weaver,C.E.,1959.The clay petrology of sediments.In:Swineford,A.(Ed.),Clays and Clay Minerals.Pergamon Press,Oxford,United Kingdom,pp.154–187. Williams,L.A.,Parks,G.A.,Crerar,D.A.,1985.Silica diagenesis,I.Solubility controls.

Journal of Sedimentary Petrology55,301–311.

Williams,C.J.,Hesselbo,S.P.,Jenkyns,H.C.,Morgans-Bell,H.S.,2001.Quartz silt in mudrocks as a key to sequence stratigraphy(Kimmeridge clay formation,Late Jurassic,Wessex Basin,UK).Terra Nova13(6),449–455.

Worden,R.H.,Charpentier,D.,Fisher,Q.J.,Aplin,A.C.,2005.Fabric development and the smectite to illite transition in Upper Cretaceous mudstones from the North Sea;an image analysis approach.In:Shaw,R.P.(Ed.),Understanding the Micro to Macro Behavior of Rock–Fluid Systems.Geological Society of London,Lon-don,United Kingdom,Special Publications,vol.249,pp.103–114.

Yau,Y.C.,Peacor,D.R.,McDowell,S.D.,1987.Smectite-to-illite reactions in Salton Sea shales:a transmission and analytical electron microscopy study.Journal of Sedimentary Petrology57(2),335–342.

Yeh,H.W.,Savin,S.M.,1977.Mechanism of burial metamorphism of argillaceous sediments:3,O-isotope evidence.Geological Society of American Bulletin88

(9),1321–1330.

Zinkernagel,U.,1978.Cathodoluminescence of Quartz and Its Application to Sandstone Petrology.In:Contributions to Sedimentology,vol.8.E.Schwei-zerbart’sche Verlagbuchhandlung(Na¨gele und Obermiller),Stuttgart,69pp.

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