diagenesis and reservoir-quality evolution of deep-water turbidites

7/28/2019 Diagenesis and Reservoir-quality Evolution of Deep-water Turbidites

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ACTA

UNIVERSITATIS

UPSALIENSIS

UPPSALA

2007

Digital Comprehensive Summaries of Uppsala Dissertations

from the Faculty of Science and Technology 279

Diagenesis and Reservoir-Quality

Evolution of Deep-Water

Turbidites: Links to Basin Setting,

Depositional Facies, and Sequence

Stratigraphy

HOWRI MANSURBEG

ISSN 1651-6214

ISBN 978-91-554-6817-0

urn:nbn:se:uu:diva-7634


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Dissertation at Uppsala University to be publicly examined in Axel Hamberg-salen,Geocentrum, Friday, March 23, 2007 at 10:00 for the Degree of Doctor of Philosophy. The

examination will be conducted in EnglishAbstract

Mansurbeg, H. 2007. Diagenesis and Reservoir-Quality Evolution of Deep-Water Turbidites:Links to Basin Setting, Depositional Facies, and Sequence Stratigraphy. Acta UniversitatisUpsaliensis. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty ofScience and Technology 279. 59 pp. Uppsala. ISBN 978-91-554-6817-0

A study of the distribution of diagenetic alterations and their impact on reservoir-quality evo-lution in four deep-water turbidite successions (Cretaceous to Eocene) from basins in active(foreland) and passive margins revealed the impact of tectonic setting, depositional facies, andchanges in the relative sea level.

Diagenetic modifications encountered in the turbiditic sandstones from the passive marginbasins include dissolution and kaolinitization (kaolin has 18OVSMOW = +13.3 to +15.2;

DVSMOW = -96.6 to -79.6) of framework silicates, formation of grain coating chloriticand illitic clays, cementation by carbonates and quartz, as well as the mechanical and chemicalcompaction of detrital quartz. Kaolinitization, which is most extensive in the lowstand systemstracts, is attributed to meteoric-water flux during major fall in the relative sea level. Preser-vation of porosity and permeability in sandstones from the passive margin basins (up to 30%and 1 Darcy, respectively) is attributed to the presence of abundant rigid quartz and feldspargrains and to dissolution of carbonate cement as well as mica and feldspars. Diagenetic modi-fications in turbidites from the foreland basins include carbonate cementation and mechanicalcompaction of the abundant ductile rock fragments, which were derived from fold-thrust belts.These diagenetic alterations resulted in nearly total elimination of depositional porosity andpermeability.

The wide range of13CVPDB values of these cements (about -18 to +22) in passivemargin basins is attributed to input of dissolved carbon from various processes of organic matteralterations, including microbial methanogenesis and thermal decarboxylation of kerogen. The

narrower range of13CVPDB values of these cements (about -2 to +7) in the forelandbasins suggests the importance of carbon derivation from the dissolution of carbonate grains.The generally wide range of18O values (about -17 to -1) of the carbonate cements re-flect the impact of oxygen isotopic composition of the various fluid involved (including marinedepositional waters, fluxed meteoric waters, evolved formation waters) and the wide ranges ofprecipitation temperatures.

Results of this study are anticipated to have important implication for hydrocarbon explo-ration in deep-water turbidites from passive and active margin basins and for pre-drilling as-sessment of the spatial and temporal distribution of reservoir quality in such deposits.

Keywords: Diagenesis, turbidites, reservoir quality, passive and active margins, basin setting,depositional facies, sequence stratigraphy

Howri Mansurbeg, Department of Electronic Publishing, Uppsala University, Villavgen 16,SE-752 36 Uppsala, Sweden

c Howri Mansurbeg 2007

ISSN 1651-6214ISBN 978-91-554-6817-0

urn:nbn:se:uu:diva-7634 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7634)


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The important thing in science is not so much to obtain new facts

as to discover new ways of thinking about them.

William Lawrence Bragg

Dedicated toMansurbeg and Shorish families


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List of Papers

This thesis is based on the following papers, which are referred to in the textby their Roman numerals.

I Mansurbeg, H., Mohamed A.K. El-ghali, Morad, S.,Plink-Bjrklund, P. (2006) The impact of meteoric water on

the diagenetic alterations in deep-water, marine siliciclasticturbidites. Journal of Geochemical Exploration, 89:254-258

II Mansurbeg, H., Morad, S., Marfil, R., El-ghali1, M.A.K.,Nystuen, J.P., Caja, M.A., Amorosi, A., Garcia, D. (2007)Diagenesis and reservoir quality evolution of palaeocenedeep-water, marine sandstones, the Shetland-Faroes Basin,British Continental Shelf. Marine and Petroleum Geology, Inreview.

III Mansurbeg, H., De Ros, L. F., and Morad, S. (2007) Diagenesisof the Urucutuca Formation (Lowe Cretaceous), Espirito Santo

Basin, eastern Brazil: Impact on the reservoir quality and hetero-geneity evolution pathways in turbiditic sandstones. SedimentaryGeology, To be submitted

IV Mansurbeg, H., Morad, S., Plink-Bjrklund, P. andEl-Ghali, M.A.K. (2007) Diagenetic alterations related to fallingstage and lowstand systems tracts of shelf, slope and basin floorsandstones (Eocene Central Basin, Spitsbergen). IAS SpecialPublication, accepted.

V Mansurberg, H., Caja, M.A., Marfil, R., Garcia, D., Morad, S.,Remacha, E., Amorosi, A. (2007) The diagenetic evolution andporosity destruction of hybrid turbiditic arenites of foreland

basin: Evidence from the Eocene Hecho Group, Pyrenees, Spain.Sedimentary Geology, To be submitted.

VI Marfil, R., Mansurbeg, H., Garcia, D., Caja, M.A., Remacha, E.,Morad, S., Amorosi, A., Nystuen, J-P. (2007) Dolomite-rich con-densed sections in overbank deposits of turbidite channels, theEocene Hecho Group, south-central Pyrenees, Spain. IAS SpecialPublication, accepted.

Reprints were made with permission from the publishers.

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Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.1 Aims of Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.2 Sequence Stratigraphy of Turbidite Deposits . . . . . . . . . . . . . . 111.3 Depositional Facies of Turbidite Deposits . . . . . . . . . . . . . . . . 131.4 Theory and Approach of Linking Diagenesis to Sequence

Stratigraphy of Deep-Water Turbiditic Sandstones . . . . . . . . . . 141.5 Sedimentary Successions Selected for Study . . . . . . . . . . . . . . 15

2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Important Eogenetic Alterations in the Deep-Water Turbiditic

Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 Most Common Mesogenetic Alterations in the Deep-Water Turbiditic

Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Porosity and Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 Predictive Models of Diagensis and Reservoir-Quality Evolution in

Deep-Water Turbiditic Sandstones . . . . . . . . . . . . . . . . . . . . . . . . . 317 Computer Modelling of Impact of Fluid Flow on Geochemical and

Mineralogical Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 Summary Of The Papers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

8.1 The Impact of Meteoric Water on The Diagenetic Alterationsin Deep-Water, Marine Siliciclastic Turbidites . . . . . . . . . . . . . 39

8.2 Diagenesis and Reservoir Quality Evolution of PalaeoceneDeep-Water, Marine Sandstones, the Shetland-Faroes Basin,British Continental Shelf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

8.3 Diagenesis of the Urucutuca Formation (Lowe Cretaceous),Espirito Santo Basin, Eastern Brazil: Impact on the ReservoirQuality and Heterogeneity Evolution Pathways in TurbiditicSandstones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.4 Diagenetic Alterations Related to Falling Stage and LowstandSystems Tracts of Shelf, Slope and Basin Floor Sandstones(Eocene Central Basin, Spitsbergen) . . . . . . . . . . . . . . . . . . . . 41

8.5 The Diagenetic Evolution and Porosity Destruction of HybridTurbiditic Arenites of Foreland Basin: Evidence from theEocene Hecho Group, Pyrenees, Spain . . . . . . . . . . . . . . . . . . 42

8.6 Dolomite-Rich Condensed Sections in Overbank Deposits ofTurbidite Channels, The Eocene Hecho Group, South-CentralPyrenees, Spain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42


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9 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4510 Summary in Swedish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

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1. Introduction

The diagenetic evolution of siliciclastic deposits is complex and controlledby several inter-related parameters (Fig. 1.1), including detrital composition,pore-water chemistry, depositional facies, paleo-climatic conditions, rate ofdeposition, and burial-thermal history of the basin (Stonecipher et al., 1984;Morad et al., 2000). The detrital composition of sandstones is strongly con-trolled by the tectonic setting of the basin, such as location in passive versus

active margin settings. Changes in the relative sea level, which occur due toeustacy and/or the tectonic uplift/subsidence, control important aspects of sed-iment diagenesis (Fig. 1.2), such as pore-water chemistry, amounts and typesof intrabasinal grains (e.g. mud intraclasts), grain size and sorting, and sedi-mentation rates, (i.e. residence time of sediment at near sea floor conditions).

Recent studies have, thus, demonstrated that the diagenetic evolution ofparalic and shallow-marine, siliciclastic deposits can be better understood andpredicted when linked to the sequence stratigraphic framework (Morad et al.,2000; Ketzer et al., 2002, 2003a, b, 2005; Salem et al., 2005; Al-Ramadan etal., 2005; El-ghali et al., 2006). Conversely, linking the distribution of diage-netic alterations to sequence stratigraphy of deep-water turbiditic sediments isdifficult, and thus not well explored in the literature. This is probably becauseof difficulties in deriving well-constrained sequence stratigraphic models fordeep-water deposits, which owes in turn to the equivocal, direct impact of ma-

jor changes in the relative sea level on these deposits. Instead, changes in therelative sea level have an indirect impact on the sequence stratigraphic frame-work and on related distribution of diagenetic alterations of turbiditic deposits.Rapid fall in the relative sea level is accompanied by erosion of the exposedshelf sediments may lead to the incorporation of intra-basinal, siliceous and/orcarbonate bioclasts. Additionally, large proportions of coarse-grained sand areby-passed across the shelf through incised valleys and delivered to the slopeand basin floor. Conversely, rapid rise in the relative sea level results in the de-position of fine-grained, hemi-pelagic sediments, whereas the coarser grainedsediments are trapped further landward on the shelf. Rapid rise in the relativesea level may also result in the derivation of mud intraclasts of various sizesby erosion of mud deposits on the slope and basin floor by means of turbiditycurrents.

Diagenetic regimes used in this summery, which are sensu Morad et al.,(2000), include: (1) eodiagenesis (


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Figure 1.1: Flow chart of the interrelationship of the main parameters that controldiagenetic evolution of siliciclastic deposits (Stonecipher et al., 1984)

Transgressive surface

Slope fanBasin floor fan

LowstandSystemsTract (LST)

TransgressiveSystemsTract (TST)

Maximum Flooding Surface (MFS)

Highstand Systems Tract (HST)

Sequence Boundary

PREVIOUS SEDIMENTARY SEQUENCE

Time

Basinflo

orfa

n

(e

arly

LST)

Slope

fanTST

late LST

HST

A

B

Figure 1.2: (A) idealized sequence stratigraphic model showing the systems tractsand key stratigraphic surfaces in shallow- and deep-water marine turbiditic siliciclas-tic deposits. (B) conceptual model of a relative sea level cycle through time, whichis divided into falling limb and rising limb separated by the lowstand systems tract(modified after Emery and Myers, 1996; Moore, 2001).

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teoric waters); and (2) mesodiagenesis (>70C; depth > 2 km), which is me-diated by evolved formation water and elevated temperature (Morad et al.,

2000).

1.1 Aims of StudyThe aims of this thesis are to unravel: (i) parameters controlling the diage-netic evolution of deep-water turbiditic sandstones based on integrating thepetrological and geochemical data into tectonic setting (passive versus activemargin basin settings), depositional facies and sequence stratigraphy, and (ii)the impact of diagenetic alterations on the temporal and spatial distribution ofreservoir quality and heterogeneity.

1.2 Sequence Stratigraphy of Turbidite DepositsSequence stratigraphy, which is the study of genetically related facies withina framework of chronostratigraphically significant surfaces, provides a pow-erful tool for unravelling and predicting the stratigraphy and architecture ofdeep-marine clastic systems (e.g. Pickering et al., 1995; Emery and Myers,1996; Richards and Bowman, 1998; Posamentier and Allen, 1999; Stow andMayall, 2000). However, sequence stratigraphy in deep-water turbiditic de-posits is difficult to constrain because it merely indirectly reflects the complex

interplay between a range of interdependent parameters on the continentalshelf, including changes in the relative sea level, tectonic setting of the basinand sediment supply (Emery and Myers, 1996). Consequently, a wide variabil-ity of facies distribution and organization of architectural elements should beexpected in the deep-water depositional environments (Reading and Richards,1994). Thus, no single global model can provide accurate description and pre-diction for turbidite systems (Normark et al., 1983; Mutti et al., 2000).

In contrast to shallow marine and paralic deposits, the identification ofkey sequence-stratigraphic surfaces in deep-water sediments, which is merelybased on analyses of seismic profiles and identification of stratal stacking pat-terns, is fraught with difficulties (Bouma and Stones, 2000). Sedimentation in

the deep water is commonly suggested to be indirectly controlled by changesin the relative sea level on the shelf. Rapid fall in the relative sea level (duringearly LST) is bringing the shoreline close to, or below the shelf break, provid-ing a mechanism for transfer of sediment into basin floors and formation ofbasin floor fans (Fig. 1.2). During deposition of the late LST (Fig. 1.2) relativesea level is stabilized and rise slowly results in bypassing sediments onto theslope areas forming slope fans. The slope fan deposits are characterized bychannel-levee complexes at the apex and front of canyon mouths (Emery andMyers, 1996).

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Deposition of the late LST is followed by a rapid rise in the relative sealevel, which results in the formation of transgressive surface (TS; Fig. 1.2);

the TS separates the LST from the overlying transgressive systems tract (TST;Fig. 1.2). In a vertical section through submarine fan deposits, packages ofturbiditic sandstone would be interpreted as LST deposits and major units ofmudstone would be considered as TST deposits. A widespread marine flood-ing surface on the shelf, which represents furthest landward migration of therelative seal level is called maximum flooding surface (MFS; Fig. 1.2). TheMFS, which separates the underlying TST deposits from the overlying high-stand systems tract (HST; Fig. 1.2) is probably recognizable in deep-waterdeposits because it may display evidence of stratigraphic condensation (lowsedimentation rates), such as burrowed surfaces, hardground, mineralization,and fossil accumulations (Posamentier and Allen, 1999).

The central assumption of sequence stratigraphic models in the deep-waterturbiditic sandstones is that sedimentation within deep-water systemsincreases during relative sea-level lowstand, while during transgressionand sea-level highstand sedimentation diminishes or temporarily halts(e.g. Shanmugam et al., 1985; Posamentier and Vail, 1988). However, anincreasing number of authors have suggested that submarine fans can bedeposited during rise in the relative sea level, such as the Amazon Fan(Flood et al., 1995) and Navy Fan (Piper and Normark, 1983). Depositionof deep-water sand during rising sea level is apparently favored by narrowshelves, incised submarine canyons, shelf-parallel currents and tectonicactivity at the basin margin and hinterland (e.g. Reading and Richards 1994;

Stow and Mayall 2000; Shanmugam, 2000). When submarine canyons areconnected with a shelf-edge delta or directly connect with the river mouth,sediment may be transported straight into the basin (e.g. Burgess and Hovius,1998).

Another controversial aspect regarding the sequence stratigraphy of thedeep-water turbiditic sediments is the placement of sequence boundary (SB).In the original sequence stratigraphical model devised in the late 1970s (Vailet al., 1977; Mitchum, 1977), the SB is placed at the base of the early LST indeep-water sediments corresponds to the correlative conformity, which formsat the start of the relative sea level fall. More recent sequence stratigraphicmodels (e.g. Hunt and Tucker, 1992) suggest that the sequence boundary

should be placed at the lowest position reached by relative sea level. Huntand Tucker (1992) argued that the correlative conformity can be traced to thetop of the prograding submarine fan complex, and thus suggested that the SBover the falling stage systems tract (FSST; also known as forced regressivesystems tract FRWST) does not match Mitchums (1977) original definitionof SB or its time equivalent marine correlative conformity in the deep-watersediments that was tied to the onset of a sea level fall.

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A B

C

Figure 1.3: Field photos showing: (A) sand-rich channel complex that belongs to theSpanish lowstand systems tract of Eocene, the Pyrenees, (B) fine-grained levee sand-stones, (C) laterally extensive carbonate-cemented sediments belonging to the trans-gressive systems tracts, which have presumably formed below marine flooding sur-faces.

1.3 Depositional Facies of Turbidite DepositsTurbidites are sediments transported beyond the shelf edge into deep waterby gravity flow and deposited on the continental slope and the basin floor.

The main depositional elements of deep-water turbiditic sandstones are basinfloor fans, slope fans, channel complexes and fine-grained levees (Figs 1.2and 1.3A, B and C). Basin floor and slope fans are the basinward portion ofthe lowstand systems tract. Channel turbidite deposits are usually composedof coarse-grained to conglomeratic sandstones, which have sharp erosionalbases and fining up successions (Fig. 1.3A). Levee-overbank deposits, whichform reservoirs lateral to the main channel (Figs 1.3B and C), show no channellags. Channel turbidite deposits are characterized by high sand/mud ratio thanthe fine-grained, levee-overbank deposits.

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1.4 Theory and Approach of Linking Diagenesis toSequence Stratigraphy of Deep-Water TurbiditicSandstonesThe primary reservoir properties of sandstones are strongly controlled by sev-eral parameters, which are related to provenance, depositional facies, rates ofsediment supply and changes in the relative sea-level. These parameters in-clude detrital mineralogical composition, grain size, sorting, spatial distribu-tion of architectural elements and meso-scale heterogeneities and sand/mudratio (Figs 1.3A, B and C). Variable extents of reservoir-quality modifica-tion occur by diagenetic alterations, which are strongly controlled by param-eters like the detrital composition of the sand, pore-water chemistry, texture,and organic-matter content. These parameters are, in turn, linked to rates of

changes in relative sea level, rates of sediment supply, and hence to the se-quence stratigraphic framework (Fig. 1.2).

The interplay between rate of sediment supply and rate of changes in therelative sea level is the main factor controlling transgression and regressionevents, i.e. creation and destruction of accommodation, on continental shelves.Changes in the relative sea level are controlled, in turn, by basin-floor sub-sidence/uplift and/or by changes in the eustatic sea-level (Posamentier andAllen, 1993). Basin floor subsidence/uplift and rates of sediment supply arecontrolled by tectonic setting of the basin. The rates of creation and destruc-tion of accommodation versus rates of sediment supply control the spatialand temporal distribution of depositional facies and the sequence stratigraphic

framework of sedimentary successions, including the formation of varioussystems tracts and key sequence stratigraphic surfaces.

Changes in the relative sea level and rates of sediment supply are accompa-nied by changes in pore-water composition (meteoric, brackish and marine)and residence time of the sediments under certain geological conditions, andhence in the pattern of diagenetic alterations of shelf and, probably, of deep-water turbiditic sediments (Morad et al., 2000; Mansurbeg et al., 2006). Theresidence time of sediment under certain geochemical conditions such as be-low the seafloor and below exposed shelf (i.e. below sequence boundaries)control magnitude of these diagenetic alterations, which include dissolutionand alteration of framework silicates and carbonate cementation.

Major fall in the relative sea level (i.e. regression) results in less accommo-dation and, perhaps, even subaerial exposure of the shelf, which is accompa-nied by: (i) incursion of under-saturated meteoric waters into exposed sedi-ments and deep-water turbiditic sandstones, which induces grain dissolutionand kaolinitization (Carvalho et al., 1995; Morad et al., 2000; Mansurbeg etal., 2006) and cementation by blocky to poikilotopic calcite in the lowstandand forced regressive wedge (or falling stage) systems tracts (Al-Ramadan etal., 2005), and (ii) erosion of exposed older shelf sediment by advancing riversand, thus, the formation of incised valleys. The intra-basinal sand grains (e.g.

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mud intraclasts, glaucony and carbonate bioclasts), derived from shelf erosionare by-passed, together with extra-basinal sediments (mainly quartz, feldspar

and rock fragments derived from outside the depositional basin), to the conti-nental slope and basin floor via the incised valleys, resulting in the depositionof submarine fans (falling stage or lowstand systems tract). Deposition is re-stricted though to lobes, which cover part of the submarine fan whilst otherparts of the fan receive mainly pelagic sediments.

Conversely, transgression events on the shelf result in: (i) domination of ma-rine pore-water composition, which results in the formation of dolomite andgrain-coating minerals (berthierine and micro-quartz), and (ii) low sedimen-tation rates and starvation in offshore as well as basin slope and floor settingsowing to sediments entrapment in landward depositional settings. Sedimenta-tion on the basin floor will be dominated by pelagic and hemipelgic sediments

(transgressive and highstand systems tracts). Low sedimentation rates in theouter shelf and slope areas favor the formation of abundant evolved glaucony(Amorosi, 1997 and Ketzer at al., 2003a) and extensive cementation by mi-crocrystalline carbonates (Al-Ramadan et al., 2005), which is enhanced bydiffusive flux of dissolved Ca and carbon into the pore water from the over-lying seawater (Morad et al., 2000). Thus, sedimentary events on the shelfare anticipated to have indirect but profound impact not only on the sequencestratigraphic framework but also on the detrital composition and diageneticevolution of deep-water marine deposits. Detrital composition of the sand de-termines its chemical and physical properties, and hence the pattern of diage-netic alterations at near surface conditions and during progressive burial and

increase in temperature (Primmer et al., 1997; Morad et al., 2000). Hence,regression-transgression events have important control on the proportion ofextra-basinal (mainly quartz, feldspar, mica and rock fragments derived fromthe hinterland) and intra-basinal (mainly carbonate grains, mud intraclasts,and glaucony derived within the basin) sand grains (Fig. 1.4).

1.5 Sedimentary Successions Selected for StudyFor comparison purposes, two basins located along passive margins(Shetland-Faeroe, Esprito Santo Basin, Eastern Brazil) and two basins

along active margins (Ainsa-Jaca and Spitsbergen) were selected for study(Fig. 1.5). The Shetland-Faeroe Basin (ca 125 km wide and 600 km long)is located between the West Shetland platform in the east and the FaeroeIslands in the west. The area is five times that of the prospective part of theNorth Sea Basin, but mainly because of extreme water depths (ca 2.5 km),it has been only slightly explored. Sequence stratigraphic studies recognizea complex basin margin, with marked basinward and landward shifts insedimentation determining the location of sand-rich depositional systems(Mitchell et al., 1993). Ebdon et al., (1995) recognized a major sequence

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boundary at the base of the Late Paleogene and subdivided the successioninto several stratigraphic sequences, based mainly on maximum flooding

surfaces, which can be correlated with their equivalents to the North SeaBasin. The reservoirs are comprised of submarine-fan sandstones depositedas early lowstand systems tracts.

The Esprito Santo Basin covers an area of 25,000 km2 in eastern Brazilpassive margin with only 3220 km2 of it is onshore. The basin basement iscomposed of Precambrian migmatites, granulites, gneisses and granites, struc-tured as a homoclinal of faulted blocks tilted towards east. Neocomian riftphase lacustrine shales of the basal Cricar Formation are the main sourcerocks of the basin (Estrella, 1984; Carvalho, 1989). The main reservoirs arethe turbidites of the Urucutuca Formation, which contain close to 60 millionbarrels of recoverable oil (Carvalho, 1989). In the onshore portion of the basin,

deposition of these turbidites occurred dominantly within submarine canyonsincised in the border of the platform during relative sea-level falls that punc-tuated the overall transgressive setting of the late Cretaceous and early Ter-tiary. Some of the turbidite successions can be connected with global, eustaticsea-level curves. Thus, deposition may have resulted from increased sedimentsupply related to tectonic reactivation in the source area and basin margin,and/or to climatically-controlled denudation rates in the source area (Bruhn,1993).

extrabasinal clasts

intrabasinal

carbonate clasts

intrabasinal

non-carbonate clasts

hybrid

arenites

regre

ssio

n regressio

n

calcarenites

glauconitic,

and/or phosphatic

arenires

lithic-, arkose-, andquartzarenites

Figure 1.4: Triangle showing possible changes in the proportion of extra-basinal andintra-basinal, framework grain composition of sandstones due to changes in the rela-tive sea level (modified from Zuffa 1980).

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hetland-FaroeBasin

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Figure1.5:Locationmapofthestudiedbasins.

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The Ainsa-Jaca Basin is located in the south central Pyrenees (Spain). ThePyrenees, extending in northern Spain and south of France are an Alpine chain

formed as a fold and thrust belt during late Cretaceous to Miocene, at the col-lisional boundary between the Iberian and the Eurasian plates, as a result of aroughly N-S crustal contraction, comprise10-12 million years of depositionof deep-marine clastics with a cumulative thickness of 4 km and providean ideal natural laboratory for studying slope-basin depositional systems. TheAinsa basin contains about 20-25 deep-water sand bodies, typically 10s mthick but packaged essentially as seven coarse clastic depositional complexes,each in the order of at least 100-300 m thick.

The Spitsbergen Basin is located on Svalbard and bounded to the west bythe West Spitsbergen fold- and thrust belt, which die out towards the easternpart. This basin was a foreland basin during the initial period of active thrust-

ing, but became a piggy-back basin (Blythe and Kleinspehn, 1998) on accountof foreland propagation of thrusting. The Lomfjorden and Billefjorden faultzones east of the Central Basin probably represent late stage reactivation ofdeep-watered reverse faults (Braathen et al., 1999). The slope and basin floorfans of Eocene age were the target of this study. The basin is rare in the sensethat a linkage of coastal-plain, shelf, slope and basin-floor facies tracts can bewalked out along large-scale shelf-margin clinoforms. The clinoforms aresuccessive time lines in the stratigraphy, generated as the basin margin ac-creted southeastwards. Each clinoform surface represents a morphologic pro-file from the coastal plain to the marine shelf and down into the deeper waterslope and basin-floor environments of the depositional system.

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2. Methodology

The studied successions occur as outcrops and in the subsurface. Sandstonecore samples that represent various depositional facies, systems tracts and keysequence stratigraphic surfaces were collected. Thin sections were preparedfor all samples subsequent to vacuum impregnation with blue epoxy. Modalanalyses of the sandstone samples were preformed by counting 300 pointsin each thin section. Scanning electron microscope (SEM) was used to study

crystal habits and paragenetic relationships among diagenetic minerals in rep-resentative samples. Polished thin sections representing sandstones from thevarious depositional facies and systems tracts encountered were coated witha thin layer of carbon for the purpose of electron microprobe (EMP) analy-ses. Cameca SX50 instrument equipped with three spectrometers and a back-scattered electron detector (BSE) was used to determine the chemical com-positions and paragenetic relationships of different cement types. Operatingconditions during analysis were an accelerating voltage of 20 kV, a measuredbeam current of 10 nA for carbonates and 12 nA for silicates, and a spot sizeof 1-5 m. The standard and count times used were wollastonite (Ca, 10 s),MgO (Mg, 10 s), strontianite (Sr, 10 s), MnTiO3 (Mn, 10 s), and hematite (Fe,10 s). Analytical precision was better than 0.1% for all elements.

Stable carbon and oxygen isotope analyses were carried out on carbonate-cemented sandstones representative of the various depositional environmentsand systems tracts in order to determine the geochemical conditions, pore wa-ters composition and/or temperature of precipitation. Calcite-cemented sam-ples were reacted with 100% phosphoric acid at 25C for one hour, and Fe-dolomite/ankerite and siderite-cemented samples were reacted at 50C forone day and six days, respectively (e.g. Al-Aasm et al., 1990). The CO 2 gasreleased was collected and analyzed using a Delta plus mass spectrometer.Samples containing calcite, dolomite and siderite were subjected to sequen-tial chemical separation treatment (Al-Aasm et al., 1990). The phosphoricacid fractionation factors used were 1.01025 for calcite at 25C (Friedmanand ONeil, 1977), 1.01060 for dolomite at 50C and 1.010454 for siderite at50C (Rosenbaum and Sheppard, 1986). Precision of all analyses was betterthan 0.05 for both 13C and 18O. Oxygen and carbon isotope data arepresented in the notation relative to the V-PDB and V-SMOW standards.

The 87Sr/86Sr isotope ratios in carbonate cements were analyzed (papers IIIand VI) using an automated Finnigan 261 mass spectrometer equipped with 9faraday collectors. Some of calcite-cemented samples from different systems

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tracts were washed with distilled water and then reacted with dilute acetic acidin order to avoid silicate leaching. Correction for isotope fractionation during

the analyses was made by normalization to 86Sr/88Sr = 0.1194. The meanstandard error of mass spectrometer performance was 0.00003 for standardNBS-987. A JEOL JEM 2010 200KV analytical transmission electron micro-scope (TEM) was used for a detailed characterization of the < 2 micron claymineral fractions.

Sulfur isotope ratios in pyrite-cemented sandstones were analyzed to un-ravel the source of sulfur (paper II). X-ray diffraction (XRD) analyses werepreformed on the fine fraction (< 20 m) from representative sandstone sam-ples using a Siemens D5000 diffractometer (paper II). A high sensitivity cath-ode CL microscope was used to study zonation in various carbonate cements(paper V). Microthermometric analyses of the fluid inclusions were preformed

in the Shetland-Faroes Basin sandstones samples (paper II) using LinkhamTH600 stage calibrated for the temperature range between -100 and 400C.The temperatures were measured using the procedure described in Shepherdet al. (1985). He-porosity and permeability measurements were performed oncore plugs (paper V).

The oxygen and hydrogen isotopes of kaolin from 11 samples were ana-lyzed, and the results are reported in relative to the Vienna Standard MeanOcean Water (V-SMOW) standard. Samples were subjected to removal of or-ganics by exposing them to NaOOH solution adjusted to a pH of 9.5 whileplaced in boiling water bath for 15 minutes, followed by centrifugation at 800rpm for 5 min. The remaining mud was centrifuged at 750 rpm for 3.3 minutes

to separate the clay fraction. Samples containing carbonates were exposed tothe same procedure above after being subjected to carbonate removal by sim-mering in a buffer solution of acetic acid for at least eight hours.

Conventional petrographic methods and the use of whole rock chemistryprovide basic information needed to discriminate between detrital inputs anddiagenetic alterations. Applying these methods to the deep marine turbiditeshelps recognizing condensed surfaces in otherwise monotonous successions,and hence aiding the sequence stratigraphic interpretation.

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3. Important Eogenetic Alterations in

the Deep-Water Turbiditic Deposits

This study shows that the types, extent and distribution pattern of eogeneticalterations in the deep-water turbiditic sandstones vary considerably betweenbasins located at passive versus active margin settings. Turbiditic sandstonesobtained from active (foreland) basins show mainly: (i) mechanical

compaction of ductile sedimentary and low-grade metamorphic rockfragments, which resulted in nearly complete elimination of depositionalporosity and permeability, and (ii) formation of minor amounts of calcite,siderite, non-ferroan dolomite cements and pyrite. Carbonate cementation ismost extensive below marine flooding surfaces, particularly in the presenceof detrital carbonates.

Eogenetic alterations in turbiditic sandstones from the passive margin set-tings include: (i) mechanical compaction, which is manifested by grain re-arrangement, bending of micas, and formation of pseudomatrix owing to duc-tile deformation of mud intraclasts, (ii) kaolinitization and dissolution of theframework silicate grains (feldspars, mica and mud intraclasts), particularly in

the channel sand and basin floor sand fans (Figs 3.1 and 3.2), (iii) cementationby blocky to poikilotopic calcite, which occurs as continuously cemented, thinor several meters thick sandstone layers or as scattered concretions (paper II:calcite cement occurs mainly below marine flooding and maximum floodingsurfaces), and (iv) formation of smectitic grain-coating clays. Kaolinitizationis most abundant in the FSST and LST sandstones and below the SB (papersII) in basins located in passive continental margins. The loosely expandedtexture of the kaolinitized silicate grains in the studied sandstones suggestsformation during near-surface eodiagenesis (Figs 3.1A, B and C). Kaoliniti-zation is attributed to the flux of meteoric water into the deep-water turbiditicsandstones during major fall in the relative seal level (Fig. 3.3; Mansurbeg

et al., 2006; Prochnow et al., 2006). However, other mechanisms of meteoricwater flux into deep-water sand, such as hyperpycnal flow and increase inhydraulic head owing to basin margin uplift, cannot be ruled out. Stable oxy-gen and hydrogen isotopes of the kaolin (18OVSMOW = +13.3 to +15.2;DVSMOW = -96.6 to 79.6) fall close to the kaolinite meteoric waterline, supporting a meteoric origin (Fig. 3.4; Morad et al., 2003; paper III).Deviation of the stable isotopic values from this line is attributed to partialconversion of kaolinite into dickite during mesodiagenesis.

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A B

C

Figure 3.1: (A) Backscattered image showing kaolinitized mica. Mica has expandedinto adjacent pores, which resulted in porosity deterioration. (B) optical micrograph(unpolarized light) showing kaolinitization of pseudomatrix. (C) SEM image display-ing morphological features of grain-replacing, kaolinite that has been transformedpartly into thicker dickite.

Passive margin

Active margin

Faroe-Shetland Basin

Hecho group

Figure 3.2: Optical micrographs (A and B; plane polarized) showing variable and suc-cessive degrees of alteration and dissolution of detrital biotite and the formation oflarge secondary porosity (the Shetland-Faroe Basin, passive margin). C and D (shownfor comparision) are optical micrographs under plane polarized and cross nicols, re-spectively, showing that calcite cementation and intergranular pressure dissolutionhave resulted in complete destruction of reservoir quality (no signs of dissolution)in Ainsa-Jaca Basin, active margin.

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Figure 3.3: Schematic model of prograding deltaic-slope facies on passive continentalmargin showing that major sea-level fall may extend the influence of meteoric wa-ter circulation (arrows) into deep-water sandstones (Modified after Bethke, 1989 andEinsele, 2000)

The occurrence of abundant carbonate cement below marine flooding andmaximum flooding surfaces is attributed to the long residence time of sed-

iments below the flooding surfaces that enhance the diffusion of dissolvedcarbon and Ca2+ from the overlaying seawater and/or to abundant intrabasi-nal carbonates. (Kantorowicz et al., 1987; Taylor et al., 1995; Morad et al.,2000; Ketzer et al., 2003b; Al-Ramadan et al., 2005).

Glaucony is a common feature and, in some cases, relatively abundant inturbiditic sandstones from sandstones obtained from basins located in passivemargin settings. The greenish colour and presence of internal micro-crackswithin the glaucony pellets suggest formation within the basin, yet probably inthe outer shelf and on the slope and has been slumped into the basin floor. Theformation of glaucony in these depositional environments occurs immediatelybelow the seafloor and was presumably enhanced by low sedimentation rates.

Conversely, glaucony is completely absent in turbiditic sandstones obtainedfrom active basin settings, being attributed to the high sedimentation ratesencountered in these basins. High sedimentation rates preclude glaucony for-mation because of the rapid establishment of iron reduction geochemical zonebelow the seafloor by rapid burial of the sediments (Ketzer et al., 2003a).

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kaolin from Urucutuca

meteoric line

weathering kaolinite (Savin and Epstein, 1970)Cretaceous of Canada (Longstaffe, 1989)

kaolin from Brent (Glassman et al., 1989)

kaolinite from Brent (McAulay et al., 1994)Dickite from Brent (McAulay et al., 1994)

18OSMOW

DSMOW

-20

0

-40

-60

-80

-100

-120

-140+5 +10 +15 +20 +25 +30 +35

Figure 3.4: Cross plot ofDVSMOW and 18OVSMOW values of diagenetic kaolinfrom different sandstones and weathering kaolin. Kaolin from the Urucutuca sand-stones (Brazil) are situated close to the meteoric water line.

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4. Most Common Mesogenetic

Alterations in the Deep-WaterTurbiditic Deposits

The distribution pattern of mesogenetic alterations is influenced to consider-able extent by the distribution of eogenetic alterations in the sandstones, whichwere in turn strongly linked to the passive versus active margin basin setting.

The most common mesogenetic alterations in the deep-water turbiditic sand-stones from the passive margin basins include: (i) clay mineral transformation,such as conversion of kaolinite into dickite and chloritization and illitization ofkaolinite and of grain coating smectite; dickite, has not been illitized owing toits more stable crystal structure than kaolinite (Morad et al.,1994), (ii) cemen-tation by quartz overgrowths of sandstones with clean quartz surfaces; the dis-solved silica needed was derived from concomitant intergranular pressure dis-solution of quartz grains in sandstones that are enriched in grain-coating illiticclays and mica, (iii) cementation by Fe-dolomite and ankerite, (iv) albitizationof detrital plagioclase and, to smaller extent, K-feldspar grains. Typical diage-netic alterations in turbiditic sandstones from the active margin basins include

albitization of detrital plagioclase and, less commonly, K-feldspar grains andthe precipitation of calcite and Fe-dolomite cement.

SEM studies indicate that the grain-coatings chloritic clays have impededthe precipitation of quartz overgrowths, and hence promoted the preservationof reservoir quality in deeply-buried sandstones (Ehrenberg, 1993; Aase et al.,1996; Lima and De Ros, 2003 and Salem et al., 2005; paper II). Various oc-currence habits of quartz cements (overgrowths, outgrowths, discrete crystals,poikilotopic and rare micro-quartz) in sandstones from the different deposi-tional facies and systems tracts of the passive margin basins indicate variousorigins (Worden and Morad, 2000). Variations in the amounts of quartz ce-ment are also attributed to facies-controlled variations in the distribution of il-

litic clay coatings and presence of mica, which exerted decisive control on theintergranular pressure dissolution of quartz grains (Oelker et al., 1996). Pres-sure dissolution acted as the most obvious source of dissolved silica neededfor quartz cementation. Conversely, sandstones that are poor in clay coatingshave been subjected to considerable degree of cementation by quartz over-growths (cf. Bloch et al., 2002). Quartz overgrowths and intergranular pres-sure dissolution are known to be significant at temperature of about 90-130Cand burial depths > 3 km (McBride, 1989; Walderhaug, 1996). Fluid inclu-

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sion thermometry indicates that quartz cementation occurred at temperaturesof 90-110C (paper II).

Dickite occurs as blocky crystals (5-15 m across) with book-like and ver-micular stacking patterns containing etched of thin kaolinite remnants. Kaolinis engulfed by, and hence predates, quartz overgrowths. Conversion of kaoli-nite to dickite is known to occur with increase in burial depth and temper-ature (paper II) through small-scale dissolution and re-precipitation (Ehren-berg, 1993; Morad et al., 1994), which is evidenced by: (i) the association ofdickite and etched kaolinite, and (ii) preservation of vermicular and bookletstacking pattern of kaolinite in dickite (paper II and IV). Kaolinite to dickiteconversion was presumably enhanced by flux of acidic waters, which main-tained low aK+/aH+ ratio, such as waters derived upon maturation of kerogen(Morad et al., 1994).

Albite in the turbiditic sandstones from the passive margin basins (paper II)occurs as numerous small, lath-like crystals (1-15 m across) that are parallelaligned to each other and to remnants of severely etched plagioclase and,less commonly, K-feldspar grains, and are hence considered as albitizedfeldspar (e.g. Morad, 1986 and Saigal et al., 1988, Morad et al., 1990). Partlyalbitized plagioclase grains have preserved their original twining pattern,whereas partly albitized K-feldspar contain irregular patches of albite andof remnants of the detrital host feldspar. Albitized feldspars, particularlyplagioclase, contain variable amounts of intragranular pores, are untwined,vacuolated and display patchy extinction patterns. Thus, these feldsparsdisplay petrographic features similar to diagenetically albitized feldspars

described by Morad (1986), Morad et al. (1990) and Saigal et al., (1988).Albitization of plagioclase acted as a source of Al3+ and Ca2+, which wereincorporated in mesogenetic clay minerals (dickite, illite and chlorite) andcarbonate cements, respectively. Albitization of K-feldspar has acted as asource of potassium needed for the formation of illite (up to 8%; Morad etal., 1990; Bjrlykke and Aagaard, 1992).

Albitized feldspar grains in arenites from the active margin basinsare apparently of both diagenetic and detrital origins. Distinguishingdiagenetically albitized feldspar from those formed in the source area isa serious problem (paper V). Nevertheless, the lack of well-developed,smooth-surfaced, parallel-aligned, tiny albite crystals and of intragranular

porosity in the feldspar, and/or the presence of sericite and epidote canbe used as evidence of albitization in the source area, such as duringhydrothermal albitization of granitic rocks (Varlamoff, 1972).

Stable oxygen and carbon isotope analyses (Fig. 4.1) show that the carbon-ate cements were precipitated at diverse geochemical conditions and/or tem-peratures. The cross plot of13C versus 18O values of carbonate cements inthe studied successions reveals the lack of correlation when carbonate cementsare considered for each basin as well as for the whole carbonate cement (Fig.4.1). This lack of correlation between 13C versus 18O values is attributed to

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-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0

-20

-15

-10

-5

0

5

10

15

20

25

Faeroe-Shetland BasinSpitsbergen BasinEsprito Santo BasinHecho groupyellow marker beds

of Hecho group

18

OPDB

13

CPDB

Figure 4.1: Cross plot of13C versus 18O values of carbonate cements in the stud-ied successions reveals the lack of correlation when carbonate cements are consideredfor each basin as well as for the whole carbonate cement. This lack of correlationis attributed to wide variations both in the sources (e.g. marine versus meteoric) ofdissolved carbon as well as in the biochemical (e.g., bacterial sulphate reduction andmethanogenesis, such as in the Esprito Santo Basin, Brazil), thermo-chemical (ther-mal decarboxylation) processes of organic matter degradation, and dissolution of car-

bonate grains.

wide variations both in the sources (e.g. marine versus meteoric) of dissolvedcarbon as well as in the biochemical (e.g., bacterial sulphate reduction andmethanogenesis, such as in the Esprito Santo Basin, Brazil), thermo-chemical(thermal decarboxylation) processes of organic matter degradation and disso-lution of carbonate grains. This postulation is supported by the wide rangeof the 13C values (Fig. 4.1), For each carbonate cement type, there is spe-cific temperature-dependent, oxygen isotope fractionation equation betweenthe mineral and pore waters, which is used to determine either the precipi-

tation temperature and/or isotopic composition of the pore water (Fig. 4.2).Assuming that the 18OVSMOW values of pore waters varied between ma-rine and evolved marine composition (-1.2 to +2), the 18O values of thecarbonate cements suggest precipitation at wide range of temperatures (Fig.4.2). The overall low 18O values may, in some cases, be related to the flux ofmeteoric waters, which have lower 18O values than marine pore waters.

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-10 0 10

-6

-10

-14

-16

150

100

50

poikilotopic

Calcite

-10 0 10

0

50

100

0

-4

-8

-12

calcite

concretions

-5

-7-9

-11Fe-dolomite

/ankerite

-10 0 1050

100

150

50

100

150

-13 -11

-9

-7-5

-10 0 10

siderite

18O

SMOW 18

OSMOW

Te

mperatureC

TemperatureC

Figure 4.2: Curves of oxygen-isotopes fractionation between calcite, siderite anddolomite/ankerite and water as a function of temperature. The shaded fields illustratethe possible ranges of precipitation temperatures of carbonate cements in the stud-ied turbidites if waters involved were of marine origin (18OVSMOW = -1.2permil;Shackleton and Kennett, 1975) and moderately evolved brine (18OVSMOW = +2.0)

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5. Porosity and Permeability

In contrast to arenites from active margin basins, fairly high porosity (12-23%)and permeability (0.6-1241 mD) values are commonly encountered in passivemargin turbiditic sandstones, being attributed mainly to variation in detritalcomposition of the sand between these basin settings. Turbiditic sandstonesfrom passive margin are rich in quartz, and thus chemically and mechanicallystable, and have better potential to form good reservoirs even upon deep burial

(paper II and III). However, some of the passive margin sandstones are rich infeldspar too, and are thus mechanically stable but chemically fairly unstable.Prolonged percolation of undersaturated meteoric water promotes feldspardissolution and kaolinitization. Arenites from the active margin basins are richin lithic fragments (low-grade metamorphic and/or carbonate rock fragments),and are thus mechanically unstable causing rapid loss in porosity and perme-ability during burial due to mechanical compaction (Bloch, 1994; papers IVand V).

Porosity in deep-water turbiditic sandstones from passive margin settings(papers II and III) contain variable amounts of intergranular, intragranular andmoldic pores, and micropores (< 10 m) to macropores. Intragranular andmoldic pores are commonly formed by partial to completely dissolution ofdetrital feldspar, mud intraclasts and mica (papers II and III). Dissolution ofthese chemically labile grains has created secondary macropores that are, inmany cases, well connected to the overall pore system in the sandstone. Sec-ondary porosity in sandstones from the passive margin basins has also beenformed by the dissolution of calcite cement (papers II and III). Significantamounts of microporosity, which induces high water saturation in the reser-voir sandstones, occur within kaolin crystals that have replaced feldspar, mudintraclasts and mica. The dissolution of framework grain and cement is moresignificant in permeable, coarser-grained, channel complexes than in the finer-grained, less permeable crevasse splay sandstones (paper III).

Helium porosity and permeability (paper III) is higher in the coarse-grainedto conglomeratic, channel complex sandstones (12-23%; av. 17% and 1.4-1241; av. 190 mD, respectively) than in the finer-grained crevasse splay sand-stones (6-15%; 0.6-53 mD; av. 12 mD), resulting in considerable degree ofreservoir heterogeneity. In some of the sandstones, reservoir heterogeneitymay occur within the same depositional facies owing to variations in the dia-genetic evolution pathways that are, in turn, related mainly to variations in thedetrital composition.

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01 001 0001

01

51

02

52

03

53

Po

ro

(ytis

%)

mreP e liba i yt m( )D

hc enna mocl p el asx notsdn es

fi en -gra deni lev nasee d enots s

ls epo a isabdn n lf- naf-roo notsdnas es

Log

Figure 5.1: Cross plot of porosity versus log permeability for channel complex, fine-grained levee, slope and basin floor fan sandstones from passive margin settings. Thelack of correlation is presumably owing to the presence of abundant microporosity aswell as intragranular and moldic pores that are poorly connected with the overall poresystem in the sandstones, which has enhanced porosity without significant contribu-tion to permeability.

The cross plot of porosity versus permeability values of sandstones fromthe passive margin reveals no correlation (Fig. 5.1), which is attributed to thepresence of considerable amounts of microporosity in the clay minerals, inintragranular pores and moldic pores that are isolated from the overall poresystems. Hence, such pores contribute to the total porosity values but little,if any, to the permeability values. Conversely, sandstones that are character-ized by high porosity and permeability values (Fig. 5.1) include those whichare rich in quartz grains and characterized by the presence of considerableamounts of intergranular pores to which moldic pores are well connected.

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6. Predictive Models of Diagensis

and Reservoir-Quality Evolution inDeep-Water Turbiditic Sandstones

Integrating the detrital composition of the sand, sequence stratigraphy, anddepositional facies is of profound importance in deciphering the spatial andtemporal distribution of diagenetic alterations and their impact on reservoir-

quality evolution pathways. The quartz-feldspar dominated framework grainsof turbiditic sandstones from the passive margins are derived predominantlyfrom uplifted granitic and gneissic basement rocks, whereas framework grainsof sandstones from the active margin settings are derived from predominantlysedimentary (carbonates and mudstones) and low-grade metamorphic rocksof fold-thrust belts (Fig. 6.1). Sand composition and its impact on reservoir-quality evolution pathways are, thus, a function of tectonic setting of the basin.

Thus, highly immature, ductile-grains rich, turbiditic sandstonesare deposited in active margin settings. Apart from few, extensivelycarbonate-cemented sandstones, such as those below marine floodingsurfaces, compaction is more important than cementation in porosity

destruction due to the presence of abundant ductile grains (Fig. 6.2). Theinfluence of meteoric waters on diagenesis of turbiditic sandstones is limitedin such basinal settings, probably because: (i) porosity and permeabilityare deteriorated early after deposition and precluding circulation of suchwaters, and (ii) buffering of the acidic meteoric waters by interaction with theabundant carbonate rock fragments.

Conversely, the deposition of quartz-feldspar rich sands, which results inmechanically stable and chemically relatively unstable sandstones, is favouredin passive margin conditions owing to the low relief, and hence low erosionrates, intense, prolonged chemical weathering in the source area, long trans-port distances, and the dominantly granitic-gneissic source rocks (Fig. 6.1).

Limited mechanical compaction of turbiditic sandstones from passive mar-gin settings would, thus, lead to porosity preservation to depths as great as3 km, particularly when the sandstones are rich in grain-coating clays, whichretarded cementation by quartz overgrowths (Pittman and Larese, 1991). Con-versely, sandstones that are poor in mica and grain-coating clays have lost theirporosity and permeability owing to extensive cementation by quartz over-growths. Considerable amounts of intragranular and moldic porosity wereformed in turbiditic sandstones from passive margin basins by the dissolution

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Quartz grainLow-grade metamorphic

rock fragmentPorosity Mud intraclast Feldspar

Calcite cement Quartz cement Kaolinitized mica Siderite Dolomite$ETRITAL

CARBONATEGRAIN

Eodiagenesis

Mesodiag

enesis

70C

!CTIVEMARGIN

Quartz

LithicsFeldspar

!CTIVEMARGIN

! "

'LAUCONY

Figure 6.1: Schematic model showing the spatial and temporal distribution of dia-genetic alterations and variations in the diagenetic evolution pathways in turbiditicsandstones deposited in active and passive margins, respectively. The block diagramsA and B are modified after Bouma and Stone (2000)

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Cement (%)

Intergranularvolume(%)

0 10 20 30 40

0

10

20

30

40

Original porosity destroyed by cementation (%)

Originalporositydestroyedbymechanical

compa

ctionandintergranularpressuresolution(%)

0

10

25

50

75

90

100

Inte

rgranula

rporosity

(%)

0%

10

20

30

0 25 50 75 100

Passive marginturbidites

Active marginturbidites

20

Figure 6.2: Cross plot of intergranular cement volume versus total intergranular vol-ume (cf. Houseknecht, 1987, modified by Ehrenberg, 1993) of the studied turbiditicsandstones showing that the intergranular porosity has been reduced mainly by com-paction rather than by cementation. In contrast to passive margin turbidites, activemargin turbidites have almost no porosity.

of framework feldspar, mud intraclasts and mica grains. Grain dissolution insandstones from passive margin basins was presumably enhanced by the slowrates of primary porosity and permeability loss owing to limited mechanicalcompaction of ductile framework grains in sandstones, which hence ensuredefficient fluid flow,.

Opposite to what was thought earlier (Bjrlykke, 1983; Bethke, 1989), weprovide evidence showing that the diagenesis and reservoir-quality evolutionof deep-water, turbiditic sandstones are not merely mediated by marine porewaters, but by meteoric waters too. Meteoric-water incursion into deep-water,passive margins turbiditic sandstones is enigmatic, but is suggested here tooccur during shallow burial as response to considerable fall in the relative sealevel (Fig. 3.3). Meteoric-water percolation has induced pervasive dissolu-tion and kaolinitization of the framework silicates, and hence in concomitantformation of considerable volume of secondary micro- and macropores, par-ticularly in LST and FSST sandstones. The macropores are, in many cases,fairly well connected to the overall pore system, and have thus contributed topermeability enhancement of the sandstones (papers II and III).

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7. Computer Modelling of Impact

of Fluid Flow on Geochemical andMineralogical Modifications

Computer modelling of the geochemical and mineralogical changes in tur-biditic sandstones from passive-margin settings induced by fluid-sediment in-teractions under the initial (i.e., initial mineralogical and organic matter com-

position of the sediment) and boundary conditions (timing, T, driving mech-anism, chemistry of the fluid involved) performed. Such computer modellingwill give quick insight into how diagenetic processes progress and what are theparameters that control the final diagenetic products in turbiditic sandstonesfrom passive and active margins and potential development of predictive mod-els of mineral-water interaction pathways (Figs 7.1A and 7.1B).

Preliminary simulations, which were conducted using a reaction transportcode (DIAPHORE) (Le Gallo et al., 1998), integrate the mineralogy, diage-netic histories and geodynamic contexts of passive versus active margins. Tur-biditic sandstones from the ShetlandFaroes Basin and from the Hecho groupdiffer in detrital mineralogy by being quartz-feldspar dominated and hybrid

arenites (dominated by carbonate and low-grade metamorphic grain), respec-tively. Compositional differences are accounted for by selecting representativemodal sandstone compositions from representative basins.

Meteoric recharge, which is anticipated to occur upon rapid fall in the rel-ative sea level on the shelf, is allowed to occur for the sedimentary pile ofthe passive margin (ShetlandFaroes) Basin. The geodynamic context con-trols also the possibilities of tilting of the sedimentary pile upon depositionand subsequent burial. Tilting controls the steepness of the temperature gra-dients that may occur along a given genetic unit, such as from proximal todistal settings. Assuming that preferential, basinward fluid flow pathways ex-isted within these units upon meteoric recharge of the continental shelf (at

lowstand), we have tentatively simulated the coupled fluid and rock composi-tional evolutions.

We have, so far, explored simple1D geometries where the moving fluid isconfined to a single, mineralogically homogeneous, sandstone interval. Evenin this simple case, the combination of downflow increase in temperatureand elemental transport drives complex patterns of fluid rock interaction, andhence substantial mineralogical changes. For the Shetland-Faroe Basin case,where the temperature gradients is expected to be the lowest, competition be-

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Flow against a temperature gradient 1C km-1 with marine + mudstone-derived waters

60C 90C60C 90C

Al

Si

K

Na

Ca

Fe

C

Cl

H+

solutesmol. kg-1

after2 ky

calcite

siderite

chlorite

illite

plagio

albite

K-felds

kaol

quartz

solids vol%

60

75

65

70

80

1

10-2

10-4

10-6

10-8

after20 ky

inlet 20km 40km inlet 20km 40km

porosityporosity

60C 90C60C 90C

Al

Si

K

Na

Ca

Fe

C

Cl

H+

solutesmol. kg-1

Al

Si

K

Na

Ca

Fe

C

Cl

H+

solutesmol. kg-1

after2 ky

calcite

siderite

chlorite

illite

plagio

albite

K-felds

kaol

quartz

solids vol%

calcite

siderite

chlorite

illite

plagio

albite

K-felds

kaol

quartz

solids vol%

60

75

65

70

80

1

10-2

10-4

10-6

10-8

after20 ky


porosityporosity

A

Flow against a temperature gradient 2C km-1 with marine + shale-derived waters

Al

Si

K

Na

Ca

Fe

C

Cl

H+

solutesmol. kg-1

after10 ky

calcite

siderite

chlorite

illite

plagio

albite

K-felds

kaol

quartz

solids vol%

60

75

65

70

80

1

10-2

10-4

10-6

10-8

after30 ky50C 100C 50C 100C


Al

Si

K

Na

Ca

Fe

C

Cl

H+

solutesmol. kg-1

Al

Si

K

Na

Ca

Fe

C

Cl

H+

solutesmol. kg-1

after10 ky

calcite

siderite

chlorite

illite

plagio

albite

K-felds

kaol

quartz

solids vol%

calcite

siderite

chlorite

illite

plagio

albite

K-felds

kaol

quartz

solids vol%

60

75

65

70

80

1

10-2

10-4

10-6

10-8

after30 ky50C 100C 50C 100C


Figure 7.1: (A) and (B) Simulated evolution of the mineralogy (upper boxes) andthe fluid chemistry (lower boxes) for a model siliciclastic reservoir from passive mar-gin (e.g. Shetland-Faroes Basin) upon downwards migration of pore waters against asmooth (1C km1) temperature gradient. The input water (left side) is seawater equi-librated at low T (60C) with the reservoir mineralogy, with some additional carbonate

(representing shale-derived water)

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tween Ca transport and kinetically controlled, T dependent, plagioclase dis-solution drives albitization (+ minor kaolin and calcite), whereas K-feldspar

is essentially stable (Figs 7.1A and 7.1B), which is in agreement with pet-rographical observations (paper II). For the avctive margin (ex. Hecho group)case, basinward flowing fluids, which are expected to experience much steepertemperature gradients, modelling predicts that albitization of the K-feldsparshould develop as a consequence of the temperature dependent Na+/K+ ac-tivity ratio in equilibrium with diagenetic albite and detrital K-feldspars.

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8. Summary Of The Papers

Paper I

8.1 The Impact of Meteoric Water on The DiageneticAlterations in Deep-Water, Marine SiliciclasticTurbidites

Meteoric-water flux and formation of kaolinite owing to the dissolution ofdetrital silicates are common features of continental and paralic sandstones.In deep-water marine sandstones, meteoric-water flux is commonlyconsidered unlikely to occur. However, the study of deep-water, marinesandstones of the ShetlandFaroe Basin on the British continental shelfrevealed widespread and extensive dissolution and kaolinitization of mica andfeldspar grains, which are attributed to meteoric-water flux during a sea-levellowstand. We suggest that this apparently enigmatic meteoric-water fluxmechanism is likely to have occurred by hyperpycnal flow. Hyperpycnal flowoccurs when river effluent directly transfers into sediment gravity flow, andenters seawater as a mixture of sediment and fresh water. The likelihood for

hyperpycnal flows increases at times when rivers and distributary channelsreach the shelf edge, and their flows are delivered directly onto the deepwaterslope.

Paper II

8.2 Diagenesis and Reservoir Quality Evolutionof Palaeocene Deep-Water, Marine Sandstones, theShetland-Faroes Basin, British Continental Shelf

Mineralogic, petrographic, and geochemical analyses of siliciclastic,lowstand, transgressive and highstand systems tract turbiditic sediments(Middle-Upper Palaeocene) recovered from six wells in the West ofShetland-Faroes Basin (British continental shelf) are used to decipher anddiscuss the diagenetic alterations and related reservoir-quality evolution. TheMiddle-Upper Palaeocene sandstones (subarkoses to arkoses) are cementedby carbonates, quartz and clay minerals. Carbonate cements (intergranularand grain replacive calcite, siderite, ferroan dolomite and ankerite) are ofeogenetic and mesogenetic origins. The eogenetic alterations have been

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mediated by marine, meteoric and mixed marine/meteoric pore waters andresulted mainly in the precipitation of calcite (18OVPDB = -10.9 and

-3.8), trace amounts of non-ferroan dolomite, siderite (18OVPDB =-14.4 to -0.6), as well as smectite and kaolinite in the LST and HSTturbiditic sandstone below the sequence boundary. Minor eogenetic sideritehas precipitated between expanded and kaolinitized micas, primarily biotite.The mesogenetic alterations are interpreted to have been mediated by evolvedmarine pore waters and resulted in the precipitation of calcite (18OVPDB= -12.9 to -7.8) and Fe-dolomite/ankerite (18OVPDB = -12.1 to-6.3) at temperatures of 50-140C and 60-140C, respectively.

Quartz overgrowths and outgrowth, which post- and pre-date the mesoge-netic carbonate cements is common in the LST and TST of distal turbiditicsandstone. Discrete quartz cement, which is closely associated with illite and

chlorite, is the final diagenetic phase. The clay minerals include intergranularand grain replacive eogenetic kaolinite, smectite and mesogenetic illite andchlorite. Kaolinite has been subjected to mesogenetic replacement by dickite,and the K-feldspar and plagioclase grains have been albitized. Dissolution ofcalcite cement and of framework grain (feldspar, volcanic fragments and mudintraclasts) has resulted in a considerable enhancement of reservoir quality.

Paper III

8.3 Diagenesis of the Urucutuca Formation (Lowe

Cretaceous), Espirito Santo Basin, Eastern Brazil:Impact on the Reservoir Quality and HeterogeneityEvolution Pathways in Turbiditic SandstonesTurbidite sandstones deposited in passive continental margins are currentlyamong the main targets of hydrocarbon exploration. However, the impact ofdiagenesis on reservoir quality of such sandstones is relatively poorly exploredin the literature. Recent studies of turbidite sandstones of different basin haveprovided evidence showing that the diagenesis and reservoir quality evolu-tion of such sandstones are not merely controlled by marine pore waters butcommonly by meteoric waters. Meteoric-water incursion in the Lower Creta-

ceous, canyon-filling turbiditic sandstones of the Esprito Santo Basin, easternBrazil, which occurred during shallow burial and as response to a considerablefall in the relative sea-level, induced pervasive dissolution and kaolinitization(18OVSMOW = +13.3 to +15.2; DVSMOW = -96.6 to 79.6) of theframework silicate grains. Intragranular dissolution macropores, which formby dissolution of feldspar, mud intraclasts and mica grains, are fairly well-connected to the intergranular pore system, and have thus enhanced perme-ability of the sandstones. The circulation of meteoric fluids probably occurred

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through contacts with Lower Cretaceous sandstones along the margins of thecanyons.

Eogenetic alterations include cementation by siderite (av. 18OVPDB = -7.2; 13CVPDB = +9.3) and pyrite. Progressive sediment burial (presentdepths = 1530-2027 m) resulted in the formation of poikilotopic calcite (av.18OVPDB = -7.7; 13CVPDB = +3.9), ferroan dolomite/ankerite (av.18OVPDB = -7.9; 13CVPDB = +2.9), partial dickitization of kaoliniteand precipitation of minor amounts of quartz overgrowths. Despite the pres-ence of various cement types, mechanical compaction was more importantthan cementation in reducing depositional porosity in the Urucutuca sand-stones.

Paper IV

8.4 Diagenetic Alterations Related to Falling Stage andLowstand Systems Tracts of Shelf, Slope and Basin FloorSandstones (Eocene Central Basin, Spitsbergen)Diagenetic alterations and detrital composition of shelf, slope and basinfloor litharenitic to sublitharenitic sandstones from the Eocene Central Basinof Spitsbergen display fairly systematic variations among the falling stage(FSST) and lowstand systems tracts (LST). The diagenetic processes inboth systems tracts include mechanical and chemical (pressure dissolution

of quartz grains) compaction, kaolinitization of detrital silicates such asmica and feldspar, cementation by carbonates and quartz overgrowths, andillitization of kaolinite. Apart from few, extensively carbonate-cementedsandstones, such as those below marine flooding surfaces, compactionis more important in porosity destruction than cementation due to theabundance of ductile grains.

Kaolinitization of detrital silicates is more common in the FSST than in theLST sandstones due to greater meteoric-water flux during sea level fall. How-ever, the mechanisms of meteoric water flux into the FSST slope depositsand basin-floor fan sandstones are enigmatic, but could have been as a con-sequence of hydraulic head creation along the basin margin during a major

fall in the relative sea level. Cementation by carbonates such as calcite anddolomite occurred in both FSST and LST sandstones, being most extensive insandstones immediately below marine and maximum flooding surfaces, whichis attributed to the presence of detrital carbonate grains below these surfaces.The Eocene central basin of Spitsbergen is a potential analogue for the studyof other deep-water reservoirs in similar basinal settings in which reservoirquality assessment is of considerable importance. This study shows that con-structing a conceptual model for the distribution of diagenetic alterations, and

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thus reservoir-quality evolution in deep-marine turbiditic sandstones is possi-ble by integrating diagenesis and sequence stratigraphy.

Paper V

8.5 The Diagenetic Evolution and Porosity Destructionof Hybrid Turbiditic Arenites of Foreland Basin:Evidence from the Eocene Hecho Group, Pyrenees,SpainHybrid turbiditic arenites of the Eocene Hecho Group (south-central Pyrenees,Spain) have been deposited in a foreland basin. The arenites show wide vari-

ation in detrital composition, which reflect variations in provenance terrainsand changes in the relative sea level. The diagenetic evolution pathways ofthe arenites are closely linked to the variation in detrital composition, partic-ularly the proportion and types of extrabasinal non carbonates (NCE), extra-basinal carbonates (CE), and intrabasinal carbonate (CI) grains. Arenites thatare enriched in carbonate grains (CE and CI) are extensively cemented by car-bonates (calcite and dolomite) and display intergranular pressure dissolutionof the carbonate grains, arenites enriched in ductile low-grade metamorphicrocks (NCE) reveal extensive mechanical compaction, whereas arenites en-riched quartz and feldspar display intergranular dissolution of quartz grains,cementation by quartz overgrowths, and albitization of detrital feldspars. Il-

litic and chloritic clays have presumably been formed by progressive illitiza-tion and chloritization of grain-coating smectite.

Paper VI

8.6 Dolomite-Rich Condensed Sections in OverbankDeposits of Turbidite Channels, The Eocene HechoGroup, South-Central Pyrenees, SpainHigh-resolution correlation of monotonous, thin-bedded turbidites is desirable

but commonly difficult. Correlation within the Eocene turbidites of the HechoGroup, south-central Pyrenees is facilitated by the occurrence of decimetre-thick, yellowish beds of micritic limestones and marlstones. These yellowbeds (YB) occur in the overbank deposits of major turbidite channel com-plexes (referred here to as the lower muddy stage). The YB occur at top ofsandy deposits within the lowstand wedge of a third-order depositional se-quence, as single or multiple beds related to high-frequency, fourth-order de-positional cycles. The upper muddy stage, which comprises the rest of thelowstand systems tract contain no YB.

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The YB are interpreted as condensed sections where surfaces of burrowedand abundant planktonic and benthic microfossil assemblages were temporar-

ily sustained by oxygen and nutrients delivered by turbidite currents. The YBare, thus, reliable markers of the early lowstand wedge prograding complex,being coeval with initiation of delta restoration.

Whole-rock and XRD analyses indicate that most YB contain detrital clayfraction and consistent excess of Fe, Mn, and P contents, which are ascribed tocondensation driving redox relocations (hardground). The YB are also richerin dolomite and calcite than the adjacent claystones, which is attributed tocolonization by biogenic algae. Dolomite crystals vary in shape, zonation pat-tern and chemical composition from early zones are nearly stoichiometric tolater more ferroan. The 18OVPDB values (-10.4 to -6.2) of Fe-dolomite,which broadly correlate with 18OVPDB values (-8.1 to -5.6) of calcite

suggest formation at elevated temperature. Likewise, dolomite has more ra-diogenic 87Sr/86Sr (0.707926 and 0.707876) than ambient seawater, suggest-ing partial derivation of Sr from detrital aluminosilicates. These laterally ex-tensive dolomitic YB can act as outstanding potential seals in the overbankdeposits for major channel complexes.

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9. Concluding Remarks

The petrological and geochemical studies of the deep-water turbiditic sand-stones from four basins along passive and active (foreland) margins have re-vealed that:

Diagenetic alterations, particularly compaction and, to lesser extent, ce-

mentation, have had a profound impact on reservoir-quality evolution path-ways

Diagenetic and reservoir-quality evolution pathways are closely linkedto basinal setting (passive versus active margins), depositional facies,sequence stratigraphy, and burial depth reached by the sandstones.

Turbiditic sandstones from active margins are strongly enriched in duc-tile grains (e.g. low-grade metamorphic rock fragments), which resulted inrapid and near complete elimination of porosity and permeability by me-chanical compaction.

In contrast to arenites from active margin settings, sandstones from thepassive margin basins are enriched in quartz and feldspar, and have thus

better retained the depositional porosity and permeability. Additionally, thereservoir quality of these sandstones display reservoir-quality enhancementowing to partial to complete dissolution of framework grains, primarilyfeldspars, mud intraclasts and micas.

In contrast to what was suggested earlier in the literature, diagenetic alter-ations in deep-marine turbiditic sandstones, particularly those deposited inpassive margin basins, are not mediated merely by marine pore waters, butin some cases even by extensive percolation of meteoric waters.

Meteoric water percolation is most evidenced (kaolinitization and disso-lution of framework silicates) in lowstand systems tract sandstones and issuggested to have occurred during major fall in the relative sea level and

consequently shelf exposure. Carbonate cementation is most common, particularly, in the vicinity of ma-

rine flooding surfaces, which is attributed, at least partly, to low sedimenta-tion rates (i.e. long residence time of the sediment below the seafloor) andpresence of considerable amounts of detrital carbonates. Detrital carbonategrains have acted as nucleation sites for carbonate cementation. The wideranges and lack of correlation between oxygen and carbon values suggestcarbonate cementation at various geochemical conditions and/or tempera-tures.

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Near total lack of glaucony in turbiditic sandstones from the active marginbasins, in contrast its common presence or, in some cases, even consid-

erable amounts in turbiditic sandstones from passive margin basins, is at-tributed to the high rates of sedimentation rates on the shelf and continentalslope.

Lack of correlation between porosity and permeability and the greater de-gree of permeability than porosity reduction in the sandstone reservoirs areattributed to the presence of abundant micro-porosity and intragranular andmoldic pores that are poorly connected to the overall pore system. Channelcomplex sandstones are characterized by better reservoir quality than thefiner-grained, crevasse splay sandstones.

In summary, this study shows that different strategies should be adoptedduring hydrocarbon exploration in deep-water turbidites in passive versus ac-

tive margin basins.

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10. Summary in Swedish

Diagenes och utveckling av reservoarkvalitet hosturbiditiska sandstenar frn djuphavet: Kopplingar tillbassngtyp, avsttningsfacies och sekvensstratigrafi.

Sammanfattning

Fr att kunna urskilja diagenetiska frndringar i turbiditiska sandstenar frndjuphavet och deras pverkan p utvecklingen av reservoarkvalitet i tid ochrum, har petrologiska och geokemiska studier utfrts p fyra successioner(Krita till Eocen), frn bassnger lokaliserade dels vid aktiva grnser (Fore-land), dels vid passiva grnser. Studien visar p den stora betydelsen av tek-tonisk omgivning, avsttningsfacies, samt frndringar i relativ havsyteniv,parametrar vilka i sin tur kontrollerade kornsammansttning, sedimentation-shastighet, sammansttning av porvatten hos de turbiditiska sandstenarna.

De allra viktigaste diagenetiska omvandlingar i turbiditsandstenarassocierade med passiva marginalbassnger inkluderar upplsning ochkaolinitisering av sandkorn (kaolin uppvisar 18OVSMOW = +13.3 till

+15.2; DVSMOW = -96.6 till 79.6), bildning av klorit hinnor runtkornen, utfllning av karbonater och kvarts som cement, samt mekaniskkompaktering och tryckupplsning av detritisk kvarts. Kaolitiseringen rmest omfattande i bassngbottendeltat och hos strmkanalsandstenarna, vilkahr till the lowstand systems tract. Dessa sandstenar har bibehllit hgreporositet (up till 30%) och permeabilitet (up till 1 Darcy) tack vare denmekaniska stabilitieten hos de detritiska kvarts-fltspatkornen, och av endelvis till fullstndig upplsning av cementmineralen samt av glimmer ochfltspat. Fretrdesvis diagenetiska modifikationer av turbiditiska sandstenarfrn foreland bassngar omfattar cementering av karbonater samt mekaniskkompaktering av de rikligt frekommande duktila sedimentra och lggradigt

metamorfa bergartsfragmenten, vilka har sitt ursprung i fold-thrust blten.Dessa diagenetiska omvandlingar resulterade i en total eliminering avursprunglig porositet och permeabilitet.

Den stora variationen i 13CVPDB vrden hos karbonatcementenfrn passiva grnser (ca -18 till +22) tyder p att upplst CO2hrrr frn varierande nedbrytnings processer av organiskt material, t exbakteriell metanogenes och termal dekarboxylering av kerogen. Mindrevariationer i 13CVPDB vrden (ca -2 till +7) hos karbonatcementenfrn foreland bassngen tyder p att upplsning av karbonatkornen var

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en viktig CO2 klla. Strre variationer i 18OVPDB vrden (ca -17till -1) hos karbonatcementen i allmnhet hnfrs till variationer i

syreisotopsammansttningen hos vattnet (inkl marint, meteoriskt ochformationsvatten) samt i bildningstemperaturen.

Denna studie frvntas komma att f stor betydelse vid letning efter olje ochgas i djupvatten turbiditsediment i passiva kontra aktiva grnser, srskilt nrdet gller utvrderingen av reservoarkvaliteten innan borrningsarbeten pbr-

jas.

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Acknowledgments

I would like to express my deepest gratitude, appreciation and respect to mysupervisor Professor Sadoon Morad, for his guidance, encouragement con-structive criticism and comments during all stages of my work. I am greatlyindebted to his help regarding matters of academic and non academic con-cerns. I thank him for contributing to my development as a person and how

to become a critical thinker and, potentially, a researcher. I would also like tothank his wife Liisa and his kids for the warm reception and friendship.

My thesis has greatly benefited from guidance and support provided byProfessor Hemin Koyi, head of Solid-Earth Geology. His unreserved encour-agement and help has greatly eased the completion of this thesis. Thank youfor teaching me how to present scientific results through your and Dr. Moradsexcellent course Scientific Writing and Presentation.

I am lucky and proud to have a chance to work with some very wellestablished scientists in the field of diagenesis, among whom are Dr. LuizFernando De Ros (Federal University of Rio Grande do Sul, Porto Alegre,Brazil) and Dr. Marcelo Ketzer (Pontifical Catholic University of Rio Grande

do Sul Environmental Institute). I highly appreciate the strong support andinspiration they have provided me during the

diagenesis and reservoir-quality evolution of deep-water turbidites

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