Rustichelli Et Al. (AAPG Bulletin)

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Sedimentologic anddiagenetic controls onpore-network characteristics

of OligoceneMiocene

ramp carbonates (MajellaMountain, central Italy)Andrea Rustichelli, Emanuele Tondi, Fabrizio Agosta,Claudio Di Celma, and Maurizio Giorgioni

A B S T R A C T

This article addresses the controls exerted by sedimentologicand diagenetic factors on the preservation and modification ofpore-network characteristics (porosity, pore types, sizes, shapes,and distribution) of carbonates belonging to the BolognanoFormation. This formation, exposed at the Majella Mountain,Italy, is composed of OligoceneMiocene carbonates depos-ited in middle- to outer-ramp settings. The carbonates consistof (1) grainstones predominantly composed of either largerbenthic foraminifera, especiallyLepidocyclina, or bryozoans;

(2) grainstones to packstones with abundant echinoid platesand spines; and (3) marly wackestones to mudstones withplanktonic foraminifera.

The results of this field- and laboratory-based study areconsistent with skeletal grain assemblages, grain sizes, sorting,and shapes, all representing the sedimentologic factors respon-sible for high values of connected primary macroporosity ingrainstones deposited on the high-energy, middle to proximalouter ramp. Cementation, responsible for porosity reductionand overall macropore shape and distribution in grainstones

to packstones deposited on the intermediate outer ramp, wasmainly dependent on the following factors: (1) amount ofechinoid plates and spines, (2) grain size, (3) grain sorting andshapes, and (4) clay amount. Differently, in the wackestones

A U T H O R S

Andrea Rustichelli Geology Division,School of Science and Technology, University ofCamerino, Via Gentile III da Varano, Camerino(Macerata), Italy; [email protected]

Andrea Rustichelli is a postdoctoral researcher atthe University of Camerino, Italy. He gained hisB.S. and M.S. degrees and Ph.D. in geologicalsciences from the University of Camerino. Hisresearch activity is mainly addressed to the strat-igraphic, sedimentologic, and structural charac-terizations of fractured carbonate reservoirs.

Emanuele Tondi Geology Division, Schoolof Science and Technology, University ofCamerino, Via Gentile III da Varano, Camerino(Macerata), Italy; [email protected]

Emanuele Tondi is an associate professor instructural geology at the University of Camerino,Italy. His research activity is mainly addressedto the study of brittle deformation and on itsapplications to solving regional and seismotec-tonic problems, as well as the recovery of geo-fluids from the subsurface. He is codirector ofthe Reservoir Characterization Project.

Fabrizio Agosta Department of Geologi-cal Sciences, University of Basilicata, VialedellAteneo Lucano 10, Potenza, Italy;[email protected]

Fabrizio Agosta is an assistant professor at theUniversity of Basilicata, Italy. He joined the uni-versity in 2010. He received his B.S. degree fromthe University of Catania (Italy) in 1997, hisM.S. degree from Saint Louis University (Mis-souri) in 2006, and his Ph.D. from StanfordUniversity (California) in 2006. He is codirectorof the Reservoir Characterization Project.

Claudio Di Celma Geology Division,School of Science and Technology, University ofCamerino, Via Gentile III da Varano, Camerino

(Macerata), Italy; [email protected]

Claudio Di Celma is a researcher at the Universityof Camerino, Italy. He gained his degree in geo-logical sciences from the University of Camerinoand his Ph.D. in earth sciences from the Uni-versity of Pisa. His research interests include se-quence stratigraphy, predictive stratigraphy, andbasin analysis. Claudio is currently working onthe sedimentology and stratigraphic architectureof deep-water siliciclastic systems.

Copyright 2013. The American Association of Petroleum Geologists. All rights reserved.

Manuscript received May 3, 2012; provisional acceptance July 2, 2012; revised manuscript received July

9, 2012; final acceptance July 31, 2012.

DOI:10.1306/07311212071

AAPG Bulletin, v. 97, no. 3 (March 2013), pp. 487524 487


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to mudstones, laid down on the low-energy, distal outer ramp,matrix is the key sedimentologic factor responsible for lowvalues of scattered macroporosity and dominance of micro-porosity. The aforementioned results may be useful to improvethe prediction of reservoir quality by means of mapping, sim-ulating, and assessing individual carbonate facies with peculiar

pore-network characteristics.

INTRODUCTION

Worldwide, more than 50% of the natural reservoirs (i.e., min-eral and hydrothermal waters, geothermal fluids, oil, and gas)consist of carbonate rocks (Schlumberger Ltd., 2007). Unlikeother types of reservoir rocks (e.g., siliciclastics), carbonatesinclude a wider variety of facies because of their peculiar bio-genic nature and reactivity to fluids (diagenetic modifica-

tions). Carbonates are, indeed, the result of a multitude ofbiological and ecological processes that may determine a widevariety of types, sizes, shapes, and loci of production of sedi-ments, which change over time (evolution of life). Biologicaland ecological processes responsible for the production ofcarbonates produce wave-resistant carbonate structures (i.e.,reefs) and can profoundly affect facies belts and platform types(e.g., Schlager, 2005, and references therein). In siliciclasticrocks, despite a more complex mineralogical composition, grainsize mainly reflects the energy of the depositional environment,

whereas sediments and grains are less variable through time,not being as dependent on biological and ecological processes(Schlager, 2005). The greater chemical reactivity of metastablecarbonate minerals implies that the original sedimentologicrock properties are modified by diagenetic processes such asmechanical and chemical compaction, cementation, dissolu-tion, and mineral transformations (Choquette and Pray, 1970;Ehrenberg and Nadeau, 2005; Schlager, 2005; Hollis et al.,2010). Hence, the nature, organization, and shapes of carbon-ate components (i.e., grains, crystals, cements, pores) result in

complex rocks with highly variable reservoir petrophysicalproperties (i.e., porosity, permeability, water and oil satura-tion, and others; Lucia, 1999; Ehrenberg and Nadeau, 2005;Schlager, 2005). It is therefore essential, when dealing withcarbonate reservoirs, to consider the geologic controls, includ-ing diagenetic history, on porosity, pore types, shapes, sizes,and connectivity. All these factors, indeed, may strongly affectthe permeability and other petrophysical properties of therocks (Anselmetti and Eberli, 1999; Kenter et al., 2006; Holliset al., 2010).

Maurizio Giorgioni Shell Italia E&P,Piazza dellIndipendenza 11B, Rome, Italy;[email protected]

Maurizio Giorgioni received his M.Sc. degreein engineering from the University of Rome in1987. He is currently working as the petro-physics lead for the Nonoperated Ventures of

Shell in Europe. His interests include the for-mation evaluation in naturally fractured car-bonates with an emphasis on the quantitativeuse of image logs.

A CKNOWLE DGE M E NTS

We thank the AAPG Editor Stephen E. Laubach,Ralf J. Weger, and one anonymous reviewer fortheir elaborate and constructive reviews of themanuscript. We also thank Maria Mutti, GianlucaFrijia, and Dr. Jessica Zamagni of the Depart-ment of Earth and Environmental Sciences, Uni-versity of Potsdam, for their support during thelaboratory analyses and data interpretation.We thank Mauro Alessandroni and Paolo Vallesifor their help during the field analyses. This workhas been supported by the Reservoir Charac-terization Project and the Ministero dellIstru-zione, dellUniversit e della Ricerca, Progetti diRilevante Interesse Nazionale 2009 (nationalcoordinator, Emanuele Tondi).The AAPG Editor thanks the following reviewersfor their work on this paper: Ralf J. Weger and ananonymous reviewer.

E DI TORS NOTE

Color versions of Figures 114 may be seen inthe online version of this article.

488 Sedimentologic and Diagenetic Controls on Pore-Network Characteristics


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This study integrates the results of field andlaboratory analyses to assess the most importantsedimentologic and diagenetic factors controlling thepreservation and modification of the pore-networkcharacteristics (i.e., porosity, pore types, sizes, shapes,and distribution) in OligoceneMiocene, skeletal-

dominated ramp carbonates exposed at the MajellaMountain, central Italy. Quantitative estimationsand new attempts for correlations among severalsedimentologic (grain size, sorting, shape factor),compositional (percentages of different types ofgrains and cements), and pore-network parameters(porosity and some pore geometrical descriptors)are proposed in this article.

The ultimate goal is to contribute to a betterinterpretation of depositional units, characterized

by peculiar pore-network characteristics, which mayconstitute reservoirs or seals in skeletal-dominatedcarbonate ramp systems. This could provide someadditional criteria useful for reservoir quality eval-uation, a key and critical theme to most organiza-tions that are involved in geofluids management in

carbonates.

GEOLOGIC FRAMEWORK

The Majella Mountain is an east-verging, thrust-related anticline formed in the Pliocene and iscomposed of several MesozoicCenozoic carbon-ate units related to different marine settings (plat-form, slope, basin, and ramp) originally pertaining

Figure 1.Geologic framework of the Majella Mountain. (A) Geologic map of the Majella Mountain (modified from Ghisetti and Vezzani, 1997).(B) Cross section of the carbonate succession exposed at the Majella Mountain (modified from Vecsei, 1991). Fm = Formation; sl = sea level.

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to the northernmost sector of the Apulian Platformrealm (Figure 1; Vecsei et al., 1998; Ghisetti andVezzani, 2002; Scisciani et al., 2002). The studyarea is located along the northern flank of theMajella Mountain (Figure 1A), where Upper Cre-taceous to upper Miocene slope-to-ramp carbon-

ates of the Tre Grotte, Orfento, Santo Spirito, andBolognano formations crop out (Figure 2). Thesecarbonates, which are unconformably capped byMessinian to lower Pleistocene marine siliciclasticdeposits, are crosscut by Pliocene normal faults,mainly northwest-southeast trending (Agosta et al.,

Figure 2. (A) Facies map and (B) stratigraphic scheme of the carbonate stratigraphic units cropping out in the study area. Fm =Formation.



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2009). In the study area, evidence of fault-relatedhydrocarbon invasion of carbonate rocks is wide-spread, mainly within the Bolognano Formation(Agosta et al., 2010).

The Bolognano Formation

The OligoceneMiocene Bolognano Formation rep-resents the most recent stratigraphic unit makingup the carbonate succession of the Majella Moun-tain (Vecsei and Sanders, 1999). This formationincludes carbonate facies characterized by a wide

variability in pore types and distribution, resultingin porosity values ranging from approximately 0 tomore than 30% (Anselmetti et al., 1997; Rustichelli,2010; Rustichelli et al., 2012). Within the BolognanoFormation, the relatively shallow-water, skeletal-dominated stratigraphic horizons are predominantlycomposed of benthic foraminifera, bryozoans, echi-noid and mollusk fragments and, in the stratigraph-ically upper part, red algae (i.e., Lithothamnion);deeper water stratigraphic horizons mainly consist

of marly limestones with planktonic foraminifera(Figure 2; Vecsei and Sanders, 1999; Pomar et al.,2004; Brandano et al., 2012).

Mutti et al. (1997, 1999), Vecsei and Sanders(1999), and Brandano et al. (2012) suggested anisolated low-angle (homoclinal or slightly distallysteepened) carbonate ramp as a depositional settingfor Bolognano Formation carbonates. The presencein the skeletal assemblages of subtropical red algaeand larger benthic foraminifera (LBF), such as Le-pidocyclina,Amphistegina,Operculina,Miogypsina,and Heterostegina, implies subtropical conditions

during the deposition of the Bolognano Formation(Pomar et al., 2004; Brandano et al., 2012), as for allcoeval OligoceneMiocene carbonates of the Med-iterranean area (Brandano and Corda, 2002; Wilsonand Vecsei, 2005; Brandano et al., 2009; Westphalet al., 2010). These types of carbonate rocks wereinterpreted by the same authors as formed under awide range of trophic conditions (from oligome-sotrophic to eutrophic), as evidenced by the pre-dominance of mixotrophic calcareous organisms

Figure 3.Scheme of the internal stratigraphic architectures of facies associations A, B, C, and E of the Bolognano Formation. Note thecyclic alternations of bed packages belonging to different facies. Facies association D is not considered because it lacks a significantnumber of representative outcrops and its facies are too variable.



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(i.e., LBF) supported in some cases by high amountsof suspension feeders (i.e., bryozoans).

The first contribution to the literature on theBolognano Formation by Crescenti et al. (1969)distinguished and characterized this formationsolely based on a lithostratigraphic approach. Only

at the end of the 1990s, after the development ofsequence stratigraphy as a new paradigm withinwhich to interpret sedimentary successions, werea few sequence-stratigraphic studies conducted forthe carbonate succession of the Majella Mountain,as a whole, and for the Bolognano Formation, inparticular. Vecsei et al. (1998) subdivided the car-bonate succession of the Majella Mountain into sixsecond-order supersequences. Among these, the en-tire Bolognano Formation represents the youngest

supersequence, which is subdivided into four third-order sequences individually made up of both rel-atively shallow-water and deep-water carbonates(Vecsei and Sanders, 1999).

ANALYTICAL METHODS

Both field work and laboratory analyses were neededto obtain an exhaustive stratigraphic, sedimen-

tologic, and petrographic characterization of thestudied carbonates.The field work included (1)geologic mapping (at a 1:5000 scale) of the studyarea, approximately 25 km2 (10 mi2) (Figures 1A,2A), aimed at subdividing the studied carbonatesuccession into a hierarchical system of stratigraphicunits (Figures 2,3); and (2) stratigraphic and sedi-mentologic logging performed along the largestoutcrops, laterally and vertically extensive from tensto hundreds of meters. In particular, characterization

of stratigraphic elements (i.e., geometries, thick-nesses, and lateral extents of individual beds and bedpackages; type and lateral extents of physical strati-graphic surfaces)and definition of vertical and lateralrelationships among distinct stratigraphic units wereaimed at defining the stratigraphic architecture ofthe studied carbonate succession at different scales,using a sequence-stratigraphic approach.

Eighty hand samples (8 per facies) of the tenmore-representative facies were collected for sub-

sequent laboratory analyses. These analyses usedthe following methods:

1. Petrographic analysis of 80 thin sections (1 persample) using an optical polarizing microscope(Nikon Eclipse E600) to qualitatively document

the sedimentologic (e.g., grain types, textures)and diagenetic characteristics (e.g., cement typesand distribution; compactionevidence), as well asthe types and distribution of macropores (poreswith diameters >20 mm; Anselmetti et al., 1998)using classifications from Choquette and Pray(1970), Lucia (1999), and Lny (2006)

2. Cathodoluminescence (CL) microscopy on tenselected polished thin sections (1 per facies) toassess the diagenetic environments in which

cements precipitated; operating conditions forthe Cambridge Image Technology Ltd., UK(CITL) Cold Cathode Luminescence (model8200 Mk3A) were maintained at approximately22-kV beam energy and 0.8-mA beam current

3. Dissolution of powders of 30 selected rock sam-ples (3 per facies) using diluted hydrochloricacid to determine the insoluble residue (vol. %)

4. X-ray diffraction analysis of powders of 20 se-lected rock samples (2 per facies) using a KM-4KUMA diffractometer equipped with diffracted

beam graphite monochromator to determine themineralogical composition of the studied rocks;the copper tube was operated at 40-kV beamenergy and 25-mA beam current and spectrawere recorded in the 2-theta angular range from3 to 65C with a 0.02 step and 1.5s per stepcounting time.

Digital image analysis of microphotographs(one per thin section), using Image-J 1.32 software,

was conducted to quantify the sedimentologic rockparameters (grain size, sorting, shape factor), thepercentages of different rock components (grains,matrix, cements, two-dimensional [2-D] porosity),as well as some pore geometrical descriptors (i.e.,perimeter over area [PoA] and dominant pore size[DomSize]; sensu Weger et al., 2009). Specifically,in the following text, as a grain size, we refer to themean value of the measured diameters assumingthat the individual grains are characterized by



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rounded shapes. In contrast, sorting is expressedas an inclusive graphic standard deviation, si(sensu Folk and Ward, 1957; Flgel, 2004):

si F84 F16=4 +F95 F5=6:6 1

where Frepresents the logarithm on base 2 of themean grain size, according to theWentworth-Uddenscale. This parameter is compared with the chartedited by Longiaru (1987) (in Flgel, 2004) for aqualitative classification of the carbonate rocks(e.g., well sorted). Shape factor, instead, is ex-pressed as the mean value of the dimensionlessratio between the perimeter (P) of each individualgrain and a parameter proportional to its area(2

ffiffiffiffiffiffiffi

pAp

). The shape factor represents the grain cir-

cularity in two dimensions; the value of 1 is asso-ciated with a circular grain (spherical in three dimen-sions [3-D]), whereas higher values are related tomore-elliptical grains. The percentages of the dif-ferent rock components were calculated by auto-matic point counting, based on recognition ofchromatic differences on each thin-section photo-micrograph. Amounts of 2-D intergranular andintragranular porosities were automatically deter-mined, taking advantage of their different sizeranges for a given facies. Pore geometrical descrip-

tors DomSize and PoA represent the dominant2-D pore size and the 2-D pore-network complex-ity, respectively. Pore geometrical descriptor PoAis the ratio between the total perimeter that en-closes the pore space on a thin section and the totalpore-space area. Generally, a small PoA value indi-cates the overall low specific surfaces (roundedshapes) of the pores. Pore geometrical descriptorDomSize is determined as the upper boundary ofpore sizes of which 50% of the porosity on a thin

section is composed. This parameter provides anindication of the pore-size range that dominates thesample. The quantification of these two pore geo-metrical descriptors is critical because they can be ef-ficiently linked to physical properties of carbonates,in particular, to permeability and sonic velocity.

To assess microporosity (pores with diameter


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Table 1.Stratigraphic and Sedimentologic Characteristics of the Stratigraphic Units Analyzed in this Study*

Facies Associations T(m)

Facies

Code T(m) % Vol. Lithologic Description

A Lepidocyclina

grainstones

3540

(Al)

Al1 0.12.0 29 Whitish to grayish, medium- to

coarse-grained bioclastic grainstones

(in some cases, pinkish or reddish

because of hydrocarbon invasion)

LBF*

Les

ech

frag

ben

and

frag

Al2 0.12.0 11 Whitish to yellowish, fine-grained

bioclastic grainstones

Red a

and

frag

sma4060

(Au)

Au1 0.12.0 28 Whitish to grayish, medium- to


(commonly reddish or blackish


LBF (

less

Ope

com

Au2 0.12.0 31 Whitish to grayish medium-grained

bioclastic grainstones (commonly

reddish or blackish because of

hydrocarbon invasion)

Les

and

frag

ben

Len

test

algaAu3 23 1 Whitish to grayish, medium- to


with centimeter-size disarticulated

valves of lamellibranchs and echinoid

spines (commonly reddish or blackish


494

Sedimentologic

andDiageneticControlsonPore-NetworkCharacteristics


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B Bryozoan

grainstones

1015 B 1015 100 Whitish to grayish, medium-grained

bioclastic grainstones (commonly

reddish or blackish because of

hydrocarbon invasion)

Bryo

of L

Ope

pro

com

plat

lamfora

Cib

Spo

C Echinoid

grainstones

to packstones

35 C1 0.11.0 52 Grayish to yellowish, fine-grained

bioclastic grainstones

Echin

dist

bry

(Ro

and

(Glo

Glo

fragma

C2 0.11.0 48 Grayish to yellowish, fine- to very

fine-grained bioclastic packstones

Echin

sma

text

fora

Glo

spo

biot

Poo

D Echinoid and

planktonicforaminifera

packstones to

wackestones

810 Whitish to yellowish, very fine-

grained bioclastic packstones tomarly wackestones

E Planktonic

foraminifera

wackestones

to mudstones

6065 E1 0.12.0 55 Grayish, marly wackestones Plank

Glo

Glo

of r

Inte

Zoo

Rustichelliet

al.

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Table 1.Continued

Facies Associations Bedding Patterns Depositional Environments

A Lepidocyclina

grainstones

Stacks of decimeter- to as much as 4-m

(13 ft)thick cross-bed packages bounded

by subhorizontal, slightly undulatory

truncation surfaces. Each package is

made up of 5- to 80-cm (231-in.)thick,

downward-stepping cross-bed foresetsdownlapping (dipping up to 18) toward

west northwest and north northwest, onto

the lower truncation surface. Individual

cross-beds are (1) planar to sigmoidal,

from 1 to 10 m (333 ft) extended in dip

direction and (2) trough-shape, as much

as tens of meters extended in strike

direction. Outcropping truncation surfaces

are from tens to hundreds of meters

laterally extended. Individual bed packages

bounded by truncation surfaces of faciesassociation A can be composed of (1)

alternations of 10-cm (4-in.)to 2-m

(7-ft)thick bed packages of different

facies or (2) only one facies type (i.e.,

facies association B). No coarsening-fining

upwarding trends were observed.

Middle to proximal outer ramp

(oligomesotrophic subtropical conditions;

water depth, 2050 m [66164 ft]).

Benthic carbonate production (LBF-

dominated) in the oligophotic zone [middle

ramp]). Seaward transport and depositionof skeletal material by unidirectional

migration of subacqueous dunes.

F

B Bryozoan

grainstones

Middle to proximal outer ramp (eutrophic

subtropical conditions; water depth,2050 m [66164 ft]). Benthic carbonate

production (bryozoan-dominated) under

aphotic conditions (middle to proximal

outer ramp). Seaward transport and

deposition of skeletal material by

unidirectional migration of subacqueous

dunes.

496

Sedimentologic



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C Echinoid

grainstones

to packstones

Stacks of laterally extensive, 5- to 70-cm

(28-in.)thick planar beds, which onlap

the truncation surfaces present at the

top of rock bodies composed of facies

associations A and/or B. Facies associations

C, D, and E are composed of alternations

of bed packages of different facies. Thethickness of individual bed packages

ranges from 10 cm (4 in.) to 1 m

Intermediate outer ramp

(oligomesotrophic subtropical

conditions; water depth, 5060 m

[164197 ft]). Seaward transport and

deposition of benthic skeletal material

(produced on the middle-outer ramp)

by action of unidirectional bottomcurrents concomitantly to plankton

and mud fallout.

F

D Echinoid and

planktonic

foraminifera

packstones to

wackestones

(3 ft; facies association C) and from

10 cm (4 in.) to 2 m (6 ft; facies

association E). No coarsening-fining

upwarding trends were observed.

Intermediate to distal outer ramp

(oligomesotrophic subtropical

conditions; water depth, >50 m

[164 ft]50100 m

[164328 ft] or more). Plankton and

mud fallout.

Rustichelliet

al.

497


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nutrient supply, photic conditions) related to spe-cific depositional environments (seeTable 1for de-tailed descriptors of facies associations and facies).

Facies association A,Lepidocyclinagrainstones,

is present at two distinct stratigraphic intervals(lower, Al; upper, Au) within the studied carbon-ate succession (Figure 2). Stratigraphic interval Alincludes a 35- to 40-m (115131-ft)thick alterna-tion of two facies: (1) medium- to coarse-grainedbioclastic grainstones (Al1) and (2) fine-grained bio-clastic grainstones (Al2). The latter facies is morecommon in the lower part of facies association Al(Figure 3). Stratigraphic interval Au includes a 40-to 60-m (131197-ft)thick alternation of two

dominant facies: (1) medium- to coarse-grainedbioclastic grainstones (Au1) and (2) medium-grained bioclastic grainstones (Au2;Figure 4A).A less common facies (Au3;Table 1) (Figure 3),

which differs from Au1 by more abundant echi-noid spines and disarticulated valves of lamelli-branchs, as much as a few centimeters in size, is alsopresent.

Facies association B, bryozoan grainstones, con-sists of 10- to 15-m (3349-ft)thick medium-grained grainstones, which mainly differs from fa-cies association A for the type of biota (bryozoansvs. LBF, especiallyLepidocyclina), dominating theskeletal grain assemblages (Table 1).

Figure 4. Outcrop view of the more-representative facies associations and facies of the Bolognano Formation, which are exposed in thestudy area. (A) Facies association Au (locality, Pian delle Cappelle). (B) Facies association C (locality, Roman Valley Quarry). The darkbeds (highlighted by horizontal arrows) represent fine-grained grainstones (facies C1), whereas the other beds, composed of fine- tovery fine-grained packstones (facies C2), present ubiquitous anostomosed pressure solution seams (highlighted by vertical arrows),which are parallel and internal to beds. (C) Facies association E (locality, Roman Valley Quarry). The thinnest beds (highlighted byarrows) represent marly mudstones (facies E2). The more competent (in relief) beds represent marly wackestones (facies E1). The 33-cm(13-in.) long hammer is for scale (see the black circle).



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:

Figure 5.(A) Cross section drawn from mapping of stratigraphic elements on a photomosaic of a wall of the Roman Valley Quarry.(B) Detail.



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Table 2.Diagenetic and Pore-Network Characteristics of the Stratigraphic Units Analyzed in This Study

Facies Associations

Facies

Code Diagenetic Description Early Diagenesis Interpretation Burial Diagenesis Interpr

A

B

Lepidocyclina

grainstones

Bryozoan grainstones

Al1

Al2

Au1

Au2Au3

B

Moderate amounts of syntaxial

overgrowth calcite cement

around echinoid plates and

spines. Low amounts ofmicrosparry calcite cement.

Rare presence of iron oxides,

glauconite, and phosphates.

Moderate amounts of syntaxial

overgrowth calcite cement

around echinoid plates and

spines. Low amounts of

microsparry calcite cement.

Iron oxides, glauconite, and

phosphates are commonly

present.

Presence of iron oxides,

glauconite, and phosphates,

pointing to an early marine

diagenesis.

Precompactional precipita

of the bulk of the syntax

overgrowth cements, an

part of microsparry cemwithin a shallow-marine

burial environment (dep

as much as a few tens o

meters). Cementation w

sourced by dissolution a

neomorphism of early

marine, high-magnesium

cements and aragonitic

biota. Syncompactional

microsparry calcite

cementation was causedC Echinoid grainstones

to packstones

C1 Abundant syntaxial overgrowth

calcite cement around

echinoid plates and spines.

Minor amounts of microsparry

calcite cement. Rare presence

of iron oxides, glauconite,

and phosphates.

pervasive, overburden-r

intergranular pressure

solution within a deep

burial environment.

C2 Abundant microsparry calcite

cement. Minor amounts of

syntaxial overgrowth calcitecement around echinoid

plates and spines. Rare

presence of iron oxides,

glauconite, and phosphates.

500

Sedimentologic



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Facies association C, echinoid grainstones topackstones, consists of 3- to 5-m (1016-ft)thickalternations of two facies, both rich in echinoidplates and spines: (1) fine-grained bioclastic grain-stones (C1) and (2) fine- to very fine-grained bio-clastic packstones (C2; Table 1) (Figures 3, 4B).

Argillaceous to marly beds, as much as 3-cm (1-in.)thick, are commonly intercalated to the two faciesdescribed above.

Facies association D, echinoid and planktonicforaminifera packstones to wackestones, is as muchas 10 m (33 ft) thick and crops out sporadically inthe study area (Figure 2A). This facies associa-tion is composed of a large variety of facies, ofwhich end members are represented by very fine-grained bioclastic packstones and marly wacke-

stones (Table 1). Fissile argillaceous to calcareousmarls, arranged in 210-cm (14-in.)thick beds,are commonly intercalated to the other facies.

Facies association E, planktonic foraminiferawackestones to mudstones, consists of a 6065-m(197213-ft)thick alternation of two facies: (1)marly wackestones (E1) and (2) marly mudstones(E2; Table 1) (Figures 2,3,4C). Both facies haveplanktonic foraminifera as predominant skeletalcomponents of the rocks.

Facies associations A and B are both arranged

in stacks of decimeter to as much as 4-m (13-ft)thick packages of cross-beds bounded by subhor-izontal large-scale truncation surfaces (Table 1)(Figures 3; 4A; 5A, B). However, facies associa-tions C, D, and E are all arranged in planar beds(Figure 4B, C), which are laterally extensive andonlap the truncation surfaces present at the top ofrock bodies composed of facies associations A and/or B (Table 1) (Figure 5A, B). Facies associationsA, C, and E are all composed of cyclic alternations

of 10-cm (4-in.) to 2-m (7-ft)thick bed packagesof different facies (Figure 3).

PETROGRAPHIC ANDPORE-NETWORK CHARACTERISTICS

The integration of data provided by different lab-oratory analyses (optical and CL microscopy, x-raydiffraction, and digital image analysis) allowed usE

Plan

kton

icforam

inifera

wac

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to characterize (1) the depositional texture andgrain types, (2) the diagenetic modification, and(3) the pore-network characteristics of the studiedcarbonate facies (Tables 13). Facies association Dis not considered in this section because laboratoryanalyses yielded poor quality data.

Depositional Textures and Grain Types

Facies associations A, B, and C contain a variety ofcalcitic, benthic skeletal grains, mainly in the formof abraded fragments; only larger and smaller ben-thic foraminifera are also present as nearly complete

Table 3.Sedimentologic, Compositional, and Pore-Network Data of the Studied Facies*

Facies Code GS** SF** S** MX** Cl** L** B** E** R** PF**

Al1 Mean

value

0.63 1.26 0.77 (m)** 0 0 49.7 3.9 5.4 0.3 0

Range 0.330.75 1.211.3 0.690.9 39.472.5 2.18.8 3.28.8 01.5

Al2 Mean

value

0.15 1.19 0.56 (w/m)** 0 0 0 0 11.7 23.2 0

Range 0.120.21 1.161.21 0.480.75 8.615.2 12.631.2

Au1 Mean

value

0.52 1.31 0.92 (m/p)** 0 0 51.6 20.1 5.2 0 0

Range 0.230.62 1.231.35 0.81.06 42.571.4 11.827.7 411.2

Au2 Mean

value

0.3 1.25 0.83 (m)** 0 0 15.9 26.9 16.6 0 0

Range 0.180.38 1.221.29 0.740.91 10.928.9 17.440.2 11.319.8

Au3 Mean

value

0.47 1.3 0.85 (m)** 0 0 35.3 20.8 14 0 0

Range 0.220.63 1.271.32 0.740.99 29.561.4 1225.4 10.216.2

B Meanvalue

0.3 1.22 0.6 (m/w)** 0 0 0.5 44.1 12.8 0 0

Range 0.180.35 1.181.26 0.480.69 01 37.968.8 8.916.5

C1(e) Mean

value

0.21 1.18 0.68 (m/w)** 2.5 0.6 23.4 10.3 35.1 2.9 0

Range 0.160.26 1.161.19 0.550.74 04 01.2 14.730.5 5.217.3 24.643.1 06.5

C1 Mean

value

0.15 1.15 0.54 (w/m)** 4 1.1 0 0 25.5 5.3 3.5

Range 0.14019 1.141.17 0.470.62 07.5 0.51.8 19.431.2 1.68.8 0.56.1

C2 Mean

value

0.14 1.15 0.37 (w/vw)** 16 2.8 0 0 20.1 7.2 7.8

Range 0.120.15 1.141.16 0.330.42 7.522 1.94 12.625.9 3.710.9 4.110.2E1 Mean

value

80 9.3 0 0 0 0 14.8

Range 6590 5.214 7.422.4

E2 Mean

value

90 13.2 0 0 0 0 7.4

Range 8495 8.117.8 3.39.9

*Mean values and ranges from eight samples per facies. Three samples per facies are considered solely for three-dimensional total porosity and microporosity.

**Quantitative parameter codes: GS = grain size (mm); SF = shape factor; S = sorting (vw = very well; w = well; m = moderate; p = poor). Rock components (% vol.): MX =

matrix; Cl = clay minerals (insoluble residue of rock); L =Lepidocyclina; B = bryozoans; E = echinoid plates and spines; R = red algae; PF = planktonic foraminifera;Ct=

total cement;Cs= syntaxial overgrowth cement;Cm= microsparry cement; Ft(2-D) = two-dimensional total porosity; Fi(2-D) = two-dimensional intergranular porosity;

Fii(2-D) = two-dimensional intragranular porosity; Ft(3-D) = three-dimensional total porosity; mF= microporosity. Pore geometrical descriptors: DS = DomSize (mm);

PoA = PoA (mm1). T/D = thickness-to-diameter ratio ofAmphisteginatests.



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tests (see Table 1) (Figure 6AF). Preservationlevels (BPTS) of LBF tests range from 1 to 3 inboth facies associations A and B and from 2 to 3in facies association C. Moreover, the grainstonesand packstones of facies association C containplanktonic foraminifera (Figure 6E, F) and mini-mal amounts of micrite-clay matrix. In contrast,

facies association E is mainly composed of micrite-clay matrix containing scattered planktonic fora-minifera as well as less abundant radiolarians andsiliceous sponge spicules (Figure 6G, H). The onlysedimentary structure typecommonly detectable byoptical microscopy in facies associations A (mainly,Figure 6C), B, and C consists of elongated grains

Table 3.

Ct** Cs** Cm** Ft(2-D)** Fi(2-D)** Fii(2-D)** Ft(3-D)** mF** DS** PoA** T/D**

1.9 1.3 0.6 21.4 14.7 6.7 0.23 58.1 0.46

1.33.2 12.1 0.41.2 14.228.8 11.520.3 4.59.3 0.150.3 5162.5 0.330.51

4 2.8 1.2 8.7 6.3 2.4 0.11 69.7 0.44

1.87 0.85 0.62.5 6.310.7 4.87.7 1.64 0.10.12 65.578 0.30.5

4.1 2.7 1.4 16.6 10.8 5.8 23.9 7.3 0.29 48.9 0.44

36.3 25.1 0.92.2 10.425.9 719.1 3.97.1 15.333.2 2.810.2 0.150.48 3659.3 0.330.5

4 2.7 1.3 15.2 9.2 6 0.15 61.9 0.42

3.35.7 2.14.6 0.82.1 9.418.9 7.712 4.37.9 0.10.21 56.671.7 0.280.49

3.2 2.1 1.1 16.3 11.3 5 0.20 54.9 0.43

1.34.2 0.63.2 0.71.6 10.322.4 7.216.8 3.96 0.170.25 52.658.7 0.310.5

4.5 3.5 1 24.6 19.4 5.2 32.1 7.5 0.23 50.1 0.39

37.2 25.6 0.42 21.228.6 1622.5 3.88.3 26.435.3 4.89.3 0.170.31 44.956.4 0.290.44

7.6 6 1.6 10.8 6.5 4.3 0.12 70.6

4.811.2 3.78.1 12.5 6.215.1 3.99.1 2.46.2 0.110.14 65.177.7

7.5 5.7 1.8 6.5 3.9 2.6 10.2 3.7 0.11 74.7 0.39

4.510.4 2.67.1 0.92.5 4.28.7 2.85.2 24.1 5.814 1.66.2 0.080.15 63.385.9 0.320.44

8.8 4.2 4.6 0.5 0.2 0.3 3.9 3.4 0.06 128.4 0.37

611.9 2.15.3 2.97.4 0.12.1 0.11 0.11.1 1.47.2 1.35.1 0.050.07 105.4139.6 0.280.4314.8 2.3 0 2.3 1.4 0 1.4 29.9 28.5 0.09 62.0

1.44.4 1.44.4 0.82.1 0.82.1 24.933.1 24.131 0.080.1 58.165

7.4 1.3 0 1.3 0.8 0 0.8 0.08 70.1

0.81.9 0.81.9 0.41.3 0.41.3 0.060.1 53.284.5



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with long axes oriented parallel to bedding (asobservable, in some cases, in the field).

Diagenetic Modification

Two types of low-magnesium calcite cements arepresent within the analyzed rocks: (1) syntaxialovergrowth cement (sensu Bathurst, 1958) aroundechinoid plates and spines and (2) equant micro-

sparry cement (Flgel, 2004) with crystal sizes ofapproximately 10 mm. Under an optical micro-scope view, both syntaxial overgrowth and micro-sparry cements are clear (inclusion free). Under aCL microscope view, both cements present a brightto dull, red-orange luminescence.

Both syntaxial overgrowth and microsparrycements are present within facies associations A,B, and C (Figure 6AD), whereas only micro-sparry cement is present within facies associa-tion E (Figure 6G). Syntaxial overgrowth cement,

in many cases, completely surrounds individualechinoid plates and spines (see plates highlightedinFigure 6AC); more rarely, this cement envel-ops two or more echinoid plates and/or spines (seeplates highlighted inFigure 6E). However, withinfacies associations A, B, and C1, microsparry ce-ment constitutes discontinuous rims around skel-etal grains or within their chambers (in some cases,totally filling them;Figure 6A). In contrast, within

facies C2, microsparry cement fills a dominantpart of both chambers of the skeletal grains andoriginal intergranular spaces. Within facies associ-ation E, microsparry cement partially or completelyfills some chambers of planktonic foraminifera(Figure 6G) and radiolarians. Rare microsparrycalcite cementdominated rocks are also presentwithin facies association E.

Authigenic minerals, such as glauconite, phos-phorite, and iron oxides, are present in minimalamounts (


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facies associations, especially in B and E. Theseminerals (1) are localized within skeletal grainchambers, (2) partially replace skeletal shells, or(3) are present in the form of predominantly 50- to200-mmsize pellets.

Evidence of physical and chemical compac-

tion are identified in the studied rocks. Withinfacies associations A, B, and C, evidence of physicalcompaction is represented by (1) plastic deforma-tion of grains characterized by internal macropores(mainly Lepidocyclinaand bryozoans) and (2) grainsbroken into several pieces and slightly dislocated(e.g.,Lepidocyclinaand lamellibranch highlightedin Figure 6C). Evidence of chemical compaction(intergranular pressure solution), represented by su-tured grain-to-grain contacts (Figure 6C, F), mainly

involves grains lacking internal macropores (la-mellibranch fragments and echinoid plates andspines, in some cases surrounded by syntaxial over-growth cement). The presence of planktonic for-aminifera and radiolarian chambers partially or to-tally filled by matrix represents further evidenceof physical compaction exclusive of facies associa-tion E (Figure 6G).

Pore-Network Characteristics

Two main types of macropores (sensu Lucia, 1999)characterize facies associations A, B, and Cintergranular and intragranular (intrafossil), sensuChoquette and Pray (1970) (Figure 6AF). Incontrast, the rocks comprising facies association Einclude only intragranular (intrafossil) macropores(Figure 6G, H). Furthermore, microporosity ispresent in all the analyzed facies associations (seeTable 3).

Based on Weger et al. (2009), grainstones of

facies associations A and B have predominant large

intergranular macropores (high DomSize values;Table 3) with relatively low specific surfaces (lowPoA values;Table 3). In contrast, grainstones andpackstones of facies association C have low DomSizeand high PoA values, indicating high specific-surfacemacropore systems. Macropore systems in mud-

stones and wackestones of facies association E showlow values of both DomSize and PoA (Table 3).

Macroporedistribution is instead uniform (sensuLny, 2006) in the grainstones of facies associa-tions A and, above all, B (Figure 6AD). Con-versely, macropores have a patchy distribution(sensu Lny, 2006) within the grainstones topackstones of facies association C, as well as in themudstones to wackestones of facies association E(Figure 6EH). As recorded by the presence of

postdiagenetic hydrocarbon residues within all in-tergranular and intragranular macropores of grain-stones (when hydrocarbon invaded), fully con-nected macropore systems characterize theserocks (facies associations A and B and facies C1).On the contrary, optical microscope observationsare consistent with scattered, isolated macroporesystems characterizing packstones, wackestones, andmudstones (facies C2, E1, and E2;Figure 6FH).

QUANTITATIVE CORRELATIONS

In this section, the more meaningful correlationsamong sedimentologic, compositional, and pore-network parameters (Table 3) are summarized.The correlation graphs show one data point foreach of the analyzed carbonate facies. Each pointrepresents the mean value obtained from eightmeasurements (only three for 3-D total porosity).

As shown in the bar chart ofFigure 7, the studied

Figure 8. Correlation graphs among several sedimentologic (grain size, sorting, shape factor) and compositional rock parameters(percentages of different types of grains and cements). All these graphs were compiled using data collected from facies associations A, B,and C. Facies association E is not considered because it is composed of matrix-supported facies, in which individual matrix particles arenot visible in thin section. The selected correlation type (i.e., linear, polynomial, logarithmic, power-law) best fits the data points of eachgraph both in this figure and in Figures 912. (A) Relationships among mean grain sizes and amounts of the most representativedepositional components (skeletal grains and matrix). (B and C) Positive linear correlations of mean grain size versus shape factor andsorting. (D) Negative linear correlations between cement amounts and mean grain size. (E) Positive linear correlation between amountsof echinoid plates and spines and syntaxial overgrowth cement.



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facies of the Bolognano Formation are made up ofdifferent mean amounts of a variety of rock com-ponents (i.e., different types of skeletal grains, ce-ments, and macropores). The amounts (percentageof total rock volume) of the main depositionalcomponents (i.e., grains that are dominating in

the skeletal assemblages, such as Lepidocyclina,bryozoans, red algae, echinoid plates and spines, aswell as matrix) documented for facies associationsA, B, and C show quite disperse ranges in the graphof Figure 8A, depending on the rock grain size.

The mean grain size is correlated to severalother sedimentologic, compositional, and pore-network parameters of the carbonate rocks com-prising facies associations A, B, and C (Figures 812). Both grain shape factor and grain sorting show

positive linear correlations with the mean grainsize (Figure 8B, C); this means that finer grainedcarbonates are better sorted and composed of more-spherical carbonate grains. Regarding the diageneticcomponents of the rock, mean amounts of bothindividual types of cement (microsparry and syn-taxial overgrowth) and total cement are all nega-tively correlated to the mean grain size (Figure 8D).Moreover, when considering the syntaxial over-growth cement, its amount (percentage of total rockvolume) is positively, linearly correlated to that of

echinoid plates and spines (Figure 8E), as similarlydocumented by Knoerich and Mutti (2003).

Regarding the pore-network characteristics ofthe rocks, as shown in Table 3, the studied faciespresent different mean amounts of 2-D and 3-Dtotal macroporosities; the former is given by thesum of various amounts of intergranular and in-tragranular porosities, and the latter, by the sumof (2-D) total macroporosity and microporosity(Figure 10A). In most cases, mean values of 2-D

and 3-D total porosities, as well as 2-D intergran-ular and intragranular porosities, all increase pro-portionally with the mean grain size (Figures 9A,10B). All porosities suddenly decrease to approx-imately 0% at the critical value of mean grain sizeof approximately 0.14 mm. A significant excep-tion to the positive trend is represented by thebryozoan-dominated, medium-grained grainstonesof facies association B. As shown inFigure 9A andB, these rocks compared to other grainstones (of

Lepidocyclina-dominated facies association A) withsimilar mean grain sizes show the highest values ofboth intergranular and 2-D total porosity (19.4and 24.6%, respectively; positive outliers in thegraphs of Figure 9A, at 0.3 mm of mean grain size).The DomSize mean values show a positive linear

correlation with the mean grain size (Figure 11A);on the contrary, PoA mean values increase as themean grain size decreases (Figure 12A). Moreover,mean values of PoA, like porosities, suddenly varyat the critical value of mean grain size of approxi-mately 0.14 mm.

The 2-D and 3-D porosities, DomSize and PoA,were also crossplottedagainst each other (Figures 9B,11B,12B) and against other sedimentologic (sort-ing and shape factor) and compositional param-

eters (total cement amount; Figures 9C, 10C, 11C,12C). Specifically, mean values of both 2-D totalporosity and DomSize are (1) positively correlatedto both intergranular and intragranular 2-D po-rosities (Figures 9B, 11B), mean grain size, andgrain shape factor and are (2) negatively corre-lated to both grain sorting and total cement amount(Figures 9C,11C). Mean values of 3-D total po-rosity are correlated to mean grain size, shape fac-tor, and cement amount, similar to 2-D total po-rosity (Figure 10C). On the contrary, PoA mean

values are (1) positively correlated to both grainsorting and total cement amount and (2) negativelycorrelated to mean grain size and grain shape factor(Figure 12C), as well as both intergranular and in-tragranular 2-D porosities (Figure 12B).

DISCUSSION

In the following paragraphs, the environmentalconditions that characterized the depositional set-ting of all five facies associations (A, B, C, D, and E;Table 1) (Figure 13) recognized in this work withinthe Bolognano Formation are first assessed. Thus,the results of our integrated field and laboratoryanalyses of these carbonates in terms of sequencestratigraphy, diagenetic history, and pore-networkcharacteristics (i.e., porosity, pore types, sizes,shapes, and distribution) are discussed in detail.



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Facies association A is made up of coarse- tomedium-grained grainstones with skeletal grain as-semblages dominated by LBF (i.e., Lepidocyclina,Amphistegina, Operculina), both as nearly com-plete tests and fragmented, with minor amountsof bryozoan and red algal fragments and echinoidplates and spines (Figures 6AC,7). Brandano et al.

(2012), in their recent study conducted on out-crops of the Bolognano Formation, many of whichcorrespond to those analyzed in this study, sug-gested production loci of the bulk of the skeletalcomponents of the grainstones of facies associa-tion A within a high-energy, wide oligophoticmiddle ramp. The same authors assessed water

Figure 9.(A) Logarithmic correlations among two-dimensional (2-D) porosities and grain size of rocks belonging to facies associationsA, B, and C. (B) Positive linear correlations among 2-D total and partial porosities. The (dominant) rock components having the highestinfluence to determine specific porosity ranges are specified in the graph. (C) Polynomial correlations among 2-D total porosity andseveral sedimentologic and compositional parameters of the rock. These relationships are represented as D, a dimensionless parameterused to compare dimensionally different units. The D is equal to (1)Xi Xmin/Xmin, for the grain size and cement amount data series; (2)

(Xi

1)

(Xmin

1) /Xmin

1, for the shape factor data series, because the lowest possible value is 1 instead of 0; and (3) Xi

Xmax/Xmin,for the sorting data series, because higher sivalues correspond to poorer sorting.



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depths ranging from approximately 20 to 40 m(66131 ft) for this ramp sector, as indicated byassociations of red algae and Amphistegina T/Dvalues. Actually, the latter ones indicated thatAmphisteginaspecimens present within the skele-tal assemblages of facies association A formed at

water depths ranging between approximately 10and 40 m (33131 ft) and, hence, also across theinner ramp at water depths less than 20 m (66 ft).The Amphistegina T/D values calculated in thiswork, comprised between 0.29 and 0.51 (seeTable 3), are fully consistent with these water

Figure 10.(A) Bar chart showing the mean values of three-dimensional (3-D) total porosity as a sum of (two-dimensional) macro-porosity and microporosity, within some of the more-representative facies of the Bolognano Formation. (B) Logarithmic correlation

among 3-D total porosity and grain size of rocks belonging to facies associations A, B, and C. (C) Logarithmic correlations among 3-Dtotal porosity and several sedimentologic and compositional parameters of the rock.



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depth assessments. To sum up, the environmentalinterpretation suggested by Brandano et al. (2012)is in full agreement with those proposed by Betzleret al. (1997), Brandano and Corda (2002), Pomaret al. (2004), and Brandano et al. (2009) for severalother upper Oligocene to lower Miocene ramp car-bonates exposed in the Mediterranean area andhaving similar grain sizes, texture, and skeletal as-semblages. Additionally, these authors suggestedoligomesotrophic subtropical conditions during

the production of the skeletal components of theaforementioned carbonates.

Facies association B, instead, is characterizedby skeletal grain assemblages dominated by bryo-zoans with minor amounts of larger and smallerbenthic foraminifera and echinoids plates andspines (Table 1) (Figures 6D, 7). Although bryo-zoans may occur everywhere, regardless of lightconditions, they commonly become abundant car-bonate producers under aphotic conditions that, in

Figure 11.(A) Positive linear correlation between dominant pore size (DomSize) and mean grain size of rocks belonging to faciesassociations A, B, and C. (B) Logarithmic correlations DomSize versus two-dimensional (2-D) total and partial porosities. (C) Linearcorrelations among DomSize and several sedimentologic and compositional parameters of the rock (represented as D).



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many cases, occur on outer ramps because photo-

dependent organisms are lacking (Brandano andCorda, 2002; Pomar et al., 2004). However, bryo-zoans may also be the dominant carbonate pro-ducers on middle ramps if nutrient supplies aresufficient to significantly reduce water transparencyand, therefore, the development of photodepen-dent organisms such as LBF and red algae, whichcommonly are the main carbonate producers ofthese depositional environments (Pomar 2001;Brandano and Corda, 2002; Mutti and Hallock,

2003; Brandano et al., 2009; Westphal et al., 2010).

The skeletal assemblages of grainstones belongingto facies association B are more consistent with thelatter interpretation because the occurrence ofeutrophic conditions during their formation, evi-denced by increased amounts of phosphates andglauconite, was assessed by Vecsei and Sanders(1999) and Mutti and Bernoulli (2003).

Both facies associations A and B present analo-gous bedding patterns (cross-bed packages; Table 1)(Figures 4A;5A, B) that have been interpreted as

Figure 12.(A) Negative power-law correlation between perimeter over area (PoA) and mean grain size of rocks belonging to faciesassociations A, B, and C. (B) Negative polynomial correlations PoA versus two-dimensional (2-D) total and partial porosities. (C) Polynomialcorrelations among PoA and several sedimentologic and compositional parameters of the rock (represented as D).



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the product of unidirectional migration of large-scale subaqueous dunes under the action of bot-tom currents (Vecsei and Sanders, 1999; Brandanoet al., 2012, and references therein). Our paleo-current data (dip directions of cross-beds after therestoration of tectonic tilting; see Table 1) areconsistent with the seaward dune migration to-

ward west northwest and north northwest, in fullagreement with that previously documented byVecsei (1991), Vecsei and Sanders (1999), andBrandano et al. (2012) (see Figures 1B, 14). Inmany cases, subaqueous dune migration deter-mines a skeletal accumulation in the middle ramp,less commonly in the proximal outerramp (Pomar,

Figure 13.(A) Sequence-stratigraphic scheme of the studied facies associations of the Bolognano Formation. The scheme is based ondata collected from tens of outcrops, tens to hundreds of meters laterally and vertically extensive and patchily distributed in the studyarea. In particular, the four more-representative outcropping stratigraphic sections are used to calibrate the scheme. Strongly dia-genetically modified facies associations represented in Figure 2 are not considered because these are related to late, fault-related dia-genetic processes that are not associated to the ramp evolution. (B) Schematic cross section of the platform margin of the MajellaMountain showing the large-scale architecture of facies associations that compose the Bolognano Formation (modified from Mutti et al.,1997). In the Mount Cavallo area, different facies associations from the studied ones have been documented by Brandano et al.(2012). (C) Ramp profile showing the depositional environments in which the studied facies associations of the Bolognano Formationformed. TST = transgressive systems tract; FSST = falling-stage systems tract; Ms = major sequence; Hs = high-frequency, small-scale

sequence.



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2001; Pomar et al., 2002, and references therein;Brandano et al., 2012). Basedon their similaritiesinbedding patterns, facies associations A and B can beconsidered as deposited in a similar setting andunder similar hydraulic conditions, probably rep-resented by a broad middle to proximal outer ramp

(Figure 13). Evidence of seaward transport pro-vided by bedding patterns of facies associations Aand B are supported by the skeletal grains com-posing them that mostly occur as abraded frag-ments (Table 1). In full agreement with Brandanoet al. (2012), preservation levels of LBF tests (BPTS),ranging from 1 to 3, are consistent with transportfor kilometric distances. Moreover, the presence ofskeletal components produced on the inner ramp(ex situAmphisteginaspecimens characterized by

high T/D values) suggests a remarkable seawardsediment transport and accumulation in deeper en-vironments, such as middle ramp and, possibly,proximal outer ramp.

Facies association C is composed of bioturbated,fine-grained bioclastic grainstones and packstones(Figure 6E, F). Brandano et al. (2012) interpretedrocks belonging to this facies association as de-posited in a generic moderate-energy, aphotic outerramp. This conclusion is supported by (1) skeletalassemblages mainly composed of fragments of

photoindependent benthic biota (echinoids, smallbenthic foraminifera, bryozoans, and lamellibranchs)and (2) the presence of planktonic foraminifera,matrix, and intense bioturbation coupled with adecrease in grain size relative to facies associationsA and B, all indicative of decreasing water energyand possibly related to a change from shallowerto deeper water. However, Buxton and Pedley(1989), Brandano and Corda (2002), and Pomaret al. (2004) proposed more specific locations

along ramp profiles for deposition of OligoceneMiocene carbonates of the Mediterranean area,

characterized by similar textures, grain sizes, andskeletal assemblages. The aforementioned authors,indeed, interpreted these carbonates as having ac-cumulated on intermediate outer ramps; typicalwater depths of approximately 50 m (164 ft), or alittle more, were suggested by Knoerich and Mutti

(2003) (Figure 13). Benthic skeletal components ofgrainstones and packstones of facies association Cwere mainly produced in the inner and middleramp, as indicated by the presence ofAmphisteginaspecimens with T/D values comprised between0.28 and 0.44 (see Table 3), indicating waterdepths ranging from approximately 10 and 40 m(33131 ft). Then, skeletal components accumu-lated in the intermediate outer ramp after a longtransport and strong reworking, as indicated by the

preservation levels (BPTS) of LBF tests rangingfrom 2 to 3. Benthic skeletal fragments accumu-lated on intermediate outer ramps have been com-monly interpreted as distal deposits of unidirec-tional (seaward) bottom currents (Pedley, 1998;Knoerich and Mutti, 2006b). In contrast, plank-tonic foraminifera and matrix, which complete theskeletal assemblages of the rocks of facies associ-ation C, mainly accumulated on the same rampsector because of fallout of planktonic foraminifera,and clay and carbonate mud, respectively (James,

1997).Facies association E is composed of strongly bio-

turbated marly mudstones and wackestones rich inplanktonic foraminifera, with minor amounts ofradiolarians and siliceous sponge spicules (Figure 6G,H). Following the interpretations of Brandano andCorda (2002), Mutti and Hallock (2003), and Pomaret al. (2004) for very similar Miocene ramp car-bonates of central Italy, the (1) diagnostic assem-blages of planktonic foraminifera (see Table 1), (2)

presence of radiolarians and siliceous sponge spic-ules, and (3) diagnostic ichnofacies associations

Figure 14.Conceptual scheme (not in scale) showing how elementary cycles of the studied facies, high-frequency sequences, andstratigraphic surfaces form over time, contributing to a major depositional sequence. (A) Emplacement of a transgressive systems tract(TST) composed of facies association C. (B) Emplacement of a cross-bed foreset belonging to a falling-stage systems tract composed offacies association A. (C) Formation of a flooding surface caused by abrupt sea level rise without deposition. This surface represents theupper boundary of a high-frequency, small-scale sequence. (D) Emplacement of a cross-bed foreset belonging to a falling-stage systemstract composed of facies association B. (E) Emplacement of a TST composed of facies association E. The lower boundary of the TST is atransgressive surface, which also represents the upper boundary of a major depositional sequence. SWB = storm wave base.



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(ChondritesandZoophycos; see Table 1) allow us tointerpret the rocks comprising facies association Eas formed on the distal outer ramp (Figure 13)within the deeper aphotic zone, under low-energy,eutrophic (upwelling-related) subtropical condi-tions. Water depths of 50 m or more have been

considered by several authors (Vecsei and Sanders,1999; Mutti and Bernoulli, 2003; Mateu-Vicenset al., 2008, and references therein) for carbonaterocks with the same planktonic foraminifera andichnofacies associations of facies association E.

Finally, facies association D is composed of avariety of facies similar to those of either faciesassociations C or E; an intermediate to distal outerramp is therefore interpreted as the depositionalenvironment (Table 1) (Figure 13).

Sequence Stratigraphy

The carbonate succession under study shows lat-eral and vertical variations of facies associationsrepresentative of different middle- to outer-rampenvironments, within an approximately 5-km(3-mi) extended sector of carbonate ramp (Table 1)(Figure 13). From a sequence-stratigraphic pointof view, this carbonate succession is interpreted

as being made up of five major depositional se-quences formed in some million years spanningfrom upper Chattian to Burdigalian, within a paleosea deepening toward north northwest (Figure 13).Downscaling, the entire stack of major sequencesis composed of both a transgressive systems tract(TST) and a falling-stage systems tract (FSST); eachsystems tract is from 10 to 40 m (33131 ft) thick(Figure 13). This interpretation is different fromthat proposed by Vecsei and Sanders (1999) for

the carbonate succession of the Bolognano Forma-tion. These authors proposed the entire BolognanoFormation as being composed of four major de-positional sequences (the two lowest ones corre-sponding to the carbonate succession analyzed inthis study), each one consisting of (1) a lower unitcomposed of skeletal limestones and interpretedas TST and (2) an upper unit composed of marlylimestones and interpreted as TST passing upwardto a highstand systems tract (HST).

Specifically, Vecsei and Sanders (1999) inter-preted the lower units of the two lowest sequences(cross-bedded grainstones equivalent to faciesassociations A and B defined in this study) as TSTon the basis of (1) the erosional features (i.e.,scours, truncation of underlying beds) of the lower

boundaries of these units (interpreted as transgres-sive surfaces [TS]), indicative of substantial sub-marine erosion; and (2) the position of these faciesassociations on a paleohigh above a former carbon-ate platform.In contrast, the results provided by thisstudy are consistent with the overall downward-stepping geometries of cross-bed foresets formingfacies associations A and B being compatible withFSST deposits (Table 1) (Figures 4A;5;13; Plintand Nummedal, 2000). Other diagnostic features

of the FSST are the presence, at the base of cross-bed packages belonging to facies association A, oflarge-scale scoured surfaces that truncate under-lying planar beds of facies associations C, D, and Eand onto which the cross-beds of facies associationA downlap (Figures 5A, B;13). Altogether, thesefeatures are consistent with the aforementionedtruncation surfaces representing regressive surfacesof erosion (RSE) (Plint and Nummedal, 2000) in-stead of TS. Along the studied carbonate rampsystem, the most likely process responsible for ma-

rine erosion and, therefore, RSE formation is theprogressive seaward shift of the middle to proximalouter-ramp settings (dominated by erosional bot-tom currents) as a consequence of sea level fall(Figure 14). Facies associations C, D, and E areinterpreted as TST deposits (Table 1) (Figure 13).This conclusion is supported by (1) south-south-eastward onlaps of planar beds of these facies as-sociations against gentle, north-northwestwarddipping, large-scale truncation surfaces, interpreted

as TS (Figures 5,13); and (2) onlaps of these bedsonto underlying grainstones (facies associations Aand B) deposited in more proximal ramp environ-ments (Figures 5,13). Vecsei and Sanders (1999)also interpreted deposits (marly limestones) corre-sponding to facies associations C, D, and E as TSTbut passing upward to HST. However, consideringthat (1) no maximum flooding surfaces are detect-able within the facies associations stated above and(2) clear (shallowing-) coarsening-upward facies



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trends were not observed (Figure 3), the presenceof HST within the studied carbonate successioncannot be detected. The absence of HST deposits,commonly interposed between TST and FSST,may be explained for the studied carbonates as aconsequence of low carbonate production rates,

which were unable to keep up with sea level rises(Mutti et al., 1997). As shown inFigure 13, bothTS and RSE can represent the major sequenceboundaries.

The individual cross-bed foresets, as much as4 m (13 ft) thick, bounded by subhorizontal,slightly undulatory truncation surfaces and form-ing unidirectional downlaps onto the lower trun-cation surfaces (Figures 3, 4A; 5), were interpretedby Vecsei and Sanders (1999) as parasequences

(sensu van Wagoner et al., 1990). In agreementwith these authors, all these truncation surfaces,internal to rock bodies composed of facies asso-ciations A and/or B, are interpreted as floodingsurfaces, pointing to abrupt transgression withoutdeposition (Figures 13,14). However, the down-ward-stepping geometries of cross-bed foresets,pointing to progradational deposition during timesof sea level fall, are not compatible with parase-quences. The latter, indeed, form as a consequenceof progradational deposition during times of sea

level rise. Hence, the individual cross-bed foresetsbounded by flooding surfaces formed during acomplete cycle of sea level rise and fall and thereforecan be interpreted as high-frequency, small-scalesequences that compose the FSST of the major se-quences (Figures 13,14).

High-frequency, small-scale sequences of fa-cies association A can be caused by elementarycycles that include the alternation of bed packagesof different facies with variable thickness, ranging

from 10 cm (4 in.) to 2 m (7 ft) (Figure 3). More-over, the TST (facies associations C, D, and E) arecomposed of elementary cycles resulting from thealternation of bed packages of different facies,with analogous variable thickness (Figure 3). Inconclusion, both TST and FSST of the major se-quences are composed of elementary facies cy-cles, which may be related to high-frequency sealevel changes. Other concurring factors control-ling the carbonate production, such as hydrody-

namic and trophic changes, may justify the wideand irregular thickness variability of the deposi-tional cycles.

Eustatic fluctuations best explain both thevertical changes of facies associations and the dis-tribution of the elementary facies cycles. Tectonics

probably had only a minor influence on sea levelchanges because the ramp of the Majella Mountainwas located in a foreland position during the lateChattian to Burdigalian (e.g., Ghisetti and Vezzani,2002; Scisciani et al., 2002, and references therein).Increased nutrient availability during times of ab-rupt eustatic sea level rise (Haq et al., 1987) mayhave facilitated the upward changes from benthicskeletal grain-dominated grainstones to carbon-ates with planktonic foraminifera as dominant

skeletal components (shifting of the lower depthof the photic zone, reduction of the benthic car-bonate production in the middle and proximalouter ramp; Mutti et al., 1997; Vecsei and Sanders,1999) (Figure 14).

Diagenetic History

Based on similarities with what was described andinterpreted by Mutti and Bernoulli (2003) for the

Bolognano Formation and by Knoerich and Mutti(2003, 2006a, b) for similar carbonates (OligoceneMiocene ramp facies) cropping out in the centralMediterranean, the diagenetic modification (i.e.,precipitation of authigenic minerals and cements,compaction) of the studied carbonates is thoughtto have occurred, over time, in three distinct dia-genetic environments: (1) early marine, (2) shallow-marine burial, and (3) deep burial. The only evi-dence of early marine diagenesis is the presence of

iron oxides, glauconite, and phosphates (Table 2).These authigenic minerals precipitate at or near thesediment-water interface and generally require in-creased nutrient availability at the sea floor (Muttiand Bernoulli, 2003). In contrast, both shallow-marine and deep burial diagenesis are inferred asresponsible for (1) the precipitation of cementsand (2) the overburden-related physical compac-tion undergone by the studied rocks. In addition,deep burial diagenesis is inferred as responsible



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for overburden-related chemical compaction (themaximum burial depth estimated is comprised be-tween 200 and 2500 m [656 and 8202 ft]) (Oriet al., 1986; Mutti, 1995; Rustichelli et al., 2012).

Cements have been distinguished as pre- andsyncompaction based on their relative spatial re-

lationships with the physical and chemical com-paction features observed in thin section. As al-ready mentioned, syntaxial overgrowth cementcompletely surrounds, in most cases, one or moreechinoid plates and spines (see plates highlightedin Figure 6A, B, D). This mode of cement growthimplicates near-surface cement precipitation fromfluids within the sediments during lithification(Agosta and Kirschner, 2003). Cement was, in-deed, able to push away the adjacent grains during

syntaxial growth over the echinoid plates and spines.In other cases, the same cement only partially en-velopes echinoid plates and spines away from grain-to-grain contacts, suggesting a higher overburdenunder which cement was not able to push awayall adjacent grains during precipitation (see plateshighlighted in Figure 6E). As suggested by thepresence of sutured grain-to-grain contacts of echi-noid plates and spines enveloped by syntaxial over-growth cement (Figure 6F), and in agreement withthat similarly documented by Knoerich and Mutti

(2006a, b), syntaxial overgrowth cement predatesthe overburden-related intergranular pressure solu-tion. According to the aforementioned observations,themain precipitation phase of syntaxial overgrowthcements probably occurred in a shallow-marineburial environment (depth, as much as a few tensof meters), before the studied rocks underwent ex-cessive physical and chemical compaction. Jameset al. (2005) and Knoerich and Mutti (2006a, b)inferred the dissolution and neomorphism of early

marine, highmagnesium calcite cements and ara-gonitic biota, not preserved at present time, as beinga possible source for low-magnesium calcite, syn-taxial overgrowth cements.

Evidence of syncompactional microsparry ce-ment, localized near sutured grain-to-grain contacts(Figure 6C), are documented within facies asso-ciations A, B, and C. Precipitation of these cementswas probably enhanced by pervasive, overburden-related intergranular pressure solution, responsible

forthe enrichmentof CaCO3 up to saturation in thediagenetic fluids (Agosta et al., 2008). Unfortu-nately, in most cases, it is very difficult to establishthe relative spatial relationships among micro-sparry cement and the physical and chemical com-paction features observed in thin sections. Despite

this limitation, a multiphase precipitation his-tory throughout both shallow-marine burial (pre-compactional) to deep burial (syncompactional)diagenetic environments is proposed also consid-ering strong similarities with syntaxial overgrowthcement (i.e., analogous clear, low-magnesium cal-cite and similar CL patterns).

Following Flgel (2004), the rare rocks of fa-cies association E dominated by microsparry calcitecement can be interpreted as the result of matrix

recrystallization to form microspar under burialdiagenesis. This conclusion is suggested by thepresence of preserved matrix within some cham-bers of planktonic foraminifera and radiolarians.

Pore-Network Characteristics

Skeletal grain assemblages, grain size, grain sort-ing, and shapes are assessed as the primary con-trols on the pore-network characteristics (2-D and

3-D porosities, pore types, sizes, shapes, and dis-tribution) of grainstones deposited on both mid-dle to proximal outer (facies associations A and B)and intermediate outer ramps (facies C1; Figures 913). Common to all types of biotic carbonate pro-duction, the skeletal grain assemblages of the stud-ied grainstones are the consequence of a multitudeof interacting factors, including (1) production lociof specific types of biota in response to specific en-vironmental factors (e.g., trophic and photic condi-

tions, hydrodynamics) and (2) grain selection duringunidirectional transport on the sea floor by cur-rents, which determined seaward deposition offiner grained grainstones (facies C1).

Size selection, rounding, and grain breakageduring transport determined the resulting meansize, sorting, and shapes of grains. All these factorsrepresent intrinsic parameters that, in turn, deter-mined the primary intergranular porosity of rocks.In particular, elongated grain shapes (expressed by



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higher values of shape factor in Figure 8B) are typ-ical of coarse-size grains, mainly consisting of com-plete tests ofLepidocyclinaand a few lamellibranchfragments, whereas finer grains (mostly fragmentsof LBF, bryozoans, and red algae, as well as echinoidplates and spines) are commonly more spherical

(Figures 6A

F;8A, B). Because of the higher frag-mentation of skeletal grains with heavier transport,grain sorting is better in rocks with smaller meangrain sizes (Figures 6AF; 8C). As widely docu-mented in literature (e.g., Lucia, 1999), well-sortedrocks with more spherical grains commonly havehigher primary intergranular macroporosity. On thecontrary, as a consequence of transport-induced grainselection and breakage, the amounts of intragran-ular macroporosity, which localizes within the

chambers of some skeletal grains (i.e., LBF, espe-cially Lepidocyclina, and bryozoans) decrease fromcoarse- to fine-grained grainstones, determining itspositive correlation with mean grain size (Figure 9A).

A significant influence of dominant skeletalcomponents of grainstones on primary macroporenetworks of facies associations A and B is assessed.Different skeletal grain assemblages characterizethe grainstones of these facies associations (Table 1)(Figures 6A, C, D;7), which were deposited undersimilar hydrodynamic conditions and are charac-

terized by sharp differences in both 2-D and 3-Dporosities (Table 3). In particular, higher meanvalues of both intergranular (19.4 vs.10.5%) andtotal 2-D and 3-D porosities (24.6 and 32.1% vs.15.5 and 23.9%) of bryozoan-dominated grain-stones (facies association B) than theLepidocyclina-dominated grainstones of facies association A(Figure 9B) depend on the better sorting of theformer grainstones (Table 3) (Figure 9C). The mod-erate to well sorting that characterizes facies asso-

ciation B (Table 3) is mainly related to the break-ing of bryozoans during transport that producedfragments with quite similar sizes (Figure 6D).Hence, rocks with higher amounts of quite uni-formly distributed, primary intergranular macro-porosity were produced. On the contrary,Lepido-cyclina either were preserved as large completetests or broke into fragments of dissimilar sizes, witha consequently wider range of grain sizes (moderateto poor sorting;Table 3) than bryozoans (Figure 6A,

C). Being mean values of intragranular macropo-rosity (commonly between 5 and 7%) and micro-porosity (7.3 vs. 7.5%) quite similar in grainstonesbelonging to both facies associations A and B (seeTable 3), a significant contribution of such porositiesin determining the 2-D and 3-D total porosity dif-

ferences can be excluded.Diagenesis did not significantly modify the

primary porosity characteristics in the coarse- tomedium-grained grainstones of facies associationsA and B but only determined a mean 2-D porosityreduction, by cementation, of 2 to 4.5% (Figure 8D).Relatively low specific-surface macropore sys-tems, with DomSize ranging from 0.1 to 0.5 mmand PoA from 35 to 80 mm1, typical of rocksdeposited in high-energy environments (Lny,

2006), characterize the highly porous grainstonesof facies associations A and B. The DomSize valuesare representative of intergranular macropores inboth facies associations A and B (Figure 11B). Theoverall low specific-surface macropore systems aremostly a consequence of the abundant subspher-ical to elliptical intragranular macropores ofLepi-docyclina in facies association A (Figure 6A, C) andbryozoans in facies association B (Figure 6D).Strong diagenetic modification (cement precipi-tation) of primary porosity, induced by the specific

dominant biota of the skeletal grain assemblages,occurred in fine-grained grainstones (facies C1).There, indeed, higher amounts of echinoid platesand spines (2043% of the total rock volume;Table 3) are commonly associated with higheramounts of syntaxial overgrowth cement (as muchas 8%;Table 3) (Figure 8E) simply because echi-noid plates and spines represent monocrystallinecalcite grains along which syntaxial overgrowth ce-ments formed in optical continuity (Flgel, 2004).

To support this conclusion, red alga-rich, fine-grained grainstones (facies Al2) are characterizedby lower amounts of both echinoid plates andspines (915% of total rock volume), and hencesyntaxial overgrowth cement (15%), than thefine-grained grainstones of facies C1 (Table 3)(Figure 6B, E). Amounts of syntaxial overgrowthcements similar to those of facies C1 are charac-teristic of well-sorted, heterozoan-dominated grain-stones (especially of the Oligocene and Miocene)



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formed in high-energy depositional settings, repre-senting the volumetrically most important cementtype (Knoerich and Mutti, 2003, 2006b; Kroh andNebelsick, 2009). Transport by bottom currentshas been interpreted as being responsible for theenrichment of components resistant to abrasion,

like echinoid plates and spines (Knoerich and Mutti,2003). In agreement with Lny (2006), patchydistribution of intergranular macropores, like that offacies C1 (Figure 6E), is related to patchy cemen-tation of these pores caused by the selective pre-cipitation of syntaxial overgrowth cements aroundscattered echinoid plates and spines.

Cementation also played a fundamental func-tion in controlling pore-network characteristics offine- to very fine-grained packstones (facies C2)

deposited on the intermediate outer ramp. Withinthese rocks, cement amounts as much as 12%(Table 3) were responsible for the reduction of pri-mary total 2-D porosity. In particular, the highestamounts of microsparry cement (37.5% of totalrock volume; Table 3) (Figure 8D) among thestudied facies characterize these packstones. Thisis probably related to high rates of cement pre-cipitation from fluids saturated because of exten-sive chemical compaction by pressure solutionseams. Because of their peculiar sedimentologic

characteristics (i.e., 24% of total rock volumemade up of clay minerals, good grain sorting, andcircularity), the studied packstones are, indeed, per-vasively crosscut by bed-parallel pressure solutionseams (Figure 4A) relative to the other facies, asdocumented by Rustichelli (2010) and Rustichelliet al. (2012) for the same carbonates analyzed inthis study. The intensity of cementation is ex-pected to be proportional to the abundance andproximity of pressure solution seams (Ehrenberg

et al., 2006a). In summary, the drastic reduction oftotal 2-D and 3-D porosities documented for faciesassociation C at a mean grain size of 0.14 mm iscaused by cementation and, to a lesser extent, thepresence of matrix (Figures 9A, C;10B, C). Macro-pores with small DomSize (ranging from 0.05 to0.15 mm), representative of both intergranular andintragranular macropores (Figure 11B), and highspecific surface (PoA ranging from 60 to 140 mm1)characterize facies association C (Table 3) (Figure 6E,

F). These small DomSize values were a conse-quence of the strong cementation of rocks of thisfacies association, which was responsible for a re-markable reduction of primary sizes of macroporesand was causing a relative enrichment in smallermacropores (mostly intragranular; Figure 11B).

Strong cementation significantly modified the pri-mary macropore shapes, especially in facies C2.

Within this facies, cementation determined a sys-tem of isolated macropores characterized, on av-erage, by higher specific surfaces (PoA rangingfrom 105 to 140 mm1) than in the other facies(Table 3).

A further well-known key factor controllingporosity is the amount of matrix (Lucia, 1999;Ehrenberg et al., 2006b; Lny, 2006). Matrix is

absent in carbonate rocks deposited on the middleto proximal outer ramp because of high-energydepositional environments and gradually increasesin content in carbonates deposited on the inter-mediate outer ramp to finally become the pre-dominant component in carbonates formed on thedistal outer ramp (Table 3) (Figures 7,13). Sedi-ments deposited in the latter environment, marlywackestones to mudstones (facies association E),are characterized by low values of macroporosity(02%); in contrast, high values of microporosity

(2431%) are contained within the wackestonesof facies E1 (Table 3) (Figure 10A). Because ofthe similarity in compositional and textural char-acteristics with facies E1 (seeFigure 6G, H), sim-ilar high values of microporosity probably char-acterize also the mudstones of facies E2. Becauseof the mud-dominated textures, planktonic fora-minifera and radiolarian chambers represented theonlyprimary (intragranular) macropores, partially ortotally filled by matrix and/or cement (Figure 6G)

during the burial-related physical and chemical com-paction. Small intragranular macropores (DomSizeranging from 0.06 to 0.1 mm) with low specificsurfaces (PoA ranging from 50 to 85 mm1), repre-sentative of the rounded shapes of planktonic fo-raminifera and radiolarian chambers, characterizewackestones to mudstones of facies association E.The microporosity dominating this facies associ-ation is assessed as matrix microporosity (sensuLucia, 1999).



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The pore-network characterization performedin this study is fundamental because the porecharacteristics can be linked to physical propertiesof carbonates, such as permeability (Anselmettiet al., 1998; Weger et al., 2009). High permeabilityvalues, commonly associated with grainstones with

(1) coarse bioclastic textures, (2) well-connectedmacropores with low specific surfaces (low PoAand high DomSize values; Ehrenberg et al., 2006b;

Weger et al., 2009), and (3) low diagenetic mod-ifications can be inferred for grainstones of faciesassociations A and B. In contrast, low perme-ability values, commonly associated with carbon-ates having small and isolated macropores withhigh specific surfaces (high PoA; Weger et al.,2009), can be deduced for the packstones of fa-

cies C2. Considering the wackestones and pack-stones of facies association E, which are char-acterized by scattered isolated macropores (i.e.,intragranular pores of planktonic foraminifera andradiolarians), their permeability is mainly controlledby the dominant matrix microporosity (Anselmettiet al., 1998; Melim et al., 2001). Finally, a fully con-nected patchy macroporosity distribution, such asthat of facies C1, may yield higher permeability, fora given porosity, than uniform macroporosity dis-tributions (Lny, 2006).

CONCLUSIONS

This article highlights the most important sedi-mentologic and diagenetic factors that determinedthe pore-network characteristics (i.e., porosity, poretypes, sizes, shapes, and distribution) of several fa-cies of the OligoceneMiocene Bolognano Forma-tion, cropping out at the Majella Mountain, central

Italy. The results of this study are consistent withthe original shapes and dimensions of the skeletalbiota, as well as the depositional processes occur-ring in specific ramp sectors, being responsible forthe types, sizes, shapes, and sorting of the grainsthat compose the sediments. These, in turn, con-trolled the subsequent diagenetic modification towhich the sediments were subjected and, in par-ticular, the cement precipitation. Both sedimen-tologic and diagenetic processes that occurred along

the different sectors of the carbonate ramp wereresponsible for the formation of carbonate rockscharacterized by a wide range of porosity amountsand arrangements.

The following are the main controlling factorson pore-network characteristics:

1. A

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