Integrated stratigraphic, palaeontological, and geochemical analysis of the uppermost Hauterivian Faraoni Level in the Fiume Bosso section, Umbria-Marche Apennines, Italy

Integrated stratigraphic, palaeontological, and

geochemical analysis of the uppermost

Hauterivian Faraoni Level in the Fiume Bosso

section, Umbria-Marche Apennines, Italy

*Rodolfo Coccioni, {Francois Baudin, *Fabrizio Cecca,

{Marco Chiari, *Simone Galeotti, {Silvia Gardin

and xGiovanni Salvini

* Istituto di Geologia, UniversitaÁ di Urbino, Campus Scienti®co, LocalitaÁ Crocicchia, 61029, Urbino, Italy{CNRS-URA 1761 et FR 32, DeÂpartement de GeÂologie SeÂdimentaire, Universite Pierre et Marie Curie, case117, 4 place Jussieu, 75252, Paris, Cedex 05, France{CNR, Centro di Studio di Geologia dell'Appennino e delle Catene Perimediterranee, c/o UniversitaÁ diFirenze, Via La Pira 4, 50121, Firenze, ItalyxDipartimento di Scienze della Terra, UniversitaÁ di Firenze, Via La Pira 4, 50121, Firenze, Italy

Revised manuscript accepted 6 August 1997

An integrated stratigraphic, palaeontological, and geochemical study has been carried out across theuppermost Hauterivian Faraoni Level of the Fiume Bosso section in the Umbria-Marche Apennines,Italy. This level represents a ®rst, prominent sign of the global changes that led to the widespreaddeposition of mid-Cretaceous organic-rich facies. Marked changes in the organic geochemical recordand micro¯oral and micro- and macrofaunal assemblages occur within the interval. They are charac-teristic for short-term deposition in strongly dysoxic bottom conditions. Such changes probably re¯ectclimatic variation which, in turn, induced variations in the palaeoceanographic regime.

# 1998 Academic Press Limited.

KEY WORDS: integrated stratigraphy; geochemistry; black shales; palaeoenvironment; palaeoclimate;Hauterivian; Umbria-Marche; Apennines; Italy.

1. Introduction

During the late Early to early Late Cretaceous a combination of factors such as

high primary productivity and/or good preservation of organic matter led to wide-

spread deposition of organic carbon(OC)-rich facies in a large variety of deposi-

tional settings (Schlanger & Cita, 1982). Some of these OC-rich layers are the

sedimentary expression of global palaeoceanographic episodes also known as

Oceanic Anoxic Events (OAEs of Schlanger & Jenkins, 1976, and Arthur et al.,1990). Several prominent, regional OC-rich horizons are recognizable within the

Cretaceous sequence of the Umbria-Marche Basin (UMB) which are useful mar-

kers for lithostratigraphic correlations (Arthur & Premoli Silva, 1982; Coccioni &

Battistini, 1989; Coccioni et al., 1987, 1989; Cecca et al., 1994a; Figure 1).

The Faraoni, Selli (=OAE 1a of Arthur et al., 1990), and Bonarelli (=OAE 2 of

Arthur et al., 1990) Levels stand out from all the others because of their very high

total organic carbon (TOC) content. Following the Valanginian±Hauterivian scat-

tered, mm-thick black shales, the uppermost Hauterivian Faraoni Level (Cecca etal., 1994a) (FL) is the ®rst, prominent, regionally correlatable, indicator of global

changes that led to the widespread deposition of mid-Cretaceous OC-rich facies.

Cretaceous Research (1998) 19, 1±23

0195±6671/98/010001 + 23 $25.00/0/cr970093 # 1998 Academic Press Limited

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Within the framework of IGCP Project 362 (Tethyan and Boreal Cretaceous)

this paper deals with an integrated stratigraphic study (ammonites, calcareous

nannofossils, foraminifera, radiolaria, and organic geochemistry) of the FL in the

Fiume Bosso section (Figures 2, 3), in order to explore in detail the effects of this

short-term event on the micro¯ora and macro- and microfauna.

2. Geological, stratigraphic, and palaeoceanographic settingThe UMB was created during early Liassic rifting which involved the shallow-

water Triassic carbonate platform that extended over the entire southern margin

of the Tethys Ocean. The UMB contains a continuous, pelagic±hemipelagic sedi-

mentary sequence of Early Jurassic±Oligocene age. The Cretaceous sequence is

lithologically subdivided into several discrete formations and members on the

basis of colour changes and carbonate content ¯uctuations along with the pre-

sence or absence of chert and black shales (see Coccioni, 1996). The following

formations can be recognized (from bottom to top): Maiolica (late Tithonian±

early Aptian), Marne a Fucoidi (early Aptian-late Albian), Scaglia Bianca (late

Albian±earliest Turonian), and Scaglia Rossa (earliest Turonian±earliest Lutetian)

(Figure 1). The Maiolica Formation consists primarily of whitish to medium grey

limestones interbedded with beige to black chert nodules or layers and dark grey

to black, organic-rich horizons with variable carbonate content. Their frequency

and thickness increase markedly towards the overlying Marne a Fucoidi For-

mation.

The FL lies within the upper member (Grey Member of Coccioni et al., 1989)

of the Maiolica Formation. According to Cecca et al. (1994a) it ranges in thick-

ness from 25 to 42 cm and is characterized by an ammonite-rich calcareous bed

(referred to as Guide-bed herein) sandwiched between alternating limestones and

black shales, the latter displaying a very high organic carbon content (up to 25

weight % of TOC). The ammonite assemblage correlates the FL to the Pseu-

Figure 2. Location of the stratigraphic interval studied (asterisk) in the Fiume Bosso section. Theoutcrop area of the section is shown on the geological map of Italy, F. 290 ``Cagli'', 1:50 000.

Uppermost Hauterivian Faraoni Level 3

dothurmannia angulicostata Zone, P. catulloi Subzone (Cecca et al., 1994a).

According to Baudin et al. (1995 and submitted), pyrolysis and palynological data

indicate that the organic matter in the FL is mainly of marine origin and predomi-

nantly amorphous. According to these authors, the medium ¯uorescence of amor-

phous organic matter, the Sulphur/Carbon (S/C) ratio, as well as the presence of

palynoforaminifera (Galeotti, 1995) suggest a dysoxic rather than an anoxic

depositional environment. Cecca et al. (1996) and Faraoni et al. (1996) recog-

nized the FL also in the Southern and Venetian Alps respectively, showing the

supraregional extension of this level.

3. Material and methods

3.1. Field workAccording to Cecca et al. (1994a) the Fiume Bosso section (lat. 43�3101100N;

long. 0� 070 0700E) is the reference section for the FL. It is located on the eastern

limb of the Monte Nerone anticline and crops out along Provincial Road No. 29

which connects Pianello to Cagli along the Bosso river valley (Figures 3, 4).

The present study concentrates on a 20.5-m-thick stratigraphical interval

located at km 9.950 which includes the FL (10±10.27 m above the base of the

section) (Figures 4, 5). This interval consists primarily of yellowish-grey to med-

ium grey limestones in 3- to 50-cm-thick beds. Limestone layers are interbedded

with 0.5- to 3-cm-thick dark grey to black, usually laminated, shales with variable

carbonate content and light brown to grey and black thin chert beds and/or

nodules. The limestone layers are heavily bioturbated, with dark grey burrows

assignable to Planolites and Zoophycos. Pyrite nodules occur mainly at the base of

the black layers. Small faults are occasionally present.

According to Channel et al. (1995), the 90-m-thick Grey Member of the Maio-

lica Formation represents c. 9 my. The average sedimentation rate of this portion

of the formation would therefore be close to 10 m/my. Hence, the studied section

encompasses a time slice close to 2 my; this is marked on the outcrop with blue

paint at metre intervals.

Ninety-one samples have been collected and marked as BO 1±91 from bottom

to top. The sample set comprises mostly limestones and black shales, but also

includes a few cherts. The black shales were collected from a deep trench to elim-

inate surface contamination. The samples were collected at 5 to 80 cm intervals

in the lower and upper part of the studied section, and bed by bed (at approxi-

mately 15-cm intervals) in its middle part (6.8±11.8 m above the base of the stu-

died section) where the FL (samples BO 42±46) lies.

3.2. Sample preparation

Calcareous nannofossilsCalcareous nannofossils were investigated semi-quantitatively from both limestone

and black shale samples. A quantitative analysis was performed on 20 closely

spaced samples (BO 31±51; from 9.32±10.90 m above the base of the studied sec-

tion) across the FL. For quantitative analysis, 300 specimens were counted in ran-

dom traverses of standard prepared smear slides from each sample. Total

abundance was estimated on the basis of the ratio of number of specimens/num-

ber of ®elds of view. The relative abundance of taxa was calculated as a percen-

4 R. Coccioni et al.

tage of a total of 300 specimens. Photomicrographs of the most important forms

are shown in Figure 6.

ForaminiferaAll samples collected were studied for planktonic foraminifera. The semiquantita-

tive analysis was primarily conducted in thin section, the predominant lithologies

Figure 3. A, Exposure of the stratigraphical interval that includes the Faraoni Level (FL). B, Close-up of Figure 3A.

Uppermost Hauterivian Faraoni Level 5

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Uppermost Hauterivian Faraoni Level 7

being hard, and subordinately on washed material from the black shales. Labora-

tory processing of the washed residues included gentle mechanical disaggregation,

oven-drying, soaking in dilute hydrogen peroxide and wet sieving through a

63 mm sieve.

A set of 27 samples from 7.15±13 m above the base of the measured section

was semiquantitatively investigated for agglutinated foraminifera. Samples were

dissolved completely in hydrochloric acid and washed through a 63 mm sieve.

Foraminiferal abundances were estimated directly by comparing the thin sec-

tion and washed residue contents per square unit (>2 cm2) to the standard % dia-

grams by Baccelle & Bosellini (1965). The classi®cation followed is based on

Banner & Desai (1988) and Loeblich & Tappan (1988). Photomicrographs of the

microfacies and some planktonic foraminifera are shown in Figures 7 and 8.

RadiolariaRadiolarian abundances were semiquantitatively estimated in thin section accord-

ing to the method of Baccelle & Bosellini (1965). The study was carried out on

58 thin sections from limestone layers and on 14 thin sections from cherts. Sev-

eral samples from the limestones and cherts were subjected to different methods

of treatment including digestion in hydrochloric, hydro¯uoric or acetic acid at

different concentrations. Black shale samples were washed with hydrogen per-

oxide and desogen, the fraction >63 mm being retained for analysis.

Organic geochemistryTen black shales were geochemically analysed. Their carbonate content (%

CaCO3) was measured using a calcimetric bomb. Total carbon and sulphur con-

tents were measured in a LECO IR-12 analyser. Programmed pyrolysis was per-

formed using a Rock-Eval II apparatus (Espitalie et al., 1985±86). This technique

provides a rapid determination of TOC content, thermal maturity and origin of

sedimentary organic matter.

Standard notations are used: S1 and S2 in mg hydrocarbons (HC) per g of

rock; Tmax expressed in �C and the TOC content in weight %. The hydrogen

index (HI = S2/TOC � 100) and oxygen index (OI = S3/TOC � 100) are

expressed in mg HC per g of TOC and mg CO2 per g of TOC, respectively.

4. Results and discussion

4.1. AmmonitesIn the FL the ammonites occur in the Guide-bed, or layer D (Cecca et al.,1994a), which displays homogeneous characteristics (e.g., in palaeontological

content, fossil preservation, lithology, and thickness) over the whole UMB.

Owing to the fossil richness of this bed, it has been possible to collect a large

fauna by sampling different localities. The data here presented do not refer only

to the Fiume Bosso section; they summarize records from other localities where

the Guide-bed is better exposed for collecting macrofossils.

Ammonites occur occasionally below layer A (Figures 4, 5). According to

Cecca et al. (1994a) rare ammonites have been found in layer B of the Monte

Spina di Gualdo section. In some sections (Stirpeto, Monte Petrano, and Gorgo a

Cerbara) the calcareous bed which directly overlies the black shale G contains

Pseudothurmannia specimens which belong to the same subzone as the fauna of

the Guide-bed.

8 R. Coccioni et al.

The fauna from the Guide-bed is particularly rich, diverse and well preserved.

Although some groups are poorly represented, overall the assemblage is taxonomi-

cally diverse (Cecca et al., 1994a). The ammonite fauna indicates the same bio-

stratigraphic interval in all sections. It corresponds to the uppermost Hauterivian

P. catulloi Subzone of the P. angulicostata Auct. Zone (Hoedemaeker & Company,

1993). The occurrence of Neolissoceras grasi indicates the very base of this subzone

(Hoedemaeker, 1995a; Hoedemaeker & Leereveld, 1995).

A direct correlation between the succession of magnetic chrons recognized by

Lowrie & Alvarez (1984) and the ammonite zones was ®rst realized in the Gorgo

a Cerbara section (Cecca et al., 1994b), and has been con®rmed in the Fiume

Bosso section (Channell et al., 1995). The FL is within the middle part of chron

CM4.

At the top of the Hauterivian an important turnover has been recognized in the

ammonite faunas of the Mediterranean Tethys, which de®nes the base of the P.catulloi Subzone (Hoedemaeker l995a). Hoedemaeker (1995b) showed that it

coincides with a diversity minimum, and correlated it with a high amplitude and

an extra rapid rate of eustatic sea level fall, marked in the ®eld (Caravaca area,

southern Spain) by a type-l sequence boundary. This would imply a telescoping

of marine biotopes and then selective pressure followed by extinction. The Guide-

bed of the FL could represent the geological record of this faunal turnover over a

distance of about 500 km at least in terms of present-day geography, because it

has also been recognized recently in the Southern and Venetian Alps (Cecca etal., 1996; Faraoni et al., 1996).

4.2. Calcareous nannofossilsNannofossils are present in all of the samples examined except in BO 39; preser-

vation is always poor. Within the limestones micrite is dominated by micarbs; in

the black shales calcareous nannofossils show evidence of slight dissolution. In

terms of calcareous nannofossil biostratigraphy, the FL lies within the NC5c

Zone of Roth (1978), modi®ed by Bralower (1987) and Channell et al. (1987).

Lithraphidites bollii is absent whereas Calcicalatina oblongata is consistently present

in all of the studied samples.

Species richness and total abundance of nanno¯oras ¯uctuate throughout the

studied interval (Figures 4, 5). The two curves are almost parallel from samples

BO 31 to 43, at the very base of the Guide-bed. They then clearly show an oppo-

site trend upwards; only in the uppermost part of the studied interval do they

seem to be parallel again. Remarkable differences in relative abundances of calcar-

eous nannofossils characterize the alternating limestone/black shale assemblages.

The limestones contain abundant nannoconids which form from 30 to 60% of the

whole assemblage. The black shales yielded less diverse assemblages (except for

sample BO 31) that are almost depleted of nannoconids and feature high relative

abundances (30±50%) of nannoliths such as Assipetra infracretacea, A. terebroden-taria and large Zeugrabdothus embergeri. The interval is also characterised by the

presence of Watznaueria barnesae, the relative abundance of which varies from 20

to 50%. High percentages of W. barnesae in the sediments are indicative of signi®-

cant diagenesis (e.g., Roth, 1986; Roth & Krumbach, 1986; Erba, 1988, 1992).

The pattern of alternating calcareous nannofossil assemblages suggests that

changes in ecological and oceanographic conditions occurred during deposition of

the latest Hauterivian Maiolica in the UMB. OC-rich facies often show very low

percentages of CaCO3 as a result of diagenetic dissolution related to oxidation of

Uppermost Hauterivian Faraoni Level 9

the organic matter. However, in many cases, they may contain abundant and well

preserved calcareous nannofossils. The absence of nannoconids in these facies has

also been explained by the onset of hypoxic or anoxic conditions at the water

depths inhabited by nannoconids (Busson & Noel, 1991). However, BreÂheÂret

(1983) and Erba (1986) recorded abundant nannoconids in black shale deposits

with no apparent relation to anoxia/dysoxia.

In the black shales of the studied interval, nannoconids are present in low to

very low percentages. Their abundance is not directly related to the CaCO3 con-

tent of the sediment as some black shale layers have a rather high CaCO3 content

(see Figure 12). The nannoconid and Assipetra spp. curves are clearly opposing

and could re¯ect competition between these calcareous nannofossil groups. A

similar demise of nannoconids and consequent bloom of Assipetra spp. was

reported by Erba (1994) at the onset of deposition of the OC-rich sediments of

the early Aptian Selli Event. However, the possibility that this trend might simply

be the result of differential dissolution cannot be ruled out.

According to Roth (1981), Roth & Bowdler (1981), Roth & Krumbach (1986)

and Erba (1986) high percentages of Biscutum constans, Zygodiscus erectus and

Parabdolithus asper are indicative of surface water fertility. In the black shales

examined here high fertility indices are absent or extremely rare, in part as a result

of dissolution: further analysis is, therefore, required to gain a better understand-

ing of these correlations.

4.3. ForaminiferaPlanktonic foraminifera were found only within the Guide-bed (sample BO 45)

and just above the FL (sample BO 47) (Figure 5). They are relatively frequent

(up to 2%) and associated with abundant, large radiolarians (Figures 7, 8). A

similar association was also recognized in the Trento Plateau area (Cecca et al.,1996) and in all of the sections noted by Cecca et al. (1994a) where, however,

these primitive, usually four-chambered, globigerina-like planktonic foraminifera

sometimes occur also just below the FL.

They are here identi®ed as Gorbachikella spp. On the basis of their almost ¯at

spiral side (see BouDagher-Fadel, 1995; BouDagher-Fadel et al., 1995) they

could be close to G. kugleri (Bolli, 1959) and G. anteroapertura BouDagher-Fadel,

Banner, Brown, Simmons & Gorbachik (1995). Gorbachikella Banner & Desai

(1988), and in particular G. anteroapertura, is believed to be the direct ancestor of

Praehedbergella Gorbachik & Moullade (1973), which ranges in age from Hauteri-

vian to Aptian (Banner & Desai, 1988; Banner et al., 1993; BouDagher-Fadel,

1995; BouDagher-Fadel et al., 1995). According to BouDagher-Fadel (1995) and

BouDagher-Fadel et al. (1995), Gorbachikella has a very restricted latitudinal

range. It is known from Trinidad (Bolli, 1959, as Globigerina; Barremian), north-

ern Mexico (Longoria, 1974, as Caucasella; late Aptian) and northern Tunisia,

where it often forms the entire planktonic foraminiferal assemblage (BouDagher-

Fadel, 1995; BouDagher-Fadel et al., 1995; Maamouri & Salaj, 1995, as Globuli-gerina; latest Valanginian to Aptian). Gorbachikella appears to be absent in central

and northwest Tethyan areas and, of course, in areas north of Tethys proper

(Banner et al., 1993; BouDagher-Fadel, 1995).

Biogeographic evidence suggests, therefore, that Gorbachikella is a less temper-

ate-tolerant genus, or even a warm-water indicator. In the present study, the lar-

gest diameter of the specimens recognized close to the FL is 240 mm.

Comparison with the largest diameter of specimens from uppermost Valanginian

10 R. Coccioni et al.

deposits (close to 220 mm; Maamouri & Salaj, 1995) and the Hauterivian-Aptian

(close to 300 mm; BouDagher-Fadel, 1995; BouDagher-Fadel et al., 1995)

suggests an increase in size through the time.

The bloom of Gorbachikella spp. that occurs close to the FL is very odd because

planktonic foraminifera are extremely rare and discontinuous in the Maiolica For-

Figure 6. Calcareous nannofossils from the Fiume Bosso section; magni®cation �3200. 1, Calcica-lathina oblongata (Worsley), crossed nicols, sample BO 37; 2, Same specimen as 1, natural light;3, Nannoconus steinmannii steinmannii Kamtner, natural light, BO 37; 4, Zeugrhabdothus embergeri(NoeÈl), crossed nicols, BO 47; 5, Same specimen as 4, natural light; 6, Assipetra terebrodentaria(Applegate, Bralower, Covington & Wise), crossed nicols, BO 37; 7, Same specimen as 6, naturallight; 8, Assipetra infracretacea (Thierstein), crossed nicols, BO 47; 9, Same specimen as 8, naturallight; 10, Rucinolithus ? sp., crossed nicols, BO 47; 11, Same specimen as 10, natural light.

Uppermost Hauterivian Faraoni Level 11

Figure 7. Foraminifera and radiolarians from the Bosso section, magni®cation �15 (A) and �30(B±D). A, Assemblage of radiolarians and Gorbachikella spp. (g); sample BO 45; B, detail ofFigure 7A; C, Assemblage of scattered, small radiolarians; BO 22; D, Assemblages of abundant,large radiolarians; BO 40.

12 R. Coccioni et al.

mation; they gradually begin to be abundant around the Barremian±Aptian tran-

sition (Micarelli et al., 1977; Coccioni et al., 1992; Cecca et al., 1994b). This

bloom could be related to the onset of the oceanographic (possibly eutrophic)

and/or climatic (probably warm) conditions that led to the deposition of the FL.

In the eastern part of the Trento Plateau area, scattered small planktonic fora-

minifera occur just below the Guide-bed (Cecca et al., 1996). The following

species were identi®ed in the Bosso section: Clavihedbergella eocretacea Neagu,

Favusella hauterivica (Subbotina), Globigerinelloides ? sp., Hedbergella aptica

Figure 8. The foraminifera Gorbachikella sp. from the Bosso section, sample BO 45; magni®cation�174. A, transverse section; B, axial section; C, transverse section; D, axial section.

Uppermost Hauterivian Faraoni Level 13

(Agalarova), H. delrioensis (Carsey), and H. sigali Moullade. The association is

characteristic for the Hedbergella sigali-Hedbergella delrioensis Zone of Coccioni &

Premoli Silva (1994).

Concerning the benthic agglutinated foraminifera, most of the samples studied

yielded moderately rich and diverse assemblages. Preservation varies from sample

to sample, ranging from fairly good to very poor. The assemblages are mainly

characterized by different species of Rhabdammina, Rhizammina, Ammodiscus,Repmanina, Glomospirella, Reophax, Pseudobolivina, Trochammina, and Trochammi-noides. However, benthic agglutinated foraminifera underwent a rapid decline

close to the FL (Figure 4). The data recorded show that during the deposition of

sediments of the interval close to, and comprising, the FL, the sea ¯oor environ-

ment was unfavourable for benthic foraminifera.

4.4. RadiolariaThe thin section analysis reveals that the abundance of radiolaria from the bottom

of the section (sample BO1) up to 60 cm below the FL (sample BO 32) is gener-

ally low, ranging from 1±7.5% (Figures 4, 5). Three distinct peaks in relative

abundance occur below (samples BO 34 and 40, 15% and 25% respectively) and

within (sample BO 45, 12.5%) the FL (Figures 4, 5). Above the FL, radiolarian

abundance returns to values generally ranging from 1 to 7.5%, with a maximum

of 10% in sample BO 90. The assemblages in thin section are generally poorly

preserved and represented by calci®ed specimens. In limestone layers close to

chert nodules and lenses where higher abundances have been observed, they are

better preserved.

The assemblage recorded from thin sections of the Guide-bed (sample BO 45) is

dominated by large forms that might be attributable to Acanthosphaera tenuispinaSquinabol. This species also occurs together with large nassellarians such as Setho-capsa (?) orca Foreman in the washed residues of several samples. Large forms have

also been observed in thin section in BO 7, 11, 21, 40, 47, 48, 70, 71, and 90.

Acid residues from limestone and chert samples from the FL and samples BO 34,

41, and 64 yielded the best preserved and most diverse radiolarian assemblages.

Assemblages from the black shale layers are depauperated and of low diversity,

and associated with abundant ®sh remains. They are, however, usually pyritized

and well preserved. The following species are recognized in the shales: Archaeodic-tyomitra cf. A. apiarium (RuÈ st), Obesacapsula cetia (Foreman), Pseudodictyomitracarpatica (Lozyniak), Sethocapsa trachyostraca Foreman, Sethocapsa uterculus (Paro-

na) sensu Foreman, Thanarla brouweri (Tan), Thanarla pulchra (Squinabol) sensuSan®lippo & Riedel, and Xitus (?) alievi (Foreman). A further, more exhaustive

study is required to estabilish if the lower abundance and diversity within the

black shales is a result of non-preservation or of adaptation to different trophic

conditions.

A radiolarian biostratigraphy for the Maiolica Formation in the Fiume Bosso

section as well as for other UMB sections, and for the coheval Biancone For-

mation in the southern Alps, was provided by Jud (1994) and Dumitrica Jud

(1995). In the Fiume Bosso section the FL lies about 3 m below the Hauterivian/

Barremian boundary de®ned by Dumitrica & Dumitrica Jud (1995). Following

the biostratigraphic scheme proposed by Jud (1994), Unitary Association (UA)

31, 32 (Zone F3, late Hauterivian) is recognized for samples BO 34 and 42, and

UA 31-34 (Zones F3±G1, late Hauterivian±early Barremian) for sample BO 64

(Figure 9).

14 R. Coccioni et al.

Fig

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Uppermost Hauterivian Faraoni Level 15

Our results indicate that large ¯uctuations in relative abundance and preser-

vation of radiolarian assemblages occur just below and within the FL. However,

no major change in taxonomic composition such as that observed previously

through the Selli and Bonarelli levels (Marcucci et al., 1991; Erbacher, 1994;

O'Dogherty, 1994) has been recognized here (Figure 9).

The present study reveals that from 60 cm below the base of the FL up to the

top of it (from samples BO 34 to 46), there is an increase in radiolarian abun-

dance. Moreover, in the same interval the radiolaria recovered from the residues

of the acid treatments are better preserved than those from the rest of the section.

The ¯uctuations in abundance and preservation of radiolaria in this interval could

be related to changes in ecological and geographical conditions. However, these

modi®cations did not lead to major changes in the taxonomic composition of the

assemblages.

4.5. Organic geochemistryMost of the black shales are carbonate-poor (<16.5% CaCO3), although those

from the FL show high carbonate contents (up to 90%) (Figure 12). TOC per-

centages range from 0.4% to 25%, with an average around 6%, and are roughly

inversely related to carbonate content. Sample BO 33, is however, organic-poor

whilst its carbonate-content is low (9.5%).

The total sulphur content of the black shales is medium to high (up to 1%) and

probably related to iron sulphides, which are the products of syndepositional bac-

terial sulphate reduction in interstitial oxygen-de®cient waters. The sulphur-TOC

relationship shows a positive correlation with a low gradient that suggests dysoxic

rather than anoxic conditions in bottom waters during the deposition of the beds

now preserved as black shales (Leventhal, 1983; Berner & Raiswell, 1984).

Total hydrocarbons (S1 + S2) expelled during Rock-Eval pyrolysis represent

the petroleum potential of a sample, expressed in kg HC per ton of rock. Moder-

ate to high potentials (1 to 10 kg/t) are indicated for most of the black shales,

whereas samples containing more than 10% TOC are very highly rated (up to

100 kg/t), implying that the organic matter has a high hydrogen content.

Temperatures of maximum pyrolytic yield (Tmax) for samples having an

organic-richness greater than 0.5% are in the range of 425±435�C with an average

around 432�C. This indicates that the organic matter did not experience high

temperatures during burial, and is below or at the base of the oil-window with

respect to petroleum generation. Consequently, the source of organic matter can

be estimated from pyrolysis data on the basis of hydrogen and oxygen indices

(Espitalie et al., 1985±86).

Figure 10. Radiolarians from the Fiume Bosso section. a, Acaeniotyle diaphorogona gr. Foreman,sample BO 41, �110; b, Acaeniotyle umbilicata (RuÈ st), BO 34, �110; c, Acanthocircus carinatusForeman, BO 41, �80; d, Acanthocircus levis (Donofrio & Mostler), BO 34, �80; e, Acanthocircustrizonalis dicranacanthos (Squinabol) emended Foreman, BO 41, �80; f, Acanthosphaera tenuispinaSquinabol, BO 34, �140; g, Archaeodictyomitra chalilovi (Aliev), BO 31, �140; h, Archaeodictyo-mitra cf. A. apiarium (RuÈst), BO 46, �160; i, Archaeospongoprunum patricki Jud, BO 41, �110; j,Cecrops septemporatus (Parona), BO 64, �110; k, Crolanium pythiae Schaff, BO 34, �160; l, Cru-cella bossoensis Jud, BO 64, �110; m, Cyclastrum infundibuliforme RuÈst, BO 64, �110; n, Deviatusdiamphidius s.l. (Foreman), BO 34, �110; o, Dictyomitra pseudoscalaris (Tan), BO 41, �110; p,Halesium (?) lineatum Jud, BO 34, �55.

16 R. Coccioni et al.

Uppermost Hauterivian Faraoni Level 17

18 R. Coccioni et al.

Three types of organic matter are usually distinguished in sedimentary rocks

(Tissot et al., 1974; Espitalie et al., 1985±86) (Figure 13). Types I and II are

related to lacustrine or marine reducing environments and are derived mainly

from algae or bacteria, whereas type III is derived from terrestrial plant remains

that have been transported to marine or non-marine environments and suffered a

moderate amount of degradation. Intermediate compositions are common, par-

ticularly between types II and III. They result from a mixing of marine and terres-

trial organic matter or from selective biodegradation of organic matter. A fourth

type (sometimes called type IV) corresponds to residual organic matter that may

be either recycled from older sediments by erosion or deeply altered by weather-

ing (Tissot, 1984). In the black shales from the Fiume Bosso section, low to med-

ium hydrogen index values (100±400 mg HC/g TOC) and medium oxygen index

values (60±100 mg CO2/g TOC), suggest an altered type II organic matter

(Figure 13).

Figure 11. Radiolarians from the Fiume Bosso section. a, Hexastylus euganeus Squinabol, sampleBO 34, �55; b, Homeoparonaella peteri Jud, BO 41, �55; c, Jacus (?) italicus Jud, BO 41, �140;d, Obesacapsula cetia (Foreman), BO 42, �160; e, Obesacapsula verbana (Parona), BO 34, �105;f, Pantanellium sp. cf. P. cantuchapai Pessagno & MacLeod, BO 34, �110; g, Podobursa sp. cf. P.quadriaculeata Steiger, BO 41, �110; h, Sethocapsa dorysphaerodes Neviani sensu Schaff, BO 41,�100; i, Sethocapsa leiostraca Foreman, BO 41, �150; j, Sethocapsa (?) orca Foreman, BO 41,�110; k, Sethocapsa uterculus (Parona) sensu Foreman, BO 46, �160; l, Spongotripus (?) satoi(Tumanda), BO34, �90; m, Stylosphaera (?) macroxiphus (RuÈst), BO 41, �55; n, Stylospongia (?)titirez Jud, BO 41. �160; o, Syringocapsa limatum Foreman, BO 41, �55; p, Suna echiodes (Fore-man), BO 41, �110; q, Thanarla pulchra (Squinabol), BO 34, �160; r, Gen. et sp. indet. A, BO34, �80.

Figure 12. Bulk geochemical data of selected samples located close to the FL: carbonate and sulfurcontent, Rock-eval pyrolysis data (-- -� not determined). Samples from the FL are within theshaded area.

Uppermost Hauterivian Faraoni Level 19

6. Conclusions

The uppermost Hauterivian Faraoni Level represents a unique short-term event

in the Maiolica Formation owing to its sedimentological and geochemical fea-

tures, and fossil content. A detailed integrated stratigraphic, palaeontological, and

geochemical analysis carried out across the FL in the Fiume Bosso section,

enabled the determination of the responses of the micro¯ora and macro- and

microfauna to the general environmental conditions leading to its deposition.

Although not entirely clear in terms of palaeoceanography and palaeoecology,

marked changes in the palaeontological and geochemical record have been

observed through the section. In particular: (1) The planktonic foraminiferal

assemblages indicate a warmer sea-surface temperature when the FL was depos-

Figure 13. Hydrogen vs. oxygen index diagram of the organic-rich samples from the Fiume Bossosection. Circles are proportional to total organic carbon content (% TOC). Type II organic matteris related to marine reducing environments and is mainly derived from algae or bacteria,whereas type III is derived from terrestrial plant remains that have been transported to marineor non-marine environments, and suffered a moderate amount of degradation. Type IV corre-sponds to residual organic matter which may be either recycled or strongly oxidized.

20 R. Coccioni et al.

ited; (2) The absence of nannoconids in the black shale layers through the FL

might indicate the onset of hypoxic or anoxic conditions at the water depths

inhabited by this group. Being more abundant in the black shale layers, Assipetraspp. probably re¯ect an adaptation to such dysoxic conditions; (3) During the

deposition of the interval comprising the FL, sea ¯oor conditions were unfavour-

able for benthic foraminifera; (4) Organic geochemical data from the Fiume

Bosso section con®rm a marine origin for the organic matter in the black shale

layers and probably re¯ect deposition in a dysoxic rather than an anoxic sea-¯oor

environment.

New insights on the biostratigraphic position of the FL have been provided by

the study of the radiolarian and calcareous nannofossil assemblages. The FL lies

within the radiolarian UA 31±32 (Zone F3) of Jud (1994) and in the calcareous

nannofossil NC5c Zone of Roth (1978), modi®ed by Bralower (1987) and Chan-

nell et al. (1987).

Acknowledgments

We thank E. Erba, H. Leereveld and I. Premoli Silva for their helpful suggestions

which greatly improved the manuscript. The authors are indebted to D. J. Batten

for correcting the paper. Thanks are also due to P. Ferrieri for assistance in oper-

ating the SEM. This paper has been supported by the MURST, 60% to R. Coc-

cioni, and is publication 286 of the CNR, Centro di Studio di Geologia

dell'Appennino e delle Catene Perimediterranee.

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