GEOLOGIA CROATICA 45 87-93 3 Fig. 2 Pl. ZAGREB 1992 

UDC 551.763.31 (450) Scientific paper 

Open Circulation Facies in the Cenomanian of the Northeastern Mar­
gin of the Friuli Platform: the !udrio Valley Case (NE Italy) 

-Dario SARTORI01, Giorgio TUNIS2 and Sandro VENTURINP 

Key words: Early-Middle Cenomanian, Margin Se­
quence, Friuli Platform, Calcisphaerulidae, Favusella, 
transgressive events 

The Early·Middle Cenomanian margin sequence of Val ludrio, 
connected with the northeastem margin of the Friuli Platform shows 
intercalated layers with pelagic organisms: Calcisphaerulidae and 
plankton ic forams, among which is Favwsella. These are interpreted 
as transgressive episodes recorded in a calbonate ramp sequence related 
to a tectonically subsiding margin. ln the Dinaric and Friuli Plat· 
forms two distinct Calcisphaerulidae and planktonic forams facies 
are distinguished for the Cenomanian. The first one, of early-middle 
Cenomanian age, which is also present in the ludrio sequence, de­
veloped in platform margin zones subjected to drawning. The sec­
ond one, of late Cenomanian age, developed in more internal areas 
of the Dinaric and Friuli Platforms, and can be related to the trans­
gression associated with the OAE 2 event. 

l. INTRODUCTION 

Several margin sequences of the Friuli Platform, 
representing the north western extension of the Dinaric 
Platform (Fig. l) during the latest Albian and Cenomanian, 
are characterized by pelagic influxes with planktonic 
organisms (COUSIN, 1981; GHETII, 1987; KOCH et 
al. , 1989; VENTURINI & TUNIS, 1990). 

The sequence of the !udrio Valley (Fig. 2) consists 
of platform margin carbonates, the outcropping lower part 
of which is V alanginian, whereas the top is Senonian. This 
paper takes into consideration the Early-Middle Cenomanian 
limestones showing marked open facies as indicated by 
the presence of planktonic organisms, with the aim of 
explaining the significance of these facies. 

2. THE CENOMANIAN OF THE IUDRIO 
VALLEY 

The latest Alb ian of the !udrio sequence marks a change 
of depositional pattern. In fact, latest Albian facies, 
represented by bioclastic packstones and grainstones, can 
be referred to as a more open environment of deposition 
with respect to the underlying platform carbonates belmging 
to the Cellina Limestone unit The following Early-Middle 
Cenomanian sequence consists of even more open facies, 
characterized by an increased energy of the system and 
very high organic productivity. The unit analyzed, about 
250 m thick, outcropping in the southwestem sector of 

1 AGIP S.p.A., 1-20097 S. D.onato Milanese, Milano 

the !udrio Valley between Albana and Bodi goi, consists 
of a succession of bioclastic sands: alternating bioclastic 
packstones and grainstones and subordinate rudstones. 
Mudstones seem to be lacking. 

Most of the grains of these carbonate sands are frag­
ments of fossils (Pl. l, l and 2 ; Pl. Il, l and 2) which are 
subjected to breakage, abrasion, and sometimes, round­
ing processes. Fine to medium sized granular calcite ce­
ments fill intergranular porosity in packstones and 
grainstones. Relict of marine phreatic cements can be also 
recognized. Rare vadose crystal si lt possibly indicates the 
occurence of sporadic subaerial exposure episodes. Many 
calcitic cemented fractures of tectonic origin are present. 

Orbitolina (Conicorbitolina) conica (D'ARCHIAC) 
(Pl. l, 1,2,3,4) is the most common macroforaminifer 
observed in bioclastic sands from the bottom to the top 
of the studied sequence. Some layexs contain Praealveolina 
gr. cretacea (D'ARCHIAC) (Pl. l, 4,5,6). 

Other foraminifers such as Trocholina sp., 
Pseudorhapydionina sp., Cuneo/ina pavonia D'ORBIGNY, 
Nezzazata simplex OMARA, Nezzazatidae, Miliolidae, 
Ophthalminidae, Textulariidae, Valvulinidae, Lituolidae, 
etc. have also been observed. 

Macrofossils are represented by rudists (mostly 
Radiolitidae and also Caprinidae) and subordinate echi­
noids, corals, brachiopods, gastropods (among which are 
nerineids). However, most of these fossils have been broken 
into fragments and compose the bioclastic fraction of the 
carbonate sands. 

These facies developed in high energy ramp envi­
ronments in which bioclastic sediments were transported 
and accumulated by wave activity. These environments 
were also influenced by sea level fluctuations which 
led to sporadic subaerial exposures. 

Wackestones and packstones with planktonic or­
ganisms, the most common of which are Calcisphaerulidae 
(Pl. II, 1.2,3), alternate with the forementioned bioclastic 
packstones and grainstones. In these facies there are . 
also some planktonic foraminifers, among which are 
Favuse/la washitensis (Pl. Il, 3, 5, 7), Favusella sp. (Pl. 
n. 4), Hedberge/la sp. (Pl. Il, 6) and extremely rare 
Rotalipora. The observed planktonic forms may also 

1 Istituto di Geologia e Paleontologia Universit& degli Studi di Trieste, P. le Europa t, 1-34127 Trieste 
3 AGIP-S.p.A .• v. C. Menotti l, 1-48023 Marina di Ravenna, Ravenna 

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UPPER CRETACEOUS 

Fig. l ·Location of the !udrio Valley (left): l. Mesozoic limestones, 2. Maastrichtian flysch, 3. Paleocene flysch, 4. Lower Eocene flysch. Paleographic map of Upper Cretaceous of Peri Adriatic 
area (right), modified from CATI et aL (1987). The arrow shows the location of the examined area. 



Sanorio, Tunis & Venturini : Cenomanian Open Facies ... 

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l MARKERS 

Keramos~haerina tergestina 

Rotorbinella scarsellai 

no significant markers 

Praeolveolino gr. cretoceo 
Colcisphaerulidae, 

Fovusello, Rofolipora 

Orbi totina 
conico 

Proeolveolino gr. cretoceo 
Fovusello, Colcisphoerulidoe 
Praealveolino gr. cretoceo 
Colcisphoerulidoe 
Fovusello, Colcisphaerulidoe 

Orbitolina cuvillieri 
Neoiroqio insolito 

Salpingorello dinorica 

Polorbitolino lenticuloris 
1\ Bocinello /lithocodium J 

cyonobocterial mots 
no significant markers 

Campanellula copuensis 

Actinoporello podolico 

Protopeneroplis trochonguloto 

4 

Fi g. 2 • Stratigraphic column of the Cretaceous limestones outcropping in the l udrio Valley. The arrow s show pelagic influxes. 
l. Mudstone-wackestone, 2. Packstone·grainstone, 3. Intraformational breccias. 4. Bacterial mats. 

-
89 

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90 Geologia Croatica 45 

NNW SSE 

TOLMIN BASIN FRIULI PLATFORM ADRIATIC PLATFORM 

l UDRIO 

' 
LATEST CENOMANIAN 

B 

EARLY- MIDDLE CENOMANIAN 

Fig. 3 - Calcisphaerulidae facies in the Cretac.epus sequence of northeastem edge of the Friuli Platform (!udrio Valley). 

be scattered in the Orbitolina bearing grainstones. As­
sociated with these planktonic organisms there are also 
benthic foraminifers typical of outer platform environ­
ment, such asLenticulina (Pl. II, 8, 9, 10) and Gave/ine/la. 

These facies rich in Calcisphaerulidae and plankton ic 
forams were deposited in more open and low energy 
environments probably during high sea level stands. 
The described sequence is overlain by bioclastic rudist 
limestones of possible late Cenomanian age. 

3. CONCLUSION 

The studied sequence is very similar to the Cenomanian 
section described by KOCH et al. (1989) outcropping in 
the area of Trnovo, where there are the same facies bearing 
Calcisphaerulidae and planktonic forams. 

These two sequences are the representatives of two 
sectors located along the same margin which were char­
acterized by the same sedimentary evolution. 

Furthermore, sediments with Favusella and 
Calcisphaerulidae have been reported by ŠRIBAR & 
PLENlČAR (1990) in the Cenomanian of southwestern 
Slovenia. 

Identical facies to those of !udrio are present in the 
early-middle Cenomanian sequence of Mrežnica Valley 
(FUČEK & GLOVACKI-JERNEJ, 1991), belonging to 
the northeastern margin of the Dinaric Platform. 

In analogy to the Trnovo sequence, also in the 

Cenomanian of l udrio there is a preci se depositional trend. 
The sequence mostly consists ofbioclastic facies lacking 
carbonate mud and deposited in high energy environment, 
with intercalated layers characterized by the presence of 
mud and planktonic foraminifers. In many zones of the 
Friuli Platform (CATI et al., 1987) and in some areas of 
the Apennine platforms (ACCORD I et al., 1987), starting 
from the Cenomanian or from the_ very late Albian, bioclast­
dominated facies replace the inner platform faci es of early 
Cretaceous. 

These facies almost always deposited on highly sub­
siding platform margins, often subjected to drowning. In 
fact, the following Senonian and Cenozoic facies o fl udrio 
record the subsequent drowning of the examined margin. 

Cenomanian facies of the l udrio Valley are charac­
terized by high sedimentation rates and bioclastic carbonates 
production. This possibly reflects the global increase of 
sea level rise occured throughout the Cenomanian. 

Calcisphaerulidae and planktonic foraminifers layers 
intercalated with the bioclastic facies of the I udrio Valley 
mark transgressive episodes recorded in a carbonate ramp 
sequence related to the tectonically subsiding margin of 
the Friuli Platform. 

The presence of Favusel/a is indicative of an envi­
ronment of deposition that was not very deep 
(KOUTSOUKOS et al ., 1989), sometimes subjected to 
subaerial exposure periods, as documented by vadose 

PLATE I 

l. Grainstone with Orbitolina (Conicorbitolina) conica (D'ARCHIAC), AJ 89, x 15 
2. Orbitolina (Conicorbitolina) conica (D'ARCHIAC), AJ 94 x 40 
3. Orbitolina (Conicorbitolina) conica (D'ARCHIAC), Gl 134, x 45 
4. Praea/veolina gr. cretd.:ea (D'ARCHIAC)·, and embryonic apparatus of Orbitolina (Conicorbitolina) conica 

(D'ARCHIAC), TJ 16 X 30 
5. Praea/veolina gr. cretacea (D'ARCHIAC), AJ 115, x 40 
6. Praealveolina gr. cretacea (D'ARCHIAC), TJ 16, x 45 



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92 

cements observed in some levels. In the Dinaric and Friuli 
Platforms, two different transgressive facies, with 
Calcisphaerulidae and planktonic foraminifers characterize 
the Cenomanian sediments. The first one (Early-Middle 
Cenomanian) is associated with the Orbitolina (C.) conica 
bioclastic sands and is typical of platform margins sub­
jected to drowning (Fig. 3A). This facies, which is present 
in the l udrio sequence, is charactmzed by Calcisphaerulidae 
and F avusel/a. 

The second facies, ascribed to the Cenomanian-Turonian 
boundary, and more precisely to the latest Cenomanian, 
if correlated with coeval faci es of the A penn ines (P ARISI 
et al., 1989) and of South-East France (GROSHENY & 
1RONCHETTI, 1991) is characterized by Calcisphaerulidae 
and Whiteinella (GUŠIĆ & JELASKA, 1990). This fa­
cies, almost always associated with anoxic or euxinic 
environments, is recorded in more internal areas of the 
platform (Fig. 3B), and, as put to evidence by JENKYNS 
(1991), can be ascribed to transgression associated with 
the OAE 2 event. 

ACKNOWLEDGEMENT 

Financial support from M.U.R.S.T. 60% "Evoluzione 
dei bacini sedimentari terziari" (resp. G . Catani) is 
gratefully acknowledged. 

4. REFERENCES 

ACCORDI, G., CARBONE, F. & SIRNA, G. (1987): 
Sedimentary events and rudist assemblages of 
Maiella Mt. (Central Italy): Paleobiogeographic 
implications. - Geol. Romana, 26, 135-147, Roma. 

CATI, A., SARTORIO, D. & VENTURINI, S. (1987): 
Carbonate platforms in the subsurfuce of the Northern 
Adriatic Area.- Mem. Soc. Geol. lt, 40,295-308, 
Roma. 

COUSIN, M. (1981): Les rapport Alpes-Dinarides. Les 
confins de l' Ital i e et de la Yugoslavie. -Soc. G eo l. 
du Nord, l , 1-521; II, 1-521, Villaneuve d'Ascq. 

FUCEK, L. & GLOVACKI-JERNEJ, Ž. (1991): The 
reflection of the global Cenomanian(furonian 
transgression; the examples from Brač Island, Dugi 
Otok Island and the Mrežnica Region.-Abstr. of 
Sec. Int. Symp. on the Adriatic Carb. Plat., 101, 
Zadar. 

GHETTI, S. (1987): Evoluzione cretacica del margine 
occidentale della Piattaforma Friulana.-Tesi di 
Douorato Sc. della Terra, 1-205, Firenze. 

Geologia Croatica 45 

GROSHENY, D. & TRONCHETTI, G. (1991): Les as­
sociations de foraminiferes du passage Cenomanien 
Turonien a Vergons. - In: CRUMIERE, J.P., 
COTILLON, P. & SCHAAF, A. (Eds.): Les 
evenement de la limite Cenomanien - Turonien. 
-Excursion post-colloque dans le Sud-Est de la 
France. Livret-Guide, 70-75, Grenoble. 

GUŠIĆ, I. & JELASKA, V. (1990): Upper Cretaceous 
stratigraphy of the Island of Brač within the gea­
dynamic evolution of the Adriatic carbonate plat­
form.-Djela Jugosl. akad. znanosti i umjetnosti, 69, 
1-160, Zagreb. 

JENKYNS, H. (1991): Impact of Cretaceous Sea Level 
Rise and Anoxic Events on the Carbonate Plat­
form of Yugoslavia.-Am. Ass. Petr. Geol. Bull., 
75 (6), 1007-1017, Tulsa. 

KOCH, R., OGORELEC, B. & OREHEK, S. (1989) : 
Microfacies and Diagenesis of Lower and Middle 
Cretaceous Carbonate ltocks ofNW-Yugoslavia. 
(Slovenia, Trnovo Area).-Facies, 21, 135-170, 
Erlangen. 

KOUTSOUKOS, E.A.M., LEARY, P.N. & HART, M. B. 
(1989):Favusella MICHAEL (1972): Evidence of 
ecophenotypic adaption of a planktonic foraminifer 
to shallow-water carbonate environments during 
the Mid-Cretaceous. - Journal of Foraminiferal 
Research, 19 (4), 324-336, Washington. 

PARISI, G., COCCIONI, R., BATTISTINI, F., PIER­
GIOVANNI, F. & ROSSI,R. (1989): The "Livello 
Bonarelli" the marker bed one of the Mid-Cretaceous 
worldwidc anoxic events .-In : COCCIONI,R., 
MONECHI, S. & PARISI,G. (Eds): Abstracts of 
the IGCP project 262, Working group 2 "Pelagic 
Facies". Univ. Urbino, 126-133, Urbino. 

ŠRIBAR, L. & PLENICAR, M. (1990): Upper Cretaceous 
assemblage zones in southwestern Slove nia. 
-Geologija, 33, 171-205, Ljubljana. 

VENTURINI, S. & TUNIS, G. (1989): Nuovi dati ed 
interpretazioni sulla tettonica del settore meri­
dionale delle Prealpi Giulie e della regione al 
conflne tra Italia e Iugoslavia.- Gortania,IO, 5-34. 

Manuscript received March, 31.1992. 
Revised manuscript accepted May, 18.1992. 

PLATE II 

l. Wackestone with Calcisphaerulidea, TJ 28, x 50 
2. Calcisphaerulidea, Gl 141, x 120 
3. Favusella washitensis (CARSEY) and Calcisphaerulidea, Gl 141, x 100 
4 Favusella sp., Gl 136 x 90 
5. Favusella washitensis (CARSEY), Gl 139 x 90 
6. Hedbergella sp., Gl 139 x 70 
7. Favuse/la washitensis (CARSEY) Gl 139 x 70 
8. Lenticulina sp. and Orbitolina sp, 136 x 50 
9. Lenticulina sp. , TJ 28, x 50 
lOLenticulina sp. , Gl 139, x 70 



Sartorio, Tunis & Venturini : Cenomanian Open Facies ... PLATE II 93