GeolCarp_Vol58_No1_71

GEOLOGICA CARPATHICA, FEBRUARY 2007, 58, 1, 71—87

www.geologicacarpathica.sk

Sedimentation and tectonics in a steep shallow-marine

depositional system: stratigraphic arrangement of the

Pliocene-Pleistocene Rometta Succession (NE Sicily, Italy)

AGATA DI STEFANO

, SERGIO LONGHITANO

and ALESSANDRA SMEDILE

University of Catania, Dipartimento di Scienze Geologiche, Corso Italia 55, 95129 Catania, Italy; distefan@unict.it; asmedile@unict.it

University of Basilicata, Dipartimento di Scienze Geologiche, Campus di Macchia Romana, 85100 Potenza, Italy;

longhitano@unibas.it

(Manuscript received January 5, 2006; accepted in revised form June 22, 2006)

Abstract: A 160 m thick Pliocene-Pleistocene sedimentary succession, cropping out in NE Sicily (Rometta Succession),
was subdivided into three unconformity-bounded units, overlying deformed bedrock: (i) a Middle Pliocene sandy-
marly R

unit; (ii) an Upper Pliocene-Lower Pleistocene biocalcarenitic R

unit; (iii) a Middle Pleistocene mudstone R

unit. The R

unit is composed of at least three sub-units, bounded by truncation surfaces, and showing aggradational

patterns of strata. Each of these sub-units records a sudden seaward-shifting of the facies tract. A stratigraphic gap of
~870 kyr at the R

boundary, marks an abrupt change from offshore transition to shoreface environments. A second

gap of

~260 kyr at the R

boundary corresponds to a sudden deepening of the environments, from shoreface to fully

offshore. The Rometta units represent three incomplete, tectonically-enhanced depositional sequences. The R

unit is a

HST of a lower sequence, marked at the top by a slightly angular unconformity. The R

unit is a HST of a younger

depositional sequence, aggrading above a ravinement surface. During these relative sea level still-stands, the local
tectonic uplift combined with the high-frequency eustatic oscillations, produced three forward-stepping sets of minor
sequences within the R

HST, simulating the typical FSST stratigraphic arrangement. The top of the R

is bounded by an

erosive surface, representing the transgressive surface of the subsequent R

depositional sequence. The R

unit is a late

TST + HST of a Pliocene-Pleistocene sequence, the LST of which probably occurs basinward. The foresetted R

biocalcarenites are unimodal in their paleocurrents. This feature resulted from shore-directed wind stress, applied to the
water surface and reflected by a steep paleocoast, generating basinward-directed bottom currents.

Key words: Pliocene—Pleistocene, NE Sicily, sedimentology, biostratigraphy and paleobathymetry, tectonics and
sedimentation.

Introduction and objectives

In NE Sicily, the Peloritani Mts represent the southernmost
flank of the Calabria-Peloritani Arc (Amodio-Morelli et al.
1976). In this area, the “Kabilo-Calabride” crystalline units
crop out widely (Lentini et al. 1994 and references therein).
They are covered by several siliciclastic sequences, Late
Eocene and younger in age, each indicating a stage in the
polyphasic tectonic evolution of the area (Lentini et al.
1995, 2000 and references therein).

Several authors have recently paid particular attention to

the Pliocene-Pleistocene successions (Di Stefano & Lentini
1995; Lentini et al. 2000). In fact, during this time interval,
the study area underwent important geodynamic events,
such as the opening of the Tyrrhenian Basin (Finetti & Del
Ben 1996). Thus the Plio-Pleistocene sediments were de-
posited in a complex geological framework, resulting from
the combination of active tectonics and eustacy.

The results presented in this paper derive from a detailed

stratigraphic analysis of these Plio-Pleistocene deposits,
cropping out in the key area of Rometta, combining facies
characteristics, biostratigraphic and paleobathymetric data,
and sequence stratigraphic interpretation.

Particular attention was devoted to the analysis of a Late

Pliocene-Early Pleistocene biocalcarenitic succession, very

well exposed in the neighbourhood of the selected area
(Fig. 1).

The Rometta biocalcarenites show some similarities

with other successions described in the Mediterranean
area (Barrier 1987; Colella & D’Alessandro 1988; Colella
1995; Colella & Vitale 1998; Tropeano & Sabato 2000;
Pomar & Tropeano 2001; Roveri & Taviani 2003). These
successions are generally interpreted as the response to par-
ticular warm/arid climatic conditions, subsequently con-
trolled by sea-level fluctuations, tectonic activity and, on a
shorter time scale, to different hydrodynamic factors as
tides, waves, currents or gravity.

The sedimentary features of the Rometta biocalcarenites

allow us to propose a depositional model, strictly linked
to the general geological framework.

Geological setting and stratigraphic framework of

the Rometta Succession

The Plio-Pleistocene deposits of the Peloritani Mts,

were illustrated in detail, from a stratigraphic and paleon-
tological point of view, by Seguenza (1873—1877) and
later by Ogniben (1960), who placed them into the so-
called “Neoautoctono” Complex.

DI STEFANO, LONGHITANO and SMEDILE

The main tectonic features of the area are represented by

a  NE-SW  oriented  normal  fault  system,  which  controls  the
present-day  setting  of  this  sector  of  the  Sicilian  Tyrrhe-
nian  coast  (Guarnieri  &  Carbone  2003).

The sedimentary succession cropping out in the Romet-

ta  area,  previously  described  by  Giunta  Ilaqua  (1956)  and
Ruggieri  et  al.  (1979),  has  been  more  recently  considered
as  a  Lower  Pliocene-Lower  Pleistocene  succession  (Vi-
olanti  et  al.  1987),  consisting  of  Lower  Pliocene  whitish
limestones  (Trubi  Formation),  Middle  Pliocene  sandy
marls,  Upper  Pliocene-Lower  Pleistocene  sands  and  bio-
calcarenites  and  Lower  Pleistocene  (Sicilian)  marly  clays.

Di Stefano & Lentini (1995) and Lentini et al. (2000)

consider  these  sediments  as  deposited  within  a  tectonical-
ly  active  geological  context,  in  connection  with  the  evo-
lution  of  the  southern  margin  of  the  Tyrrhenian  Basin.
These  authors  subdivided  the  succession  into  four  uncon-
formity  bounded  stratigraphic  units,  ranging  in  age  from
Early  Pliocene  to  Middle  Pleistocene.  The  lowermost  unit,
corresponds  to  the  Early  Pliocene  Trubi  Formation  (Auct.),
widespread  in  Sicily  (Ogniben  1960).  The  subsequent  unit
(R

in Fig. 1) is made up of Middle Pliocene marls; it is

followed by bioclastic sands and calcarenites (R

Fig. 1), Late Pliocene to Early Pleistocene in age; the up-
per unit (R

in Fig. 1) is mainly represented by blue marly

clays, Middle Pleistocene in age.

In the Rometta area, the Pliocene-Pleis-

tocene sedimentary succession is mainly
represented by the units R

—R

, and has a

total  thickness  of  160 m.  It  unconformably
overlies  a  substrate,  which  consists  of  fold-
ed  crystalline  rocks  (Aspromonte  Nappe),
Middle-Upper  Miocene  siliciclastic  rocks
of  the  San  Pier  Niceto  Formation  (Auct.),
and  Messinian  evaporites  (Fig. 2).

Until now, the relationships among the

different  Plio-Pleistocene  lithological  units
was  not  clarified  and  there  was  no  detailed
description  of  the  different  facies.

Methods

The stratigraphic framework of the Rom-

etta  Succession  is  based  on  data  collected
over  290 m  of  sedimentary  logging  and
sampling  and  on  the  detailed  mapping  of
the  units  across  the  studied  area.

The

logged

sections

(Sottocastello,

Rometta  and  San  Cono  sections),  which
embrace  the  whole  Pliocene-Pleistocene
NE  Sicily  succession  except  for  the  Trubi
Formation,  are  shown  in  Fig. 1  and  sum-
marized  in  Fig. 3.

A detailed facies analysis was carried

out to detect the main sedimentary charac-

Fig. 2. Stratigraphic column of the lithological units cropping out
around the study area. The R

, R

and R

units form the Rometta

Succession.

Fig. 1. Schematic geological map of the study area.

SEDIMENTATION AND TECTONICS IN A STEEP SHALLOW—MARINE DEPOSITIONAL SYSTEM (ITALY)

on  the  basis  of  benthic  foraminiferal  characteristics  taking
care  to  identify  the  displaced  or  reworked  fauna  often
present  in  the  sands  and  calcarenite  samples.  The  termi-
nology  adopted  for  the  bathymetrical  zonation  is  sensu
Perès  &  Picard  (1964),  simplified  for  the  neritic  and  epi-
bathyal  zones  by  Sgarrella  &  Moncharmont  Zei  (1993).

In our study, we adopted the nannofossil zonal scheme of

Rio  et  al.  (1990)  and  the  planktonic  foraminiferal  scheme  of
Cita  (1975),  emended  by  Sprovieri  (1992)  (Fig. 4).  We  fol-
lowed  the  chronostratigraphic  framework  proposed  by  Cita
et  al.  (1996)  for  the  Pliocene,  and  the  one  proposed  by  the
“Italian  Commission  on  Stratigraphy”  for  the  Early—Middle
Pleistocene  (Van  Couvering  1997).

A total of 40 samples were collected for the micropale-

ontological study, located along the sections as indicated
in Fig. 4.

Micropaleontology and sedimentology of the study

sections

Biostratigraphy and paleobathymetry

The sandy marls of the R

unit, outcropping at the base

of  both  the  Sottocastello  and  the  San  Cono  sections,  yield
abundant,  well  preserved  planktonic  foraminifers  referable
to  the  MPl5a  Biozone,  Middle  Pliocene  in  age  (Table1 ).
Excellent  nannofossil  assemblages  of  the  MNN16a  Bio-
zone  confirm  this  assumption.

For micropaleontological purpose, the Sottocastello sec-

tion provides the most favourable lithologies for the lower-
most part of the R

unit. The microfaunal content has been

attributed  to  the  Upper  Pliocene  MPl6  Biozone.  The  top-
most  sample  of  the  Sottocastello  section  yields  Neoglobo-
quadrina  pachyderma  (sx)  and  Globigerina  cariacoensis,
this  last  species  marking  the  base  of  the  homonymous  bio-
zone  and  the  Pliocene/Pleistocene  boundary.  The  nanno-
fossil  assemblage  is  referable  to  the  Upper  Pliocene
MNN19a  Biozone.  The  finding  of  Gephyrocapsa  oceanica
s.l.  (sensu  Rio  et  al.  1990)  in  the  highest  sample,  indicates
that  the  top  of  the  section  may  be  attributed  to  the  Early
Pleistocene  MNN19b  Biozone,  thus  confirming  the  fora-
miniferal  data.

Thin sandy layers in the middle part of the San Cono

section  are  clearly  referable  to  the  Early  Pleistocene  (San-
ternian)  (MNN19b/c  Biozones)  due  to  the  presence  of  Ge-
phyrocapsa  oceanica  s.l.

Samples of the topmost part of the section have been at-

tributed  to  the  MNN19d  Biozone,  characterized  by  the
presence  of  Gephyrocapsa  “large”  (sensu  Rio  et  al.  1990),
indicating  an  Early  Pleistocene  (Emilian)  age.  The  plank-
tonic  foraminiferal  content  in  this  section  is  not  indicative.

The nannofossil content of the R

unit is characterized

by  the  occurrence  of  Gephyrocapsa  sp. 3  (Rio  et  al.  1990),
which  defines  the  Middle  Pleistocene  MNN19f  Biozone.
The  foraminiferal  assemblage  is  typical  for  a  Pleistocene
age  (G.  truncatulinoides  excelsa  Biozone),  but  does  not
add  further  constraints  to  the  age  defined  on  the  basis  of
the  nannofossils.

The biostratigraphic analysis allowed us to detect two

significant  stratigraphic  gaps  within  the  studied  succes-
sions.  Their  temporal  duration  is  inferred  on  the  basis  of  the
age  assigned  to  the  recognized  bioevents  (Fig. 4).  The  first
gap  is  recorded  at  the  R

boundary and is constrained

by  the  last  common  occurrence  of  Discoaster  tamalis
(2.82 Ma;  Sprovieri  et  al.  1998)  and  the  last  occurrence  of
Discoaster  brouweri  (1.95 Ma;  Sprovieri  et  al.  1998),  thus
its  minimum  value  is  870 ka.  The  second  gap,  at  the  R

boundary, is estimated to span a minimum of 260 kyr,
which corresponds to the duration of MNN19e Biozone.

The results of the quantitative study on benthic fora-

minifers are reported in Fig. 5 and Table 2.

The benthic content of the R

unit is characterized by

consistent  percentages  of  Cibicides  lobatulus,  C.  reful-
gens,  Asterigerinata  planorbis,  Elphidium  spp.,  Hanzawa-
ia  rhodiensis  and  Angulogerina  angulosa  (Fig. 5,  samples
SC3  and  SC8)  which  define  an  upper  circa-littoral  envi-
ronment  (inferred  paleobathymetry  50—100 m;  Table 2).
The  presence  of  specimens  indicative  of  a  much  deeper
environment,  such  as  Planulina  ariminensis,  Cassidulina
carinata,  Oridorsalis  umbonatus,  Cibicidoides  kullember-
gi,  is  recorded  within  almost  all  the  examined  samples.
Such  species  may  derive  from  the  erosion  of  the  Trubi  For-
mation,  for  which  an  epibathyal  environment  has  been  in-
ferred  (Violanti  et  al.  1987).

The benthic association of the R

unit differs from the

previously  described  for  the  lower  abundance  and  specific
diversity,  and  for  the  worse  degree  of  preservation.  Shallow
water  species  such  as  Elphidium  crispum  and  Ammonia  spp.
defines  an  infra-littoral  environment  (inferred  paleobathym-
etry  0—50 m;  Table 2)  (Fig. 5,  samples  SC9  and  SC22).  The
benthic  assemblages  of  the  R

unit at Sottocastello (Fig. 5,

samples ST11 and ST15) suggest a slightly deeper environ-
ment, due to the scarcity of the Ammonia group.

The benthic foraminifers of the R

unit is composed of

common  Cassidulina  carinata,  C.  crassa  and  Globocassi-
dulina  subglobosa  and  subordinate  Melonis  spp.,  Uvigeri-
na  peregrina  and  Sphaeroidina  bulloides  (Fig. 5,  sample
RM3).  Sporadic  specimens  of  Planulina  ariminensis,  Hoe-
glundina  elegans  and  Hyalinea  baltica  are  also  recorded.
This  assemblage  defines  a  lower  circa-littoral—upper  epi-
bathyal  environment  (Table 2).  According  to  Sgarrella  &
Moncharmont  Zei  (1993)  such  an  association,  with  abun-
dant  Cassidulina  spp.  and  Globocassidulina  subglobosa  is
referable  to  a  depth  interval  between  120  and  350 m.  Shal-
low-water  forms  are  considered  to  be  displaced  from  the
older  substratum  or  from  coeval  marginal  areas.

Sedimentology of the Rometta Succession

The facies association was subdivided into seven sedi-

mentary types (Table 3), characterized by different later-
al/vertical distributions.

The R

unit

The Middle Pliocene R

unit, up to 20 m thick, consists

of alternating grey silty marls and sandstones (see Sot-

SEDIMENTATION AND TECTONICS IN A STEEP SHALLOW—MARINE DEPOSITIONAL SYSTEM (ITALY)

tion  of  suspended  fines,  while  the  planar-  and  rippled-lam-
inated  sandy  horizons  correspond  to  the  record  of  frequent
storm-fair  weather  sequences  described  in  offshore  envi-
ronments  by  Johnson  &  Baldwin  (1986).

The R

unit

The Upper Pliocene-Lower Pleistocene R

unit, from 30

to  120 m  thick  (see  San  Cono,  Sottocastello  and  Rometta
sections  in  Figs. 3  and  4),  represents  the  main  volume  of
the  studied  succession.  In  the  Rometta  area  this  unit  shows
its  maximum  thickness  and  overlies  the  R

unit and the

oldest substratum above a sligthly angular unconformity.
In outcrop, the unit dips at 10º—20º toward the NNE.

Several facies have been distinguished on the basis of

sedimentological characteristics.

The facies R2a consists of siliciclastic normal graded,

poorly  sorted  and  matrix  supported  granules,  organized
into  1—2 m  thick  tabular  beds,  related  to  massive  grain-
flows  deposits.  This  facies,  cropping  out  mainly  in  the
southernmost  zone  of  the  study  area,  occurs  alternating
with  the  other  facies  along  the  stratigraphic  succession
(Sottocastello  section,  Fig. 6D,E).

The facies R2b is the most common and was subdivided

into four subfacies (R2b

1—4

). Cross-laminated (current rip-

ples) and cross-stratified (dunes) biocalcarenites form the
subfacies R2b

and R2b

, respectively (Fig. 6E,F). The

dunes are sharp-based and composed of stacked tabular

cross-sets  up  to  1 m  thick,  with  foresets  inclined  up  to  30º
and  dipping  towards  N10—20  and  N340—360.  Upper  phase
plane  beds  of    laminated  granules  and  pebbles  form  the
subfacies  R2b

, interbedded with subfacies R2b

and

R2b

in the northern area (see Sottocastello section), and

with  facies  R2a  in  the  southern  area  (San  Cono  section).
Locally,  isotropic  HCS  (Hummocky  Cross-Stratification
sensu  Midtgaard  1996)  of  bioclastic  sands  and  granules
(subfacies  R2b

) occur with crests parallel to the paleo-

shoreline  (Sottocastello  section,  Fig. 7A).  In  the  down-cur-
rent  flank  of  the  HCS,  scour-and-fill  backset  cross-laminae
occur  (Fig. 8A).  The  facies  R2c  is  represented  by  slump
deposits,  1.5 m  thick  and  10—15 m  wide,  occurring  SW  of
Rometta  within  the  facies  R2b  deposits;  this  facies  is
made  up  of  deformed  laminae  of  bioclastic  sands  and
granules  showing  a  direction  of  gravitative  translation  to-
ward  NNE,  obtained  from  the  axis  inclination  of  the  crests
(Fig. 7B).

The facies R2d, consisting of 10—12 m thick debris-flow

channel fills comprised within the subfacies R2b

and

R2b

, occurs in the Sottocastello area. Such deposits show

a  concave/planar  geometry,  and  are  made  of  chaotic  and
matrix-supported  bioclastic  cobbles  and  boulders,  massive
and  poorly  sorted.  Each  block  contains  traces  of  cross-
lamination,  indicating  a  provenance  from  the  R2b  depos-
its  (Fig. 8B).  The  channel  axes  have  a  NNE-orientation
(Fig. 8C)  and  are  base-marked  by  erosional  surfaces  that
truncate  the  underlying  facies.

Table 2: Depth-ranges of the main benthic foraminifers identified in the Plio-Pleistocene units of the Rometta Succession and inferred
paleobathymetry for each unit.

DI STEFANO, LONGHITANO and SMEDILE

At the south-western extremity of Rometta village

(Rometta  section),  the  facies  R2b  merges  landwards  into
normal-graded,  up  to  4 m  thick  bioclastic  grain-flow  de-
posits,  containing  intrusive-rock  cobbles  and  fossil  frag-
ments  (facies  R2e

, Fig. 8D); these beds alternate with thin

wave-rippled beds (facies R2e

, Fig. 8E). The paleocurrent

measurements  develop  towards  the  NE.  These  facies  corre-
late  basinwards  with  the  facies  R2d,  following  a  basal
truncation  surface.

The facies association of the R

unit describes a facies

tract belonging to a ramp-type shelf, where a beachface
(facies R2e

and R2e

) rapidly passes into a lower shore-

face,  where  sedimentation  takes  place  below  the  fair-
weather  wave  base.  In  this  setting,  storm-generated  HCS
and  frequent  gravitative  debris-  and  grain-flow  occur.

The R

unit

The Middle Pleistocene R

unit forms the relief of the

highest  Rometta  Hills  (up  to  563 m  a.s.l.)  and  represents
part  of  the  town’s  substrate.  The  unit  consists  of  15—20 m
of  brown  and  grey  mudstones,  and  onlaps  onto  the  R

unit,  above  an  erosive  surface.  The  rare  outcrops  of  this
unit  and  the  intense  vegetation  cover  do  not  allow  its  fa-
cies  description  in  detail  (see  Rometta  section  in  Fig. 3).

These deposits are referable to an open offshore envi-

ronment.

Depositional architecture and sequence

stratigraphic interpretation

The surfaces bounding the R

unit are two unconformi-

ties, marking abrupt changes in the sedimentary facies and
in the micropaleontological content.

The first lower slightly angular unconformity (inclined

2º—4º), separates the lower unit (R

) from the intermediate

unit (R

), recording a stratigraphic gap quantified into at

least 870 kyr. The top of the R

unit is marked by a bed of

reddish sandstone, which is abruptly truncated by the first
unconformity.

The upper unconformity separates the intermediate unit

from the uppermost unit R

, and marks a gap of at least

260 kyr; above this irregular surface, the offshore mud-
stones of the upper R

unit develop.

The R

biocalcarenitic unit is composed of a set of at

least  three  high-frequency  sequences,  characterized  by
identical  facies  tracts  and  bounded  by  truncation  bound-
aries.  Along  these  surfaces,  a  basinward  shifting  of  the  fa-
cies  is  evident.

Each high-frequency sequence shows an aggradational-

to-progradational  type  architecture  and  indicates  that  the
sedimentation  developed  during  a  relative  rise  and    still-
stand  of  the  sea  level.  The  occurrence  of  erosional  surfaces
of  marine  regression  bounding  each  high-frequency  se-
quence  indicate  a  relative  sea-level  fall.

Therefore, the stratigraphic arrangement of the com-

posed R

unit may suggest that the sedimentation oc-

curred during a falling stage of the relative sea level, but

Table 3:

edimentary

facies

association

the

Rometta

Succession.

are

the

recognized

unconformity

bounded

units.

DI STEFANO, LONGHITANO and SMEDILE

boundary  shows  a  shallowing,  regressive  trend  of  the  sedi-
mentary  facies  (from  offshore  transition  to  shoreface),  the
hiatus  between  these  two  adjacent  environments  repre-
sents  a  sequence  boundary  that  can  be  interpreted  as  the
effect  of  a  transgression  rather  than  a  regression.

Consequently, the R

unit must be interpreted in a dif-

ferent way.

To justify the stratigraphic organization of the Rometta

Succession, with special emphasis on the R

unit, a new rel-

ative curve of the sea-level changes must be reconstructed,

Fig. 6. Outcrop photographs of the R

and R

units near Rometta. A – Erosion along the lower surface of the R

unit, lying above the

Messinian evaporites. B – Surface bounding the Middle Pliocene R

unit and the Plio-Pleistocene R

unit; note the low-angle angular un-

conformity (Sottocastello section). C – Detail of B; note the bed occurring on top of the R

unit, used as key bed for stratigraphic correla-

tions. D – Massive siliciclastic beds (R2a facies) alternating with cross-stratified beds (R2b facies, San Cono section). E – Massive siliciclastic
beds (R2a facies) alternating with ripple- and dune-bedded biocalcarenitic beds (R2b

and R2b

facies respectively), belonging to R

unit (San

Cono section). F – Alternating R2b

, R2b

R2b

facies (San Cono section); note the uni-modal direction (N-trending) of foresets.

considering  that  the  sedimentation  probably  occurred  dur-
ing  a  stage  of  late  sea-level  rise  and  consequent  highstand,
combining  the  high-frequency  eustatic  oscillations  with
the  effect  of  a  tectonic  uplift  of  the  area.

In fact, if a strong linear uplift trendline is superimposed

to  the  medium-frequency  eustatic  curve  during  a  still-
stand,  the  resulting  tendency  (relative  curve)  is  a  falling
line  that  expresses  a  relative  fall  of  the  sea  level.  If  we  con-
sider  that  the  sea-level  highstand  was  probably  character-
ized  by  high-frequency  sea-level  oscillations,  the  resulting

SEDIMENTATION AND TECTONICS IN A STEEP SHALLOW—MARINE DEPOSITIONAL SYSTEM (ITALY)

Fig. 7. Road-cut along the Sottocastello section. A – Example of isotropic hummocky cross-stratified (HCS) bed within the R

unit; the

direction of the paleo-flow is from left to the right. The crests of HCS are parallel to the paleo-shoreline. See detail in the box in figure 8A.
B – Interval of the San Cono section showing spectacular slump deposits. The crests of the deformed laminae indicate the direction of
gravitative movement (paleo-dip).

effect is a composite falling curve of the relative sea level
(Fig. 9, inset).

During the sedimentation of the R

biocalcarenites, a

tectonic  uplift  of  the  coastal  sector  may  have  occurred
contemporaneously  to  high-frequency  eustatic  oscilla-
tions.  The  combined  effect  of  the  tectonics  and  eustatism
may  have  produced  abrupt  basinward-shifting  of  the  fa-
cies,  simulating  an  apparent  fall  of  the  sea-level.  During
the  high-frequency  oscillations,  the  relative  sea-level  fall,
constrained  the  entire  system  to  sweep  basinwards.  In  this
situation,  mass-movement  processes  were  favoured  (Posa-
mentier  &  Morris  2000),  resulting  in  the  formation  of
channel  complexes  along  the  regressive  surfaces  (Fig. 9).

The occurrence of syndepositional unconformities bound-

ing the minor R

sequences and the progressive basinward

shifting  of  the  facies  tract  provides  evidence  that  uplift
was  active  at  least  from  the  Late  Pliocene.  Considering  the
late  Gelasian-Emilian  age  of  the  R

unit (about 700 ka)

and  the  topographic  heights  at  which  it  is  preserved  near
Rometta  (about  500 m  a.s.l),  an  average  uplift  rate  on  the
order  of  0.7 mm ·kyr

—1

can be estimated for this part of the

Tyrrhenian paleocoast since late Late Pliocene.

At the end of the deposition of the R

unit (relative sea-

level  highstand),  the  subsequent  sea-level  drop  produced
a  truncation  surface,  representing  the  base  of  a  younger  se-
quence  (sequence  boundary).  The  absence  of  any  traces  of

continental deposits does not confirm the exposure of the
unit during the sea-level fall.

Thus, the R

—R

units represents three incomplete depo-

sitional  sequences,  deposited  within  a  very  active  geolog-
ical  setting,  where  the  tectonics  played  a  fundamental  role
in  the  control  of  sedimentation.

The lower R

unit represents the highstand systems tract

(HST) of the oldest depositional sequence. The intermediate
R

unit is the HST of a new depositional sequence, which

developed  during  a  period  of  tectonic  uplift.  The  TST
(Transgressive  Systems  Tract)  is  probably  recorded  only
by  the  ravinement  surface  marking  the  top  of  the  R

unit.

The set of minor sequences forming the HST (R

unit), rep-

resents  the  sedimentary  record  of  the  sum  of  the  tectonic  up-
lift  and  the  sea-level  high-frequency  oscillations  during  a
phase  of  stillstands  (Fig. 9,  inset).

The influence of uplift in controlling small-scale se-

quence  development  is  also  recognizable  in  the  volumetric
development  of  individual  systems  tracts  and  in  the  control
exercised  on  the  sequence  arrangement.  This  characteristic
is  also  very  frequent  near  continental  margins,  where  the
tectonics  were  strongly  active  during  sedimentation,  impos-
ing  its  influence  on  the  smaller  time  scale  high-frequency
eustatic  oscillations  (e.g.  Cantalamessa  &  Di  Celma  2004).

The stratigraphic gap of at least 870 kyr recognized at

the R

sequence boundary is therefore interpreted as

DI STEFANO, LONGHITANO and SMEDILE

Fig. 8. Outcrop photographs of the R

and R

units. A – Detail of the figure 7A; here the down-current flank of the HCS is partially scoured and

filled by backset laminae; this process is related to supercritical flows, producing vortex migrating up-current. B – Detail of the channel fill de-
posits (R2d facies); note the tabular lamination within the block in the centre of the picture (Sottocastello section). C – Roadcut showing a trans-
versal section of a channelfill deposits (R2d facies); the dotted arrow indicates the translation direction (Sottocastello section). D – Proximal
coarse-grained facies of the R

unit; each single bed, 1—2 m thick, is made of normal-graded massive biocalcarenites (R2e

) alternating with wave

rippled thin beds (R2e

facies, Rometta section). E – Wave ripples of the R2e

facies. F – Massive and normal-graded (arrows) biocalcarenites

of the R2e

facies, intercalated with the thin horizons of the R2e

facies; note the abundance of bioclasts in the upper bed.

the result of an Early—Middle Pliocene phase of tectonic
uplift; the reddish fine level occurring on top of the R

unit

can  be  regarded  as  a  condensed  level,  deposited  during
the  sea-level  stillstand  that  preceded  the  beginning  of  the
first  sea-level  drop.

The absence of any traces of subaerial exposure, that may

form  during  the  sea-level  lowstand  and  usually  characteriz-
es  the  top  of  a  HST,  may  be  related  to  erosion  during  the
subsequent  sea-level  rise  and  identifies  such  a  surface  as  a
transgressive  erosion  surface  (Walker  &  Plint  1992;  Hunt  &

Tucker  1995).  The  hypothetical  lowstand  systems  tract  de-
posits  of  the  depositional  sequence  and  the  subsequent  ear-
ly  TST  have  to  be  searched  basinwards  (i.e.  to  the  north),  in
a  presently  down-faulted  area  partially  covered  by  the  Ho-
locene  coastal  plain  sediments  of  the  Tyrrhenian  shoreline.

The main part of the R

depositional sequence (TST) de-

veloped  in  a  sector  far  from  the  study  area,  near  the  coastal
areas;  in  fact,  NW  of  Rometta,  the  Middle  Pleistocene
“Argille  di  Spadafora”  Formation  (Auct.)  represents  the
early  TST  of  the  sequence  and  is  referable  to  the  R

unit

SEDIMENTATION AND TECTONICS IN A STEEP SHALLOW—MARINE DEPOSITIONAL SYSTEM (ITALY)

Fig. 9. Bi-dimensional reconstructed section across the Rometta Succession. The whole succession is the result of the superimposition of three,
third-order depositional sequences. The R

unit is the top of a HST belonging to the oldest sequence. The top of the R

unit, represents a ra-

vinement surface, on which the HST of the R

unit aggrades. The R

unit is composed of a set of simple high-frequency sequences, bounded

by regressive surfaces of marine erosion. The LST may be deposited in a position too far to be recognized in the study area (basinward). The
subsequent relative sea-level rise forms a late TST, onlapping onto a new transgression surface (top of the R

unit). The R

unit occurring on

top of the section and forming the highest Rometta Hill, can be interpreted as the whole TST + HST, in which the occurrence of a maximum
flooding surface can be supposed. The combined influence of the high-frequency eustatism and the tectonic uplift produces the sedimentation
of simple sequences within the R

unit, simulating a regressive stratigraphic arrangement of the facies (inset; see text for further details).

cropping out at Rometta. The R

unit is here interpreted as

the late TST + HST; our stratigraphic resolution of the R

unit  does  not  allow  us  to  identify  the  maximum  flooding
surface  separating  these  two  systems  tracts  (Fig. 9).  The
deposition  of  the  offshore  mudstones  of  the  R

unit

records a strong and sudden tectonic subsidence, responsi-
ble for the deepening of the sedimentary basin.

Above this sequence, not recognizable in the outcrop

near  Rometta  but  occurring  elsewhere  in  NE  Sicily,  a
younger  prograding  regressive-system  develops  (Middle—
Late  Pleistocene  “Ghiaie  di  Messina”  Formation  (Auct.)
(see  coastal  areas  in  Fig. 1).

Depositional and paleogeographical setting of R

unit

The depositional architecture of the R

unit, does not

show  a  ‘traditional’  progradational  geometry  (i.e.  clino-
forms  or  basal  downlapping  surfaces  at  outcrop-scale  of  ob-
servation).  The  absence  of  prograding  architectures  is
typical  of  depositional  settings  characterized  by  a  sea-floor
gradient  too  steep  to  provide  a  stable  substrate  for  prograd-
ing  deposits  (e.g.  ramp-type  inner  shelf,  e.g.  Plint  &  Norris
1991  and  references  therein).

The main component of the R

unit consists of bioclasts

represented by skeletal remains of mainly epifaunal organ-

isms  (pectinids,  ostreids  and  corals).  The  benthic  foramin-
iferal  association  and  the  sedimentary  facies  association
indicate  that  deposition  took  place  on  the  inner-middle
ramp-type  shelf,  not  deeper  than  50—80 m.

Observing the S-to-N-longitudinal facies tract of the

unit (Fig. 10), the system rapidly evolves seaward from

beachface coarse-grained facies (R2e

1—2

, estimated paleo-

bathymetry:  1—5 m),  to  lower  shoreface  cross-bedded  bio-
calcarenites  (R2a—d,  estimated  paleobathymetry:  from  30
to  50 m),  suggesting  a  reflective-type  high-gradient  paleo-
bottom-profile  (Orton  &  Reading  1993),  characterized  by
a  ‘resonant  domain’  of  a  steep  beach  face  zone,  in  which
the  oscillatory  wave  motion  reworks  the  sediment.

These features, recognizable in each single point where

the  succession  was  studied,  suggest  that  deposition  oc-
curred  on  a  ramp-type  depositional  system  (Plint  &  Norris
1991),  characterized  by  the  quick  deepening  of  the  sea-floor
below  the  fair-weather  wave  base.

This character is documented by three main features: (i) the

total  absence  of  wave-influenced  transitional  beachface-to-
shoreface  facies,  typical  instead  of  a  slow-shoaling  dissipa-
tive  coastal  domain,  (ii)  the  occurrence  of  several  mass-flow
deposits  (slumps  and  debris-filled  channel  complexes),  as-
sociated  with  a  high-gradient  bottom  profile,  and  (iii)  the
presence  of  shore-normal  oriented  HCS-bedded  horizons,
associated  with  sedimentary  structures  (backset  laminae)

SEDIMENTATION AND TECTONICS IN A STEEP SHALLOW—MARINE DEPOSITIONAL SYSTEM (ITALY)

that imply quick increasing of the flow-velocity, localized
at a paleodepth of 50—70 m.

These sedimentary structures were commonly associated

with  steep-slope  environments  (e.g.  delta  slope,  see  Mas-
sari  1996;  Colella  &  Vitale  1998)  where  flow  acceleration
produces  simultaneous  excavation  and  filling  of  scours  by
landward-dipping  laminae  under  supercritical  flow.  In  our
setting,  these  structures  indicate  a  local  steepening  of  the
paleo-bottom  profile,  due  to  the  increasing  of  the  dip-an-
gle  along  the  HCS  down-current  flank.

The present-day dip displayed by the R

unit in the out-

crop  has  to  be  considered  as  the  sum  of  an  original  deposi-
tional  inclination,  increased  by  subsequent  local  uplift.
Considering  that  the  original  depositional  dip  of  these  fa-
cies  can  be  estimated  at  up  to  5º  (Fig. 10),  and  that  the
present-day  strata  dip  is  of  10º—20º,  the  amount  of  tectonic
tilt  can  be  quantified  as  5º—15º.

The paleocurrent directions measured on the cross-bed-

ded strata and the axis trend of the gravitative flows show
a common NNE-trending orientation.

This uncommon environmental setting is inferred to be

connected  to  wind-driven  surficial  currents  (sensu  Swift  et  al.
1983),  impacting  against  a  steep  bottom  profile  and  reflected
to  form  basinward-directed  bottom  currents  (Duke  et  al.
1991).  These  currents  occur  both  in  normal  and  in  high-ener-
gy  phases  of  wave  motion,  producing  different-in-velocity
offshore-migrating  tractive-flows.  During  the  very-high  ener-
gy  stages  (storms),  the  wave  motion  may  interrupt  the  forma-
tion  of  the  orbital  motion  of  currents,  producing  only
reflective/resonant  oscillatory  long-movement,  which  justi-
fies  the  origin  of  HCS  (Harms  et  al.  1982;  Walker  et  al.  1983;
Duke  1990)  in  the  inner  shelf.

Such a coastal setting can be compared to the present

Tyrrhenian  coast  of  NE  Sicily,  characterized  by  analogous
morphological  conditions  (Gamberi  &  Marani  2006);  fur-
thermore,  the  lateral  extension  of  the  biocalcarenitic  unit
and  the  occurrence  of  the  interfingered  siliciclastic  grain-
flow  deposits  deriving  from  a  western  (lateral)  margin  of
the  area,  suggest  the  paleogeographical  setting  of  a  ‘semi-
enclosed  gulf’  or  embayment  (Fig. 11).

Conclusion

A detailed stratigraphic analysis was performed on the

NE  Sicily  Pliceneo-Pleistocene  succession,  cropping  out
in  the  key  area  of  Rometta,  which  provided  sedimentolog-
ical,  biostratigraphic  and  paleobathymetric  data.

Three sedimentary units (R

, R

and R

) form the suc-

cession,  respectively  Middle  Pliocene,  Late  Pliocene-Ear-
ly  Pleistocene  and  Middle  Pleistocene  in  age.  They  are
separated  by  two  main  angular  unconformities,  which
mark  important  changes  in  lithological  characters,  biogen-
ic  content,  depositional  environments  (from  offshore  tran-
sition  to  shoreface  to  open  offshore  again),  and  are
accompanied  by  two  main  sedimentary  gaps  spanning  at
least  870  and  260 kyr  respectively.

A sequence stratigraphy interpretation suggest that the

Rometta Succession is composed by the superimposition of

three incomplete, tectonically-enhanced, third-order depo-
sitional sequences. The lower R

unit forms the topmost of

a  late  TST + HST  of  a  Middle  Pliocene  depositional  se-
quence,  deeply  eroded  by  a  subsequent  first  sea-level  drop.
During  the  subsequent  transgression,  a  younger  deposition-
al  sequence  evolves,  onlapping  the  R

unit sediments onto

a ravinement surface (top of the R

unit) and forming a HST

in the Rometta area. The internal organization of the R

HST  simulates  a  Falling  Stage  Systems  Tract  (Hart  &  Long
1996;  Plint  &  Nummedal  2000),  since  it  is  composed  by  a
set  of  high-frequency  minor  sequences,  separated  by  erosive
surfaces  showing  a  basinward  shift  of  the  facies  tract.

The set of minor sequences record the interaction be-

tween  high-frequency  oscillations  of  the  sea  level  under
the  influence  of  the  coastal  tectonic  uplift,  during  which
the  coastal  systems  prograded  along  a  steep  sea  floor.

The mudstone of the R

unit, onlapping the topmost

bounding surface of the HST belonging to the R

unit, has to

be interpreted as the whole late TST + HST of the youngest
sequence, closing a new cycle of relative sea-level change.

The R

unit does not show prograding surfaces, com-

monly  associated  with  various  examples  of  coastal  sys-
tems  developing  during  relative  sea-level  still-stands;  the
absence  of  prograding  architectures  is  typical  of  deposi-
tional  settings  characterized  by  a  very  steep  sea-floor  gra-
dient,  where  clinoforms  cannot  develop.

In this framework the R

unit represents the HST of a

NNE-developing  depositional  sequence,  whose  distal
counterpart  (LST + TST)  has  been  down-dropped  by  recent
normal  faults  and  is  presently  covered  by  the  Holocene
coastal  sediments  of  the  northern  Sicilian  shoreline.

The lithofacies of the R

unit, represented by shoreface

beds  and  cross-stratified  ramp-type  shelf  deposits,  identifies
a  reflective-type  high-gradient  coastal  domain.  The  steep
gradient  favoured  the  generation  of  mass-flow  deposits,
translating  basinward.  The  ramp-type  cross-stratified  depos-
its  form  a  set  of  strata  in  which  a  variety  of  tractive  struc-
tures  occur,  denoting  the  action  of  medium  to  high  velocity
uni-directional  basinward-directed  flows.  The  latter  may  de-
rive  from  the  influence  of  wind-driven  surficial  water  move-
ments  that,  directed  and  impacting  against  a  steep  sea-cliff,
generated  basinward-directed  backflows.

Acknowledgments:  We  are  grateful  to  Prof.  Diego  Puglisi
(University  of  Catania),  Prof.  Luisa  Sabato  (University  of
Bari)  and  Assoc.  Prof.  Jozef  Michalík  for  the  accuracy  in
revising  the  manuscript.  Discussions  with  Dr.  Pierpaolo
Guarnieri  (University  of  Catania)  on  regional  geology
were  very  productive.  We  are  also  grateful  to  Dr.  Marcello
Tropeano  (University  of  Bari)  for  the  precious  suggestions
on  sequence  stratigraphy  interpretations.  This  research
was  supported  by  “Ateneo  Grants  (ex  60 %—2003—/2005)”
to  Agata  Di  Stefano  and  Fabio  Lentini.

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