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Overview of the Montalbano Jonico area and section: a proposal for a boundary stratotype for the lower–middle Pleistocene, Southern Italy Foredeep
ARTICLE IN PRESS
Quaternary International 131 (2005) 5–10
Overview of the Montalbano Jonico area and section: a proposal for a boundary stratotype for the lower–middle Pleistocene, Southern Italy Foredeep Neri Ciaranfi, Assunta D’Alessandro Dipartimento di Geologia e Geofisica, Universita` di Bari, Via E.Orabona 4, 70125 Bari, Italy Available online 25 September 2004
Abstract In the southernmost part of the Southern Apennine Foredeep crops out a well-exposed and continuous succession, about 500 m thick, of muds and muddy silts and several interbedded volcaniclastic layers. On the basis of nannofossil biostratigraphy it ranges from ‘‘large’’ Gephyrocapsa to Pseudoemiliania lacunosa Zones that indicate the upper part of the Lower Pleistocene and the lower part of the Middle Pleistocene. The vertical distribution of both invertebrate fossil assemblages and teleostean otoliths points out changes in the primary environmental parameters, particularly bathymetry, sedimentation rate and oxygen concentration. The observations allowed the reconstruction of several deepening–shallowing cycles within a general regressive framework. The Montalbano Jonico composite section is likely to represent a regressive portion of a third-order cycle in which relevant tectonic pulses should be the main reason for the general shallowing, possibly related to the beginning of the filling-up phase of the southern part of the Apennines Foredeep. The two recognized fourth-order cycles could be related to tectonoeustatic causes. The higher-frequency cyclicity, represented by several fifth-order cycles, seems to be mainly connected with astronomical relationships. The Montalbano Jonico section could be suitable for defining the Lower/Middle Pleistocene boundary stratotype: the potential GSSP could be located close to the ‘‘small’’ Gephyrocapsa/P. lacunosa zonal boundary, near a biohorizon rich in Delectopecten vitreus, a muddy dark-grey sapropelitic layer rich in Chondrites ichsp. and in oxygen isotopic stage 25. Another potential location of the GSSP of Middle Pleistocene could be near the volcaniclastic horizon V4, close to the isotopic stage 19 boundary. r 2004 Elsevier Ltd and INQUA. All rights reserved. Keywords: Marine sediments; Quaternary stratigraphy; Cyclostratigraphy
1. Introduction The Southern Apennines Foredeep represents a subsiding sedimentary basin, limited westward by the external Apennine thrust belt and eastward by the carbonate units of the Apulia Foreland. Its origin is related to the Late Tertiary and Quaternary evolution of the east verging Chain–Foredeep–Foreland System, as a consequence of a west-dipping subduction of the Adriatic continental lithosphere under the Apennines’ continental one (Fig. 1).
Corresponding author.
E-mail address: [email protected] (N. Ciaranfi).
During the Pleistocene in the southernmost Foredeep areas, a few deep and narrow depocentral troughs were affected by a strong, almost continuous subsidence in which the deposition of thick hemipelagic successions, punctuated by several muddy turbidities episodes, took place. During the Early Pleistocene the southernmost trough, the Lucania Basin, migrated north east, changing physiography as a result of the uplifting Apennines border moving eastward as well as the depocentral areas and the foreland border, which became progressively involved in trough evolution. Starting from the Middle Pleistocene, the decrease of the subsidence rate produced a generalized shallowing phase, leading to the exposure of the regressive part of the succession.
1040-6182/$ - see front matter r 2004 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2004.07.003
ARTICLE IN PRESS 6
N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10
2. Montalbano Jonico succession
Fig. 1. Schematic geologic map and location of Montalbano Jonico area.
In addition to the roles of tectonics and sediment supply, the Pleistocene siliciclastic successions were also affected by sea-level fluctuations related to changes in global continental ice volumes. A better comprehension of the interplay between glacio-eustatic, tectonics and sediment supply factors has important implications for a correct understanding of the paleogeographic evolution of the Foredeep area during the Pleistocene. The thick hemipelagic clay and silty-clay deposits, cropping out in the Montalbano Jonico area, provide excellent stratigraphic sections in which the history of sea-level changes during the Lower and Middle Pleistocene can be reconstructed in detail. The possible location of the Middle Pleistocene GSSP is still the subject of controversy: it could be traced close to the top of the Jaramillo reversal, isotopic stage 25 and the small Gephyrocapsa/Pseudoemiliania lacunosa nannofossil zonal boundary (Cita and Castradori, 1994), grossly approximating the time of ca. 0.95 Myr, or near the Matuyama-Brunhes magnetic reversal (Richmond, 1996), in isotopic stage 19, grossly approximating the time of ca. 0.78 Myr. According to Azzaroli (in Cita and Castradori, 1994) the last location of the boundary could be easily recognizable in the land records on the basis of mammal faunas. Detailed multidisciplinary stratigraphic studies indicate that both possible positions of the boundary are exposed along the Montalbano Jonico composite Section: ‘‘lower’’ in the 5 Agosto Section, ‘‘higher’’ in the Ideale Section (Figs. 3 and 4).
The Montalbano Jonico succession is well exposed along a steep slope of the Agri River in Southern Lucania, where it lies within a monocline setting gently dipping SE (Fig. 2). The poorly stratified succession forms part of a coarsening upward cyclothem made of muddy clays and muddy sands, measured in detail for a thickness of more than 500 m. According to calcareous nannofossil biostratigraphy (Marino, 1996; Ciaranfi et al., 2001) the succession ranges between the late Lower Pleistocene and the early Middle Pleistocene. The basal part has been referred to the top of the ‘‘large’’ Gephyrocapsa Zone (according to the scheme of Rio et al., 1990), the intermediate part— for a thickness of 135 m—to the ‘‘small’’ Gephyrocapsa Zone and the topmost part—for the whole thickness of 334 m—to the Pseudoemiliania lacunosa Zone. The Montalbano Jonico Section represents one of the more recent, continuous and extensive onland marine Pleistocene successions. In the badland area southwest of Montalbano Jonico village, several partial stratigraphic sections have been correlated by means of detailed observations mainly based on physical and palaeontological features (Fig. 3). Several elements have been used to correlate selected sections (Ciaranfi et al., 1997, 2001); volcaniclastic layers (V1–V9), and a set of ‘‘light’’ and ‘‘dark’’ bands with laterally traceable fossil concentrations. The volcaniclastic layers, made up of pure ashes or sands rich in volcanics and occasionally of pumice clasts, were accumulated by gravity flows. All the layers are referred to an alkaline undersatured volcanism and probably have a Southern Italy source (De Rosa in Ciaranfi et al., 1996). Petrographical and geochemical similarities among these layers do not allow using them directly as lithohorizons. Specific macrofossil accumulations observed in the field near each volcaniclastic layer provide a precise identification and allow their use as marker beds. In addition, a set of alternating dark and light muddy bands showing a relevant lateral continuity, constancy in facies and biofacies, as well as cyclic allogenic successions, have been used for stratigraphic correlations too (Figs. 3 and 4). In the Montalbano area, the composite section is broken in two intervals; the lower stratigraphic interval (A in Fig. 4), about 180 m thick, consists of massive bioturbated muds and includes the volcaniclastic layer V1 and several muddy turbidities. The macrofossil assemblages suggest deposition in an upper slope setting whose paleoenvironmental evolution reveals a general shallowing trend (Fig. 4) punctuated by a number of depth fluctuations, possibly related to climatic changes but also influenced by tectonic pulses (Girone, 2000). At different stratigraphic layers, four dysoxic regimes have been recognized and identified as sapropelitic intervals
ARTICLE IN PRESS N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10
7
Fig. 2. (A) Schematic geologic map of Montalbano Jonico area, (B) Schematic cross-section along the eastern steep slope of Montalbano Jonico.
ARTICLE IN PRESS N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10
8
VENUS BASSA
GIUSEPPE
DITO DEL DIAVOLO
V1
VECCHIETTO IDEALE
SALVATORE
V3
V9 V8 Poorly exposed
V2
Covered poorly exposed
MOLINO
V7 V6
Covered
I.M.
V5 5 AGOSTO
V4
Covered
V9 V1
V3
poorly exposed
poorly exposed
V2
LEGENDA ENTALINA
Conglomerate
Sand
Sandy silt
Light mud
Dark mud Volcaniclastic layer
Delectopecten vitreus horizon Silty sand
Sapropel
Pseudoemiliania lacunosa Zone
small Gephyrocapsa Zone
10 m 0m
large Gephyrocapsa Zone
Fig. 3. Correlation among the partial stratigraphic sections reconstructed in the Montalbano Jonico area.
according to benthic and planktonic foraminifera assemblages (Stefanelli et al., 2004). The macrobenthic content (skeletons and trace fossils) is indicative of three lower dysoxic up to exaerobic zones, plus two short severe fluctuations, in a background of a generally poor oxygenated (around or just below 2.0 ml/l) interstitial waters (D’Alessandro et al., 2001). In particular, the 5 Agosto section (Fig. 3) contains the small Gephyrocapsa/ Pseudoemiliania lacunosa zonal boundary that occurs in a distinct sapropel layer (Maiorano et al., 2004). The upper stratigraphic interval (B in Fig. 4), more than 300 m thick, mainly consists of silty muds and silty sands in the uppermost part. The volcaniclastic layers V2–V9 and some light and dark bands are included in this part of the succession. This interval was mainly deposited in inner to outer shelf environments, and contains circalittoral palaeocommunities. Cyclic pattern of the allogenic successions together with taphonomic
observations, recognition of sapropelitic layers as well as the oxygen isotope record allows inference of several high frequency cycles (Ciaranfi et al., 1997, 2001).
3. Discussion and conclusions In the southernmost part of Lucania Basin, the Montalbano Jonico composite section represents a well-exposed, continuous and extended succession of hemipelagic deposits. The section is constrained in a well-known Lower–Middle Pleistocene stratigraphic framework based on nannofossil biostratigraphy, sapropel and oxygen isotope stratigraphy. In this section, the GSSP of Middle Pleistocene could be defined in two different locations. The lowest one is in the 5 Agosto section within the Ideale section close to the small Gephyrocapsa/Pseudoemiliania lacunosa zonal boundary
ARTICLE IN PRESS N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10 δ 18 O PDB
benthic foraminifers
benthic invertebrates
9 taphofacies
otoliths
280 260
V9 V8
240
V7 V6 V5
220
INTERVAL B
Pseudoemiliania lacunosa zone
200 180 160 140 V4
19
120 V3
100
20
80
21 60 40
22 20
V2
0 160
LCO R. asanoi
23 24
140
25
V1 100
FCO R. asanoi 80 60 40
(A)
5. 0
4. 0
3. 0
2. 0
1. 0
(B)
deepening
(C)
500 m
(D)
500 m
(E)
Slope
Outer
Inner
tobe investigated
Middle
10 m0
circalittoral bathyal
20 0
large Gephyr. zone
?
circalittoral bathyal
INTERVAL A
small Gephyrocapsa zone
FO Gephyr. sp. 3 120
Shelf
Fig. 4. Composite section of Montalbano Jonico and correlation among the main stratigraphic results and the paleobathymetric interpretation obtained by means of different approaches. (A) from Brilli et al. (2000), modified; (B) from Stefanelli (2004); (C) from Ciaranfi et al. (2001); from D’Alessandro et al. (2001); (D) from Girone (2000); (E) from Soldani (unpublished data).
that can be correlated to oxygen isotope stage 25 and to a sapropel layer interpreted as OIS 19 (Maiorano et al., 2004), according to Kroon et al. (1998). The higher potential GSSP for the Middle Pleistocene could be located close to oxygen isotope stage 19 which falls near the Brunhes–Matuyama boundary (Shackleton et al., 1990). The cyclothems identified in the Montalbano Jonico succession can be best explained in an astrocyclostratigraphical framework. The cyclicity of the lower part of the succession (partial sections Fosso Giuseppe and 5 Agosto) is clearly identified and can be connected with variations of 41,000 years orbital obliquity period (sixth order). For the upper part of the succession (partial sections Venus bassa, Dito del Diavolo, Ideale, Salvatore–Vecchietto and Molino) the cyclostratigraphic interpretation, based both on isotope stratigraphy and the presence of stenothermal cold species, results also are clear (Stefanelli, 2004). In this part of the studied section the main environmental parameters, such as water depth, sedimentation rate and substrate consis-
tency, reveal not only a sixth-order cyclicity but also variations of 100,000 years orbital eccentricity (fifth order) also registered in oxygen-18 isotope composition in the tests of the benthic foraminifers Cassidulina carinata and Uvigerina peregrina (Brilli et al., 2000). There is an overall good match between cyclothems inferred on the base of benthic associations and the available oxygen isotope ice-volume curve extending from OIS 25 to OIS 19. The Montalbano Jonico composite section is well exposed and fulfils most of the geological requirements listed by Remane et al. (1996) as the basis for a correct establishing boundary stratotypes: continuous sedimentation, high deposition rate and absence of synsedimentary disturbances.
Acknowledgement This study was financed by the Italian Ministery of University and Scientific Research (Grant MURST 40%—1999; no. 9904194543, to N. Ciaranfi).
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References Brilli, M., Lerche, I., Ciaranfi, N., Turi, B., 2000. Evidence of precession and obliquity orbital forcing in oxygen-18 isotope composition of Montalbano Jonico section (Basilicata, Southern Italy). Applied Radiation and Isotopews 52, 957–964. Ciaranfi N., D’Alessandro A., Marino M., 1997. A candidate section for the Lower–Middle Pleistocene Boundary (Apennine Foredeep, South Italy). Proceedings of the 30th International Geological Congress vol. 11, pp. 201–211. Ciaranfi, N., Marino, M., Sabato,, L., D’Alessandro, A., De Rosa, R., 1996. Studio geologico-stratigrafico di una successione infra e mesopleistocenica nella parte sud-occidentale della Fossa bradanica (Montalbano Jonico, Basilicata). Bollettino Societa` Geologica Italiana 115, 379–391. Ciaranfi, N., D’Alessandro, A., Girone, A., Maiorano, P., Marino, M., Soldani, D., Stefanelli, S., 2001. The Pleistocene sections in the Montalbano Jonico area and the potential GSSP for Early–Middle Pleistocene in the Lucania Basin (Southern Italy). Memorie di Scienze geologiche di Padova 53, 67–83. Cita, M.B., Castradori, D., 1994. Workshop on marine sections of Gulf of Taranto (Southern Italy) usable as a potential stratotypes for the GSSP of the Lower, Middle and Upper Pleistocene. Il Quaternario 7, 677–692. D’Alessandro, A., La Perna, R., Ciaranfi, N., 2001. Paleontological indications of sea-level fluctuations in the deep-sea deposits of the Bradano Trough (Southern Italy), Lower–Middle Pleistocene. Buatois, L.A., Mangano G., convenors, Secunda Reunion de Icnologia del Mercosur, 24–28 September 2001, p. 39. Girone A., 2000. Lo studio delle associazioni a otoliti in sezioni pleistoceniche dell’ Italia meridionale. Doctoral Thesis. University of Bari, 86pp. Kroon, D., Alexander, I., Little, M., Lourens, L.J., Mattehewson, A., Robertson, A.F.H., Sakamoto, T., 1998. Oxygen isotope and sapropel stratigraphy in the eastern Mediterranean during the last
3.2 million years. In: Robertson, A.H.F. (Ed.), Proceedings of Ocean Drilling Project, Scientific Results, Vol. 160. Texas A & M University, Austin, pp. 81–190. Maiorano, P., Marino, M., Di Stefano, E., Ciaranfi, N., 2004. Calcareous nannofossil events in the Lower–Middle Pleistocene transition at Montalbano Jonico section (Southern Italy) and ODP Site 964 (Ionian Sea): calibration with isotope end sapropel stratigraphy. Riv. It. Paleont. e Strat. 110, 547–557. Marino, M., 1996. Quantitative calcareous nannofossil biostratigraphy of the Lower–Middle Pleistocene Montalbano Jonico section (Southern Italy). Paleopelagos 6, 347–360. Remane, J., Bassett, M.G., Cowie, J.W., Gohrbandt, K.H., Lane, H.R., Michelsen, O., Naiwen, W., 1996. Revised guidelines for establihment of global chronostratigraphic standards by the International Commission on Stratigraphy (ICS). Episodes 19, 77–81. Richmond, G.M., 1996. The INQUA-approved provisional LowerMiddle Pleistocene boundary. In: Turner, C. (Ed.), The Early Middle Pleistocene in Europe. Balkema, Rotterdam, pp. 319–327. Rio, D., Raffi, I., Villa, G., 1990. Pliocene–Pleistocene calcareous nannofossil distribution patterns in the Western Mediterranean. In: Kastens, K. (Ed.), Proceedings of Ocean Drilling Project, Scientific Results, vol. 107. Texas A & M University, Austin, pp. 513–533. Shackleton, N.J., Berger, A., Peltier, W.R., 1990. An alternative astronomical calibration of the lower Pleistocene timescale based on ODP Site 677. Transactions of the Royal Society of Edinburgh Earth Sciences 81, 251–261. Stefanelli, S., 2004. Benthic foraminiferal assemblages as tools for paleoenvironmental reconstruction of the early–middle Pleistocene Montalbano Jonico composite section. Boll. Soc. Paleont. It. 43, 281–299. Stefanelli, S., Capotondi, L., Ciaranfi, N., 2004. Foraminiferal record and environmental changes during the deposition of the early– middle Pleistocene sapropels in Southern Italy. Paleoclim, Paleoecol, Paleogeogr, in press.
Quaternary International 131 (2005) 5–10
Overview of the Montalbano Jonico area and section: a proposal for a boundary stratotype for the lower–middle Pleistocene, Southern Italy Foredeep Neri Ciaranfi, Assunta D’Alessandro Dipartimento di Geologia e Geofisica, Universita` di Bari, Via E.Orabona 4, 70125 Bari, Italy Available online 25 September 2004
Abstract In the southernmost part of the Southern Apennine Foredeep crops out a well-exposed and continuous succession, about 500 m thick, of muds and muddy silts and several interbedded volcaniclastic layers. On the basis of nannofossil biostratigraphy it ranges from ‘‘large’’ Gephyrocapsa to Pseudoemiliania lacunosa Zones that indicate the upper part of the Lower Pleistocene and the lower part of the Middle Pleistocene. The vertical distribution of both invertebrate fossil assemblages and teleostean otoliths points out changes in the primary environmental parameters, particularly bathymetry, sedimentation rate and oxygen concentration. The observations allowed the reconstruction of several deepening–shallowing cycles within a general regressive framework. The Montalbano Jonico composite section is likely to represent a regressive portion of a third-order cycle in which relevant tectonic pulses should be the main reason for the general shallowing, possibly related to the beginning of the filling-up phase of the southern part of the Apennines Foredeep. The two recognized fourth-order cycles could be related to tectonoeustatic causes. The higher-frequency cyclicity, represented by several fifth-order cycles, seems to be mainly connected with astronomical relationships. The Montalbano Jonico section could be suitable for defining the Lower/Middle Pleistocene boundary stratotype: the potential GSSP could be located close to the ‘‘small’’ Gephyrocapsa/P. lacunosa zonal boundary, near a biohorizon rich in Delectopecten vitreus, a muddy dark-grey sapropelitic layer rich in Chondrites ichsp. and in oxygen isotopic stage 25. Another potential location of the GSSP of Middle Pleistocene could be near the volcaniclastic horizon V4, close to the isotopic stage 19 boundary. r 2004 Elsevier Ltd and INQUA. All rights reserved. Keywords: Marine sediments; Quaternary stratigraphy; Cyclostratigraphy
1. Introduction The Southern Apennines Foredeep represents a subsiding sedimentary basin, limited westward by the external Apennine thrust belt and eastward by the carbonate units of the Apulia Foreland. Its origin is related to the Late Tertiary and Quaternary evolution of the east verging Chain–Foredeep–Foreland System, as a consequence of a west-dipping subduction of the Adriatic continental lithosphere under the Apennines’ continental one (Fig. 1).
Corresponding author.
E-mail address: [email protected] (N. Ciaranfi).
During the Pleistocene in the southernmost Foredeep areas, a few deep and narrow depocentral troughs were affected by a strong, almost continuous subsidence in which the deposition of thick hemipelagic successions, punctuated by several muddy turbidities episodes, took place. During the Early Pleistocene the southernmost trough, the Lucania Basin, migrated north east, changing physiography as a result of the uplifting Apennines border moving eastward as well as the depocentral areas and the foreland border, which became progressively involved in trough evolution. Starting from the Middle Pleistocene, the decrease of the subsidence rate produced a generalized shallowing phase, leading to the exposure of the regressive part of the succession.
1040-6182/$ - see front matter r 2004 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2004.07.003
ARTICLE IN PRESS 6
N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10
2. Montalbano Jonico succession
Fig. 1. Schematic geologic map and location of Montalbano Jonico area.
In addition to the roles of tectonics and sediment supply, the Pleistocene siliciclastic successions were also affected by sea-level fluctuations related to changes in global continental ice volumes. A better comprehension of the interplay between glacio-eustatic, tectonics and sediment supply factors has important implications for a correct understanding of the paleogeographic evolution of the Foredeep area during the Pleistocene. The thick hemipelagic clay and silty-clay deposits, cropping out in the Montalbano Jonico area, provide excellent stratigraphic sections in which the history of sea-level changes during the Lower and Middle Pleistocene can be reconstructed in detail. The possible location of the Middle Pleistocene GSSP is still the subject of controversy: it could be traced close to the top of the Jaramillo reversal, isotopic stage 25 and the small Gephyrocapsa/Pseudoemiliania lacunosa nannofossil zonal boundary (Cita and Castradori, 1994), grossly approximating the time of ca. 0.95 Myr, or near the Matuyama-Brunhes magnetic reversal (Richmond, 1996), in isotopic stage 19, grossly approximating the time of ca. 0.78 Myr. According to Azzaroli (in Cita and Castradori, 1994) the last location of the boundary could be easily recognizable in the land records on the basis of mammal faunas. Detailed multidisciplinary stratigraphic studies indicate that both possible positions of the boundary are exposed along the Montalbano Jonico composite Section: ‘‘lower’’ in the 5 Agosto Section, ‘‘higher’’ in the Ideale Section (Figs. 3 and 4).
The Montalbano Jonico succession is well exposed along a steep slope of the Agri River in Southern Lucania, where it lies within a monocline setting gently dipping SE (Fig. 2). The poorly stratified succession forms part of a coarsening upward cyclothem made of muddy clays and muddy sands, measured in detail for a thickness of more than 500 m. According to calcareous nannofossil biostratigraphy (Marino, 1996; Ciaranfi et al., 2001) the succession ranges between the late Lower Pleistocene and the early Middle Pleistocene. The basal part has been referred to the top of the ‘‘large’’ Gephyrocapsa Zone (according to the scheme of Rio et al., 1990), the intermediate part— for a thickness of 135 m—to the ‘‘small’’ Gephyrocapsa Zone and the topmost part—for the whole thickness of 334 m—to the Pseudoemiliania lacunosa Zone. The Montalbano Jonico Section represents one of the more recent, continuous and extensive onland marine Pleistocene successions. In the badland area southwest of Montalbano Jonico village, several partial stratigraphic sections have been correlated by means of detailed observations mainly based on physical and palaeontological features (Fig. 3). Several elements have been used to correlate selected sections (Ciaranfi et al., 1997, 2001); volcaniclastic layers (V1–V9), and a set of ‘‘light’’ and ‘‘dark’’ bands with laterally traceable fossil concentrations. The volcaniclastic layers, made up of pure ashes or sands rich in volcanics and occasionally of pumice clasts, were accumulated by gravity flows. All the layers are referred to an alkaline undersatured volcanism and probably have a Southern Italy source (De Rosa in Ciaranfi et al., 1996). Petrographical and geochemical similarities among these layers do not allow using them directly as lithohorizons. Specific macrofossil accumulations observed in the field near each volcaniclastic layer provide a precise identification and allow their use as marker beds. In addition, a set of alternating dark and light muddy bands showing a relevant lateral continuity, constancy in facies and biofacies, as well as cyclic allogenic successions, have been used for stratigraphic correlations too (Figs. 3 and 4). In the Montalbano area, the composite section is broken in two intervals; the lower stratigraphic interval (A in Fig. 4), about 180 m thick, consists of massive bioturbated muds and includes the volcaniclastic layer V1 and several muddy turbidities. The macrofossil assemblages suggest deposition in an upper slope setting whose paleoenvironmental evolution reveals a general shallowing trend (Fig. 4) punctuated by a number of depth fluctuations, possibly related to climatic changes but also influenced by tectonic pulses (Girone, 2000). At different stratigraphic layers, four dysoxic regimes have been recognized and identified as sapropelitic intervals
ARTICLE IN PRESS N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10
7
Fig. 2. (A) Schematic geologic map of Montalbano Jonico area, (B) Schematic cross-section along the eastern steep slope of Montalbano Jonico.
ARTICLE IN PRESS N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10
8
VENUS BASSA
GIUSEPPE
DITO DEL DIAVOLO
V1
VECCHIETTO IDEALE
SALVATORE
V3
V9 V8 Poorly exposed
V2
Covered poorly exposed
MOLINO
V7 V6
Covered
I.M.
V5 5 AGOSTO
V4
Covered
V9 V1
V3
poorly exposed
poorly exposed
V2
LEGENDA ENTALINA
Conglomerate
Sand
Sandy silt
Light mud
Dark mud Volcaniclastic layer
Delectopecten vitreus horizon Silty sand
Sapropel
Pseudoemiliania lacunosa Zone
small Gephyrocapsa Zone
10 m 0m
large Gephyrocapsa Zone
Fig. 3. Correlation among the partial stratigraphic sections reconstructed in the Montalbano Jonico area.
according to benthic and planktonic foraminifera assemblages (Stefanelli et al., 2004). The macrobenthic content (skeletons and trace fossils) is indicative of three lower dysoxic up to exaerobic zones, plus two short severe fluctuations, in a background of a generally poor oxygenated (around or just below 2.0 ml/l) interstitial waters (D’Alessandro et al., 2001). In particular, the 5 Agosto section (Fig. 3) contains the small Gephyrocapsa/ Pseudoemiliania lacunosa zonal boundary that occurs in a distinct sapropel layer (Maiorano et al., 2004). The upper stratigraphic interval (B in Fig. 4), more than 300 m thick, mainly consists of silty muds and silty sands in the uppermost part. The volcaniclastic layers V2–V9 and some light and dark bands are included in this part of the succession. This interval was mainly deposited in inner to outer shelf environments, and contains circalittoral palaeocommunities. Cyclic pattern of the allogenic successions together with taphonomic
observations, recognition of sapropelitic layers as well as the oxygen isotope record allows inference of several high frequency cycles (Ciaranfi et al., 1997, 2001).
3. Discussion and conclusions In the southernmost part of Lucania Basin, the Montalbano Jonico composite section represents a well-exposed, continuous and extended succession of hemipelagic deposits. The section is constrained in a well-known Lower–Middle Pleistocene stratigraphic framework based on nannofossil biostratigraphy, sapropel and oxygen isotope stratigraphy. In this section, the GSSP of Middle Pleistocene could be defined in two different locations. The lowest one is in the 5 Agosto section within the Ideale section close to the small Gephyrocapsa/Pseudoemiliania lacunosa zonal boundary
ARTICLE IN PRESS N. Ciaranfi, A. D’Alessandro / Quaternary International 131 (2005) 5–10 δ 18 O PDB
benthic foraminifers
benthic invertebrates
9 taphofacies
otoliths
280 260
V9 V8
240
V7 V6 V5
220
INTERVAL B
Pseudoemiliania lacunosa zone
200 180 160 140 V4
19
120 V3
100
20
80
21 60 40
22 20
V2
0 160
LCO R. asanoi
23 24
140
25
V1 100
FCO R. asanoi 80 60 40
(A)
5. 0
4. 0
3. 0
2. 0
1. 0
(B)
deepening
(C)
500 m
(D)
500 m
(E)
Slope
Outer
Inner
tobe investigated
Middle
10 m0
circalittoral bathyal
20 0
large Gephyr. zone
?
circalittoral bathyal
INTERVAL A
small Gephyrocapsa zone
FO Gephyr. sp. 3 120
Shelf
Fig. 4. Composite section of Montalbano Jonico and correlation among the main stratigraphic results and the paleobathymetric interpretation obtained by means of different approaches. (A) from Brilli et al. (2000), modified; (B) from Stefanelli (2004); (C) from Ciaranfi et al. (2001); from D’Alessandro et al. (2001); (D) from Girone (2000); (E) from Soldani (unpublished data).
that can be correlated to oxygen isotope stage 25 and to a sapropel layer interpreted as OIS 19 (Maiorano et al., 2004), according to Kroon et al. (1998). The higher potential GSSP for the Middle Pleistocene could be located close to oxygen isotope stage 19 which falls near the Brunhes–Matuyama boundary (Shackleton et al., 1990). The cyclothems identified in the Montalbano Jonico succession can be best explained in an astrocyclostratigraphical framework. The cyclicity of the lower part of the succession (partial sections Fosso Giuseppe and 5 Agosto) is clearly identified and can be connected with variations of 41,000 years orbital obliquity period (sixth order). For the upper part of the succession (partial sections Venus bassa, Dito del Diavolo, Ideale, Salvatore–Vecchietto and Molino) the cyclostratigraphic interpretation, based both on isotope stratigraphy and the presence of stenothermal cold species, results also are clear (Stefanelli, 2004). In this part of the studied section the main environmental parameters, such as water depth, sedimentation rate and substrate consis-
tency, reveal not only a sixth-order cyclicity but also variations of 100,000 years orbital eccentricity (fifth order) also registered in oxygen-18 isotope composition in the tests of the benthic foraminifers Cassidulina carinata and Uvigerina peregrina (Brilli et al., 2000). There is an overall good match between cyclothems inferred on the base of benthic associations and the available oxygen isotope ice-volume curve extending from OIS 25 to OIS 19. The Montalbano Jonico composite section is well exposed and fulfils most of the geological requirements listed by Remane et al. (1996) as the basis for a correct establishing boundary stratotypes: continuous sedimentation, high deposition rate and absence of synsedimentary disturbances.
Acknowledgement This study was financed by the Italian Ministery of University and Scientific Research (Grant MURST 40%—1999; no. 9904194543, to N. Ciaranfi).
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