Pliocene-Lower Pleistocene Chronostratigraphy: a Re-Evaluation of Mediterranean Type Sections

Pliocene-lower Pleistocene chronostratigraphy: A re-evaluation of Mediterranean type sections

D. RIO Dipartimento di Geologia, Paleontologia e Geofísica, Universita degli Studi di Padova, 35137 Padova, Italia R. SPROVIERI Dipartimento di Geologia e Geofísica, Universita degli Studi di Palermo, 90134 Palermo, Italia R. THUNELL Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208

ABSTRACT INTRODUCTION Numerous regional stage sequences have been established for the Neogene (for example, Cali- The Pliocene-Pleistocene stages defined for Chronostratigraphic units are rock units fornia, New Zealand, USSR), but the stages for the Mediterranean region are generally used which represent specific intervals of geologic the Mediterranean Neogene are commonly used as the standard chronostratigraphic units for time, and when taken together, form a compos- as the "standard stages" in most geologic time the upper Neogene and Quaternary. The re- ite stratigraphic sequence representing all of scales (Berggren and Van Couvering, 1974; Har- cently developed calcareous plankton bio- Earth history. Recognition of chronostratigraph- land and others, 1982; Berggren and others, chronology based on results from Ocean ic units, both regionally and globally, is a 1985; Haq and others, 1987). All of the Medi- Drilling Program Leg 107 and numerous out- fundamental step in establishing time correla- terranean Pliocene-Pleistocene stages and the crop sections provides the necessary time tions. Within the hierarchy of chronostratigraph- relative stratotype sections have been established control for evaluating the ages and strati- ic units, the "stage" represents a relatively in Italy (Fig. 1). The only formally defined graphic relationships for the various Plio- short interval of geologic time; the stage has chronostratigraphic boundary, however, is the cene-Pleistocene stages and their associated been referred to as "the basic working unit of Pliocene/Pleistocene boundary (Aguirre and stratotypes. Our results indicate that the cur- chronostratigraphy" (Hedberg, 1976, p. 71). Pasini, 1985). rently accepted stratotypes do not provide a continuous stratigraphic representation for all of Pliocene-early Pleistocene time. On the basis of these findings, we propose a revised chronostratigraphic scheme for this time period. A tripartite subdivision is proposed for the Pliocene Series. The Zanclean Stage is retained for the lower Pliocene, represent- 44° N ing the interval from the Miocene/Pliocene boundary (ca. 4.93 Ma) to ca. 3.5 Ma. The middle Pliocene is represented by the Piacen- zian Stage, and it incorporates strata depos- ited from ca. 3.5 to 2.5 Ma. None of the currently used Pliocene stages fully represents the upper Pliocene (ca. 2.5 to 1.6 Ma). As a result, late Pliocene time lacks an ade- 40° N quately defined chronostratigraphic unit. The Selinuntian Stage appears to be the most appropriate stage for the lower Pleisto- cene (ca. 1.6 to 0.8 Ma). It can be divided into three stratigraphically continuous substages (Santernian, Emilian, and Sicilian). The Cala- brian Stage, which is commonly used to des- 36° N ignate the lowest part of the Pleistocene, 5°E 10°E 15° E 20° E should be abandoned because its stratotype does not include a record of the first 500,000 Figure 1. Map showing locations of the Pliocene-Pleistocene stage type sections and ODP yr of Pleistocene time. sites discussed in this paper.

Geological Society of America Bulletin, v. 103, p. 1049-1058, 6 figs., 2 tables, August 1991.

1049

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/8/1049/3381324/i0016-7606-103-8-1049.pdf by guest on 26 September 2021 Figure 2. Polarity stratigraphy for ODP Sites 652 and 654 (Channel! and others, 1990), the MAGNETIC BI0Z0NES Vrica section (Tauxe and others, 1983), the Capo Spartivento section (Channell and others, 1988), POLARITY and the Gela section (Channell and others, in press). The stratigraphie positions of the bioevents TIME listed in Table 1 are shown for each ODP site and land section. SCALE

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In principle, it should be possible to recognize TABLE 1. CALCAREOUS PLANKTON BIOSTRATIGRAPHIC EVENTS AND ESTIMATED AGES the Mediterranean Pliocene-Pleistocene stages Bioevent Estimated age (Ma) Reference globally and in all depositional settings. Unfor- tunately, such correlation has been hampered by 1. Beginning of Emitíanla huxleyi acme 0.085 Rio and others (1990a) 2. Emiliania huxleyi LO 0.26 several factors. First, many of the Italian strato- 3. Pseudoemilianìa lacunosa HO 0.46 type sections were proposed in shallow to mar- 4. Gephyrocapsa sp. 3 LO (S2) 0.95 Rio and others (in press) 5a. Gephyrocapsa spp. >5.5 ti HO (SI) 1.10 ginal marine sequences and were selected on the 5b. Halicosphaera sellii HO (SI) 1.10 6. Gephyrocapsa spp. >5.5 fi LO (LG) 1.32 basis of major changes in lithofacies and/or mac- 7. Cyclococcolithus macintyrei HO (CM) 1.49 Rio and others (1990a) rofossil assemblages (Carloni and others, 1971). 8. Gephyrocapsa oceanica s.l. LO (Go) 1.62 Rio and others (in press) 9. Discoaster brouweri HO (Db) 1.85 Rio and others (1990a) Second, provinciality of the Mediterranean 10. Globorotaíia ínflala LO (Gì) 1.99 Hilgen (1988) 11. Globorotaíia bononiensis HO 2.33 fauna and flora has created problems in biostrat- 12. Discoasler pentaradiatus HO (Dp) 2.41 Rio and others (1990a) igraphically correlating the Mediterranean re- 13. Discoasler tamalis HO (Dt) 2.60 14. Sphacrmtlim'l!op*L\ spp. HO (Sph) 3.07 Zachariasse and others (1989) gion and the open ocean (Cita, 1973; Thunell, 15. Globorotaíia bononiensis LO 3.16 1979; Berggren, 1981; Rio and others, 1984). 16. Globorotaíia puncticulala HO (Gp) 3.38 17. Globorotaíia margarilae HO (Gm) 3.71 Langereis and Hilgen (1990) Finally, the inability to acquire good magneto- 18. Reticulofenestra pseudoumbilicus HO 3.58 Rio and others (1990a) 19. Discoasler asymmelricus LO (Da) 3.84 Channell and others (1990) stratigraphic data from most of the stratotypes 20. Globorotaíia puncticulala LO (Gp) 4.15 Channell and others (1988) has complicated the assignment of numerical 21. Globorolalia margarilae LO (Gm) 4.64 ages to the individual stages and has further im- LO = lowest occurrence; HO = highest occurrence. peded their correlation to extra-Mediterranean marine sequences (Rio and others, 1984). These problems have led to the conflicting use of some stage names (for example, Calabrian) and to the (Channell and others, 1990). The magnetostra- been reviewed in detail by Berggren (1971), development of disparate chronostratigraphic tigraphy presented in Figure 2 provides the abso- Berggren and Van Couvering (1974), and Cita scales (Harland and others, 1982; Rio and Spro- lute time control for the biochronology used in (1975b). In the following sections, we briefly vieri, 1986; Haq and others, 1987). our study. discuss only those stages which are frequently The goal of this paper is to discuss problems One of the objectives of Ocean Drilling Pro- used in the literature (Table 2). With the excep- with the currently accepted stage subdivisions of gram (ODP) Leg 107 in the Tyrrhenian Sea was tion of the Pliocene/Pleistocene boundary the Mediterranean Pliocene-lower Pleistocene to collect a continuous Pliocene-Pleistocene pe- (Aguirre and Pasini, 1985; Pasini and others, in (and its associated stratotypes) and to propose lagic sequence that would serve as a "deep-sea press), none of the Pliocene or Pleistocene stages an alternative chronostratigraphic scheme. To type section" and allow for direct correlation and their associated boundaries has been for- achieve this, a magnetobiochronology is pre- between the open-ocean record and the land- mally defined by the International Commission sented for the Mediterranean region that allows based marine sections in Italy (Kastens, Mascle, on Stratigraphy. As a result, the actual time both correlation of the Italian stratotype sections and others, 1987). Site 653 (40°15'N, 11°26'E) period represented by these stages is debated to the deep-sea record and estimation of the ab- was hydraulically piston-cored with this ob- due to different philosophical approaches to solute time represented by the various stratotype jective in mind. This site contains an excellent stratigraphy. sections. Our results clearly indicate that all of calcareous plankton biostratigraphy (Fig. 2) Pliocene-early Pleistocene time is not repre- (Glacon and others, 1990; Rio and others, 1. Miocene/Pliocene Boundary sented by the currently used stages and that 1990), but unfortunately the magnetic properties major revisions are needed to improve the of the sediments were such that a polarity stra- The Miocene/Pliocene boundary has tradi- chronostratigraphic resolution of this time tigraphy could not be resolved (Channell and tionally been considered to be coincident with interval. others, 1990). Fortunately, Sites 652 (40°21'N, the restoration of open-marine conditions in the 12°08'E) and 654 (40°34'N, 10°41'E), which Mediterranean following the Messinian salinity MAGNETOBIOCHRONOLOGY were rotary-drilled, yielded good magnetostra- crisis. Accordingly, Cita (1975b) proposed the tigraphy and biostratigraphy, particularly for the establishment of the boundary stratotype at For the present study, we have used the Pliocene (Fig. 2). Biostratigraphic correlation of Capo Rossello (Sicily), where the upper Mio- planktonic foraminiferal zonation of Cita Sites 652,653, and 654 and land sections allows cene Arenazzolo Formation (a brackish-water (1975a), as emended by Rio and others (1984), for calibration of bioevents in Site 653 with the facies) is overlain by the lower Pliocene Trubi and the calcareous nannofossil zonation of Raffi polarity time scale (Fig. 2). The resultant cal- Formation (an open-marine facies). Correlation and Rio (1979), as emended by Rio and others careous plankton biochronology (Fig. 3; Table of this boundary to the open-ocean record has (1990). In order to properly evaluate the time 1) provides a high-resolution time frame for been difficult because of the lack of a magneto- significance of the stage type sections and to Pliocene-Pleistocene time in the Mediterranean. stratigraphy in the type section and due to the correlate the Mediterranean record with the In particular, it provides a basis for correlating fact that upper Miocene strata at Capo Rossello global geologic record, it is necessary to calibrate the deep-sea and the land-based marine records, are nonmarine. and for evaluating the appropriateness and dura- these biostratigraphic schemes to the polarity According to Berggren and others (1985), the tions of stage stratotypes. time scale. Recently, some successful magneto- Miocene/Pliocene boundary is coincident with stratigraphic studies have been carried out on the basal part of the Gilbert Chronozone and has Italian land sections (Tauxe and others, 1983; PLIOCENE-PLEISTOCENE an age of —5.35 Ma. The magnetostratigraphic Zijderveld and others, 1986; Channell and oth- CHRONOSTRATIGRAPHY results from ODP Leg 107 (Channell and others, 1988; Hilgen and Langereis, 1988; Zachari- ers, 1990), as well as new results from land sec- asse and others, 1989, 1990), as well as on The history of development of Mediterranean tions in Calabria (Zijderveld and others, 1986; deep-sea material from the Tyrrhenian Sea Pliocene-Pleistocene chronostratigraphy has Channell and others, 1988) and Sicily (Hilgen

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FORAMINIFERA NANNOFOSSILS Figure 3. Mediterranean calcareous plank- MAGNETIC « ton biochronology for the Pliocene-Pleisto- POLARITY •a s BIOSTRATIGRAPHIC EVENTS cene derived from a calibration of the TIME SCALE bioevents listed in Table 1 with the polarity stratigraphy illustrated in Figure 2. increase E. hvxleyh z -e z E. hiLxleyii and Langereis, 1988), however, indicate that the

P. lacunosa r boundary is slightly younger. According to the latter studies, the Miocene/Pliocene boundary occurs slightly below the Thvera Subchrono- zone, within the upper part of the lowest re- versed interval of the Gilbert Chronozone. Ages

0.90 of 4.83 and 4.93 Ma have been estimated for the 097 I S2L boundary by Zijderveld and others (1985) and Gt. trunc. excels a SIL Channell and others (1988), respectively. The V g Capo Rossello section can be biostratigraphically correlated to ODP Site 653 and in turn related to the geomagnetic polarity time scale Gephyrocapsa > 5.5M t (Fig. 4). < Although there is now better control on the ss C. macintyreir < increase left age of the Miocene/Pliocene boundary in the >• G. oceanica S.LL D N. pachyderma Mediterranean, the selection of Capo Rossello as E<- a Ö S f a a stratotype remains a problem from a stratigraphic point of view. The lithologic break I D. brouweri-D. triradiatusr from nonmarine to marine sediments at the increase boundary is found throughout the Mediterra- Gt. inflata D. triradiatusi nean and is simply not amenable to biostratigraphic correlation. In order to properly define the Miocene/Pliocene boundary in a continuous marine sequence, a boundary stratotype should Gt. bononiensis be selected from outside the Mediterranean D. pentaradiatus r ? / yCHLg region.

CL. 8. D. tamalis 2. The Pliocene Series s -e, e N. atlantica Of the many stages proposed over the years 202 I for the Pliocene Series, only three are currently 2.99 L I Piacenzian (Table 2). Mayer (1867, 1889) in- Gt. bononiensis troduced the Tabianian Stage as the lowermost ci subdivision of the Pliocene, and the Tabiano Bagni section in northern Italy was later pro- Ct. puncticvlata E posed by laccarino (1967) as the stratotype for

S I Spkenotithus spp. r this stage. In the type section, the Tabianian consists of -140 m of blue clay. Biostratigraphic ^ H. R. pseudoumb. r correlation of the Tabianian type section to Ct. margaritae NN15 ODP Site 653 reveals that the basal Pliocene is NN14 CO D. asymmetricus L actually missing at Tabiano Bagni (Fig. 4). Spe- E FCO cifically, Globorotalia margaritae is present at the base of the blue clay, indicating that all of z z biozone MPL1 and perhaps part of MPL2 (Cita, Gt. puncticvlata H. sellii l 1975a) are missing at this locality. The top of the Tabianian type section is approximately coincident with the highest occurrence of G. a Cu •3 margaritae (ca. 3.7 Ma). Clearly, the Tabianian •S z as defined in its type locality cannot be used as a s z o reo z stage that is intended to include the lowest Plio- Gt. margaritae cene. End acme The Zanclean Stage was also established to o, 5o , Sphaeroidinellopsis to Co represent the lower part of the Pliocene (Se-

guenza, 1868). According to Seguenza (1868), TABLE 2. COMMONLY USED CHRONOSTRATIGRAPHIC UNITS FOR THE MEDITERRANEAN PLIOCENE-PLEISTOCENE TIME the Zanclean is above the upper Miocene and Stratotype Calcareous plankton below the middle or upper Pliocene Piacenzian biostratigraphic data Stage. As originally described, the Zanclean consists of foraminiferal-rich Trubi marl and A. Boundaries 1. Miocene/Pliocene Capo Rossello section, Cita and Gartner, 1973; sandy layers. The Trubi marl is a pelagic ooze Sicily (Cita, 1975b) Rio and others, 1984

that represents the re-establishment of open- 2. Pliocene/Pleistocenc Vrica section, Pasini and others, in press marine conditions in the Mediterranean at the Calabria (Aguirre and Pasini, 1985) beginning of the Pliocene. The Capo Rossello B. Pliocene Stages section in Sicily has been designated as the strat- 1. Piacenzian (Mayer, 1858) Castell'Arquato section. Colalongo and others, 1974; otype for the Zanclean Stage (Cita and Gartner, Piacenza Province Rio and others, 1988

1973; Cita, 1975b). In its type location, the Capo Rossello section, Cita and Gartner, 1973; 2. Zanclean (Seguenza, 1868) Agrigento Province, Sicily Rio and others, 1984 Zanclean is composed of—100 m of Trubi marl, (Cita and Gartner, 1973)

which lies unconformably on the Messinian Chiesa Nuova section, Iaccarino, 1967; 3. Tabianian (Mayer, 1867) brackish-water Arenazzolo unit (Fig. 4). Parma Province Raffi and Rio, 1980; (Iaccarino, 1967) Sprovieri, unpub. data The Zanclean stratotype has been studied in detail by Rio and others (1984) and can easily C. Pleistocene Stages 1. Calabrian (Gignoux, 1913) Santa Maria di Catanzaro section, Bayliss, 1969; Rio, 1974; be correlated to ODP Site 653 (Fig. 4). The Calabria (Bayliss, 1969) Sprovieri and others, 1973; lowest common occurrence of G. margaritae Ruggieri and others, 1984 2. Santernian Santemo River valley section, Colalongo, 1968; (ca. 4.64 Ma) at Capo Rossello is -11.50 m (Ruggieri and Sprovieri, 1977) Bologna (Ruggieri and others, 1975) Ruggieri and Sprovieri, 1977; above the base of the Trubi, and the Spkaeroidi- Raffi and Rio, 1980; Ruggieri and others, 1984 nellopsis Acme Zone (MPL1 of Cita, 1975) is 3. Emilian Santerno River valley section, Colalongo, 1968; below this level. Although the sharp transition (Ruggieri and Selli, 1950) Bologna Ruggieri and others, 1975; Ruggieri and others, 1984; from Arenazzolo to Trubi at Capo Rossello cer- Rio and others, in press

tainly represents a sharp environmental break, 4. Sicilian (Doderlein, 1872) Cava Puleo section, Ruggieri and Sprovieri, 1977; the stratotype for the Zanclean at least contains Ficarazzi, Palermo DiStefano and Rio, 1981; (Ruggieri and Sprovieri, 1977) Ruggieri and others, 1984 the lowermost Pliocene biozone. A significant S. Selinuntian No stratotype Ruggieri and Sprovieri, 1979; hiatus, however, occurs at the top of the Zan- (Ruggieri and Sprovieri, 1969) Ruggieri and others, 1984 clean stratotype (Fig. 4). The interval between the highest occurrence of Globorotalia puncticulata (ca. 3.4 Ma) and the highest occurrence of Discoaster tamalis (ca. 2.6 Ma) is missing, rep- and consequently the base of the Piacenzian 3. Pliocene/Pleistocene Boundary resenting a gap in the record of 700,000 to stratotype, do not correspond to the highest oc- 800,000 yr. currence of G. margaritae in the Mediterranean The age and recognition of the Pliocene/ The Piacenzian Stage was established by as previously thought (Cita, 1973; Berggren and Pleistocene boundary have long been controver- Mayer (1858), and its proposed stratotype is the Van Couvering, 1974; Rio and others, 1984) but sial issues. This is due, in large part, to different Castell'Arquato section in the Arda Valley of rather is slightly younger. Based on our biochro- philosophical approaches to defining the bound- northern Italy (Barbieri, 1967). The sequence in nology, the age of the base of the Piacenzian is ary (see Berggren and van Couvering, 1974; the Arda Valley was long considered to be con- between 3.6 and 3.4 Ma (between the highest Pelosio and others, 1980). Beginning with tinuous from the lower Pliocene through the occurrence of R. pseudoumbilicus and the high- Forbes (1846), many workers have defined the lower Pleistocene. The lower part of the se- est occurrence of G. puncticulata, respectively) Pliocene/Pleistocene boundary on the basis of quence consists of the epibathyal "Tabianian" (Fig. 4). climatic criteria (Beard, 1969; Lamb and Beard, blue clay, whereas the middle and upper parts of The top of the Piacenzian stratotype is above 1972; Boellstorff, 1978; Beard and others, the sequence are represented by littoral silty clay the highest occurrence of D. tamalis and below 1982). These workers equate the Pliocene/ and sand. the highest occurrence of D. pentaradiatus (Fig. Pleistocene boundary with the beginning of A re-examination of the biostratigraphy of the 4). This confines the upper limit of the Piacen- Northern Hemisphere glaciation. Recent studies, Castell'Arquato type section (Rio and others, zian to the short D. pentaradiatus Zone, with an however, clearly indicate that this important 1988; Raffi and others, 1989) and the correla- age of between 2.6 and 2.4 Ma. These nannofos- climatic event occurred at ca. 2.5 Ma (Backman, tion of this section to ODP Site 653 indicate that sil results are supported by the planktonic foram- 1979; Shackleton and others, 1984) and thus several problems exist with the Piacenzian strat- iniferal biostratigraphy. Both G. bononiensis predates the beginning of the Pleistocene. otype as it is presently defined (Fig. 4). First, a and G. crassaformis are present at the top of the In contrast, the correct approach to defining significant hiatus exists between the base of the Piacenzian stratotype, placing this level within the Pliocene/Pleistocene boundary is based on Piacenzian and the underlying "Tabianian" blue the lower or middle part of MPL 5. Globorotalia stratigraphic principles and recognizes the need clays. Planktonic foraminiferal biozone MPL3 inflata is not present at the top of the section, for establishing a boundary stratotype. The and the correlative C. rugosus and R. pseu- contrary to what has previously been reported boundary is a unique time horizon, and there- doumbilicus nannofossil zones are missing. This (Colalongo and others, 1974). Thus, the Piacen- fore, should represent a universal standard of represents a stratigraphic gap of at least 600,000 zian stratotype does not extend to the Pliocene/ reference for dating purposes. The Le Castella yr. The unconformity is marked by an indurated Pleistocene boundary as presently defined in the section in Calabria, southern Italy, was the first glauconitic horizon, and the benthic foraminif- Vrica section. As a result, there is a stratigraphic section to be proposed as a boundary stratotype eral and mollusc assemblages indicate a sudden gap of 0.8 to 1.0 m.y. between the top of the (see Pelosio and others, 1980). Several strati- change from epibathyal to littoral conditions Piacenzian stratotype section and the Pliocene/ graphic problems, however, exist with this (Rio and others, 1988). The age of this level, Pleistocene boundary. stratotype, making it unsuitable for defining the

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/103/8/1049/3381324/i0016-7606-103-8-1049.pdf by guest on 26 September 2021 Figure 4. Biostratigraphic correlation of Pliocene-Pleistocene stage and boundary ODP SITE 653 stratotype sections to ODP Site 653. The bioevents referred to as 1-21 are listed in BI0STRA11GRAPHY CO s Table 1. FORAMS NANNO Ssa se

STRATOTYPE SECTIONS I

S. MARIA 0to1 * DI CATANZARO 13 30 — 2 S FICARAZZI 40. H 50. n "3 is «cu I®

60 _ Small SANTERNO Gephyr. VR1CA

Large Gephyr. folic, sella Caie. TTULCint.

•m

•S3

LO Disc. CU •pent.

« cj CU

ds » Qi co CO ft. TABIANO BAGNI

çC

C\2

M PI 1

AGE Berggren and Von Couvering Van E^singa Ruggieri et al Ruggieri et al. Berggren Haq & Van Eysinga Haq et ni. (Ma) 1974 1979 1984 et al 1985 1986 1987

Tyrrhenian Tyrrhenian íyrrheniar

Milazzian Milazzian Milazzian

Milazzian

0.5 Sicilian Sicilian

Sicilian Sicilian

Emilian

Emilian Emilian

c c D o 1.0 Emilian U o CO co c c c o o D CT> C c c O o C c O c _Q o V) _o O Calabrian ZJ i— E Z5 E c

1.5 - c c D o CO co

Figure 5. Comparison of different uses of Pleistocene stages in different published time scales.

Pliocene/Pleistocene boundary (Pelosio and boundary (Pasini and others, in press). The recognizing the boundary both in the Mediter- others, 1980). marker bed is just above the top of the Olduvai ranean and the open ocean (Rio and others, in The problem of establishing an acceptable Subchronozone, yielding an age of -1.65 Ma press). Pliocene/Pleistocene boundary appears to have for the Pliocene/Pleistocene boundary (Tauxe been resolved with the acceptance of the Vrica and others, 1983). The highest occurrence of 4. The Pleistocene Series section (Calabria, southern Italy) as the strato- Discoaster brouweri at the base of the Olduvai type for the boundary (Aguirre and Pasini, and the lowest occurrence of Gephyrocapsa Seven chronostratigraphic units have been 1985). The top of laminated layer "e" in the oceanica s.l. slightly above the top of the Oldu- proposed for the marine Pleistocene Series in Vrica section is the marker horizon for the vai provide two good biostratigraphic events for Italy (Fig. 5). The stratigraphic relationships and

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MAGNETIC CALCAREOUS PLANKTON STANDARD AGES BIOSTRATIGRAPHY POLARITY POSITION 0F F0RAMS NANN0 TIME Berggren SCALE Cita,1975a Rio et al. STRATOTYPE SECTIONS et al., 1985 PROPOSED (emend.) 1990a acme H. hialeyi

o E. huxleyi a> Í-! C o~> G. oceanica i Cl> -Ö 0.5 _ OS -a CQ 3 « CSQ SS CL, G gg o P. lacunosa en S

tu tí 1.0. Dá -o Figure 6. Stratigraphie po- Small Gephyr. W S tu M o e- o sitions of stage stratotype tì cib Ë—< s g> S sections based on the biostra- Large Gephyr. GO (S 03 C (1985) is indicated on the -o a> M PI 6 a> right, along with the new 2.0. E chronostratigraphy proposed ta D. brouweri d in this paper.

2.5 _ LO M CL. \ \ \ \ \ M D. pentarad. O DÛ -=C

ÖCD a> 5 -s 3.0. i ca3 o fri c- D. tamalis ë § • -eC S -a e-a G -ö

M PI 4 -

-=c1 S s 's 's 's R. E— psevdoumb. Cd 13 a> a> C. Cu a G 4.0 _ M PI 3 Z ^ E-i rugosus M^ .28 o OS Pd .2 Cd Ö S CL CQ ¡-J -«c CS3 S-, C-J O to tO Cd w 4.5 _ PI 2 Amaurol. tricornicidatiis

M PI 1

correlations of these units, however, are poorly terranean Pleistocene chronostratigraphy is lim- singa, 1986; Haq and others, 1987) use some established, rendering them virtually useless out- ited to a discussion of these five units (Calabrian, combination of these five stages to subdivide the side the Mediterranean. Five of these units have Santernian, Emilian, Sicilian, and Selinuntian). lower-middle Pleistocene (Fig. 5); as a result, been defined in type or boundary stratotype sec- Most recent time scales (for example, Van there are significant discrepancies concerning the tions and can be biostratigraphically recognized Eysinga, 1975; Ruggieri and others, 1984; time represented by these stages. In addition, (Table 2). Our evaluation of the status of Medi- Berggren and others, 1985; Haq and Van Ey- both the Calabrian and Santernian Stages have

been used to represent the lowermost Pleisto- by a biocalcarenite bed above the dominance of didate for the Zanclean/Piacenzian boundary, cene. The Calabrian was defined by Gignoux small Gephyrocapsa (Fig. 4), the age of which is as suggested by Mazzei and others (1979). (1913) and subsequently designated as the estimated at -0.92 Ma. standard lowest Pleistocene stage at the 18th In- The Selinuntian was originally introduced as 2. Top of the Piacenzian Stage and Threefold ternational Geological Congress. More recently, a superstage for the lower Pleistocene, incorpo- Subdivision of the Pliocene Series Ruggieri and Sprovieri (1977) proposed the rating the Santernian, Emilian, and Sicilian Santernian as an alternative to the Calabrian for Stages (Ruggieri and Sprovieri, 1979); however, One of the unexpected findings of the present the lowermost Pleistocene. no stratotype section was indicated for this study is that the interval of time from 2.5 to 1.6 A biostratigraphic evaluation of the type sec- chronostratigraphic unit. The base of the Seli- Ma is not represented in any of the previously tions for the five lower and middle Pleistocene nuntian Superstage is defined by the Pliocene/ proposed stratotype sections (Fig. 4). In particu- units permits precise correlation with ODP Site Pleistocene boundary at Vrica, and its top is lar, the top of the Piacenzian Stage is dated at ca. 653 (Fig. 4). This correlatation allows us to de- coincident with the top of the Sicilian. More 2.5 Ma in the stratotype section at Castell'Ar- termine the ages, durations, and stratigraphic re- recently, Rio (1982) and Ruggieri and others quato. This places the end of the Piacenzian Age lationships of the various units. The most (1984) suggested that it would be more appro- very close to the initial development of extensive striking result is that the Calabrian stratotype priate to consider the Selinuntian as the stage North Hemisphere glaciation (Shackleton and section (Selli, 1971) at Santa Maria di Catan- representing all of the lower Pleistocene, with others, 1984). zaro (Calabria) is equivalent to, or younger than, the Santernian, Emilian, and Sicilian being rele- The Piacenzian Stage can be retained as a the Sicilian Stage as defined at Ficarazzi (Pa- gated to substage status. chronostratigraphic unit, but the usefulness of lermo). Specifically, the base of the Calabrian at extending it to the Pliocene/Pleistocene bound- 1 Santa Maria di Catanzaro (G-G bed of Gig- PROPOSED CHRONOSTRATIGRAPHY ary is debatable. We propose that the Piacenzian noux, 1913) is above the lowest occurrence of AND DISCUSSION Stage be limited only to that stratigraphic inter- Globorotalia truncatulinoides excelsa, which val present in the stratotype section (ca. 3.5-3.6 occurs below the Jaramillo Subchronozone at The calcareous plankton biochronology dis- to 2.5 Ma). According to this definition, the top ca. 1.1 Ma (Table 1). This is consistent with the cussed above (Fig. 3 and Table 1) provides the of the Piacenzian Stage would approximately conclusion of Ruggieri and Sprovieri (1977), basis for evaluating the stratigraphic relation- correspond to the beginning of the "glacial" Pli- who had suggested that the two stages (Cala- ships and usefulness of the Mediterranean Plio- ocene and should be easily recognized in both brian and Silician) were nearly synchronous. cene/Pleistocene stages. In particular, it allows marine and continental records. Therefore, the Calabrian Stage as it is presently us to determine the chronostratigraphy and to Utilizing this definition of the Piacenzian defined does not represent the lowermost Pleis- establish the appropriate stratigraphic criteria for Stage results in the interval from 2.5 to 1.6 Ma tocene, because there is a gap of at least 0.6 m.y. recognizing these stages on a global basis. It also not being represented by a chronostratigraphic between the Pliocene/Pleistocene boundary and allows us to determine whether or not the pro- unit. To rectify this situation, we propose a the base of the Calabrian stratotype section. posed stages form a complete stratigraphic se- threefold subdivision of the Pliocene Series, with On the basis of their observation that the Cal- quence representing all of Pliocene through the Zanclean and Piacenzian representing the abrian is younger than generally assumed, Rug- early Pleistocene time. The stratigraphic posi- lower and middle Pliocene, respectively, and an gieri and Sprovieri (1977) proposed the Santer- tions and durations of the stage stratotypes have unnamed stage for the upper Pliocene. This nian Stage to fill the gap between the Pliocene/ been determined (Fig. 6) using the discussed bio- proposal represents a major change in Pliocene Pleistocene boundary and the base of the Emi- chronology. Clearly, the stages as presently chronostratigraphy, but we believe that the lian (ca. 1.3 Ma). The lowest occurrence of G. defined do not represent a continuous record, threefold stage system provides a more practical oceanica s.l. (ca. 1.60 Ma) is just below the base and this poses problems for their recognition and subdivision of the Pliocene. The middle and of the Santernian type section (Santerno River usage. upper Pliocene would now approximately corre- valley, Bologna) (Rio and others, in press), and late with the "preglacial" and "glacial" Pliocene, as previously mentioned, this occurrence is just 1. Zanclean Stage and Zanclean/ respectively, and the recognition of three stages above the Pliocene/Pleistocene boundary mark- Piacenzian Boundary would enhance the chronostratigraphic resolu- er bed in the Vrica section. The top of the San- tion of the Pliocene. ternian or the base of the Emilian is marked by The absence of biozone MPL 1 at the base of the lowest occurrence of the benthic foraminifer the Tabianian type section means that at least 3. The Lower Pleistocene and the Hyalinea baltica. This event slightly postdates 250,000-300,000 yr of the early Pliocene are Calabrian Stage Problem the lowest occurrence of Gephyrocapsa spp. not represented (Fig. 6). Therefore, the Tabian- >5.5 fxm, which has been dated at ca. 1.32 Ma ian cannot be used as a chronostratigraphic unit As it is presently defined, the Calabrian strato- (Fig. 4). The Emilian Stage extends to just representing the lower Pliocene. Conversely, the type incorporates only the uppermost part of the below the lowest occurrence of Globorotalia Zanclean appears to represent the lower Plio- lower Pleistocene (Fig. 6). This raises the ques- truncatulinoides excelsa. cene. As shown in Figure 4, all of Pliocene time tion as to whether or not it is appropriate to use The Sicilian Stage was defined by Doderlein before the Piacenzian Age is represented in the the Calabrian as a chronostratigraphic unit rep- (1872), with a stratotype proposed by Ruggieri Capo Rossello section. The presence of an un- resenting most of the lower Pleistocene, as is and Sprovieri (1977) in the Ficarazzi section conformity, however, at the base of the Piacen- done in most time scales (Fig. 5). Two alterna- (Palermo, Sicily). The base of the Sicilian Stage zian Stage (Fig. 4), which by definition is the top tive options exist for the chronostratigraphy of is coincident with the lowest occurrence of of the Zanclean Stage (MacQueen and Oriel, the lower Pleistocene. First, the lower Pleisto- Globorotalia truncatulinoides excelsa, which 1977), requires the establishment of a boundary cene could be divided into three stages (Santer- slightly postdated the beginning of the domi- stratotype section for the Zanclean/Piacenzian nian, Emilian, and Sicilian), which, when taken nance interval of the small Gephyrocapsa (Di boundary. The Capo Rossello section, which together, appear to represent the entire time in- Stefano and Rio, 1981) (Fig. 4). At its type has a continuous record across the highest oc- terval from ca. 1.6 to 0.8 Ma. The other option locality, the top of the Sicilian Stage is marked currence of R. pseudoumbilicus, is a good can- is to incorporate all of this time interval into the

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Selinuntian Stage (Ruggieri and others, 1984). Pliocene deep sea record. A revision: Rivista Italiani di Paleontologia e Raffi, I., Rio, D., and Sprovieri, R., 1989, New stratigraphic data on the Stratigrafia, v. 81, p. 527-544. Piacenzian stratotype: Bolletino della Società Paleontologica Italiana, We suggest that the latter be adopted because 1975b, The Miocene-Pliocene boundary. History and definition, in v. 108, p. 183-1%. Saito, T., and Burckle, L. H., eds., Late Neogene Epoch boundaries: Rio, D., 1974, Remarks on late Pliocene-early Pleistocene calcareous nanno- the duration of the Selinuntian would be more Micropaleontology Special Publication, Volume 1, p. 1-30. fossil stratigraphy in Italy: Ateneo Parmense, Acta Naturalia, v. 10, Cita, M. B., and Gartner, S., 1973, Studi sul Pliocene e sugli strati di passaggio p. 409-449. in keeping with that of most other stages (Hed- dal Miocene al Miocene. IV. The stratotype Zanclean. Foraminiferal 1982, The fossil distribution of coccolithophore genus Gephyrocapsa berg, 1976; Rio, 1982). The Selinuntian Stage and nannofossil biostratigraphy: Rivista Italiani di Paleontologia e Strat- Kamtner and related Plio-Pleistocene chronostratigraphic problems: In- igrafia, v. 79, p. 503-558. itial reports of the Deep Sea Drilling Project, v. 68, p. 325-343. would, thus, be defined as the interval extending Colalongo, M. L., 1968, Cenozone a Foraminiferi e Ostracodi nel Pliocene e Rio, D., and Sprovieri, R., 1986, Biostratigrafia integrata del Pliocene- basso Pleistocene della serie del Santerno e del-l'Appennino romagnolo: Pleistocene inferiore mediterraneo in un'ottica di stratigrafia sistemica: from the Pliocene/Pleistocene boundary (as it is Giornale di Geologia, v. 35, p. 29-61. Bolletino della Società Paleontologica Italiana, v. 25, p. 65-85. represented in the Vrica section) to the top of the Colalongo, M., and Sartoni, S., 1979, Schema biostratigrafico per il Pliocene e Rio, D., Sprovieri, R., and Raffi, I., 1984, Calcareous plankton biostratigraphy il basso Pleistocene in Italia: Contributo Preliminare Carta Neotectonica and biochronology of the Pliocene-lower Pleistocene succession of Sicilian Substage (-800,000 yr B.P.). In this Italiana PuWicazione no. 251, p. 645-654. the Capo Rossello area, Sicily: Marine Micropaleontology, v. 9, Colalongo, M. L., Elmi, C., and Sartoni, S., 1974, Stratotypes of Pliocene and p. 135-180. way, the Santernian, Emilian, and Sicilian are Santemo River section: Mémoiies Bureau de Recberches Géologiques Rio, D., Sprovieri, R., Raffi, 1, and Valleri, G., 1988, Biostratigrafia e paleoeco- retained as substages within the Selinuntian. The et Minières, v. 78, p. 603-624. logia della sezione stratipica del Piacenziano: Bolletino della Società Di Stefano, E., and Rio, D., 1981, Biostratigrafia a nannofossili e biocronologia Paleontologica Italiana, v. 27, p. 213-238. Selinuntian also has some climatic significance del Siciliano nella località di Ficarazzi (Palermo-Sicilia): Ateneo Rio, D., Raffi, I., and Villa, G., 1990a, Pliocene-Pleistocene calcareous nanno- Parmense—Acta Naturalia, v. 17, p. 97-111. fossil distribution paneras in the western Mediterranean: Proceedings in that the top of this stage approximates the Doderlein, P., 1872, Note illustrative della carta geologica del Modenese e del of the Ocean Drilling Program, Scientific Results, Volume 107, Reggiano: Memoria IH, Modena, Italy, 76 p. p. 513-533. time at which there was an intensification of Forbes, E., 1846, On the connection between the distribution of the existing Rio, D., Sprovieri, R., Thunell, R., Vergnaud-Grazzini, C., and Glacon, C., Pleistocene glaciations and the establishment of fauna and flora of the British Isles and the geographical changes which 199(H), Pliocene-Pleistocene paleoenvironmental history of the western have affected their area, especially during the epoch of the Northern Mediterranean: A synthesis of ODP Site 653: Proceedings of the Ocean a strong 100,000-yr eccentricity cycle in the ice- Drift: Great Britain Geological Survey Memoir, Volume 1, p. 336-432. Drilling Program, Scientific Results, Volume 107, p. 513-533. Gignoux, M., 1913, Les formations marines Pliocenes et quaternaires de l'Italie Rio, D., Backman, J., and Raffi, I., in press, Calcareous nannofossil biochro- volume record (Shackleton and Opdyke, 1976; du sud et de la Sicìle: Lyon, France, Annals University Lyon, v. 36. nology and the Pliocene/Pleistocene boundary, in Van Couvering, J. A., Pisias and Moore, 1981; Ruddiman and Raymo, Glacon, G., Rio, D., and Sprovieri, R., 1990, Calcareous plankton Pliocene- ed., The Pliocene/Pleistocene boundary: Definition and worldwide Pleistocene biostratigraphy in the Tyrrhenian Sea (western Mediterra- correlation: Cambridge, England, Cambridge University Press. 1988). nean, Leg 107): Proceedings of the Ocean Drilling Program, Scientific Ruddiman, W., and Raymo, M., 1988, Northern Hemisphere climatic regimes Results, Volume 107, p. 683-693. during the past 3 Ma: Possible tectonic connections: Royal Society of Haq, B., and Van Eysinga, F., 1986, Geological timetable: Amsterdam, The London Philosophical Transactions, ser. B, v. 318, p. 411-430. ACKNOWLEDGMENTS Netherlands, Elsevier Publishers. Ruggieri, G., and Selli, R., 1950, II Pliocene e il Postpliocene dell'Emilia: Haq, B., Hardenbol, J., and Vail, P.. 1987, Chronology of fluctuating sea levels Giornale di Geologia, v. 20, p. 1-14. since the Triassic: Science, v. 235, p. 1156-1167. Ruggieri, G., and Sprovieri, R., 1977, Ricerche sul Siliciano di Palermo. Le Harland, W„ Cox, A., Llewellyn, P., Pickton, C., Smith, A. and Walters, R., argille del fiume Oreto: Bolletino della Società Paleontologica Italiana, We thank W. Berggien, W. Cavazza, R. In- 1982, A geologic time scale: Cambridge, England, Cambridge Univer- v. 94, p. 1613-1622. gersoll, and G. Vai for their careful reviews of sity Press, 131 p. 1979, Selinuntiano, nuovo superpiano per il Pleistocene inferiore: Bolle- Hedberg, H. D., ed., 1976, International stratigraphic guide. A guide to strati- tino della Società Paleontologica Italiana, v. 96, p. 797-802. this paper. This study was partially supported by graphic classification, terminology and procedure: New York, Wiley, Ruggieri, G., Buccheri, G., Greco, A., and Sprovieri, R., 1975, Un affioramento 200 p. di Siciliano nel quadro della reviosione della stratigrafia del Pleistocene NATO Grant 870119 to R. Thunell and D. Rio, Hilgen, F. J., and Langereis, C. G., 1988, The age of the Miocene-Pliocene inferiore: Bolletino delta Società Geologica Italiana, v. 94, p. 889-914. boundary in the Capo Rossello area (Sicily): Earth and Planetary Ruggieri, G., Rio, D., and Sprovieri, R., 1984, Remarks on the chronostrati- and MPI grants to D. Rio and R. Sprovieri. 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