Tethyan magnetostratigraphy from Pizzo Mondello (Sicily) and correlation to the Late Triassic Newark astrochronological polarity time scale Giovanni Muttoni† Department of Earth Sciences, University of Milan, Via Mangiagalli 34, I-20133 Milan, Italy Dennis V. Kent Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA and Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA Paul E. Olsen Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA Piero Di Stefano Department of Geology and Geodesy, University of Palermo, Corso Tukory 131, I-90134 Palermo, Italy William Lowrie Stefano M. Bernasconi Fátima Martín Hernández Departement Erdwissenschaften, ETH-Zentrum, CH-8092 Zürich, Switzerland ABSTRACT early part of the Newark APTS. We prefer marine stages, historically based on ammonoid option #2 in which the Carnian-Norian biostratigraphy, to continental successions. For We present the magnetostratigraphy and boundary based on conodonts, as well as the Late Triassic, an astrochronology anchored stable isotope stratigraphy from an expanded its closely associated positive δ13C shift, cor- to magnetostratigraphy and radiometric dates is (~430-m-thick) Upper Triassic marine lime- respond to Newark magnetozone E7 at ca. available from the Newark continental section stone section at Pizzo Mondello, Sicily, and 228–227 Ma (adopting Newark astrochronol- (Kent et al., 1995; Kent and Olsen, 1999; Olsen review published biostratigraphic informa- ogy), implying a long Norian with a duration and Kent, 1999), while magnetostratigraphy is tion that can be used to defi ne the location of ~20 m.y., and a Rhaetian of ~6 m.y. dura- thus far available in conjunction with marine of the conodont Carnian-Norian and Norian- tion. These ages are in fact not inconsistent biostratigraphy in the Tethyan realm. Continen- Rhaetian boundaries in this section. Pizzo with the few high-quality radiometric dates tal astrochronology and marine biostratigraphy Mondello offers good potential for magneto- that are available for Late Triassic time scale can therefore be correlated using the global stratigraphic correlation of marine biostrati- calibration. Based on its good exposure, record of polarity reversals for the construction graphic and chemostratigraphic data with accessibility, stratigraphic thickness and of an integrated Late Triassic time scale. Funda- the continental Newark astrochronological continuity, and multiple chronostratigraphic mental steps in this direction have already been polarity time scale (APTS) for development correlation possibilities, we propose Pizzo taken, but the issue is not yet settled (e.g., Mut- of an integrated Late Triassic time scale. Mondello as global stratigraphic section and toni et al., 2001a; Krystyn et al., 2002; Gallet et The relatively stable average values of δ18O point for the base of the Norian. al., 2003; Channell et al., 2003). centered on 0‰ are a strong indication that In this paper, we present magnetostrati- the Cherty Limestone at Pizzo Mondello Keywords: magnetostratigraphy, biostratig- graphic and chemostratigraphic data and suffered very little diagenetic overprinting. raphy, Late Triassic, Tethys, Sicily, Newark review biostratigraphic data from the literature, The conodont Carnian-Norian boundary astrochronological polarity time scale. from a ~430-m-thick Upper Triassic pelagic is located 12.5 m above a positive shift of limestone section located at Pizzo Mondello δ13C. A statistical approach was applied to INTRODUCTION in Sicily (Italy). This study represents the con- evaluate various Pizzo Mondello to Newark tinuation and, as far as magnetostratigraphy is magnetostratigraphic correlations. Two cor- Two apparently contrasting options for the concerned, completion of a magneto-biostrati- relation options have the highest correlation Late Triassic geomagnetic polarity time scale, graphic study conducted on the same section coeffi cients. In option #1, the base of Pizzo based on magnetostratigraphic data from the from its base up to meter level ~150 across the Mondello correlates with the middle part Tethys marine realm (Turkey) and continental conodont Carnian-Norian boundary (Muttoni of the Newark APTS, whereas in option #2, North America (western United States and et al., 2001a). the base of Pizzo Mondello starts toward the Newark Basin), are reported in Gradstein et Pizzo Mondello offers good potential for al. (1995). Resolving uncertainty about the correlation with the Newark APTS by virtue †E-mail: [email protected]. Late Triassic time scale requires correlation of of its simple diagenetic history, which allowed GSA Bulletin; September/October 2004; v. 116; no. 9/10; p. 1043–1058; doi: 10.1130/B25326.1; 11 fi gures; 1 table. For permission to copy, contact [email protected] © 2004 Geological Society of America 1043 MUTTONI et al. Figure 1. The Pizzo Mondello section is located in Sicily (A), and particularly in the Sicani Mountains of central-western Sicily (B). The section crops out near the village of Bivona at the locality La Cava along the Acque Bianche Creek (C, D) (section coordinates: topographic sheet 266 I NE “Bivona”; lat. 37.6°N, long. 13.4°E). preservation of the original magnetostrati- al., 2002). The aim of this paper is to correlate GEOLOGY graphic signal, as well as stratigraphic continu- marine age-diagnostic fossils as well as stable ity, with strata in strict stratigraphic superposi- isotope data from the Pizzo Mondello magne- The Pizzo Mondello section is located in tion, and relatively high rates of sedimentation tostratigraphic section to the Newark APTS the Neogene fold-and-thrust belt of the Sicani (20–30 m/m.y.) compared to classic Tethyan for construction of an integrated Late Triassic Mountains of western Sicily (Fig. 1). The sections of the Hallstatt type (e.g., Krystyn et time scale. Sicani Mountains are composed mainly of 1044 Geological Society of America Bulletin, September/October 2004 TETHYAN MAGNETOSTRATIGRAPHY FROM PIZZO MONDELLO (SICILY) Muttoni et al. (2001a)a this study Figure 2. The Late Triassic Pizzo Mondello section, whose ~150-m-thick basal part strad- dling the conodont Carnian- Norian boundary was studied by Muttoni et al. (2001a). The upper part of the section, up to meter level ~430 in the upper- most Norian, is the subject of this study. pelagic sediments of Permian to Cenozoic age, Muttoni et al. (2001a) analyzed the magne- from the lower ~150 m of the section (samples deposited in a Tethyan basinal setting of Afri- tostratigraphy and conodont biostratigraphy Pm1–46; Fig. 3). These authors placed the Car- can (Gondwanan) affi nity (Di Stefano, 1990; of units (i) and (ii) (Fig. 3). In this paper, we nian-Norian boundary in a conservative strati- for additional information, see Muttoni et al., present magnetostratigraphic data essentially graphic interval between the last occurrences of 2001a). The section, relatively well exposed and from unit (iv), chemostratigraphic data from the M. polygnathiformis and M. nodosus at meter continuous (Fig. 2), starts at the base with a few whole section [units (i) to (iv)], as well as an level 66.5 (sample Pm18) and the fi rst occur- meters of (unsampled) poorly outcropping marls overall interpretation of the available biostrati- rence of E. triangularis at meter level 105.5 and marly limestones of early-late Carnian age graphic data from the literature. (sample Pm31). Krystyn et al. (2002) reported of the uppermost Mufara Formation (Di Stefano data from fi ve new samples (samples K1–5; and Gullo, 1997; Buratti and Carrillat, 2002) BIOSTRATIGRAPHY Fig. 3), made an overall reinterpretation of the (Fig. 3). These are overlain by ~430 m of evenly conodonts distribution of Muttoni et al. (2001a), bedded to nodular cherty calcilutites, hereafter Triassic stage boundaries are historically and placed the Carnian-Norian boundary close referred to as Cherty Limestone (known also established using ammonoids. These are pres- to the last occurrence of M. communisti at meter as “Halobia” Limestone; De Capoa Bonardi, ent at Pizzo Mondello (Gemmellaro, 1904); level ~97 in the upper part of the stratigraphic 1985). The Cherty Limestone is overlain by a however, they have not yet been studied with interval of Muttoni et al. (2001a). A positive few tens of meters of poorly exposed lower to modern stratigraphic criteria. The age of the carbon isotope shift (described below) is located middle Rhaetian calcilutites and marls (Portella Pizzo Mondello section is therefore based 12.5 m below Krystyn et al.’s (2002) conodont Gebbia Formation), which are disconformably on conodont biostratigraphy as a proxy for Carnian-Norian boundary (Fig. 3). overlain by Jurassic sediments (Gullo, 1996). the ammonoid zonation (e.g., Krystyn, 1980; The Cherty Limestone is subdivided, from base Krystyn et al., 2002). The Norian and Rhaetian to top, into four lithostratigraphic units (Fig. 3): i. A basal 3-m-thick interval located just The Carnian-Norian Boundary The breccia level of unit (iii) is within the above the Mufara Formation and characterized early Norian (Gullo, 1996; A. Nicora, 2003, by calcilutites with rare chert nodules; The ammonoid Carnian-Norian boundary personal commun.) and does not seem to be ii. A 143.5-m-thick interval of dm-thick, well- is approximated by conodonts using the fi rst associated with a major biostratigraphic gap. bedded white calcilutites with black chert nod- appearances of Metapolygnathus communisti A, The overlying unit (iv) contains Norian con- ules,