Stratigraphic, geochronologic, and paleomagnetic constraints on Late Cretaceous volcanism in northern Israel

Segev, A., Sass, E., Ron, H., Lang, B., Kolodny, Y., McWilliams, M. 2002. Stratigraphic, geochronologic, and paleomagnetic constraints on Late Cretaceous volcanism in northern Israel. Isr. J. Earth Sci. 51: 297–309. Late Cretaceous volcanism in northern Israel is represented by basaltic pyroclastics and lavas at two adjacent localities at Mount Carmel and the Umm el Fahm area. Four Cenomanian and one Senonian volcanic intercalation occur in the marine succession. These volcanic rocks were dated by the Ar/Ar and K–Ar techniques using whole rock, amphibole megacrysts, and plagioclase fractions. Paleomagnetic measurements were performed on the Senonian pyroclastics. Amphibole from the oldest Cenomanian volcanic unit in Mount Carmel (the Kerem Maharal pyroclastics, at the base of the Chalk Complex) yielded an age of 97.1 ± 1.7 Ma. The penultimate Cenomanian volcanic unit in Mount Carmel (basalt at Nahal Raqefet and Muhraqa) yielded a whole-rock age of 96.7 ± 0.5 Ma. The youngest Cenomanian volcanic intercalation in the Umm el Fahm area (basalt at Me-Ammi) yielded a whole-rock age of 95.4 ± 0.5 Ma. Amphiboles from the Senonian Bat Shelomo pyroclastics, the youngest volcanic unit in the area, yielded an age of 82.0 ± 1.3 Ma. Three conclusions may be drawn from our new radiometric ages: (1) The major volcanic events operated synchronously at Mount Carmel and the Umm el Fahm area. (2) The chalk complex of Mount Carmel and the Deir Hanna Formation in the Umm el Fahm area are stratigraphically correlated. (3) The new radiometric results agree with biostratigraphically-derived ages, but provide better time constraints for the lithostratigraphic units. The data help to settle previous correlation controversies: the Albian–Cenomanian boundary is set below the top of the Yagur Formation, and the Cenomanian–Turonian boundary, above the base of the Muhraqa Formation. INTRODUCTION Mount Carmel and the Umm el Fahm area are the only localities in northern Israel where Late Cretaceous volcanic activity is recorded (Sass, 1968, 1980; Sass and Bein, 1982; Garfunkel, 1989). Basaltic volcanic units, predominantly pyroclastics at Mt. Carmel and mostly flows in the Umm el Fahm area, are interbedded within a ~300-m-thick sequence of marine carbonates. These units have great potential for use in stratigraphic correlation. Conventional stratigraphic correlation has been difficult in this area for three reasons: 298 Israel Journal of Earth Sciences Vol. 51, 2002 1. Facies changes are common in the Mount Carmel sequence, related to the proximity of the area to the platform edge during the Cenomanian and Turonian, and to the effect of protruding structures (reefs, volcanoes) on adjacent and distal environments. In contrast, the Umm el Fahm area was located at the inner part of the platform and is characterized by monotonous and gradual facies variations. 2. The Mount Carmel sequence is intensively faulted (Picard and Kashai, 1958; Ron et al., 1990), making it difficult to track facies changes across fault blocks. 3. Mount Carmel is separated from the adjacent Umm el Fahm area by a syncline (Fig. 1), that does not allow direct comparison of stratigraphic boundaries across the different platform subenvironments (edge, inner part). Stratigraphic correlation using the volcanic units has been only partly successful due to their limited geographic extent. While correlation is theoretically feasible for distances up to ~10 km, it is impractical for larger distances, such as between the northern and southern parts of Mount Carmel, or between Mount Carmel and the Umm el Fahm area. Using the absolute ages of the volcanic rocks and imposing the constraints of geomagnetic polarity data, we hoped that correlation would be possible over a larger area. This paper presents a preliminary chronostratigraphic framework for the Upper Cretaceous section in Mount Carmel and the Umm el Fahm area, integrating new Ar/Ar age determinations and paleomagnetic analyses with published biostratigraphic data. GEOLOGICAL SETTING Mount Carmel (MC) and the Umm el Fahm area (UFA) are elevated topographic features separated by a syncline (Fig. 1). Both consist of Cretaceous marine successions, subdivided into two parts (Fig. 2), the older Judea Group (hard carbonate rocks) and the overlying Mount Scopus Group (mostly soft carbonates and marls). The Mount Scopus Group is quite uniform across a wide area in northern Israel, but Judea Group sections at both localities are quite dissimilar. Stratigraphic relationships within the Judea Group of Mount Carmel (Fig. 2) are quite complicated, as marked facies changes occur across short and long distances (Kashai, 1958; Picard and Kashai, 1958; Bein, 1974, 1977; Sass, 1980; Sass and Bein, 1982). Central and northern Carmel are made up principally of the “Main Chalk Complex” (Picard and Kashai, 1958), which overlies the dolomitic Yagur Formation. In contrast, in the southern part, the equivalent section consists mostly of limestones, dolomites, and reef structures. Lithostratigraphic correlation between the northern and southern areas is uncertain and controversial. The Main Chalk Complex is overlain by a succession of reef-related limestones (reef cores, reef talus, bioclastic limestones), dolomite in places, and an intermediate marl unit (comprising the Muhraqa, Daliyya, and Umm E Zinat formations). Southward, the marl unit wedges out and disappears, reef structures are scarce, and an undivided limestone succession (the Shune Formation) is found. Locally developed volcanic rock units, mostly pyroclastic, are common as lenticular intercalations in the chalk and in the equivalent limestone/dolomite succession. Each of these units has a limited lateral extent (up to ~6 km) and a maximum thickness of ~60 m. Stratigraphic relationships in the Umm el Fahm area are much simpler, and the major lithostratigraphic units retain their identity over the entire area (Fig. 2). The Cretaceous section, roughly equivalent to that at MC, consists of the Deir Hanna and Sakhnin formations, dolomitic divisions that display no evident similarity or correlation with MC. The only similarity is the occurrence of volcanic intercalations in both areas, but there are significant differences between the two areas. The volcanic intercalations in the UFA are restricted to the Deir Hanna Formation. Most of the volcanic units at MC occur in the Cenomanian chalk and equivalent limestone/dolomite sections, while a single one is contained in the younger Senonian En Zetim Formation. Most of the volcanic rocks in the UFA are basaltic lava flows, with the exception of the youngest unit, which consists of pyroclastics. The opposite is true at MC, where most of the volcanic units are pyroclastics, and basaltic lava flows terminate the local volcanic activity. Of the five volcanic units in the UFA, only the two lower ones have a restricted extent. The other units persist across the entire areas of their exposed host stratigraphic units, with variations in thickness. In summary, the Judea Group sections at MC and the UFA are quite dissimilar. This observation, combined with the scarcity of index fossils in dolomites and in most limestones, has produced controversy in stratigraphic correlations (Fig. 2). According to some authors (e.g., Bartov et al., 1981; Flexer et al., 1981), the Chalk Complex at MC correlates with both the Deir Hanna and Sakhnin formations of the UFA, and A. Segev et al. Late Cretaceous volcanism in northern Israel 299 150 160 155 165 170 175 145