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The Siquisique Ophiolites, Northern Lara State, Venezuela: a Discussion on Their Middle Jurassic Ammonites and Tectonic Implications

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The Siquisique Ophiolites, Northern Lara State, Venezuela: a Discussion on Their Middle Jurassic Ammonites and Tectonic Implications The Siquisique ophiolites, Northern Lara State, Venezuela: A discussion on their Middle Jurassic ammonites and tectonic implications P. E. BARTOK Sohio Petroleum Company International, Exploration Department, 5151 San Felipe, Houston, Texas 77210 O. RENZ Naturhistorisches Museum, Augustinergasse 2, Basel CH-4001, Switzerland G.E.G. WESTERMANN McMaster University, Hamilton, Ontario, Canada L8S 4M1 ABSTRACT by O. Renz and G. Coronel (1959, unpub. data) basalts. The age would, therefore, confirm a pre- that indicated a Late Jurassic age and, more Callovian marine incursion into a proto-Carib- Ammonites from the pillow basalt associa- recently, by Stephan (1980) that suggested an bean rift. tions of the Siquisique ophiolites located in Early Cretaceous (Barremian) age for this west-central Venezuela indicate a minimum general area. REGIONAL GEOLOGY Bajocian to early Bathonian age for em- The new ammonite collection discussed in placement of the complex. The ammonites this paper indicates an age at least as old as Discussions on the geologic setting of the Si- have been identified as IStephanoceras Bajocian for the initial formation of the Siqui- quisique ophiolites have been, and continue to (Skirroceras) cf. macrum (Quenstedt), lEmi- sique ophiolites. The fossils appear to lie in al- be, controversial. Siquisique's veritable isolation leia ex gr. multiformis (Gottsche) et quen- tered shaley sediments enveloped by pillow from contemporaneous rock units, its complex stedti Westermann, and IParkinsonia sp. This association of cosmopolitan Pacific and Tethyan elements aids in the location of the western end of the Middle Jurassic seaway set between the Tethys and the Pacific Oceans (Hispanic Corridor). The apparent age of the ammonites indicates that some of the Siquisique sediments, pillow basalts, and serpentines are the oceanic remnants of an arrested early phase of rifting between North and South America. INTRODUCTION Establishing the age and structural setting of the Siquisique ophiolite complex, cropping out in west-central Venezuela, has been an elusive quest. New ammonite collections from this se- quence provide evidence for its minimum age and thus yield information pertaining to the early rifting of North and South America. The Siquisique complex lies within a region affected by Mesozoic through Tertiary deformation. Its samples were studied by Schilling and Niggli (in Shell International, 1965) and classified as an ophiolite assemblage. Early investigators, including O. Renz, in the Barqulsimeto - Flysch Basin Merida Andes-Plunging below with large debris flows con- Barquislmeto- Flysch Basin 1940s and 1950s, had postulated a Cretaceous taining Jurassic and Cretaceoua age for the strata associated with the Siquisique components Siquisique Ophiolites ophiolites because they were lithologically sim- Coastal Range Moderate to high ilar to some of the Cretaceous sediments of the Pre-Paleocene Metamorphlam V.O. Villa de Cura Volcanics Merida Andes located to the southwest (Fig. 1). Later, some ammonites were found in this area Figure 1. General location map of the Siquisique ophiolites, west-central Venezuela. Geological Society of America Bulletin, v. 96, p. 1050-1055, 5 figs., August 1985. 1050 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/8/1050/3445007/i0016-7606-96-8-1050.pdf by guest on 02 October 2021 SIQUISIQUE OPHIOLITES, VENEZUELA 1051 geology, and lack of geophysical exploration have inhibited an understanding of its age and mode of emplacement. The Siquisique complex is surrounded by upper Tertiary sequences to the north. These overlie Mesozoic units that have been poorly explored but that appear to be a more basinal equivalent of the sediments present in the Mara- caibo Basin (Bartok and others, 1981). A Paleocene-Eocene flysch sequence containing Jurassic and mainly Cretaceous olistostromes crops out south of the study area. Two opposing views have been generally considered as pre- ferred hypotheses for emplacement of the Siqui- sique complex: (1) long-distance translation of an obducted slab of Mesozoic oceanic crust over the South American craton (Stephan, 1980) and (2) parautochthonous to autochthonous forma- tion of the Siquisique complex. The latter view is preferred by the present authors. The possibility of a westward extension of the Villa de Cura island-arc complex to include the Siquisique area (Fig. 1) (Sebastian Bell, 1983, personal commun.) appears improbable because of the Villa de Cura's geochemical affinity with, and similar age to, the Netherlands Antilles island-arc complex (Beets and others, 1984). Furthermore, the Bocono megashear (Figs. 1 and 2), having a 200-km dextral displacement (Schubert, 1984), would have placed the Siqui- sociated with northern South America terranes tamaria and Schubert, 1974). The samples dis- sique unit in a more southerly position at the have been dated. Examples of these igneous/ cussed in this report are among the oldest time of emplacement (Maze, 1984). In fact, by metamorphic units are the Sebastopol Complex sedimentary or metasedimentary sequences invoking the same offset and extending the area (±425 Ma), located in the central Coastal Range documented in the region. influenced by the Bocono fault as far north as near Caracas (Gonzales de Juana and others, Marine Jurassic early rift sequences are well the Netherlands Antilles trend, the reconstruc- 1980), and the El Amparo granite (±265 Ma) represented in the Gulf of Mexico area (Imlay, tion would juxtapose the Villa de Cura and the cropping out on the Paraguana Peninsula (San- 1943) but poorly documented in northern South Netherlands Antilles trends (Fig. 2). The possibility that the Siquisique region con- stitutes a principal suture between the Caribbean and South American plates was disputed in some parts by Bonini (1984). He contended that recently gathered aeromagnetic data indicates the existence of such a suture lying along an east-west trend located near the city of Coro (Fig. 1). This does not preclude the possibility of an earlier aborted rift, allowing for ultramafic assemblages to be introduced into a marine setting. There is ample evidence for rifting in northern South America as early as the Triassic (Bene- detto and Odreman, 1977; Salvador and Green 1980). Extensive red-bed deposition has been reported throughout the Caribbean Basin (Maze, 1984), and Jurassic marine incursions have also been observed (Renz, 1956, 1960; Geyer, 1976; Schmidt-Effing, 1981). It is within this rift framework that the Siquisique ophiolites were emplaced. Both igneous/metamorphic sequences and Figure 3. Early Middle Jurassic reconstruction of Pangea (Bernoulli, 1981; Westermann, fossil-bearing sediments and metasediments as- 1984), with approximate location of Hispanic Corridor. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/96/8/1050/3445007/i0016-7606-96-8-1050.pdf by guest on 02 October 2021 1052 BARTOK AND OTHERS America. The oldest Mesozoic marine rift se- the Macuira Group (Renz, 1960; MacDonald, orogenic phase referred to as the Caribbean oro- quences recorded in the region (Fig. 3) are the 1968). The Rancho Grande Formation is over- gen and connected with the influx of extensive Sinemurian to Pliensbachian sediments located lain by paralic sequences of the Cocinas Group debris flows into the Barquisimeto-Guarico in the Huayacocotla Basin, Mexico (Schmidt- (Geyer, 1977), the upper unit of which contains Flysch Basins (Renz, 1982, p. 66), and (3) the Effing, 1981), and at Morrocoyal, along the Kimmeridgean ammonite suites (Renz, 1956, Andean orogeny (late Miocene-Pliocene) which northern limits of the Colombian Central Cor- 1960, p. 322). Strongly deformed normal ma- resulted in the dominant folding observed in the dillera (Geyer, 1976). Other Jurassic marine se- rine Cretaceous sediments overlie both series. Falcon Basin. quences from either the parautochthonous or These sediments are, in turn, partially covered The similarities of the sedimentary sequences allochthonous Caribbean province are now by Tertiary paralic to marine sequences (Lock- among the Guajira, Paraguana, and Siquisique documented in the Cuban Pinar del Rio prov- wood, 1966). areas, combined with their general temporal af- ince (Wiezbowski, 1976), the Colombian Gua- The basement complex of the Paraguana Pe- finity, suggest that they may represent co-genetic jira (Renz, 1956, 1960), the Paraguana Penin- ninsula is made up of the Permian El Amparo isolated terranes. The structural relationships of sula (MacDonald, 1968), and the Siquisique granite which intrudes phyllite-grade metamor- the three cannot be established, nor can their region (present report). Ammonite assemblages phics. These are overlain by an arkose com- original position be determined. The one com- in the first three suggest an Oxfordian to Titho- posed of granite wash; its sand grains contain mon element among them is that they are all nian age for their marine component. Geyer conspicuous blue quartz commonly found in the located north of, or on, the Oca and the Falcon (1977) inferred that the associated units underly- Guayana Shield granites, as well as in granites Basin fault systems (Fig. 1), as well as west of ing the fossiliferous sequences in the Guajira located north of the Cuiza fault in the Guajira the Bocono fault. may be as old as Middle Jurassic. This latter age (Renz, 1960). This unit is followed by the slaty is now documented for the Siquisique area. shales of the Pueblo Nuevo Formation that in-
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