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Radiolarian biochronology and paleoceanography of Pacific Terranes in Central America and the Caribbean

Abstract

Mesozoic radiolarian biochronology has made great advances in the last decades and has been the basis of a fundamental re-evaluation of the geologic history of the world's major Mesozoic ocean basins: Panthalassa and Neotethys. Most of their ocean floor has been subducted, except for the Pigafetta Basin in the NE Pacific, where Middle-Late Jurassic radiolarites were drilled beneath the extant ocean floor (ODP Site 801, Ogg, et al. 1992, Matsuoka 1992). While remnants of Tethyan and Panthalassan MORB's are rare, oceanic plateaus, seamounts and intra-oceanic arcs are abundantly preserved in Circum-Caribbean, Circum-Pacific and Himalayan terranes. All these terranes share a similar Late Palaeozoic to early Late Cretaceous paleoceanography, which is expressed by the dominance of long, continuous series of radiolarian-rich, ribbon-bedded chert (radiolarites) and siliceous shale/mudstone (Baumgartner 2013). These open-ocean, low- to mid-latitude paleo-environments can be characterized by warm-temperate mesotrophic surface waters with a scarcity of calcareous plankton (hence, a generally shallow CCD), where radiolarians did not have to compete for food with other plankton. Upwelling has been invoked by many authors to explain radiolarites. It certainly resulted in higher radiolarian productivity along the equatorial convergence, the E-Panthalassa margin and perhaps along intra-oceanic arcs and plateau margins (Fig.1). A "Mega-Monsoon" situation was envisaged for the Neotethys (Fig. 1, De Wever et al. 2014, Ikeda et al. 2017) accounting again for marginal upwelling. However, upwelling alone cannot explain Mesozoic radiolarite occurrences throughout Circum-Pacific terranes. Si and O stable isotope (B.le et al. 2017) data seem to indicate that the Mesozoic world oceans were less under-saturated in silicic acid than the modern oceans, resulting in better radiolarian preservation. In contrast, the much smaller Jurassic-Early Cretaceous "Intra-Pangean Basins" (IPB), such as the Central Atlantic, Proto-Caribbean and the Gulf of Mexico shared an oceanographic setting with more oligotrophic surface waters resulting in the predominance of claystones (below CCD) and pelagic carbonates (Ogg et al. 1983). Jurassic Radiolarites have not been recovered from the early Central Atlantic, nor from the Late Jurassic - early Cretaceous Proto-Caribbean. Here, Middle Jurassic clay-rich sediments gave way to the first planktonic carbonates since the Late Jurassic. These IPB nannofossil carbonates were dominated by Nannoconus during the latest Jurassic and Early Cretaceous. This nannofossil group was virtually absent from Panthalassa. It is noteworthy that during the middle and Late Cretaceous biosiliceous events do exist in the IPB: they are generally discontinuous and correlated with the well known Oceanic Anoxic Events and resulted in short successions of dark green to black, organic-rich cherts. This coarse, global Mesozoic paleoceanographic subdivision allows the safe conclusion that the Circum-Caribbean occurrences of Late Triassic to Early Cretaceous red ribbon bedded radiolarites and associated mafic oceanic basement rocks are of Panthalassan-Pacific origin. Radiolarites are not compatible with coeval pelagic limestone series formed in the IPB. The following review of radiolarian work on the Caribbean Plate and adjacent areas will support this conclusion. Here we distinguish 3 main categories of radiolarian-rich siliceous sediments (Fig.2). 1. Ribbon radiolarites (predominantly red, but may be green or black in restricted basins, or related to OAEs) are typical open ocean sediments, formed far from detrital sources, such as arcs and continents. Chert/shale couplets are thought to represent short term orbital cycles (20-100 kyr, Ikeda et al. 2010) in which the shale is the background (aeolian) sedimentation and the chert reflects high radiolarian productivity episodes. In the Circum-Caribbean realm this facies is, without exception, related to mafic/ultramafic basement/plateau/primitive island arc rocks. For the description of terranes see Baumgartner et al. this volume. Rhaetian Radiolaria were recovered from a block in the El Castillo Serpentinite M.lange, Mesquito Composite Oceanic Terranes (MCOT Fig. 2, S. Nicaragua, Baumgartner et al. 2008). Pliensbachian-Lower Toarcian Radiolaria (Bandini et al. 2011a) were recovered from thnly ribbon-bedded radiolarites of the Santa Rosa Accretionary Complex (SRAC, Fig. 2), Santa Elena Peninsula. These radiolarites are pervasively intruded by 174 -177 Ma old (Toarcian-Aalenian) Petit-Spot-like alkaline sills (Buchs et al. 1913, Pilet et al. 2016). Several other tectonic slivers in the SRAC contain ribbon radiolarites yielding Middle Jurassic to Albian radiolaria (Bansini et al. 2011a). A Late Albian-Early Cenomanian age was reported by Schmidt-Effing (1980) from the SRAC exposed in the Potrero Grande tectonic window. Aalenian to Cenomanian Radiolaria from ribbon-bedded radiolarites in a possible stratigraphic relation with MORB-type basalts (Joly et al 1998) were obtained from the Berneja Complex (Fig. 2), Puerto Rico, by Bandini et al. (2011b). Earlier work by Montgomery et al (1994a) stated an Early Jurassic oldest age, which was revised by Bandini et al.(12011b). Bajocian to Bathonian, Oxfordian-Kimmeridgian to Albian and Coniacian-Santonian Radiolaria were recovered by Baumgartner (1984), Denyer & Baumgartner (2006) and Bandini et al. (2006) from many ribbon radiolrarite outcrops of the Nicoya Complex s. str. (NCC, Fig.2) documenting its long open ocean history including several plateau basalt and gabbro intrusions ranging in age from 139 to 83 Ma. Late Middle to early Late Jurassic, poorly preserved Radiolaria were reported by Montgomery et al. (1994 a, b) from the El Aguacate Chert, Duarte Complex (DUARTE; Fig.2), Central Hispaniola (Dominican Republic) who stated a Late Jurassic age, revised since in Sandoval (2015). The Duarte Complex represents the only on-land outcrop known of the Caribbean "double crust", i. e. Panthalassan MORB (Loma La Monja Ophiolite) overlain by ribbon radiolarites (El Aguacate) and then intruded and overlain by mid Cretaceous CLIP-type plateau basalts, and finally by the arc-related Late Cretaceous Tireo Group (see below). Kimmeridgian-Tithonian Radiolaria were described from La D.sirade (Guadeloupe, DES, Fig. 2) from red interpillow ribbon chert of the basal Complex (Montgomery et al 1992, 1994a, b, Cordey & Corn.e 2009). While Montgomery & Kerr (2009) argue for a mixed pelagic-hydrothermal origin along an East Pacific mid-ocean ridge, Neill et al. (2010) argue for a Proto-Caribbean, back-arc spreading-ridge origin of the La D.sirade igneous rocks. This interpretation is based on geochemical arguments concerning the mantle source beneath "an east-dipping Andean/Cordilleran subduction". It is in conflict with the absence of pelagic carbonates, typical for the Proto-Caribbean Late Jurassic. Coniacian-Santonian Radiolaria were recovered from ribbon radiolarites in stratigraphic contact with basalts of the Azuero Plateau (Fig. 2), the W-edge of the CLIP (Kolarski et al. 1995), This has been considered to represent the oldest, autochthonous basement of Panama (Lissina 2005, Buchs et al. 2009, 2010). However, the recent discovery of Late Hauterivian-Barreminan radiolarians in a radiolarite pebble of a Miocene fluviatile conglomerate in the Canal Zone (Kukoc et al. 2017), suggests that Early Cretaceous and older, far-travelled plateau fragments similar to the Nicoya Complex s. str., out of Panthalassa, accreted along, or form the basement of the CLIP. Coniacian-Campanian Radiolaria were recovered by Arias (2003) from the CLIP segment (Fig2) of the Herradura Promontory (Fig. 2), Central Costa Rica. Campanian-Maastrichtian Radiolaria were described by Diserens (2003) from radiolarite lenses in the the Inner Osa Igenous Complex from the Golfo Dulce area and the Burica Peninsula, and also from oceanic seamount fragments in the Osa M.lange (Fig. 2,Buchs et al. 2009). Most interestingly, Eocene Radiolaria were recovered from 20m sized blocks and clasts of red ribbon radiolarite in the Osa MÈlange (AzÈma et al. 1983, Buchs et al. 2009, Diserens 2003, Fig. 2), These are the youngest known ribbon radiolarites, probably related to the Eastern Tropical Pacific upwelling environment. 2. Arc-related, green, tuffaceous cherts/siliceous mudstone/shales are typical for areas close to intra-oceanic or andean-type arcs. Irregular interbedding with ash layers, muddy to sandy arc-derived turbidites contain evidence for the type of arc origin of the detrital component (Andjic et al. submitted). A high content of volcanic glass and hence, abundant mobile silica "protects" radiolaians from dissolution during diagenesis, resulting in pristine opal preservation. These sediments may occur in many pelagic-hemipelagic settings. In the Circum-Caribbean area these lithologies are often coeval with ribbon radiolarites of Pacific origin underlining the complex interplay between Plateau and seamount fragments that still form outboard of the Mid-American trench, while island arc environments are recorded along the convergent margins of the CLIP. Turonian- Coniacian Radiolaria were described by Sandoval et al. (2015) form grey tuffaceous cherts of the Pedro Brand section attributed to the are-related Tireo Group (TIREO, Fig. 2), Central Dominican Republic. Campanian and Middle-Late Eocene Radiolaria were found in tuffaceous cherts of the San Blas (arc) Complex (SAN BLAS, Fug. 2), cropping out in the San Miguel Gulf of Eastern Panama (Barrat et al. 2014). 3. Local - global anoxic event-related dark green or black chert inetrbedded with black shale form usually discontinuous and thin sequences that may be interstratified with pelagic limestones. They are typical for OAEs worldwide. Examples in the Caribbean region include: Bajocian-Bathonian gray interpillow limestone that yielded ammonites (Bartok et al. 1985) and associated black chert containing radiolarians (Sandoval 2015) of unknown origin in the Matatere Formation (MATA, Fig,2) of the Petacas Creek, Siquisique, Venezuela. These occurrences were interpreted as part of the Siquisique Ophiolite. In contrast, our studies in the Guaparo Creek reveal Albian-Cenomanian Radiolaria in dark geen to black cherts in stratigraphic contact with the Siquisique Ophiolite (SIQU, Fig 2). This age is in accordance with recent concordant U-Pb ages from zircons extracted from gabbos of 115.7 . 5.6 Ma (Kerr et al. personal communication). Late Jurassic black detrital chert in the Siuna Serpentinite M.lange (SSM, Fig. 2, Baumgartner et al. 2008) possibly formed in a restricted fore-arc basin. Late Valanginian- Early Aptian black siliceous limestone and chert occur in the overlap sequence of the SSM (OL, Fig. 2). Aptian Radiolaria were recovered by Bandini et al. (2011 a) from a black chert and shale level at Playa Carrizal, Santa Rosa Accretionary Complex (SRAC, Fig. 2), Santa Elena Peninsula, Costa Rica. This occurrence is undoubtedly related to OAE 1a, the Selli Event. Albian-Cenomanian Radiolaria were recovered by Sandoval (2015) from bedded chert and tuffaceous shales of the Santa Teresa Formation (S. TER, Fig. 2) in the Cocuyo Quarry, Central Cuba of the Placetas Belt. Coniacian-Santonian Radiolaria occur in dark green to balck cherts in the Loma Chumico Formation of the Manzanillo Terrane (MANZ, Fig. 2), Nicoya Peninsula, Costa Rica (Andjic et al. submitted, abstract this volume). Here, arc-derived tuffs and restricted (anoxic) conditions in a silled forearc basin have both favoured radiolarian preservation. These occurrences may be related to OAE 3. Campanian and Paleocene Radiolaria occur in black, siliceous shales of the Cansona Formation (CANSONA, Fig. 2), San Jacinto Belt, Sin˙ Domain, Colombia. Radiolarian biogeography Although we globally assume a paleo-oceanographic control on the distribution of certain radiolarian taxa in the Mesozoic, the further we go back in time, the less we know about the global distribution of water masses. A simple paleo-latitudinal model of radiolarian distribution, initially proposed by Pessagno and Blome (1986 with revisions of Pessagno et al. 1993) defines the "Boreal/Tethyan" boundary at approximately 30. N and S, expressed by a sharp decline of Parvicingula-type radiolaian species and a sharp increase in abundance of pantanelliid radiolarian taxa. These faunal differences do exist, but the alledged paleo-latitudes cannot be used at their face-value. Important latitudinal displacements of Middle American terranes are inferred from this model in many articles, despite a clear contradiction with largely E—W trending plate tectonic vectors in the area (Pindell & Kenan 2011). Conversely, parvicingulid-rich assemblages may represent "temperate" faunas sedimented beneath 12 "margin-related" Eastern Boundary Currents and thus indicate E—W displacement of terranes across Panthalassa and its Eastern margin (Bandini et al., 2011b, p. 388). The architecture of the arc-related sedimentary basins has been largely controlled by three factors: 1) subsidence caused by tectonic mechanisms, especially linked to the angle and morphology of the incoming plate. The subduction of aseismic ridges and slab segments with rough crust were important drivers for subduction erosion, controlling the shape of individual forearc and trench-slope basins, the lifespan of sedimentary basins and the subsidence and uplift patterns; 2) subsidence caused by slab rollback and resulting trench retreat; 3) eustatic sea-level changes and 4) sediment dispersal systems. Especially, slab rollback and resulting trench retreat are very important factors for basin subsidence. From the sedimentary and tectonic record of the Nicaraguan and North Costa Rican arc segment it is evident that two periods of trench retreat occurred during the Cenozoic. The first trench retreat occurred during the Late Eocene to Oligocene and the second trench retreat during Miocene/Pliocene times, indicated by increased subsidence in the forearc and backarc basins, extension in the intraarc area and shift of the volcanic arc.