Abstract Ordovician Japan formed a mature arc-trench system developed along the palaeo-Pacific (Panthalassa) margin of the Greater South China (GSC) continental block. GSC consists of South China, East China Sea, SW–NE Japan and the Khanka–Jiamusi–Bureya megablock in the Far East; Paleozoic GSC was thus, in total, twice as large as the South China components by themselves (Yangtze and Cathaysia). The Ordovician crust of Proto-Japan comprised coeval arc-related rocks, such as granitoids, supra-subduction zone ophiolites and fore-arc basin strata, although most of them were considerably fragmented. The Ordovician and middle–late Paleozoic fossils from Japan are highly limited but suggest that Proto-Japan was positioned in the low-latitude domains probably of the palaeo-Pacific Ocean in connection to Paleo-Tethys. GSC became separated from Rodinia in the Neoproterozoic, and its Proto-Japan segment evolved as a collision-free subduction margin for nearly 500 myr since the mid-Cambrian. The GSC framework provides critical constraints to the palaeogeographical reconstruction of circum-Pacific continental blocks. First, the Cambro-Ordovician GSC should have been isolated from Australia/India/East Antarctica that formed East Gondwana by a relatively wide ocean domain for keeping ‘subduction potential’. Second, the Cathaysian margin of GSC should have faced to an extensive ocean without major continents since the Cambrian. The palaeo-Pacific is the only possible candidate for this.

ABSTRACT This chapter expands upon a model, first proposed in 1998 by Busby and others, in which Mesozoic oceanic-arc rocks of Baja California formed along the Mexican continental margin above a single east-dipping subduction zone, and were extensional in nature, due to rollback of an old, cold subducting slab (Panthalassa). It expands on that model by roughly tripling the area of the region representing this fringing extensional oceanic-arc system to include the western third of mainland Mexico. This chapter summarizes the geologic, paleomagnetic, and detrital zircon data that tie all of these oceanic-arc rocks to each other and to the Mexican margin, herein termed the Guerrero-Alisitos-Vizcaino superterrane. These data contradict a model that proposes the oceanic-arc rocks formed in unrelated archipelagos some 2000–4000 km west of Pangean North America. Following the termination of Permian–Triassic (280–240 Ma) subduction under continental Mexico, the paleo-Pacific Mexico margin was a passive margin dominated by a huge siliciclastic wedge (Potosí fan) composed of sediments eroded from Gondwanan basement and Permian continental-arc rocks. I propose that a second fan formed further north, termed herein the Antimonio-Barranca fan, composed of sediment eroded from southwest Laurentian sources. Zircons from these two fans were dispersed onto the ocean floor as turbidites, forming a unifying signature in the Guerrero-Alisitos-Vizcaino superterrane. The oldest rocks in the Guerrero-Alisitos-Vizcaino superterrane record subduction initiation in the oceanic realm, producing the 221 Ma Vizcaino ophiolite, which predated the onset of arc magmatism. This ophiolite contains Potosí fan zircons as xenocrysts in its chromitites, which I suggest were deposited on the seafloor before the trench formed and then were subducted eastward. This is consistent with the geophysical interpretation that the Cocos plate (the longest subducted plate on Earth) began subducting eastward under Mexico at 220 Ma. The Early Jurassic to mid-Cretaceous oceanic arc of western Mexico formed above this east-dipping slab, shifting positions with time, and was largely extensional, forming intra-arc basins and spreading centers, including a backarc basin along the continental margin (Arperos basin). Turbidites with ancient Mexican detrital zircons were deposited in many of these basins and recycled along normal fault scarps. By mid-Cretaceous time, the extensional oceanic arc began to evolve into a contractional continental arc, probably due to an increase in convergence rate that was triggered by a global plate reorganization. Contraction expanded eastward (inboard) throughout the Late Cretaceous, along with inboard migration of arc magmatism, suggesting slab shallowing with time.

Abstract In this paper, we present a detailed review of upper Pliensbachian–lower Toarcian kerogen assemblages from the southern areas of the West Tethys shelf (between Morocco and northern Spain) and demonstrate the use of the Phytoclast Group as a tracer of palaeoenvironmental changes in the early Toarcian. The kerogen assemblages in the studied sections from the southern areas of the West Tethys shelf are dominated by the Phytoclast Group and terrestrial palynomorphs, although punctual increases in amorphous organic matter, freshwater ( Botryococcus ) and marine microplankton (dinoflagellate cysts, acritarchs and prasinophyte algae) were observed at specific stratigraphic intervals. The opaque/non-opaque phytoclasts ratio was used to trace changes in palaeoclimate and other palaeoenvironmental parameters and reflect climate gradients associated with water availability during early Toarcian. During the Pliensbachian–Toarcian and Jenkyns events, changes in kerogen assemblages in the southern areas of the West Tethys shelf correlated with changes in the northern Tethys and Panthalassa shelf. The acceleration of the hydrological cycle associated with the aforementioned events was less intense in the northern Gondwana, southern and western Iberian basins, a reflection of the palaeogeographic position of these basins within the semi-arid climate belt when compared with the northern Iberian region and other northern areas of the West Tethys and Panthalassa shelf, inserted in winter-wet and warm temperate climate belts. Amorphous organic matter enrichment associated with the Pliensbachian–Toarcian and Jenkyns events reflects an increase in primary productivity linked with increased continental weathering, fluvial runoff and riverine organic matter, and nutrient input into marine areas, inducing water column stratification and promoting the preservation of organic matter.

Abstract The Dun Mountain ophiolite and related oceanic-arc rocks (Otama Complex) formed above a westward-dipping subduction zone within Panthalassa, with implications for the emplacement of Cordilleran-type ophiolites and arcs elsewhere. The ophiolite is overlain by the Mid–Late Permian Upukerora Formation (up to 850 m), a predominantly very coarse breccia-conglomerate that mainly accumulated by mass flow. Lesser amounts of sediment accumulated from turbidity currents and as background hemipelagic sediments. The succession unconformably overlies ophiolitic basaltic or, rarely, gabbroic rocks after a regional hiatus. Much of the coarse clastic debris was derived from the underlying ophiolite. However, clasts of plagioclase-phyric basalt, felsic volcanics and quartz-bearing intrusive rocks, including plagiogranite, are over-represented compared to the ophiolite. The evolved igneous material was derived from an incipient oceanic arc (the Otama Complex) that bordered or covered the ophiolite, especially in the south. The coarse clastic material accumulated following the activation of north–south-trending, subaqueous, extensional growth faults within the underlying oceanic crust. Large blocks of mainly basalt, diabase and gabbro were also shed down fault scarps from relatively shallow-water to deeper-water settings. Fault-controlled talus accumulated soon after Mid-Permian docking of the ophiolite and oceanic arc with SE Gondwana to initiate the Mid-Permian–Mid-Triassic Maitai continental margin forearc basin.

Abstract: A review of Permian fusuline biostratigraphy is made in this paper in order to improve the correlation of Permian strata globally. Permian fusuline biostratigraphy in the Tethyan and Panthalassan regions can be correlated roughly because the fusulines had good faunal communications between these two regions. However, fusuline faunas from the North American Craton region were devoid of almost all neoschwagerinids and dominated exclusively by schwagerinids during the Guadalupian (Middle Permian) because of the blockage caused by the vast Pangaea supercontinent. This renders the correlation of Middle Permian biostratigraphy and chronostratigraphy between the Tethyan region and North American region challenging. Significant evolutionary key points in fusulines include the first occurrence of Pseudoschwagerina or Sphaeroschwagerina during the earliest Permian, first occurrence of Pamirina and Misellina during the Yakhtashian and Bolorian, and the extinction of all schwagerinids and neoschwagerinids by the end of the Midian.