Irwin's (1972) terrane concept fathered tectonostratigraphy and has done much to decipher complex geology throughout the Circum-Pacific region, Caribbean, and elsewhere in the world. The present chapter analyzes the tectonostratigraphy of seemingly unrelated Jurassic terranes utilizing an accurate chronostratigraphic framework. Faunal paleolatitudinal data, paleomagnetic data (where available), and microfacies analysis have been utilized in the tectonostratigraphic interpretations.
Four terranes/subterranes are analyzed herein: (1) the Izee terrane (Blue Mountains, northeastern Oregon), (2) the Rogue Valley subterrane (southwestern Oregon), (3) the Smith River subterrane (northwestern California), and (4) the San Pedro del Gallo terrane (east-central and central Mexico, western Cuba). Paleolatitudinal data indicate that all of these terranes/subterranes have undergone tectonic transport.
The Izee terrane originated at low paleolatitudes (Central Tethyan province) during the Late Triassic and migrated to higher paleolatitudes (Southern Boreal province: 30° N) by the late Bathonian (Middle Jurassic). Northward movement is postulated to have occurred along a megashear analogous to the present-day San Andreas fault system.
The Rogue Valley and Smith River subterranes both originated at low paleolatitudes (Central Tethyan province) during the Callovian and were transported to higher paleolatitudes (Southern Boreal province) by the the middle Oxfordian (early Late Jurassic).
The Huayacocotla remnant of the San Pedro del Gallo terrane originated at high Southern Boreal paleolatitudes (30–40° N) during the late Bathonian or early Callovian and, subsequently was transported from northwest to southeast along the west side of the Walper megashear. By the latest Tithonian (Late Jurassic), the Huayacocotla remnant had been transported to low paleolatitudes (Central Tethyan province).
Unconformities in the Bathonian to Callovian interval in the Izee terrane(?) and in the Huayacocotla remnant of the San Pedro del Gallo terrane are believed to reflect the breakup of Pangea. As demonstrated by the author in previous reports, each remnant of the San Pedro del Gallo terrane shows the same paleobathymetric fingerprint: (1) marine deposition at inner neritic depths during the Callovian to early Oxfordian (Middle to early Late Jurassic), (2) marine deposition at outer neritic depths during the late Oxfordian (Late Jurassic), and (3) sudden deepening to upper abyssal depths from the early Kimmeridgian (Late Jurassic) until the end of the Cretaceous. The sudden deepening event (outer neritic to upper abyssal) during the early Kimmeridgian is associated with a disconformity and hiatus in all San Pedro del Gallo remnants (early Kimmeridgian strata overlie middle Oxfordian strata). This event reflects the opening of the Gulf of Mexico.
Combined faunal and floral data indicate that the San Pedro del Gallo terrane was in a back-arc position at approximately the same latitude as the Foothills terrane of the Sierra Nevada during the middle Oxfordian. Given the faunal data as well as some paleomagnetic data, it is probable that these San Pedro del Gallo remnants might represent some of the missing Upper Jurassic back-arc deposits from farther north (i.e., western Nevada?).
In the Smith River subterrane, the disconformable contact between the volcanopelagic facies and Galice Formation sensu lato reflects a sudden influx of siliciclastic turbidite from a Jurassic volcanoplutonic arc source area and from older rocks of the accreted continental margin that lay inboard of the Nevadan island-arc complex. The same event is represented by the deposition of the siliciclastic turbidite of the Monte del Oro and Mariposa Formations (Foothills terrane, western Sierra Nevada) and by that of the Galice Formation sensu stricto (Rogue Valley subterrane).
