AGE AND GENERIC ASSIGNMENT OF YABEINA COLUMBIANA (GUADALUPIAN FUSULINACEA) IN SOUTHERN BRITISH COLUMBIA

Journal of Paleontology, Mar 2007 by Kobayashi, Fumio, Ross, Charles A, Ross, June R P

ABSTRACT-

The morphologic variation in Yabeina columbiana (Dawson) was carefully studied using probable topotype specimens from the Marble Canyon-Hat Creek area, southern British Columbia, and the material was compared with related species of neoschwagerinids from various parts of the circum-Pacific region. In the five Marble Canyon-Hat Creek samples examined, we found considerable individual variation in important characters, such as the size of the proloculi, and shape and development of primary and secondary transverse septula in relation to the growth stage of the test. These differences gradually changing from specimen to specimen within and among samples are thought to represent intraspecific variation within this species. Wide individual variations are also found in three different species of Yabeina from Japan, Yabeina sp., Y. kaizensis (Huzimoto), and K globosa (Yabe).

Most North American species of Yabeina, such as Yabeina columbiana, have morphological features such as the occurrence of primary and secondary transverse and axial septula in later whorls and the average size of proloculi that reasonably place them as early species in the genus Yabeina. Yabeina columbiana is neither a Lepidolina nor a Colania as some authors had previously thought. Evolved forms of Neoschwagerinidae in the western Cordillera of North America consist of Yabeina cordillerensis Ross, Y. cascadensis (Anderson), Y. columbiana (Dawson), Y packardi Thompson and Wheeler, and Lepidolina dunbari (Skinner and Wilde).

The earliest North American Yabeina is thought to be Y. cordillerensis from northwestern British Columbia where it is associated with Afghanella sp., Pseudodoliolina sp., and the Wordian ammonoid Waagenoceras. This assemblage is closely comparable to that in the lowest zone of the Midian Stage in the Tethyan realm, the Afghanella robbinsae and Yabeina archaica Zone. The remainder of the known North American Cordilleran species of Yabeina are assignable to the second zone of the Midian Stage, the Yabeina globosa and Lepidolina multiseptata Zone and to the Japanese Yabeina globosa Zone. This zone is considered equivalent to the Capitanian Stage at the top of the Guadalupian Series in southwestern North America. Morphological and faunal analyses of these North American Cordilleran species of Yabeina and Lepidolina and most of the associated species of schwagerinids (for example, Chusenella andersoni, C. atlinensis, and Schwagerina pavilionensis) suggest ages that range through the late Guadalupian. The highest zone of the Tethyan Midian lacks Yabeina and other neoschwagerinids and is based on the ammonoids Eoaraxoceras and Anderssonoceras. This zone is found in sediments of post-Capitanian (post-Guadalupian) age in northern Mexico.

INTRODUCTION

FUSULINACEANS. AMMONOIDS, corals, and other marine fauna, especially of Permian age, in many of the accreted terranes of western North America, have many Tethyan and Panthalassan affinities. These faunas are dissimilar at the species, genus, and family levels to faunas of the same age from cratonic North America. They led to the recognition of a series of accreted terranes forming the western Cordillera (Monger and Ross, 1971). The Tethyan neoschwagerinid and verbeekinid fusulinaceans in some of these terranes are taken as evidence that the terranes have been displaced great distances, hundreds or even thousands of kilometers, from their late Paleozoic places of origin. They were emplaced in the Jurassic and Cretaceous as parts of the accreted belts extending from Alaska to central California.

The first record of Tethyan fusulinaceans was "Loftusia columbiana" from the Marble Canyon Limestone in British Columbia by Dawson (1879). It preceded the identification of "Schwagerina craticulifera" from South China by Schwager in 1883, which Yabe (1903) designated as the type species of his genus Neoschwagerina. Dunbar (1932) recognized Dawson's specimens as a neoschwagerinid and applied the name Neoschwagerina columbiana (Dawson, 1879). Later, topotype specimens studied by Thompson and Wheeler (1942) were assigned to Yabeina Deprat, 1914. Skinner and Wilde (1966) redescribed the Marble Canyon Limestone fauna from many more collections, and, according to them, recognized Yabeina columbiana (Dawson, 1879) and eight additional species of Yabeina.

The shape and size of the test, proloculus size, and development and morphology of septula are variable in topotype specimens of Yabeina columbiana. These characters are more or less similar to those of Yabeina globosa (Yabe, 1906), widely distributed in the Jurassic terranes of Japan and originally described as "Neoschwagerina globosa" from the Akasaka Limestone by Yabe (1906).

Neoschwagerinids are the endemic group of fusulinaceans. Those known from circum-Pacific regions originated on reefal buildups in Panthalassa, and some of these reefal buildups later were dispersed by a plate tectonic process to western North America (Ross and Ross, 1981, 1987; Kobayashi, 1997a). These neoschwagerinid faunas first appeared near the beginning of the Middle Permian (Guadalupian) and help define the Tethyan-Panthalassan paleobiogeographic boundary (Kobayashi, 1997a).