Radiolarians from the Lamar Limestone, Guadalupe Mountains, West Texas

Abstract

Well-preserved radiolarians are described from a road-cut of the upper Lamar Limestone Member of the Bell Canyon Formation along Highway 62/180 in the Delaware basin of West Texas. The upper part of the Lamar Limestone contains early Capitanian (late Guadalupian) conodonts and fusulinaceans and is assigned to the Reichelina lamarensis and the Jinogondolella postserrata zones, respectively. A total of 31 species were recovered from 17 samples in a ~6m section of micritic laminated limestone. Twenty species are reported from this locality for the first time, including 6 new species; Copiellintra ferula, Copiellintra laurelae, Hegleria agnusiforma, Hegleria globosa, Rectotormentum fengi, and Stigmosphaerostylus wildei. Sectioning and transmitted light microscopy of the spongy taxa reveals internal structures and allows for a more natural grouping of genera and species based on aspects of wall structure, rather than external geometry or presumed internal structure. All of the spongy taxa lack an entactinarian spicule and the genera Copicyntra, Copiellintra, Copicyntroides and Hegleria are reassigned to families within the Spumellaria. Lamar radiolarian assemblages show fluctuations in their faunal composition, alternating between albaillellarian-dominated assemblages composed mostly of Follicucullus spp. and spumellarian-dominated assemblages composed largely of spongy taxa of spherical, oblate, to discoidal shape (Copicyntra, Copiellintra, Copicyntroides, Klaengspongus, Tetrapaurinella, and Hegleria). By far the most common radiolarians are spongy spumellarians and albaillellarians, but latentifistularians also occur sporadically in samples, and entactinarians are rare and occur throughout the section. These marked faunal fluctuations are interpreted to be environmentally driven and is the subject of ongoing investigations using geochemical proxies to reveal paleoecological controls.