Abstract There are thousands of problematic organisms — organisms unassigned to a specific phyletic group, or ones that were assigned to different groups by different workers. We have simply picked a few that are particularly distinctive and/or that are important in rocks of hydrocarbon exploration interest. We list prior phyletic assignments and age ranges below and provide descriptions and keys to recognition in the figure captions. Receptaculitids - grouped with sponges, corals, dasycladacean green algae, or problematica — common from Early Ordovician to Late Devonian, with smaller, more globular forms extending into the Permian Nuia - grouped with problematic codiacean algae or as an unassigned organism — Late Cambrian-Ordovician Palaeoaplysina - grouped with sponges, phylloid algae, or hydrozoans — Mid. Pennsylvanian-Early Permian Tubiphytes - variously grouped with cyanobacteria/blue-green algae, red algae, calcareous sponges, foraminifers, hydrozoans — at least Late Carboniferous to Late Jurassic Lithocodium - grouped as codiacean algae or loftusiid foraminifers — Late Triassic to Early Cretaceous (Albian) Hensonella - grouped as mollusks (scaphopods), coralline red algae, or dasycladacean green algae — Cretaceous (Hauterivian-Albian) A cross section of the wall structure of Calathium sp., with its central cavity and moderately well-preserved radiating wall structure. Calathids are the earliest receptaculitids — they had ovoid or tubular skeletons that strongly resemble sponges (one of the groups in which receptaculitids commonly are classed). The sparry calcite-filled areas (and micrite-filled circles) are recrystallized, originally aragonitic, elongate pillars that constituted the skeletal wall (see Nitecki et al., 1999); the rest of the micritic sediment has filled areas of former void spaces or sites of later-decomposed organic tissues.

Abstract The Ordovician Whiterock Series of western Utah, Nevada, and southern California constitutes a vast carbonate platform that grew during a single offlap-onlap cycle, 12 m.y. in duration, in late Arenig through Llandeilo time, when most of the North American continent was exposed to subaerial weathering. Evolution of the platform took place in four phases during which carbonate sedimentation initially kept pace with, then generally exceeded, the rate of relative subsidence. The margin of the platform was initially occupied by a carbonate-shoal complex rich in Nuia and calathid algal reefs, but at its climax it became composed mostly of Girvanella-rich oncolites and receptaculitid algae. Seaward of the margin, slope deposits consist of fine-grained carbonate and terrigenous clastic sediments, largely as parted to ribbon limestones with hardgrounds and slumped horizons, punctuated by limestone conglomerates. Rapid accretion of massive prograding oncolite-sand shoals during the second phase impeded water circulation to the open platform shoreward, or east, of them. The result was lagoonal accumulation of euxinic black shales and intercalated storm deposits as tongues of coquina, oncolite, and fossiliferous rudstone in an intra-shelf basin. Slowing of relative sea-level rise during phase 3 is indicated, especially in the south, by extensive peritidal deposits, which prograded westward precisely over the most substantial parts of the previous oncolite-rimming facies and assumed their function as the shelf margin. Shoreward and northward, the shallow shelf was covered by burrowed carbonate mud. Quartz sands prograded from the northeast toward the southwest and west, eventually overwhelming most of the carbonate platform. Dolomitization and karstification in a seemingly anomalous southwest-northeast, narrowly elongate area from the Talc City Hills to the Sheep Range appear to have taken place prior to deposition of quartz sands. The vast scale of this carbonate platform is such that all its elements may not be seen at a single location, in contrast, for example, to the Permian Basin sediments of the Guadalupe Mountains of New Mexico. Rather, the three-dimensional geometry of the White-rockian platform is evident only through careful measurement of stratigraphic sections and interpretation of depositional facies patterns, which are then tied together through detailed biostratigraphic correlation. The unique nature of the sediments that compose this platform is a function of its equatorial setting on a leeward continental margin and the lack of any large skeletal metazoans during this interval of Ordovician time.