Catalog - Globigerina umbilicata

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.

Globigerina umbilicata

Citation: Globigerina umbilicata Orr & Zaitzeff 1971

Type specimens: Plate 1, figures 1-4

Type sample (& lithostrat): Rio Del Formation (Wildcat Group)

Type age (chronostrat): late Pliocene

Type locality: Centerville Beach south of Eureka, Humboldt County, California.

Type repository: Eugene, Oregon; University of Oregon Museum of Natural History at Eugene.

Test, low trochospiral, chambers ovate to flattened. Five to six chambers in final whorl of adult specimens, three to four in final whorl of juveniles. Wall calcareous, perforate; microstructure consists of short crystals of calcite arranged normal to test wall. Most adult specimens exhibit some secondary calcification on the outer test wall, juveniles may be spinose. Sutures are deeply impressed and tend to remain visible even when a thick crust of calcite develops during secondary calcification resulting in deeply impressed sutures similar to those on Globigerinoides conglobatus. Sutures on Globigerina umbilicata (plate 1, fig. 2 ) do not connect with supplementary apertures as in the case of Globigerinoides conglobatus. Aperture large, umbilical to interiomarginal with a small, thin, simple lip bordering the final aperture and each previous aperture. All previous apertures remain open to the umbilicus. A few specimens were found with a small accessory chamber (bulla) situated adjacent to the youngest and oldest chambers on the final whorl (plate 1, fig. 1). The bulla may be distinguished from the youngest chamber on the test by the size disparity and from the oldest chamber (on the h a 1 whorl) by the difference in surface texture. The surface of the bulla is invariably smoother than any of the chambers. Pores on the bulla are easily distinguished regardless of the state of secondary calcification of the remainder of the test. The pores are smaller and more closely spaced than pores on the chambers. The bulla has a thin wall and is not ordinarily part of the regular geometric trochoidal coil of the test.

The holotype measures 450 microns (maximum diameter) ; twenty paratypes average 400 microns. Coiling is random at the type locality.

Remarks: Globigerina umbilicata co-occurs with Globigerina bulloides (plate1,fig.4) at the type locality, but differs from that species by its less inflated chambers in the final whorl and impressed sutures on the spiral side. Be (1967) has noted that G. bulloides usually has five chambers in the final whorl of juvenile specimens and four in the adult, G. umbilicala has three to four chambers in the final whorl of juvenile specimens and five to six in the adult. G. umbilicata is morphologically very close to G. bulloides and is considered to be a Pliocene derivative of that species. G. umbilicata also closely resembles the Pleistocene species G. quadrilatera Galloway and Wissler, but differs from that species by its less inflated chambers, greater size and greater number of chambers in the final whorl. The bulla is not used here as a diagnostic character because it is considered to be too ephemeral. For some time during a study of the Wildcat Group microflora and fauna, specimens described here as Globigerina umbilicata were tabulated as Globigerina bulloides. Closer examination however indicated it was possible to subdivide particularly adult specimens on the basis 'of the number of chambers in the ultimate whorl, the flattened chambers and the deeply impressed sutures regardless of the amount of secondary calcification. Because the variation from Globigerina bulloides is not continuous in any samples we opted to describe a new species. A comparison of our material with Pliocene material in the principal author's reference collection as well as Miocene, Pleistocene and Holocene material from California and elsewhere failed to turn up additional specimens of Globigerina umbilicata or any evidence of a continuous intermediate series with Globigerina bulloides. The examination of several samples of topotype material collected by the principal author in 1966 from the beach areas of Rimini and Ravenna, Italy also failed to uncover continuous series with or succinct specimens of Globigerina umbilicata in the Globigerina bulloides populations. The frequency of Globigerina umbilicata within its observed stratigraphic range in the upper member of the Rio Del Formation is very sporadic and is best compared to that of Globigerina bulloides. Specimens of the new species are found in ratios as high as 20% (G. umbilicata/G. bulloides) to a low of 1% or absent.

Type locality: Globigerina umbilicata was recovered from various localities throughout the upper member of the Rio Del Formation (Wildcat Group) where it crops out along Centerville Beach south of Eureka, Humboldt County, as well as in the same stratigraphic interval along the Eel River west of Rio Del, California. The type locality is a thick grey mudstone 2100 feet south of Fleener Creek on Centerville Beach in SW¼, NE¼, SW¼, Section 13, T2N, R3W. Considerable evidence exists for a complete Pliocene section here and the upper member of the Rio Del Formation has been placed in the late Pliocene by a number of authors (Stewart & Stewart, 1949; Ogle, 1953; Faustman, 1964; Ingle, 1968) on the basis of molluscs, and benthonic and planktonic foraminifera.

References:

Orr, W. N. & Zaitzeff, J. B. (1971). A new planktonic foraminiferal species from the California Pliocene. Journal of Foraminiferal Research. 1(1): 17-19. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina umbilicata Orr & Zaitzeff 1971

Globigerina umbilicata

References:

Add Comment

Comments