Catalog - Globorotaloides atlanticus

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Globorotaloides atlanticus

Citation: Globorotaloides atlanticus Spezzaferri & Coxall, in Coxall & Spezzaferri 2018

Type specimens: Holotype (32509) and paratypes (32510, 32511 and 32512)

Type sample (& lithostrat): ODP Hole 667A

Type age (chronostrat): Upper Oligocene Zone O7,

Type locality: Sierra Leone Rise, eastern equatorial Atlantic Ocean

Type repository: Fribourg; Natural History Museum of Fribourg, Switzerland.

Type of wall: Spinose (?). Normal perforate, coarsely cancellate, sacculifer-type wall texture, with a distinctly honeycomb appearance. Pore density: ~40 pores/50 μm2."

Test morphology: Test outline lobate, axial periphery rounded; 2-2½ whorls of inflated chambers arranged in a flattened globorotaliiform-trochospire; 11-14 chambers in adult tests, 5-7, more frequently 6 slightly compressed chambers in the final whorl, increasing moderately in size. Sutures depressed, radial on both sides, straight, slightly curved on umbilical side. Umbilicus moderately wide, covered by a bulla extending around equatorial margin and having a thickened lip or rim; 2-3 infralaminal apertures around the bulla spanning umbilical sutures, or at the edge of the bulla on the equatorial margin. Where the bulla has broken the primary aperture can be seen as an umbilical-extraumbilical arch at the base of the last chamber, surrounded by a lip.

Holotype maximum diameter 0.29 mm, breadth 0.24 mm, thickness 0.15 mm.

Named atlanticus because of its discovery and more common occurrence in the equatorial Atlantic Ocean.

Globorotaloides aff. G. hexagonus (Natland).—Spezzaferri, 1994:47 pl. 36, figs. 4a-c [upper Oligocene Zone P22, ODP Hole 667A, eastern equatorial Atlantic Ocean]. [Not Natland, 1938.]
Globorotaloides sp.—Quilty, 1976:649, pl. 17, figs. 5, 6 [Zone N2, DSDP Hole 320B, Nazca Plate, southeastern Pacific Ocean].

DDISTINGUISHING FEATURES: Globorotaloides atlanticus differs from Globorotaloides stainforthi, from which it evolved, in having a distinctive umbilical-to-equatorial bulla that extends around the peripheral margin, an equatorially directed primary aperture and more numerous chambers in the final whorl. The bulla in Globorotaloides stainforthi is more strictly umbilical. Globorotaloides atlanticus is distinguished from Protentelloides primitivus, to which it gave rise, by having straight sutures on the spiral side, compared with recurved or sigmoidal sutures in Protentelloides, more inflated chambers and a flattened umbilical-to-equatorial bulla.

DISCUSSION: Globorotaloides atlanticus forms part of the plexus of Oligocene bullate Globorotaloides. The most important diagnostic feature of this morphotype is the position of the bulla that extends from the umbilicus around to the equatorial margin. In this respect we view G. atlanticus as being transitional between G. stainforthi, where the bulla is umbilical, to Protentelloides spp., where the bulla forms on the equatorial margin. It is unclear whether or not Globorotaloides atlanticus and contemporaneous G. hexagonus and Protentelloides were spinose. The type material of G. atlanticus shows signs of dissolution and recrystallization, including contact dissolution around other biogenic sediment particles such as sponge spicules (linear impressions in Pl. 4.4, Figs. 1, 9 and 11). This obscures any evidence for or against spines.

PHYLOGENETIC RELATIONSHIPS: Globorotaloides atlanticus evolved from Globorotaloides stainforthi by extension of the bulla towards the equatorial margin. It gave rise to Protentelloides primitivus, which is supported both by morphological similarities and similar pore densities between G. hexagonus and P. primitivus.

STRATIGRAPHIC RANGE: The range of G. atlanticus has been determined at equatorial Atlantic Ocean DSDP Site 354 and ODP Site 667 as upper Oligocene Zone O7 to lower Miocene Zone M3. This is supported by more sporadic occurrences at South Atlantic Ocean DSDP Site 526 and rare appearances at equatorial Indian Ocean Site 709. These limits are based on the biostratigraphies of Spezzaferri (1994) and new observations made during this study. Globorotaloides atlanticus appears to be most common in O7, where all the examples shown on Plate 4.4 are from.

GEOGRAPHIC DISTRIBUTION: Low latitude, equatorial. The best-described records are from the equatorial Atlantic Ocean (Spezzaferri, 1994), but it has also been observed in the equatorial Pacific (Quilty, 1976) and Indian Oceans (Spezzaferri, 1995).

STABLE ISOTOPE PALEOBIOLOGY: Relatively high δ18O and low δ13C compared to other species indicating a deep sub-thermocline habitat (Spezzaferri and Coxall, unpublished) and or life in cool, nutrient rich upwelled water, as has been suggested for Globorotaloides sp. from assemblage-based bioprovince analysis (Spezzaferri, 1995).

References:

Coxall, H. K. & Spezzaferri, S. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene Catapsydrax, Globorotaloides, and Protentelloides. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 46(Chap 4): 79-124. gs

Quilty, P. G. (1976). Planktonic foraminifera DSDP Leg 34, Nazca Plate. Initial Reports of the Deep Sea Drilling Project. 34: 629-703. gs O

Spezzaferri, S. (1994). Planktonic foraminiferal biostratigraphy and taxonomy of the Oligocene and lower Miocene in the oceanic record. An overview. Palaeontographia Italica. 81: 1-187. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotaloides atlanticus Spezzaferri & Coxall, in Coxall & Spezzaferri 2018

Globorotaloides atlanticus

References:

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