Catalog - Globorotalia kingmai

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Globorotalia kingmai

Citation: Globorotalia kingmai Scott et al. 1990

Type specimens: Holotype and 71 paratypes registered as TF1631

Type sample (& lithostrat): Sample V22/f6552

Type locality: southeast side of Te Mata Peak, Hawkes Bay (Altonian)

Type repository: Lower Hutt; N.Z Geological Survey foraminiferal collections

Spiral orientation
Shell outline: Subcircular to weakly elliptical. The outline is distinctive with broad, occasionally deep, reentrants at all sutures (Fig 16A,D). The re-entrant above the aperture is only slightly deeper than its predecessors.
Chamber packing and coiling: Most specimens have c.14-17 chambers, arranged in 3 whorls. The outer whorl has 4-5 chambers while early whorls have c.5 chambers. Dextral coiling (42 specimens) predominates (28 sinistral).
Chamber shape: Commonly late-formed chambers are moderately elongated in the coiling direction (Fig. 16A,D) but some kummerform chambers are almost equidimensional. The outer margin forms a low, symmetrical arch. Leading and trailing sections are poorly defined: adjacent to their attachments they are almost linear but further out they move into broad zones of moderate curvature which join the low central section. The inner margin consists of 2-3 short sections. These are often almost aligned but the trailing section in some chambers is elevated and may extend almost radially. Increase in chamber length is slow in late-formed chambers but width sometimes increases quite rapidly (Fig.16D). On earlier chambers the outer margins tend to form higher arches without readily identifiable sections. On chambers in the outer whorl surfaces adjacent to the inner margin are only slightly convex but curvature increases strongly towards the periphery. There is no rim. Sutures are relatively deep and surfaces of adjacent chambers are sometimes strongly offset downward in the coiling direction.

Axial orientation
Shell outline: Shape varies considerably from inflated, discoidal forms (common) to rarer biconvex individuals with weakly compressed peripheries.
Outline of early whorls: The rate of whorl translation is often high and a prominent dome is usually present (Fig.16B). The convex outlines of individual chambers is sometimes visible.
Outline of last chamber: Due to the high rate of whorl translation the short spiral section is offset from the early whorls (Fig. 16 B,E). Initially, this section is slightly convex but curvature increases outwards. The junction between spiral and umbilical sections is poorly defined and forms a zone (sometimes broad) of increased curvature. In compressed chambers the periphery lies in this zone but may be sited more medially on radially inflated chambers (the common form). In such chambers curvature of the umbilical section increases away from the periphery, although there is no distinct apex at the extremity (Fig. 16B). In more compressed chambers (Fig. 16E) some parts of the umbilical section are almost linear. In both types elevation in the umbilical direction is often minor.
Outline of earlier chambers: The (n-2)th or (n-3)th chambers are visible. Their outlines are moderately inflated. Definition of a slightly curved spiral section is often much weaker than on the last chamber. Variation is wide: in some specimens these chambers are almost semicircular but in a few compression exceeds that of the last chamber.
Aperture: The opening is a low arch but is occasionally almost slit-like. It is bordered by a thin, slightly projecting lip.

Umbilical orientation and wall topography
The umbilicus is narrow (Fig. 16F). Sutures are deep, almost linear and radially directed. Chamber surfaces are convex and only weakly elevated. The last chamber has narrow pores which are widely spaced on the flat wall. Pore pits are developed on preceding chambers and the topography becomes honeycomb-like (Fig. 16A,D).

VARIATION: Specimens in GRW6 (Walters 1965 fig. 2; Waiomoko River, Gisborne district; Altonian) closely resemble those in V22/f6552.

DISCRIMINATION: In spiral view some individuals closely resemble Globorotalia praescitula and might be taken as teratological variants. However, the outline of G kingmai usually is much more lobulate and late chambers are narrower (radial direction). Offsets between chambers are more conspicuous than in G. praescitula due to the higher rate of whorl translation. In axial orientation the spiral face of the shell is often higher than in G. praescitula and the contour of the dome formed by the early whorls is less regular due to the greater convexity of chambers. The outlines of late chambers often show significant radial inflation, a feature seen only in the earliest collections of G. praescitula and then only weakly. The aperture is lower in G. kingmai than in G. praescitula. Due to the variability displayed by G. kingmai no single character will necessarily separate it from accompanying specimens of G. praescitula. In combination, rate of whorl translation, lobulation, inflation of late chambers and low aperture are likely to be the most useful.

RELATIONSHIPS: So little is known of the distribution of Globorotalia kingmai that inferences about its origin depend on comparative morphology. Among lower Miocene taxa the closest resemblance is with G. praescitula. In spiral orientation the outline of the middle whorl resembles that of G. praescitula and may indicate phyletic connection. The surface topographies of the 2 species are similar. As in other globorotalids it is in late ontogeny that distinctive features such as strong re-entrants between chambers and lobulation arise. Axially, the inflated outlines of late chambers represent a departure from a major trend in G. praescitula and G. miozea and might be interpreted as evidence of divergence. However, a fuller stratigraphic record of the species is needed to test these conjectures. Globorotalia explicationis may have descended from G. kingmai.

DISTRIBUTION: Altonian. V22/f6552 and GRW6 are upper Altonian collections. There is a tentative record in U24/f363 (Wainui River, southern Hawkes Bay; lower Altonian). It occurs with Globorotalia zealandica in core 44-5-77 at DSDP Site 593, Tasman Sea.

References:

Scott, G. H., Bishop, S. & Burt, B. J. (1990). Guide to some Neogene Globorotalids (Foraminiferida) from New Zealand. New Zealand Geological Survey, Paleontological Bulletin. 61: 1-135. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia kingmai Scott et al. 1990

Globorotalia kingmai

References:

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