pforams@mikrotax - Praeglobotruncana delrioensis

Citation: Praeglobotruncana delrioensis (Plummer, 1931)

Basionym: Globorotalia delrioensis

Synonyms:

Praeglobotruncana barbui Neagu 1962
Globorotalia marginaculeata Loeblich and Tappan 1946
Praeglobotruncana prahovae Neagu 1969

Taxonomic discussion: This species displays wide morphological variability mainly regarding the number of chambers of the last whorl (5 to 7) and the shape of the chambers (globular to compressed). It is distinguished by having an imperforate band on the equatorial periphery.
[From Loeblich and Tappan (1961): "This species has been confused in the past with the younger species Praeglobotruncana stephani (Gandolfi), and has even been regarded as synonymous by Bronnimann and Brown (1956, p. 531), Ziegler (1957, p. 199) and Banner and Blow ( 1959, p. 8). The two species are quite distinct morphologically, as can be seen by an examination of type material, such as the topotypes herein illustrated. Praeglobotruncana stephani is planoconvex and has angular to rhomboidal chambers, and is somewhat larger in size. It also occurs higher in the Cenomanian than does the nearly wholly biconvex P. delrioensis. There is considerable variation in the amount of compression of the present species, with all gradations from the somewhat compressed and subangular tests, like the holotype (and the topotype here shown in figure 10), to the almost globular chambered forms described as Globorotalia marginaculeata, but now considered conspecific. Praeglobotruncana delrioensis is probably ancestral to P. stephani. In the type area in Texas, it occurs in Albian and lower Cenomanian strata (upper Washita group) and the younger P. stephani occurs in the Eagle Ford group. This lineage excellently demonstrates several of the evolutionary trends suggested by Bronnimann and Brown ( 1956, p. 515) in that there is an increase in size (P. stephani being larger than P. delrioensis), an increased angularity of chambers from the rounded ones of adult P. delrioensis to the subrhomboidal ones of the planoconvex P. stephani, and an increase in the height of coiling." [copied from Chronos database]

Original description: Test broadly elliptical to round in peripheral outline, strongly lobate, singly carinate, about equally biconvex, periphery marked by short, conspicuous, spinose processes; chambers 5 or six in each convolution, roughened somewhat by small blunt beadlike elevations of shell matter especially toward the peripheral margin on each side; dorsal sutures marked by beaded shell material, moderately curved; ventral sutures depressed and radiate; umbilicus distinct, small, shallow, closed; aperture a narrow slit on the inner edge of the base of the septal face under a narrow extended rim. Average diameter about .3 mm.

Geological Range:
Last occurrence (top): within Marginotruncana schneegansi zone (89.75-92.51Ma, top in Turonian stage). Data source:
First occurrence (base): within P. appenninica zone (100.50-101.92Ma, base in Albian stage). Data source: [copied from Chronos database]

References:

Leckie, M. (1984). Mid-Cretaceous planktonic foraminiferal biostratigraphy off Central Morocco, Deep Sea Drilling Project Leg 79, Sites 545 and 547. Initial Reports of the Deep Sea Drilling Project. 79: 579-620. gs

Loeblich, A. R. & Tappan, H. (1961). Cretaceous planktonic foraminifera: Part I-Cenomanian. Micropaleontology. 7: 257-304. gs

Neagu, T. (1969). Cenomanian planktonic foraminifera in the southern part of the eastern Carpathians. Rocznik Polskie Towarzystwo Geologiczne = Annales de la Société Géologique de Pologne. 39: 132-181. gs

Pessagno, E. A. (1967). Upper Cretaceous planktonic foraminifera from the western Gulf Coastal Plain. Palaeontographica Americana. 5: 245-445. gs O

Petrizzo, M. R. & Huber, B. T. (2006). Biostratigraphy and taxonomy of late Albian planktonic foraminifera from ODP Leg 171B (western North Atlantic Ocean). Journal of Foraminiferal Research. 36: 166-190. gs

Plummer, H. J. (1931b). Some Cretaceous foraminifera in Texas. University of Texas Bulletin. 3101: 109-203. gs

test outline:	Subcircular	chamber arrangement:	Trochospiral	edge view:	Spiroconvex	aperture:	Umbilical-extraumbilical
sp chamber shape:	Inflated	coiling axis:	Very low	periphery:	Single keel	aperture border:	Thick lip
umb chbr shape:	Subtriangular	umbilicus:	Narrow	periph margin shape:	Subangular	accessory apertures:	None
spiral sutures:	Strongly depressed	umb depth:	Deep	wall texture:	Smooth	shell porosity:	Finely Perforate: 1-2.5µm
umbilical or test sutures:	Moderately depressed	final-whorl chambers:	5-6	N.B. These characters are used for advanced search. N/A - not applicable

Praeglobotruncana delrioensis

References:

Add Comment

Comments (1)