Globorotalia conoidea Walters

Hanagata, S & Nobuhara, T, 2015, Illustrated guide to Pliocene foraminifera from Miyakojima, Ryukyu Island Arc, with comments on biostratigraph, Palaeontologia Electronica (Cambridge, England) 33 (8), pp. 1-142 : 42

Globorotalia conoidea Walters

Figures 15.5, 15.6

1965 Globorotalia miozea conoidea Walters , p. 124, fig. 8.

1974 Globorotalia aff. cibaoensis Ujiié and Ōki , pl. 5, figs. 1—4.

1977 Globorotalia miozea conoidea Walters — Berggren, p. 298, pl. 2, figs. 9—31.

1978 Globorotalia miozea conoidea Walters — Keller (a), pl. 1, figs. 7—10.

1983 Globorotalia (Globoconella) conoidea Walters — Kennett and Srinivasan, p. 112, pl. 26, figs. 4—6.

1985 Globorotalia (Globorotalia) miozea conoidea Walters — Ibaraki, p. 132, pl. 10, figs. 12—14.

1985 Globorotalia (s.s.) aff. pliozea Hornibrook — Ujiié, p. 113, pl. 14, figs. 5—7.

1985 Globorotalia conoidea Walters — Jenkins, p. 276, figs. 7.14, 7.15.

Remarks. Specimens from Miyakojima Island exhibit a transitional form between G. conoidea and Globorotalia conomiozea . It has four chambers in the final whorl similar to G. conomiozea , while the umbilical side is less vaulted than typical G. conoidea as figured by Kennett and Srinivasan (1983). Natori (1976, table 2) showed in his range chart that G. conomiozea evolved into G. conoidea ; whereas Kennett and Srinivasan (1983) noted the opposite and showed that G. conoidea disappeared in the uppermost Miocene. In Miyakojima Island, G. conomiozea disappears earlier than G. conoidea as noted by Natori (1976) in Okinawa-jima, both in the Pliocene. Based on those reports, it can be stated that G. conoidea and G. conomiozea are potentially useful indicators of the upper Miocene to lower Pliocene of subtropical to temperate seas, but their ranges vary between areas, and further stratigraphic studies are called for.

Occurrence. Common in the upper part of the Yonahama Formation.

Figures

FIGURE 15. Family Epistominidae and Globorotaliidae. All scale bars = 0.1mm, unless otherwise indicated. 1, 2. Hoeglundina elegans (d'Orbigny) large form, 1: MPC-26324 from sample 2-2 (Minebari Formation, PL5); 2: MPC- 26325 from sample 4 (Minebari F., PL5). 3, 4. Clavatorella aff. suturanii Giannelli and Salvatorini, 3: MPC-25930 from sample 5 (Minebari F., PL5); 4: MPC-25931 from sample MK01 (Yonahama F., PL2). 5, 6. Globorotalia conoidea Walters, 5: MPC-25968 from sample 7 (Yonahama F., PL4); 6: MPC-25969 from sample 8-2 (Yonahama F., PL4). 7, 8. Globorotalia conomiozea Kennett, 7: MPC-25970 from sample 3 (Onogoshi F., PL1); 8: MPC-25971 from sample 6 (Yonahama F., PL2). 9, 10. Globorotalia crassaformis (Galloway and Wissler), 9: MPC-25972 from sample MK02A (Minebari F., PL5); 10: MPC-25973 from sample MK02B (Minebari F., PL5). 11, 12. Globorotalia cultrata (d'Orbigny), 11: MPC-25974 from sample MK01 (Yonahama F., PL2); 12: MPC-25975 from sample MK02A (Minebari F., PL5).