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Impagidinium cantabrigiense
Impagidinium cantabrigiense De Schepper and Head, 2008, p.106–107, pl.2, figs.1–16.
Holotype: De Schepper and Head, pl.2, figs.1–3.
Age: latest Pliocene–mid Pleistocene.
Original description (De Schepper and Head, 2008):
Impagidinium cantabrigiense sp. nov. (Plate 2)
TYPE. Holotype, sample DSDP 610A-5-5,52-54 cm (44.32 mbsf), slide 2, England Finder reference H44/0; ROMP 57995; Pl. 2, Figs 1-3. Age: ca. 0.82Ma, Subchron C1r.1r, just below the Bruhnes/Matuyama boundary, Early Pleistocene.
DIAGNOSIS. A small suturocavate Impagidinium species with smooth inner wall, spherical to subspherical central body and incomplete tabulation. Shagreenate to finely granulate tegillum forms crests locally of even height, but lower towards apex and higher towards antapex. Crests absent or weakly expressed on dorsal surface along posterior cingular margin; no crests within sulcus.
OCCURRENCE. Latest Pliocene through Middle Pleistocene of Hole 610A (Fig. 2), with a lowest occurrence in sample 610A-11-1, 49-54 cm, in the Olduvai Subchron (C2n), calcareous nannofossil zone NN19, planktonic foraminifer zone PL6-N22, at ca. 1.86 Ma. It occurs infrequently and in low abundance (<3% of total assemblage) until just before the Jaramillo Subchron (0.99-1.07 Ma) and from then onwards becomes more common (3-10%) and peaks (13% in sample 610A-5-5, 52-54 cm) at ca. 0.82 Ma just before the Bruhnes/Matuyama boundary. It has a highest occurrence in the highest sample processed from Hole 610A, which is of Middle Pleistocene age and dated at 0.53 Ma. Also recorded from the Early and Middle Pleistocene of Zakynthos Island, Greece and from the Early (post-Jaramillo) and Middle Pleistocene of ODP Site 963, offshore Sicily (M. Papanikolaou, pers. comm.).
DESCRIPTION. Central body small and spherical to subspherical, sometimes bearing small, faintly discernible apical protuberance of about 0.5 µm high. Sutural crests partially delimit gonyaulacoid tabulation. Central body comprises two wall layers that are closely adpressed except at bases of sutural crests. Pedium solid, smooth. Tegillum thin (<0.3 µm) solid; has shagreenate to finely granulate outer surface; forms suturocavate crests that may be hollow along entire height (e.g. Pl. 2, figs 10, 16) or hollow only at their base (e.g. Pl. 2, figs 3, 14). Both types may be present on same cyst. Some crests may be entirely solid (e.g. Pl. 2, figs 2, 6) but suturocavate crests always present. Crests are entire, locally of even height, but highest on hypocyst, reaching maximum height at antapex. Epicyst bears lower crests; at apex they are invariably low and almost half the height of crests at antapex. A funnel-like structure may occur at antapex, formed by convergence of cavate crests surrounding antapical plate (Pl. 2, figs 2,7). Crests incompletely express tabulation, especially in dorsal and ventral areas. On dorsal surface, anterior cingular margin expressed by a crest, whereas posterior cingular margin is not. A crest demarcates boundary between two cingular plates (possibly 3c and 4c) immediately below archeopyle. On some specimens both anterior and posterior cingular margins are vaguely recognisable on ventral surface, where cingulum meets sulcus. Outline of sulcus expressed by crests. No crests present within sulcus, but tabulation occasionally traced by faint lineation, including along anterior margin of posterior sulcal plate. Archeopyle 1P (plate 3"), with sharp angles and operculum free. Archeopyle approximately congruent with plate boundaries.
DIMENSIONS. Holotype: cyst length (including crests), 43 µm; cyst width (including crests), 40 µm; central body length (excluding crests), 27µm; central body width (excluding crests), 25 µm; minimum apical crest height, 4 µm; maximum antapical crest height, 12µm. Range (minimum, average and maximum measurements are given): central body maximum diameter, 25 (29.0) 36µm; maximum diameter including crests, 38 (46.8) 54µm; maximum apical crest height, 4 (5.8) 8 µm; maximum antapical crest height, 9 (11.7) 15µm. Nineteen specimens measured.
COMPARISON. Impagidinium japonicum Matsuoka, 1983 has crests of equal height in apical and antapical areas. Impagidinium velorum Bujak, 1984 has smooth to shagreenate, membranous sutural crests, that are also higher (19-25 µm) and of equal height over the entire cyst.
ETYMOLOGY. Named after the city of Cambridge (Latin, Cantabrigium), where this species was first identified.
AUTECOLOGY. An oceanic cyst, reported from the oceanic realm in the present study (DSDP Hole 610A) and from the deep shelf of the Mediterranean (ODP Site 963 and Zakynthos, Greece; M. Papanikolaou, pers. comm.). The transition from a warm to cold interval at ca. 0.82 Ma (MIS 20) in Hole 610A is marked by high numbers of Impagidinium pallidum Bujak, 1984 and Nematosphaeropsis labyrinthus (Ostenfeld, 1903) Reid, 1974, the latter becoming the dominant species in the assemblage. Also at this time, Impagidinium cantabrigiense sp. nov. has its highest recorded abundance for Hole 610A and remains abundant during the cold phase. Therefore, Impagidinium cantabrigiense sp. nov. seems related to transitional phases from warm to cold surface waters in open-marine settings, suggesting a preference for cooler conditions.
Holotype: De Schepper and Head, pl.2, figs.1–3.
Age: latest Pliocene–mid Pleistocene.
Original description (De Schepper and Head, 2008):
Impagidinium cantabrigiense sp. nov. (Plate 2)
TYPE. Holotype, sample DSDP 610A-5-5,52-54 cm (44.32 mbsf), slide 2, England Finder reference H44/0; ROMP 57995; Pl. 2, Figs 1-3. Age: ca. 0.82Ma, Subchron C1r.1r, just below the Bruhnes/Matuyama boundary, Early Pleistocene.
DIAGNOSIS. A small suturocavate Impagidinium species with smooth inner wall, spherical to subspherical central body and incomplete tabulation. Shagreenate to finely granulate tegillum forms crests locally of even height, but lower towards apex and higher towards antapex. Crests absent or weakly expressed on dorsal surface along posterior cingular margin; no crests within sulcus.
OCCURRENCE. Latest Pliocene through Middle Pleistocene of Hole 610A (Fig. 2), with a lowest occurrence in sample 610A-11-1, 49-54 cm, in the Olduvai Subchron (C2n), calcareous nannofossil zone NN19, planktonic foraminifer zone PL6-N22, at ca. 1.86 Ma. It occurs infrequently and in low abundance (<3% of total assemblage) until just before the Jaramillo Subchron (0.99-1.07 Ma) and from then onwards becomes more common (3-10%) and peaks (13% in sample 610A-5-5, 52-54 cm) at ca. 0.82 Ma just before the Bruhnes/Matuyama boundary. It has a highest occurrence in the highest sample processed from Hole 610A, which is of Middle Pleistocene age and dated at 0.53 Ma. Also recorded from the Early and Middle Pleistocene of Zakynthos Island, Greece and from the Early (post-Jaramillo) and Middle Pleistocene of ODP Site 963, offshore Sicily (M. Papanikolaou, pers. comm.).
DESCRIPTION. Central body small and spherical to subspherical, sometimes bearing small, faintly discernible apical protuberance of about 0.5 µm high. Sutural crests partially delimit gonyaulacoid tabulation. Central body comprises two wall layers that are closely adpressed except at bases of sutural crests. Pedium solid, smooth. Tegillum thin (<0.3 µm) solid; has shagreenate to finely granulate outer surface; forms suturocavate crests that may be hollow along entire height (e.g. Pl. 2, figs 10, 16) or hollow only at their base (e.g. Pl. 2, figs 3, 14). Both types may be present on same cyst. Some crests may be entirely solid (e.g. Pl. 2, figs 2, 6) but suturocavate crests always present. Crests are entire, locally of even height, but highest on hypocyst, reaching maximum height at antapex. Epicyst bears lower crests; at apex they are invariably low and almost half the height of crests at antapex. A funnel-like structure may occur at antapex, formed by convergence of cavate crests surrounding antapical plate (Pl. 2, figs 2,7). Crests incompletely express tabulation, especially in dorsal and ventral areas. On dorsal surface, anterior cingular margin expressed by a crest, whereas posterior cingular margin is not. A crest demarcates boundary between two cingular plates (possibly 3c and 4c) immediately below archeopyle. On some specimens both anterior and posterior cingular margins are vaguely recognisable on ventral surface, where cingulum meets sulcus. Outline of sulcus expressed by crests. No crests present within sulcus, but tabulation occasionally traced by faint lineation, including along anterior margin of posterior sulcal plate. Archeopyle 1P (plate 3"), with sharp angles and operculum free. Archeopyle approximately congruent with plate boundaries.
DIMENSIONS. Holotype: cyst length (including crests), 43 µm; cyst width (including crests), 40 µm; central body length (excluding crests), 27µm; central body width (excluding crests), 25 µm; minimum apical crest height, 4 µm; maximum antapical crest height, 12µm. Range (minimum, average and maximum measurements are given): central body maximum diameter, 25 (29.0) 36µm; maximum diameter including crests, 38 (46.8) 54µm; maximum apical crest height, 4 (5.8) 8 µm; maximum antapical crest height, 9 (11.7) 15µm. Nineteen specimens measured.
COMPARISON. Impagidinium japonicum Matsuoka, 1983 has crests of equal height in apical and antapical areas. Impagidinium velorum Bujak, 1984 has smooth to shagreenate, membranous sutural crests, that are also higher (19-25 µm) and of equal height over the entire cyst.
ETYMOLOGY. Named after the city of Cambridge (Latin, Cantabrigium), where this species was first identified.
AUTECOLOGY. An oceanic cyst, reported from the oceanic realm in the present study (DSDP Hole 610A) and from the deep shelf of the Mediterranean (ODP Site 963 and Zakynthos, Greece; M. Papanikolaou, pers. comm.). The transition from a warm to cold interval at ca. 0.82 Ma (MIS 20) in Hole 610A is marked by high numbers of Impagidinium pallidum Bujak, 1984 and Nematosphaeropsis labyrinthus (Ostenfeld, 1903) Reid, 1974, the latter becoming the dominant species in the assemblage. Also at this time, Impagidinium cantabrigiense sp. nov. has its highest recorded abundance for Hole 610A and remains abundant during the cold phase. Therefore, Impagidinium cantabrigiense sp. nov. seems related to transitional phases from warm to cold surface waters in open-marine settings, suggesting a preference for cooler conditions.