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Pyxidinopsis meadensis
Pyxidinopsis meadensis Willumsen, 2011, p.230,233, figs.12A–D.
Holotype: Willumsen, 2011, figs.12A–B.
Age: late Maastrichtian–early Paleocene.
Original description (Willumsen, 2011)
Type unit and locality. Mead Hill Formation, Mead Stream section, Clarence Valley, Marlborough.
Etymology. After Mead Stream, Clarence Valley, Marlborough.
Types. Holotype, Wharanui Point, P30/f269, slide L18268/1, 6 μm, EF: C30 (Fig. 12A, B). Paratype, Mead Stream P30/f906, L18315/3, 6 μm, EF: D29,2.
Diagnosis. Large subspherical to oval Pyxidinopsis with a thick, complex wall structure. The surface is covered by a reticulum with low muri delimiting numerous small, irregular lumina forming a rugulate surface ornamentation. Thickening and development of low spines occurs at the muri junctions. The operculum (Fig. 12C) is mostly free, but can be attached to the archeopyle margin (Fig 12A).
Description. Large, subspherical to oval proximate dinoflagellate cyst with a complex wall structure. Autophragm only. Surface ornamentation consists of an irregular reticulum formed by lumina with a diameter of <5 μm. The variation in the height and thickness of each muri and development of solid spines at the junctions gives this cyst its characteristic irregular reticulate to rugulate ornamentation. The paratabulation is indicated by a precingular rhombic to rounded triangular archeopyle, formed by the loss of paraplate 3″. The operculum has an iso-deltaform camerate shape and is commonly attached to the archeopyle margin along the contact between cingular plates or paraplate 2″ or 4″ (Fig. 12A, B). Total diameter 75(87)94 μm [10 specimens measured].
Remarks. Pyxidinopsis meadensis sp. nov. differs from P. ardonensis Jan du Chêne, 1988, Pyxidinopsis epakros and Pyxidinopsis everriculum by being larger and having a very robust irregular reticulate to rugulate surface ornamentation; from P. challengerensis Habib, 1976 by having a complete reticulum consisting of muri with spine-like projections in the corners of the irregular lumina; from P. waipawaense Wilson, 1988 by being almost twice the size, having a different surface ornamentation and thinner wall. Some of the specimens illustrated as P. waipawaense by Fensome & Williams, 2004 (Scotian Margin Palyatlas: http://gsc.nrcan.gc.ca/marine/scotianmargin) appear similar to P. meadensis sp. nov. on the basis of their wall structure and development of solid spines at the junctions of the muri. Pyxidinopsis meadensis differs from Cerebrocysta (Bujak in Bujak et al., 1980) by having a precingular archeopyle formed by the loss of paraplate 3″. It also has a reticulate surface instead of a random surface ornament of low crests. In stratigraphic studies, where only the operculum of P. meadensis is recovered, this species is still easily recognizable (Fig. 12C).
Age and distribution. The FO of Pyxidinopsis meadensis occurs below the sampled interval, but its LO is within the early Paleocene radiolarian Zone RP2. Pyxidinopsis meadensis is common to very abundant in the dinocyst assemblages in the uppermost Maastrichtian to lowermost Paleocene sections examined from the Marlborough region, but it is relatively rare in sections studied from the Canterbury region (Willumsen 2003). Pyxidinopsis meadensis is recorded in sections from Branch Stream, Fairfield Quarry, Grey River, Mead Stream, mid-Waipara River, Wharanui Point and Woodside Creek. In connection with a study of Maastrichtian and uppermost Campanian strata from the Australian Northwest Shelf, Robin Helby recorded this species from the Parry-1 Well (pers. comm. April 2006).
Holotype: Willumsen, 2011, figs.12A–B.
Age: late Maastrichtian–early Paleocene.
Original description (Willumsen, 2011)
Type unit and locality. Mead Hill Formation, Mead Stream section, Clarence Valley, Marlborough.
Etymology. After Mead Stream, Clarence Valley, Marlborough.
Types. Holotype, Wharanui Point, P30/f269, slide L18268/1, 6 μm, EF: C30 (Fig. 12A, B). Paratype, Mead Stream P30/f906, L18315/3, 6 μm, EF: D29,2.
Diagnosis. Large subspherical to oval Pyxidinopsis with a thick, complex wall structure. The surface is covered by a reticulum with low muri delimiting numerous small, irregular lumina forming a rugulate surface ornamentation. Thickening and development of low spines occurs at the muri junctions. The operculum (Fig. 12C) is mostly free, but can be attached to the archeopyle margin (Fig 12A).
Description. Large, subspherical to oval proximate dinoflagellate cyst with a complex wall structure. Autophragm only. Surface ornamentation consists of an irregular reticulum formed by lumina with a diameter of <5 μm. The variation in the height and thickness of each muri and development of solid spines at the junctions gives this cyst its characteristic irregular reticulate to rugulate ornamentation. The paratabulation is indicated by a precingular rhombic to rounded triangular archeopyle, formed by the loss of paraplate 3″. The operculum has an iso-deltaform camerate shape and is commonly attached to the archeopyle margin along the contact between cingular plates or paraplate 2″ or 4″ (Fig. 12A, B). Total diameter 75(87)94 μm [10 specimens measured].
Remarks. Pyxidinopsis meadensis sp. nov. differs from P. ardonensis Jan du Chêne, 1988, Pyxidinopsis epakros and Pyxidinopsis everriculum by being larger and having a very robust irregular reticulate to rugulate surface ornamentation; from P. challengerensis Habib, 1976 by having a complete reticulum consisting of muri with spine-like projections in the corners of the irregular lumina; from P. waipawaense Wilson, 1988 by being almost twice the size, having a different surface ornamentation and thinner wall. Some of the specimens illustrated as P. waipawaense by Fensome & Williams, 2004 (Scotian Margin Palyatlas: http://gsc.nrcan.gc.ca/marine/scotianmargin) appear similar to P. meadensis sp. nov. on the basis of their wall structure and development of solid spines at the junctions of the muri. Pyxidinopsis meadensis differs from Cerebrocysta (Bujak in Bujak et al., 1980) by having a precingular archeopyle formed by the loss of paraplate 3″. It also has a reticulate surface instead of a random surface ornament of low crests. In stratigraphic studies, where only the operculum of P. meadensis is recovered, this species is still easily recognizable (Fig. 12C).
Age and distribution. The FO of Pyxidinopsis meadensis occurs below the sampled interval, but its LO is within the early Paleocene radiolarian Zone RP2. Pyxidinopsis meadensis is common to very abundant in the dinocyst assemblages in the uppermost Maastrichtian to lowermost Paleocene sections examined from the Marlborough region, but it is relatively rare in sections studied from the Canterbury region (Willumsen 2003). Pyxidinopsis meadensis is recorded in sections from Branch Stream, Fairfield Quarry, Grey River, Mead Stream, mid-Waipara River, Wharanui Point and Woodside Creek. In connection with a study of Maastrichtian and uppermost Campanian strata from the Australian Northwest Shelf, Robin Helby recorded this species from the Parry-1 Well (pers. comm. April 2006).