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Cleistosphaeridium oxfordianum
(Plate X, 1–10)
Previous Australian usage: Cleistosphaeridium cf. ancorum, Sepispinula cf. ancorifera (unpublished well reports).
Holotype: Plate X, 1–3
Diagnosis: An intermediate-sized, spherical, acavate, proximochorate dinoflagellate cyst. Autophragm granulate to vermiculate, displaying numerous conical and flat processes with dolabrate and licrate terminations. Tabulation gonyaulacalean, archeopyle apical, Type (tA), operculum free. Etymology: ‘oxfordianum’ after the geologic stage from which it was first observed and is most abundant.
Material: Palynological strew samples; 2842 m, Io-1; 2822m, Jansz- 1; 2810 m, 2811 m Jansz-3; 3205.73 m, 3215.62 m, Laminaria-2.
Age: Callovian–Kimmeridgian (V. tabulata–D. swanense zones; Fig. 5)
Lithostratigraphic occurrence: The Laminaria, Elang, Frigate,Montara, lower Vulcan and Iris Marl fms of the Bonaparte Basin. The Calypso Fm, Dingo Claystone, Jansz Sandstone and Eliassen Fm of the Northern Carnarvon Basin.
Description: An intermediate-sized, spherical to subspherical, acavate, proximochorate dinoflagellate cyst. Autophragm 1–2 μmthick, densely covered by fine grana and/or vermiculae and numerous solid processes of roughly equal length. Processes ranging from thin and conical to tubular with either a circular or flat cross-section. Processes are distally asymmetrical and variably furcate with distinctive dolabrate or licrate terminations, producing processes that range from narrow pick-like types to broad-fanned forms (Fig. 10). Processes often linked proximally via short solid ridges forming small groups of two to three elements with distal terminations, usually free, infrequently connected via thin trabeculae. Tabulation indicated by archeopyle sutures and prominent sulcal notch; cingulum seldom indicated. Archeopyle apical, Type (tA), operculumfree, commonlywith short accessory sutures. Archeopyle shape inconsistent, suggesting intraspecific variability in the precingular series; gonyaulacalean tabulation formula:?pr, 4′, 6–7″,?6c,?6″’, 1p, 1″”,?s.
Dimensions: (24 specimens measured)
Length without operculum: 45.4 (54) 61.5
Width: 49 (59) 73
Max. process length: 4.5 (7) 11
Comparison and remarks: The genus ImpletosphaeridiumMorgenroth, 1966 emend. Islam, 1993 shares many key characteristics with Cleistosphaeridium, but its broader circumscription makes its use problematic (Eaton et al., 2001, p. 174; Fauconnier and Masure, 2004, p. 337). This new species is therefore assigned to Cleistosphaeridium on the premise that it possesses variably dolabrate processes. However, the faint penitabular condition of its processes, and the possible presence of a 7″ plate on some specimens, prevent a confident attribution.
Both Cleistosphaeridium? oxfordianum and the type species Cleistosphaeridium diversispinosum Davey et al., 1966 share highly comparable processes (Fig. 10). Cleistosphaeridium? oxfordianum differs from the type species in having a greater number of processes (>100) that are shorter (10–30% of the overall cyst body in length) than those of the type species (25–40%) (Eaton et al., 2001; Fauconnier and Masure, 2004). On specimenswith predominantly flat processes or process groups, the processes may align to forma pseudo-reticulum (Plate X, 1).
Previous Australian usage: Cleistosphaeridium cf. ancorum, Sepispinula cf. ancorifera (unpublished well reports).
Holotype: Plate X, 1–3
Diagnosis: An intermediate-sized, spherical, acavate, proximochorate dinoflagellate cyst. Autophragm granulate to vermiculate, displaying numerous conical and flat processes with dolabrate and licrate terminations. Tabulation gonyaulacalean, archeopyle apical, Type (tA), operculum free. Etymology: ‘oxfordianum’ after the geologic stage from which it was first observed and is most abundant.
Material: Palynological strew samples; 2842 m, Io-1; 2822m, Jansz- 1; 2810 m, 2811 m Jansz-3; 3205.73 m, 3215.62 m, Laminaria-2.
Age: Callovian–Kimmeridgian (V. tabulata–D. swanense zones; Fig. 5)
Lithostratigraphic occurrence: The Laminaria, Elang, Frigate,Montara, lower Vulcan and Iris Marl fms of the Bonaparte Basin. The Calypso Fm, Dingo Claystone, Jansz Sandstone and Eliassen Fm of the Northern Carnarvon Basin.
Description: An intermediate-sized, spherical to subspherical, acavate, proximochorate dinoflagellate cyst. Autophragm 1–2 μmthick, densely covered by fine grana and/or vermiculae and numerous solid processes of roughly equal length. Processes ranging from thin and conical to tubular with either a circular or flat cross-section. Processes are distally asymmetrical and variably furcate with distinctive dolabrate or licrate terminations, producing processes that range from narrow pick-like types to broad-fanned forms (Fig. 10). Processes often linked proximally via short solid ridges forming small groups of two to three elements with distal terminations, usually free, infrequently connected via thin trabeculae. Tabulation indicated by archeopyle sutures and prominent sulcal notch; cingulum seldom indicated. Archeopyle apical, Type (tA), operculumfree, commonlywith short accessory sutures. Archeopyle shape inconsistent, suggesting intraspecific variability in the precingular series; gonyaulacalean tabulation formula:?pr, 4′, 6–7″,?6c,?6″’, 1p, 1″”,?s.
Dimensions: (24 specimens measured)
Length without operculum: 45.4 (54) 61.5
Width: 49 (59) 73
Max. process length: 4.5 (7) 11
Comparison and remarks: The genus ImpletosphaeridiumMorgenroth, 1966 emend. Islam, 1993 shares many key characteristics with Cleistosphaeridium, but its broader circumscription makes its use problematic (Eaton et al., 2001, p. 174; Fauconnier and Masure, 2004, p. 337). This new species is therefore assigned to Cleistosphaeridium on the premise that it possesses variably dolabrate processes. However, the faint penitabular condition of its processes, and the possible presence of a 7″ plate on some specimens, prevent a confident attribution.
Both Cleistosphaeridium? oxfordianum and the type species Cleistosphaeridium diversispinosum Davey et al., 1966 share highly comparable processes (Fig. 10). Cleistosphaeridium? oxfordianum differs from the type species in having a greater number of processes (>100) that are shorter (10–30% of the overall cyst body in length) than those of the type species (25–40%) (Eaton et al., 2001; Fauconnier and Masure, 2004). On specimenswith predominantly flat processes or process groups, the processes may align to forma pseudo-reticulum (Plate X, 1).