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Oligosphaeridium varifenestratum
(Plate VI, 1–12)
Previous Australian usage: Oligosphaeridium cf. ‘complex’, Oligosphaeridium cf. ‘pulcherrimum’, Oligosphaeridium cf. ‘diluculum complex’ (unpublished well reports; Sinclair, 2012).
Holotype: Plate VI, 3
Diagnosis: A moderately large species of Oligosphaeridium with a smooth to microgranulate, spherical to subspherical central body. Cyst adorned with long, mesotabulate, variably fenestrate, funnel-shaped processes with irregular, denticulate margins. Pairs of processes may be linked distally by thin trabeculae. Cingular and sulcal plates lack processes. Tabulation gonyaulacacean; archeopyle apical, Type (tA), operculum free.
Etymology: ‘varifenestratum’ in reference to the highly variable fenestrate processes.
Material: Palynological strew samples; 2842 m Io-1; 2881 m, Jansz- 1; 2810 m, Jansz-3; 3179 m, Laminaria-2; 3074.9 m Pyxis-1.
Age: Oxfordian (W. spectabilis Zone; Fig. 5).
Lithostratigraphic occurrence: The Frigate and lower Vulcan fms of the Bonaparte Basin. The Dingo Claystone, Jansz Sandstone and Eliassen Fm of the Northern Carnarvon Basin.
Description: A large acavate, skolochorate dinoflagellate cyst with a spherical to subspherical central body that has smooth to microgranulate ornament. Cyst adorned with long, mesotabulate, variably fenestrate, funnel-shaped processes with irregular, denticulate margins. Funnel-shaped processes ranging in length from half to equal the central body diameter, are solid to hollow, variably flared and fenestrate, and may be split longitudinally. Fenestration commonly restricted to the distal third of the processes. Size, shape and distribution of the fenestrae are highly variable on individual specimens, ranging fromsmall circular to large rounded polygonal lumina (>10 μm). The distal rim of the funnel is subcircular to polygonal, and may reflect the plate outline (Plate VI, 12). Thin trabeculae may infrequently connect pairs of processes distally or tether the distal termination of a process to the cyst body. Trabeculae are frequently broken with remnants appearing as irregular digits or ribbons trailing from the distal process margins. Numerous filaments or root-like structures anchor the base of the process to the central body. Tabulation standard gonyaulacacean; formula:?pr, 4′, 6″,?6c, 6″’, 1p, 1″”,?5–6 s. Archeopyle apical, Type (tA), operculum free.
Dimensions: (32 specimens measured)
Total length: 81 (114) 147
Total width: 94 (115) 149 Central body length without operculum: 36 (49) 68 Central body width: 38 (53) 60 Process length: 12 (33) 60
Comparison and remarks: Oligosphaeridium? varifenestratum has been documented in numerous unpublished well reports since the mid 1990's but has never been formally described. The highly variable pattern of fenestration of this species is comparable to that of Orthotrichum fenestratum Duxbury, 1980, O. pulcherrimum Deflandre and Cookson, 1955 (Davey and Williams, 1996) and O. perforatum Gocht, 1959 (Fig. 8). Oligosphaeridium? varifenestratum differs from the type species, Oligosphaeridium complex White, 1842 (Davey and Williams, 1966), in having wider, distally flared, fenestrate processes with irregular digitate to trabeculate extensions. Oligosphaeridium? varifenestratum is comparable to Oligosphaeridium pulcherrimum and Oligosphareidum perforatum subsp. colum Duxbury, 1983, but is distinct in having processes that have more variable distal fenestrae and are distally surmounted by irregular spines/ digits, variable distal fenestrae, and distal extensions. Oligosphaeridium? varifenestratum is distinct from Oligosphaeridium fenestratum Duxbury, 1980 in having processes with variably subcircular–subpolygonal crosssections and narrower distal terminations. In contrast, Oligosphaeridium perforatum, lacks distal extensions and features processes with a smoothedged conical flare.
The presence of distally linked processes on Oligosphaeriumhas previously been documented from Oligosphaeridium? trabeculosum Singh, 1983, and Oligosphaeridium? junctum Bailey and Loy, 1997, described from the Cenomanian of Canada and Hauterivian of theUK, respectively. Neither of these species possesses fenestrate processes, and in both cases, the number of distally linked processes is greater than that of Oligosphaeridium? varifenestratum, Although the remnants of fine distal trabeculae are frequently present, only one or two pairs of process are ever linked. As members of the genus Rigaudella Below, 1982, have much more robust trabeculae that are present between all processes, this species is preferably, although questionably, assigned to Oligosphaeridium. As such, Oligosphaeridium? varifenestrata is unique in possessing fenestrate processes that are infrequently linked via distal trabeculae. Oligosphaeridium pulcherrimum has been documented from the Kimmeridgian of Europe (Gitmez, 1970), Oxfordian–Tithonian of the Middle East (Gitmez and Ertug, 1999) and the Kimmeridigian–Tithonian of India (Jain et al., 1984; Kumar, 1986).When present, the illustrated material is often only ambiguously assignable at species level. Given the high degree of similarity it is possible that some of these specimens may be conspecific with Oligosphaeridium? varifenestratum.
Previous Australian usage: Oligosphaeridium cf. ‘complex’, Oligosphaeridium cf. ‘pulcherrimum’, Oligosphaeridium cf. ‘diluculum complex’ (unpublished well reports; Sinclair, 2012).
Holotype: Plate VI, 3
Diagnosis: A moderately large species of Oligosphaeridium with a smooth to microgranulate, spherical to subspherical central body. Cyst adorned with long, mesotabulate, variably fenestrate, funnel-shaped processes with irregular, denticulate margins. Pairs of processes may be linked distally by thin trabeculae. Cingular and sulcal plates lack processes. Tabulation gonyaulacacean; archeopyle apical, Type (tA), operculum free.
Etymology: ‘varifenestratum’ in reference to the highly variable fenestrate processes.
Material: Palynological strew samples; 2842 m Io-1; 2881 m, Jansz- 1; 2810 m, Jansz-3; 3179 m, Laminaria-2; 3074.9 m Pyxis-1.
Age: Oxfordian (W. spectabilis Zone; Fig. 5).
Lithostratigraphic occurrence: The Frigate and lower Vulcan fms of the Bonaparte Basin. The Dingo Claystone, Jansz Sandstone and Eliassen Fm of the Northern Carnarvon Basin.
Description: A large acavate, skolochorate dinoflagellate cyst with a spherical to subspherical central body that has smooth to microgranulate ornament. Cyst adorned with long, mesotabulate, variably fenestrate, funnel-shaped processes with irregular, denticulate margins. Funnel-shaped processes ranging in length from half to equal the central body diameter, are solid to hollow, variably flared and fenestrate, and may be split longitudinally. Fenestration commonly restricted to the distal third of the processes. Size, shape and distribution of the fenestrae are highly variable on individual specimens, ranging fromsmall circular to large rounded polygonal lumina (>10 μm). The distal rim of the funnel is subcircular to polygonal, and may reflect the plate outline (Plate VI, 12). Thin trabeculae may infrequently connect pairs of processes distally or tether the distal termination of a process to the cyst body. Trabeculae are frequently broken with remnants appearing as irregular digits or ribbons trailing from the distal process margins. Numerous filaments or root-like structures anchor the base of the process to the central body. Tabulation standard gonyaulacacean; formula:?pr, 4′, 6″,?6c, 6″’, 1p, 1″”,?5–6 s. Archeopyle apical, Type (tA), operculum free.
Dimensions: (32 specimens measured)
Total length: 81 (114) 147
Total width: 94 (115) 149 Central body length without operculum: 36 (49) 68 Central body width: 38 (53) 60 Process length: 12 (33) 60
Comparison and remarks: Oligosphaeridium? varifenestratum has been documented in numerous unpublished well reports since the mid 1990's but has never been formally described. The highly variable pattern of fenestration of this species is comparable to that of Orthotrichum fenestratum Duxbury, 1980, O. pulcherrimum Deflandre and Cookson, 1955 (Davey and Williams, 1996) and O. perforatum Gocht, 1959 (Fig. 8). Oligosphaeridium? varifenestratum differs from the type species, Oligosphaeridium complex White, 1842 (Davey and Williams, 1966), in having wider, distally flared, fenestrate processes with irregular digitate to trabeculate extensions. Oligosphaeridium? varifenestratum is comparable to Oligosphaeridium pulcherrimum and Oligosphareidum perforatum subsp. colum Duxbury, 1983, but is distinct in having processes that have more variable distal fenestrae and are distally surmounted by irregular spines/ digits, variable distal fenestrae, and distal extensions. Oligosphaeridium? varifenestratum is distinct from Oligosphaeridium fenestratum Duxbury, 1980 in having processes with variably subcircular–subpolygonal crosssections and narrower distal terminations. In contrast, Oligosphaeridium perforatum, lacks distal extensions and features processes with a smoothedged conical flare.
The presence of distally linked processes on Oligosphaeriumhas previously been documented from Oligosphaeridium? trabeculosum Singh, 1983, and Oligosphaeridium? junctum Bailey and Loy, 1997, described from the Cenomanian of Canada and Hauterivian of theUK, respectively. Neither of these species possesses fenestrate processes, and in both cases, the number of distally linked processes is greater than that of Oligosphaeridium? varifenestratum, Although the remnants of fine distal trabeculae are frequently present, only one or two pairs of process are ever linked. As members of the genus Rigaudella Below, 1982, have much more robust trabeculae that are present between all processes, this species is preferably, although questionably, assigned to Oligosphaeridium. As such, Oligosphaeridium? varifenestrata is unique in possessing fenestrate processes that are infrequently linked via distal trabeculae. Oligosphaeridium pulcherrimum has been documented from the Kimmeridgian of Europe (Gitmez, 1970), Oxfordian–Tithonian of the Middle East (Gitmez and Ertug, 1999) and the Kimmeridigian–Tithonian of India (Jain et al., 1984; Kumar, 1986).When present, the illustrated material is often only ambiguously assignable at species level. Given the high degree of similarity it is possible that some of these specimens may be conspecific with Oligosphaeridium? varifenestratum.