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Craspedodinium swanense
Craspedodinium swanense Riding and Helby, 2001f, p.143,145,147, figs.1A-L,2A-H.
Holotype: Riding and Helby, 2001f, fig.1L.
Age: Kimmeridgian.
Original description (Riding & Helby, 2001f)
A species of Craspedodinium, ovoidal in outline and dorsoventrally flattened. A low wide, solid apical protuberance or boss is developed on the endophragm and the periphragm mirrors this outline of this feature. Circumcavate or bicavate in cyst organisation. The endophragm is relatively thick (1-2 µm) and smooth, scabrate, rugulate and/or microreticulate; generally not folded. Periphragm thin (<0.5 µm), diaphanous, smooth and may be folded. These low, distally smooth periphragmal folds may partially reflext a gonyaulacalean paratabulation, especially around the paracingulum and the hypocyst. Epicyst and hypocyst normally subequal in lengthl the hypocyst, however, may be slightly longer. Accesoory archaeopyle sutures may be developed.
Dimensions. The specimens of Craspedodinium swanense studied are from sidewall core samples in Buang-1 well at 3504.00 m and 3505.20 m and Jabiru-8A well at 1842.50m. The dimensions of material from both wells are given here separately, to effect comparisons. Note that the secondary dorsoventral flattening may have distorted some of the specimens. In particular, some specimens are anomalously wide due to severe compression.
Measurements of specimens from 3504.00m and 3505.20m in Buang-1 well (µm; n=27): Min. (Mean) Max.
Length of pericyst incl. operculum: 85 (99) 110
Length of pericyst excl. operculum: 80 (105) 123
Length of endocyst incl. operculum: 80 (93) 100
Length of endocyst excl. operculum: 70 (95) 112
Width of pericyst at paracingulum: 81 (99) 118
Width of endocyst at paracingulum: 79 (96) 111
Maximum width of pericoel: 3 (6) 10
Width of operculum in dorsoventral view: 35 (46) 57
Depth of operculum in dorsoventral view: 47 (55) 61
Height of apical protuberance: 3 (4.5) 5
Width of apical protuberance: 7 (10) 11
Note that only 4 entire cysts were measured, out of an assemblage of 27 specimens. This disparity has given rise to the apparently anomalous average and maximum lengths of the pericyst and endocyst.
Measurements of specimens from 1842.50m in Jabiru-8A well (µm; n=24): Min. (Mean) Max.
Length of pericyst incl. operculum: 77 (92) 100
Length of pericyst excl. operculum: 67 (84) 100
Length of endocyst incl. operculum: 76 (90) 98
Length of endocyst excl. operculum: 58 (77) 89
Width of pericyst at paracingulum: 75 (93) 111
Width of endocyst at paracingulum: 70 (88) 105
Maximum width of pericoel: 2 (5) 12
Width of operculum, dorsoventral view: 37 (47) 56
Depth of operculum, dorsoventral view: 53 (58) 67
Height of apical protuberance: 3 (4) 5
Width of apical protuberance: 5 (8) 12
Note that only 5 entire cysts were measured, out of an assemblage of 24 specimens. This disparity has given rise to the apparently anomalous average and maximum lengths of the pericyst and endocyst in both the entire cyst and the loisthocyst. It is clear from the above data that the Buang-1 well material is consitently slightly larger than the specimens from Jabiru-8A well.
Comments. Specimens of Craspedodinium swanense may be elongate or wider than long. The pericoel is normally best developed at the antapex, where it can approach, but rarely exceed, 10µm. This cavity, where developed, is normally 1-2 µm wide in the equatorial regions. However, the two cyst layers are frequently closely appressed in the midlateral areas. Occasionally, the periphragm may be missing, probably removed by mechanical damage. The outline of the operculum and the accessory archaeopyle sutures indicates the presence of four apical and six precingular paraplates. Furthermore, the low folds in the periphragm may partially indicate the paracingulum and, more rarely, a hypocystal paratabulation of six postcingulars and a singly antapical paraplate. Folds indicating the precingular paraplates are relatively rare. This paratabulation is clearly gonyaulacalean, with a formula of 4', 6", Xc, 6"', 1?p, 1"", Xs. A similar paratabulation pattern is evident from the specimens of the genotype, Craspedodinium indistinctum (see Morgan, 1980 and Riding & Helby, 2001f). Accessory archaeopyle sutures may form deep splits between the precingular paraplates of the endophragm. The robust endophragm exhibits significant variation in ornamentation. Material from the Buang-1 well is scabrate to rugulate and furthermore the rugulate forms may also be irregularly microreticulate. By contrast, the endophragm in the specimens from the Jabiru-8A well is smooth.
Comparison. The genotype, Craspedodinium indistinctum, differs from C. swanense in lacking an apical boss/protuberance on the endocyst and having trabeculate endophragmal processes at the cyst periphery and the apical paraplate series. Craspedodinium americanum Habib 1970 is subcircular in outline, not paratabulate and much smaller than C. swanense. The Late Cretaceous species Craspedodinium turonicum Prössl 1990 is also significantly smaller than C. swanense. Furthermore, it has an antapical constriction and a strongly reticulate periphragm (Prössl, 1990). In addition, the three other species of Craspedodinium lack apical protuberances formed by the endophragm. Cygnusicysta taltarniana Riding and Helby 2001f is consisitently circucavate and significantly smaller than Craspedodinium swanense. Furthermore, apart from the principal archaeoyle suture, C. taltarniana lacks any indication of paratabulation. Craspedodinium is similar to other cavate genera with apical archaeopyles such as Leberidocysta Stover and Evitt 1978. However, Leberidocysta has delicate periphragm which is extremely susceptible to mechanical damage (Cookson & Eisenack, 1962).
Derivation of name. Form the Dingodinium swanense Zone, to which this species is confined.
Holotype and type locality. Figure 1L, CPC 35656, Buang-1 well, sidewall core at 3504.00m
Stratigraphical distribution. Craspedodinium swanense is confined to the Kimmeridgian Dingodinium swanense Zone (6aiia-6aib) of the Timor Sea region (Helby & Partridge in prep.)
Holotype: Riding and Helby, 2001f, fig.1L.
Age: Kimmeridgian.
Original description (Riding & Helby, 2001f)
A species of Craspedodinium, ovoidal in outline and dorsoventrally flattened. A low wide, solid apical protuberance or boss is developed on the endophragm and the periphragm mirrors this outline of this feature. Circumcavate or bicavate in cyst organisation. The endophragm is relatively thick (1-2 µm) and smooth, scabrate, rugulate and/or microreticulate; generally not folded. Periphragm thin (<0.5 µm), diaphanous, smooth and may be folded. These low, distally smooth periphragmal folds may partially reflext a gonyaulacalean paratabulation, especially around the paracingulum and the hypocyst. Epicyst and hypocyst normally subequal in lengthl the hypocyst, however, may be slightly longer. Accesoory archaeopyle sutures may be developed.
Dimensions. The specimens of Craspedodinium swanense studied are from sidewall core samples in Buang-1 well at 3504.00 m and 3505.20 m and Jabiru-8A well at 1842.50m. The dimensions of material from both wells are given here separately, to effect comparisons. Note that the secondary dorsoventral flattening may have distorted some of the specimens. In particular, some specimens are anomalously wide due to severe compression.
Measurements of specimens from 3504.00m and 3505.20m in Buang-1 well (µm; n=27): Min. (Mean) Max.
Length of pericyst incl. operculum: 85 (99) 110
Length of pericyst excl. operculum: 80 (105) 123
Length of endocyst incl. operculum: 80 (93) 100
Length of endocyst excl. operculum: 70 (95) 112
Width of pericyst at paracingulum: 81 (99) 118
Width of endocyst at paracingulum: 79 (96) 111
Maximum width of pericoel: 3 (6) 10
Width of operculum in dorsoventral view: 35 (46) 57
Depth of operculum in dorsoventral view: 47 (55) 61
Height of apical protuberance: 3 (4.5) 5
Width of apical protuberance: 7 (10) 11
Note that only 4 entire cysts were measured, out of an assemblage of 27 specimens. This disparity has given rise to the apparently anomalous average and maximum lengths of the pericyst and endocyst.
Measurements of specimens from 1842.50m in Jabiru-8A well (µm; n=24): Min. (Mean) Max.
Length of pericyst incl. operculum: 77 (92) 100
Length of pericyst excl. operculum: 67 (84) 100
Length of endocyst incl. operculum: 76 (90) 98
Length of endocyst excl. operculum: 58 (77) 89
Width of pericyst at paracingulum: 75 (93) 111
Width of endocyst at paracingulum: 70 (88) 105
Maximum width of pericoel: 2 (5) 12
Width of operculum, dorsoventral view: 37 (47) 56
Depth of operculum, dorsoventral view: 53 (58) 67
Height of apical protuberance: 3 (4) 5
Width of apical protuberance: 5 (8) 12
Note that only 5 entire cysts were measured, out of an assemblage of 24 specimens. This disparity has given rise to the apparently anomalous average and maximum lengths of the pericyst and endocyst in both the entire cyst and the loisthocyst. It is clear from the above data that the Buang-1 well material is consitently slightly larger than the specimens from Jabiru-8A well.
Comments. Specimens of Craspedodinium swanense may be elongate or wider than long. The pericoel is normally best developed at the antapex, where it can approach, but rarely exceed, 10µm. This cavity, where developed, is normally 1-2 µm wide in the equatorial regions. However, the two cyst layers are frequently closely appressed in the midlateral areas. Occasionally, the periphragm may be missing, probably removed by mechanical damage. The outline of the operculum and the accessory archaeopyle sutures indicates the presence of four apical and six precingular paraplates. Furthermore, the low folds in the periphragm may partially indicate the paracingulum and, more rarely, a hypocystal paratabulation of six postcingulars and a singly antapical paraplate. Folds indicating the precingular paraplates are relatively rare. This paratabulation is clearly gonyaulacalean, with a formula of 4', 6", Xc, 6"', 1?p, 1"", Xs. A similar paratabulation pattern is evident from the specimens of the genotype, Craspedodinium indistinctum (see Morgan, 1980 and Riding & Helby, 2001f). Accessory archaeopyle sutures may form deep splits between the precingular paraplates of the endophragm. The robust endophragm exhibits significant variation in ornamentation. Material from the Buang-1 well is scabrate to rugulate and furthermore the rugulate forms may also be irregularly microreticulate. By contrast, the endophragm in the specimens from the Jabiru-8A well is smooth.
Comparison. The genotype, Craspedodinium indistinctum, differs from C. swanense in lacking an apical boss/protuberance on the endocyst and having trabeculate endophragmal processes at the cyst periphery and the apical paraplate series. Craspedodinium americanum Habib 1970 is subcircular in outline, not paratabulate and much smaller than C. swanense. The Late Cretaceous species Craspedodinium turonicum Prössl 1990 is also significantly smaller than C. swanense. Furthermore, it has an antapical constriction and a strongly reticulate periphragm (Prössl, 1990). In addition, the three other species of Craspedodinium lack apical protuberances formed by the endophragm. Cygnusicysta taltarniana Riding and Helby 2001f is consisitently circucavate and significantly smaller than Craspedodinium swanense. Furthermore, apart from the principal archaeoyle suture, C. taltarniana lacks any indication of paratabulation. Craspedodinium is similar to other cavate genera with apical archaeopyles such as Leberidocysta Stover and Evitt 1978. However, Leberidocysta has delicate periphragm which is extremely susceptible to mechanical damage (Cookson & Eisenack, 1962).
Derivation of name. Form the Dingodinium swanense Zone, to which this species is confined.
Holotype and type locality. Figure 1L, CPC 35656, Buang-1 well, sidewall core at 3504.00m
Stratigraphical distribution. Craspedodinium swanense is confined to the Kimmeridgian Dingodinium swanense Zone (6aiia-6aib) of the Timor Sea region (Helby & Partridge in prep.)