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Cribroperidinium corrugatum
Cribroperidinium corrugatum Riding and Helby, 2001f, p.147,149-150, figs.3A-I,4A-B.
Holoytype: Riding and Helby, 2001f, fig.3A.
Type locality: CPC 35663, Alaria-1 well, conventional core sample at 3318.58m
Stratigraphical distribution: Cribroperidinium corrugatum is confined to the Kimmeridgian middle to upper Dingodinium swanense Zone (6ai/6aii) in the Timor Sea region (Foster, this volume; Helby&Partridge, in prep.)
Age: Kimmeridgian.
Original description (Riding and Helby, 2001f):
Description - A large species of Cribroperidinium with a prominet apical horn. The species is slightly dorsoventrally flattened and is elongate subquadrangular in dorsoventral or lateral view. The subquadrangular outline is due to the relatively small diameter of the antapical (1’’’’) paraplate. The autophragm is thick (1.5-2.5 µm), with a strong corrugate ornamentation. Parasutures, indicating a sexiform gonyaulacalean paratabulation pattern, are marked by slender perforate crests of variable height (2-20 µm), which may be reduced to aligned, distally trabeculate short processes and are highest at the hypocystal periphery and particularly at the antapex. The corrugate ornament is arranged as irregular ridges, which vary from 2 to 5 µm in width. They are rounded and random in orientation and often coalesce freely. The anastomosing nature and the density of insertion of the ridges is extremely variable. Some are entirely random and in other specimens, a crude reticulation may be present. The paracingulum is indicated by relatively thick parasutural ridges and is relatively narrow for such a large cyst. Parasulcus indicated by crests or ridges, not subdivided.
Dimensions (µm; n=32) inclusive of parasutural crests where appropriate: Min.(Mean)Max.
Length of cyst incl. apical horn: 102(130)175
Length of epicyst incl. apical horn: 40(63)87
Length (height) of paracingulum: 4(6)9
Length of hypocyst: 44(62)85
Length of apical horn: 12(23)36
Equatorial width of cyst: 90(102)117
Height of parasututal crests: 2(7)20
The measured specimens are from cores in Alara-1 well at 3319.95m, 3318.58m and 3315.95m and a sidewall core at 1842.50m in Jabiru-8A well.
Comments – this large and characteristic species is variable in size (see dimensions, above) and outline (Fig. 3). It appears to lack intratabular growth ridges. Cribroperidinium corrugatum is distinguished by the distinctive corrugate ornamentation, as defined by Tappan & Loeblich (1971, p. 387). The thick autophragm is covered by rounded ridges, which are variable in width, density of insertion and the degree of coalescence within individual specimens and populations (Figs. 3-4). In some specimens, the corrugate ridges are best developed on the hypocyst (Fig. 3B). Where the ridges are inserted relatively sparsely, the cyst may appear to be somewhat degraded (Fig. 4B). The ridges are rarely discontinuous; this phenomenon may be due to preservational effects. Both the apical and parasutural crests are variable in size and morphology (Fig. 3) They appear to be formed entirely of periphragm. Some parasutural cest are entire, however, most are reticulate with subcircular to ellipsoidal fenestrae, which vary from 2 to 5 µm in diameter. The fenestrae may expand such that the crests become rows of trabeculate short spines.
Comparison – Cribroperidinium corrugatum is distinguished from the other species of this genus by the characteristic corrugate ornamentation. The majority of the species of Cribroperidinium have smooth, scabrate or microreticulate autophragms. Cribroperidinium janinae Górka 1982 and C? muderongense (Cookson and Eisenack 1958) Davey 1969 have a granulate autophargm, but entirelt lack any corrugate ornamentation. This species appears to lack intratabular growth ridges, which are typical of most Cretaceous and Palaeogene Cribroperidinium. However thid does not preclude assignment to Cribroperidinium (Helens 1984). The antapical paraplate (1’’’’) is extremely small (Fig. 3). This genus typically comprises species with relatively large antapical paraplates (Helens, 1984). Gonyaulacalean genera may exhibit such size variations at the antapex. Ctenidodinium Deflandre 1939 emens. Benson 1985 normally has a relatively large 1’’’’ paraplate. The Mid Jurassic species Ctenidodinium combazii Dupin 1968 is similar to C. corrugatum in that it has a small antapical paraplate (Riding et al., 1985. Pl. 1).
Derivation of name: From the Latin corrrugatus meaning ridges or wrinkled and referring to the characteristic corrugate ornament.
Holoytype: Riding and Helby, 2001f, fig.3A.
Type locality: CPC 35663, Alaria-1 well, conventional core sample at 3318.58m
Stratigraphical distribution: Cribroperidinium corrugatum is confined to the Kimmeridgian middle to upper Dingodinium swanense Zone (6ai/6aii) in the Timor Sea region (Foster, this volume; Helby&Partridge, in prep.)
Age: Kimmeridgian.
Original description (Riding and Helby, 2001f):
Description - A large species of Cribroperidinium with a prominet apical horn. The species is slightly dorsoventrally flattened and is elongate subquadrangular in dorsoventral or lateral view. The subquadrangular outline is due to the relatively small diameter of the antapical (1’’’’) paraplate. The autophragm is thick (1.5-2.5 µm), with a strong corrugate ornamentation. Parasutures, indicating a sexiform gonyaulacalean paratabulation pattern, are marked by slender perforate crests of variable height (2-20 µm), which may be reduced to aligned, distally trabeculate short processes and are highest at the hypocystal periphery and particularly at the antapex. The corrugate ornament is arranged as irregular ridges, which vary from 2 to 5 µm in width. They are rounded and random in orientation and often coalesce freely. The anastomosing nature and the density of insertion of the ridges is extremely variable. Some are entirely random and in other specimens, a crude reticulation may be present. The paracingulum is indicated by relatively thick parasutural ridges and is relatively narrow for such a large cyst. Parasulcus indicated by crests or ridges, not subdivided.
Dimensions (µm; n=32) inclusive of parasutural crests where appropriate: Min.(Mean)Max.
Length of cyst incl. apical horn: 102(130)175
Length of epicyst incl. apical horn: 40(63)87
Length (height) of paracingulum: 4(6)9
Length of hypocyst: 44(62)85
Length of apical horn: 12(23)36
Equatorial width of cyst: 90(102)117
Height of parasututal crests: 2(7)20
The measured specimens are from cores in Alara-1 well at 3319.95m, 3318.58m and 3315.95m and a sidewall core at 1842.50m in Jabiru-8A well.
Comments – this large and characteristic species is variable in size (see dimensions, above) and outline (Fig. 3). It appears to lack intratabular growth ridges. Cribroperidinium corrugatum is distinguished by the distinctive corrugate ornamentation, as defined by Tappan & Loeblich (1971, p. 387). The thick autophragm is covered by rounded ridges, which are variable in width, density of insertion and the degree of coalescence within individual specimens and populations (Figs. 3-4). In some specimens, the corrugate ridges are best developed on the hypocyst (Fig. 3B). Where the ridges are inserted relatively sparsely, the cyst may appear to be somewhat degraded (Fig. 4B). The ridges are rarely discontinuous; this phenomenon may be due to preservational effects. Both the apical and parasutural crests are variable in size and morphology (Fig. 3) They appear to be formed entirely of periphragm. Some parasutural cest are entire, however, most are reticulate with subcircular to ellipsoidal fenestrae, which vary from 2 to 5 µm in diameter. The fenestrae may expand such that the crests become rows of trabeculate short spines.
Comparison – Cribroperidinium corrugatum is distinguished from the other species of this genus by the characteristic corrugate ornamentation. The majority of the species of Cribroperidinium have smooth, scabrate or microreticulate autophragms. Cribroperidinium janinae Górka 1982 and C? muderongense (Cookson and Eisenack 1958) Davey 1969 have a granulate autophargm, but entirelt lack any corrugate ornamentation. This species appears to lack intratabular growth ridges, which are typical of most Cretaceous and Palaeogene Cribroperidinium. However thid does not preclude assignment to Cribroperidinium (Helens 1984). The antapical paraplate (1’’’’) is extremely small (Fig. 3). This genus typically comprises species with relatively large antapical paraplates (Helens, 1984). Gonyaulacalean genera may exhibit such size variations at the antapex. Ctenidodinium Deflandre 1939 emens. Benson 1985 normally has a relatively large 1’’’’ paraplate. The Mid Jurassic species Ctenidodinium combazii Dupin 1968 is similar to C. corrugatum in that it has a small antapical paraplate (Riding et al., 1985. Pl. 1).
Derivation of name: From the Latin corrrugatus meaning ridges or wrinkled and referring to the characteristic corrugate ornament.