Back
Fusiformacysta challisiana
Fusiformacysta challisiana Riding and Helby, 2001e, p.117,119, figs.4A-L.
Taxonomic junior synonyms: Helbycysta verrucosa and Komewuia challisiana (names not validly published), both according to Riding and Helby (2001e, p.119).
Holotype: Riding and Helby, 2001e, fig.4A.
Age: Callovian-Oxfordian.
Riding & Helby, 2001e:
Previous australian usage: Komewuia sp. 555 (verrucate) – Helby., Dissiliodinium verrucate ‘555’ – Morgan. Helbycysta verrucosa – Morgan. Komewuia challisiana – Helby.
Description: A sepcies of Fusiformacysta with a type 3P Archeopyle and a biconical outline, with or without and apical horn or protuberance. Specimens vary from those with a rounded apical extremity to occasional forms with small apical horns or protuberances. The antapical region is rounded to almost flat. Most commonly, the species is elongate, but may also be subequant or wider than long. Indications of parayabulation comprise with type 3P Archeopyle and a lineation of ornamentation along the posterior margin of the paracingulum. Isolated opercular paraplates are common in the loisthocyst. A regular shaped, dark brown accumulation body may be present in the cyst. The relatively robust autophragm bears verrucae and/or reticulum. The entirely verrucate forms are reltively densly covered in low-relief (0.5-1 µm high) verrucae or grana, which are variable in shape. These elements are normally ovoidal, although rarely some coalescence of verrucae result in irregularly shaped, rounded vermiculae. The width of verrucae or grana varies from 0.5 to 6 µm. Formes which are verrucate and reticulate both are generally reticulate in the vicinity of the paracingulum, with fenestrae varying in width from 1 to 5 µm, the average being 2 µm.
Dimensions (µm, n=24): Min.(Mean)Max.
Maximum length of cyst: 71(89)103
Width of cyst at paracingulum: 67(82)96.
The measured specimens are from sidewall cores in Arunta-1 well at 1805.00m, Challis-11 ST1 well at 1552.50m and Rowan-1 well at 3183.0m.
Comments: Fusiformacysta challisiana is a large form which has a distinctive ornamentation. It may be either verrucate or, occasionaly, verrucate and reticulate. In the partially reticulate forms, the reticulum is best developed in the equatorial area (Figs 4J-L). Thi variablility in ornamentational style is unusual. In some specimensthe presence of a small anterior intercalary paraplate (K paraplate of Evitt, 1985) is suggested by angulation of the principal Archeopyle suture.
Comparison: Fusiformacysta challisiana differs from F. terniana Riding & Helby (this volume) int the typical lack of apical and antapical horns and the precesnse of a largely verrucate autophragm. Fusiformacysta salasii s significanlntly more elongate than F. challisiana, withextremely long polar horns and smooth autophragm. The Tithonian to Berriasian species F. tumida Backhouse 1988 is also more slender than F. challisiana and is ornamented by small (<1 µm wide), nontabular grana. Fusiformacysta sp. cf. F. tumida from the Late Jurassic Polda Formation of the Eyre Peninsula, South Australia closely resembles F. challisiana, but generally has more prominent polar horns. Like the type material from the Perth Basin (Backhouse 1988), these Polda specimens were recovered from a paralic succession (Gatehouse & Cooper, 1982).
Derivation of name: From Challis-11 ST1 well, from which material of this species was first recovered.
Holotype and type locality: Figure 4A, CPC 35543, Challis-11 ST1 well, sidewall core at 1552.50m.
Stratigraphical distribution. Fusiformacysta challisiana ranges from the Callovian Rigaudella aemula Zone (7aii) to the Oxfordiam Wanaea clathrate Zone (6b) of the Timor Sea (Foster, this volume; Helby and Perdridge, in prep.). It is generally a background component and is most consisteny between the upper part of the lower Rigaudella aemula Zone (7aiia) to the lower Wanaea spectabilis Zone (6ciiia).
Taxonomic junior synonyms: Helbycysta verrucosa and Komewuia challisiana (names not validly published), both according to Riding and Helby (2001e, p.119).
Holotype: Riding and Helby, 2001e, fig.4A.
Age: Callovian-Oxfordian.
Riding & Helby, 2001e:
Previous australian usage: Komewuia sp. 555 (verrucate) – Helby., Dissiliodinium verrucate ‘555’ – Morgan. Helbycysta verrucosa – Morgan. Komewuia challisiana – Helby.
Description: A sepcies of Fusiformacysta with a type 3P Archeopyle and a biconical outline, with or without and apical horn or protuberance. Specimens vary from those with a rounded apical extremity to occasional forms with small apical horns or protuberances. The antapical region is rounded to almost flat. Most commonly, the species is elongate, but may also be subequant or wider than long. Indications of parayabulation comprise with type 3P Archeopyle and a lineation of ornamentation along the posterior margin of the paracingulum. Isolated opercular paraplates are common in the loisthocyst. A regular shaped, dark brown accumulation body may be present in the cyst. The relatively robust autophragm bears verrucae and/or reticulum. The entirely verrucate forms are reltively densly covered in low-relief (0.5-1 µm high) verrucae or grana, which are variable in shape. These elements are normally ovoidal, although rarely some coalescence of verrucae result in irregularly shaped, rounded vermiculae. The width of verrucae or grana varies from 0.5 to 6 µm. Formes which are verrucate and reticulate both are generally reticulate in the vicinity of the paracingulum, with fenestrae varying in width from 1 to 5 µm, the average being 2 µm.
Dimensions (µm, n=24): Min.(Mean)Max.
Maximum length of cyst: 71(89)103
Width of cyst at paracingulum: 67(82)96.
The measured specimens are from sidewall cores in Arunta-1 well at 1805.00m, Challis-11 ST1 well at 1552.50m and Rowan-1 well at 3183.0m.
Comments: Fusiformacysta challisiana is a large form which has a distinctive ornamentation. It may be either verrucate or, occasionaly, verrucate and reticulate. In the partially reticulate forms, the reticulum is best developed in the equatorial area (Figs 4J-L). Thi variablility in ornamentational style is unusual. In some specimensthe presence of a small anterior intercalary paraplate (K paraplate of Evitt, 1985) is suggested by angulation of the principal Archeopyle suture.
Comparison: Fusiformacysta challisiana differs from F. terniana Riding & Helby (this volume) int the typical lack of apical and antapical horns and the precesnse of a largely verrucate autophragm. Fusiformacysta salasii s significanlntly more elongate than F. challisiana, withextremely long polar horns and smooth autophragm. The Tithonian to Berriasian species F. tumida Backhouse 1988 is also more slender than F. challisiana and is ornamented by small (<1 µm wide), nontabular grana. Fusiformacysta sp. cf. F. tumida from the Late Jurassic Polda Formation of the Eyre Peninsula, South Australia closely resembles F. challisiana, but generally has more prominent polar horns. Like the type material from the Perth Basin (Backhouse 1988), these Polda specimens were recovered from a paralic succession (Gatehouse & Cooper, 1982).
Derivation of name: From Challis-11 ST1 well, from which material of this species was first recovered.
Holotype and type locality: Figure 4A, CPC 35543, Challis-11 ST1 well, sidewall core at 1552.50m.
Stratigraphical distribution. Fusiformacysta challisiana ranges from the Callovian Rigaudella aemula Zone (7aii) to the Oxfordiam Wanaea clathrate Zone (6b) of the Timor Sea (Foster, this volume; Helby and Perdridge, in prep.). It is generally a background component and is most consisteny between the upper part of the lower Rigaudella aemula Zone (7aiia) to the lower Wanaea spectabilis Zone (6ciiia).