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Cygnusicysta taltarniana
Cygnusicysta *taltarniana Riding and Helby, 2001e, p.114, figs.1A–L.
Holotype: Riding and Helby, 2001e, fig.1L.
Age: Jurassic (late Callovian)–Early Cretaceous.
Original description (Riding & Helby, 2001e)
A species of Cygnusicysta, that is subsircular in dorsoventral view. Generally equant in overall length and width, occasionally slightly elongate. Endophragm relatively thick (up to 2µm), microreticulate or having low relief ornamentation. The ornament may be microgranulate, scabrate, or rugulate. Periphragm thinner, microgranulate to smooth (0.5-1.5µm). Pericoel normally relatively narrow (generally 2-5µm wide). The operculum is normally free. Accumulation bodies are frequently present inside the cyst.
Dimensions (µm; n=40): Min. (Mean) Max.
Length of pericyst (incl. operculum): 37 (48) 64
Length of pericyst (excl. operculum): 34 (44) 60
Length of endocyst (incl. operculum): 36 (42) 59
Length of endocyst (excl. operculum): 31 (40) 52
Width of pericyst: 32 (45) 68
Width of endocyst: 30 (40) 53
Maximum separation of wall layers: 1 (4) 13
The measured specimens are all from a sidewall core sample at 2820.00m in Taltarni-1 well.
Comments. Specimens are often crushed and this can increase the overall length, and width as well as the width of the pericoel.
Comparison. Although Cygnusicysta is a monospecific genus, C. taltarniana is similar to some spieces assigned to Leberidocysta. In particular, Leberidocysta? pergamentacea (Burger 1980) Burger 1980 is an Early Cretaceous species which is not unequiocally cavate (Burger 1980, p. 88). If cavation is developed, it may be sporadic and the pericoel is extremely thin. Leberidocysta defloccata (Davey & Verdier 1973) Stover & Evitt 1978 has an extremely wide pericoel. The Late Cretaceous Leberidocysta? flagellichnia Schiøler 1993 is holocavate (Schiøler, 1993, p. 110). Liberidocysta? scabrata Jain & Taugourdeau-Lantz 1973) Stoer & Evitt 1978 is larger than C. taltarniana and has a thick, spongy wall. Cygnusicysta taltarniana is superficially similar to Craspedodinium swanense Riding & Helby 2001e; however, the latter is significantly larger, and has periphragmal folds reflecting paratabulation and essentially smooth periphragm and endophragm.
Derivation of name. From the Taltarni-1 well.
Holotype and type locality. Figure 1L CPC 35528, Taltarni-1 well, sidewall core sample at 2820.00 m.
Stratigraphical districbution. Cygnusicysta taltarniana ranges widely as a rare component of assemblages from the later Callovian to the Early Cretaceous. However, it occurs as a stratigraphically significant acme in the Oxfordian, lower part of the middle Wanaea spectabilis Zone (6ciib) in wells in the Montara Field and in the adjacent Vulcan Sub-Basin in the Timor Sea.
Holotype: Riding and Helby, 2001e, fig.1L.
Age: Jurassic (late Callovian)–Early Cretaceous.
Original description (Riding & Helby, 2001e)
A species of Cygnusicysta, that is subsircular in dorsoventral view. Generally equant in overall length and width, occasionally slightly elongate. Endophragm relatively thick (up to 2µm), microreticulate or having low relief ornamentation. The ornament may be microgranulate, scabrate, or rugulate. Periphragm thinner, microgranulate to smooth (0.5-1.5µm). Pericoel normally relatively narrow (generally 2-5µm wide). The operculum is normally free. Accumulation bodies are frequently present inside the cyst.
Dimensions (µm; n=40): Min. (Mean) Max.
Length of pericyst (incl. operculum): 37 (48) 64
Length of pericyst (excl. operculum): 34 (44) 60
Length of endocyst (incl. operculum): 36 (42) 59
Length of endocyst (excl. operculum): 31 (40) 52
Width of pericyst: 32 (45) 68
Width of endocyst: 30 (40) 53
Maximum separation of wall layers: 1 (4) 13
The measured specimens are all from a sidewall core sample at 2820.00m in Taltarni-1 well.
Comments. Specimens are often crushed and this can increase the overall length, and width as well as the width of the pericoel.
Comparison. Although Cygnusicysta is a monospecific genus, C. taltarniana is similar to some spieces assigned to Leberidocysta. In particular, Leberidocysta? pergamentacea (Burger 1980) Burger 1980 is an Early Cretaceous species which is not unequiocally cavate (Burger 1980, p. 88). If cavation is developed, it may be sporadic and the pericoel is extremely thin. Leberidocysta defloccata (Davey & Verdier 1973) Stover & Evitt 1978 has an extremely wide pericoel. The Late Cretaceous Leberidocysta? flagellichnia Schiøler 1993 is holocavate (Schiøler, 1993, p. 110). Liberidocysta? scabrata Jain & Taugourdeau-Lantz 1973) Stoer & Evitt 1978 is larger than C. taltarniana and has a thick, spongy wall. Cygnusicysta taltarniana is superficially similar to Craspedodinium swanense Riding & Helby 2001e; however, the latter is significantly larger, and has periphragmal folds reflecting paratabulation and essentially smooth periphragm and endophragm.
Derivation of name. From the Taltarni-1 well.
Holotype and type locality. Figure 1L CPC 35528, Taltarni-1 well, sidewall core sample at 2820.00 m.
Stratigraphical districbution. Cygnusicysta taltarniana ranges widely as a rare component of assemblages from the later Callovian to the Early Cretaceous. However, it occurs as a stratigraphically significant acme in the Oxfordian, lower part of the middle Wanaea spectabilis Zone (6ciib) in wells in the Montara Field and in the adjacent Vulcan Sub-Basin in the Timor Sea.