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Dissimulidinium purattense
Dissimulidinium purattense Riding and Helby, 2001g, p.200,202,204, figs.11A-P.
Taxonomic junior synonym: Ampulladinium robustum (name not validly published), according to Riding and Helby (2001g, 200).
Holotype: Riding and Helby, 2001g, figs.11C-D.
Age: Tithonian.
(Riding & Helby, 2001g):
1986 Ampulladinium robustum; Parker, p. 29 pl. 1, figs. 1-3.
1994 Dissimulidinium sp. A; Bint & Marshall, fig. 5.4.
1994 Dissimiulidinium sp. B; Bint & Marshall, fig. 5.5.
Description: a species intermediate in size and trilobite to elongate subquadrate in lateral view, A slight equatorial constriction in normally present. The prominent hypocystal lobes are distally rounded and the dorsal lobe is markedly larger than the ventral lobe. The apicystal lobe (apical area) is flattened sitally. Autophragm relatively thick (1-2 µm), smooth to scabrate, Occasionally the autophragm is irregularly microreticulate with sub circular lacunae up to 1 µm. wide. The autophragm is covered in slender, solid processes which are distally capitate or bifurcate. Most processes are 1-1.5 µm wide, but occasionally attain 3 µµ in width. Intratabular processes are extremely rare on the paracingulum. No specimens were observed in the ventral view, therefor the presence of processes on the parasulcus is uncertain. The paracingular sutures commonly have aligned parasutural processes and some parasututral and/or penitabular processes may be present. The principal archeopyle suture is inclined ventrally; short accessory archeopyle sutures may be developed.
Dimensions (µm, n=30): Min(Mean)Max.
Length of entire cyst excl. Spines : 52(62)71
Length of loisthocyst excl. spines: 43(60)76
Maximum width of hypocyst: 40(52)72
Maximum width of epicyst: 28(39)51
Width of equatorial constriction: 22(35)47
Maximum length of sines 6(9)14
The measured specimens are from conventional core in Lambert-2 well at 3101.00m, sidewall core from Cossack-1 well at 3025.00m, Puratte-1 well at 172.00m and Scafell-1 well at 1421.00m and 1418.00m and ditch cuttings from Broome-1 Bore at 297.79m.
Comments: this species of Dissimulidinium is characterized by a robust autophragm, the slight equatorial constriction and the cover of nontabular, parasutural and penitabular processes. It is strongly laterally compresses and no specimens were observed in dorsoventral view. Specimens can be readily oriented by the disparity in size of the dorsal lobes and the sloping principal archeopyle suture. The possible partial parasutural/penitabular arrangement of the processes is entirely consistent with a gonyaulacalean paratabulation (see May et al., 1987, fig. 2). The majority of the processes are nontabular and a full paratabulation has not yet been recorded. It is relatively common for parasutural processes to surmount the paracingular sutures. On the larger hypocyst in some specimens, discontinuous aligned rows of processes are present. In many of these cases these are closely spaced parallel rows, which are strangely suggestive of a penitabular arrangement (Bint & Marshall (1994)). Bint & Marshall (1994) distinguish two morphotypes of this genus. Dissimulidinium sp. A has a substantial cover of processes and Dissimulidinium sp. B has a slightly thicker autophragm and marginally fewer processes. These authors indicated that the two morphotypes have stratigraphically distinct ranges (Bint & Marshall, 1994). Both morphotypes are included here in D. purattense.
Comparison: Dissimulidinium purattense differs from the genotype, D. lobispinosum, in lacking a deeply incised equatorial constriction, having relatively wide processes which are evenly distributed over the cyst and ma be parasutural/penitabular. Furthermore the epicyst and equatorial regional are widerin D. purattense than D. lobispinosum (May et al., 1987).
Derivation of name: From the Puratte-1 well, where we first recorded this species.
Type locality: CPC 35952 from a sideall core sample in Scafell-1 well at 1421.00m.
Stratigraphical distribution: D. purattense is confined to the Tithonian, rangeing from the uppermost Dingodinium jurassicum Zone (5ai) to the mid Pseudoceratium iehiense Zone (4cic) (Foster, this volume; Helby & Partridge, in prep.
Taxonomic junior synonym: Ampulladinium robustum (name not validly published), according to Riding and Helby (2001g, 200).
Holotype: Riding and Helby, 2001g, figs.11C-D.
Age: Tithonian.
(Riding & Helby, 2001g):
1986 Ampulladinium robustum; Parker, p. 29 pl. 1, figs. 1-3.
1994 Dissimulidinium sp. A; Bint & Marshall, fig. 5.4.
1994 Dissimiulidinium sp. B; Bint & Marshall, fig. 5.5.
Description: a species intermediate in size and trilobite to elongate subquadrate in lateral view, A slight equatorial constriction in normally present. The prominent hypocystal lobes are distally rounded and the dorsal lobe is markedly larger than the ventral lobe. The apicystal lobe (apical area) is flattened sitally. Autophragm relatively thick (1-2 µm), smooth to scabrate, Occasionally the autophragm is irregularly microreticulate with sub circular lacunae up to 1 µm. wide. The autophragm is covered in slender, solid processes which are distally capitate or bifurcate. Most processes are 1-1.5 µm wide, but occasionally attain 3 µµ in width. Intratabular processes are extremely rare on the paracingulum. No specimens were observed in the ventral view, therefor the presence of processes on the parasulcus is uncertain. The paracingular sutures commonly have aligned parasutural processes and some parasututral and/or penitabular processes may be present. The principal archeopyle suture is inclined ventrally; short accessory archeopyle sutures may be developed.
Dimensions (µm, n=30): Min(Mean)Max.
Length of entire cyst excl. Spines : 52(62)71
Length of loisthocyst excl. spines: 43(60)76
Maximum width of hypocyst: 40(52)72
Maximum width of epicyst: 28(39)51
Width of equatorial constriction: 22(35)47
Maximum length of sines 6(9)14
The measured specimens are from conventional core in Lambert-2 well at 3101.00m, sidewall core from Cossack-1 well at 3025.00m, Puratte-1 well at 172.00m and Scafell-1 well at 1421.00m and 1418.00m and ditch cuttings from Broome-1 Bore at 297.79m.
Comments: this species of Dissimulidinium is characterized by a robust autophragm, the slight equatorial constriction and the cover of nontabular, parasutural and penitabular processes. It is strongly laterally compresses and no specimens were observed in dorsoventral view. Specimens can be readily oriented by the disparity in size of the dorsal lobes and the sloping principal archeopyle suture. The possible partial parasutural/penitabular arrangement of the processes is entirely consistent with a gonyaulacalean paratabulation (see May et al., 1987, fig. 2). The majority of the processes are nontabular and a full paratabulation has not yet been recorded. It is relatively common for parasutural processes to surmount the paracingular sutures. On the larger hypocyst in some specimens, discontinuous aligned rows of processes are present. In many of these cases these are closely spaced parallel rows, which are strangely suggestive of a penitabular arrangement (Bint & Marshall (1994)). Bint & Marshall (1994) distinguish two morphotypes of this genus. Dissimulidinium sp. A has a substantial cover of processes and Dissimulidinium sp. B has a slightly thicker autophragm and marginally fewer processes. These authors indicated that the two morphotypes have stratigraphically distinct ranges (Bint & Marshall, 1994). Both morphotypes are included here in D. purattense.
Comparison: Dissimulidinium purattense differs from the genotype, D. lobispinosum, in lacking a deeply incised equatorial constriction, having relatively wide processes which are evenly distributed over the cyst and ma be parasutural/penitabular. Furthermore the epicyst and equatorial regional are widerin D. purattense than D. lobispinosum (May et al., 1987).
Derivation of name: From the Puratte-1 well, where we first recorded this species.
Type locality: CPC 35952 from a sideall core sample in Scafell-1 well at 1421.00m.
Stratigraphical distribution: D. purattense is confined to the Tithonian, rangeing from the uppermost Dingodinium jurassicum Zone (5ai) to the mid Pseudoceratium iehiense Zone (4cic) (Foster, this volume; Helby & Partridge, in prep.