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Durotrigia magna
Durotrigia magna Riding and Helby, 2001d, p.73,75, figs.6A-F.
Holotype: Riding and Helby, 2001d, fig.6B.
Age: Late Callovian.
Original description.
Previous Australian usage: M.P. 831 - Helby, Durotrigia sp. 831 - Helby
Description: An intermediate to large species of Durotrigia, subcircular to ellipsoidal in outline. The species is slightly distally flattened. Autophragm robust, relatively thick and redily folded; it is microscabrate and/or microreticulate. Continuous or discontinuous low parasultural ridges are developed which may occasionally be irregularly denticulate. The denticles, where developed, are short, slender, solid and distally pointed. Ridges bordering the paracingulum are consistenly developed and represent the highest parasutural ornament (c. 1µm). A relatively small, solid, distally foliate apical horn is present. The parasulcus is relatively narrow, not surrounded by high ridges or subdivided and is slightly indented. Archaeopyle compound, most ccommonly formed by loss of three precingular paraplates.
Dimensions. (µm; n=38): Min. (Mean) Max.
Length of cyst excl. apical horn: 89 (105) 126
Width of cyst at paracingulum: 82 (105) 124
Length of apical horn: 5 (10) 16
All measured specimens are form conventional core in Undan-3 well at 3057.00 m
Comments. Durotrigia magna is a relatively large species, which is normally equant/subequant in terms of cyst body length and width (Fig. 6). An apical horn is developed which is very small and spongeous to solid; it varies in colour from light to extremely dark; the foliate distal tip is distinctive (Fig. 6D). The large, multi-paraplate precingular archaeopyle (up to 5P, but generally no more than 3P) means that individuals may be compressed to such an extent that the dorsoventral flattening is exaggerated (Fig 6E). Largely longitudinal folds readily develop on the autophragm.
Comparison. The other five species of Durotrigia, described from the Mid Jurassic (Bajocian-earliest Callovian) of northwest Europe (Williams et al., 1998, p. 205-206) are all significantly smaller than D. magna. It is by far the largest species in the genus and is most similar to Durotrigia aspera Bailey * Partington, 1991, which has irregular parasutural ridges and a thick autophragm. However, D. aspera is smaller than D. magna and has coarsely granulate autophragm. Durotrigia asketa Bailey 1990 has distinctive fenestrate/distally denticulate parasutural crests and tuberculate/verrucate intratabular ornament (Bailey, 1990, fig. 3). The parasutural ridges of Duotrigia daveyi are consistently and relatively densely denticulate. Durotrigia filapicata (Gocht, 1970) Riding & Bailey 1991 is covered by a dense, low relief ornament and the parasutural ridges are surmounted by trabeculate denticles. The autophragm of Durotrigia vesculata Bailey 1990 is differentiated and extremely thick (Bailey, 1990, pl.1)
Derivation of name. From the Latin magnus meaning large or great.
Holotype and type locaility. Figure 6B, CPC 35386, Undan-3 well, conventional core sample at 3057.00m.
Stratigraphical distribution. Durotrigia magna has been recorded from the Upper Callovian strata of the Timor Sea region. It ranges from the upper part of the Wanaea digitata Zone (7bi) to the lower part of the Rigaudella aemula Zone (7aiibii). (Foster, this volume; Helby & Partridge in prep). In the Bayu-Undan Gas Field it occurs as an acme (bioevent 7aiibiib) which is commonly associated with maximum flooding surface of Arditta (1996, figs 2-4).
Holotype: Riding and Helby, 2001d, fig.6B.
Age: Late Callovian.
Original description.
Previous Australian usage: M.P. 831 - Helby, Durotrigia sp. 831 - Helby
Description: An intermediate to large species of Durotrigia, subcircular to ellipsoidal in outline. The species is slightly distally flattened. Autophragm robust, relatively thick and redily folded; it is microscabrate and/or microreticulate. Continuous or discontinuous low parasultural ridges are developed which may occasionally be irregularly denticulate. The denticles, where developed, are short, slender, solid and distally pointed. Ridges bordering the paracingulum are consistenly developed and represent the highest parasutural ornament (c. 1µm). A relatively small, solid, distally foliate apical horn is present. The parasulcus is relatively narrow, not surrounded by high ridges or subdivided and is slightly indented. Archaeopyle compound, most ccommonly formed by loss of three precingular paraplates.
Dimensions. (µm; n=38): Min. (Mean) Max.
Length of cyst excl. apical horn: 89 (105) 126
Width of cyst at paracingulum: 82 (105) 124
Length of apical horn: 5 (10) 16
All measured specimens are form conventional core in Undan-3 well at 3057.00 m
Comments. Durotrigia magna is a relatively large species, which is normally equant/subequant in terms of cyst body length and width (Fig. 6). An apical horn is developed which is very small and spongeous to solid; it varies in colour from light to extremely dark; the foliate distal tip is distinctive (Fig. 6D). The large, multi-paraplate precingular archaeopyle (up to 5P, but generally no more than 3P) means that individuals may be compressed to such an extent that the dorsoventral flattening is exaggerated (Fig 6E). Largely longitudinal folds readily develop on the autophragm.
Comparison. The other five species of Durotrigia, described from the Mid Jurassic (Bajocian-earliest Callovian) of northwest Europe (Williams et al., 1998, p. 205-206) are all significantly smaller than D. magna. It is by far the largest species in the genus and is most similar to Durotrigia aspera Bailey * Partington, 1991, which has irregular parasutural ridges and a thick autophragm. However, D. aspera is smaller than D. magna and has coarsely granulate autophragm. Durotrigia asketa Bailey 1990 has distinctive fenestrate/distally denticulate parasutural crests and tuberculate/verrucate intratabular ornament (Bailey, 1990, fig. 3). The parasutural ridges of Duotrigia daveyi are consistently and relatively densely denticulate. Durotrigia filapicata (Gocht, 1970) Riding & Bailey 1991 is covered by a dense, low relief ornament and the parasutural ridges are surmounted by trabeculate denticles. The autophragm of Durotrigia vesculata Bailey 1990 is differentiated and extremely thick (Bailey, 1990, pl.1)
Derivation of name. From the Latin magnus meaning large or great.
Holotype and type locaility. Figure 6B, CPC 35386, Undan-3 well, conventional core sample at 3057.00m.
Stratigraphical distribution. Durotrigia magna has been recorded from the Upper Callovian strata of the Timor Sea region. It ranges from the upper part of the Wanaea digitata Zone (7bi) to the lower part of the Rigaudella aemula Zone (7aiibii). (Foster, this volume; Helby & Partridge in prep). In the Bayu-Undan Gas Field it occurs as an acme (bioevent 7aiibiib) which is commonly associated with maximum flooding surface of Arditta (1996, figs 2-4).