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Mendicodinium morgenrothii
Mendicodinium morgenrothum Butler, 1995
Holotype: Butler, 1995, pl.1, fig.1
Paratype: Butler, 1995, pl.1, fig.2
Locus typicus: Northwest Hutton Field, northern North Sea
Stratum typicum: Aalenian-lowermost Bajocian
Diagnosis: Butler, 1995, p. 25
Cysts proximate, outline subcircular. Autophragm scabrate or micropunctate ornamented with scattered to densely distributed verrucae. Tabulation not indicated although cingulum delined by reduced ornament. Archaeopyle epitractal, presumed tAtP.
Description: Butler, 1995, p. 25
Outline is subcircular in dorso-ventral compression. The hypotract is slightly larger than the epitract. The cysts are proximate with autophragm only which is approximately 1 Ám in thickness and sometimes folded. The autophragm is scabrate, micropunctate or microfossulate and ornamented with scattered to densely distributed verrucae which may occur as clusters touching adjacent verrucae but never coalescing or fusing. This ornament occurs on both ventral and dorsal surfaces. It is consistently reduced in the cingular region only, where the autophragm is smooth or scabrate. An omphalus is usually present, attatched to the inner surface of the cyst, generally in the sulcal region. There is no evidence of tabulation, apart from the laevo-rotatory cingulum precluding classification of the species at order and family level. The archaeopyle is epitractal, presumed type tAtP. The hypotract and epitract remain attatched at the sulcal - presumed 1" plate boundary.
Dimensions. Body diameter at the paracingulum 51-89 Ám, mean 62.5 Ám, holotype 66 Ám; verrucae 1-2 Ám in diameter (although occasionally upto 5 Ám and 1-2 Ám in elevation (17 measured specimens).
Affinities: Butler, 1995, p. 25
Mendicodinium morgenrothum sp. nov. is distinguished from Mendicodinium granulatum Kumar, 1986 which is granulate, from Mendicodinium microreticulatum Kumar, 1986 which is microreticulate and from Mendicodinium caperatum Brideaux, 1977 which is granulate and microreticulate. It is differentiated from Mendicodinium groenlandicum (Pocock & Sarjeant, 1972) Davey, 1979 which is unornamented and from the type species Mendicodinium reticulatum Morgenroth, 1970 which is reticulate.
Remarks: Butler, 1995, p. 25-26
This species has been consistently encountered in Ness Formation strata across the North Viking Graben and generally occurs in association with other dinocysts such as Nannoceratopsis gracilis Alberti, 1961 emend van Helden, 1977, Nannoceratopsis senex van Helden, 1977 and Mancodinium semitabulatum Morgenroth, 1970. The presence of Nannoceratopsis triceras Drugg, 1978 in the overlying Ness Formation interval from the type well indicates an age no younger than the lowermost Bajocian H.discites Ammonite Zone (Woollam & Riding, 1983; Riding et al., 1991; Mitchener et al., 1992). Regional evidence and the first downhole appearance (FDA) of the Family Phallocystaceae D÷rh÷fer & Davies, 1980 (or the Parvocysta group of dinocysts of Woollam & Riding, 1983) in the underlying fully marine upper Drake Formation (Dunlin Group) suggests an age no older than the latest Toarcian or earliest Aalenian for the overlying deltaic Brent Group (Woollam & Riding, 1983; Prauss, 1989; Riding et al., 1991). However, this latter datum may be debatable as there is a major change in facies associated with the deposition of the more brackish Brent Group.
Holotype: Butler, 1995, pl.1, fig.1
Paratype: Butler, 1995, pl.1, fig.2
Locus typicus: Northwest Hutton Field, northern North Sea
Stratum typicum: Aalenian-lowermost Bajocian
Diagnosis: Butler, 1995, p. 25
Cysts proximate, outline subcircular. Autophragm scabrate or micropunctate ornamented with scattered to densely distributed verrucae. Tabulation not indicated although cingulum delined by reduced ornament. Archaeopyle epitractal, presumed tAtP.
Description: Butler, 1995, p. 25
Outline is subcircular in dorso-ventral compression. The hypotract is slightly larger than the epitract. The cysts are proximate with autophragm only which is approximately 1 Ám in thickness and sometimes folded. The autophragm is scabrate, micropunctate or microfossulate and ornamented with scattered to densely distributed verrucae which may occur as clusters touching adjacent verrucae but never coalescing or fusing. This ornament occurs on both ventral and dorsal surfaces. It is consistently reduced in the cingular region only, where the autophragm is smooth or scabrate. An omphalus is usually present, attatched to the inner surface of the cyst, generally in the sulcal region. There is no evidence of tabulation, apart from the laevo-rotatory cingulum precluding classification of the species at order and family level. The archaeopyle is epitractal, presumed type tAtP. The hypotract and epitract remain attatched at the sulcal - presumed 1" plate boundary.
Dimensions. Body diameter at the paracingulum 51-89 Ám, mean 62.5 Ám, holotype 66 Ám; verrucae 1-2 Ám in diameter (although occasionally upto 5 Ám and 1-2 Ám in elevation (17 measured specimens).
Affinities: Butler, 1995, p. 25
Mendicodinium morgenrothum sp. nov. is distinguished from Mendicodinium granulatum Kumar, 1986 which is granulate, from Mendicodinium microreticulatum Kumar, 1986 which is microreticulate and from Mendicodinium caperatum Brideaux, 1977 which is granulate and microreticulate. It is differentiated from Mendicodinium groenlandicum (Pocock & Sarjeant, 1972) Davey, 1979 which is unornamented and from the type species Mendicodinium reticulatum Morgenroth, 1970 which is reticulate.
Remarks: Butler, 1995, p. 25-26
This species has been consistently encountered in Ness Formation strata across the North Viking Graben and generally occurs in association with other dinocysts such as Nannoceratopsis gracilis Alberti, 1961 emend van Helden, 1977, Nannoceratopsis senex van Helden, 1977 and Mancodinium semitabulatum Morgenroth, 1970. The presence of Nannoceratopsis triceras Drugg, 1978 in the overlying Ness Formation interval from the type well indicates an age no younger than the lowermost Bajocian H.discites Ammonite Zone (Woollam & Riding, 1983; Riding et al., 1991; Mitchener et al., 1992). Regional evidence and the first downhole appearance (FDA) of the Family Phallocystaceae D÷rh÷fer & Davies, 1980 (or the Parvocysta group of dinocysts of Woollam & Riding, 1983) in the underlying fully marine upper Drake Formation (Dunlin Group) suggests an age no older than the latest Toarcian or earliest Aalenian for the overlying deltaic Brent Group (Woollam & Riding, 1983; Prauss, 1989; Riding et al., 1991). However, this latter datum may be debatable as there is a major change in facies associated with the deposition of the more brackish Brent Group.