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Sindridinium borealis
From Fensome et al., 2019:
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Original description Nøhr-Hansen et al., 2017:
Sindridinium borealis gen. et sp. nov. figures 1–16; , figures 1–12; , figures 1–9
Derivation of name: ‘Boreas’ Greek North.
Holotype: figure 1, GGU sample no. 522076-4 EF U53-1.
Type locality: Section 30 of Nøhr-Hansen Citation1993 and GEUS PAL-3 2011, Tværdal, Geographical Society Ø, North-East Greenland (72°58’N, 23°02’W).
Description: Double-walled dinocysts with oval to slightly elongate ambital outline. The endo- and periphragm are entirely tightly adpressed and only distinct at the archaeopyle margins (e.g., figures 7, 15; , figure 3). Horns absent. Endophragm thin (< 1 µm), periphragm normally thicker (> 1 µm). The periphragm is smooth (e.g. , figures 1, 11; , figures 1, 6) or bears scattered atabular grana, verrucae or tubercles; the density of the ornament varies on different individuals. Tabulation not expressed. Cingulum rarely suggested by faint folds. Sulcus frequently seen as a shallow, rather straight longitudinal depression flanked by folds, grana, verrucae or tubercles on the periphragm (e.g. , figure 2; , figure 3). One to three large nodular accummulation bodies (omphali) and a variable number of smaller ones frequently occur on the inner side of the sulcus (e.g., figures 1, 4, 16).
Archaeopyle inferred to be type tAtI. Its dorsal suture, when well preserved, is weakly curved to subrectangular, or rarely slightly angular; on the ventral face, the archaeopyle suture is slightly narrower, gently curved to weakly subtriangular. A conspicuous v-shaped, centrally located notch reminiscent of the posteriorly extended apical plate 1’ in many species of modern Peridinium appears on the archaeopyle suture of many of the south-east England specimens (figures 5, 8, 11) and on some of the specimens from the south-western Barents Sea (figures 8, 16; , figure 4). The operculum is free or adnate and has a rounded subpolygonal (subpentagonal) outline (–) with a broad dorsal side and a narrower, subtriangular ventral side. On some specimens, the periphragm has been affected by microbial activity and appears scabrate to granulate (figure 4).
Dimensions
Greenland specimens:
Holotype: Pericyst length 63 µm, breadth 52 µm, width of archaeopyle 21 µm.
Range: Cysts with operculum in situ: length 50 (64) 86 µm × breadth 40 (53) 77 µm, width of archaeopyle 19 (23) 35 µm (15 specimens). Cysts without operculum: Length 47 (60) 73 µm × breadth 48 (55) 62 µm, width of archaeopyle 17 (22) 31 µm (15 specimens).
Norwegian specimens:
Range: Length 47 (54) 66 µm × breadth 45 (52) 52 µm (14 specimens).
England specimens:
Range: Length 39 (49.3) 58 µm × breadth 31 (42.8) 54 µm (30 specimens).
Distribution: The species was first reported from the Troms and Hammerfest basins, offshore north-west Norway (Costa Citation1985) and later described as Ovoidinium? sp. 1 from North-East Greenland (Nøhr-Hansen Citation1993). Recently Ovoidinium? sp. 1 was reported from the Troms and Hammerfest basins offshore north-west Norway (Radmacher 2014) and from the Trunch Borehole, Norfolk, south-eastern England.
Stratigraphic range: Resampling and restudy of the approximately 415-m-thick succession in Tværdal on Geographical Society Ø (section 30 of Nøhr-Hansen Citation1993, Pal-3/2011, figure 3) have revealed a horizon with an assemblage of the ammonite Schloenbachia varians at 349 m indicating an earliest Cenomanian age (Mantelliceras mantelli–dixoni ammonite zones, undivided). The ammonite level corresponds to the lower part of the S. borealis gen. et sp. nov. acme, whereas the FO of S. borealis gen. et sp. nov. occurs at a lower level, presumably of latest Albian age.
The ammonite-correlated age obtained from North-East Greenland corresponds to the observations from the Ferriby Chalk Formation in the Trunch Borehole, Norfolk south-eastern England, where S. borealis gen. et sp. nov. first occurs from the Mantelliceras mantellii Zone (questionably above the Lower Cenomanian δ13C Event I and below the δ13C Virgatus Beds Event of Jarvis et al. Citation2006) to the Mantelliceras dixoni Zone (LO immediately below the middle Cenomanian δ13C I Event; Lower Cenomanian) in the Trunch borehole. Radmacher et al. (Citation2014) reported a late Abian age.
Comparisons: Sindridinium borealis gen. et sp. nov. has an obvious archaeopyle and often a distinct sulcus, in contrast with Fromea amphora which has a circular margin to its apical pylome, and equatorial folds, and lacks any trace of a sulcus. The accummulation bodies often seen in Sindridinium gen. nov. never seem to occur in Fromea amphora. Hexagonifera glabra, from the Senonian of Australia (Cookson & Eisenack Citation1961), somewhat resembles S. borealis gen. et sp. nov. but its archaeopyle is type I (2a). Isolated endocysts of Leberidocysta may resemble S. borealis gen. et sp. nov., but Leberidocysta is circumcavate and its archaeopyle suture has a strong zigzag shape with an offset sulcal notch. S. borealis gen. et sp. nov. differs from S. anaanae gen. et sp. nov. by being acavate.
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Original description Nøhr-Hansen et al., 2017:
Sindridinium borealis gen. et sp. nov. figures 1–16; , figures 1–12; , figures 1–9
Derivation of name: ‘Boreas’ Greek North.
Holotype: figure 1, GGU sample no. 522076-4 EF U53-1.
Type locality: Section 30 of Nøhr-Hansen Citation1993 and GEUS PAL-3 2011, Tværdal, Geographical Society Ø, North-East Greenland (72°58’N, 23°02’W).
Description: Double-walled dinocysts with oval to slightly elongate ambital outline. The endo- and periphragm are entirely tightly adpressed and only distinct at the archaeopyle margins (e.g., figures 7, 15; , figure 3). Horns absent. Endophragm thin (< 1 µm), periphragm normally thicker (> 1 µm). The periphragm is smooth (e.g. , figures 1, 11; , figures 1, 6) or bears scattered atabular grana, verrucae or tubercles; the density of the ornament varies on different individuals. Tabulation not expressed. Cingulum rarely suggested by faint folds. Sulcus frequently seen as a shallow, rather straight longitudinal depression flanked by folds, grana, verrucae or tubercles on the periphragm (e.g. , figure 2; , figure 3). One to three large nodular accummulation bodies (omphali) and a variable number of smaller ones frequently occur on the inner side of the sulcus (e.g., figures 1, 4, 16).
Archaeopyle inferred to be type tAtI. Its dorsal suture, when well preserved, is weakly curved to subrectangular, or rarely slightly angular; on the ventral face, the archaeopyle suture is slightly narrower, gently curved to weakly subtriangular. A conspicuous v-shaped, centrally located notch reminiscent of the posteriorly extended apical plate 1’ in many species of modern Peridinium appears on the archaeopyle suture of many of the south-east England specimens (figures 5, 8, 11) and on some of the specimens from the south-western Barents Sea (figures 8, 16; , figure 4). The operculum is free or adnate and has a rounded subpolygonal (subpentagonal) outline (–) with a broad dorsal side and a narrower, subtriangular ventral side. On some specimens, the periphragm has been affected by microbial activity and appears scabrate to granulate (figure 4).
Dimensions
Greenland specimens:
Holotype: Pericyst length 63 µm, breadth 52 µm, width of archaeopyle 21 µm.
Range: Cysts with operculum in situ: length 50 (64) 86 µm × breadth 40 (53) 77 µm, width of archaeopyle 19 (23) 35 µm (15 specimens). Cysts without operculum: Length 47 (60) 73 µm × breadth 48 (55) 62 µm, width of archaeopyle 17 (22) 31 µm (15 specimens).
Norwegian specimens:
Range: Length 47 (54) 66 µm × breadth 45 (52) 52 µm (14 specimens).
England specimens:
Range: Length 39 (49.3) 58 µm × breadth 31 (42.8) 54 µm (30 specimens).
Distribution: The species was first reported from the Troms and Hammerfest basins, offshore north-west Norway (Costa Citation1985) and later described as Ovoidinium? sp. 1 from North-East Greenland (Nøhr-Hansen Citation1993). Recently Ovoidinium? sp. 1 was reported from the Troms and Hammerfest basins offshore north-west Norway (Radmacher 2014) and from the Trunch Borehole, Norfolk, south-eastern England.
Stratigraphic range: Resampling and restudy of the approximately 415-m-thick succession in Tværdal on Geographical Society Ø (section 30 of Nøhr-Hansen Citation1993, Pal-3/2011, figure 3) have revealed a horizon with an assemblage of the ammonite Schloenbachia varians at 349 m indicating an earliest Cenomanian age (Mantelliceras mantelli–dixoni ammonite zones, undivided). The ammonite level corresponds to the lower part of the S. borealis gen. et sp. nov. acme, whereas the FO of S. borealis gen. et sp. nov. occurs at a lower level, presumably of latest Albian age.
The ammonite-correlated age obtained from North-East Greenland corresponds to the observations from the Ferriby Chalk Formation in the Trunch Borehole, Norfolk south-eastern England, where S. borealis gen. et sp. nov. first occurs from the Mantelliceras mantellii Zone (questionably above the Lower Cenomanian δ13C Event I and below the δ13C Virgatus Beds Event of Jarvis et al. Citation2006) to the Mantelliceras dixoni Zone (LO immediately below the middle Cenomanian δ13C I Event; Lower Cenomanian) in the Trunch borehole. Radmacher et al. (Citation2014) reported a late Abian age.
Comparisons: Sindridinium borealis gen. et sp. nov. has an obvious archaeopyle and often a distinct sulcus, in contrast with Fromea amphora which has a circular margin to its apical pylome, and equatorial folds, and lacks any trace of a sulcus. The accummulation bodies often seen in Sindridinium gen. nov. never seem to occur in Fromea amphora. Hexagonifera glabra, from the Senonian of Australia (Cookson & Eisenack Citation1961), somewhat resembles S. borealis gen. et sp. nov. but its archaeopyle is type I (2a). Isolated endocysts of Leberidocysta may resemble S. borealis gen. et sp. nov., but Leberidocysta is circumcavate and its archaeopyle suture has a strong zigzag shape with an offset sulcal notch. S. borealis gen. et sp. nov. differs from S. anaanae gen. et sp. nov. by being acavate.