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Impagidinium bacatum
Impagidinium bacatum Londeix et al., 1992
Holotype: Londeix, Benzakour and De Vernal, 1992: Plate 1, figures 1, 9
Locus typicus: Punta Piccola section,
Stratum typicum: Upper Pliocene
Age: Late Pliocene
Synonymy
1985 - Leptodinium sp. A Corradini in Guerrera et al., pl.1, fig. 4 a,b; tab.I, II.
1992 - Impagidinium bacatum Benzakour, Pl. 2, fig.
Original diagnosis: Londeix, Benzakour and De Vernal, 1992, p. 696-700
Subspherical to ovoidal cyst. Surface of cysts distinctly punctate to micropunctate. Gonyaulacacean paratabulation indicated by low vacuolate parasutural septa. Sulcal paraplates not delineated by septa except for partial indication of the posterior sulcal and, in some specimens, the right sulcal paraplates. The archeopyle is precingular, of P(3"") type.
Description: Londeix, Benzakour and De Vernal, 1992, p. 696-700
Proximate acavate cyst, with a subspherical to ovoidal shape. The wall is moderately thick (1 to 1.5 Ám), two-layered and made up of closely appressed endophragm and periphragm. Under optical microscopy, the wall appears fairly and densely punctate to micropunctate. The paratabulation is plainly expressed by low parasutural septa (about V25 of the equatorial cyst diameter): they typically appear as alignments of vacuoles that are more or less circular, with an average diameter of 1,um. Under scanning electron microscopy, the wall surface appears to be scabrate to wealdy chagrinate, and is sparsely and irregularly penetrated by minute pores (pl. 1, figs. 5-6, 8). The septa are low ridges having the same texture as the wall. It seems that only the endophragm is weakly punctate to microperforate, and that the periphragm is chagrinate to irregularly microperforate. The beaded pattern of septa can be interpreted as an inner differentiation of the periphragm in the septa region. The paratabulation, as expressed by septa and archeopyle, is gonyaulacoid with the formula (in Kofoid notation): 4", 6", 6c, 6"", lp, 1"", ps, rs. The paraplates 1" and 4" are symmetrical; however, their boundaries are not always fully expressed. Similarly, the boundaries between the paraplates 1" and 2", as like 3" and 4" are not always expressed (pl. 1, fig. 6). The paraplate 6" is subtriangular and not in contact with paraplate 1" (Fig. 3). The paraplate 1"" is only occasionally expressed. The vertical paracingular septa are generally lower than the others and not always completely developed. The paracingulum is laevorotary, being ofEset 1 to 1.5 times its width. The parasulcus is slightly curved inward. The paraplate 6c often becomes very narrow near the parasulcus (Fig. 3). The parasulcal paraplate ps is very often expressed (although its anterior boundary may be not completely developed), instead of the rs, which is rarely perceptible. The archeopyle is precingular, of P(3"") type; the operculum is simple and free.
Dimensions - Holotype: total cyst length = 50 Á m; total cyst width = 51 Ám; septa height = 1.8-2.0 Ám. Range: total cyst length = 50(59)72 Ám; total cyst width = 43(56)67 Ám; septa height = 0.7(1.6)2.4 Ám. Number of measured specimens = 17. The number in parentheses corresponds to the average value of the measured parameter, and those flanking it, to the extreme values.
Comparisons - The beaded vacuolate structure of its septa distinguishes Impagidinium bacatum from all other species of the genus Impagidinium as with those of Pterodinium EISENACK, 1958 emend SARJEANT, 1985 and Leptodinium KLEMENT, 1960 emend SARJEANT, 1982. From the upper Pannonian of Bulgaria, Apteodinium mecsekense (NAGY, 1969) HELENES, 1984 and Leptodinium ? reticulatum (NAGY, 1969) HELENES, 1984 have a cyst surface that resembles to that of I. bacatum. The wall of A. mecsekense is, however, described as entirely devoid of tabulation on the ventral side; the edges of the existing tabulation are strongly developed. The apices of the tabulae and the ends of the zone are tapering (Nagy 1969, p. 292). L. ? reticulatum has a surface coarsely reticulate (op. cit., p. 293). A comparable species from the Danian of California, Impagidinium pentahedrias DAMASSA, 1979 has a densely granulate cyst wall surface texture. In contrast to I. bacatum, this characteristic is also visible by SEM observation (Damassa 1979, Pl. 4, fig. 6) and the septa are not vacuolar. From the Eocene of Australia, Impagidinium maculatum (COOKSON & ElSENACK, 1961) STOVER & EVTIT, 1978 has plate surfaces that are distinctly dotted, but the ledges are low, thin and hyaline (Cookson & Eisenack 1961, P.40).
At first glance, septa of the Australian Campanian species Impagidinium margarihferum (COOKSON &
EISENACK, 1960) STOVER & Evrrr, 1978 could be confused with those of I. bacatum, but I. margantiferum has plates bordered by ledges, which are perforated by a single row of holes (Cookson & Eisenack 1960, p. 5) instead of being vacuolar. Furthermore, the plate surface of I. margaritiferum seems to be scabrate rather than micropunctate. The structure of the plate areas and septa of I. bacatum seems to be identical to those of Spiniferites hyalospinosus (HANSEN, 1977) STOVER & WILLIAMS, 1987, but the presence of processes distinguishes this Danish Danian species.
BIOSTRATIGRAPHY: Impagidinium bacatum was first recorded (as Leptodinium sp. A) by Corradini in Guerrera et al. (1985) who reported it only in the Narbone formation (upper Pliocene) of two Sicilian drill cores (Log 41 and Log 42; Fig. 1). In more recent studies (Benzakour 1992), I. bacatum was observed in two Pliocene exposures in Sicily (Punta di Maiata and Punta Piccola sections) and also in the offshore Tunisian borehole Jiriba-1 (Flgs. 1, 2). The first occurrence of I. bacatum is recorded in the Punta di Maiata section (palynological sample PM 01) in the planktonic foraminifers zone MPL 2 of Cita (1975)(= Globorotalia margaritae Zone of Spaak 1983), below the base of the Nunivak magnetic subchron, at about 43 million years (Ma). The last occurrence of I. bacatum has been observed in the Jiriba-1 borehole, at a depth of 840 m, approximately in the middle of the MPL 5 zone of Cita (1975) and of the Globorotalia crassaformis Zone of Spaak (1983). Interpolation from planktonic foraminiferal datums permits an age of about 2.4 Ma to be proposed for the known disappearance of I. bacatum. On the basis of available records, I. bacatum may be regarded as an endemic Mediterranean species occurring in Pliocene sediments from about 4.3 to 2.4 Ma.
PALEOECOLOGY: I. bacatum has been reported only in marine Mediterranean sediments from pelagic (Sicilian sections) as well as neritic (Tunisian borehole) environments (Benzakour 1992). Its maxirnum abundance (up to 15% of dinoflagellate cyst assemblages; Flg. 2) occurs at the top of the Rossello composite section, in sediments corresponding to the A-group laminites cluster (e.g. Verhallen 1987; Driever 1988; de Visser 1990; Zachariasse et al. 1990). 1. bacatum belongs to a peculiar dinoflagellate cyst assemblage dominated by Spiniferites hyperacanthus (DEFLANDRE & COOKSON, 1955) COOKSON & EISENACK, 1974 and characterized by the notable occurrence of the thick walled species Operculodinium israelianum (ROSSIGNOL, 1962) WALL, 1967, Tectatodinium pellitum WALL, 1967 and Achomosphaera callosa MATSUOKA, 1983. The co-acme of these four thick walled species is a peculiar feature of the Sicilian upper Pliocene assemblages. The correlation betweenthe percentages of I. bacatum and A. callosa, T. pellitum and O. israelianum reaches values of 0.92, 0.87 and 0.86 respectively. A. callosa is an extinct species of unknown ecology. T. pellitum is still present in modern marine sedi;nents, but occurs as a minor component (never up to 9%) of recent dinocysts assemblages (e.g. Wall et al. 1977; Turon 1984). It appears to be mainly associated with warm-temperate to sub-tropical waters with variable salinity conditions (Wall & Dale 1968; Wall et al. 1977; Harland 1983). O. israelianum is known from Miocene through Recent sediments (Matsuoka 1983; Jan du Chene & Londeix in preparation). At present, the major center of abundance of O. israelianum is in the Caribbean Sea, i.e. in tropical-subtropical environments, often marked by highly saline and/or stratified conditions (Wall et al. 1977; Harland 1983). I. bacatum is a probable warm water stenothermic species, rather tolerant toward salinity and distality. Its disappearance at 2.4 Ma may be related to a cooling event, as recorded on a global scale (e.g. Shackleton et al. 1984; Bloemendal & de Menocal 1989). The maximum occurrence of I. bacatum is recorded in upper Pliocene laminites which have been associated with water mass stratification and deep euxinism (e.g. Kidd et al. 1978; SUC et al. 1991) as the result of an influx of continental fresh water following a rainfall intensification (e.g. Kidd et aL 1978; Rossignol-Strick 1983, 1985; Rudiman et al. 1989) and/or positive sea level pulsation (e.g. Suc et al. 1991).
Holotype: Londeix, Benzakour and De Vernal, 1992: Plate 1, figures 1, 9
Locus typicus: Punta Piccola section,
Stratum typicum: Upper Pliocene
Age: Late Pliocene
Synonymy
1985 - Leptodinium sp. A Corradini in Guerrera et al., pl.1, fig. 4 a,b; tab.I, II.
1992 - Impagidinium bacatum Benzakour, Pl. 2, fig.
Original diagnosis: Londeix, Benzakour and De Vernal, 1992, p. 696-700
Subspherical to ovoidal cyst. Surface of cysts distinctly punctate to micropunctate. Gonyaulacacean paratabulation indicated by low vacuolate parasutural septa. Sulcal paraplates not delineated by septa except for partial indication of the posterior sulcal and, in some specimens, the right sulcal paraplates. The archeopyle is precingular, of P(3"") type.
Description: Londeix, Benzakour and De Vernal, 1992, p. 696-700
Proximate acavate cyst, with a subspherical to ovoidal shape. The wall is moderately thick (1 to 1.5 Ám), two-layered and made up of closely appressed endophragm and periphragm. Under optical microscopy, the wall appears fairly and densely punctate to micropunctate. The paratabulation is plainly expressed by low parasutural septa (about V25 of the equatorial cyst diameter): they typically appear as alignments of vacuoles that are more or less circular, with an average diameter of 1,um. Under scanning electron microscopy, the wall surface appears to be scabrate to wealdy chagrinate, and is sparsely and irregularly penetrated by minute pores (pl. 1, figs. 5-6, 8). The septa are low ridges having the same texture as the wall. It seems that only the endophragm is weakly punctate to microperforate, and that the periphragm is chagrinate to irregularly microperforate. The beaded pattern of septa can be interpreted as an inner differentiation of the periphragm in the septa region. The paratabulation, as expressed by septa and archeopyle, is gonyaulacoid with the formula (in Kofoid notation): 4", 6", 6c, 6"", lp, 1"", ps, rs. The paraplates 1" and 4" are symmetrical; however, their boundaries are not always fully expressed. Similarly, the boundaries between the paraplates 1" and 2", as like 3" and 4" are not always expressed (pl. 1, fig. 6). The paraplate 6" is subtriangular and not in contact with paraplate 1" (Fig. 3). The paraplate 1"" is only occasionally expressed. The vertical paracingular septa are generally lower than the others and not always completely developed. The paracingulum is laevorotary, being ofEset 1 to 1.5 times its width. The parasulcus is slightly curved inward. The paraplate 6c often becomes very narrow near the parasulcus (Fig. 3). The parasulcal paraplate ps is very often expressed (although its anterior boundary may be not completely developed), instead of the rs, which is rarely perceptible. The archeopyle is precingular, of P(3"") type; the operculum is simple and free.
Dimensions - Holotype: total cyst length = 50 Á m; total cyst width = 51 Ám; septa height = 1.8-2.0 Ám. Range: total cyst length = 50(59)72 Ám; total cyst width = 43(56)67 Ám; septa height = 0.7(1.6)2.4 Ám. Number of measured specimens = 17. The number in parentheses corresponds to the average value of the measured parameter, and those flanking it, to the extreme values.
Comparisons - The beaded vacuolate structure of its septa distinguishes Impagidinium bacatum from all other species of the genus Impagidinium as with those of Pterodinium EISENACK, 1958 emend SARJEANT, 1985 and Leptodinium KLEMENT, 1960 emend SARJEANT, 1982. From the upper Pannonian of Bulgaria, Apteodinium mecsekense (NAGY, 1969) HELENES, 1984 and Leptodinium ? reticulatum (NAGY, 1969) HELENES, 1984 have a cyst surface that resembles to that of I. bacatum. The wall of A. mecsekense is, however, described as entirely devoid of tabulation on the ventral side; the edges of the existing tabulation are strongly developed. The apices of the tabulae and the ends of the zone are tapering (Nagy 1969, p. 292). L. ? reticulatum has a surface coarsely reticulate (op. cit., p. 293). A comparable species from the Danian of California, Impagidinium pentahedrias DAMASSA, 1979 has a densely granulate cyst wall surface texture. In contrast to I. bacatum, this characteristic is also visible by SEM observation (Damassa 1979, Pl. 4, fig. 6) and the septa are not vacuolar. From the Eocene of Australia, Impagidinium maculatum (COOKSON & ElSENACK, 1961) STOVER & EVTIT, 1978 has plate surfaces that are distinctly dotted, but the ledges are low, thin and hyaline (Cookson & Eisenack 1961, P.40).
At first glance, septa of the Australian Campanian species Impagidinium margarihferum (COOKSON &
EISENACK, 1960) STOVER & Evrrr, 1978 could be confused with those of I. bacatum, but I. margantiferum has plates bordered by ledges, which are perforated by a single row of holes (Cookson & Eisenack 1960, p. 5) instead of being vacuolar. Furthermore, the plate surface of I. margaritiferum seems to be scabrate rather than micropunctate. The structure of the plate areas and septa of I. bacatum seems to be identical to those of Spiniferites hyalospinosus (HANSEN, 1977) STOVER & WILLIAMS, 1987, but the presence of processes distinguishes this Danish Danian species.
BIOSTRATIGRAPHY: Impagidinium bacatum was first recorded (as Leptodinium sp. A) by Corradini in Guerrera et al. (1985) who reported it only in the Narbone formation (upper Pliocene) of two Sicilian drill cores (Log 41 and Log 42; Fig. 1). In more recent studies (Benzakour 1992), I. bacatum was observed in two Pliocene exposures in Sicily (Punta di Maiata and Punta Piccola sections) and also in the offshore Tunisian borehole Jiriba-1 (Flgs. 1, 2). The first occurrence of I. bacatum is recorded in the Punta di Maiata section (palynological sample PM 01) in the planktonic foraminifers zone MPL 2 of Cita (1975)(= Globorotalia margaritae Zone of Spaak 1983), below the base of the Nunivak magnetic subchron, at about 43 million years (Ma). The last occurrence of I. bacatum has been observed in the Jiriba-1 borehole, at a depth of 840 m, approximately in the middle of the MPL 5 zone of Cita (1975) and of the Globorotalia crassaformis Zone of Spaak (1983). Interpolation from planktonic foraminiferal datums permits an age of about 2.4 Ma to be proposed for the known disappearance of I. bacatum. On the basis of available records, I. bacatum may be regarded as an endemic Mediterranean species occurring in Pliocene sediments from about 4.3 to 2.4 Ma.
PALEOECOLOGY: I. bacatum has been reported only in marine Mediterranean sediments from pelagic (Sicilian sections) as well as neritic (Tunisian borehole) environments (Benzakour 1992). Its maxirnum abundance (up to 15% of dinoflagellate cyst assemblages; Flg. 2) occurs at the top of the Rossello composite section, in sediments corresponding to the A-group laminites cluster (e.g. Verhallen 1987; Driever 1988; de Visser 1990; Zachariasse et al. 1990). 1. bacatum belongs to a peculiar dinoflagellate cyst assemblage dominated by Spiniferites hyperacanthus (DEFLANDRE & COOKSON, 1955) COOKSON & EISENACK, 1974 and characterized by the notable occurrence of the thick walled species Operculodinium israelianum (ROSSIGNOL, 1962) WALL, 1967, Tectatodinium pellitum WALL, 1967 and Achomosphaera callosa MATSUOKA, 1983. The co-acme of these four thick walled species is a peculiar feature of the Sicilian upper Pliocene assemblages. The correlation betweenthe percentages of I. bacatum and A. callosa, T. pellitum and O. israelianum reaches values of 0.92, 0.87 and 0.86 respectively. A. callosa is an extinct species of unknown ecology. T. pellitum is still present in modern marine sedi;nents, but occurs as a minor component (never up to 9%) of recent dinocysts assemblages (e.g. Wall et al. 1977; Turon 1984). It appears to be mainly associated with warm-temperate to sub-tropical waters with variable salinity conditions (Wall & Dale 1968; Wall et al. 1977; Harland 1983). O. israelianum is known from Miocene through Recent sediments (Matsuoka 1983; Jan du Chene & Londeix in preparation). At present, the major center of abundance of O. israelianum is in the Caribbean Sea, i.e. in tropical-subtropical environments, often marked by highly saline and/or stratified conditions (Wall et al. 1977; Harland 1983). I. bacatum is a probable warm water stenothermic species, rather tolerant toward salinity and distality. Its disappearance at 2.4 Ma may be related to a cooling event, as recorded on a global scale (e.g. Shackleton et al. 1984; Bloemendal & de Menocal 1989). The maximum occurrence of I. bacatum is recorded in upper Pliocene laminites which have been associated with water mass stratification and deep euxinism (e.g. Kidd et al. 1978; SUC et al. 1991) as the result of an influx of continental fresh water following a rainfall intensification (e.g. Kidd et aL 1978; Rossignol-Strick 1983, 1985; Rudiman et al. 1989) and/or positive sea level pulsation (e.g. Suc et al. 1991).