The genus Boltovskoyella (foraminifera) from Patagonia

Four species of the genus Boltovskoyella Malumián & Masiuk are recognized in Patagonia, among them, B. paleocenica sp. nov., which is described from Danian shallow marine sediments. Considering that the previous records of Boltovskoyella are from the Middle-Late Eocene, this new species represents the oldest known occurrence of the genus. Boltovskoyella seems to be endemic to Patagonia, shows opportunistic features and prefers temperate-warm water settings.


INTRODUCTION
Since its description, Boltovskoyella Malumian & Masiuk has been regarded as restricted to the Eocene-Oligocene of southernmost South America and New Zealand (Malumian & Masiuk, 1972). The two species described from Patagonia are some of the most characteristic Middle-Late Eocene species endemic to the Austral Basin (Malumian, 1994). Both frequently dominate low diversity assemblages of shallow marine environments. The New Zealand record is considered to belong to another genus.
Collection across the Cretaceous-Palaeogene boundary in northwestern Patagonia has yielded a new species of Boltovskoyella from the Danian. The main purpose of this paper is to describe the new species in the context of a compilation of Boltovskoyella in Patagonia.

STRATIGRAPHIC SETTING
The marine Palaeogene of Argentina occurs mainly in Patagonia, where it was deposited in several basins by generally shallow seas, resulting in transgressive and regressive successions of alternating marine and non-marine sediments with marked hiatuses. The basins have always been in temperate latitudes with restricted access to the open ocean, so planktonic numbers are low and correlation with standard P zones, if attainable, is generally indirect. There is no record of larger foraminifera. Three major Palaeogene transgressions occurred in Patagonia. The first began in the Maastrichtian and persisted into the Danian; the latter contains a cosmopolitan Midway-type foraminifera1 assemblage. The second transgression (Middle-Late Eocene), contains several endemic species (Malumian, 1994). The third (Oligocene-Early Miocene) carries an assemblage with subantarctic influence (Malumian & Naiiez, 1991).

MATERIAL
Specimens were studied from the following localities (Fig. 1); references are given for additional information on associated foraminifera and stratigraphy.

DISTRIBUTION OF THE GENUS B O L T 0 VSKOYELLA
Three species were included in the original description of the genus (Malumiin & Masiuk, 1972). The type species B. argentinensis was described from beds tentatively assigned to the Late Eocene, and B. patagonica from the Oligocene, probably Early Oligocene; both species were recorded from the subsurface of the Austral Basin, Argentina. The third species is Heminwayina zealandica, described by Hornibrook (1 961 At that time, in Argentina the genus was known only from the subsurface, being dominant in low diversity assemblages which lacked planktonic foraminifers. This conspicuous occurrence led to the recognition of a 'Boltovskoyella assemblage' or 'Boltovskoyella beds' (MalumiLn, 1982;Malumian & Ramos, 1984).
The new species of Boltovskoyella mentioned by Masiuk et al. (1976) from the YPF.Ch.PV.es-1 Peninsula de Valdes well, occurs at 719-729 mbsl in a nearly monospecific benthic assemblage without planktonic forms. This horizon overlies Late Danian beds and was originally dated as Eocene (Masiuk et al., 1976). Malumian (1993) identified the specimens as belonging to B. paleocenica sp. nov. here described, and assigned the horizon to the Danian, based on correlation with the outcrops of the NeuquCn Basin.
Boltovskoyella argentinensis and B. patagonica are known from the Middle-Late Eocene of the Austral Basin, from both Chilean and Argentine localities. In Argentina, B. patagonica was recorded from the following localities: (a) Its type locality, SC-1 well, 630 mbsl (type sample) and 571-578 mbsl. Specimens were also recorded in thin sections from 55G562 mbsl. The beds containing B. patagonica were dated as Oligocene, probably Early Oligocene (Malumian et al., 1971). They lack planktonic microfossils, but horizons at 648-658 mbsl were assigned to the Globigerapsis index index and Globorotalia inconspicua inconspicua Zones of Jenkins (1966), based on the occurrence of Globigerinatheka index (Finlay), Subbotina sp. cf. S. linaperta (Finlay) and Truncorotaloides collactea (Finlay) (Malumian et al., 1971). Uphole at 251-252 mbsl there is a benthic foraminiferal assemblage of Oligocene-Early Miocene age. The beds containing B. patagonica are tentatively included in the Man Aike Formation, of Middle-Late Eocene age (cf. Malumian & Naiiez, 1989;Malumian, 1992Malumian, , 1994. (b) Gran Bajo de San Julian, southeast of the Laguna del Carbon, at the base of the outcropping Palaeogene succession (Malumian & Naiiez, 1989;Nafiez, 1990). The beds containing B. patagonica, tentatively included in the Man Aike Formation, underlie beds of the San Julian Formation dated as latest Eocene+arliest Oligocene (P 17 Zone of Blow, 1969), by means of planktonic foraminifers (Bertels, 1975). The whole foraminifera1 assemblage from the Man Aike Formation at this locality is very similar to that of the SC-1 well at 630 mbsl. (c) SEC-7 well, 114 and 117 mbsl, Man Aike Formation.
Identification of the fragmentary, very scarce specimens, is tentative (Malumian, 1992). They occur associated with Testacarinata inconspicua (Howe) and T . aculeata (Jenkins), which range from the Globigerinatheka index Zone to the Testacarinata inconspicua Zone (Late Middle to Early Late Eocene; Jenkins, 1985), or from the P11 to Pi4 Zones (Blow, 1979). Some of the associated benthic foraminifera are common to the La Despedida Formation, of Middle-Late Eocene age (Malumian, 1992).
In Argentina, Boltovskoyella argentinensis was recorded from two localities: (a) Its type locality, LA. x-1 La Aurora well, 645-655 mbsl and 665-675 mbsl (type sample). Malumian & Masiuk (1972) assigned these horizons a late Eocene age, based on correlation with the SC-3 well, also in the Austral Basin. They are tentatively included here in the Man Aike Formation, of Middle-Late Eocene age. (b) Rio Turbio coal measures area. The specimens come from the upper member of the Rio Turbio Formation, from both below and above the coal seams. The section below the coal seams was assigned a Late Middle to Early Late Eocene age, based on the occurrence of Testacarinata inconspicua, and to the NP16 Zone of Martini (1971), Middle Eocene, based on the abundance of Chiasmolithus modestus Perch-Nielsen. The section above the coal seams lacks planktonic foraminifera and calcareous nannoplankton, their age being considered the same as the levels below the coal seam or slightly younger (Carrizo et al., 1990).
In Chile, B. argentinensis was identified as Patelinella inconspicua by Caiion (fide Malumian & Naiiez, 1989) in the Puerto Nuevo Formation, who highlighted its character as a guide species. Malumian & Naiiez (1989) mentioned its association with Subbotina angiporoides minima and Globigerinatheka index. Martinez-Pardo & Martinez-Guzman (1989) assigned to Boltovskoyella a post Oligocene, probably Early-Middle Miocene age, for the Chilean area of the Austral Basin, and mentioned that B. patagonica and B. argentinensis co-occur in surface samples and may be conspecific.
However, Hromic (1990) recognized Boltovskoyella in the Puerto Nuevo and Santa Clara Formations (Tierra del Fuego Island, Chile), which correspond to the earliest part of the Miradorian Stage (Natland et al., 1974). The base of the Miradorian Stage is Late Eocene and the upper part Early Oligocene, according to its calcareous nannoplankton (Mobil Oi1,Jide Hromic, 1990 , 1996) and distribution of Boltovskoyella spp. in Patagonia. Units are marine formations unless otherwise stated.

w t h e l ? s h
a higher stratigraphical range than B. patagonica (Hromic,1 990). This record clarifies the stratigraphical relationship between the two species, suggesting that B. argentinensis survived B. patagonica.
In summary, Boltovskoyella is recorded from the Danian and the Middle-Late Eocene (Fig. 2). The lack of record in the Late Palaeocene-Early Eocene may be related to the fact that marine sediments of this age are very scarce and palaeoecologically unsuitable for the genus. On the other hand, despite the large number of samples and localities studied from the Maastrichtian of the Neuqutn-Colorado Basin, some of them of a very shallow setting, Boltovskoyella was not recorded (cf. MalumiLn et al., 1995), although other asterigerinatids occur.
In the Peninsula de Valdts well, the specimens which probably belong to B. paleocenica sp. nov., come from a dolomite and are associated with abundant bryozoa. These horizons correspond to the shallowest palaeodepth recorded for the Latest Cretaceous-cenozoic succession in this well (Masiuk et al., 1976).
Boltovskoyella paleocenica sp. nov. was recorded from only very shallow, restricted environments, despite the high number of samples studied from more open marine Danian sediments. Its occurrence in carbonate lithologies, including oolites, suggests a preference for relatively warm-water settings.
In the SC-1 well, B. patagonica occurs in a low diversity assemblage, associated with abundant miliolids at 571-578 mbsl (Malumihn et al., 1971), which would correspond to an inner shelf, restricted environment, of probably hypersaline waters. Records from the Man Aike Formation at the SEC-7 and CB.es-6 wells, and from the upper member of the La Despedida Formation also correspond with shallow-water environments.
Boltovskoyella argentinensis is the dominant species in its type  sample (Malumian & Masiuk, 1972). In the Rio Turbio Formation, in the D-60 well, it occurs in a very low diversity assemblage, the dominant species being Elphidium rioturbiense Malumian, with B. argentinensis the second most abundant (Malumian, 1994). This assemblage corresponds to a very shallow environment, of probably hyposaline waters. Boltovskoyella argentinensis also has been recorded, with few specimens, from open marine settings, such as that of the Puerto Nuevo Formation. The occurrence of Boltovskoyella spp. as dominant in marginal environments and scarce in open marine ones suggests an opportunistic character (Levinton, 1970). Also, they seem to have inhabited hyposaline to hypersaline waters. Their preference for temperate-warm waters is supported by the occurrence in carbonate, even oolitic settings in the Neuqukn and Peninsula de Valdks Basins, the occurrence in a coal-bearing unit, such as the Rio Turbio Formation, and by association with discoasters in the Man Aike Formation (Concheyro, 1991).
The planoconvex, high trochospiral test, coarsely perforate on the spiral side and imperforate on the umbilical side, suggests that the life habitat of Boltovskoyella was epifaunal (cf. Corliss & Chen, 1988 The relationship between New Zealand and Patagonia Middle-Late Eocene foraminiferal assemblages is believed to be less close than was thought before (Malumian, 1994) and the restriction of Boltovskoyella to Patagonia weakens it even more. However, links remain, by genera such as Cribrorotalia, Notorotalia, Antarcticella and Nwnmodiscorbis.
Boltovskoyella paleocenica sp. nov. seems to be one of the few Danian species endemic to Patagonia. The Danian foraminiferal assemblage of this region has been regarded as cosmopolitan, of Midway type (Berggren & Aubert, 1975), corresponding mostly to an inner-middle shelf environment (MalumiPn, 1979 utilui (Bertels). This situation contrasts with the marked endemism of the foraminiferal assemblages from the Maastrichtian of northern Patagonia (Malumian et al., 1995) and the moderate endemism in the Middle-Late Eocene (Malumian, 1994). Strong palaeoaustral (cool-temperate) benthic faunal affinities were noted for Late Cretaceous-Early Eocene times along the South Pacific margin (Fleming, 1962;Stevens, 1973Stevens, , 1980. Based on molluscan faunas, Zinsmeister (1979) proposed the name Weddellian province for a shallow-water region extending from southeast Australia to southern South America. According to Casadio (1994), the molluscan faunas from the Maastrichtian of the NeuquCn Basin have a strong affinity with those from the Weddellian province, but in the Early Danian they were succeeded by subtropical forms.
In contrast with the normal marine foraminiferal assemblages, those from the very shallow, marginal environments from the Danian of Patagonia appear to be dominated by or have a high endemic content. Malumiin & CaramCs (1995) indicated that Buliminella isabelleana is one of the endemic species of more palaeogeographic significance, due both to its frequency and abundance. It frequently occurs in monospecific or high dominance assemblages in extreme, shallow, stressed environments. Boltovskoyella paleocenica sp. nov., apparently restricted to northern Patagonia, also dominates or is an important element of shallow assemblages. Thus, two foraminiferal assemblages of marginal marine affinity may be differentiated in the Danian of Patagonia: one, rather widely distributed, dominated by B . isabelleana, of infaunal, detritivorous habit (Malumian & CaramCs, 1995), probably developed on soft, organic-rich bottoms. The other, more restricted, dominated by B. paleocenica sp. nov., of epifaunal habit, corresponds to relatively warm-water, carbonate settings, probably on harder or sandy bottoms. Boltovskoyella has not been found in the Palaeocene of Antarctica (cf. Huber, 1988), probably because of the higher latitude.  Malumian & Masiuk, 1972 Remarks: Malumian & Masiuk (1972) differentiated Boltovskoyella from other genera mainly by its conical test, with a high dorsal side and imperforate ventral side with supplementary chambers. The unique character of Boltovskoyella among the Asterigerinatidae was pointed out by Loeblich & Tappan (1987), due to its very high spire forming a parallel-sided cone and its broad umbilicus; they indicated that the systematic position of the genus needs additional study. Other feature of Boltovskoyella is the very coarsely perforate spiral side, in contrast with the imperforate umbilical side. The type species of Eoeponideliu, E. linki Wickenden, is uniformly perforate on both spiral and umbilical sides and has a lower trochospiral test (see illustrations of McDougall, 1987 andLoeblich &Tappan, 1987). Asterigerinata has a low trochospiral test, with coarse pores on the supplementary chamberlets; few pores also seem to occur on the umbilical side of the main chambers, according to observation under light microscope of topotypes of A . dominicunu Bermudez, type species of Asterigerinata. Biasterigerina differs by having a densely perforate umbilical side, with very narrow and elongate supplementary chamberlets.

SYSTEMATIC DESCRIPTIONS
None of the eight specimens of Heminwayina zealundica observed (seven from the type sample, kindly sent by Dr H. Morgans, and one from loc. S168/494 from the Whaingaroan Stage of New Zealand, which was sent by late Dr Hornibrook to Dr Malumian) has a very high spire. One of the topotypes was examined under SEM, showing its umbilical side with coarse pores on part of the main chambers and on the distal part of the supplementary chambers. These features appear to be enough to exclude this species from Boltovskoyella. Malumian & Masiuk,I972 (PI. 1,P1. 2, 1972 Boltovskoyella argentinensis MalumiLn & Masiuk: 2, pl. 1, figs 3 4 .

Material and localities:
Austral Basin, Santa Cruz Province. LA.
In the Rio Turbio area, B. argentinensis was recognized from the upper member of the Rio Turbio Formation. Two forms may be differentiated: (a) Specimens from the Adaro I1 well, very smrce and not well preserved, are subcylindrical and seem to have a smooth surface, fitting well with topotypes.
(b) Specimens from the D-60 well (Pl. 1; figs 11-12) differ from topotypes by the more elongated test, triangular in section but with rounded angles, a tapering initial end, a stronger tendency to biseriality and uncoiling, having 2-3 chambers in the last whorl, generally 2%. The wall is always more rugose, with raised interpore walls, sometimes coalescing into longitudinal ridges. However, some specimens show gradational characteristics to topotypes, with rounded base (Pl. 1; fig. 12) or more rounded section.
Specimens from D-60 well are stratigraphically higher than those from the Adaro I1 well and might belong to a new species, younger than Boltovskoyella argentinensis. For the present, as some gradational characteristics are seen, specimens from the D-60 well are included in B. argentinensis. MalumiLn & Masiuk, 1972 (PI. 1, figs 1-3; P1. 2, fig. 4; Fig. 4 (54) Material and localities. Austral Basin, Santa Cruz province. SC-1 Santa Cruz well, 571-578 mbsl, 25 specimens; 630 mbsl (type sample), 31 specimens. Samples GB019 and GB1, Gran Bajo de San Julian, southeast of the Laguna del Carbhn, at the base of the outcropping Cenozoic succession, 26 specimens. Remarks. Specimens from the type sample are characterized by the moderately high trochospiral test, subconical in shape, 5-7, generally 6, chambers in the first whorl, rapidly reducing to 3 %-5, generally 3%-4 chambers in the final whorl; periphery angular to carinate; ovoid to reniform supplementary chambers; surface on the spiral side with coarse pores (2-4 pm) and sutures commonly raised, umbilical surface imperforate, with nodes. A coarse perforation seen on the last supplementary chamber of specimen of PI. 2, fig. 4(b) may be a boring, as it does not systematically occur in other chamberlets or specimens. At higher enlargements some small (c. 0.3 pm) and irregularly scattered holes are seen; most of them appear to be due to dissolution.

Boltovskoyella patagonica
Two fragmentary specimens referred to Boltovskoyella? sp. from the CB.es-6 Campo Bola well, 594604mbsl and 654-664mbsl (Naiiez, 1990), and two fragmentary specimens referred to Boltovskoyella patagonica? from the SEC-7 well, 117mbsl (Malumihn, 1992) may belong to this species. Initial fragments of topotypes of B. patagonica and B. argentinensis are differentiated by the smoother surface and more thickened sutures of the latter.
One fragmentary specimen referred to as B. patagonica from outcrops of the lower member of the Rio Turbio Formation (Torre, pers. comm.) seems to be a Cribrorotalia species.
Boltovskoyella sp. cf. B. patagonica Malumian & Masiuk (Pl. 1, Material and locality. Austral Basin, Tierra del Fuego Island, Argentina. Section near La Aurelia farm, La Despedida Formation, upper member. At 540m from the base of the section (Malumian, 1989). Five specimens. Description. Trochospiral test, spiral side moderately high, umbilical side flat to very slightly concave, periphery carinate. Initial part of the spiral side obscured, spiral and intercameral sutures thickened, flush or slightly raised; chambers semilunate in shape, 3-3% in the last whorl; sutures on the umbilical side slightly depressed. Aperture interiomarginal, arcuate, with lip. Supplementary chambers obscured by ornamentation on the umbilical surface, but seem to be rather elongate and lobulate. Wall densely perforate on the spiral side, except on the sutures, imperforate on the umbilical side. Umbilical surface with grooves and nodes, the latter concentrated near the aperture. Remarks. These specimens were referred to as B. patagonica by Malumian & Naiiez (1989, p. 257). They differ from B. patagonica by being larger, with fewer chambers in the last whorl, more semilunate in shape, supplementary chambers apparently more elongate, and with grooves on the umbilical surface, rather than nodes only. Asterigerina sp. mentioned from the same sample by Malumian (1989) and Malumian & Nafiez (1989)  Remarks. There is wide variation in the spire height, number and degree of inflation of chambers in the last whorl, elongation of the supplementary chambers, degree of concavity of the umbilical side, and characteristics of the umbilicus. Specimens with a low test, probably juvenile forms, usually have an umbilical plug and subangular periphery (PI. 3; figs 2(a-b)), whereas higher specimens have a broadly rounded periphery and Naiiez a depressed, wide and deep umbilicus, apparently left open by the collapse of the supplementary chambers and plug (Pl. 3; figs l(a-b), 5). Moderately high tests (PI. 3; figs l(b), 10) are the most abundant; higher tests (Pl. 3; fig. 8) are common, whereas the elongate, very high specimens tending to form parallel-sided cones ( Fig. 4 (1-2)) are rare. Coiling is mostly sinistral (89% of 193 specimens from sample M-6, and 68% of 228 specimens from sample PSN 58). Although regular preservation precludes reliable observation at very high enlargements, umbilical side appears imperforate. Assignment of this species to the genus Boltovskoyella is due to its high spiral side, which in some specimens tends to form a parallel-sided cone, and its coarsely perforate spiral side, contrasting with the imperforate umbilical side. Comparisons. It differs from B. argentinensis mainly by the shorter, generally conical rather than cylindrical test, and higher number of chambers in the last whorl.
It differs from B. patagonica by having more chambers in the last whorl ( 5 4 rather than generally 3%), a more rounded periphery, higher and more inflated chambers, and triangular supplementary chambers.
Type material of Asterigerina primaria Plummer, from the Palaeocene of the Gulf Coastal Plain was kindly sent by Dr G. Buckley for comparison (slide 33101 of the Plummer collection housed at the Field Museum of Natural History, Chicago). The slide contains four specimens from station 67, one of them matching very well to that illustrated by Plummer (1927). They have a more lenticular test, the umbilical side flat to slightly convex, an acute, keeled periphery and bigger and less elongated supplementary chambers. There are pores on the last supplementary chamber of one specimen, although a SEM photograph would be needed to be sure. Asterigerina primaria is known from the Palaeocene of the Gulf Coast, Denmark and SW France (Berggren & Aubert, 1975).
Boltovskoyella paleocenica sp. nov. differs from Eoeponidella Zinki Wickenden, from the Upper Cretaceous of Canada, by the generally higher and more conical test and imperforate umbilical side.
Boltovskoyella seems to have a tendency to elongation and reduction in the number of chambers per whorl, similar to that mentioned by Revets (1987) for other lineages of trochospiral foraminifera. B. paleocenica, from the Danian, is relatively short and has the highest number of chambers in the last whorl (5-6). It would follow B. patagonica, with 3 %-4 chambers in the last whorl (Pl. 1; fig. l(a)); later typical forms of B. argentinensis, with 3 chambers (Pl. 1; fig. lO(a)), and finally the form illustrated from the Rio Turbio area (Pl. 1; fig. 1 l), which clearly tends to biseriality and is even more elongate than typical B. argentinensis.