Maximum Middle Jurassic transgression in East Greenland : evidence from new ammonite finds , Bjørnedal , Traill Ø

A Middle – lower Upper Jurassic sandstone-dominated succession, more than 550 m thick, with mudstone intercalations in the middle part is exposed in Bjørnedal on Traill Ø, North-East Greenland. A number of ammonite assemblages have been found, mainly in the mudstones. They indicate the presence of the Lower Callovian Cadoceras apertum and C. nordenskjoeldi Chronozones. The mudstones represent northern wedges of the Fossilbjerget Formation hitherto known only from Jameson Land to the south. In Bjørnedal they interfinger with sandstones of the Pelion and Olympen Formations. The presence of the Fossilbjerget Formation in this region indicates complete drowning of the Middle Jurassic sandstone-dominated Pelion Formation during maximum Middle Jurassic transgression. A new species, Kepplerites tenuifasciculatus, is described in the appendix by J.H. Callomon. The holotype and paratype are from Jameson Land, East Greenland, but the species is also found in Bjørnedal, Traill Ø, North-East Greenland.

The Mesozoic deposits of the Traill Ø area in North-East Greenland were studied by Donovan (1953) during Lauge Koch's East Greenland expeditions (Fig. 1).Middle Jurassic exposures are few and scattered and fossils are scarce, allowing only a few tie-points to the biostratigraphically well-dated succession in Jameson Land to the south (Callomon 1993).A succession of dark micaceous, silty mudstones in an otherwise sandstone-dominated succession in the Bjørnedal valley, south-east Traill Ø was described by Donovan (1953;Fig. 2).Only a few poorly preserved and unidentifiable ammonite fragments were recovered.Hence the exact stratigraphic position and age of the mudstones were unknown and have remained as such until reexamination of the locality and intensive search for ammonites was carried out during fieldwork in the Traill Ø area in 1996 (Alsen 1998).New finds of ammonites indicate an Early Callovian age (Cadoceras apertum Chronozone) of the mudstones (Fig. 3), which are referred to the Fossilbjerget Formation, previously known only from Jameson Land (Surlyk et al. 1973).This paper presents the new finds of ammonites in the Bjørnedal area and the implications of these for the sequence stratigraphic interpretation of the basin.
The Traill Ø area forms the northwards continuation of the Jurassic Jameson Land Basin within the East Greenland rift basin.Huge amounts of sand-dominated sediments were introduced into the basin mainly from the north in Middle Jurassic times and were transported southwards by marine currents along the basin axis.A thick succession of Middle Jurassic marine sediments, mainly sandstones, was deposited in northern Jameson Land and progressively thins distally towards the south.The proximal areas in Traill Ø acted as a bypass area for much of late Middle Jurassic time and the succession is generally thinner compared with the more distal areas in Jameson Land (Surlyk 2003).
The south-easternmost part of Traill Ø constituted an eastwards-tilted fault block, in contrast to other Jurassic fault blocks in East Greenland which are tilted westwards (Donovan 1953;Carr 1998;Surlyk 2003).A detailed analysis of the Middle Jurassic succession in the Vaelddal area close to the crest of the eastwardstilted block was recently undertaken by Carr (1998;Fig. 1).He demonstrated that as a result of synsedimentary movements of the Vaelddal Fault during Middle Jurassic time the sedimentary evolution of the Bjørnedal area differed somewhat from that of other parts of the region.The Middle Jurassic succession in this block shows palaeocurrent directions to the east in contrast to the axial, southwards-oriented palaeocur-rent directions seen elsewhere.The sandstone/mudstone ratio also decreases and the succession shows proximal to distal facies changes in the same direction (Vosgerau et al. 2004, this volume).

Stratigraphy
The lithostratigraphical scheme for the Jurassic of East Greenland was erected by Surlyk et al. (1973), Surlyk (1977Surlyk ( , 1978) ) and Birkelund et al. (1984).The scheme is under revision and many units have been raised in rank (see Surlyk 2003, fig. 5).In the Traill Ø area, the Middle -lower Upper Jurassic succession now includes the Bristol Elv, Pelion, Fossilbjerget and Olympen Formations in ascending order (Fig. 4).The Bristol Elv Formation is probably not exposed in Bjørnedal.It is of pre-Late Bajocian but probably still Middle Jurassic age and includes fluvial pebbly sandstones and thin coaly shales (Therkelsen & Surlyk 2004, this volume).The Pelion Formation consists of shallow-marine sand- stones with bivalves, belemnites, ammonites and plant fragments.The formation rests on Triassic strata or on the Bristol Elv Formation.It is overlain by, or interfingers at the top with, offshore, dark, micaceous, silty mudstones of the Fossilbjerget Formation.A regressive wedge in the top part of the Pelion Formation interrupts the overall backstepping Pelion-Fossilbjerget couplet, and belongs to the Parnas Member of the Pelion Formation (Surlyk 2003).The Fossilbjerget Formation is overlain by the lower Upper Jurassic Olympen Formation, which also consists of shallow marine sandstones themselves quite similar to the sandstones of the Pelion Formation below, making recognition of the Olympen Formation difficult.
The Middle Jurassic succession in the Bjørnedal area is poorly exposed.The area described here corresponds to the 'northern part of Bjørnedal' of Donovan (1953).An intensive search for ammonites was made in dark, silty, micaceous mudstones exposed in small sections along the Bjørnedal river, Locality 1, and in a small section in a gully at Locality 2 (Figs 2, 5).Three ammo-nite assemblages were recovered; two ammonite species have been identified, one of them previously known from Jameson Land but hitherto undescribed.
The description of the Middle Jurassic succession in Bjørnedal is based mainly on Donovan (1953), since fieldwork was focused solely on the mudstones in its middle part.The succession is subdivided into five lithological units, A-E in ascending order (Figs 4,5).Unit A belongs to the Pelion Formation and consists of about 200 m of sandstones containing Cranocephalites, which suggests correlation with the Upper Bajocian C. pompeckji Chronozone (Fig. 3) and indetermi- Parnas Member, representing the last regressive tongue of the overall backstepping Pelion Formation.Unit D consists of about 40-50 m of black, silty mudstones with intercalated sandstones and indeterminable ammonites.It belongs to the upper part of the Fossilbjerget Formation.A 50 m core (GGU 303124) drilled at Locality 2 (Fig. 2) through most of this unit records a development from offshore black mudstones with occasional storm sandstone beds, 5-10 cm thick, into offshore transition zone mudstones with an upwards increasing content of fine-grained sandstone (Fig. 6).
At the top, a syenite sill, c. 3 m thick, occurs between the mudstones and the base of the sandstones of the overlying lower Upper Jurassic Olympen Formation (Unit E).This formation consists of about 220 m of apparently massive sandstones interbedded with irregular beds of dark micaceous mudstones with traces of plants (Donovan 1953).It is overlain by Upper Jurassic black mudstones of the Bernbjerg Formation containing Late Oxfordian ammonites (Amoeboceras serratum Sowerby 1813; Price & Whitham 1997).
Description.Only two-fifths of the last whorl is preserved, as an imprint in silty mudstone.The fragment, a macroconch, comprises most of the body chamber of an adult specimen with an estimated maximum diameter of 130 mm.Its umbilical seam is uncoiling and the ribs near the aperture are strongly projected forward.Primary ribs are coarse and strongly curved.Each primary rib gives rise to four secondary ribs, which persist to the venter.Secondary ribbing is very fine and dense.Secondary ribs are almost straight but seem to curve slightly backwards near the venter giving an overall sinuous appearance of the primary and secondary ribs.
Comparison.The species is consistently more densely, finely ribbed than any other species of Kepplerites from East Greenland, with little, if any, modification of the primary ribbing in the adult stage.Horizon.The assemblage was collected at a small exposure in the streambed of the Bjørnedal River in Bjørnedal, Traill Ø.The succession was not measured, but belongs to unit B (Fig. 4).
Description.The fragments seem to be those of macroconchs.Description.The inner whorls are finely and densely ribbed and seem to be evolute.The outer whorls are evolute, with very coarse and blunt primary and secondary ribbing.The whole assemblage seems to consist of fairly slim variants.
Comparisons.The specimens are referred to as C. cf.nordenskjoeldi, which has the above-mentioned characteristic style of ribbing.This is supported by their stratigraphical position above K. tenuifasciculatus.
Age and distribution.This is the first find of the species outside the Fossilbjerget and Olympen areas in central Jameson Land.C. cf.nordenskjoeldi indicates an Early Callovian age (C.nordenskjoeldi Chron; Fig. 3).
Description.The macroconch is medium-sized and evolute, and comprises most of a whorl of the bodychamber.Ribbing is dense and relatively strong up to the aperture.Primaries divide into secondaries on the middle of the flank.The specimen shows no adult modification and could be a juvenile.Maximum diameter measures 61.5 mm.The other specimen, probably a microconch, is small and relatively evolute.Ribbing is dense and sharp with primaries and secondaries.Maximum diameter is 30 mm.
Age.The assemblage is too poorly preserved for determination to specific level.The specimens are possibly early Cadoceras of Early Callovian age (J.H. Callomon, personal communication 1997; Fig. 3).

Plate 1
All specimens are figured natural size.The sections span the shaly Fossilbjerget Formation underlain by the sandy Pelion Formation and capped by the sandstones and shales of the Olympen Formation (Surlyk et al. 1973;Larsen & Surlyk 2003).The three sections differ only in detail.Section 43 is shown in weathering-profile in Figure 2. It was previously shown in outline by Surlyk et al. (1973, fig. 23).Lithologically, the sediments consist predominantly of shaly siltstones or very fine-grained sandstones, barely consolidated except in concretionary layers that punctuate the succession as markers or in scattered calcitic or phosphatic concretions.Some of the beds are highly glauconitic, indicating condensed, sediment-starved intervals and comparison with adjacent areas, e.g. at the mountains Olympen and Mikael Bjerg (Fig. 1), shows that the succession incorporates numerous hiatuses of variable durations.The age-diagnostic ammonites can be recovered only from the hard beds.Their biostratigraphy in terms of faunal horizons, however, is with only few exceptions as close to complete as present knowledge allows (Callomon 1993, fig. 4).The only horizon in the interval under discussion not so far recognized in the Fossilbjerget-Olympen area is J23, that of Kepplerites vardekloeftensis.It may have been lost in a hiatus, marked by a sharp lithological break, under the glauconitic ironstones of beds 9-13 (Fig. 2, Section 43).The type-horizon of Kepplerites tenuifasciculatus, J27, is bed 14, an indurated, shaly, non-glauconitic, light brown fine-grained sandstone, 0.2 m thick, lying with sharp contact on the hard, ferruginous and highly glauconitic sandstone marker of bed 13 below (Fig. 2, Section 43).The contact probably marks another hiatus that would account for the considerable break, both in composition and morphologies, between the faunas of beds 13 and 14.The fauna of bed 13 consists predominantly of Cadoceras (apertum), with only minor Kepplerites (cf.traillensis).That of bed 14 is dominated by monospecific Fm m Bed m Bed Gp Fig. 2. Diagrammatic sections in weathering profile through the Fossilbjerget Formation at its type locality on the southern slopes of Fossilbjerget, central Jameson Land; section 43 is located 3 km west of section 42.Note that the beds in the two sections are numbered independently -discussion of bed numbers in the text refers to those in Section 43.Lithostratigraphy at left, standard chronostratigraphy -substages and zones -at right.Diagonal hatching: glauconitic.Numbers J18-J35: the ammonite faunal horizons recognized in Jameson Land (see Callomon 1993).The horizon of Kepplerites tenuifasciculatus is J27.Cranocephal., Cranocephaloide.
Description.All the available material consists of crushed internal moulds and measurements of dimensions (Table 1) are of limited value.The figured specimens are typical; both are complete adult macroconchs with strongly uncoiling seams on the last whorl.The microconchs remain unknown.The ribbing is characteristically dense and fine, the primaries rising retroradially on the umbilical wall, then swinging in a strongly forwards-directed curve on the umbilical shoulder into accentuated prorsiradiate ribbing on the whorlside, dividing into fasciculate sheaves (tenuifasciculate) of secondaries at about a third flank-height, rising uncurved to the venter, persisting with little or no loss of strength to the simple, somewhat sinuous peristome.There is no evidence of the lateral accentuation of the primaries into tubercles seen in other species of Kepplerites, especially in the younger ones and subsequently in the descendant, Kosmoceras.Inner whorls are not seen, so whether the earliest stages already have tabulate venters is not known.
Comparisons.The evolution of major morphological characters in the genus Kepplerites, leading to Kosmoceras in the Middle Callovian, was very gradual.Differentiation of successive transients relies on relatively minor variations of size and ribbing, often perceptible only by the trained eye in assemblages of more than a single specimen in which the range of intraspecific variability can be assessed.Changes were not continuously orthogenetic: characters could 'progress' and 'regress' with time largely independently, leading to frequent partial homoeomorphies.
In descending order: 1. Kepplerites traillensis Donovan 1953 (plate 17, figs 1a, b, holotype;plate 18, figs 1a, b), faunal horizons 24-26, is similar in size, coiling and style of ribbing but significantly less densely ribbed, with only c. 31 primaries per whorl (before the onset of the modifications on the final stage of the adult bodychamber found in all the Kosmoceratidae).The type material came from mount Morris Bjerg on Traill Ø, about 5 km north-east of the coast of Kong Oscar Fjord to the south-west.It was found in isolation, both stratigraphically and faunistically, so the position of its faunal horizon in the general succession has to be deduced by correlation with the more continuous successions in Jameson Land.The closest resemblance is to the forms found also on the southern slopes of Fossilbjerget, sections 42 and 43, horizons 24-26, as minor components in faunas dominated by Cadoceras apertum (Callomon & Birkelund 1985).K. traillensis is also, among all the known faunas of Greenland, the one closest to the type-species K. keppleri (Oppel): cf.Buckman (1922, plate 289A, B, lectotype, evolute inflated variant with slightly tabulate venter); Quenstedt (1886, plate 77, figs 1-5, S. Germany); Page (1989, fig. 5.1a, b, England).The resemblance is close but may not be exact, so that both specific names are retained for the time being.It indicates, however, a close time correlation and provides the basis for the assignment of the Apertum Zone already to the Lower Callovian.Callomon 1993 (p. 102), faunal horizon 23.The holotype (Spath 1932, plate 25, figs 2a, b, complete adult) and paratype (Spath 1932, plate 25, figs 1a, b, complete adult phragmocone) came from the calyx limestone, a prominent concretionary marker-bed in the Fossilbjerget Formation along the length of the outcrops above Neill Klinter, the line of cliffs on the west side of Hurry Inlet and traceable inland as far as Katedralen on Ugleelv (Fig. 1); level 560 m in sections of Rosenkrantz reproduced by Spath (1932, p. 126, fig. 10).

Kepplerites vardekloeftensis
The species resembles K. tenuifasciculatus in coiling, size and density of primary ribbing but the secondary ribbing is coarser and fades on the bodychamber.The two species are closely homoeomorphic but stratigraphically separated by the transients described above, which differ appreciably.Sokolov & Bodylevsky (1931, p. 79, plate 5, figs 1, 2) resembles K. tenuifasciculatus in coiling and finesse of ribbing, but is smaller: adult size 105 mm, septate to 70 mm.The ribbing (45 primaries per whorl) differs, however, on the whorl-side in that, after the initial forwards twist at the umbilical margin, it curves backwards again, the secondaries reaching the venter rectiradially.

Kepplerites svalbardensis
The species occurs in Greenland as a minor component in fauna 22, the dominant element of which is K. peramplus Spath.The latter is so distinctive, characterised by its great size (adult diameters 200 mm or more), involute and compressed inner whorls (see also Dietl & Callomon 1988, figs 4, 5), that there seems little doubt about the separate biospecific identities of the two taxa.They are not linked by intermediates and represent one of the rare cases in which the specific diversity at one horizon of an evolving generic clade rises above the monospecific.The faunal horizon can be followed from southern Hurry Inlet (types of K. peramplus) as far as the mountains Mikael Bjerg and Fossilbjerget, sections 42 and 43 (see above; Fig. 1).
Upwards, the record of Kepplerites in Greenland becomes tenuous.Occasional specimens have been found in the Nordenskjoeldi Zone, horizons 28-29, but the preservation is too poor to be able to say much of interest other than that they are still of the general appearance and size of K. traillensis or K. tenuifasciculatus.The next horizon to yield keppleritids is horizon 32.The forms at this horizon are, however, quite distinct: small, evolute and round-whorled, typical of the chronosubgenus Gowericeras that makes an abrupt appearance in much of northern Europe and thereby characterizes the Koenigi Zone.

Plate 1
Complete adults, natural size; arrows mark the position of the last septum at the onset of the adult bodychamber.Section, bed and faunal horizon as above.

Fig. 5 .Family
Fig. 5. View of Bjørnedal towards the north-west.The succession exposed on the southern flank of Lycett Bjerg is subdivided into lithostratigraphical units.1-3, indicate localities (Fig. 2).The Fossilbjerget Formation section in the centre of the photograph is 40-50 m thick.(Photo: S. Piasecki).

GFig. 1 .
Fig. 1.Sketch-map of the Jameson Land area with place names mentioned in the text.

Superfamily Stephanocerataceae Neumayr 1875 Family Kosmoceratidae Haug 1887 Genus Kepplerites Neumayr & Uhlig 1892 Kepplerites cf. tenuifasciculatus Callomon 2004
. It is difficult to trace or correlate key surfaces from Jameson Land across Kong Oscar Fjord to the Traill Ø area, in part because of the rather limited and generally poor outcrops on Traill Ø.In Jameson Land, the base of the Pelion Formation appears to be almost isochronous everywhere and of early Late Bajocian age (Cadoceras borealis Chron; Fig.3).The formation is overlain by the Fossilbjerget Formation, with a strongly diachronous boundary younging sourcewards towards the north.This reflects drowning of the marine sanddominated depositional systems of the Pelion Formation during the Middle Jurassic at maximum transgression.A sandstone wedge of the Parnas Member (Pelion Formation) is intercalated in the Fossilbjerget Forma-Chron; Fig.3).Unit C is a mainly scree-covered interval, about 60 m thick, probably consisting mostly of sandstones.Finds of Cadoceras sp. in loose blocks in the scree indicate an Early Callovian age (Cardoceras nordenskjoeldi Chron; Fig.3).The unit belongs to the 2 3 1 tion and represents the last, Early Callovian, regressive tongue of the overall backstepping Pelion Formation.The Fossilbjerget Formation is overlain by the prograding sandstones of the Olympen Formation.Systematic palaeontologySpecimens with MGUH numbers are stored at the Geological Museum, University of Copenhagen, Denmark.
Callomon 1993)bution.K. tenuifasciculatus occurs in central Jameson Land and on Traill Ø.In central Jameson Land it is found at a level above K. traillensis (faunas 24-26 ofCallomon 1993).K. traillensis is thought to correlate closely with the horizon of K. keppleri in Europe, which defines the base of the Callovian.K. tenuifasciculatus is thus of Early Callovian age (C.apertum Chron; Fig.3).

Table 1 .
Measurement of dimensions