Palaeoenvironmental significance of trace fossils from the shallow marine Lower Jurassic Neill Klinter Formation, East Greenland

Palaeogeography, Palaeoclimatology, Palaeoecology, 79 (1990): 221 248

221

Elsevier Science Publishers B.V., Amsterdam

Palaeoenvironmental significance of trace fossils from the shallow marine Lower Jurassic Neill Klinter Formation, East Greenland Gregers D a m The Geological Survey of Greenland. Ostervoldgade 10, DK-1350 Copenhagen K, Denmark

Received July 10, 1989; revised and accepted April 11, 1990)

ABSTRACT Dam, G., 1990. Palaeoenvironmental significance of trace fossils from the shallow marine Lower Jurassic Neill Klinter Formation, East Greenland. Palaeogeogr., Palaeoclimatol., Palaeoecol., 79:221 248. The shallow marine deposits of the Lower Jurassic Neill Klinter Formation of East Greenland contain a diverse assemblage of well-preserved trace fossils. Thirty-four ichnotaxa are distributed among 11 different ichnocoenoses, characterized by Diplocraterion habichi, Diplocraterion parallelum, Arenicolites isp. l,Arenicolites isp. 2, Cochlichnus, Curvolithos, Taenidium, Ophiomorpha, Rhizocorallium, Phoebichnus and Planolites. The ichnocoenoses are interpreted in the light of their trophic and ethological properties and show a strong correlation with the sedimentary environments. Their distribution reflects changes in factors controlled by water depth and bottom water oxygenation. Evidence for opportunistic recolonization following major enivironmental changes has also been preserved. The Diplocraterionparalellum ichnocoenosis occurs typically in foreshore and shoreface environments as well as tidal sandwave field environments on the inner shelf. Together with Diplocraterion habichi ichnocoenosis it also characterizes transgressive surfaces where they form omission suites. The Cochlichnus ichnocoenosis has the highest diversity and is characteristic of tidally-influenced rippled inner shelf environments. The Phoebichnus ichnocoenosis occurs in oxygen-limited shelf environments that were exploited thoroughly by a population of opportunistic organisms. The Curvolithos ichnocoenosis occurs in the distal portion of subaqueous fan delta environments and in open shelf settings and the Arenicolites isp. 2 ichnocoenoesis in the proximal portion of subaqueous fan delta environments. The Planolites, Rhizocorallium, Taenidium, Ophiomorpha and Arenicolites isp. 1 ichnocoenoses are characteristic of storm-dominated shelf environments. The ichnocoenoses of the Neill Klinter Formation are taxonomically identical, or nearly so, to the trace fossil assemblages of other marine Jurassic and Lower Cretaceous sandstones of East Greenland. They often occur in similar lithofacies, which underlines their use in palaeoenvironmental interpretations.

Introduction

The Jurassic succession of Jameson Land, East Greenland contains rich trace fossil assemblages at several stratigraphic intervals. Earlier work on the marine Jurassic trace fossils includes detailed descriptions of new and well-known ichnospecies (Heinberg, 1970, 1973, 1974; Bromley and Asgaard, 1972), as well as analyses of the relationship between lithofacies and ethologic characteristics of the trace fossil assemblages (Ffirsich and Heinberg, 1983; Heinberg and Birkelund, 1984). Heinberg and Birkelund (1984) subdivided the 0031-0182/90/$03.50

© 1990 Elsevier Science Publishers B.V.

Middle Jurassic Vardekloft Formation into a series of ichnocoenoses. They demonstrated that a relation exists among the ichnocoenoses, grain size, sedimentary structures and inferred palaeo water depth. This information was used to subdivide the Skolithos and Cruziana ichnofacies of Seilacher (1964, 1967) into six depth-controlled ichnocoenoses, which were present across the wide sandy Middle Jurassic shelf, and to make inferences concerning the depositional regime and the evolution of the basin. The ichnocoenoses were, however, not related to any specific depositional shelf environments. Ffirsich and Heinberg (1983) used

222 the combination of sedimentary facies, macrobenthos and trace fossils to reconstruct an offshore sand bar complex of the Upper Jurassic Aldinger Elv Member. The trace fossils occur in spatially distinct environmentally controlled assemblages which are very similar to those found elsewhere in the Middle Jurassic of East Greenland (Surlyk and Clemmensen, 1983; Heinberg and Birkelund, 1984). This is also the case for the trace fossil assemblages of the Neill Klinter Formation described here. However, in contrast to the study of Heinberg and Birkelund (1984) the Early Jurassic assemblages are not only related to factors controlled by water depth, but also to oxygenation at the sea bottom and to opportunistic recolonization of habitats after major environmental changes. The aim of the present paper is to describe the trace fossil assemblages, relate them to depositional environments and interprete their environmental implications. The taxonomy of the trace fossils is treated in Dam (1990).

Geological setting The shallow marine sequence of the Neill Klinter Formation ranges from the Lower Pliensbachian to the Toarcian (Rosenkrantz, 1929; Surlyk et al., 1973; Sykes, 1974). The sediments are restricted to the Jameson Land Basin, situated on the southernmost block of the Mesozoic rift basin of East Greenland and mark the first fully marine inundation since the Zechstein transgression. The Neill Klinter Formation overlies the lacustrine, deltaic and braidplain deposits of the RhaetianHettangian/Sinemurian Kap Stewart Formation and is overlain by the restricted shelf deposits of the Upper Toarcian?-Upper Bajocian? Sortehat Member (Surlyk et al., 1973; Surlyk et al., 1981; Dam, 1989). The Early Jurassic basin was limited to the west by a N - S striking major fault zone and to the east by a SSW-NNE elongated landmass largely corresponding to the present-day Liverpool Land (Fig.l). The basin was limited to the north by a cross-fault in Kong Oscars Fjord (Surlyk et al., 1981). The southern boundary is unknown, but the basin may have extended further south than Scoresby Sund. The Neill Klinter Formation is

G.DAM exposed in a belt along the edge of the basin and varies in thickness between 230 and 320 m, the thickness increasing towards the central and northern parts of the basin. The formation consists of three members, the R~evekl~ft Member (base), the Gule Horn Member and the Ostreaelv Member (top) (Surlyk et al., 1973). This subdivision also reflects the overall depositional environments represented by the formation (Fig.2).

Ichnofauna The Lower Jurassic Neill Klinter Formation includes an assemblage of diverse and wellpreserved trace fossils including 34 ichnospecies. Each ichnospecies has been, where possible, attributed to a behavioural pattern (ethology) and to a particular group of organism (Fig.3) (Dam, 1990). In this paper they are related to a spatially distinct assemblage of ichnofossils (ichnocoenosis), in order to reconstruct the original palaeobiotopes. The ichnofossil assemblages reflect a wide variety of behavioural categories including dwelling, resting, feeding, locomotion and grazing. Possible trace makers are annelids (or other worm-like organisms), ophiuroids and/or asteroids, holothurians, actinarian anemones, gastropods, bivalves, aplacophores, crustaceans and other arthropods (Fig.3). Five ethological classes are recognized in the Neill Klinter Formation.' They comprise: Domichnia: Burrows made for shelter by infaunal organisms, mostly suspension-feeders or in some cases deposit-feeders and carnivores. The burrows include Ancorichnus ancorichnus, Arenicolites isp. 1, 2 and 3, Diplocraterion habichi,

Diplocraterion parallelum, Monocraterion tentaculatum, Ophiomorpha nodosa, Palaeophycus alternatus, Palaeophycus isp., Parahaentzschelinia surlyki and Bergaueria isp. (Fig.4). Repichnia: Locomotion traces produces by organisms tunneling through or across the sediment surface. This ethological class includes Cochlichnus anguineus, Cruziana isp., Curvolithos multiplex and type 1 and 2 trackways (Fig.5). Pascichnia: Trails or burrows produced by the combination of the activities of deposit-feeding and locomotion. This category may represent

223

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION. GREENLAND

A

B SCORESBY LAND

o~ °

~..~o~°

//I

/

JAMESON LAND

-71 o

C o n s t a b l e Pynt

~,~;?/i~

I 25 km 214°

%

~ l

Neill Klinter Formation

S C O R E S B Y SUND

bysund

22 I°

Measuredsections

Fig.1. Outcrops of the Neill Klinter Formation in Jameson Land and Scoresby Land (based on G G U maps and Surlyk et al., 1973), and location of measured sections (B). Outline of the Jameson Land Basin in Pliensbachian-Toarcian time (C).

surface trails produced by animals grazing on the sea floor, or burrows produced by infaunal deposit-feeders. This ethological class includes Gyrochorte cornosa, Helminthopsis rnagna, Planolites beverleyensis, Scolicia isp. and Taenidium serpentinum (Fig.6).

Fodinichnia: Burrows made by infaunal depositfeeders systematically mining the sediment for food; these structures may also provide shelter for the organisms. The burrows include Gyrophyllites kwassicensis, Jamesonichnites heinbergi, Nereites isp., Phoebichnus trochoides, Phycodes auduni,

224

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INNER TIDAL SHELF SANDSTONE SHEETS

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Ichnocoenoses I~

Diplocrater~on Arenicolites{Type 1) Curvoldhos Cochliehnus Planoldes

Fig.2. Summarized columnar section with the position of ichnocoenoses and fossils and interpretation of the Neill Klinter Formation along the eastern margin of the basin.

PALAEOENV|RONMENTAL

SIGNIFICANCE

OF

TRACE

FOSSILS

FROM

NEILL

ICHNOSPECIES

ETHOLOGICAL CLASSIFICATION

Ancorichnus

Domichnla/Repichnia

ancorichnus

Domichnia

KLINTER

FORMATION.

225

GREENLAND

POSSIBLE ORIGINATOR

TROPHIC CLASSIFICATION

Annelid (or other worm-like organism)

Suspension-feeder

Deposit feeder

Arenicolltes

isp. i

Arenicolites

isp.

2

l)omi¢hnia

Annelid

(or

other

worm-like

organism)

Suspension

feeder

A,renlvolites

isp,

3

Dt,mlchnia

Armelid

(or

other

worm l i k e

organism)

Suspension

feeder

Cubichnia

Ophiorid

Domiehnia/Cubiehnia

A;t inarian

Repichnia/Pascichnia

Anneiid

Repi< h n i a

Arthropod?

Repichnia

Gastropod

i,~mi¢:hnla

Anne~ld

(o1

:ipl,craterion parallelum

])omic}mia

annelid

(or other

C~gro-horte co~)sa

}ast iehnid

Aplat 0phore

Ggrophgilites

~wassacensls

}'t,dinichnia

Heimnthops~s

maqna

Pascichnia

A~teriac~tes Bergaueria

L~rahrlcalis isp.

()chli(hnus d r l q u l r ~ e u s ~ruzlana

isp.

~ulvo¢itho~

multipiex

I)lpiocrateri©n

habJch2

J~onichnJt~.z

heJnbezgJ

MonocraterJon Nereltes

t~,rltac:ulatum

isp,

Ophi,~[pha

nodosa

P31aeophycus alternatus

isp.

P~ideoph~cus

P1rahaetzschellnia

surlyki

?~ldiam

~erpontinum

buspension

feeder

Suspension-feeder

DeDosil - feed('r

' Annel i,l ( el othtr

worm

[ ike ~I gan ism)

Deposit

feeder

Deposit

fe(,del

I}t,posil-feedel 5u%pells} t)l] {t'edet ] ike ulg;lnism)

Domicimia

I)eposi~

leeder

Domichn ia

?

tru~tatean

i)omichnia/Pugit:hnia

Bivalve

/

F*}dinichnia

?

Pasclthnia

annelid

(oJ- otiler w o r m - l i k e

organism)

Suspensi

'n l e e , i e [

Depo~il

~oodot

iJep~,sit

Ieedel

Deposit

feeder

Deposit

leed~,T

t)ep,,sit t~,~dL,,

Fodinichnia

Ctusta(ean/annolid

Deposit feedel

pascichllia

lie l o t h u t J a n / P o } v< h e e l e

[)opos } [ " f e ~ d e r

Pas~ it hTlia

~odinichnia

Annelid/Arthopod?

i)ept)sit

Yba,ras~Jnolde~

isp.

pt~(~ini(hllia

Thaiassinid

I)ep,~sit-teede:

Trackway,

Type

I

Repichnia

Arthropod

Carnivore

Fra<:kwav,

Type

2

gepichnia

Decapod

Carnivore

T~ichichnua

lsp.

like organism)

leed~,E

i" i l l i c h i ~ i a

,rregulare

worm

organism)

Deposit

Fodlnithnia

isp.

worm l i k e

Ihal;ls~inid

Pbycodes bromley]

Rhizocorallium

?

Carnivore other

Domiehnla

P h y c o d e s audunJ

.qZOilCia

? like organism)

Carnivore

Annel id (L~I other wolm

Fodini~hnia

isp.

other worm

Fodinichnia

(:ubithnia

Pldnc;iite~ b e v ~ r l e ~ n s i s

Carnivore

Domi(hnia

Ph,~ebichnus

vb~OSillhOn

(or

asteroid

sea anemone

Fodinichnia

pelec~ipodJchr)u~, a m g g d a l ( i d e ~ tt,c,boldes

and/or

c lUSl;lte~lll

h,ed,,r

~Glyphea r,~=enk:arltz~ )

(Crab}

Fig.3. Ethological and trophic classification and possible originator of trace fossils from the Neill Klinter Formation, East Greenland (from Dam, 1990).

Fig.4.

Diplocraterion parallelum, full relief. Domichnial burrow made for shelter by an infaunal suspension-feeder.

226

G. DAM

cypodichnus amygdaloides, and possibly Bergaueria isp. (Fig.8). Ichnocoenoses and their environmental implications Eleven ichnocoenoses are recognized in the Neill Klinter Formation. Each ichnocoenosis comprises a spatially distinct assemblage of ichnofossils and is named after one of its most distinctive members (Fig.9). Fig.5. Cruzianaisp., convexhyporelief.Repichniallocomotion trace producedby an organismtunnellingthrough or across the sediment surface.

Phycodes bromleyi, Phycosiphon isp., Rhizocorallium irregulare, Thalassinoides isp. and possibly Teichichnus isp. (Fig.7). Cub&hnia: Surface impressions in the sediment that remain after an organism has made a temporary pause at the sediment surface. The impressions include Asteriacites lumbricalis, Pele-

The Diplocraterion habichi ichnocoenosis This ichnocoenosis is monospecific only including the extremely long slender, vertical U-burrows of D. habichi formed by suspension-feeders. The ichnocoenosis is known from several stratigraphic levels of the Jurassic and Lower Cretaceous of Jameson Land (Heinberg and Birkelund, 1984; Surlyk and Noe-Nygaard, 1989) and is interpreted as indicating a relatively high-energy, aerated environment. Heinberg and Birkelund (1984) sug-

Fig.6. Taenidium serpentinum and Gyrochorte comosa, convex epireliefs. Pascichnial structures produced by the combination of deposit-feedingand locomotion.

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

227

Fig.7. Phycodes bromleyi, convex hyporelief. Fodinichnial structures made by infaunal deposit-feeder systematicallymining the sediment for food. gested that the long tubes were formed as protective shelters against unstable conditions on the sea floor, with high water agitation, but low rate of sedimentation. In the Neill Klinter Formation the D. habichi ichnocoenosis is present just underneath a transgressive surface, suggesting that it here forms an omission suite.

The Diplocraterion parallelum ichnocoenosis

Fig.8. Pelecypodichnus amygdaloides, convex hyporelief. Cubichnial surface impressions in the sediment made by bivalves.

This ichnocoenosis is dominated by different suspension-feeder dwelling burrows (domichnia), including Diplocraterion parallelum, Monocraterion tentaculatum and Rhizocorallium irregulare, and rare Gyrochorte comosa and Ophiomorpha nodosa. Similar ichnocoenoses showing a low diversity, dominated by domichnial burrows formed by suspension-feeders in deposits reflecting a high-energy environment, have commonly been observed in both modern and ancient shallow subtidal to intertidal deposits (e.g. Frey and Mayou, 1971; F/irsich, 1975; McCarthy, 1979; Howard and Frey, 1984). Representatives of this ichnocoenosis are also present just underneath the lower transgressive surface of the Ra~vekloft

228

G. DAM

isp. 1, present on top of high-vicosity flow deposits. This assemblage was probably formed by annelids or crustaceans producing permanent domiciles at distinct stratigraphic levels suggesting an opportunistic behaviour. Studies of modern and ancient opportunistic behaviour have shown that the most common opportunistic organisms colonizing marine habitats after major environmental changes are tube-dwelling suspension-feeding polychaetes, producing dwelling burrows of Skolithos ichnofacies (McCall and Tevesz, 1983; Vossler and Pemberton, 1988). The present ichnocoenosis is very similar to these burrows and suggests that major environmental changes in the bottom substrate were followed by short periods of well-aerated conditions in the bottom water with no net sedimentation and abundant food supply in suspension.

E O

E

zO: z~. TRACE FOSSILS Ancorichnus ancorichnus Arenicolites isp.

C

Arerlico]ites [sp. 2 ArenicolJtes Jsp.

A C C A R R R A CC

]

Ast~riacites lumbrlcalis Bergaueria [sp. I Cochlichnus anguineus
multiplex

Diplocraterion

habichi

Dipfocraterzon

paralielum

G y r o c h o r t e comosa G~rophylli~es

A A R

kwasslcensls

Helminthopsis magna JamesonJchnite~ helnbergi Monocraterion tentaculatum

C R C

A

]

C C CCAC R R C

C

C

Nereites isp. OphJomorpha nodosa

R

Palaeophycus a~ternatus

R C C

Paiaeophycus isp.

A R C

Pelecypodichnus amggdaloides Phoebichnus trochoides Ph~codes auduni Phgcodes bromleyi Phycosiphon isp, P]anoiites beverlegensis Rhizocorallium irregulare

Taenidium serpentinum Teichichnus isp. Thalassincides isp,

Trackway, Type 1 Trackway, Type 2

C

C

Parahaetzschelinia surlgk]

Scollcla iSp.

C R C

C

C C R C C R C A R C R A R C C R R

A R

R C

C

Fig.9. The trace fossil assemblage of the Neill Klinter Formation and its distribution within the ichnocoenoses. R = rare, C = common, A = abundant.

Member, suggesting that they form here an omission suite (cf. Seilacher, 1978; Wescott and Utgaard, 1987).

The Arenicolites isp. 1 ichnocoenosis This ichnocoenosis constitutes a monospecific trace fossil assemblage composed of Arenicolites

The Arenicolites isp. 2 ichnocoenosis This ichnocoenosis is also monospecific. Arenicolites isp. 2 differs from Arenicolites isp. 1 by lacking a burrow lining, showing a great morphologic variability and irregularity, and by having a more scattered distribution. For these reasons Arenicolites isp. 2 must have acted as shelters for only a short period of time and not as permanent domiciles. Arenicolites isp. 2 ichnocoenosis represents a low diversity assemblage of organisms that adapted itself to a well-aerated high-energy environment of great physical instability.

The Cochlichnus ichnocoenosis This ichnocoenosis contains the most diverse trace fossil assemblage of the Neill Klinter Formation, including abundant Arenicolites isp. 3 and Cochlichnus anguineus, common Ancorichnus ancorichnus, Asteriacites lumbricalis, Bergaueria isp., Jamesonichnites heinbergi, Diplocraterion parallelum, Gyrochorte comosa, Palaeophycus alternatus, Phoebichnus trochoides, Phycodes auduni, Phycodes bromleyi, Planolites beverleyensis, Taenidium serpentinum, Thalassinoides isp. and rare Arenicolites isp. 1, Cruziana isp., Curvolithos multiplex, Helminthopsis magna, Ophiomorpha nodosa, Pelecypodichnus amygdaloides, Phycosiphon isp., Rhizocorallium irregulare, Teichichnus isp. and Type 2

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION. GREENLAND

229

trackways. The ichnocoenosis reflects a wide variety of feeding habits and behavioural categories (Fig.3), indicating a well-aerated medium to low-energy shallow water environment, with abundant food supply for both suspension- and depositfeeders and mobile carnivores.

that show a high degree of bioturbation (up to 100%). The dominance of burrows of depositfeeders in isolated horizons indicates periods of low energy. Pascichnia-dominated ichnocoenoses like this occur where bottom water and the interstitial water is dysaerobic (cf. Ekdale and Mason, 1988).

The Curvolithos ichnocoenosis

The Ophiomorpha ichnocoenosis

This ichnocoenosis is dominated by Curvolithos multiplex but also includes common Thalassinoides isp., Ophiomorpha nodosa, Rhizocorallium irregulare, Gyrochorte comosa, Planolites beverleyensis, Arenicolites isp. 1, Diplocraterion parallelum and Palaeophycus isp., and rare Cruziana isp. and Taenidium serpentinum. The Curvolithos ichnocoenosis generally shows a high degree of bioturbation (up to 100%) indicating a relatively slow sedimentation and little physical reworking. The assemblage reflects a diverse fauna of infaunal and epifaunal suspension- and deposit-feeding organisms, as well as carnivores. The trophically diverse fauna occurred in a welt-aerated environment of intermediate energy where fine organic detritus could still settle out.

This ichnocoenosis consists exclusively of Ophiomorpha. Heinberg and Birkelund (1984) suggested that this ichnocoenosis indicates conditions of moderate to high sediment influx and a low rate of reworking due to the construction of such complex structures as clay-ball-lined walls. Moreover, they showed that sedimentation was periodic, causing a successive upward extension of shafts. The occurrence of Ophiomorpha alone in amalgamated sandstones indicate physically unstable (i.e. high storm frequency) conditions which favour opportunistic behaviour (Rhoads et al., 1985; Vossler and Pemberton, 1989).

The Rhizocorallium ichnocoenosis This ichnocoenosis consists primarily of Rhizoeorallium irregulare, Gyrochorte comosa, Parahaentzschelinia surlyki, Curvolithos multiplex, Nereites isp., and rare Scolicia isp., Gyrophyllites kwassicensis and trackways (Type 1). It represents the activity of both deposit-feeding organisms and carnivores. The ichnocoenosis is present in zones that represent well-aerated periods of relative lowenergy conditions. The apparent absence of suspension-feeding organisms suggests no or little organic detritus in suspension.

The Taenidium ichnocoenosis This ichnocoenosis is dominated by Taenidium serpentinum with occasional occurrence of Gyrochorte comosa and Curvolithos multiplex. The ichnocoenosis corresponds to the Muensteria ichnocoenosis of Heinberg and Birkelund (1984). The ichnocoenosis generally occurs in isolated beds

The Phoebichnus ichnocoenosis The Phoebichnus ichnocoenosis is monospecific, including only the complex burrow Phoebichnus trochoides, which occur in very large numbers in isolated horizons. This fodinichnial trace was produced by an infaunal deposit-feeder, systematically mining the sediment for food in one particular place (Bromley and Asgaard, 1972). The low monospecific occurrence of an exclusively depositfeeding organism, present in highly bioturbated beds (up to 100%), is indicative of a very quiet environment in which organic rich material was deposited (Heinberg and Birkelund, 1984). This type of stationary fodinichnial ichnocoenosis probably exemplifies an oxygen-limited environment that was exploited thoroughly by a population of opportunistic organisms (cf. Ekdale and Mason, 1988).

The Planolites ichnocoenosis This ichnocoenosis embraces common Planolites beverleyensis, Taenidium serpentinum, Gyrochorte comosa, Helminthopsis magna, rare Phycosiphon

230 isp., Phoebichnus trochoides and Gyrophyllites kwassicensis. The former 3 ichnofossils were produced by infaunal organisms combining the activity of deposit-feeding and locomotion, thus producing endostratal pascichnia burrows. Phycosiphon isp., Phoebichnus trochoides and Gyrophyllites kwassicensis are fodinichnia burrows, created by deposit-feeding organisms that systematically mined the sediment for food in one particular place. The low diversity suggests a limitation of oxygen within the sediment (cf. Ekdale and Mason, 1988). However, the dominance of pascichnia over stationary fodinichnia suggests that the interstitial environment supporting production of pascichnia must have been characterized by at least some oxygen to allow respiration. Endostratal pascichnia are normally uncommon in wellaerated sediments where most digestible organic detritus is decomposed (Ekdale and Mason, 1988), and a dysaerobic bottom environment is suggested for this ichnocoenosis. Depositionai environments and ichnocoenoses The Neill Klinter Formation consists of 7 major sedimentary environments, including; (1) shoreline, (2) inner tidal shelf, (3) storm-dominated shelf, (4) bioturbated shelf, (5) subaqueous fan delta, (6) Gilbert-type delta, and (7) omission surfaces. Shoreline environments Three shoreline environments are recognized. They are barred shoreline, wave-dominated, microtidal shoreline and wave-tide influenced shoreline environments. The R~evekl~ft Member is made up of barred shoreline deposits. It is exposed along the southeastern margin of the basin. Deposition is initiated by a transgressive pebble lag conglomerate rich in belemnites. Poorly sorted medium to very coarsegrained massive-bedded and high-angle cross-

G. DAM bedded sandstones, representing migrating foreshore ridges dominate the member (Figs.10A and 11). Body fossils are common in the sandstones and include a rich marine fauna composed of about 140 species of brachiopods, gastropods, cephalopods, bivalves, echinoderms and crinozoans (listed by Rosenkrantz, 1934). Trace fossils are only occasionally observed owing to the high energy levels that existed during deposition of the foreshore sediments. Elements of the Diplocraterion parallelum ichnocoenosis occur throughout and are dominated by long (up to 50cm) slender Diplocraterion parallelum, showing both protrusive and retrusive spreiten. The ichnocoenosis reflects a high-energy well-aerated intertidal to shallow subtidal environment. The relative long burrow of Diplocraterion parallelum and the presence of both protrusive and retrusive spreiten, indicates that the burrow acted as a protective shelter against the high energy and unstable conditions of the foreshore. Wave-dominated shoreline deposits consist of sheet-like coarsening-upward sequences, 1-6 m thick (Fig.l 2A). The lower parts are composed of sandy siltstone with starved ripples, grading upward into wave-worked ripple-laminated finegrained sandstones. Low-angle beach lamination, rootlet horizons and thin autochthonous coal seams lie on top of some of the sequences, suggesting emergence or near-emergence. The lagoonal mudstones commonly contain fish scales and plant remains. The trace fossil assemblage of the wavedominated shoreline sandstones is monospecific, including only Diplocraterion parallelum, suggesting an intertidal to shallow subtidal highenergy environment (Ffirsich, 1975). D. parallelum is restricted to specific horizons, which are highly bioturbated (up to 100%), that can be followed for several hundreds of metres, probably representing prolonged periods of non-deposition (Fig.12B). Wave-tide dominated shoreline deposits are

Fig.I0. Diplocraterionparallelum ichnocoenosisoccurringin a A. barred shorelineenvironment, B. along omissionsurfacesand C. in a tidal sandwave field environment. Dp=Diplocraterion parallelum; On=Ophiomorpha nodosa; Ri=Rhizocoralliurn irregulare; Mt = Monocraterion tentaculaturn.

231

P A L A E O E N V I R O N M E N T A L S I G N I F I C A N C E OF T R A C E FOSSILS F R O M N E I L L K L I N T E R F O R M A T I O N , G R E E N L A N D

D I P L O C R A T E R I O N PARALLELUM I C H N O C O E N O S I S ENVIRONMENTAL

INDICATIONS

High-energy, w e l l - a e r a t e d shallow subtidal or intertidal environments DEPOSlTIONAL

ENVIRONMENTS

A) Foreshore ridges B) Omission suites along transgressive surfaces C) Tidal s a n d w a v e fields

/ lc. 1.5 m

A •.~ O n

J

Transgressive surface

Delta plain deposits

I

c. 1.5 m

C

232

G. DAM

Fig.ll. Poorly sorted medium to very coarse-grained planar cross-bedded sandstone with shell fragments of the R~evekloftMember representing migrating foreshore ridges. Hammer 28 cm long.

Fig.12. A. Sheet-like coarsening-upward ,sequences reflecting small wave-influenced prograding shorelines. B. Highly bioturbated Diplocraterion parallelum horizon (arrow) within a coarsening-upward sequence. Sequence approximately 2.5 m thick.

composed of coarsening-upward sequences caused by seaward progradation of barrier islands. The sequences are up to 46 m thick and composed of wave-tide dominated shoreface, tidal inlet, washover and lagoonal deposits. The heterolithic shore-

face sandstones are wave and current ripple laminated and symmetrical, asymmetrical and interference ripple forms are frequently preserved. Occasionally, landward-directed tabular crossbedding closely interbedded with current ripple

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

r

233

upper parts include elements of the Diplocraterion parallelum ichnocoenosis. This mixed assemblage reflects an increase in energy. The wave-tide dominated shoreface deposits are overlain erosively by lateral extensive tidal channel and washover channel deposits.

Inner tidal shelf environments

i

Fig.13. Lenticular and wavy-beddingof the rippled inner tidal shelf sand sheets. Hammer 28 cm long.

lamination resembling ridge and runnel systems, and thin rip-current channel-fill sequences with seaward-directed cross-bedding are present. The lower parts of the wave-tide dominated shoreface sequences are characterized by elements of the Cochlichnus ichnocoenosis, whereas the

The inner tidal shelf deposits are composed of heterolithic facies interbedded with cross-bedded sandstones, 4-16 m thick (Figs. 13 and 14). Several features of the cross-bedded cosets suggest a subtidal environment (cf. Terwindt, 1988), including: (1) Waxing and waning currents, suggested by cross-sets showing laterally consistent series of reactivation surfaces, mud drapes and mud intraclasts along foresets; (2) Bipolar currents, suggested by bidirectional cross-bedding and cross-lamination; (3) Rapid changes in flow pattern, suggested by abrupt facies changes; (4) absence of indications of subaeric exposures. Palaeocurrent directions suggest that the cosets both represent tidal sandwave fields on the inner shelf and subtidal channel deposits. The heterolithic facies are arranged in coarsening-upward and fining-upward sequences, 1-5 m

Fig.14. Cross-bedding of the megarippled inner tidal shelf sand sheets. Each set shows abundant laterally consistent reactivation surfaces, mud drapes and mud intraclasts along foresets.

234

o. DAM

thick, occasionally bounded by a basal discontinuous lag of mudstone intraclasts and plant remains. Bedding planes show lunate current ripples and wave ripples. Internal structures of the sandstones comprise wave and current produced bidirectional ripple cross-lamination and occasionally hummocky cross-stratification and solitary sets of cross-bedding. The heterolithic facies implies a dominantly tide-influenced rippled inner shelf environment, marked by periods of current and wave activity alternating with slack tidal phases. The ichnocoenoses of the inner tidal shelf sand sheets are clearly related to energy of the bottom water. The heterolithic facies of the rippled tidal

shelf environment are characterized by the Cochlichnus ichnocoenosis, the most diverse trace fossil assemblage of the formation (Fig. 15). The ethological diversity of this ichnocoenosis indicates a well-aerated medium to low-energy shelf environment and abundant food supply for both suspension- and deposit-feeders and mobile carnivores. The tides probably supplied with large amounts of nutrient-rich water in order to sustain the rich bottom-living fauna. The rippled sandstone sheets, deposited onto the seafloor during tides, seems not to have constituted-any major danger for the organisms as the ichnocoenosis is repeated vertically through the sequences.

COCHLICHNUS ICHNOCOENOSIS ENVIRONMENTAL

INDICATIONS

Well-aerated, medium to l o w - e n e r g y shallow marine environment Abundant f o o d supplies

~Pb

DEPOSITIONAL ENVIRONMENT Rippled t i d a l l y - i n f l u e n c e d inner shelf

Pha

Subaqueous Gilbert-type fan deltas

~

:

Hm

~2 p~Q

c. 30 cm

C

Fig. 15. Cochlichnus ichnocoenosis. A a = Ancorichnus ancorichnus; A 1 = Arenicolites isp. 1; A 3 = Arenicolites isp. 3; A I = Asteriacites lumbricalis; B = Bergaueria isp.; C = Cochlichnus isp.; Cr = Cruziana isp.; C m = Curvolithos multiplex; Dp = Diplocraterion parallelum; Gc = Gyrochorte comosa; H m = Helminthopsis magna; Jh = Jamesonichnites heinbergi; On = Ophiomorpha nodosa; Paa = Palaeophycus alternatus; P a = P e l e c y p o d i c h n u s amygdaloides; P t = P h o e b i c h n u s trochoides; P h a = P h y c o d e s auduni; P h b = P h y c o d e s bromelyi; P = Phycosiphon isp.; P b = Planolites beverleyensis; R i = Rhizocorallium irregulare; Ts = Taenidium serpentinum; T = Teichichnus isp.; Th = Thalassinoides isp.; T 2 = Trackway, type 2.

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

The cross-bedded sandstone sheets and the cross-bedded parts of the heterolithic facies are dominated by abundant occurrences of Diplocraterium parallelum (Fig. 10C). Diplocraterion parallelum is restricted to thin heterolithic units separating cross-bedded sets that can be followed laterally for several hundreds of metres, limited only by the extent of the exposures. Diplocraterion parallelum associations like this are indicative of high-energy, shallow subtidal or intertidal environments (Ffirsich, 1975).

235

Proximal storm deposits are composed of amalgamated HCS and SCS sequences up to 12m thick, composed of well-sorted, micaceous, finegrained sandstones. Shell layers with a mixed fauna frequently occur along hummocky surfaces. The lack of intervening shale layers suggests that the proximal storm sandstones were deposited above fair-weather wave base (Fig. 17).

Storm-dominated shelf environments The deposits of the outer storm-dominated shelf consist of interbedded hummocky cross-stratified (HCS) micaceous sandstones and mudstones and amalgamated HCS and swaley cross-stratified (SCS) sandstones arranged in coarsening-upward sequences. Distal HCS sandstones are fine-grained and composed of thin to thick bedded (5-150 cm) parallel-sided, laterally persistent sandstone beds, often topped by symmetrical wave ripples and mudstones (Fig.16). With decreasing sand content the sandstones get thinner and consist of discontinuous patches of sandstone with incipient wave ripples. The distal storm deposits were formed on the shelf at depth below fair-weather but above storm-wave base.

Fig. 17. Hummockyand swaleycross-stratifiedproximal stormsandstones. Lens cap 55 mm in diameter.

Fig. 16. Laterally persistent distal storm-sandstonesinterbedded with homogeneousmudstones. Deposited on the shelfat depth below fair-weather but above storm-wavebase. Pen 14cm long (arrow).

236

Gravelly sheets, up to 30 cm thick, molded into symmetrical ripples, and massive beds of poorly sorted sandstones are occasionally present in the storm-influenced shelf deposits in the southeastern part of the basin. The former are associated with storm sandstones, and are best interpreted as storm-produced gravelly wave ripples (cf. Leckie, 1988). The massive beds, up to 2 m thick, are composed of poorly sorted sandstones with "floating" gravel, pebbles and boulders, belemnites, transported bivalves and occasionally ooids (Fig.18). An autochthonous fauna of encrusting oysters is attached to some boulders resting on top of the massive beds. The poor sorting of the sediment and the presence of "floating" clasts suggests that the beds were deposited from highviscosity flows (cf. Lowe, 1982). The storm-dominated shelf deposits contain 5 distinct ichnocoenoses. Two ichnocoenoses, Arenicolites isp. 1 and Ophiomorpha, is monospecific comprising only suspension-feeding burrows, while Planolites, Rhizocorallium and Taenidium ichnocoenoses consist predominantly of traces of deposit-feeders. The Planolites ichnocoenosis is characteristic of the distal storm-dominated shelf deposits, and possibly it represents an equilibrium ~chnocoenosis of infaunal deposit-feeders indicating a dysaerobic sedimentary environment (Fig. 19). The occurrence of fodinichnia burrows (Phoebichnus trochoides

G. DAM

and Gyrophylites kwassicensis), indicating a dysaerobic environment within the sediment, may be a response to storm burial of organic matter which could create local anoxic conditions. Rhizocorallium and Taenidium ichnocoenoses occur in sandy fair-weather deposits in between the storm sandstones (Figs.19 and 20). They show a repeated presence within successive fair-weather deposits. The frequent presence of fugichnia in the storm deposits indicate a rather robust fauna that were able to escape from the blanket sediments (i.e. burrow up through it) and re-establish itself quickly. The Ophiomorpha ichnocoenosis is present throughout the amalgamated HCS sandstones (Fig.21). This ichnocoenosis reflects a well-aerated, but physically unstable (i.e. high storm frequency) environment which has favoured opportunistic behaviour. The high-viscosity flow deposits, interbedded with distal storm-dominated shelf deposits, represent major environmental changes in substrate conditions on the shelf. The bottom was recolonized by high densities of opportunistic tubedwelling suspension-feeders (Arenicolites isp. 1 ichnocoenosis) (Fig.22). Unlike deposit-feeders, suspension-feeders are not encountered frequently in low-oxygen environments (Ekdale and Mason, 1988) and the presence of the Arenicolites isp. 1

Fig.18. Submarine high-viscosity flow deposits present within storm-generated heterolithic beds. The deposits are composed of massive, poorly sorted beds that can be followed laterally for several kilometres. Hammer 28 cm long.

PALAEOENVIRONMENTAL

237

SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

PLANOLITES AND TAENIDIUM ICHNOCOENOSES ENVIRONMENTAL INDICATIONS Periods of low-energy O x y g e n - l i m i t e d environment Gc

DEPOSlTIONAL ENVIRONMENT

~./ ,/ ,' / / / / ,,' ;/! / 3' ,'

f

S t o r m - d o m i n a t e d inner shelf environment, at depth below f a i r - w e a t h e r but above s t o r m - w a v e base

~ --

c. 30 cm

't I: I I

;.

/, ¸ /

l

/ jr ,

,

,

-

Pt

Fig. 19. Planolites and Taenidium ichnocoenoses. Gc = Gyrochorte comosa: G k = G yrophyllites kwassicensis; H m = Helminthopsls magna; Pb = Planolites beverleyensis; Ph = Phycosiphon isp.; P t = Phoebichnus trochoides; Ts = Taenidium serpentinum.

ichnocoenosis and encrusting oysters therefore suggest limited periods with aerated bottom conditions and abundant food supply in suspension on the shelf. This association of predominantly suspension and deposit-feeding ichnocoenoses in storm deposits has commonly been observed in the geological record. It is generally agreed that the suspension-feeding trace fossil represent the activities of opportunistic organisms recolonizing the substrate following storm disruption (e.g. Pemberton and Frey, 1984; Claussen and Vilhjalmsson, 1986; Vossler and Pemberton, 1988, 1989). These observations are also valid in the Neill Klinter Formation, in as much as Arenicolites isp 1 occur

in the probable storm-induced high-viscosity flow deposits and Ophiomorpha ichnocoenosis throughout the HCS sandstones. Bioturbated open shelf environments

The bioturbated shelf sandstones are composed of heavily bioturbated (95-100%), poorly sorted muddy fine to medium-grained sandstones. Phosphatic concretions and body fossils are common accessories. The muddy sandstones can be followed throughout the basin and probably represent a bioturbated open shelf environment. The open shelf deposits is characterized by the Curvolithos and Phoebichnus ichnocoenoses. Both ichno-

G. DAM

238

RHIZOCORALLIUM

ICHNOCOENOSIS

ENVIRONMENTAL INDICATIONS Well-aerated environment characterized by short periods of relatively low energy Little or no organic detritus in suspension DEPOSITIONAL ENVIRONMENT Storm-dominated inner shelf

1 t c. 30 cm

Fig.20.

Rhizocorallium ichnocoenosis. C m = Curvolithos multiplex; Gc = Gyrochorte comosa; G k = Gyrophyllites kwassicensis; N = Nereites isp.; Ps = Parahaentzschelinia surlyki; R i = Rhizocorallium irregulare; S = Scolicia isp.; T1 = Trackway, type 1.

coenoses indicate slow sedimentation, little physical reworking and abundant food supplies (Figs.23 and 24). However, the Curvolithos ichnocoenosis is indicative of a well-aerated shelf environment, whereas the Phoebichnus ichnocoenosis suggests an oxygen-limited environment.

Subaqueous fan delta environments The fan delta deposits consist of wedges of wellsorted medium to coarse-grained, occasionally glauconitic, cross-bedded sandstones, representing the subaqueous portion of westward prograding fan deltas. Each sequence is up to 40 m thick and is bounded by a basal lag conglomerate composed of reworked phosphatic concretions, body fossils and extraclasts (Fig.25). Distally the sets thin and the

sandstones are often wave- and storm-reworked or bioturbated (up to 100%). The proximal fan delta sandstones are characterized by the Arenicolites isp. 2 ichnocoenosis that indicates a high-energy well-aerated environment, large net sedimentation rate and great physical instability (Fig.26). The bioturbated distal delta sandstones is characterized by the Curvolithos ichnocoenosis, indicating a well-aerated environment with slow sedimentation, little physical reworking and abundant food supplies.

Gilbert-type delta environment The heterolithic Gilbert-type delta deposits are composed of giant-scale, low-angle cross-bedding with a thickness up to 18m. Cross-strata are

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINT|:.R FORMATION, GREENLAND

239

OPHIOMORPHA ICHNOCOENOSIS ENVIRONMENTAL INDICATIONS Moderate to high sediment influx Periodic sedimentation Physically unstable conditions DEPOSITIONAL ENVIRONMENT Amalgamated storm-sandstones

50200 cm

Fig.21. Ophiomorpha ichnocoenosis. On = Ophiomorpha nodosa.

dipping less than 5° (Fig.27). Along foresets, mudstone layers alternate with intrasets of crossbedded sandstones with muddrapes and mudflake clasts. They are produced by tidal megaripples migrating down the foresets of the delta. Mudstone layers represent still-stand phases of the tides. Trace fossils only occur in small numbers along bottomsets of the deltas and include elements of the Cochlichnus ichnocoenosis, suggesting a shal-

low shelf environment subject to well-aerated, medium to low-energy conditions and abundant food supply.

Omission surfaces At Constable Pynt the delta plain deposits of the Kap Stewart Formation are very heavily burrowed by Diplocraterion parallelum just below the trans-

240

G. DAM

ARENICOLITES ENVIRONMENTAL

ISP. 1

ICHNOCOENOSIS

INDICATIONS

Short periods of w e l l - a e r a t e d conditions in the bottom w a t e r No net sedimentation Abundant food supplies DEPOSITIONAL

ENVIRONMENT

H i g h - v i s c o s i t y s e d i m e n t - g r a v i t y flows deposited at depth below f a i r - w e a t h e r but above s t o r m - w a v e base

c. l m

Fig.22. Arenicolites isp. 1 ichnocoenosis.A1 = Areicolites isp. 1. gressive lag conglomerate of the Ra~vekleft Member. This assemblage make up an omission suite formed during and possibly after the early Pliensbachian transgression and is characteristic of many transgressive surfaces (Seilacher, 1978; Wescott and Utgaard, 1987) (Fig.10B). Preservation of this suite suggests a minimal scouring and reworking of the delta plain deposits of the Kap Stewart Formation during the Early Pliensbachian transgression. A thin transgressive pebble conglomerate is occasionally present at the boundary between the subaqueous delta sandstones of the Ostreaelv Member and the overlying bioturbated shelf

sandstones or the restricted shelf deposits of the Sortehat Member. West of Carlsberg Fjord the top of the delta sandstones are very heavily burrowed by Diplocraterion habichi just below the pebble conglomerate (Fig.28). The long tubes of D. habichi suggests that the burrow acted as a protective shelter against high energy and unstable conditions. This assemblage probably also makes up an omission suite.

Regional implications Previous studies on the Jurassic to Lower Cretaceous marine sandstone of East Greenland

241

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

CURVOLITHOS ENVIRONMENTAL

ICHNOCOENSIS INDICATIONS

Well-aerated, low to intermediateenergy environment Relatively slow sedimentation Abundant food supplies DEPOSITIONAL ENVIRONMENT Bioturbated shelf Distal portion of subaqueous fan deltas

2 = '

¸ ,)c. 25 cm

Ts

A1

% P

l

v

r Pb

Fig.23. Curvolithos ichnocoenosis. A I = A renicolites isp., type I; Cr = Cruziana isp.; Cm = Curvolithos multiplex; Dp= Diplocraterion parallelum; Gc = Gyrochorte comosa; On = Ophiomorpha nodosa; P = Palaeophycus isp.; Pb = Planolites beverleyensis; Ri = Rhizocorallium irregulare; Ts = Taenidium serpentinum; Th = Thalassinoides isp. Host rock is 100% bioturbated. document trace fossils from the Middle Jurassic Vardekloft Formation (Birkelund and Heinberg, 1975; Heinberg and Birkelund, 1984) and the Upper Jurassic to Lower Cretaceous Raukelv of Jameson Land (Surlyk and Noe-Nygaard, 1989, in press), the Middle to Upper Jurassic Vardekloft Formation of Wollaston Forland, Kuhn O and Hochstetter Forland (Surlyk and Clemmensen, 1983), and the Middle Jurassic to Lower Cretaceous Chargot Bugt, Kap Leslie and Hartzt]eld Formations of Milne Land (H~kansson et al., 1971; Heinberg, 1973).

Thirteen trace fossils were recognized in the Vardekloft Formation distributed among six ichnocoenoses by Heinberg and Birkelund (1984). The ichnocoenoses are nearly identical to and occur in similar environments as in the Neill Klinter Formation and include the D i p l o c r a t e r i o n habichi,

Ophiomorpha,

Curvolithos,

Taenidium

[ M u e n s t e r i a of Birkelund and Heinberg (1984)] and R h i z o c o r a l l i u m ichnocoenoses. Heinberg and Birkelund (1984, fig.27) compared the Vardekloft Formation ichnocoenoses with Recent onshoreoffshore transects. The P h o e b i c h n u s , R h i z o c o r a l -

242

G. DAM

PHOEBICHNUS ICHNOCOENOSIS PALAEOENVIRONMENTAL INDICATIONS Oxygen-limited, low-energy environment with abundant food supplies Slow sedimentation Little physical reworking DEPOSITIONAL ENVIRONMENT Bioturbated shelf

-/.L/(.i c. l O c m

Fig.24.

Phoebichnus

ichnocoenosis.

P t = Phoebichnus trochoides.

Fig.25. Cross-bedded sandstones belonging to the proximal subaqueous fan delta deposits succeeding bioturbated shelf deposits. Person in lower righthand comer for scale (circle).

lium, Curvolithos and Taenidium ichnocoenoses generally occur in bioturbated (up to 100%) very fine to fine-grained sandstones. Heinberg and Birkelund interpreted the sediments as deposited in

Hostrock is 100% bioturbated.

a lower offshore environment. The Curvolithos ichnocoenosis is also characteristic of bioturbated (up to 100%) medium to very coarse-grained sandstones associated with thick (up to 50 m) generally cross-bedded sandstones similar to the distal subaqueous fan delta deposits of the Neill Klinter Formation. Heinberg and Birkelund (1984) interpreted the sediments as upper shoreface deposits. The dominantly cross-bedded medium-to coarse-grained sandstones, characterized by the Ophiomorpha ichnocoenosis, where also interpreted as shoreface deposits formed under strong wave action. Apart from the cross-bedded sandstones the Ophiomorpha ichnocoenosis also occur in what Heinberg and Birkelund (1984) describe as low-angle cross-bedded units which appear cyclically in between fine-grained loose sand below and bioturbated sandstone above. These beds could very well be hummocky cross-stratified storm

243

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

A R E N I C O L I T E S ISP. 2 I C H N O C O E N O S I S ENVIRONMENTAL INDICATIONS Well aerated environment characterized by continuously high energy Large net sedimentation DEPOSITIONAL ENVIRONMENT Proximal portion of

c. 5 m

Fig.26. Arenicolitesisp. 2 ichnocoenosis. A2 = Arenicolitesisp. 2.

sandstones interbedded with fair-weather deposits. The Diplocraterion habichi ichnocoenosis occur in medium to coarse-grained sandstones interpreted as deposited on the lower offshore. However, in the Vardekleft Formation this ichnocoenosis is also characteristic of glauconized omission surfaces, rich in ammonites, that formed by shoreface ravinement during transgressions (F. Surlyk, pers. comm., 1989). In its northern extent, in the Wollaston Forland area, the Pelion Member is dominantly composed of large and giant-scale cross-bedded, structure-

less, horizontally laminated, cross-laminated sandstones and sandstones rich in ostreid bivalves. The sediments are arranged in coarsening-upward sequences, 10-20 m thick, and were deposited in a shallow tidal-influenced sandy embayment (Surlyk and Clemmensen, 1983). The trace fossil assemblage consists of Teichichnus, Planolites, Diplocraterion, Monocraterion, Pelecypodichnus and Curvolithos, including elements of both the Diplocraterion and Cochlichnus ichnocoenoses of the Neill Klinter Formation. The Upper Jurassic Jakobstigen Member of the

244

G.DAM

Fig.27. HeterolithicGilbert-typedelta complex composed of two smaller and one larger coarsening-upwardsequence. The larger sequence is madeup of giant-scale, low-anglecross-bedding,with cross-strata dipping less than 5°. Alongforesets,mudstonelayers alternate withintrasetsof cross-beddedsandstoneswith muddrapesand mudflakeclasts. Personin upper righthandcorner for scale.

Wollaston Forland area is dominantly composed of heterolithic sediments, including; rhythmites, lenticular and flaser laminated sandstone, structureless and ripple cross-laminated sandstone, arranged in small coarsening-upward sequences. The sediments were deposited on the inner shelf dominantly under the influence of wave activity, however, with some indications of tidal activity (Surlyk and Clemmensen, 1983). The trace fossil assemblage consists of Gyrochorte, Diplocraterion, Monocraterion, Taenidium, Rhizocorallium and Chondrites, including elements of the ichnocoenoses occuring in the storm-dominated deposits of the Neill Klinter Formation. The mudstones are only characterized by Chondrites (Surlyk and Clemmensen, 1983). The ichnofauna of the shallow marine offshore sand bar complex of the Upper Jurassic Aldinger Elv Member of Milne Land was described and discussed by Fiirsich and Heinberg (1984). Eleven different ichnospecies are present in the sand bar complex, distributed among 4 ichnocoenoses. They are the Curvolithos, Anchorichnus/Taenidium, Planolites, and Thalassinoides ichnocoenoses. The Curvolithos ichnocoenosis represents the ocean slope of the sand bar, at depth and wave conditions characteristic of the upper offshore zone. The

Ancorichnus/Taenidium ichnocoenosis occur in lower offshore facies and the Planolites ichnocoenosis in a somewhat more exposed position of the sand bar complex. The Thalassinoides ichnocoensis is monospecific, indicate a quiet environment with only little reworking and represents the lowest energy levels of the four ichnocoenosis present in the Aldinger Elv Member. The late Jurassic-early Cretaceous Raukelv Formation of Jameson Land consists of sheets of giant-scale cross-bedded sandstones of linear sand bank origin and large-scale sandstones also of sheet geometry representing fields of migrating sandwaves. The sandbanks and sandwave fields were probably formed in relatively deep water. The sandstone sheets are capped by glauconitized, pebbly omission surfaces burrowed by Diplocraterion habichi, reflecting extended periods of non-deposition, similar to the omission surfaces occurring in the Neill Klinter and Vardekleft Formations. From the above summary of previous studies it is clear that the trace fossil assemblage of the Neill Klinter Formation constitute the most diverse assemblage present and includes all ichnotaxa, or nearly so, previously documented from the Jurassic to Lower Cretaceous marine sandstones of East

245

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

DIPLOCRATERION

HABICHI ICHNOCOENOSIS

ENVIRONMENTAL INDICATIONS High-energy well-aereated environments DEPOSITIONAL ENVIRONMENTS Omission suites along transgressive

C.

1.5 m

Fig.28. Diplocraterion habichi ichnocoenosis. Dh = Diplocraterion habichi.

Greenland. Moreover, it shows that the ichnocoenoses are characteristic of specific depositional environments within this succession. Only two ichnocoenoses described so far from the Jurassic and Lower Cretaceous of East Greenland are not present in the Neill Klinter Formation. They are the Thalassinoides and the Chondrites ichnocoenoses. They are both monospecific and created by organisms that systematically mined the sediment for food in one particular place and exemplifies an oxygen-limited environment that was exploited thoroughly by a population of opportunistic animals (Bromley and Ekdale, 1984; Ekdale and Mason, 1988). The Chondrites ichnocoenosis occurs in the mudstones of the Jakobstigen Member of Wollaston Forland (Surlyk and Clemmensen, 1983) and in the Olympen Forma-

tion of Jameson Land (Birkelund and Heinberg, 1975). The Thallasinoides ichnocoenosis occurs in interbedded sandstones and mudstones at the lower transitional boundary between the sandstones of Aldinger Elv Member and the underlying Kosmocerasdal mudstone (Ffirsich and Heinberg, 1983). It also occurs in a similar setting in the transition strata between the sandstones of the Pelion Member and the mudstones of the overlying Fossilbjerget Member where it is part of the Phoebichnus ichnocoenosis (Birkelund and Heinberg, 1975; Heinberg and Birkelund, 1984). Conclusions

The Neill Klinter trace fossils constitute a most diverse assemblage and includes all ichnotaxa, or

246 nearly so, previously documented from the Jurassic and Lower Cretaceous marine sandstones of East Greenland. Eleven ichnocoenoses are recognized, characterized by Diplocraterion habichi, Diplocraterion parallelum, Arenicolites isp. 1, Arenicolites isp. 2, Cochlichnus, Curvolithos, Rhizocoralliurn, Taenidium, Ophiomorpha, Phoebichnus, and Pianolites. Analyses of the trophic and ethological characteristics of the ichnocoeses is valuable in the detailed facies reconstruction of the depositional environments of the Neill Klinter Formation. The ichnocoenoses indicate that the fauna was influenced by factors controlled by water depth and water oxygenation. Evidence for opportunistic recolonisation has also been preserved in the Neill Klinter Formation. Shoreface, foreshore as well as sandwave fields on the inner shelf, i.e. well-aerated high-energy shallow subtidal to intertidal environments, is characterized by the Diplocraterion parallelum ichnocoenosis. Heterolithic rippled inner shelf deposits is characterized by the Cochlichnus ichnocoenosis. This ichnocoenosis is reflecting a high diversity and a wide variety of feeding and behavioural categories and indicates a well-aerated, overall low-energy environment with high concentrations of both detrital and suspended food. Storm-dominated shelf deposits contain 5 distinct ichnocoenoses. Two ichnocoenoses, Arenicolites isp. 1 and Ophiomorpha, is monospecific and represent the activities of opportunistic organisms recolonizing the substrate following major storm disruption. The Planolites, Rhizocorallium, and Taenidium ichnocoenoses were predominantly formed by deposit-feeders and generally occur in fair-weather deposits in between storm sandstones. The Phoebichnus ichnocoenosis is monospecific only including the complex fodinichnial burrow system of Phoebichnus trochoides. This ichnocoenosis exemplifies a oxygen-limited shelf environment that was exploited thoroughly by a population of opportunistic organisms. Subaqueous fan delta deposits contain two ichnocoenoses. Arenicolites isp. 2 ichnocoenosis occurs in the proximal cross-bedded portion of the deltas and indicate a well-aerated high-energy environment characterized by great physical instability. Distal subaqueous delta deposits is charac-

G.DAM terized by the Curvolithos ichnocoenosis that indicate a well-aerated environment of low to medium energy. This ichnocoenosis is also characteristic of aerated open shelf environments. Pebbly omission surfaces, formed by either transgressive shoreface erosion or extended periods of non-deposition, is characterized by the Diplocraterion habichi and Diplocraterion parallelum ichnocoenoses. The ichnocoenoses occur in similar sedimentary environments throughout the Jurassic and Lower Cretaceous of East Greenland. Only two ichnocoenoses of the Jurassic-lowermost Cretaceous of East Greenland do not occur in the Neill Klinter Formation. They are the Thallasinoides and Chondrites ichnocoenoses and exemplifies oxygen-limited environments that were exploited thoroughly by a population of opportunistic organisms. The repetition of and the close association between ichnocoenoses and specific depositional environments underlines their palaeoenvironmental significance. The Jurassic and Lower Cretaceous formations of East Greenland have many features in common with equivalent formations in other North Atlantic basins. The presence of spatially distinct trace fossil assemblages, throughout the Jurassic and Lower Cretaceous of East Greenland, suggests that the combination of diagnostic ichnocoenoses, facies and comparative studies may be a helpful tool in palaeoenvironmental interpretations of North Atlantic core material of the same age.

Acknowledgements The paper is part of a Ph.D.-project supervised by Finn Surlyk and financed by British Petroleum Development, London. I am indebted to Finn Surlyk, Richard Bromley, Claus Heinberg and two anonymous referees for numerous discussions and constructive reviews of the manuscript. Thanks are also due to Jacob Lautrup, Bodil Sikker Hansen, Jette Halskov and Vibber Hermansen for technical assistance and Jan Audun Rasmussen, Anders Boesen and Mads Willumsen for good company in the field. The paper is published with the approval of the Geological Survey of Greenland.

PALAEOENVIRONMENTAL SIGNIFICANCE OF TRACE FOSSILS FROM NEILL KLINTER FORMATION, GREENLAND

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