the precambrian turbidite-tempestite transition as displayed by the amphibolite-facies...

Sedimenta(v Geology, 58 (1988) 195 216 195 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

The Precambrian turbidite-tempestite transition as displayed by the amphibolite-facies Puolankajarvi Formation, Finland

K . L A A J O K I a n d E. K O R K I A K O S K I *

Department of GeoloKv, University of Oulu, Linnanmaa, 90570 Oulu (Finland)

Received May 18, 1987: revised version accepted Janua~ 11, 1988

Abstract

Laajoki, K. and Korkiakoski, E., 1988. The Precambrian turbidite tempestite transition as displayed by the amphibolite-facies Puolankaj~irvi Formation, Finland. In: M.J. Jackson (Editor), Aspects of Prolerozoic Sedimentary Geology. Sediment. Geol., 58: 195-216.

The Puolankaj~irvi Formation (PjF) forms the lowermost unit of the progradational Central Puolanka Group. It is at least 2200 Ma old metamorphosed to amphibolite facies, displays polyphase deformation, and is commonly near vertical or overturned. The PjF is about 1500-2000 m thick and 30 km in strike length but grades into gneisses both below and at its northern extension. Thus, the original sediments could have been much thicker and perhaps hundreds of kilometres long in strike length.

The lower part of the PjF consists of graded-bedded mica schists and associated massive or graded arkosites, at least 500-1000 m thick, which represent metamorphosed turbidites deposited by low-concentration and high-concentration turbidite currents, respectively. The turbiditic unit is overlain and partly interfingers with semipelitic mica schists containing combined-flow-origin hummocky cross-stratification and related structures indicating that these rocks, about 100-200 m thick, were originally fine sands and silty muds deposited by storm waves and other shelf processes.

Large-scale cross-bedded quartzite interbeds at the top of the PjF indicate a progradational change into the overlying Akanvaara Formation of shallower-water origin.

The PjF shows a change of relatively thin-bedded turbidites to tempestites which is interpreted as representing either the distal and middle parts of a relatively steep shelf or the upper slope and the distal-middle part of a narrow shelf.

Introduction

S e d i m e n t o l o g i c a l s t u d i e s of P r e c a m b r i a n sedi -

m e n t a r y r o c k s h a v e i n c r e a s e d e n o r m o u s l y o v e r t he

p a s t few y e a r s a n d m a n y d e t a i l e d a n d c o m p r e h e n -

s ive p a p e r s c o n c e r n i n g t he l i t h o l o g y a n d sed i -

m e n t o l o g y o f a n c i e n t s e d i m e n t a r y r o c k s f r o m the

P r e c a m b r i a n s h i e l d a r e a s a re n o w a v a i l a b l e .

A m o n g t h o s e r o c k s s t u d i e d in m o s t d e t a i l a re t he

* Present address: Geological Survey of Finland, P.O. Box 77, 96101 Rovaniemi, Finland.

0037-0738/88/$03.50 © 1988 Elsevier Science Publishers B.V.

l i t t l e d e f o r m e d or m e t a m o r p h o s e d p l a t f o r m a l a n d

e p i / p e r i c o n t i n e n t a l c o v e r r o c k s o f t he C a n a d i a n

S h i e l d a n d t he K a a p v a a l c r a t o n . T h i s p a p e r re-

p o r t s a n a t t e m p t a t a s i m i l a r d e t a i l e d s e d i m e n t o -

log ica l s t u d y o f a m o r e m e t a m o r p h o s e d a n d de-

f o r m e d s e q u e n c e .

T h e Puo lanka j~ i rv i F o r m a t i o n ( h e r e a f t e r P j F ) is

a p s a m m i t i c - s e m i p e l i t i c - p e l i t i c u n i t m e t a m o r -

p h o s e d to u p p e r a m p h i b o l i t e g r a d e a n d c o m p l e x l y

d e f o r m e d ; i t n o w c o n s i s t s o f m e t a p e l i t e s

a n d m e t a p s a m m i t e s f o l d e d to a n e a r ve r t i c a l pos i -

t ion . D e s p i t e t h e u b i q u i t o u s p o r p h y r o b l a s t s of

s t a u r o l i t e , g a r n e t , a n d a l u s i t e , b io t i t e , etc., in the

196

metapelites, the pervasive schistosities and the complicated refolding many outcrops still show enough primary sedimentary features for a conventional facies analysis to be applied. The main problem encountered is the uneven distribution and relatively small size of the outcrops which

hinder the measurements of continuous stratigraphic sections and lateral tracing of stratigraphic units.

Despite these drawbacks and shortcomings, we can confidently outline the sedimentology of the PjF. The most interesting result is that the lowermost turbiditic metasediments of the PjF, which are of deep-water origin, are abruptly prograded by rocks showing evidence of storm activity. This work has significantly increased our regional un- derstanding of the Puolanka area; so much so that we feel systematic sedimentological studies should routinely accompany Precambrian stratigraphic

and tectonic work.

Terminology

All the rocks studied are metamorphic and therefore standard metamorphic rock names are applied when describing their present lithologies. However, in the sedimentological part of this study the terms sand, mud and silt are used to refer to what are thought to have been the original sediments. Due to the pervasive recrystattization and neomineralization, the psammitic rocks are granoblastic and the pelitic rocks lebidogranoblas- tic and so, it is not possible to determine the original grain sizes. However, original grain size has been estimated from the sizes of quartz and plagioclase. The grain-size scale of Wentworth (1922) is used for all except clay because all clay minerals have been neomineralized to micas, whose sizes are much greater than the original ones. Mud is used to refer to those mica-rich parts of a rock thought to have originally contained both clay and silt in about equal amounts.

The term facies is used descriptively to refer to a sedimentary rock body which can be dis- tinguished from its surroundings by grain size, primary structures and other distinctive features (cf. Selley, 1982, p. 264; Pickering et al., 1986, p. 79; Reading, 1986, p. 4). Those facies which are

closely associated with each other are grouped into a facies association. In this usage a facies/subfacies and facies association reflect, a particular process and environment or sub-environment, respectively (cf. Walker, 1979; Read- ing, 1986). Bed thickness definitions follow In- gram (1954) and turbidite terminology follows Bouma (1962).

Lithostratigraphic and lithodemic terms are used as defined by the North American Commis- sion on Stratigraphic Nomenclature (1983) except that the term bed is used both for an individual stratum representing a single sedimentation event and a lithostratigraphic unit smaller than a member, as well as for the smallest lithodemic metasedimentary unit which can be delineated from its surroundings.

Stratigraphy and lithological distribution

The PjF forms the lowermost formation of the r eg ress ive /p rograda t iona l Central Puolanka Group (CPG) described recently by Laajoki (1986a). This group outcrops on the western margin of the early Proterozoic Kainuu Schist Belt where it underlies the quartzites of the Jatuti tectofacies (Fig. 1). The basement to the group is not exposed, but the PjF grades metamorphically into the gneisses mapped as a lithodemic unit called the Kettukangas Paragneiss (KP) (Figs. 2 and 3). The upper contact of the PjF is gradational into the Akanvaara Formation (AvF) which is a cross-bedded metapsammite unit (see Laaj0ki. 1986a).

The KP, which occupies the area west of the PjF, represents the more metamorphosed lower part of the PjF. This lithodemic KP unit consists of thin to medium-thick banded feldspar gneisses with less frequent mica schist beds. Depending on the grade of metamorphism and intensity of deformation, the KP rocks may show typical gneissic structures without any distinctive sedimentary structures (Fig. 4). The original stratigraphic thickness of the KP cannot be measured accu- rately, but the sparse outcrop information in- tegrated with structural interpretations suggest that it may have been at least 1000 m.

197

725C

6~ O0

~ 3 ~ 3 - - - - 722(

-¢

LEGEND:

I

Faults:

27 ° 30' 28 ° 30'

I • Serpentinite etc. Ristij~irvi Granodiorite (1850 Ma)

JATULI & KALEVA TECTOFACIES

Parekangas Fm.(P k F)!I ] 0 ~ KAINUU GROUP

Ak . . . . . . . l Puolankaj~lrvi Fm.(PjF ~ <~

~ z ~ KURKIKYLX GROUP ~//~._~ Kettukangas Pgn.(KP~l

WEST-PUOLANKA I :~ I O. ~ ARCHAEAN BASEMENT PARAGNEISS

• .~ Top of Strata

- - - -@ @ Pudasjilrvi @ V~yryltinkyl~i - Per~korpinen

,i

--!13(3

Fig. 1. Simplified geological map of the northern end of the Kainuun Schist Belt. The inset shows the location of the map area. The

area of Fig. 2 is framed.

198

L...J

SW-PG

SW POE

_ / ,

/

-.'. ,~ /

.'.'V , ~: - / "2 Y .'::,~1~ , ,? , / Av ; "-

) ~ I~(C' /I \ :

~%~, Z . . . . @ - ; /

L~ ~.~:¢~ /

SW - PGC

S W - P G C

/ /

/ SW-PGC

/ / / /

/ / /

/ • / ".'.'KETTU- ',

/ . : ' . .~ ~A NGAS

/ /

KP

L~Lh" SW- PGC

,~( . ,~KETTU KAL L 0

,//~K~¢I / :

/

/ / / Pj F

., 'f

f

3: I/ , , , .

I &vF / C:

-- /

IZ

• . z ~ - d ~ - ~ I - 7, SO ' I / :: ;: /- ~ ' ~ - / ~ I '~ l

: * : / / h F us~A s~.~: • , ,, ,' ,, 1 / / / = ~ / '

, , >z / . , / l

, < /+ ~ZZ~p'TI--' / \

/ ~EKKOK,~ PJ ~

c ~ :': I / ,/ . . . . . . . . . . . . . . . . . . . . . . . .

S I M P L I F I E D G E O L O G I C A L M A P

O F C E N T R A L S O U T H E R N P U O L A N K A

Strat igraphy and primary sedimentary facies,

Pelrekangas Formation (not indicated)

- I~4) - - ( 4 ~) . . . . . (~ )~ -Sed . . . . . tary contact

t~kanvaara FormatJon (AvF)

I _. Cross-bedded arkoslte I L ~ and feldspar guartzite

Sediment ary contact - - @ . . . . 3 . . . . @ - ( p a r t l y t ec ton i zed )

Puolankaj~lrw Formation (PIF)

Mica-schist w~th cross-bedded feldspar guartzite interbeds (Facies 4)

Cross-bedded or r ipp le-bedded metasemipelite (Facies 3)

Graded bedded mica schist mostly ataurol i te-bearing (Facies 2)

SillJmanJt e- gar net -mica schist (Facies 2?) /Fac ies 2 rock w i th Facies t in te rbeds

--'2~&- - :12 "= " ( ~ - - Sed imentary -meta morphic contact

Kettukangas Paragneiss K P

Graded or massive arkos~te (Facies 1)

Tectona- - - . : ~ = ~ 1 - : 1 - - metamorphic contact ,

S o u t h - w e s t e r n Paragneiss Complex (SW-PGC)

Feldspar *- mica-rmh gneisses (mostly paragneisses)

[ _ ~ Ket tukal l io- type guartzl tegnelsses (Higher-grade metamorphic, der ivat ives of (AvF)

Intrusive rocks:

Serpentinite and metagabbf a

- - q ~ ~ j Pegmatite granite and granite

Note Beds in KP PjF and AvF are mostly

vert ical or sl ight ly overturned to the east and face to the east. In SW-PGC

the rocks are folded and mlgmatlzed in a complicated way

Base map:

Reduc t ion of the Bas=c Map 1 200QO of Fmland~

Maanmi t tausha lh tus

Scale 3 6 i . . . . . . . . . . . . . . . . . . ~ km

i . . . . . . . . . . . . . . . . . . .

Fig. 2. Simplified geological map of the central southern Puolanka area showing the distribution of the PjF rocks and their stratigraphic relationships. Only the areas with sufficiently extensive outcrops to be invesugated with confidence arc indicated by lithological symbols.

199

J A T U L , T E C T O F A C I E S

I / / ~ ~ / / / P ~ r e k a n g a s / / , " Forma on / ~ - I

°='T ~ t - " "" " . . . . "" ~ ] . . . . " , " ~ . ". A k a n v a a r a Format on - . , "~

" 8 ~ iz . . . . . ~ -- - mm ' m l l .. - - ~ ~ "

~ ' / ~ ~ r ~ . F 3 4 ~ " m I ..... I /

kl. f i [ ' . / f ~ Fac,es 3 ~ Fac ies a s s o c i a t i o n A ~ q .x~ ~-~ ~.! ~ ~ v~,, 2 ~ • ~ . \ . . . . ~,~ °~ ~ "~

• \

C O n t a c t ' - - - . / . /

3 . = . ~ . 1 -

0 10 / 2O 30 ~0 510 60 k~

Lamminvaar a H ie tan iemi H o n k a v a a r a K e t t u k a n g a s V i h a j a r v i Suks ihar ju H u o S ~ l a m p i Koiv&kko

Honkaniemi Kapus tasuo

610 510 610 3 S 20 10 0

Fig. 3. Recons t ruc t ion of the s t ra t igraphic sect ion of the PjF and its l i t hodemic der ivat ives f rom the geological map of Figs. 1 and 2.

The effect of the pos t - sed imen ta ry Huos iu s l amp i Faul t on the spac ing of the Suks ihar ju and Huos iu s l amp i is a m i n i m u m es t imat ion.

The PjF is about 1000 m thick in its northern

parts and is estimated to be more than 1500 m thick in the south. It consists of the following

metamorphic lithologies: (1) massive or graded arkosites, (2) porphyroblastic mica schists, which

often show grading, (3) semipelitic, feldspar-rich

mica schists, which are often cross-bedded or rippled, and (4) cross-bedded arkosite and quartzite interbeds in mica schists (unit 4 is restricted to the upper part of the formation). These rocks make up primary sedimentary Facies 1, 2, 3 and 4 as shown in the legend of Fig. 2.

Where not tectonic, the upper contact with the AvF appears to be grada t iona l - - the amount of cross-bedded quartzite increases gradually until this lithology becomes dominant in the AvF.

There are four major areas where the PjF is

well-enough exposed to permit detailed lithologi-

cal and stratigraphic analysis. These are, from south to north, Kapustasuo, Suksiharju, Honka- niemi and Honkavaara (Fig. 2). The information from these four areas has been condensed into two summary stratigraphic columns showing the main variation between the northern and southern parts

Fig. 4. A KP paragne i s s showing mica-r ich and fe ldspar-r ich l i thologies , 2 k m west of Huos ius l ampi . Pho to K. Laajoki . Compass for

scale.

200

SOUTHERN SECTION

(COMPOSITE)

Metres

1500

lOO0.

5oo_

NORTHERN SECTION

clay sil._~t san_d

_ ~ o FA~IES m a j o r

r

~:r_~ 22Z22.

kl. 1 /I ) ~--- . - .

i ~ :~,~, ,~

~ c " ' . " . .

I . J

i . ¸ /

(

/ t a - -

i I J

i /

. . . . . / - - . . . . . . . . .

clay silt ~ d

]1 ~ A C I E S = [ I ~ mgjor )1 ) -m lno r

I I

I I !

1 -

r~ . . . . . . . . . . . . . . . . . 15kin . . . . . . . . . . .

~ posi t ive-t ransi t ion (sand : shale ratio increases) negative transit ion

t_~ vert ical and horizontal cad

Fig. 5. Simplified stratigraphic column of the southern (Koivikko-Kapustasuo) and northern (Ketttukangas-Honkaniemi) parts of the PjF and interrelations of the sedimentary facies. Notice that the southern column is a composite one with large stratigraphic gaps. (see Fig. 3).

of the area (Fig. 5). In the south, the PjF is divided into three members. The lower member consists of interbedded lithologies 1 and 2, the middle member of alternating sharply defined

units of lithologies 2 and 3 and the upper member mainly of mica schists with cross-bedded quartzite interbeds (Fig. 5). In the north, at Honkamemi,

the middle member appears to be absent and the PjF is here divided into the lower and the upper members. At Honkavaara (further north), how-

ever, solitary outcrops of lithology 2 occur within lithology 3.

The overlying AvF is at least 800 m tl~clc and consists almost entirely of cross-bedded arkosites and quartzites. It is a maturing-upwards sequence interpreted as representing an inner-shelf-coastal environment (Laajoki, 1996a). The A v F is overlain by the P~trekangas Formation (PkF) of wavy bedded or graded bedded phyllites and mica schists with cross-bedded quartzite interbeds. This se-

quence which is at least 500 m thick seems to be tidal (Laajoki, 1986a). The PjF-AvF-PkF sequence, totalling at least 2500-4000 m. forms a

prograding sequence, which accumulated at some time between about 2540 Ma and 2200 Ma ago as

indicated by zircon determinations from interbedded and cross-cutting basic rocks (Laajoki, 1986a).

The total strike length of the PjF and the KP is about 60 km (Fig. 3). The overlying AvF and the

PkF continues to Pal tamo in the south (Fig. l). PjF-type rocks occur near Paltamo and also south of Lake Oulujarvi suggesting a mimmum strike

length of 120 km for the original sedimentary system. As discussed by Laajoki (1986a) these rocks may correlate with the Lapponian rocks in Lapland, about 300 km north of Puolanka. If so. the PjF may have formed part of a huge sedimentary system interpreted by Laajoki (1986b) as either a narrow sea or a large inland basin.

In the following sections the sedimentary facies

201

and facies associations of the PjF are described

and a model is presented for the basin in which they were deposited.

Primary sedimentary facies of the PjF

On the basis of their primary structures and estimated primary grain sizes the PjF metasediments are divided into four major facies. These are num-

bered 1 to 4 in the order in which they appear in the stratigraphic column. Facies 2 and 3 contain

many subfacies and Facies 1 grades into Facies 2.

Facies 1: massiue sands

Description This facies consists of light brown sandstone

beds which are mostly tens of centimetres thick

but sometimes up to 1.5 m thick. They usually occur either as thick amalgamated sand units or as single beds within Facies 2 rocks (Figs. 6 and 7).

At their lower contacts, flame or load cast struc-

tures occur, whereas the upper contact is mostly planar. The beds are predominantly massive, but

many of the thicker beds show faint planar laminations in their upper parts, overlain in places

by wavy lamination (Fig. 8). It is not always possible to determine whether this lamination is

primary or due to the schistosity parallel with the

bedding. The grain size within a single bed ranges mostly from coarse sand at the base to medium

sand at the top. Some of the thickest beds at Nuottim~iki contain a thin muddy upper seam

which is now sericite schist and at Honkavaara

mudstone-capped sandstones occur representing a

transition to Facies 2b (Fig. 8). Sole structures have not been found, but most bed contacts are

sheared.

The main minerals are quartz and plagioclase

with minor biotite and muscovite. As a whole the facies is composed of rather clean quartz-plagio-

clase sand.

Interpretation Facies 1 is probably equivalent to the "aren-

aceous facies" of Mutti and Ricci Lucchi (1978).

the "massive sandstone facies" of Walker (1978)

and "facies B I . I " of Picketing et al. (1986); al-

though dewatering structures are not present in

these Finnish examples. Picketing et. al. (1986) interpret their facies

BI.1 as representing rapid deposition from a high-concentration turbidity current by the freez-

ing of a dense cohesionless suspension. Because our Facies 1 occurs within, and grades into, beds

of undisputable turbiditic origin this interpretation is also favoured for the PjF. The massive and graded sandstone beds are T~ turbidites and those

with laminated upper divisions, a r e T:, b or T,h , turbidites. The rare muddy upper drapes may

represent sediments deposited from suspension

from the waning tail of the current or represent background fallout.

Fig. 6. Single Facies 1 beds (white) amidst staurolite-mica schist and garnet-mica schist. Honkaniemi. Photo K. Laajoki.

202

Fig. 7. Three thick, amalgamated Facies 1 beds at Koivikko, Nuott imaki. Top to the left upper corner. Photo K. Laajoki.

Facies 2: graded muddy sands

This facies consists of very-thin-bedded to thin-bedded mudstone-capped graded sandstone or muddy sandstone beds. On the basis of the metamorphic mineral content, which reflects the differences in the original clay content, two subfacies (2a and 2b) are delimited. Facies 2b in-

cludes mudstone-capped sandstone interbeds gradational into Facies 1 sandstones.

Facies 2a." clay-richer (porphyroblastic) muddy sands

This facies is characterized by graded bedded mica schists with beds usually only 0.5-3 cm thick and the bedding thickness is fairly constant which

Fig. 8. Stacked Ta-Ta, turbidite beds of Facies 1 at Honkavaara. Top to the left. The bed left of the label (16 cm long) shows wavy lamination interpreted as a C division. Photo E: Korkiakoski.

203

Fig. 9. A typical outcrop of Facies 2a, showing constant bedding thickness. The beds are overturned and their tops are towards the lower left corner. The pen is 13 cm. Photo K. Laajoki.

gives the rock a varve- l ike appea rance (Fig. 9).

The lower halves of the graded s t ra ta consis t of

fe ldspar- and quar tz- r ich fine sands tone or silt-

stone, whereas the uppe r par t s were or ig inal ly rich

in clay as ind ica ted by their present r ichness in

micas, s t a u r o l i t e / a n d a l u s i t e and garnet (Fig. 10).

In thicker beds (i.e. more than 3 cm thick) the

lower sand par t is dominan t . Ra re wavy lamina-

t ion (c l imbing r ipples?) and smal l -scale cross-

l amina t ion are present . Fac ies 2a c o m m o n l y forms

un i fo rm uni ts up to tens of meters thick or, in the

south, it m a y occur as thin units only a few tens of

cent imet res thick in be tween Fac ies 1 and 3 rocks.

In the nor th , rocks of this subfacies are most ly

s t auro l i t e -bear ing and the separa t ion be tween the

sandier lower par t s and the micaceous upper par t s

is c learer (Fig. 11). This may be pa r t ly due to the

d i f ferent m e t a m o r p h i c his tor ies of these two areas.

Fig. 10. Facies 2a Suksiharju rock showing development of abundant andalus~te (puffed up) in the upper parts of the graded strata: top to the left. The hoe is 73 cm. Photo K. Laajoki.

204

1 Fig. 11. Facies 2a rock at Honkaniemi showing fluctutation in bed thickness. Top to the right (east). Note: the sandy beds in the section covered by the scale (16 cm) showing distribution grading and very thin upper muddy parts: and the very thin ( < 0.5 cm) graded beds between the right-hand end of the scale and the sandy bed on the right of the photo. Dark spots are staurolite. Photo E

Korkiakoski.

Subfacies 2a also includes mud-rich varieties which alternate with the sandier beds containing rare plane- or cross-laminations (Fig. 12).

Facies 2b: clay-poorer (non-porphyroblastic) graded muddy sands

A typical Facies 2b rock is a non-porphyrobtas- tic mica schist showing graded bedding with a

feldspar and quartz-rich lower part and a biotite and muscovite-rich upper part (Fig. 13). Because these rocks do not contain porphyroblasts their primary chemical composition can not have been as rich in aluminium as that of Facies 2a. The bed thickness is very thin or thin but the beds are in general thicker than in Facies 2a and their lower sandy subdivisions are slightly coarser grained.

Fig. 12. A sandy Facies 2a bed about 10 cm thick showing parallel and wavy laminations. Photo K. Laajoki.

205

Fig. 13. A Facies 2b sandstone bed about 5 cm thick showing distribution grading and a very thin mud cap. Photo K. Laajoki.

Interpretation Although grain-size determinations are only ap-

proximate it is most likely that our Facies 2 is

equivalent to facies C2.3, D2.1, D2.3 or E2.1 of Pickering et al. (1986). All of these are interpreted

by them as having been deposited by low-concentration turbidity currents. The PjF rocks are

mostly Tae turbidites with rare Tab e and Tabce

turbidities, which are characteristic of those facies

in the scheme of Pickering et al. (1986).

Facies 3: cross-stratified fine sands and accociated facies

Facies 3 consists of metasemipelites relatively poor both in micas and porphyroblasts. These are

interpreted as metamorphosed equivalents of cross-stratified and rippled fine sandstones. Based mainly on the character of the pr imary structures, Facies 3 has been subdivided into five subfacies. Facies 3a is dominant in the north and the rest are

encountered in the south.

Facies 3a: hummocky cross-stratified sands This subfacies, preserved only at Honkaniemi,

includes fine-grained micaceous sandstone with sets from a few centimetres up to 10-15 cm thick of low-angle or smooth, convex-up cross-stratification. The sets are often overlain by formconform-

able sand laminae and separated by mud drapes with sharp upper contacts.

Three styles of cross-stratification occur. First,

is cross-stratification with subhorizontal or slightly undulating first-order truncation surfaces and

low-angle even lamination dipping mostly to the north, but also showing opposite dip directions (Fig. 14). The original sediment was a micaceous fine sand. The first-order surfaces are veneered by

thin mud drapes. The spacing of the undulation is

rather short: from about 0.5 m up to 1.5 m. Secondly, Fig. 15 displays a low-angle

cross-stratification which differs from the undulating type in that the first-order surfaces are mainly

subhorizontal, hummocky-swale structures are either poorly-developed or lacking and the num-

ber of mud drapes is greater. Thirdly, in those cases where the m u d / s a n d

ratio is close to 1 : 1 the sand produces bedforms with internal very low-angle bi-directional cross-laminations overlain by form-conformable even sandstone laminae or sandstone occurs as

beds displaying flat or undulating laminations.

Facies 3b: complexly cross-laminated sands Tabular or near-tabular sets (around 10 cm

thick) of complexly cross-laminated fine-grained micaceous sandstone capped by thin mudstone

206

Fig. 14. A. A Facies 3a rock showing smooth low-angle cross-stratification and low-angle truncation. Photo K. LaajokJ. B. Line drawing. The thicker lines indicate smooth first-order truncation surfaces and thinner ones the third order laminar surfaces. Notice the low-angle second-order truncation surfaces and the low dip angles of the even lamination.

layers (now andalusite-rich mica schist) (Fig. 16) characterize this subfacies. It is the dominan t facies in the Suksiharju area. Internally, the sets are

cross-laminated in a complex way. Typical of this internal structure are very thin wavy or smooth

laminations and m a n y irregular erosional and sec-

ond-order t runcat ion surfaces separating the different laminae bundles (Fig. 17).

Mudstones separa t ing the sandstone sets form

either cont inuous layers or shorter t rough fillings,

whose mud content may increase gradually towards the sharp upper surface (Fig. 17B).

Facies 3c: Tabular planar cross-bedded sands This subfacies occurs only at Kapus tasuo where

it is characterized by planar cross-bedded sand-

stone sets f rom a few centimetres to twenty centimetres thick. The sets are solitary and are separated f rom each other by Facies 3e (see below) (Fig. 18).

207

Fig. 15. A. Facies 3a rock showing bidirectional low-angle cross-stratification capped by mud drapes. Photo K. Laajoki. B. Line drawing. Mud drapes are hatched. Notice the subhorizontal first-order truncation surfaces (thicker lines) and the low-angle third-order laminar surfaces. The diagonal thin lines outlines S 4 foliation and andalusite veins are shown by letter A. Notice the anti formal structure just above the label "top".

Facies 3d: Ripple cross-laminated sands

One outcrop at Suksiharju conta ins a uni t of

r ippled sandstone about 2 m thick. The ripple

cross- laminat ions are unidi rect ional bu t their up-

per boundar ies are relatively symmetrical a l though

asymmetrical profiles also occur (Fig. 19). The

ripple sets are draped by thin m u d d y flasers or

seams and their lower boundar ies are straight or

slightly undula tory .

Facies 3e: Horizontal laminated silty muds Facies 3c sets are separated by mica schist beds

a few centimetres or tens of centimetres thick

which are most ly so schistose that their pr imary

structures can no longer be seen (Fig. 18). In rare

cases, however, they display horizontal l amina t ion

with l amina thickness of about 0.5 cm or less and

faint grading in grain size.

208

!

. . . . ~ . . . . . . . . . . . . . . . . . . . . ]

Fig. 16. Five tabular Facies 3b sets (numbered from 1 to 5) separated by mud layers (now rich in andalusite). The beds are upside down. Photo K. Laajoki.

Fig. 17. A, A close-up of a facies 3b rock showing internal cross-lamination in three sets separated by mud drapes. Photo K: Laajoki. B. Line drawing showing first-order surfaces (" master bedding") (thicker lines) and wavy third-order laminar surfaces. Notice the andalusite aggregates (A) in the lower drape, the graded appearance of the second drape and the metamorphic segregation (MS) in the upper fight comer.

209

Fig. 18. Stacking of Facies 3c and 3e sets at Kapustakangas. Photo K. Laajoki. Top to the left.

In terpretation

Facies 3a: Based mainly on comparisons with published examples of hummocky cross-stratified sandstones, Facies 3 a is interpreted as a hummocky cross-stratified facies. Our undulating cross-stratified beds (Fig. 14) are closely compara- ble to those illustrated by Dott and Bourgeois (1982), especially their H, HF, and HFM sequences: and also to those illustrated by de Raaf et al. (1977, fig. 8), especially their type 11. Our low-angle cross-stratification (Fig. 15) more closely resembles that described by Nottvedt and Kreisa

(1987) which, although resembling hummocky cross-stratification, was formed by combined-flow, not just oscillatory flow. The bedforms in our sequences which are richest in mudstones appear identical to the FXM model described by Dott and Bourgeois (1982, fig. 24).

The origin of hummocky cross-stratification is variably ascribed to: the action of oscillatory storm waves (e.g. de Raaf et al., 1977; Dott and Bourgeois, 1982); combined-flow storm currents (Swift et al., 1983; Allen, 1985: Nottvedt and Kreisa, 1987); or turbidity currents (Walker et al.,

Fig. 19. Ripple cross-laminated and mud draped Facies 3d. The length of the label is 16 cm. Photo E. Korkiakoski.

210

1983). Because symmetrical hummocky-swale structures are less common than the low-angle cross-stratification with preferred northern dip, we

favour a largely combined-flow model for the origin of our Facies 3a. Although Walker et al.

(1983) ascribe hummocky cross-stratification to

turbidity currents, we have not identified their B

and P divisions in our rocks; so we see little

evidence of turbidity current action in Facies 3a. The mud drapes and layers represent either

deposition from wainmg storm currents or from

suspension during fair weather.

Facies 3b: We have not found any description in the literature of facies with which this facies

could readily be compared. The many second-order

truncation surfaces and the wavy nature of the laminations indicate, however, that flow condi-

tions were variable and probably of the combined type. In Nottvedt 's and Kreisa's (1987) bed-form phase diagram (their fig. 4) this facies may represent energy conditions a little lower than those which form hummocky cross-stratification.

Facies 3c: This facies represents a bedform

formed by unidirectional traction currents. Facies 3d: On the basis of the symmetrical

ripple profiles this facies is interpreted as repre-

senting mostly wave generated bedforms, but because other diagnostic features of a wave origin

(de Raaf et al., 1977) seem to be lacking combined flow origin is not totally excluded ~cf. Harms. 1969. 1979).

Facies 3e: Because the internal structure of the laminae of this facies are not preserved its origin

cannot be deduced. It may represent a high-energy plane-bedded facies.

General

As a whole, in comparison with Facies 2. Facies 3 represents clearly higher-energy deposits, formed

mostly in fine-grained sand under combined flow conditions. The restriction of Facies 3a to the

north indicates that energy conditions were higher there than in the south where Facies 3b-3e dominate.

Facies 4: cross-bedded medium sand

Description

This facies is only exposed at Huosiuslampi

and east of Honkaniemi in the uppermost part of PjF (Fig. 2) where overturned and refolded cross-

bedded quartzite beds occur within strongly schistose mica schists lacking primary structures.

The sands are trough cross-bedded with sets up to

a few tens of centimetres thick and the cosets up

to about 0.5-1 m thick (Fig. 20).

L .

Fig. 20. A close-up of an outcrop of Facies 4 showing trough cross-bedding. The beds are inverted. Photo K. Laajoki.

Interpretation

Facies 4 represents sands deposited by traction

currents. A more detailed interpretat ion is

hindered by the poor outcrops.

Rocks associated with Facies 4

The uppermost rocks in the PjF which contain the interbeds of Facies 4 are so strongly deformed that their original facies cannot be determined. They are mica schists or feldspar-rich metase-

mipelites. A few of the latter show relict bedding

structures of probable turbidite origin and some

ripple cross-lamination.

Facies associations of the PjF

The facies described above can be grouped into four broad facies associations called A, B, C and

D in stratigraphic order from the oldest to the youngest (Fig. 3).

Facies Association A: alternation of Facies 1 +

Facies 2

Description

The lower part of the PjF is characterized by

the repetition of Facies 1 or Facies 2 rocks. This is exemplified best at Nuottim~iki in the south where

these two facies alternate through 500 m of section (Figs. 2 and 5). Here Facies 1 forms either solitary beds or units up to 50 m thick within Facies 2a

rocks. Facies 2b has not been identified here but it

is common at Honkaniemi, 20 km to the north,

where Facies 1 alternates with Facies 2a and Facies 2b. The underlying KP also seems to be composed

of this facies association.

Interpretation

There can be little doubt that this facies association represents part of a turbiditic system, but the main question is whether the sediments accumulated in a basinal, deep-water fan, slope or shelf environment. The apparent "distal" and "basinal" nature of Facies 2 suggests a basin plane deposit, but turbidites in those are typically base-truncated Tcd e turbidites (e.g. Mutti, 1977), and these are very rare at Puolanka. However,

211

there are no coarse-grained turbidites, indicating

that the facies is not proximal. As discussed in the

next section, Facies 2a is closely associated with

Facies 3 which shows evidence of abundant storm-wave activity, thus suggesting that Facies 2a probably represents a relatively shallow-water sediment deposited somewhere below storm wave

base. Facies 1 and Facies 2 rocks resemble some

slope deposits such as those described by Mutti

and Ricci Lucchi (1978) and Lundegard et al. (1985), but the sequences at Puolanka lack slumps

which are diagnostic of slope deposits. Taking into

account these facts we propose that Facies Associ-

ation A probably represents either upper slope or

outer shelf deposits, which according to Mutti and

Ricci Lucchi (1978) are difficult to distinguish one from another.

Facies Association B: alternation of Facies 2a and

Facies 3

Description

The best established stratigraphic relations in the PjF are that Facies 2a and Facies 3 are in-

terstratified at Suksiharju and Kapustasuo (Figs. 2 and 5), and that Facies 1 and Facies 3 do not

occur in association. The thickness of alternating Facies 2a and 3

units varies from a few tens of metres to about 200

m at Kapustasuo. The transition from Facies 2a to Facies 3, where observed, is sharp.

Intrepretation

The alternation of "bas inal" Facies 2a and storm-generated Facies 3 indicates deposition close to the zone of storm-wave base and, secondly, that the height of the wave base was suddenly and drastically changed, raised and lowered repeatedly at least five times.

Facies Association C: Facies 3a 3e

Description

This association comprises only Facies 3 deposited in the area between storm-wave base and the shallower environment in which the AvF was deposited. It contains many different sub-associa-

212

tions. At Kapustakangas there are regular repe- titions of Facies 3b, 3c and 3e; in the Suksiharju area Facies 3b and 3d are dominant, while at Honkaniemi Facies 3a is prominent. Obviously these differences between the north and south relate to amount of storm influence during sedimentation and probably reflect slightly different water depths in these parts of the basin.

Interpretation

On the basis of the common occurrence of storm-generated deposits and the shallow-water nature of the overlying AvF it is concluded that this association was deposited on an inner shelf shorewards of the line marking the base of the

storm waves.

Facies Association D: Facies 4 and associated rocks

A convincing interpretation for this facies cannot be presented due to the lack of environmen- tally diagnostic features. However, an origin as subtidal sandwaves, close to the palaeoshoreline, would not be unreasonable in this stratigraphic

situation.

Basin models

The PjF represents a fragmentary and arbitrary section of the lower part of the progradational sedimentary fill (the Central Puolanka Group) of the lowermost allochthonous western basin of the early Proterozoic Kainuu Schist Belt. Its depositional basement is not known, neither are its northern and southern extensions. All these, to- gether with the fact that outcrops are sporadic (Fig. 3) make any basin reconstruction extremely difficult. Consequently, we have to be content with giving only a two-dimensional basin model and discussing briefly the tectonosedimentological context of the PjF in terms of the early Protero- zoic sedimentary evolution of the Fennoscandian Shield in northern Finland.

Taking into account the stratigraphy, the facies relations and their interpretations given in this and an earlier paper (Laajoki, 1986a), the PjF was deposited in a prograding system whose deeper parts were occupied by sediments deposited by turbidity currents, the middle part by storm-gener-

ated and related fine sands and the upper part by shallow-water sands.

These kinds of progradational turbidite-shallow-water sediment transitions are common in the ancient sedimentary rock records and many are well documented. They have mostly been interpreted as representing either submarine an d /o r delta deposits (e.g. Link and Welton, 1982: Picker- ing, 1982), outer shelf-pro-delta sediments prograded by delta complexes (e.g. Allen, 1960) or transitions from a turbidite basin to a shallow shelf (Van de Kamp et al., 1974; Graham, 1982; Lamens, 1985).

Because the PjF turbidites are monotonously rather thin-bedded and fine-grained and the transition from distal basinal turbidites to coarse proximal channel deposits cannot be established a canyon-fed submarine fan seems not to have ex- isted at Puolanka.

Although the AvF has not yet been studied in detail it is known to be composed of uninformalty cross-bedded sands without any upwards coarsen- ing cycles typical of deltaic sequences, so that a delta-fed system seems unlikely. The tempestites of Facies 3 prove that the Puolanka system in- cluded at least a narrow shelf, so the two most probable models to explain the turbidite. shallow-water transition displayed by the PjF are a slope-shelf or an outer- inner shelf transition.

The choice between these two possibilities de- pends largely on the interpretation of Facies As- sociation A; does it represent (a) upper-slope or (b) outer-shelf turbidites? Since there is insuffi- cient proof Of either~ Fig. 21 gives two models based on these alternatives.

In the first model (Fig. 21A) Facies Association A represents distal outer-shelf turbidites and minor background sediments. The turbidites may be related to the storm activity which produced the tempestitic Facies 3 (cf. Hamblin and Walker. 1979). We have not, however, identified storm- generated sand beds that could be expected to occur in the outer-shelf laminated muds like those, for instance, from recent shelves l e.g. Reinecke and Singh, 1980; Aigner and Reinecke. 1982; Al- len, 1982) or those from ancient ones Ifor references, see Marsaglia and Klein. 1983: Johnson and Baldwin, 1986; cf. Soegaard and Eriksson.

Sea level

Formation ~ Akanvaara ~L Parekangas

Formation = Formation

Shelf Tidal f lat

outer inner

=L j j

Storm wave base Facies ass, D

G Facies ass. C

Facies ass. B

Facies associat ion A

213

Sea level

Upper slope 1 outer

Shelf 2 Tidal f lat

inner

Shelf brake = storm wave base

Facies associat ion A

Facies ass. D

Facies ass. C

Legend : Facies ass.B

Facies 4 - ' 3

" 2 1

Fig. 21. Two arbitrary sections of the PjF showing the lateral facies association distributions. A. Rather steep shelf model. B. Narrow shelf model.

1985). This model presumes to explain the thick

amalgamated Facies 1 units at Koivikko and

Honkaniemi in particular as the results of re-

peated and prolonged major storm periods with

relatively insignificant background sedimentation.

This model agrees with that of Graham (1982)

who wonders whether many of the turbidites could

not be storm generated and formed as sheet-like

deposits down slopes devoid of typical fan mor-

phology.

The second choice is a narrow-shelf model (Fig. 21B) in which case the storm-wave base and shelf

break/slope neck must have been at about the same depth. The Facies 3 sediments were de-

posited on the outer parts of the narrow shelf and probably some of the sediments spilled over the

shelf break onto the upper slope. In this model

Facies Association A could represent a lev6e com-

plex of a deep-water fan whose feeder channel and

lobe systems were outside the PjF outcrop area or

are not exposed and upon which Facies 3 re-

peatedly prograded.

In this connection it is pertinent to remember

that the majority of the ancient turbidite system,

of which the PjF forms only a small fraction, is

now represented by the West Puolanka Paragneiss

(Fig. 1) and its northern and western extensions.

These compose one of the major crustal shorten-

ing zones of the Fennoscandian Shield. This of

course leaves the door open for many specula-

tions. Like Shanmugan et al. (1985) we stress that the

turbidite facies association scheme based on mod-

ern fans may not always be appropriate for inter-

preting ancient submarine fan environments. Sec- ondly, recent studies show that a turbidite system

214

may be more complex and varied than the tradi- tional one point source fan model; see for instance the basin types 1-3 of van de Kamp et al. (1974), the submarine ramp facies model of Heller and Dickinson (1985), the line and multiple point source models of Chan and Dott (1983) and Lundegard et al. (1985) and the discussions by Miall (1984, p. 305) and Reading (1987). Clearly, a new approach how to classify turbidite systems is needed; the facies analysis technique (e.g. Picker- ing et al., 1986) is useful for descriptions, but for environmental analyses to know lateral variabil- ities within the system is essential.

The rapid sea-level changes indicated by Facies Association B call for closer discussion. The sea- level changes are generally attributed either to eustatic or local causes or both. Of the global sea-level changes glacioeustatic and tectonoeu- static ones are considered the most important for the pre-Quaternary (Harms, 1984). Shanmugam et al. (1985) attribute the control of the growth of Phanerozoic submarine fans to eustatic sea-level changes caused by glaciation: with growth occur- ring mainly during glacials (low sea level). Early Proterozoic glaciations are known from the Fen- noscandian Shield (Marmo and Ojakangas, 1984) and from North America (e.g. Young, 1973). Con- sequently, glacioeustasy may be one possible control for the repetition of Facies 2 and 3, although the regular and sharp nature of this repetition indicates that this is not very likely. For the same reason tectonoeustasy also seems unlikely and so it is felt that these changes were probably caused by more local tectonic factors, e.g. basement fault- ing.

Finally, in terms of regional stratigraphic evolution Laajoki (1986b, 1988) has recently divided the Karelian formations in Finland into four cycles or tectofacies: the Sumi-Sariola, the Kainuu-Lapponi, the Jatuli and the Kaleva which correspond to the continental rift, the narrow sea (the Red sea type), the open sea and the foredeep stage. In this scheme the PjF represents the rocks of the second cycle (Kainuu-Lapponi), which were transgressed by the Jatuli. R~siinen (1986) states that the Lapponi quartzites, which show evidence of tidal activity and are correlative with the AvF, form part of a transgressive sequence. The Pre-

cambrian stratigraphy of Lapland is, however, poorly understood and the rocks underlying the Lapponi quartzites are not sufficiently well exposed that the transgressive or regressive nature of the complete cycles could readily be established. Furthermore, the relationship between the Lap- poni and Jatuli and the palaeoenvironment of the abundant volcanic rocks and associated iron-formations of the upper Lapponi have not yet been completely clarified. Because of the vertical bedding positions the overall progradational/regressive nature of the CPG at Puolanka is well founded, although the topmost PkF may also indicate some deepening of the basin at the final stage of sedimentation of the CPG. The present ob- servations, therefore, support the idea that the CPG was deposited during the opening stage of the Karelia sea on a rifted continental margin and later transgressed by the open-sea stage Jatuli sediments.

Conclusions

The main results of our study can be condensed into the following conclusions.

(l) A conventional sedimentological approach can be applied with reasonable success to rather highly metamorphosed and complexly deformed Precambrian strata and should routinely accompany stratigraphic and tectonic work on metamorphic, supracrustal terrains.

(2) As has been discussed in many recent papers (Graham, 1982; Link and Welton, 1982; Chan and Dott, ]983; Heller and Dickinson. 1985, La- mens, 1985; Lundegard et al., 1985; Shanmugam et al., 1985; etc.), and confirmed here by the PjF, many ancient turbidite sequences are not readily modelled by the classical canyon-fed deep-sea fan system (e.g. Mutti and Ricci Lucci, 1978).

(3) The PjF is one of the oldest (at least 2200 Ma old) metasedimentary formations from which storm-generated deposits have so far been described. Because tempestites have a key role in reconstructing ancient continental margins special attention should be paid to mapping them in Precambrian shield areas.

(4) The palaeoenvironmental setting of the PjF was either the outer to middle parts of a relatively

b r o a d , s t eep shel f , or t h e u p p e r s lope a n d t he

o u t e r p a r t s of a n a r r o w shelf .

Acknowledgements

T h i s s t u d y is b a s e d o n a r e s e a r c h p r o j e c t fi-

n a n c e d b y t he A c a d e m y of F i n l a n d a n d is a

c o n t r i b u t i o n to I G C P 160. K .L . is g r a t e f u l to K.

E r i k s s o n , R. O j a k a n g a s a n d A. S i e d l e c k a for f ru i t -

fu l d i s c u s s i o n s d u r i n g t he I G C P 160 e x c u r s i o n to

t h e s e o u t c r o p s . T h e E n g l i s h o f t he m a n u s c r i p t h a s

b e e n c h e c k e d b y Mrs . She i l a H i c k s , P h . D . T h e

r e f e r ee s K. E r i k s s o n , M.J . J a c k s o n a n d K. T u c k -

wel l m a d e m a n y v a l u a b l e s u g g e s t i o n s w h i c h g r e a t l y

h e l p e d to c l a r i fy a n d i m p r o v e seve ra l p o i n t s in t he

p a p e r .

References

Aigner, T. and Reineck, H.-E., 1982. Proximality trends in modern storm sands from the Helgoland Bight (North Sea) and their implications for basin analysis. Senckenber~ana Marit., 14: 183-215.

Allen, J.R.L., 1960. The Mam Tor sandstones: a "turbidite" facies of the Namurian deltas of Derbyshire. England. J. Sediment. Petrol., 30: 193-208.

Allen, J.R.L., 1982. Sedimentary Structures: Their Character and Physical Basis, Vol. 2. Developments in Sedimentology 30. Elsevier, Amsterdam, 663 pp.

Allen, P.A., 1985. Hummocky cross-stratification is not produced purely under progressive gravity waves. Nature, 313: 562-564.

Bouma, A.H., 1962. Sedimentology of Some Flysch Deposits. Elsevier, Amsterdam, 168 pp.

Chan, M.A. and Dott, R.H., Jr., 1983. Shelf and deep-sea sedimentation in Eocene forearc basin, West Oregon--fan or non-fan? Am. Assoc. Pet. Geol. Bull., 67: 2100-2116.

de Raaf, J.F.M., Boersma, J.R. and van Gelder, A., 1977. Wave-generated structures and sequences from a shallow marine succession, Lower Carboniferous, County Cork, Ireland. Sedimentology 24: 451-483.

Dott, R.H., Jr. and Bourgeois, J., 1982. Hummocky stratification: significance of its variable bedding sequences. Geol. Soc. Am. Bull., 93: 663-680.

Graham, J.R., 1982. Transition from basin-plane to shelf deposits in the Carboniferous flysch of southern Morocco. Sediment. Geol., 33: 173-194.

Hamblin, A.P. and Walker, R.G., 1979. Storm-dominated shallow marine deposits: The Fernie-Kootenay (Jurassic) transition, southern Rocky Mountains. Can. J. Earth Sci., 16: 1673-1690.

Harms, J.C., 1969. Hydraulic significance of some sand ripples. Geol. Soc. Am. Bull., 80: 363-396.

Harms, J.C., 1979. Primary sedimentary structures. Annu. Rev. Earth Planet Sci., 7: 227-248.

215

Harms, J.C., 1984. Pre-Quaternary sea-level changes. Annu. Rev. Earth Planet Sci., 12: 205-243.

Heller, P.L. and Dickinson, W.R., 1985. Submarine ramp facies model for delta-fed, sand-rich turbidite system. Am. Assoc. Pet. Geol. Bull., 69: 960-976.

Ingram, R.L., 1954. Terminology for the thickness of stratification and parting units in sedimentary rocks. Bull. Geol. Soc. Am., 65: 937-938.

Johnson, H.D. and Baldwin, C.T., 1986. Shallow siliclastic seas. In: H.G. Reading (Editor), Sedimentary Environ- ments and Facies. Blackwell Scientific Publications, Ox- ford, pp. 229-282.

Laajoki, K., 1986a. The Central Puolanka Group--a Pre- cambrian regressive metasedimentary sequence in northern Finland. Bull. Geol. Soc. Finland, 58:179 193.

Laajoki, K., 1986b. The Precambrian supracrustal rocks of Finland and their tectono-exogenic evolution. Precambr. Res., 33: 67-85.

Laajoki, K., 1988. NenS.kangas-type conglomerates--an evidence of a major break in the sedimentation of the early Proterozoic (Karelia) quartzites in Kainuu, northern Fin- land. Geol. Surv. Finl., Spec. Pap., 5:91 107.

Lamens, J., 1985. The transition from turbidite to shallow-water sedimentation in the lower Salmian (Tremadocian, Lower Ordovician) of the Stavelot Massif, Belgium. Sediment. Geol., 44:121 144.

Link, M.H. and Welton, J.E., 1982. Sedimentology and res- ervoir potential of Matilija Sandstone: an Eocen sand-rich deep-sea fan and shallow-marine complex, California. Am. Assoc. Pet. Geol. Bull., 55:1514 1534.

Lundegard, P.D., Samuels, N.D. and Pryor, W.A., 1985. Upper Devonian turbidite sequence, central and southern Appa- lachian basin: contrasts with submarine fan deposits. Geol. Soc. Am. Spec. Pap., 201: 107-121.

Marmo, J. and Ojakangas, R.W., 1984. Lower Proterozoic glaciogenic deposits, eastern Finland. Geol. Soc. Am. Bull., 95:1055 1062.

Marsaglia, K.M. and Klein, G. deV., 1983. The paleogeogra- phy of Paleozoic and Mesozoic storm depositional systems. J. Geol., 91: 117-142.

Miall, A.D., 1984. Principles of Sedimentary Basin Analysis. Springer-Verlag, New York, N.Y., 490 pp.

Mutti, E., 1977. Distinctive thin-bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South-central Pyrenee, Spain). Sedimentology, 24: 107-131.

Mutti, E. and Ricci Lucchi, F., 1978. Turbidites of the northern Apennines: introduction of facies analysis. Int. Geol. Rev., 20: 125-166.

North American Commission on Stratigraphic Nomenclature, 1983. North American Stratigraphic Code. Am. Assoc. Pet. Geol. Bull., 67: 841-875.

Nottvedt, A. and Kreisa, R.D., 1987. Model for the combined- flow origin of hummocky cross-stratification. Geology, 15: 357-361.

Picketing, K.T., 1982. A Precambrian upper basin-slope and prodelta in northeast Finnmark, north Norway--a possible

216

ancient upper continental slope. J. Sediment. Petrol., 52: 171-186.

Pickering, K.T., Stow, D.A.V., Watson, M.P. and Hiscott, R.N., 1986. Deep-water facies, processes and models; a review and classification scheme for modern and ancient sediments. Earth-Sci. Rev., 23: 75-174.

Ras~inen, J., 1986. On the Lapponia quartzites in the Sodankyl~-Savukoski area, northern Finland. 17e Nordiska Geologm6tet, Helsingfors Universitet, May 12-15, 1986, Abstracts, pp. 166.

Reading, H.G., 1986. Facies. In: H.G. Reading (Editor), Sedi- mentary Environments in Facies. Blackwell Scientific Pub- lications, Oxford, pp. 4-19.

Reading, H.G., 1987. Fashions and models in sedimentology: a personal perspective. Sedimentology, 34: 3-9.

Reinecke, H.-H. and Singh, I.B,, 1980. Depositional sedimentary environments with reference to terrigenous clastics. Springer-Verlag, Berlin, 549 pp.

Selley, R.C., 1982. An Introduction to Sedimentotogy. Academic Press, London, 417 pp.

Shanmugam, G., Damuth, J.E. and Moiola, R.J., 1985. Is the turbidite facies association scheme valid for interpreting ancient submarine fan environments? Geology, 13: 234-237.

Soegnard, K. and Eriksson, K.A., 1985. Evidence of tide, storm, and wave interaction on a Precambrian siliclastic

shelf: the 1,700 m.y. Ortega Group, New Mexico. J. Sedi- ment. Petrol., 55: 672-684.

Swift, D.J.P., Figueiredo, A.G., Jr., Freeland, G:L. and Oertel, G.F., 1983. Hummocky cross-stratification and megarip- pies: a geological double standard? J. Sediment. Petrol.. 53: 1295-1317.

van de Kamp, P.C., Harper, J.D., Conniff, J.J. and Morris, D.A., 1974. Facies relationships in the Eocene-Oligocene in the Santa Ynez Mountains, California. J. Geol. Sot., London, 130: 545-565.

Walker, R.G., 1978. Deep-water sandstone facies and ancient submarine fans: models for exploration for stratigraphic traps. Am. Assoc. Pet. Geol. Bull., 62: 932-966.

Walker, R.G., 1979. Facies and facies models, 1. General models. In: R.G. Walker (Editor), Facies Models. Geosc. Can., Reprint Ser., 1: 1-7.

Walker, R.G., Duke, W.L. and Leckie, D.A., 1983. Hummocky stratification: significance of its variable bedding sequences: discussion and reply. Geol. Soc. Am. Bull., 94: 1245-1251.

Wentworth, C.K., 1922. A scale of grade and class terms for clastic sediments. J. Geol., 30: 377-392.

Young, G.M., 1973. Tillites and ahiminous quartzites as possible time markers for middle Precambrian (Aphebian) rocks of North America. Geol. Assoc. Can. Spec. Pap., 12: 97-127.

the precambrian turbidite-tempestite transition as displayed by the amphibolite-facies...

Documents