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Precambrian Research 228 (2013) 177– 193

Contents lists available at SciVerse ScienceDirect

Precambrian Research

journa l h omepa g e: www.elsev ier .com/ locate /precamres

racking lateral �13Ccarb variation in the Paleoproterozoic Pechenga Greenstoneelt, the north eastern Fennoscandian Shield

aula E. Salminena,∗, Juha A. Karhua, Victor A. Melezhikb,c

Department of Geosciences and Geography, P.O. Box 64 (Gustaf Hällströmin katu 2a), 00014 University of Helsinki, FinlandGeological Survey of Norway, Leiv Erikssons vei 39, N-4791 Trondheim, NorwayCentre for Geobiology, University of Bergen, Allegaten 41, N-5007 Bergen, Norway

r t i c l e i n f o

rticle history:eceived 29 March 2012eceived in revised form8 November 2012ccepted 3 January 2013vailable online 11 January 2013

eywords:arbon

a b s t r a c t

The Kuetsjärvi Sedimentary Formation (KSF) records the global Paleoproterozoic (ca. 2200–2100 Ma)positive �13C excursion of sedimentary carbonates. This event is here called as the Lomagundi-Jatuliisotopic excursion. In this study, lateral �13Ccarb variation in the KSF and local basinal factors amplifyingglobal �13Ccarb value were investigated and a secular �13C curve for the KSF was constructed. Sedimentarycarbonate samples from a new drillcore (Drillcore 5A) from the KSF were analysed for �13C, �18O andselected major and trace elements. The �13C values of the samples vary from 5 to 8‰ (VPDB) and the�18O values from −18 to −10‰ (VPDB). Most of the samples have retained their primary C isotopiccomposition, as they do not show correlation between the Mn/Sr ratios and the �13C and �18O values.

sotopesolomitealeoproterozoicennoscandiahemostratigraphy

The new results were compared to those previously obtained from another drillcore (Drillcore X) fromthe KSF (ca. 25 km along strike from Drillcore 5A). Both cores show a similar kind of generally upwarddecreasing trend in �13C, excluding some negative and positive spikes in Drillcore X and samples closeto a contact with a Fe-picrite dyke in Drillcore 5A. A secular �13C curve of the KSF was constructed basedon the least altered �13C data from the cores 5A and X. The secular �13C curve of the KSF may representthe latest part of the Lomagundi-Jatuli isotopic excursion.

. Introduction

The Paleoproterozoic positive �13C excursion of sedimentaryarbonates provides evidence for a major perturbation in the globalarbon cycle (e.g. Baker and Fallick, 1989a,b). Based on well-dateduccessions, this event has been constrained to between ca. 2200nd 2100 Ma (Karhu and Holland, 1996). The extreme enrichmentn 13C was first reported from Jatulian sedimentary carbonatenits in Russian Karelia (Galimov et al., 1968), in the Peräpohjaelt of Finland (Schidlowski et al., 1975) and most thoroughly inhe Lomagundi Basin, Zimbabwe (Schidlowski et al., 1975, 1976).ccordingly, the excursion is here referred as the Lomagundi-Jatuli

sotopic excursion (LJIE). Since the first reports, the LJIE has beenocumented in many other localities worldwide, including Scot-

and (Baker and Fallick, 1989a), Ukraine (Zagnitko and Lugovaya,989), North America (e.g. Bekker et al., 2003a; Melezhik et al.,997), South-America (e.g. Bekker et al., 2003b), Africa (e.g. Bekker

t al., 2001; Buick et al., 1998), Australia (Lindsay and Brasier, 2002),ndia (e.g. Maheshwari et al., 1999; Sreenivas et al., 2001) andhina (Tang et al., 2011). On the Fennoscandian Shield, sedimentary

∗ Corresponding author. Tel.: +358 9 19150834; fax: +358 9 19150826.E-mail address: paula.salminen@helsinki.fi (P.E. Salminen).

301-9268/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.precamres.2013.01.005

© 2013 Elsevier B.V. All rights reserved.

carbonate successions with highly positive �13C values are knownin Norway (Baker and Fallick, 1989b; Melezhik and Fallick, 1996),Finland (e.g. Karhu, 1993), Sweden (Karhu, 1993; Melezhik andFallick, 2010) as well as in Karelia and Kola Peninsula in NW Russia(e.g. Karhu, 1993; Karhu and Melezhik, 1992; Melezhik et al., 1999;Melezhik and Fallick, 1996; Yudovich et al., 1991).

The shape of the Paleoproterozoic secular �13Ccarb trend is notknown in detail. The compilation of Karhu and Holland (1996)defined a single carbon isotope excursion lasting 100–200 Ma, butthe details of the curve are poorly known. Defining the shapeof the Paleoproterozoic secular �13Ccarb trend is important forchemostratigraphic purposes because chemostratigraphy can beused as a tool in correlating distant sections and global events inthe Proterozoic, where biostratigraphic correlation methods can-not be applied (e.g. Sial et al., 2010). The �13C values of marinesedimentary carbonate units reflect the �13 composition of dis-solved inorganic carbon (DIC) in seawater at the time of deposition(e.g. Holser et al., 1988). As the residence time of DIC in the oceans islonger than the mixing time of the oceans, the ocean basins are rel-atively homogeneous relative to the isotopic composition of carbon

and major �13C variations in marine carbonates can be correlatedover a wide area (e.g. Scholle and Arthur, 1980).

The Paleoproterozoic Kuetsjärvi Sedimentary Formation(KSF) of the Pechenga Greenstone Belt in the north eastern

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ennoscandian Shield is one of the sedimentary successions thatecords the LJIE. Previous investigations have reported high �13Calues in sedimentary carbonates, ranging from 2 to 10‰ (e.g.arhu, 1993; Karhu and Melezhik, 1992; Melezhik et al., 2003,004; Melezhik and Fallick, 1996, 2001, 2003). Drillcore-basedata suggest that the least-altered �13C values exhibit a smoothecreasing stratigraphic trend from 8.9 to 5.8‰ with severalhort-term positive and negative spikes with an amplitude up to.7‰ (Melezhik et al., 2005). Such spikes could be explained eithery unusually rapid restructuring of the global carbon reservoirr due to amplification by local factors in 13C-enrichement ineawater.

Consequently the objectives of this paper are (i) the investi-ation of lateral, basinal variations of �13Ccarb values by studyingnd comparison/contrasting two distant, densely sampled, coredections, (ii) the deciphering of local basinal factors possibly ampli-ying the global �13Ccarb value, and (iii) the construction of aetailed secular �13Ccarb curve by combining two datasets.

The objectives are achieved by investigation and detailed samp-ing of a core from a newly made drillhole that intersected the entirehickness of the Kuetsjärvi Sedimentary Formation. The obtainednalyses of carbon isotopic composition will be compared with data

eported from another cored section located at a distance of ca.5 km along strike (Melezhik et al., 2005).

Fig. 1. Location of (a) the Kuetsjärvi Sedimentary Formation and (b) D

search 228 (2013) 177– 193

2. Geological setting and lithostratigraphy

The KSF is a part of the Pechenga Greenstone Belt, which belongsto a larger, approximately 1000 km long, discontinuous volcano-sedimentary belt in the north-eastern part of the FennoscandianShield (e.g. Melezhik and Sturt, 1994) (Fig. 1). This larger belt hasbeen interpreted as an intracontinental rift developing into anintercontinental rift with a subsequent aborted oceanic phase andarc–continent collision (e.g. Melezhik and Sturt, 1994), but moreextensive ocean opening followed by oceanic floor subduction andarc–continent collision has also been suggested (Berthelsen andMarker, 1986).

The Pechenga Greenstone Belt comprises the North and SouthPechenga groups (e.g. Melezhik and Sturt, 1994). The KSF belongsto the North Pechenga Group, which consists of four pairedsedimentary–volcanic cycles (Fig. 1), separated by either non-depositional unconformities or faults (Melezhik and Sturt, 1994).Berthelsen and Marker (1986) suggested that the ca. 2400–2000 Masediments of the North Pechenga Group have been accumulatedin environments ranging from terrestrial through shallow- todeep-water marine. Melezhik and Fallick (2005) and Melezhiket al. (2005) interpreted the depositional environment of the KSF

as evolving from deltaic through shallow lacustrine to a sea-influenced rift-bound lake.

rillholes 5A and X. Modified from Melezhik and Fallick (2005).

P.E. Salminen et al. / Precambrian Research 228 (2013) 177– 193 179

F illcores

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ig. 2. Lithology of Drillcore 5A, the �13C and �18O values of the samples from Drmall-scale cavities) and surface cements.

The thickness of the KSF varies from 20 to 120 m. It haseen informally divided into Quartzite and Dolostone membersMelezhik and Fallick, 2005). The formation has been deposited on

paleo-weathering crust developed on top of the basaltic andesitesf the Ahmalahti Volcanic Formation and it is overlain by the sub-erially erupted volcanic rocks of the Kuetsjärvi Volcanic FormationMelezhik and Fallick, 2005; Predovsky et al., 1974).

A minimum depositional age of 2058 ± 2 Ma for the KSF haseen constrained from detrital zircons in volcaniclastic con-

lomerates within the Kuetsjärvi Volcanic Formation and in theverlying Kolosjoki Sedimentary Formation (Melezhik et al., 2007).he youngest detrital zircon age provides a robust depositionalge of the middle and upper parts of the Kuetsjärvi Volcanic

5A and the estimated proportion of dolomite crusts, carbonate fills (in veins and

Formation (Melezhik et al., 2007). A depositional age of the overly-ing Kolosjoki Sedimentary Formation has been recently constrainedat 2056.6 ± 0.8 Ma (Martin et al., 2013). A maximum depositionalage of 2505.1 ± 1.6 Ma for the KSF has been obtained from theMount Generalskaya gabbronorite intrusion (Amelin et al., 1995),which is erosively overlain by basal conglomerates of the Never-skrukk Formation; the lowermost formation in the North PechengaGroup (Fig. 1).

The metamorphic grade of the Pechenga Belt ranges

from prehnite–pumpellyite facies in the central part toepidote–amphibolite facies in the eastern and to amphibolitefacies (kyanite–staurolite zone) in the Western parts (Petrov andVoloshina, 1995). The KSF rocks have been exposed to epigenetic

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lteration by chemically reducing fluids which resulted in bleach-ng and discolouration of “red beds”, reduction of Fe3+ to Fe2+ andepletion in Fetot concentrations (Melezhik, 1992).

Previous research (e.g. Melezhik and Fallick, 2005) has shownhat carbonate rocks of the KSF include stromatolitic, micritic,parry and resedimented sandy dolostones. In places the dolo-tones have been dedolomitised. The siliciclastic rocks includeottled arkosic siltstone and hematite-bearing mudstone as well

s arkosic, quartzitic and tuffitic sandstone. Terrestrial siliciclas-ic and carbonate “red beds” are identified and subaerial exposureurfaces are common. Melezhik and Fallick (2001) reported hot-pring travertines, and Melezhik et al. (2004) recognised calichend silcrete.

.1. Drillcore 5A section

Hole 5A was drilled in the central part of the Pechengareenstone Belt (Fig. 1) by the FAR-DEEP (Fennoscandian Arcticussia–Drilling Early Earth Project) of the ICDP (International Sci-ntific Continental Drilling Program) to sample the KSF. DrillcoreA is the subject of the current research. Brief characteristics of theored rocks are presented below, whereas detailed core-log andhoto-documentation of main rocks types have been presented inalminen et al. (2013).

The ca. 158 m deep Hole 5A intersected ca. 117 m of the KSFs well as a few tens of metres of overlying and underlying vol-anic rocks. The cored succession underwent a greenschist faciesbiotite–actinolite zone) metamorphic alteration. The drilled KSFection has been informally subdivided into four members, whichrom the oldest to the youngest are the Arkosic, Lower Dolostone,uartzite and Upper Dolostone members (Fig. 2). The base of the

ormation lies at 145 m, on a paleo-weathering crust that waseveloped on the basaltic andesite lavas of the Ahmalahti Volcanicormation. The depositional top of the formation is defined by therst alkali basalts of the Kuetsjärvi Volcanic Formation at 24 m. The

ormation is intersected by a 5 m thick Fe-picrite dyke at 92–97 m.The Arkosic member (144.7–96.6 m) is a siliciclastic-

ominated unit whose basal part comprises a ca. 0.5 m thick,heared, banded, calcareous sericite–biotite–chlorite schist inter-reted as a paleo-weathering crust (e.g. Melezhik and Fallick, 2005).he basal schist has a transitional contact with a schistose basalticndesite of the Ahmalahti Volcanic Formation, which was alterednto a calcareous sericite–chlorite–albite–biotite–actinolite schist.he upper part of the member is in contact with a Fe-picrite dyke.he member is composed mainly of arkosic sandstone, calcareousiliciclastic rock (marl) and interbedded sandstone–siltstone–shaleith minor calcarenite, limestone and graywacke.

At 144.7–140.9 m, the succession contains rhythmicallynterbedded, low-angle cross-laminated and graded arkosicandstone, and parallel-laminated or low-angle cross-laminatediltstone and shale. The sandstone beds have erosional base. Theamination commonly shows syn-sedimentary disruption. Theseocks are overlain by sheared limestone–sandstone–siltstone140.9–136.0 m) with calcarenite and dolarenite beds; the lat-er contain intervals that preserve graded beds, low-angleross-lamination and lenticular bedding

At 136.0–132.6 m, the succession continues with dark-coloured,ndistinctly bedded graywacke that interlaminates with tectoni-ally modified sandstone–siltstone and intensely sheared shale.

hen primary structures are preserved, the rocks show parallel,enticular and trough cross-bedding.

The overlying unit (132.6–106.0 m) is composed of arkosic

andstone–siltstone having a sharp contact with the underly-ng graywacke–siltstone. This sandstone–siltstone unit is definedy irregular intercalation of dark-coloured, haematite-bearing,ne- to medium-grained sandstone beds (1–50 cm) and thinner

search 228 (2013) 177– 193

(0.5–10 cm), light-coloured siltstone. On a smaller scale, thesandstone–siltstone unit is characterised by parallel laminationand low-angle, tabular cross-bedding. Graded beds and small-scale,sand-filled channels are present. There is a general stratigraphictrend from fine- and medium-grained sandstone to fine-grainedsandstone (Salminen et al., 2013).

The uppermost part of the Arkosic member (106.0–96.7 m)includes irregularly interbedded arkosic sandstone, siltstone andcalcareous sandstone–siltstone with thin shale layers. The sand-stone has parallel and low-angle tabular and trough cross-bedding.The calcareous sandstone–siltstone shows parallel lamination.Some siltstone–shale beds have lensoidal lamination.

The Lower Dolostone member (92.0–52.2 m) has a tectonicallymodified contact with the underlying Fe-picrite dyke at 92.0 m.It comprises dolarenite, sparry dolostone, micritic dolostone, twoarkosic sandstone beds and 1- to 3-m-thick, dolomite-cemented,quartz sandstone layers. The lower part of the member is domi-nated by resedimented carbonates (mainly dolarenites), whereasthe upper part by sparry and micritic dolostones. All dolostonesshow mainly irregular bedding. Some dolarenite intervals exhibitcrude, parallel bedding whereas rare beds of micritic dolostonesare parallel laminated. Abundant clastic quartz grains are commonin carbonate beds. The quartz grains are regularly scattered, sorted,angular to rounded.

Evidence for erosional and dissolution processes can beobserved throughout the member. Some erosional surfaces areencrusted and cemented by silica or dolomite, which have beenidentified by previous workers as silcrete and calcrete, respectively(e.g. Melezhik et al., 2004). Veins and veinlets, small-scale dissolu-tion voids and cavities filled with quartz, dolomite and rare calciteare common. One to 10 cm thick, laminated, irregularly banded ormassive dolomite crusts are commonly associated with the dis-solution cavities and erosional surfaces. The carbonate fills andcrusts are variegated in colour. Small-scale stalactites, stalagmitesand mounds can be observed in some intervals. Dolomite precipi-tates similar to carbonate fills can also be found on uneven surfacesand cementing surface rock fragments. The proportion of thesesurface cement, dolomite crust and carbonate infill varies through-out the stratigraphy and averages at around 18% (Fig. 2). Similarcrusts as well as some cavity and void fills and veins elsewherein the KSF have been previously interpreted as hot springs traver-tine (Melezhik et al., 2004; Melezhik and Fallick, 2001). Based onmorphological similarities, small-scale stalactites, stalagmites andmounds observed in Drillcore 5A, have been tentatively interpretedas travertine (Salminen et al., 2013).

The Quartzite member (52.2–40.3 m) is a siliciclastic-dominated unit having a sharp lower contact with pale pinkdolarenite. It is composed mainly of quartzitic sandstone thoughthe basal part (52.2–51.5 m) consists of interbedded dolarenite,dolorudite and graywacke with large dolostone clasts. One doloru-dite bed contains angular clasts of dark-coloured jasper, with aproblematic structure, which may represent micro-stalactites ortectonically inverted micro-stromatolites. The boundary betweenthe Quartzite member and the underlying Lower Dolostonemember is defined by a subaerial exposure, erosion and incorpo-ration of previously deposited dolostone clasts in the overlyinggraywacke bed. The basal bed is sharply overlain by dark-grey,parallel-laminated graywacke, which passes into beige and greyparallel-laminated arkosic sandstone, followed by thickly interbed-ded, massive or indistinctly laminated quartz sandstone anddark-coloured clayey sandstone. Overall, this part of the mem-ber exhibits thinly laminated graywacke at the base followed by

parallel-bedded arkosic in the middle and, then, thickly beddedquartzitic sandstone on top, which defines a thickening-upwardsequence (Salminen et al., 2013). The quartzitic sandstones becomemore mature and indistinctly bedded up section. The uppermost

P.E. Salminen et al. / Precambrian Re

Fig. 3. Micritic dolostone (on the left and in the middle) and interbedded massiveaD

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sub-cycle have been interpreted to suggest a flooding event fol-

nd ripple cross-laminated sandstone (on the right) from the depth of ca. 40 m inrillcore 5A. Core diameter is ca. 5 cm.

art (ca. 1 m thick) of the member comprises thin, rhythmicallyedded, mud-draped sandstone units (Fig. 3). Some intervals show

enticular bedding.The Upper Dolostone member (ca. 40.3–23.7 m) has a sharp

rimary contact with the underlying rocks, whereas its upperontact with the Kuetsjärvi Volcanic Formation is tectonicallyodified. The member is composed of dolarenite, calcarenite,

tromatolitic dolostone, micritic dolostone (Fig. 3), limestone andalcareous sandstone–siltstone–shale (marl) and a quartz sand-tone bed at 28.9–28.4 m. The lower part of the member isominated by micritic dolostone, the middle part by stromatoliticolostone and the upper part by micritic dolostone, calcarenite and

ntensively sheared calcareous sandstone–siltstone–shale. All sed-mentary carbonate rocks have pink or variegated colour with a

ottled appearance. Bedding is irregular and disrupted by buck-ing, desiccation and dissolution processes.

Micritic dolostone, dolarenite and dolomitic sandstone–iltstone in the lower and middle parts of the member show crudearallel bedding. Some dolarenite beds in the upper part of theember have graded bedding and contain rounded and platy,

nsorted intraclasts of micritic and stromatolitic dolostones. Detri-al quartz grains are common in all types of dolostones.

Sromatolitic dolostones have flat lamination and an undulatoryr weakly domed structure and are typically composed of thin,rregular laminae of micritic dolomite and thicker layers of sparryolomite, containing intraclasts and quartz detritus. Silica-filledenestrae, voids and desiccation are common.

Like the Lower Dolostone member, the Upper Dolostone mem-er has also been affected by dissolution and erosion processes.he carbonate rocks contain filled voids and cavities whose size

ncreases progressively upward. Some cavities are filled with quartzandstone. Dolomite crusts show both upward and downwardrowth and also contain dissolution cavities. The crusts have

search 228 (2013) 177– 193 181

thickness ranging from a few centimetres to ca. 20 cm and theyhave laminated, massive or clotted fabric. The average proportionof dolomite crusts and carbonate fills in the total thickness is 18%(Fig. 2). Similar to the Lower Dolostone member such dolomitecrusts have been tentatively interpreted as travertine (Salminenet al., 2013).

Reconstruction of depositional environments of the KSFbased on the interpretation of sedimentary features documented incore from Drillhole 5A has been reported by Salminen et al. (2013)with a brief summary presented below.

The KSF has been considered as a succession comprising threesandstone-carbonate cycles of uneven thicknesses. The first cycle(ca. 9 m; the lower part the Arkosic member) comprises a sand-stone sub-cycle (immature arkosic arenite and siltstone) and acarbonate sub-cycle (calcareous sandstone–shale with minor cal-carenite). The sedimentological features of the sandstone sub-cycleare defined by thin layers of a fine to medium grain-size sandand fine silt. Both the sandstone and siltstone are characterisedby combination of parallel and low-angle cross-lamination, troughcross-bedding, normal grading and syn-sedimentary disruption.Some sandstone layers have an erosional base. The overall sedimen-tological pattern has been interpreted to represent deposition byturbidity currents and suspension fallout in a deltaic environment.The carbonate sub-cycle rocks show the combination of gradedbeds, low-angle cross-lamination and rare lenticular bedding. Thelatter may suggest influence of tides with the overall deposition ina tidally influenced delta-front setting (Salminen et al., 2013).

The second cycle (ca. 80 m) contains also two sub-cycles. Thefirst (ca. 30 m of the middle and upper parts of the Arkosic mem-ber) represents a succession fining upward from graywacke andshale to variegated, fine- and medium-grained arkosic arenites thatbecome progressively finer-grained towards the top. All lithologiesshow mainly parallel lamination and, less commonly, small-scaletabular and trough, low-angle cross lamination. Bedding surfacesare predominantly straight and sharp. The overall sedimentologicalfeatures have been interpreted to represent a deltaic environ-ment (Salminen et al., 2013). There is no obvious evidence oftidal reworking, though the lensoidal lamination in the uppermostsiltstone-shale interval might have been produced by tidal currents.

The overlying carbonate sub-cycle (ca. 40 m; the Lower Dolo-stone member) has a gradual contact through a ca. 10-m-thick unitof parallel-laminated, calcareous sandstone–siltstone with rarebeds of arkosic sandstone. The characteristic feature of sub-cyclecarbonate rocks is abundant clastic quartz, redeposition of previ-ously accumulated carbonate material, irregular, crude bedding orstratification affected by repetitive subaerial erosional and disso-lution processes. These features, together with numerous intervalscontaining apparent travertine crusts and mounds are very unlikelyconsistent with marine settings. In addition, there is no indication ofreworking by waves, apart from gentle, symmetrical sand-ripplescovered by travertine crust. Consequently, Salminen et al. (2013)have inferred a shallow lacustrine environment.

The third cycle (ca. 28 m), with similarly thick sandstone (theQuartzite member) and carbonate (the Upper Dolostone member)sub-cycles has a base marked by subaerial erosion and incor-poration of the previously deposited dolostones as clasts intothe lower part of the sandstone sub-cycle. The latter comprisesthe thickening-upward sequence followed by indistinctly bed-ded and chemically mature (95 wt% SiO2; Salminen et al., 2013)quartzitic sandstone with a metre-thick upper part composed ofthinly interbedded sandstone-mudstone couplets with lenticularbedding. The sedimentological features of the lower part of the

lowed by deposition of parallel-laminated and bedded sandstonesin a delta-front and/or prodelta environment which, at the end, wasinfluenced and reworked by tides (Salminen et al., 2013).

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The carbonate sub-cycle (the Upper Dolostone member) has sharp contact with the underlying tidally influenced siliciclas-ic unit. The basal bed is composed of pale pink and variegated,rudely bedded dolostones incorporating a significant amount ofeworked carbonate clasts followed by interval with flat-laminatednd desiccated stromatolites and red-coloured travertine, henceuggesting wide-spread subaerial and oxic conditions. The stro-atolites are associated with a thin interval containing three

olarenite units with mud drapes. In the upper part of the cycle,he dolostone show crude bedding, abundant intraclasts and highmpurity (40 wt% SiO2; Salminen et al., 2013). Amount of dis-olution voids progressively increase upward. Their size reachesimensions of microkarst (>10 cm in height). The sub-cycle endsith crudely bedded dolarenite and calcarenite sharply overlain

y calcareous shale buried under subaerially erupted volcanic rockseaching thickness of 2 km. The overall sedimentological featuresf the carbonate sub-cycle are consistent with a shallow-waternvironment affected by frequent erosional and dissolution pro-esses, and resedimentation. Although initially deposited on tidallynfluenced rocks, many features (e.g. stromatolite morphology, redolouration and abundant travertine) are not readily consistentith an open marine setting. Hence, a lacustrine environment has

een suggested as the most likely option (Salminen et al., 2013).hin, mud-draped dolarenite layers in the middle of the sub-cyclendicate that the lake was periodically influenced by tides, henceuggesting a short-term connection with sea and episodic inter-ention of seawater.

.2. Drillcore X section

Hole X has been drilled approximately 25 km northwest of Drill-ore 5A (Fig. 1). It has been investigated by Melezhik et al. (2003,004, 2005) and Melezhik and Fallick (1996, 2001, 2003). The lat-st description of the core and interpretation of the depositionaletting has been given by Melezhik and Fallick (2005). The succes-ion has been informally subdivided into Quartzite and Dolostoneembers (Melezhik and Fallick, 2005) (Fig. 4). Because the car-

on isotope record from Drillcore 5A will be compared in detailo that from Drillcore X, the stratigraphic sequence in Drillcore X isescribed shortly below based on the study by Melezhik and Fallick2005).

The base of the formation is defined by a paleo-weatheringrust (dolomitised phlogopite–chlorite–sericite schist) developedn amygdaloidal basaltic andesites of the Ahmalahti Volcanic For-ation.The Quartzite member is comparable to the Arkosic member

n the core 5A. Its basal beds are composed of arkosic sand-tone, sericitic mudstone, sandy, micritic dolostone, allochemicalolostone and flat-pebble conglomerate. This rock association isverlain by hematite-bearing sandstone and sericitic mudstone,hich are followed by mottled siltstone, hematite-rich sericiticudstone and subordinate sandy, sparry dolostone and limestone.

he topmost beds of the member consist of dolomite-cementeduartzitic and arkosic sandstone and sandy, micritic and sparryllochemical dolostone. The rocks in the Quartzite member of Drill-ore X have been interpreted to be deposited in distal braidplain,raided delta and lacustrine environments (Melezhik and Fallick,005).

The Dolostone member in Drillcore X is divided into twoarts by a siliciclastic dominated interval comparable to theuartzite member of the core 5A section. Below the siliciclasticnit, the member is composed of sparry and micritic dolostone,

nd dolarenite; all rocks contain quartz sand. These are followedy stromatolitic dolostone, dolarenite and sparry dolostone withravertine crusts, dolocrete and silcrete; probable evaporate (sul-hate) nodules replaced by dolomite have been observed. The

search 228 (2013) 177– 193

succession ends with sericite–chlorite mudstone and dolomitebreccias.

Beds above the siliciclastic unit are composed of dolarenite, algalmicritic dolostone and micritic dolostone containing travertinecrusts, dolocrete and silcrete; probable evaporate (sulphate) nod-ules replaced by dolomite have been reported. This rock assemblageis overlain by sheared micritic and sparry dolostones followed bytufaceous sandstone and dolostone breccia. The Dolostone mem-ber was interpreted by Melezhik and Fallick (2005) as a successionrecording lateral migration of carbonate-dominated shoreline andshallow-lacustrine settings, under a mostly arid climate.

The KSF rocks intersected by Drillcore X underwent greenschistfacies (biotite–actinolite zone) metamorphism (Melezhik et al.,2003).

3. Materials and methods

With a couple of exceptions, the samples were collected fromthe Upper and Lower Dolostone members. In addition, one whole-rock and one micro-drilled sample was obtained from dolarenitein the basal part of the Quartzite member. These samples are inthe following treated together with the samples from the LowerDolostone member.

In total, 48 samples were chosen for whole-rock analysis. Drill-core samples were crushed and powdered and analysed for theisotopic composition of carbon and oxygen, the elemental con-tent of total carbon, the whole-rock elemental composition byXRF and the composition of acid-soluble fraction by ICP-MS. Thedolomite/calcite ratio of the samples was determined by XRD.

The whole rock samples were supplemented by 58 micro-drilledsubsamples (ca. 10–20 mg) obtained from selected areas in thedrillcore using a 1.8 mm diamond grinding bit. Most of them wereobtained immediately above or below the whole-rock samples. Thesubsamples were analysed for the isotopic composition of carbonand oxygen and for the elemental composition of acid soluble frac-tion by ICP-MS.

The dolomite/calcite ratio of the samples was determinedby a Philips PW3020 powder diffraction goniometer, X’PertPW3710 MPD control unit and a PW1830 generator using a semi-quantitative X-ray diffraction (XRD) method.

The contents of Ctot were determined by a Vario Microcube CNSanalyser, using a sulphanilamide standard. The detection limit forCtot was 40 ppm, and based on 32 measurements of the referencematerial (NCS DC73306), the accuracy (1�) for the determinationof Ctot was 0.27 wt%. The contents of Stot were also analysed, but thelevels remained below the detection limit of 40 ppm in all samples.

The contents of SiO2, Al2O3, MgO, CaO, Na2O, K2O and P2O5in whole-rock samples were determined using a Philips PW1480X-ray fluorescence spectrometer. Based on multiple analyses ofreference samples (SARM 40, COQ-1), the average accuracy (1�)(excluding Na2O) was 6.8% and the average precision (1�) (exclud-ing Na2O) was 2.8%. The detection limits were 0.033 wt% forSiO2, 0.021 wt% for Al2O3, 0.003 wt% for CaO, 0.014 wt% for MgO,0.039 wt% for Na2O, 0.008 wt% for K2O and 0.006 wt% for P2O5. Theaccuracy and precision have not been determined for Na2O becauseits content was below the detection limit in most of the drillcoresamples and one of the reference materials (SARM40).

The concentrations of acid-soluble Mg, Ca, Mn, Sr and Fe weredetermined using an Agilent 7500ce/cx ICP-MS. Powdered samples(ca. 9–13 mg) were leached in 0.5 M acetic acid (5 ml) for 16 h underroom temperature. The final results were calculated in relation tothe acid soluble fraction. Duplicate samples and reference samples

(SARM 40, COQ-1) were analysed to estimate the quality of the pro-cedure. For the whole-rock analyses the average precision (1�) was14.0% including extraction. The detection limits for a 10 mg samplewere 2.9 ppm for Mg, 67.4 ppm for Ca, 0.3 ppm for Mn, 0.7 ppm for

P.E. Salminen et al. / Precambrian Research 228 (2013) 177– 193 183

F lues oF

Spff

aasovV

ig. 4. Lithostratigraphical profiles of Drillcores 5A and X and the �13C and �18O vaallick (2005) and Drillcore X data is adopted from Melezhik et al. (2005).

r and 3.0 ppm for Fe. For the micro-drilled samples the averagerecision (1�) was 7.6% including extraction. The detection limitsor a 10 mg sample were 9.2 ppm for Mg, 82.7 ppm for Ca, 0.9 ppmor Mn, 0.5 ppm for Sr and 4.7 ppm for Fe.

The isotopic composition of C and O was determined using Thermo Finnigan Delta Plus Advantage mass spectrometer in continuous flow mode. The isotopic composition was mea-

ured from phosphoric acid liberated CO2 gas using 125–170 �gf sample powder. The isotope ratios are expressed using the con-entional �-notation as a per-mil difference from the internationalPDB standard. An in-house dolomite quality standard indicated a

f the samples from the cores. Drillcore X lithology is simplified from Melezhik and

long-term reproducibility (1�) of 0.09‰ for C and 0.20‰ for O(n = 39). An in-house calcite quality standard indicated a repro-ducibility (1�) of 0.07‰ for C and 0.11‰ for O (n = 9).

All analytical work was done at the Department of Geosciencesand Geography, University of Helsinki.

4. Results

Results from Drillcore 5A are presented in Tables 1–3. Mn/Sr andMg/Ca weight ratios were calculated from the elemental contentsof the acid soluble (ICP-MS) fraction.

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Table 1Proportion of dolomite in total carbonate (XRD), the contents of Ctot and the XRF data of the whole-rock samples from Drillcore 5A.

Sample Top depth (m) Lithology Dol (wt%) Ctot (wt%) SiO2 (wt%) Al2O3 (wt%) MgO (wt%) CaO (wt%) Na2O (wt%) K2O (wt%) P2O5 (wt%)WR 5A1 24.66 Dolomitic calcarenite, sandy 14 7.99 19.81 0.79 12.38 34.42 0.10 <0.008 0.05WR 5A2 25.11 Micritic calcitic dolostone, sandy 68 10.12 9.36 1.03 16.11 33.17 0.20 <0.008 0.06WR 5A3 25.87 Dolomitic calcarenite, sandy 23 8.83 16.60 1.11 8.94 37.81 0.34 0.02 0.02WR 5A4 26.81 Micritic calcitic dolostone, partly

with quartz grains86 9.79 18.44 0.84 14.72 28.14 0.20 0.02 0.02

WR 5A5 27.00 Dolarenite, sandy 94 9.71 16.42 1.62 17.86 25.38 <0.039 0.32 0.03WR 5A12 30.61 Stromatolitic dolostone, sandy 98 9.82 17.19 1.41 17.74 24.92 <0.039 0.62 0.03WR 5A14 31.63 Stromatolitic dolostone, sandy 98 9.70 16.97 2.00 17.67 24.56 <0.039 0.87 0.02WR 5A15 32.10 Micritic dolostone, sandy 98 10.09 15.20 1.31 18.30 25.51 <0.039 0.61 0.04WR 5A16 32.51 Stromatolitic dolostone, sandy 99 10.64 11.02 1.65 18.90 26.48 <0.039 0.73 0.02WR 5A17 32.76 Stromatolitic dolostone, sandy 100 8.24 26.43 3.27 15.24 20.73 <0.039 1.46 0.03WR 5A18 33.78 Micritic dolostone 100 10.20 14.03 1.96 18.27 25.38 <0.039 0.84 0.03WR 5A19 34.42 Dolarenite, abundant quartz

grains100 8.52 31.76 0.66 14.83 20.67 <0.039 0.34 0.02

WR 5A21 35.42 Stromatolitic dolostone, sandy, 99 10.12 16.26 2.29 17.65 24.47 <0.039 1.05 0.05WR 5A25 37.38 Micritic dolostone, sandy 100 9.65 20.91 1.62 16.75 23.45 <0.039 0.71 0.03WR 5A26 38.29 Micritic dolostone, sandy, quartz

grains100 9.33 25.06 1.01 15.93 22.55 <0.039 0.50 0.09

WR 5A27 39.30 Micritic dolostone, quartz grains,clayey material

98 10.19 15.85 1.83 17.93 24.78 <0.039 0.84 0.07

WR 5A29 51.84 Dolarenite, sandy 98 11.91 5.20 0.75 19.64 29.00 <0.039 0.32 0.23WR 5A30 52.74 Micritic dolostone, quartz grains 99 10.76 14.34 0.90 17.99 26.05 <0.039 0.62 0.09WR 5A35 55.83 Micritic dolostone 99 10.79 15.25 0.50 17.80 26.18 <0.039 0.27 0.10WR 5A41 59.24 Micritic dolostone, quartz grains 99 11.11 13.91 1.10 18.33 25.92 <0.039 0.51 0.05WR 5A42 59.80 Micritic dolostone, quartz grains,

slightly brecciated99 10.45 19.07 1.01 17.25 24.47 <0.039 0.41 0.10

WR 5A45 60.94 Micritic dolostone, quartz grains,slightly brecciated

99 9.46 26.78 1.00 15.51 22.17 <0.039 0.46 0.08

WR 5A46 61.56 Micritic dolostone, slighlybrecciated

99 12.67 3.90 0.29 20.22 29.91 <0.039 0.15 0.17

WR 5A52 63.29 Micritic dolostone, abundantquartz grains

98 10.07 22.77 0.76 16.25 23.71 <0.039 0.49 0.08

WR 5A53 63.45 Micritic dolostone, abundantquartz grains

98 8.44 34.79 0.88 13.82 19.83 <0.039 0.47 0.05

WR 5A54 64.14 Micritic dolostone, brecciated 98 13.02 2.09 0.16 20.66 30.69 <0.039 0.04 0.13WR 5A55 64.56 Micritic dolostone, slightly

brecciated97 12.59 3.00 1.09 20.55 29.49 <0.039 0.40 0.18

WR 5A60 67.55 Dolarenite, quartz grains 98 9.01 29.66 1.27 14.98 21.05 <0.039 0.67 0.04WR 5A62 68.45 Dolarenite, quartz grains 99 11.04 16.17 0.29 17.70 25.98 <0.039 0.10 0.07WR 5A64 69.37 Dolarenite, sandy, quartz grains 92 9.62 26.13 0.60 13.95 24.73 <0.039 0.26 0.10WR 5A67 70.56 Dolarenite, sandy, quartz grains 100 8.65 32.36 0.97 14.72 20.27 <0.039 0.46 0.09WR 5A68 71.01 Micritic dolostone, quartz grains 100 11.82 10.81 0.26 19.07 27.53 <0.039 0.11 0.05WR 5A72 73.73 Micritic dolostone, slightly

brecciated100 13.13 1.39 0.09 21.16 30.50 <0.039 0.03 0.09

WR 5A73 74.75 Micritic dolostone, brecciated 100 13.08 1.78 0.30 21.12 30.09 <0.039 0.11 0.05WR 5A75 75.57 Micritic dolostone 100 11.40 14.91 0.22 18.25 26.24 <0.039 0.09 0.04WR 5A84 78.44 Micritic dolostone, slightly

brecciated98 13.25 1.32 0.20 21.06 30.51 <0.039 0.08 0.11

WR 5A89 79.75 Dolarenite, sandy, quartz grains 97 9.28 26.64 1.27 16.02 22.04 <0.039 0.67 0.09WR 5A90 80.98 Dolarenite, some quartz grains 100 11.52 13.37 0.30 18.63 26.68 <0.039 0.14 0.08WR 5A100 83.51 Dolarenite, some quartz grains 100 12.11 6.78 0.19 20.04 28.78 <0.039 0.10 0.02WR 5A101 84.18 Dolarenite, some quartz grains 99 11.13 13.39 0.35 18.62 26.67 <0.039 0.19 0.08WR 5A103 85.22 Micritic dolostone, brecciated 100 12.76 1.14 0.29 21.32 30.30 <0.039 0.12 0.07WR 5A104 85.99 Micritic dolostone, some quartz

grains, slightly brecciated99 12.12 5.89 0.21 20.14 29.16 <0.039 0.09 0.12

WR 5A105 86.30 Micritic dolostone, some quartzgrains, brecciated

100 12.63 2.38 0.21 20.90 30.19 <0.039 0.10 0.09

WR 5A106 86.98 Dolarenite, sandy, abundantquartz grains

100 7.68 38.24 0.71 13.58 18.61 <0.039 0.35 0.01

WR 5A108 89.23 Dolarenite, some quartz grains,with sandy layer

99 10.95 14.52 0.46 18.53 26.18 <0.039 0.15 0.05

WR 5A109 90.52 Micritic dolostone, brecciated,with quartz grains and chloriteveinlets

99 9.84 21.80 0.68 17.36 23.55 <0.039 0.10 0.03

WR 5A110 91.68 Micritic dolostone, slightlybrecciated

100 12.76 1.75 0.16 21.10 30.19 <0.039 <0.008 0.06

WR 5A111 91.89 Micritic dolostone, brecciated,with quartz grains and chloriteveinlets

100 11.55 9.58 0.43 19.31 27.34 <0.039 <0.008 0.02

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Table 2The isotopic composition of C and O and the elemental composition of acid-soluble fraction of the whole-rock samples from Drillcore 5A.

Sample Top depth (m) Lithology �13Ccarb, VPDB (‰) �18Ocarb, VPBD (‰) Mg/Ca Mn/Sr Ca (ppm) Mg (ppm) Mn (ppm) Sr (ppm) Fe (ppm)

WR 5A1 24.66 Dolomitic calcarenite, sandy 4.9 −17.6 0.09 0.93 264,408 23,249 847 915 1997WR 5A2 25.11 Micritic calcitic dolostone, sandy 6.2 −17.4 0.35 0.36 243,686 84,606 205 575 1698WR 5A3 25.87 Dolomitic calcarenite, sandy 6.1 −16.5 0.10 0.63 248,913 25,424 301 480 1101WR 5A4 26.81 Micritic calcitic dolostone, partly with quartz

grains6.7 −15.0 0.49 0.99 229,666 112,098 241 244 1619

WR 5A5 27.00 Dolarenite, sandy 6.6 −14.7 0.62 1.32 167,003 104,258 231 175 3313WR 5A12 30.61 Stromatolitic dolostone, sandy 6.6 −12.0 0.65 0.50 240,016 155,291 165 332 1875WR 5A14 31.63 Stromatolitic dolostone, sandy 6.7 −12.6 0.65 0.74 183,792 119,712 179 242 2502WR 5A15 32.10 Micritic dolostone, sandy 6.7 −12.2 0.65 0.68 205,312 133,574 176 261 2216WR 5A16 32.51 Stromatolitic dolostone, sandy 7.1 −13.0 0.68 0.53 190,934 128,893 120 227 1720WR 5A17 32.76 Stromatolitic dolostone, sandy 7.2 −13.0 0.67 0.78 187,949 126,648 172 221 2427WR 5A18 33.78 Micritic dolostone 7.2 −12.4 0.67 0.61 195,201 130,634 150 244 1647WR 5A19 34.42 Dolarenite, abundant quartz grains 7.2 −12.5 0.69 0.41 165,817 114,729 84 205 784WR 5A21 35.42 Stromatolitic dolostone, sandy, 7.1 −12.2 0.66 1.44 194,342 127,570 336 233 1322WR 5A25 37.38 Micritic dolostone, sandy 7.5 −12.4 0.67 1.08 214,016 143,462 280 259 1502WR 5A26 38.29 Micritic dolostone, sandy, quartz grains 7.3 −13.3 0.66 2.25 226,277 149,450 545 242 3329WR 5A27 39.30 Micritic dolostone, quartz grains, clayey

material7.5 −14.0 0.65 3.82 202,521 132,208 808 212 4333

WR 5A29 51.84 Dolarenite, sandy 8.0 −12.4 0.65 19.78 214,577 139,100 2148 109 7651WR 5A30 52.74 Micritic dolostone, quartz grains 7.7 −12.5 0.67 20.97 213,043 142,004 2059 98 2903WR 5A35 55.83 Micritic dolostone 7.7 −11.2 0.66 4.45 196,234 129,073 410 92 1410WR 5A41 59.24 Micritic dolostone, quartz grains 7.5 −11.2 0.67 6.66 199,385 132,682 552 83 3083WR 5A42 59.80 Micritic dolostone, quartz grains, slightly

brecciated7.6 −11.6 0.67 7.93 173,932 115,697 553 70 2145

WR 5A45 60.94 Micritic dolostone, quartz grains, slightlybrecciated

7.6 −12.0 0.67 4.50 187,794 125,322 382 85 1811

WR 5A46 61.56 Micritic dolostone, slighly brecciated 7.5 −12.0 0.66 5.11 162,604 107,655 432 84 1613WR 5A52 63.29 Micritic dolostone, abundant quartz grains 7.5 −11.7 0.66 4.68 157,427 103,840 376 80 1508WR 5A53 63.45 Micritic dolostone, abundant quartz grains 7.6 −11.9 0.66 3.55 164,235 108,675 311 88 1771WR 5A54 64.14 Micritic dolostone, brecciated 7.6 −11.6 0.65 4.68 166,875 108,129 345 74 967WR 5A55 64.56 Micritic dolostone, slightly brecciated 7.8 −11.7 0.66 6.94 165,670 109,649 606 87 2182WR 5A60 67.55 Dolarenite, quartz grains 7.7 −12.5 0.66 8.70 149,107 98,661 499 57 2071WR 5A62 68.45 Dolarenite, quartz grains 7.5 −12.4 0.67 15.66 162,856 108,922 870 56 2219WR 5A64 69.37 Dolarenite, sandy, quartz grains 7.3 −12.8 0.53 8.34 181,767 96,313 588 71 1656WR 5A67 70.56 Dolarenite, sandy, quartz grains 7.3 −12.3 0.67 9.99 171,845 114,386 625 62 1936WR 5A68 71.01 Micritic dolostone, quartz grains 7.6 −12.1 0.67 7.11 182,479 122,436 435 61 1530WR 5A72 73.73 Micritic dolostone, slightly brecciated 7.9 −11.3 0.65 5.83 184,739 119,544 383 66 1160WR 5A73 74.75 Micritic dolostone, brecciated 8.0 −10.8 0.66 3.53 182,861 120,899 256 73 997WR 5A75 75.57 Micritic dolostone 7.6 −11.7 0.65 4.99 185,583 121,017 365 73 1172WR 5A84 78.44 Micritic dolostone, slightly brecciated 8.1 −11.7 0.64 3.64 194,397 124,340 317 87 1095WR 5A89 79.75 Dolarenite, sandy, quartz grains 7.8 −13.2 0.62 5.54 190,579 118,548 442 80 2659WR 5A90 80.98 Dolarenite, some quartz grains 8.1 −13.0 0.65 4.88 182,688 118,038 291 60 1044WR 5A100 83.51 Dolarenite, some quartz grains 8.3 −12.0 0.66 2.06 164,773 108,675 173 84 666WR 5A101 84.18 Dolarenite, some quartz grains 8.0 −12.9 0.67 6.91 303,805 202,561 699 101 2486WR 5A103 85.22 Micritic dolostone, brecciated 8.2 −12.6 0.65 3.50 184,928 120,975 279 80 946WR 5A104 85.99 Micritic dolostone, some quartz grains,

slightly brecciated8.0 −13.4 0.64 3.85 278,722 178,331 484 126 1911

WR 5A105 86.30 Micritic dolostone, some quartz grains,brecciated

8.1 −13.9 0.64 3.63 198,666 127,594 328 90 969

WR 5A106 86.98 Dolarenite, sandy, abundant quartz grains 8.2 −14.1 0.66 3.07 189,091 124,035 369 120 2035WR 5A108 89.23 Dolarenite, some quartz grains, with sandy

layer8.0 −16.2 0.66 3.52 198,689 130,489 348 99 1556

WR 5A109 90.52 Micritic dolostone, brecciated, with quartzgrains and chlorite veinlets

7.6 −16.5 0.66 4.88 312,921 207,223 907 186 3931

WR 5A110 91.68 Micritic dolostone, slightly brecciated 7.7 −16.4 0.65 4.68 202,522 130,801 507 108 2144WR 5A111 91.89 Micritic dolostone, brecciated, with quartz

grains and chlorite veinlets7.2 −16.7 0.65 9.10 185,908 121,384 1046 115 7402

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Table 3The isotopic composition of C and O and the elemental composition of acid-soluble fraction of the micro-drilled subsamples from Drillcore 5A.

Subsample Depth (m) Lithology �13Ccarb, VPDB (‰) �18Ocarb, VPDB (‰) Mg/Ca Mn/Sr Ca (ppm) Mg (ppm) Mn (ppm) Sr (ppm) Fe (ppm)

MD 5A1 24.64 Dolomitic calcarenite, sandy 5.1 −17.5 0.02 1.14 270,089 6240 1231 1083 2806MD 5A2A 25.20 Micritic calcitic dolostone,

sandy6.3 −17.2 0.43 0.36 197,366 85,454 161 452 1426

MD 5A2B 25.19 Micritic calcitic dolostone,sandy

6.1 −18.0 0.31 0.30 202,726 63,597 162 539 1389

MD 5A3 25.98 Dolomitic calcarenite, sandy,siliceous

6.6 −15.4 0.45 0.77 153,922 68,601 214 277 1831

MD 5A4 26.92 Micritic calcitic dolostone,sandy, quartz grains

6.9 −14.1 0.53 0.92 170,909 90,469 178 193 1024

MD 5A9 28.77 Dolarenite, sandy, quartzgrains

7.0 −12.6 0.71 0.77 135,640 95,703 127 166 2440

MD 5A12 30.70 Stromatolitic dolostone, sandy 6.9 −11.7 0.69 0.39 127,072 87,937 84 213 1080MD 5A14 31.72 Stromatolitic dolostone, sandy 7.0 −12.8 0.68 0.71 146,781 100,329 164 230 2979MD 5A15 32.09 Micritic dolostone, sandy 6.6 −12.7 0.66 0.72 119,534 79,194 127 176 2129MD 5A16 32.60 Stromatolitic, micritic

dolostone, sandy7.0 −12.5 0.68 0.41 120,284 81,909 70 170 1203

MD 5A17 32.83 Stromatolitic, micriticdolostone, sandy

7.3 −12.9 0.68 0.61 119,608 81,149 100 165 1583

MD 5A18 33.88 Micritic dolostone, sandy 7.1 −11.9 0.68 0.50 119,037 81,024 85 173 981MD 5A19 34.40 Dolarenite, sandy, quartz

grains7.3 −13.0 0.67 0.42 130,682 87,277 77 185 934

MD 5A21 35.41 Stromatolitic dolostone, sandy 7.1 −12.6 0.68 1.28 172,109 117,618 315 246 1596MD 5A24 37.19 Micritic dolostone, sandy,

quartz grains7.3 −12.9 0.68 1.23 127,743 86,744 222 180 1581

MD 5A25 37.38 Micritic dolostone, sandy,quartz grains

7.3 −13.2 0.67 1.07 143,371 96,424 232 218 1364

MD 5A26 38.39 Dolarenite, sandy, quartzgrains

7.4 −12.9 0.65 1.87 150,191 97,807 365 196 2641

MD 5A27 39.25 Micritic dolostone, sandy 7.3 −14.6 0.67 3.85 122,519 81,523 578 150 3096MD 5A29 51.94 Dolarenite, sandy 7.8 −12.6 0.65 14.47 149,631 96,839 1173 81 5591MD 5A30A 52.83 Micritic dolostone, sandy,

quartz grains7.5 −12.2 0.67 17.81 144,666 96,224 1397 78 2325

MD 5A30B 52.85 Micritic dolostone, sandy,quartz grains

7.6 −12.5 0.64 16.68 148,432 95,638 1401 84 2684

MD 5A34 54.96 Micritic dolostone, quartzgrains

7.7 −11.1 0.67 7.47 132,345 89,062 516 69 2716

MD 5A35 55.81 Micritic dolostone, sandy,quartz grains

7.7 −10.4 0.67 4.80 125,087 83,697 316 66 1570

MD 5A41 59.21 Micritic dolostone, quartzgrains

7.5 −11.6 0.66 4.12 111,850 74,291 215 52 950

MD 5A42 59.92 Micritic dolostone, quartzgrains

7.5 −11.9 0.66 9.55 150,532 98,853 705 74 2989

MD 5A45 61.05 Micritic dolostone, quartzgrains

7.6 −12.0 0.69 3.85 146,405 100,597 304 79 1319

MD 5A46 61.69 Micritic dolostone, siliceous 7.7 −11.5 0.66 3.59 160,450 106,684 291 81 1239MD 5A52A 63.27 Micritic dolostone, quartz

grains7.5 −12.4 0.66 8.51 118,670 78,543 513 60 2375

MD 5A52B 63.25 Micritic dolostone, quartzgrains

7.4 −13.0 0.58 4.20 119,849 69,999 259 62 1374

MD 5A53 63.51 Micritic dolostone, laminaewith quartz grains

7.9 −12.3 0.70 3.61 105,491 74,135 178 49 1098

MD 5A54 64.12 Micritic dolostone, somequartz grains and sparite

7.7 −12.4 0.68 4.84 143,022 97,131 319 66 1028

MD 5A55 64.53 Micritic dolostone, brecciated 7.8 −11.8 0.68 7.24 164,842 111,292 608 84 2803MD 5A56 64.72 Micritic dolostone 7.7 −12.2 0.66 6.70 145,092 96,056 445 66 1436

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Table 3 (Continued)

Subsample Depth (m) Lithology �13Ccarb, VPDB (‰) �18Ocarb, VPDB (‰) Mg/Ca Mn/Sr Ca (ppm) Mg (ppm) Mn (ppm) Sr (ppm) Fe (ppm)

MD 5A58 66.85 Dolarenite 7.7 −12.6 0.66 2.86 141,347 93,315 117 41 283MD 5A60 67.63 Dolarenite, sandy, slightly

brecciated7.8 −12.5 0.72 10.25 93,477 66,885 330 32 1504

MD 5A62 68.44 Dolarenite, abundant quartzgrains

7.3 −12.6 0.64 21.94 149,691 96,286 1038 47 2715

MD 5A64 69.46 Dolarenite 7.5 −12.3 0.70 7.42 122,738 85,586 320 43 1242MD 5A67 70.53 Dolarenite, quartz grains 7.7 −12.3 0.70 9.27 100,982 70,850 344 37 1102MD 5A68 71.00 Micritic dolostone 7.6 −12.0 0.67 7.30 153,488 103,446 363 50 1106MD 5A72 73.71 Micritic dolostone, slightly

brecciated8.0 −10.9 0.70 5.68 115,513 80,397 219 38 948

MD 5A73 74.74 Micritic dolostone, brecciated 8.0 −10.5 0.71 2.98 151,817 107,649 198 66 882MD 5A75 75.56 Micritic dolostone, slightly

brecciated7.8 −11.3 0.69 4.77 148,482 102,308 294 62 926

MD 5A82 77.63 Dolarenite, abundant quartzgrains

8.1 −12.3 0.70 3.73 123,107 86,125 228 61 1437

MD 5A84 78.54 Micritic dolostone 8.1 −12.3 0.67 2.96 147,180 98,702 162 55 531MD 5A89 79.73 Dolarenite, sandy, some quartz

grains8.0 −13.3 0.70 4.82 120,787 84,587 240 50 1514

MD 5A90 81.09 Dolarenite, some quartz grains 8.1 −12.8 0.69 2.59 141,438 97,295 122 47 425MD 5A100 83.48 Dolarenite, some quartz grains 8.2 −13.0 0.69 3.81 132,537 90,860 201 53 810MD 5A101 84.16 Dolarenite, some quartz grains 7.8 −13.0 0.68 6.30 157,025 106,579 314 50 1160MD 5A103A 85.20 Micitic dolostone 8.3 −12.8 0.69 2.74 147,008 100,797 185 68 942MD 5A103B 85.21 Micitic dolostone 8.3 −12.5 0.71 2.97 137,910 98,395 175 59 689MD 5A104 86.08 Micritic dolostone, some

quartz grains7.9 −13.6 0.70 2.78 147,969 103,183 166 60 685

MD 5A105 86.42 Micritic dolostone, brecciated 8.3 −13.9 0.68 2.08 140,341 95,362 130 63 374MD 5A106A 86.98 Dolarenite, sandy, quartz

grains8.0 −14.0 0.71 3.67 68,856 48,791 134 37 791

MD 5A106B 86.96 Dolarenite, sandy, quartzgrains

7.9 −14.4 0.70 3.06 124,209 87,510 241 79 1464

MD 5A108 89.21 Dolarenite, some quartz grains 7.9 −16.0 0.70 2.76 150,293 105,319 183 66 2281MD 5A109 90.52 Micritic dolostone, some

quartz grains, brecciated7.7 −16.6 0.69 3.43 165,084 113,333 314 92 1527

MD 5A110 91.79 Micritic dolostone, slightlybrecciated

7.8 −16.6 0.69 3.68 129,569 88,984 247 67 1132

MD 5A111 91.99 Micritic dolostone, brecciated 7.5 −16.7 0.67 10.97 149,116 99,982 921 84 7236

188 P.E. Salminen et al. / Precambrian Re

0 5 10

15

20

20

40

60

80

Ctot (wt%)

Depth(m)

Whole-rock (Group 1)

Whole-rock (Group 2)

Whole-rock (Group 3)

0 10

20

30

40

20

40

60

80

SiO2 (wt%)

0 1 2 3 4

20

40

60

80

Al2O3 (wt%)

0 0.1

0.2

0.3

20

40

60

80

P2O5 (wt%)

Fig. 5. Ctot, SiO2, Al2O3 and P2O5 contents of the whole-rock samples from Drillcore5

ncic(

2S1KciycTdm0w

0u

The Mn/Sr ratios of sedimentary carbonates can be used to esti-

A.

XRD determinations indicate that most whole-rock samples areearly pure dolostones. The uppermost samples contain more cal-ite (14–86 wt% of the total carbonate), and accordingly, they aredentified as dolomitic limestones and calcitic dolostones. The Ctot

ontent of the whole-rock samples varies from 7.7 to 13.3 wt%Fig. 5).

The MgO content of the whole rock samples varies from 8.9 to1.3 wt% and the CaO content from 18.6 to 37.8 wt%. The averageiO2 content of the whole-rock samples is 15.5 wt%, varying from.1 to 38.2 wt% (Fig. 5). The high SiO2 content relative to Al2O3,2O and Na2O implies that the main siliciclastic component in thearbonate rocks is quartz; this is complemented by petrographicnvestigations. The average Al2O3 content in the whole rock anal-ses is 0.9 wt%, varying from 0.1 to 3.3 wt% (Fig. 5). The averageontent of K2O is low (0.4 wt%) with a range from <0.008 to 1.5 wt%.he concentration of Na2O in most of the samples is below theetection limit of 0.04 wt%, and only four samples from the upper-ost part of the section contain measurable contents of Na2O, from

.1 to 0.3 wt%. The P2O5 content is low, from 0.01 to 0.2 wt% (Fig. 5),ith an average value at 0.07 wt%.

The average Mg/Ca ratio of the dolomitic whole-rock samples is.65 and that for the micro-drilled samples is 0.68 (Fig. 6). The fourppermost samples have lower Mg/Ca ratios between 0.1 and 0.5.

search 228 (2013) 177– 193

In general, the Mg/Ca ratios are almost identical in whole-rock andmicro-drilled samples.

The Mn/Sr ratios are higher in the Lower Dolostone member(2.1–22) than in the Upper Dolostone member (0.30–3.9), withthe same pattern in the whole-rock and the micro-drilled samples(Fig. 6). The Mn/Sr ratios are often higher in dolarenite samplesas compared to micritic samples. The Mn/Sr ratios are also ele-vated in samples close to the Quartzite member and the Fe-picritedyke.

The average Mn content is higher in the Lower Dolostone mem-ber (whole-rock samples 580 ppm, micro-drilled samples 400 ppm)than that in the Upper Dolostone member (whole-rock samples300 ppm, micro-drilled samples 250 ppm) (Fig. 6). The Mn contentshows a generally upward decreasing trend.

The average Sr content is higher in the Upper Dolostone mem-ber (whole-rock samples 320 ppm, micro-drilled samples 280 ppm)than that in the Lower Dolostone member (whole-rock samples88 ppm, micro-drilled samples 61 ppm) (Fig. 6). The Sr contentshows an increasing trend upward in the section.

The Fe content of the whole-rock samples varies widely, from ca.670 to 7700 ppm (a sample below the Quartzite member) (Fig. 6).The variation in the Fe content (280–7200 ppm) in the micro-drilledsamples is similar to that in the whole-rock samples (Fig. 6). Theaverage amount of Fe in the whole-rock samples is 2100 ppm andin the micro-drilled samples 1700 ppm.

The whole-rock �13C values vary from 7.2 to 8.3‰ (VPDB, aver-age 7.8‰) in the Lower Dolostone member and from 4.9 to 7.5‰(average 6.8‰) in the Upper Dolostone member (Figs. 2 and 4).The �13C values of the micro-drilled samples vary from 7.3 to8.3‰ (average 7.8‰) in the Lower Dolostone member and from5.1 to 7.4‰ (average 6.9‰) in the Upper Dolostone member(Figs. 2, 4 and 8). The differences in the �13C values between thewhole-rock and micro-drilled samples from comparable depths aresystematically <0.5‰. Both the whole rock and the micro-drilledsamples show a generally decreasing �13C trend upward in thesuccession.

The whole-rock �18O values vary from −16.7 to −10.8‰ (VPDB,−12.8‰ on average) in the Lower Dolostone member and from−17.6 to −12.0‰ (−13.8‰ on average) in the Upper Dolostonemember (Figs. 2 and 4). The �18O values of the micro-drilled sam-ples vary from −16.7 to −10.4‰ (−12.8‰ on average) in the LowerDolostone member and from −18.0 to −11.7‰ (−13.8‰ on aver-age) in the Upper Dolostone member (Figs. 2 and 4). The variationin the �18O values is similar in the whole-rock and the micro-drilled samples. The lowest �18O values are in samples obtainedclose to the Fe-picrite dyke and in the dolomitic limestone and cal-citic dolostone samples from the top. The differences in the �18Ovalues between the whole-rock and the micro-drilled samples fromcomparable depths vary from zero to 1.3‰.

Two separate subsamples were micro-drilled from five sam-ples. The differences in the values between the subsamples werenegligible (0–0.2‰) for �13C and small (0.3–0.8‰) for �18O.

Carbon and oxygen isotope and elemental data from the whole-rock and micro-drilled samples were in general similar to eachother (Figs. 2, 4 and 6). However, a minor difference can be observedin the Mn and Sr concentrations, which are systematically lower inthe micro-drilled samples.

5. Discussion

5.1. Post-depositional alteration

mate the effects of meteoric diagenesis on the primary carbonisotope ratios (e.g. Kaufman and Knoll, 1995; Veizer, 1983). Carbon-ate rocks affected by meteoric waters are usually depleted in Sr and

P.E. Salminen et al. / Precambrian Research 228 (2013) 177– 193 189

0 0.2

0.4

0.6

0.8

20

40

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80

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0.10.2 1 2 1020

20

40

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80

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Whole-rock (Group 2)

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20

100

200

1000

2000

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40

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80

Mn

1020

100

200

1000

2000

20

40

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80

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200

1000

2000

10000

20000

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40

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80

, Sr an

eiNea

LbeQm

eicpmpb

bd

Mg/Ca Mn/Sr

Fig. 6. The Mg/Ca and Mn/Sr ratios and the Mn

nriched in Mn, leading to high Mn/Sr ratios. Mn/Sr ratios exceed-ng 10 have been proposed to imply post-depositional alteration ineoproterozoic dolostones (Kaufman and Knoll, 1995). Melezhikt al. (1999, 2005) suggested that Mn/Sr ratios of >6 may implylteration of primary �13C values in Paleoproterozoic dolostones.

In Drillcore 5A, the Mn/Sr ratios of carbonate are higher in theower Dolostone member than in the Upper Dolostone member,ut in general all Mn/Sr ratios remain <10. Higher Mn/Sr valuesxceeding 10 are met in the samples from the basal part of theuartzite member and in a few samples of the Lower Dolostoneember.The samples can be divided into three groups with distinct

lemental and isotopic characteristics. Group 1 contains the major-ty of samples, from 29 to 89 m. Group 2 includes the uppermostalcite-bearing samples (5 whole-rock and 4 micro-drilled sam-les). Group 3 comprises the samples (4 whole-rock and 4icro-drilled samples) close to the contact with the underlying Fe-

icrite dyke. The whole dataset shows a weak positive correlation

etween the �13C and �18O values (r = +0.40).

The dolomite samples of Group 1 do not show any correlationetween the �13C and �18O values. Furthermore, the Mn/Sr ratioso not correlate with either the �13C or �18O values (Fig. 7). It can be

(ppm) Sr (ppm ) Fe (ppm )

d Fe contents of the samples from Drillcore 5A.

concluded that the primary carbon isotope composition has likelybeen retained in the samples of Group 1.

The samples in Group 2 have distinctly lower �13C and �18Ovalues in comparison to those in the underlying Group 1. The �13Cand �18O values show moderate, but statistically insignificant, pos-itive correlation (Fig. 7). The Mn/Sr ratios are low and do not showsignificant correlation with either the �13C or �18O values (Fig. 7).Based on the lack of covariation, the isotope signatures of carbon inthe calcite-bearing samples of Group 2 are judged to have retainedtheir original depositional values.

Group 3 samples have distinctively (2–3‰) lower �18O val-ues and ca. 1‰ lower �13C values than the respective values inGroup 1. In the whole-rock samples from Group 3, the Mn/Sr ratiosshow strong negative correlation with the �13C values (r = −0.97)and �18O values (r = −0.96) (Fig. 7). In the micro-drilled samples,the Mn/Sr ratios are highly correlative with the �13C values andmoderately correlative with �18O values, but the correlations arestatistically insignificant. The �13C and �18O values show strong

(r = +1.00) positive correlation in the whole-rock samples and mod-erate (r = +0.68) but statistically insignificant correlation in themicro-drilled samples (Fig. 7). Co-variations between Mn/Sr, �13Cand �18O are interpreted to indicate alteration of the primary

190 P.E. Salminen et al. / Precambrian Research 228 (2013) 177– 193

4 5 6 7 8 9

-18

-16

-14

-12

-10

13CVPDB ,0/00

18OVPDB,0/ 00

Micro-drilled (Group 1)

Micro-drilled (Group 2)

Micro-drilled (Group 3)

Whole-rock (Group 1)

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4 5 6 7 8 90

5

10

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25

13CVPDB ,0/00

Mn/Sr

-18 -16 -14 -12 -100

5

10

15

20

25

18OVPDB ,0/00

Mn/Sr

s and

cF

dktbopfots

5

iw2ttsceivtm

Fig. 7. Co-variation plots: the �13C and �18O value

arbon an oxygen isotope signatures close to the contact with thee-picrite dyke.

The proportion of carbonate fills, surface precipitates andolomite crusts varies greatly along the section (Fig. 2). Theseinds of carbonate precipitates were avoided in this study, althoughheir complete absence in whole rock samples probably could note avoided due to their abundance. Nevertheless, the �13C valuesf sedimentary carbonates do not show any covariation with theroportion of cavity infills and surface precipitates/crusts. There-ore, it appears that the process(es) responsible for the dissolutionf carbonate and the precipitation of infills and surface precipi-ates/crusts did not affect significantly the primary carbon isotopeignature of sedimentary carbonates.

.2. Secular ı13C curve

In order to define the secular evolution of the �13C values dur-ng deposition of the KSF, the carbon isotope record of this study

as compared to data published from Drillcore X (Melezhik et al.,005). The distance between the two drillholes is ca. 25 km alonghe strike, and comparison of their records can therefore be usedo discriminate between the local and regional nature of the �13Cignal. Samples showing the effects of secondary alteration at theontact with the Fe-picrite dyke (Group 3, Drillcore 5A) have beenxcluded from the comparison. The study of Melezhik et al. (2005)

ncluded also data on dolomitic travertine deposits and a calciteeinlet; these were also excluded from this comparison. In addition,heir data for carbonate samples from thin lenses in the Quartzite

ember of Drillcore X have been excluded from the comparison.

the Mn/Sr ratios of the samples from Drillcore 5A.

Melezhik et al. (2005) speculated that these carbonate samples maynot have retained their original isotopic composition, as they arehosted by permeable quartzites and have Mn/Sr > 4–6.

The �13C values of the whole-rock samples from the Dolo-stone member of Drillcore X vary from 5.8 to 8.9‰ (Figs. 4 and 8)(Melezhik et al., 2005). In Drillcore 5A, the �13C values of the sam-ples show a similar range from 4.9 to 8.3‰. Both cores show agenerally upward decreasing trend in �13C values, thus showingsimilar �13C stratigraphic evolution.

Four stratigraphic levels in Drillcores 5A and X can be corre-lated on lithostratigraphic basis (Fig. 4). The lowermost calibrationline is associated with the transition from siliciclastic-dominatedto carbonate sedimentation in the area. The second line is relatedto the transition from carbonate sedimentation to siliciclastic sedi-mentation in the middle of both sections. The third calibration linemarks again the transition from siliciclastic to carbonate sedimen-tation. The uppermost correlation line is presented by the initiationof basaltic volcanism in the area. Following the lithostratigraphicsubdivision and depositional cycles of the KSF documented in Drill-core 5A, the carbonate unit between the two lowermost tie linesforms the Lower Dolostone member (Fig. 4) or the carbonate sub-cycle of the second depositional cycle. The siliciclastic-dominatedrocks between the second and the third tie lines form the silici-clastic unit, which represent the Quartzite member in Drillcore 5Aor the sandstone sub-cycle of the third cycle, and the siliciclastic

rocks at 295.5–297.7 m in Drillcore X (Fig. 4). The carbonate unitbetween the two uppermost tie lines forms the Upper Dolostonemember (Fig. 4) or the carbonate cycle of the third depositionalcycle.

P.E. Salminen et al. / Precambrian Research 228 (2013) 177– 193 191

Fig. 8. Combined secular �13C curve of the Kuetsjärvi Sedimentary Formation (Upper and Lower Dolostone members and an intermittent siliciclastic-dominated unit) basedo ovin

D

tiacdeDr(t

amtsds(m

n the primary �13C data from Drillcores 5A and X. The curve represents a 7-point m

rillcore X data is adopted from Melezhik et al. (2005).

A combined secular �13C evolution curve was constructed onhe basis of data from Drillcores 5A and X (Fig. 8). In order to min-mise the contribution from carbonates filling cavities and voidss well as those comprising stalagmites, stalactites, mounds andrusts (possible travertine), the Drillcore 5A data from the micro-rilled samples was used. However, both types of the samplesxhibit rather similar �13C values (Fig. 2). The lower and upperolostone members and the siliciclastic unit of Drillcore X were

escaled to match their thicknesses in Drillcore 5A. Moving average7 data points) was generated from the combined data to representhe secular �13C trend.

In the Lower Dolostone member, the �13C values first show general upward decrease from 8.5 to 7.4‰, and after a subtleinimum, the �13C values remain around 7.7‰ up to the siliciclas-

ic unit. In the Upper Dolostone member, the �13C values show amooth upward decrease from 7.7 to 7.2‰, followed by a sharper

ecreasing trend from 7.2 to 6.0‰. The overall �13C trend recon-tructed on the basis of combined data from Drillcores 5A and XFig. 8) appears to record primary, unaltered �13C values of sedi-

entary carbonates.

g average of all data. Also shown are the general �13C trends in Drillcores 5A and X.

Melezhik et al. (2005) suggested that short-term stratigraphicexcursions of �13C might have been driven by evaporation andinfluxes of 12C-rich waters. In fact, several short-term posi-tive and negative �13C spikes with the amplitude up to 1.7‰recorded in Drillcore X section (Melezhik et al., 2005) havenot been documented in Drillcore 5A. This implies that suchspikes in Drillhole X profile represent amplifications causedby local factors whose nature remains to be studied. On theother hand, Drillcore 5A does not show any correlation between�13C and the abundances of possible travertines, filled cavities,veins and surficial precipitates/crusts (Fig. 2). Hence, the influ-ence of 13C-depleted hydrothermal waters on the background�13C values inferred in Drillcore X has not been documented inDrillcore 5A.

5.3. Global correlation

The sedimentary carbonate rocks of the KSF define a �13C trenddecreasing from 8 to 5‰ within 100-m-thick section. Several othersedimentary carbonate successions deposited between ca. 2200

1 ian Re

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ttabtcotvme

mGdapeottd

Fe(dbar

sst1stKda

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5

n

92 P.E. Salminen et al. / Precambr

nd 2100 Ma define a similar evolutionary trend, possibly reflecting common global signal.

Melezhik and Fallick (2010) reported �13C data from theedimentary dolostones of the Kalix Greenstone Belt (ca.100–1800 Ma) in Sweden. The �13C values oscillate generallyetween 2 and 4‰, but a second order positive excursion from 4‰p to 8‰ and back to 4‰ is identified in the middle and upperarts of the succession. The �13C values of the second order posi-ive excursion are similar magnitude as the �13C values in DrillcoreA. The Kalix carbonates have been interpreted to be deposited in

shallow-marine environment.Comparable �13C trend have also been reported from a 1700 m

hick section of the Nash Fork Formation (ca. 2200–1970 Ma), inhe Wyoming Craton (Bekker et al., 2003a). The �13C values show

weak upward decreasing trend from ca. 8 to 6‰ in L2–M1 mem-ers, in the lower and middle Nash Fork Formation. However, inhe overlying M2 member, the �13C values are variable betweena. 6 and 8‰, and extremely high �13C values (up to 28‰) werebserved in the basal part of the formation (L1 member). In addi-ion, the uppermost Nash Fork Formation shows a shift to low �13Calues between 0 and 3‰ (members M3 and U1). The Nash Fork for-ation has been interpreted to be deposited in a shallow-marine

nvironment.Préat et al. (2011) reported 13C-rich dolostones in the FC For-

ation of the Francevillian Group in the Djibalonga sub-basin (SEabon). They found a stratigraphic trend with �13C values generallyecreasing from ca. 9 to −3‰. Slightly negative �13C values werelso found below this section. The FC Formation has been depositedrior to ca. 2080 Ma (e.g. Horie et al., 2005), and according to Préatt al. (2011), available age constraint suggests a pencontemporane-us deposition of the Franceville Series and 13C-rich carbonates ofhe Fennoscandian Shield. Hence, those parts of the FC Formationhat show the �13C evolution from 9 down to 6‰ might have beeneposited coevally with the KSF.

The �13C values reported from the Paleoproterozoic Tulomozeroormation (>1980 Ma) in the northern Onega Lake area, West-rn Russia, are generally higher than the �13C values in the KSFMelezhik et al., 1999). The �13C values show a generally, upwardecreasing trend, from 17 to 8‰. The Tulomozero sequence haseen interpreted to be a combination of shallow-marine depositsnd non-marine “red beds”. The upper part of the section likelyepresents a tidally influenced environment.

High �13C values have been reported from several carbonateuccession in Finland (Karhu, 1993). Three separate successionshow a distinct upward decrease in �13C. In the Kiihtelysvaara sec-ion (<2115 Ma), the �13C values show a decreasing trend from ca.0 to 2‰. In the Kuusamo Belt (<2405 Ma), the �13C values firsthow an increasing trend from 8 to 12‰ followed by a decreasingrend from 11 to 4‰. The Rantamaa Formation (2106 ± 8 Ma,arhu et al., 2008) of the Peräpohja Belt records a transition fromolomites highly enriched in 13C (�13C-11‰) to dolomites moder-tely enriched in 13C (�13C-5‰).

Many of these sedimentary sections with an upward decreasing13C values are associated with the final part of the Paleoprotero-oic carbon isotope excursion, when the �13C values in sedimentaryarbonates returned back to values close to 0‰. This event is con-trained to an interval from 2110 to 2060 Ma (Karhu, 1993; Karhund Holland, 1996). Accordingly, it is suggested that the depositionf the KSF may represent the latest part of the Paleoproterozoicarbon isotope excursion. This is consistent with the minimumepositional age of the KSF at 2060 Ma (Melezhik et al., 2007).

.4. Cause for 13C-enrichment in sedimentary carbonates

Several factors can cause 13C-enrichment in sedimentary carbo-ates on a local scale. These include high bioproduction in a closed

search 228 (2013) 177– 193

basin (e.g. Bein, 1986; Botz et al., 1988; Hollander and McKenzie,1991), possibly associated with stromatolite build-up (e.g. Burneand Moore, 1987; Des Marais et al., 1992), intense evaporation in ahypersaline environment (e.g. Friedman, 1998; Stiller et al., 1985),fermentative diagenesis (e.g. Irwin et al., 1977) and the activity ofhot springs (e.g. Friedman, 1970). These local effects appear to be anunlikely cause for the highly positive �13C values of the sedimentarycarbonates of the KFS, because a nearly equal carbon isotope evo-lutionary trend is observed in two locations separated by 25 km.However, a basin-wide 13C enrichment related to excessive bio-production in a closed basin cannot be completely excluded onthe basis of similar carbon isotope evolution in different parts ofthe basin. Nevertheless, the �13C evolution trend (Fig. 8) is com-parable to isotopic curves from other sedimentary carbonate unitsdeposited during the same time period. Therefore we conclude thatthe carbon isotope curve for the KSF most likely reflects the globalevolution of the surficial carbon reservoir.

6. Conclusions

A continuous drillcore section (Drillcore 5A) of sedimentary car-bonates from the Kuetsjärvi Sedimentary Formation (KSF) of thePechenga Greenstone Belt, NW Russia was investigated and sam-pled to study the evolution of �13C in Paleoproterozoic sedimentarycarbonates. The �13C values of the samples vary from 5 to 8‰.Excluding contact-altered samples, primary carbon isotope com-positions have likely been retained in the samples, based on thelack of covariation between Mn/Sr ratios and the isotopic ratios ofcarbon and oxygen. The �13C values were compared to publisheddata from sedimentary carbonates in another drillcore (Drillcore X)at a distance of 25 km. The following conclusions were reached:

- In general, no basinal �13C variations were observed. Severalpositive and negative spikes documented in the published data(Drillcore X) were not recorded in this study (Drillcore 5A), imply-ing apparent local effects as the cause of the spikes.

- A secular �13C curve constructed on combined records from Drill-core 5A and X shows a decreasing trend from 8 to 5‰ occurringwithin a 100-m-thick section of sedimentary carbonates.

- Comparison of the KSF secular �13C trend to carbon isotope evo-lution curves from other Paleoproterozoic carbonate successionssuggests that the deposition of carbonate sediments in the KSFmay represent the latest part of the Paleoproterozoic carbon iso-tope excursion; this is consistent with the minimum depositionalage of the KSF constrained at ca. 2060 Ma.

Acknowledgements

PES was supported by Väisälä Foundation (Finnish Academy ofScience and Letters) and the Finnish Doctoral Program in Geol-ogy. VAM was supported by the Norwegian Research Council (grant191530/V30). This is the FAR-DEEP ICDP contribution # 11.

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