Geo log i cal Quar terly, 2015, 59 (1): 229–238 DOI: http://dx.doi.org/10.7306/gq.1205
De vo nian siliciclastic rocks
of the Babí lom lo cal ity (south ern Moravia, Czech Re pub lic):
sed i men tary en vi ron ment re con struc tion and prov e nance study
Jurand WOJEWODA1, *, Slavomír NEHYBA2, Hel ena GILÍKOVÁ3 and Da vid BURIÁNEK3
1 Wroc³aw Uni ver sity, In sti tute of Geo log i cal Sci ences, De part ment of Struc tural Ge ol ogy and Geo log i cal Map ping, Pl. Maksa Borna 9, 50-204 Wroc³aw, Po land
2 Masaryk Uni ver sity, Fac ulty of Sci ence, De part ment of Geo log i cal Sci ences, Kotláøská 267/2, 611-37 Brno, Czech Re pub lic
3 Czech Geo log i cal Sur vey, Branch Brno, Leitnerova 22, 658-69 Brno, Czech Re pub lic
Wojewoda, J., Nehyba, S., Gilíková, H., Buriánek, D., 2015. De vo nian siliciclastic rocks of the Babí lom lo cal ity (south ern Moravia, Czech Re pub lic): sed i men tary en vi ron ment re con struc tion and prov e nance study. Geo log i cal Quar terly, 59 (1):
229–238, doi: 10.7306/gq.1205
Anchimetamorphosed sand stones and con glom er ates of the so-called “Basal De vo nian Clastics”, that build a hill (ridge) named Babí lom, are con sid ered to be of Lower to Mid dle De vo nian age. Al though they are strongly tec toni cally af fected, many sed i men tary fea tures are well-pre served and dis tinct. Both the fa cies and struc tures typ i cal of al lu vial fans and rivers were rec og nized in the sed i men tary as so ci a tion at Babí lom. Among oth ers, there are chan nel lags with imbricated grains, cross-bed ding, and debrites. The way-up di rec tion is clearly seen via re pet i tive coars en ing-up wards se quences. As sum ing a lack of ro ta tion of the suc ces sion in the X–Y plane, the main palaeodrainage was to wards the north and the ma jor sup ply of ma te rial was from the east. The high ma tu rity of the rocks sug gests der i va tion from older de pos its and/or highly weath ered source rocks. The mag matic rocks of the Brunovistulicum are pos si bly the pri mary source of the sed i ments.
Key words: south ern Moravia, Brno Mas sif, De vo nian siliciclastics, fa cies anal y sis, heavy min er als, al lu vial fan.
INTRODUCTION
In Czech geo log i cal lit er a ture, the term “Basal De vo nian Clastics” is used for the red monomictic quartz-peb ble con - glom er ates, quartz arenites, subarkoses, and ar kos es with interbeds of lam i nated siltstone, as well as for polymict con - glom er ates which are ex posed in sev eral ar eas of south ern Moravia (e.g., Dvoøák, 1978, 1998; Gilíková, 2007). These de - pos its have also been named the Old Red Sed i ments (Skoèek, 1980; Zukalová and Chlupáè, 1982). The best known oc cur - rences of these clastics are in the Moravian Karst area, be - tween Bílovice nad Svitavou and Ochoz u Brna (Gilíková et al., 2010), in the Babí lom – Èervený kopec Zone be tween Svinošice and Lelekovice, and in the Èebínka Zone near the town of Tišnov (Hanžl et al., 2007). These rocks are also known from nu mer ous deep bore holes along the south east ern mar gin of the Bo he mian Mas sif (Vavrdová et al., 2003; Mikuláš et al., 2008).
Spec tac u lar out crops of De vo nian clastic rocks in the Babí lom des ti na tion (Fig. 1) have at tracted the in ter est of a num ber
of in ves ti ga tors (Dvoøák, 1960; Melichar et al., 1999; Nehyba et al., 2001; Gilíková, 2007; Buriánek et al., 2008). The aim of this pa per is to pres ent re sults of sedimentological and pet ro graph i - cal stud ies car ried out in sev eral iso lated ex po sures in this zone, that ad dress the ques tions of:
– depositional pro cesses and set tings, – evo lu tion of the depositional en vi ron ment, – source ar eas,
– and dem on strate ap pli ca bil ity of sedimentological tech - niques in tec toni cally de formed coarse clastic.
GEOLOGICAL SETTING
The siliciclastic sed i men tary rocks of the Babí lom – Èervený kopec Zone crop out over the N–S elon gated area bor - dered by the metabasites of the so-called Cen tral Ba sic Belt to the west and the granodiorites of the Brno Batholith to the east (see Fig. 1). The zone mainly con sists of quartz-peb ble con - glom er ates, typ i cally thickly-bed ded. Ac cord ing to geo phys i cal data, the depth-range of these pre sum ably ter res trial sed i men - tary rocks is about 600 m, and is lim ited by a tec tonic bound ary (fault?) (Melichar et al., 1999; Hanžl et al., 2007). Their ex act strati graphic po si tion is not known be cause of the ab sence of any palaeontological data. Nev er the less, the Early to Mid dle De vo nian age is es ti mated, based on com par i son to the Mid dle
* Corresponding author, e-mail: jurand.wojewoda@ing.uni.wroc.pl Re ceived: Jan u ary 6, 2014; ac cepted: Oc to ber 14, 2014; first pub lished on line: De cem ber 11, 2014
and Up per Givetian lime stone lo cated a few hun dred metres to the south from the Babí lom lo cal ity (Fig. 1; Hladil, 1992; Hanžl et al., 2007).
The sand stone and con glom er ate beds dip steeply (60–85°) to the west (260–300°) and form a strik ing rocky ridge mor phol ogy at pres ent. The rocks have been de formed un der brit tle and brit tle-duc tile re gimes, as in di cated by sets of sty lo - lites, veins, and shear zones (Roupec, 1994).
There also oc cur iso lated blocks of siliciclastic rocks, sup - pos edly re sult ing from frost weath er ing dur ing the Pleis to cene, which were trans ported over a dis tance greater than 1 km from the source rock at the Babí lom lo cal ity.
METHODS OF STUDY
The Babí lom mor pho log i cal ridge con sists of a suite of iso - lated rock nests which have lim ited ver ti cal and lat eral ex tent.
This makes the con struc tion of a con tin u ous sed i men tary log pro file ex tremely dif fi cult. The lithofacial sub di vi sion and palaeo current es ti ma tions were based on tex tural and struc - tural fea tures, fol low ing Walker and James (1992) and Gra ham (2004). Seven ma jor lithofacies were rec og nized. Their in ter - pre ta tion and dis tri bu tion pro vided the ba sis to build a sche - matic sec tion of the suc ces sion, as well as to es ti mate the sed i - men tary and en vi ron men tal set tings and their evo lu tion in time (Fig. 2). Fa cies codes are used ac cord ing to Miall (1996). The 230 Jurand Wojewoda, Slavomír Nehyba, Helena Gilíková and David Buriánek
Fig. 1. Geo log i cal map of the lo cal ity stud ied Mod i fied map ac cord ing Hanžl et al. (2007)
max i mum peb ble size (MPS) was ob tained from the mea sure - ment of the lon gest axis (A-axis) of the 10 larg est found clasts.
Thin-sec tions of the sand stones from the lower part of the sec tion were ob served un der a po lar iz ing mi cro scope and a CL-mi cro scope with a “hot cath ode” (CL-mi cro scope Si mon- Neuser HC2-LM, Fac ulty of Sci ence, Masaryk Uni ver sity, Brno, Czech Re pub lic). Trans lu cent heavy min eral as sem blages (grain size 0.06–0.25 mm) were stud ied in only one sam ple.
The chem i cal com po si tions of the se lected heavy min er als (8 gar net grains and 5 tour ma line grains) were stud ied in fur ther de tail us ing the Cameca SX-100 elec tron microprobe at the De - part ment of Geo log i cal Sci ences, Fac ulty of Sci ence, Masaryk Uni ver sity in Brno. The chem i cal com po si tions of in di vid ual grains were in ves ti gated in a wave dis per sion mode un der the fol low ing con di tions: 15 kV ac cel er a tion volt age, 5 mm of the elec tron beam di am e ter, 30 nA cur rent, in te gra tion time 20 s.
Solely Ka X-ray lines were used as stan dards: augite (Si, Mg), orthoclase (K), jadeite (Na), chro mite (Cr), almandine (Al), an - dra dite (Fe, Ca), rhodo nite (Mn), TiO2 (Ti). The for mu lae of gar - nets were re cal cu lated as sum ing 12 ox y gen at oms per for mula unit (apfu). For mu lae of tour ma lines were ob tained on the ba sis of 31 (O, OH, F), as sum ing OH + F = 4 apfu and B = 3 apfu. The ab bre vi a tions of min eral names cor re spond to Kretz (1983).
LITHOFACIES DESCRIPTION
Fa cies Sr (Fig. 3A) is rep re sented by red dish-brown rip ple cross-strat i fied non-uni formly grained sand stone. It was rec og -
nized in the low er most sec tion of the sed i men tary sec tion. Two subfacies of Sr can be iden ti fied: fine-grained, well-sorted sand - stone, and me dium- to coarse-grained, poorly-sorted sand - stone, lo cally with siltstone flasers. Al though both subfacies al - ter nate ir reg u larly, the coarser-grained one seems to be more com mon up-pro file. The Sr fa cies cosets are at least 3 m thick, how ever, the bed shapes could not be spec i fied due to the qual - ity and size of the ex po sure.
Red dish-brown, very fine pla nar-lam i nated sand stone to siltstone rep re sents the fa cies Ml. Usu ally it forms ca. 30 cm thick intralayers within the up per part of the Sr fa cies coset.
Siltstone flasers re cog nised within the coarse-grained Sr sub - facies are mac ro scop i cally sim i lar to facies Ml.
Fa cies Sp (Fig. 3C) con sists of poorly sorted coarse- grained, low an gle pla nar cross-strat i fied sand stone with scat - tered quartz peb bles (MPS is 1.5 cm), whereas fa cies St (Fig.
3B, D) dif fers from the up per one only by the pres ence of trough cross-strat i fi ca tion. The set tops of St fa cies are usu ally ero - sional (con cave), whereas their bases are sharp and un even.
The thick ness of in di vid ual sets of fa cies St and Sp does not ex - ceed 30 cm. Fa cies Sp and St were both rec og nized in sev eral small ex po sures in the mid dle part of the sec tion.
Fa cies Gt (Figs. 3D and 4C) is a clast to ma trix-sup ported, trough cross-strat i fied con glom er ate. Peb ble shapes are very var ied. The pre ferred ori en ta tion of the lon gest axes of the elon - gated and bladed peb bles is par al lel to the axis of the bed ding troughs. The peb bles are sub-an gu lar to sub-rounded. En rich - ment of the peb bles (MPS of quartz is 5 cm) along the chan nel bot toms, form ing “peb ble clus ters” (Fig. 4B; Teisse yre, 1977;
Devonian siliciclastic rocks of the Babí lom locality (southern Moravia, Czech Republic)... 231
Fig. 2. Sche matic sed i men tary log of Babí lom lo cal ity De vo nian basal clastics with el e men tary sketch of depositional en vi ron ment
MPS – max i mum peb ble size
Hein, 1984; Wittenberg and Newson, 2005), was lo cally doc u - mented. The beds usu ally have ero sional and con vex bases, how ever, in di vid ual beds re veal a shape of broad chan nels with com pound infill and nu mer ous re ac ti va tion sur faces. The thick - ness of the in di vid ual chan nels reaches up to sev eral metres.
Fa cies Gm (Figs. 3C and 4D) con sists of crude pla nar-strat - i fied to structureless con glom er ate. The con glom er ate is clast to ma trix (sandy) sup ported. The MPS of quartz peb bles is 4 cm, how ever, the ma jor ity of grains do not ex ceed 2 cm. Bed - ding-par al lel pre ferred ori en ta tion of the lon gest axes of the elon gated and bladed peb bles was rarely rec og nized. The beds of Gm fa cies have ir reg u lar and ero sive bases and wedge- or tab u lar -shapes.
Red dish-brown coarse- to very coarse-grained pla nar- strat i fied sand stone, poorly sorted with an ad mix ture of quartz peb bles (MPS up to 1.5 cm), was as signed as fa cies Sl.
Intrabeds of fa cies Sl were re cog nized within the main beds of fa cies Gm. Sand stone beds of fa cies Sl typ i cally have len tic u - lar shapes and are about 20 cm thick. The bases are sharp, un even, and ir reg u lar while the tops are ero sional. Fa cies Gm with intrabeds of fa cies Sl was rec og nized in the up per part of the sec tion stud ied in sev eral small ex po sures. Con glom er - ates of fa cies Gm dom i nate in the up per most part of the sec - tion, where they lo cally al ter nate with fa cies Gt. Con vex-down bases of the beds and ero sive tops are typ i cal. In di vid ual beds have tab u lar- to broadly-con vex shapes and can be traced over a dis tance of sev eral metres (mostly over the lat eral ex - tent of the ex po sures).
DEPOSITIONAL ENVIRONMENT
Fa cies Sr and Ml were rec og nized in the lower part of the sec tion. They are re lated to trac tion cur rents and shal low wa ter con di tions. Fa cies Sr is in ter preted as a prod uct of de po si tion from wan ing cur rents un der the lower flow re gime. It can be con nected with the top most parts of the dunes or the bar flanks.
Fa cies Ml was de pos ited mainly from sus pen sion set tling, with very lim ited bedload trans port (weak cur rents). Such de po si tion over the up per parts of sandy beds prob a bly re flects the con di - tions in low-re lief flood plains (cf. Allen, 1964; Jack son, 1978, 1981; Miall, 1985), or so-called “overbank fines” (cf. Miall, 1996). The overbank de pos its are usu ally in ter preted as ev i - dence of a flu vial set ting, es pe cially of high sin u os ity to me an - der ing style. Sig nif i cant vol umes of fine-grained floodplain ma - te rial are not in cor po rated within braided stream fa cies mod els due to the sig nif i cant role of lat eral re work ing (Miall, 1996).
How ever, a num ber of an cient braided sys tems con tain sig nif i - cant amounts of pre served floodplain ma te rial, com ple ment ing the coarse-grained chan nel fill (e.g., Desloges and Church, 1987; Mack and Seager, 1990; Bentham et al., 1993). En - hanced floodplain pres er va tion (de pos its in as so ci a tion with coarse-grained braided flu vial de pos its or flu vial fan) could be con nected with the rapid for ma tion of the depositional space vol ume, e.g. in re sponse to rapid tec tonic sub si dence and/or scarp for ma tion. Here, we in ter pret the lower part of the sec tion (see Fig. 4) as hav ing orig i nated due to de po si tion in a mar - ginal/lat eral part of a flu vial (me an der ing?) sys tem, the for ma - 232 Jurand Wojewoda, Slavomír Nehyba, Helena Gilíková and David Buriánek
Fig. 3. De vo nian basal clastic sed i ments (sand stones and con glom er ates)
A – rip ple cross-lam i nated sand stone (fa cies Sr) and lam i nated muds (fa cies Ml), B – trough-cross bed ded sand - stone (fa cies St), C – pla nar cross-bed ded sand stone (fa cies Sp) and mas sive con glom er ates (fa cies Gm), D – trough-cross bed ded sandy con glom er ates (fa cies St) and clast to ma trix-sup ported, trough cross-strat i fied con - glom er ate (fa cies Gt)
tion of at tached bars (point bars?), and de po si tion in an ad ja - cent overbank/floodplain area.
The mid dle part of the sec tion con sists of fa cies Sp and St.
Fa cies Sp rep re sents foresets formed on the lee-sides of mi - grat ing sand dunes un der the lower flow re gime. A higher con - tent of peb bles and gran ules along the chan nel bases can be ex plained by “gravel overpassing”, which is con nected with bedform mi gra tion (cf. Miall, 1996). Fa cies St is in ter preted as be ing de pos ited in trac tion stream-flows un der the lower flow re gime. It can be re lated to the mi gra tion of 3D dunes, which filled mi nor chan nels or de pres sions, e.g. cut and fill struc tures.
This part of the suc ces sion is in ter preted as a sed i ment as sem - blage of dom i nantly mid-chan nel bars and dunes (Bridge, 1993;
Miall, 1996).
The up per part of the suc ces sion, pri mar ily con sist ing of con glom er ates of fa cies Gt, is in ter preted as a prod uct of de po - si tion from steady trac tion flows and the for ma tion of gravel chan nel bars and dunes, or the infill of mi nor chan nels. Fa cies Gt is con nected with two par tial depositional en vi ron ments. Al - ter na tion of fa cies Gt with fa cies St and Sp is in ter preted as the sed i ment of a braided river, with the dom i nant role of mi grat ing in-chan nel bedforms (see Fig. 4). Other depositional en vi ron - ments con nected with fa cies Gt are the dis tal or me dial parts of an al lu vial fan, where fa cies Gt al ter nates with fa cies Gm – such a sit u a tion was rec og nized in the up per most part of the pro file.
Poorly de vel oped hor i zon tal strat i fi ca tion and very rare grain imbrication within fa cies Gm sug gests rapid de po si tion from trac tion flows as low-re lief over grow ing gravel car pets. This fa - cies rep re sents the coars est and least mo bile bed-load ma te - rial, de pos ited in the ax ial parts of chan nels im me di ately af ter the ero sional stage as a re sponse to the di min ish ing of the peak flood. The up per most part of the sec tion is in ter preted as a sed i -
ment as sem blage typ i cal of al lu vial fan set tings. We can only spec u late about the “wet” type of the fan, with ep i sodic sheet flood de po si tion and sig nif i cant vari a tions in dis charge. Sheet flood-dom i nated sys tems are of ten con nected with an arid to semi-arid cli mate, with a pos si bly sea sonal and strongly fluc tu - at ing wa ter dis charge (cf. Blair and McPherson, 1994; Hampton and Hor ton, 2007).
The un steady flow con di tion and rapid changes in the flow dy nam ics are also sup ported by the com mon oc cur rence of fa - cies Sl within the con glom er ates of fa cies Gm. Fa cies Sl re flects de po si tion from trac tion flows near a tran si tion phase be tween the lower and up per flow re gimes (both up per and lower flow re - gime plane beds). Sl fa cies can be re lated to the fi nal stages of the chan nel fill ing, washed out phases over the top of the dune/sheet, or aggradation on a plane or low-an gle bed in pe - riph eral fan sec tions. Al ter na tion of fa cies Sl and mas sive con - glom er ate Gm is, ac cord ing to Todd (1989) and Blair (1999), typ i cal of de po si tion in al lu vial fans, dom i nated by a surficial stream trib u tary sys tem.
PETROGRAPHY AND HEAVY MINERAL COMPOSITION
Quartz to arkosic sand stone, re flect ing rel a tively good me - chan i cal re work ing, con sti tutes the ma trix in the con glom er atic fa cies and also in fa cies Sr. Sub-rounded monocrystalline quartz grains dom i nate in sand stone fa cies (Fig. 5). Partly sericitized feld spars oc cur in vari able amounts (up to 10 wt.%). The perth - ites were ob served in K-feld spar only oc ca sion ally. Micas con sti - tute up to 2 wt.% of the min eral com po nents. Mus co vite pre dom i - Devonian siliciclastic rocks of the Babí lom locality (southern Moravia, Czech Republic)... 233
Fig. 4. De vo nian basal clastic sed i ments (con glom er ates)
A – mas sive con glom er ate show ing up-cur rent clast imbrication; B – peb ble clus ter rip ple;
C – trough cross-bed ded con glom er ate (fa cies Gt) and mas sive con glom er ate (fa cies Gm), D – ma trix-sup ported grains (fa cies Gm)
nates in arkosic sand stone, but baueritized bi o tite is also pres - ent. Granitoids, volcanites, gneiss es, quartzites, and siltstones were ob served as rock frag ments. The ce ment has a coat-pore char ac ter and is com posed of seri cite, small grains of quartz, and Fe ox ides and hy drox ides, which usu ally also form grain coat -
ings. Sili ci fi ca tion within/of the quartz grains is com mon. Sev eral types of quartz grains (with out lu mi nes cence, light blue, blue and red) were ob served un der a CL mi cro scope (Fig. 6). The twinning and car bon iza tion of some grains were de ter mined in feld spars us ing CL mi cros copy (Gilíková, 2007).
234 Jurand Wojewoda, Slavomír Nehyba, Helena Gilíková and David Buriánek
Fig. 5. Mi cro pho to graph of arkosic sand stone Fig. 6. The sev eral types of quartz in CL-mi cro scope
T a b l e 1 Rep re sen ta tive chem i cal com po si tion of gar net
Grain HG16/198 HG16/200 HG16/201 HG16/203 HG16/204 HG16/205 HG16/206 HG16/207
SiO2 36.56 36.22 37.53 38.27 37.54 37.88 37.16 37.80
TiO2 0.30 0.09 0.00 0.00 0.07 0.06 0.14 0.00
Al2O3 20.21 19.85 20.80 22.25 20.58 20.89 20.68 20.86
Fe2O3calc 0.69 1.64 0.41 1.12 0.76 0.34 0.46 0.17
FeOcalc 3.65 18.34 21.70 13.23 17.58 21.57 12.73 27.87
MnO 35.59 21.83 14.68 22.62 14.07 9.44 17.81 6.53
MgO 0.40 1.37 2.32 4.25 1.80 2.91 0.00 3.16
CaO 2.79 0.39 3.25 1.59 7.74 7.04 10.77 3.96
Y2O5 0.00 0.24 0.06 0.00 0.00 0.00 0.00 0.07
To tal 100.19 99.99 100.75 103.33 100.14 100.14 99.76 100.43
Si 2.987 2.977 3.005 2.955 3.003 3.008 2.995 3.014
Ti 0.019 0.006 0.000 0.000 0.004 0.004 0.008 0.000
Al 1.946 1.923 1.963 2.025 1.940 1.956 1.965 1.960
Fe3+ 0.042 0.101 0.025 0.065 0.046 0.020 0.028 0.010
Mg 0.049 0.168 0.277 0.490 0.214 0.345 0.000 0.376
Fe2+ 0.249 1.261 1.453 0.854 1.176 1.433 0.858 1.858
Mn 2.463 1.520 0.996 1.480 0.953 0.635 1.216 0.441
Ca 0.244 0.034 0.279 0.131 0.663 0.599 0.930 0.339
Y 0.000 0.011 0.003 0.000 0.000 0.000 0.000 0.003
SCat. 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000
Alm 8 41 48 29 39 47 28 61
Adr 2 1 1 3 2 1 1 1
Grs 6 0 8 1 20 19 30 11
Prp 2 6 9 17 7 12 0 13
Sps 83 52 33 50 32 21 41 15
Alm – almadine, Adr – an dra dite, Grs – grossular, Prp – pyrope, Sps – spessartine
Zir con strongly dom i nates in the trans lu cent heavy min eral as sem blage of quartz to arkosic sand stone, form ing 60.5 wt.%.
Rutile (13.0 wt.%), ap a tite (13.0 wt.%), gar net (9.5 wt.%), and tour ma line (2.5 wt.%) rep re sent the fur ther typ i cal heavy min er - als. Monazite, min er als of the epidote group, and ti tan ite are only ac ces sory (never exceeding 1.5 wt.%).
The chem i cal com po si tion of two heavy min er als, i.e. gar net and tour ma line, was stud ied in de tail (Ta bles 1 and 2). It was pos si ble to fully ana lyse only five grains of Fe-dravite to Al- schorl tour ma line [Fe/(Fe + Mg) = 0.38–0.77; Na = 0.56–0.77; Al = 6.1–6.5 apfu] (Fig. 7A) . In di vid ual grains show os cil la tory zon ing, con trolled mainly by foitite sub sti tu tion ÿAl Na–1(Fe,Mg)–1 and the con tents of Ca (0.01–0.07 apfu) and F (0.00–0.18 apfu) are low.
The anal y sis of gar net com po si tion (8 grains) re vealed the strong dom i nance (about 66%) of alman dine- spessar tine- grossular gar net (Alm28–61 Sps15–40 Grs8–30 Adr1–2 Prp0–12). The rest (34%) is formed mostly by the spessar tine type of gar net (Sps50–83
Alm8–41 Prp2–17 Grs0–6 Adr1–3).
PROVENANCE STUDY
The con tent of the ul tra-sta ble heavy min er als (tour ma line + zir con + rutile) is very high (89.5 wt.%). An gu lar zir cons dom i - nate, con sti tut ing 60.5 wt.% of the spec tra of trans lu cent heavy min er als. The high con tent of the ul tra-sta ble min er als, to gether with the ab so lute dom i nance of quartz grains, in di cates a deeply weath ered source area and/or a source from re peat edly recycled older deposits.
The im por tant role of acidic mag matic rocks, i.e. gran ites and granodiorites, in the pre dicted pri mary source seems to be con firmed by the com mon oc cur rence of clasts of granitoids (Kfs + Qtz ± Pl), as well as frag ments of perthitic K-feld spar.
Frag ments of acidic vol ca nic rocks, quartzites, and gneiss es were also rec og nized. Cathodoluminescence (CL) shows sev - eral sources of quartz grains. Bright red lu mi nes cence is typ i cal of high-tem per a ture quartz de rived from vol ca nic rocks, such as rhy o lite. Quartz with light blue lu mi nes cence was prob a bly de - Devonian siliciclastic rocks of the Babí lom locality (southern Moravia, Czech Republic)... 235
T a b l e 2 Rep re sen ta tive chem i cal com po si tion of tour ma line
Grain HG16/1 HG16/2 HG16/3 HG16/4 HG16/5
SiO2 36.84 35.59 35.93 37.44 36.11
TiO2 0.09 0.33 0.27 0.09 0.11
Al2O3 32.26 31.19 31.89 31.78 32.96
Cr2O3 0.00 0.01 0.01 0.04 0.02
FeO 9.17 12.68 11.30 7.74 12.97
MgO 5.79 3.75 3.62 7.06 2.17
CaO 0.40 0.22 0.29 0.16 0.08
MnO 0.19 0.07 0.00 0.02 0.26
Na2O 2.30 2.37 1.72 2.21 1.72
K2O 0.05 0.06 0.02 0.01 0.03
F 0.00 0.34 0.05 0.00 0.00
H2O * 3.67 3.40 3.54 3.69 3.59
B2O3 * 10.64 10.33 10.32 10.68 10.41
O=F 0.00 0.14 0.02 0.00 0.00
To tal 101.39 100.21 98.92 100.91 100.43
Po si tion T+Z+Y
Si4+ 6.018 5.987 6.051 6.092 6.028
Al3+ 6.211 6.183 6.329 6.094 6.486
Ti4+ 0.011 0.042 0.034 0.011 0.014
Fe2+ 1.252 1.784 1.592 1.053 1.810
Mg2+ 1.409 0.941 0.909 1.712 0.541
Mn2+ 0.027 0.010 0.000 0.002 0.037
Cr3+ 0.000 0.001 0.001 0.006 0.002
Po si tion X
Ca2+ 0.069 0.039 0.052 0.029 0.014
Na+ 0.729 0.773 0.562 0.697 0.555
K+ 0.009 0.012 0.004 0.001 0.007
Va cancy 0.192 0.176 0.383 0.273 0.423
OH 4.000 3.818 3.975 4.000 4.000
F- 0.000 0.182 0.025 0.000 0.000
B3+ 3.000 3.000 3.000 3.000 3.000
rived from acid plutonic rocks, such as gran ite. The grains with clear blue lu mi nes cence were prob a bly de rived ei ther from gran ite or high-grade gneiss. The quartz grains with out CL were prob a bly de rived from low-tem per a ture source rocks, for ex am - ple, older sed i men tary rocks or low-grade metasedimentary rocks (Nehyba et al., 2001).
Sim i lar spec tra of rocks are char ac ter is tic of Bruno vistu - licum (see Dudek, 1995; Fin ger et al., 2000), thus, this geo log i - cal unit is the most prob a ble source area of siliciclastic rocks at the Babí lom lo cal ity.
The chem i cal com po si tion of the gar nets and tour ma lines stud ied is also com pa ra ble to the com po si tion of these min er als from Brunovistulicum rocks (see Leichmann, 1996; Èopjaková, 2007; Buriánek, 2010). Gar nets can be de rived from the fol low - ing source ar eas: rhyolites of the Metadiorite Zone of the Cen tral Ba sic Belt of the Brno Mas sif and/or granodiorites, gran ites, pegmatites, gneiss es, and calc-sil i cate rocks of Bruno vistu licum (Fig. 7B). Sim i larly, some tour ma lines were prob a bly de rived from hy dro ther mal quartz veins of the Metadiorite Zone of the Brno Batholith, and/or from rhyolites (prob a bly of early Pa leo zoic 236 Jurand Wojewoda, Slavomír Nehyba, Helena Gilíková and David Buriánek
Fig. 7. Chem i cal com po si tion of tour ma lines and gar nets within sand stones from the Babí Lom lo cal ity com pared with sup posed source rocks from the Brunovistulicum
A – ter nary plots Fe–Mg–Al and Na+K–Ca–X for tour ma lines; B – ter nary plots Sps–Alm–Grs+Adr, Prp–Sps–Grs+Adr, Prp–Grs+Adr–Alm for gar nets
age; Buriánek and Gilíková 2011). Gran ites that con tain tour ma - line are rare in re cent ero sional lev els of the Brno Batholith, but may be pres ent in the rocks of its up per lev els (Fig. 7A).
CONCLUSIONS
De spite tec tonic de for ma tion of the De vo nian siliciclastic rocks in the Babí lom lo cal ity, it was pos si ble to iden tify the pri - mary tex tural and struc tural sed i men tary fea tures, such as clast imbrication, cross-bed ding, ero sional sur faces, peb ble clusters, and others.
The de pos its stud ied ac cu mu lated in a ter res trial set ting:
first in a me an der ing river, then in a braided river, and fi nally on an al lu vial fan.
The high ma tu rity of the sed i ments sug gests that sed i men - tary ma te rial was de rived from older de pos its and/or highly weath ered source rocks. The mag matic rocks of Bruno vistu - licum are pos tu lated as the pri mary source of the sediments.
As sum ing that the De vo nian rocks crop ping out at the Babí lom lo cal ity have not been ro tated lat er ally, it can be de duced that the source area was lo cated to the east, but the dom i nant palaeotransport was to wards the north.
Ac knowl edge ments. The pa per was sup ported by the fol - low ing grants: Czech Geo log i cal Sur vey 390003 – Ba sic Geo - log i cal Map ping of the Brno Ag glom er a tion and the Moravian Karst, scale 1:25 000 and 1017/S/ING – in ter nal grant of Wroc³aw Uni ver sity. The sup port is grate fully ac knowl edged.
We give thanks for help ful dis cus sions to S. Burliga, and for re - views to J. Otava, A. Pøichystal and A. Wysocka.
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238 Jurand Wojewoda, Slavomír Nehyba, Helena Gilíková and David Buriánek
