R O C Z N I K P O L S K I E G O T O W A R Z Y S T W A G E O L O G I C Z N E G O A N N A L E S D E L A S O C I £ T £ g £ O L O G I Q U E D E P O L O G N E Tom (Volume) X X X IV — 1964 Zeszyt (Fascicule) 1—2 K raków 1964
K R ZY SZ TO F B IR K E N M A JE R , A L A N E. M. N A IR N
STUDIA PALEOMAGNETYCZNE SKAŁ POLSKICH
I. PERMSKIE S K A Ł Y OGNIOWE OBSZARU K RAKO W SKIEG O I PEWNE W Y N IK I Z GÓR ŚW IĘTO KRZYSKICH
(Fig. 9)
f
P alaeomagnetic Studies of Polish Rocks
I. The P e rm ia n Igneous Rocks of the K r a k ó w D is tr ic t and Some Results f r o m the H o ly Cross M ountains
(Figs. 1—9, Tabs. 1—3)
STRESZCZENIE
Opracowanie zawiera wyniki pomiarów kierunku naturalnego magne
tyzmu szczątkowego w skałach wieku permskiego, triasowego i prawdo
podobnie karbońskiego. W permskich skałach ogniowych obszaru krakow
skiego został stwierdzony stały magnetyzm szczątkowy, gdy w osadowych skałach pstrego piaskowca w Górach Świętokrzyskich stwierdzono ma
gnetyzm szczątkowy zmienny. Wykonano również pewną ilość oznaczeń temperatur punktu Curie badanych skał ogniowych. Przeprowadzona jest dyskusja wyników na tle stosunków geologicznych badanych skał.
* * *
A b s t r a c t . Th e re su lts of th e m e a su re m e n ts of th e d irec tio n of n a tu r a l re m a n e n t m a g n etism in rocks of P e rm ia n , T riassic, a n d possibly C arb o n ife ro u s age a r e re p o rte d . A s ta b le m ag n etiz atio n w as fo u n d in th e P e rm ia n rocks of th e K ra k ó w d istric t, w h ilst th e T riassic B u n ts a n d s te in of th e K ielce area , a n d th e possibly C a r
bo n ifero u s igneous rocks fro m B ard o (Holy Cross Mts.) w e re u n sta b ly m agnetized.
A lim ite d n u m b e r of C u rie p o in t te m p e ra tu re s w ere m e a su re d using a n a u to m a tic a lly re c o rd in g C h ev a llie r balance. T h e significance of th e se re su lts in th e ir geological
c o n te x t is discussed.
IN TR O D U C TIO N
Since the development and availability of sensitive magnetometers capable of measuring the directions of natural remanent magnetism in rocks, a magnetism which is characteristically of very low intensity (as low, or lower than 10-7 e.m.u./c.c. in some sedimentary rocks), investiga
tions have spread rapidly and widely. A considerable volume of data now exists which has been summarized by C o x and D o e l l (1960) and which can be found in a series of tables published by I r v i n g (1960, 1961). Of more particular interest here are the summary of European results in N a i r n (1960).
15 Rocznik PTG t. X X X IV z. 1—2
— 226 —
In the summer of 1961 the authors began collections of Polish rocks with the collection of orientated samples of Permian igneous rocks, mostly lavas, from the vicinity of Krakow, and also of Triassic Bunt- sandstein and the possibly Carboniferous intrusion of Bardo in the Holy Cross Mountains. These results are here recorded.
It is not intended to discuss here the general problems of origin of magnetization and method of measurement. For information of this kind the reader is referred to survey papers by C o x and D o e l l (1960), C o l l i n s o n and N a i r n (I960), and by R u n c o r n (1956).
FIE L D S A M P L IN G
In general it has been found advisable to collect rocks from quarries or deep road cuttings whenever and wherever possible for by this means the effects of weathering and of lightning may be avoided. Inevitably, however, it is also necessary to collect from surface outcrops.
In collecting orientated samples of sedimentary rocks, it was usual to obtain at least three from different horizons spaced through the exposed outcrop thickness. As the number of samples must obviously depend upon local conditions no set number can be given, but rather, as a generalization, about one sample every 2 to 3 metres may be taken.
Each is regarded as representing a single instant in time, and a sample mean is calculated from up to four measurements per sample.
In the case of igneous rocks extrusive or intrusive, the length of time taken for all points at any given outcrop to have cooled through the Curie point temperature of the ferromagnetic mineral or minerals involved, is so short in comparison with the period of secular variation, that the magnetization at that point may be regarded as a single instant.
As such it must obviously be effected by secular variation. Consequently site mean directions are used based on measurements on up to six samples per site.
Orientation is measured by use of a geological compass corrected for local secular variation — only in a very few cases is the local magnetic anomaly or the permanent magnetism of the rock of sufficient intensity to affect the accuracy o f the compass. The strike of the bedding plane of sedimentary rock samples is found by use of small spirit level. In the case of igneous rocks it was usually more convenient to measure the dip and strike of any plane or joint surface and make a correction in the labora
tory based on observation of the dip and strike of the enclosing sedimen
tary rocks.
LA B O R A TO R Y M EA SU R EM EN TS AND A N A LY SIS
Each orientated sedimentary sample represents a different unit bounded above and below by bedding planes. Consequently each must represent a different interval of time; however with the variation in grain size and the general absence of information on rates of deposition, it is not possible to state how long an interval is represented within the sample. It was, therefore, assumed that each sample approximated to a single ,,instant” of time, and a mean was obtained using up to four 2.5 cm discs 1 cm in thickness cut from one or two cylinders. The direc-
— 2 27 —
tion of natural remanent magnetism was measured using a sensitive magnetometer of the type described by C o l l i n s o n et al. (1957), The computation of the directions and intensity of magnetization were carried out on a high speed electronic computer using a programme devised by Dr. L. M o l y n e u x .
From each igneous sample up to four cores were cut, but more usually only a single core from each was used without perceptible loss in accu
racy. Site means were then computed. A ll igneous rocks were subjected to A.C. demagnetization in-fields of increasing magnitude as a test o f stability and as a means of removing secondary components of magneti
zation.
In general, demagnetizing field stages of 75, 150, and 250 oe, produced in a coil by 50 cycle mains current tuned by a bank of condensers to obviate harmonics, were used. Smooth field reduction was obtained by withdrawing from an electrolyte tower one electrode by means of a small electric motor driving a pulley with a conical thread. The specimen, mounted in field free space (to less than 50y), was rotated about two axes within the demagnetizing coil.
The Curie point temperature and thermo-magnetic curves were obtained for a number of samples by using an automatically recording Chevallier balance, in which a small specimen of a few grams weight rested on a torsion arm within a furnace in an asymmetrical magnetic field (up to 1650 oe maximum) of an electro-magnet. The change in magnetic properties with heating is reflected in the movement of the torsion arm, the balance deflection falling to zero at the Curie point.
Typical curves from the Rudno lavas are illustrated in Fig. 7.
Mean directions of magnetization using sample means (sediments) or site means (igneous rocks) and the computation of ancient pole positions were carried out on an electronic computer using programmes devised by Dr. L. M o l y n e u x . The statistic devised by F i s h e r (1953) was used to obtain the mean, a, the semi-angle of the cone o f confidence about the mean, and K a parameter which is a measure of dispersion. The formulae for the calculation of the confidence limit o f the mean and K are given below:
Where N is the number of measurements used;
P the probability level required (usually 95%);
R the vector mean of N measurements;
a is the semi-angle of the cone of confidence;
K is a measure of scatter.
This statistic is used almost without exception in rock magnetism, and discussion centres mainly around the choice of N , here the sample mean for sedimentary and the site mean for igneous rocks. In the caste of demagnetized igneous rocks, the direction adopted as best representing the true original site magnetization was that at which the K value was a maximum (i.e. scatter a minimum).
N — R
15*
— 228 —
D ISC U SSIO N O F R ESU LTS
1. P e r m i a n I g n e o u s R o c k s o f t h e K r a k ó w D i s t r i c t The igneous rocks of the Kraków district (Fig. 1) belong to late- -Variscian magmatic cycle. The oldest are porphyry tuffs and blocks of porphyry contained in slump breccias of the uppermost Visean marine sediments of Orlej (cf. D ż u ł y ń s k i 1952; C z a r n i e c k i & Ł y d k a 1958). The lava is of rhyolitic type.
Fig. 1. S ch em a ty cz n a m a p a n a jw a ż n ie jsz y c h p ó źn o p aleo zo iczn y ch s k a ł ogniow ych o bszaru k rak o w sk ieg o . 1 — d iab azy ; 2 — p o rfiry ; 3 — m e la firy
Fig. 1. S ch e m a tic m a p of m o st im p o r ta n t la te P alaeozoic ig n eo u s rocks of th e K r a k ó w d istrict. 1 — D iab ase; 2 — P o rp h y ry ; 3 — M e la p h y re
A group of small quartz porphyry sills, dykes etc. crossing Devonian and Lower Carboniferous carbonate rocks of the Dębnik Anticline are related to the Upper Carboniferous Asturic phase ( K o z ł o w s k i 1955).
A similar age is also suggested ( K o z ł o w s k i 1955, p. 83) for a porphyry laccolith of Zalas-Głuchówki (Orlej) which intruded into uppermost Visean-Namurian marine deposits ( D ż u ł y ń s k i 1955) though a Lower Permian age cannot be excluded (cf. S i e d l e c k i 1952, 1954).
A Lower Permian age is established for extrusive quartz porphyry at Miękinia which rests upon either Namurian beds or upon the Lower Permian Myślachowice Conglomerate (cf. S i e d l e c k i 1956, p. 454).
Petrologieally the porphyries vary from dacites to rhyodacites (cf. C z a r n i e c k i & Ł y d k a 1958).
A number of diabase (hypersthene-quartz diabase) sills have been found in bore holes (cf. S i e d l e c k i 1954) within Upper Carboniferous sediments. The only known outcrop of this rock is at Niedźwiedzia Góra.
These diabases are also referred to Asturic phase (cf. S i e d l e c k i 1951, 1952), but a Lower Permian age cannot be excluded.
The melaphyres are all extrusive rocks (lava flows) of an undoubted lower Permian age as they are younger than, or partly coeval with, the Low er Permian Myślachowice Conglomerate (cf. B i r k e n m a j e r 1952;
S i e d l e c k i 1951, 1952; S i e d l e c k i & Ż a b i ń s k i 1953). Mineralo- gically they correspond to augite andesites and related rocks. The mela-
— 2 29 —
phyre lavas are largely grouped along two lines which partly correspond to late-Variscian (Saalic) faults bordering the so-called Nieporaz-Brodła Graben stretching NW-SE (cf. S i e d l e c k i & Ż a b i ń s k i 1953). Along the south-western fault there occurred linear eruptions which produced melaphyre lava flows of Mirów, Belweder (Poręba Żegoty), Alwernia, Regulice, and along the north-eastern fault lavas were extruded between Rudno and Zalas.
The youngest are Lower Permian porphyry- and melaphyre tuffs and tuffites, partly pseudo-tuffs, the latter formed from weathered porphyries and melaphyres mostly during the Lower but possibly also during the Upper Permian (cf. S i e d l e c k i 1951, 1952, 1954; S i e d l e c k i & Ż a b i ń s k i 1953).
Notwithstanding differences in mineral composition and geological form, the chemical character of the igneous rocks of the Kraków district is very similar (cf. R o z e n 1909; B r o d e r 1931). Diabases and mela- phyres are more basic than the porphyries, all are comagmatic. The rocks in question were subjected to alteration, which can be partly attributed to late-magmatic solutions rich in K 20 which caused calification of both porphyries and melaphyres (cf. S i e d l e c k i 1954) although these pheno
mena have also been explained by a special type of weathering ( R o z e n 1909). Opinions have also been expressed ( B o l e w s k i 1939) that the rocks rich in K aO („potash trachytes” ) are products of independent lava extrusions. These opinions are not supported by geological evidence.
M i ę k i n i a
A t Miękinia there occurs a Low er Permian red quartz porphyry lava flow about 60 m thick. It rests in part upon the Namurian marine deposits and partly upon the Lower Permian Myślachowiee Conglomerates (including red clays), the latter found by Z a j ą c z k o w s k i (cf. S i e d l e c k i 1956, p. 454). The porphyry is covered by Lower Triassic in some places or by Quaternary deposits in others. The lava flow is believed to be horizontal.
The two sites examined, described below as Miękinia 1 and Miękinia 2r were separated by a small valley cutting through porphyry, which expo
sed Namurian shales. Miękinia 1 is an old (northern) quarry where samples (P p48-53) were collected from the upper part o f the lava flow which shows well developed thick columnar jointing. Miękinia 2 is a new (southern) quarry where samples (P p54-57) were collected from the low er part of the lava flow (lower exploitation level) which shows well developed thin platy jointing, about 10— 12 m above the bottom o f the flow as determined by bore holes evidence.
R e g u l i c e
A t Regulice there occur two Lower Permian melaphyre flows exposed in a big (eastern) quarry near the railway station (Fig. 2). The first lava flow (Regulice 1) is about 40 m thick. It begins with a thin basal breccia of melaphyre resting immediately upon arkose sandstones resembling the Karniowice Sandstones (Upper Stephanian ?) well exposed in the eastern part of the eastern quarry. The contact plane dips 170° ENE 10°. Further west the bottom breccia almost disappears and the horizontally jointed melaphyre rests on a thin conglomerate of the Myślachowiee Conglo
merate (Lower Permian) type, underlain by sandstones similar to the Karniowice Sandstone (cf. S i e d l e c k i 1951, 1952). Farther up from the contact the melaphyre becomes massive with vertical or oblique
— 230 —
joint planes (samples P p80-83); still higher vesicles and amygdales appear which become more and more frequent in the upper part of the flow (samples P p76-79).
Of the upper flow (Regulice 2) only the lower part (2— 3 m thick) is exposed in the eastern quarry. This flow also begins with thin mela- phyre breccia tilted 0° E 15°, followed by massive, vertically jointed melaphyre (samples P p84, 85) and is covered by Quaternary deposits.
w e
Fig. 2. S ch em aty czn y p rz e k ró j przez w y le w m elafiro w y w R eg u licach (łom w schodni).
1 — p iask o w ce k a rn io w ic k ie ; 2 — zlep ień ce m y śla c h o w ic k ie ; 3 — p o d s ta w o w a b re k c ja m e lafiro w a ; 4 — m a sy w n y m e la fir; 5 — m e la fir p o ro w aty i m igdałow cow y;
6 — osady czw arto rz ęd o w e i h a łd y ; 7 — g ra n ic a łom ów ; 8 — n u m e ry p ró b e k Fig. 2. S ch em atic cross-section of m e la p h y re flow s a t R egulice (eastern q u arry ).
1 — K arn io w ice S an d sto n e; 2 — M y ślach o w ice C o n g lo m erate; 3 — M e lap h y re b asal b re c c ia ; 4 — M assiv e jo in te d m e la p h y re ; 5 — V esicu la r a n d a m y g d a lo id a l m e la
p h y re ; 6 — Q u a te r n a ry d e p o sits a n d d u m p h e a p s ; 7 — L im its of th e q u a r r ie s ; 8 — N u m b e r of sam p le
Further west there occur masses of amygdaloidal and vesicular melaphyre which may be considered as belonging to the second flow. There the melaphyre is covered by Lower Triassic sediments.
R u d n o
A t Rudno 5 melaphyre flows crop out. We sampled the rocks exposed in small quarries west of Tenczynek Castle (Fig. 3), A ll the flows though differing in thickness have the following common features: basal mela
phyre (or melaphyre-sedimentary) breccia, massive vertically jointed melaphyre in the middle and vesicular, or amygdaloidal melaphyre in the upper part (Fig. 4). A ll the samples mentioned below were taken from the middle, massive, part of melaphyre flows.
The first flow (Rudno 1) represented by samples P p86-90 is at least 12 m thick. The base, not exposed in the quarry, is exposed further east, S of the castle (cf. B i r k e n m a j e r 1952; S i e d l e c k i 1951), where below the melaphyre the Myślachowice Conglomerate is found. The flow seems horizontal.
The second flow (Rudno 2) represented by samples P p91-94 is about
12 m thick; the melaphyre breccia at the bottom is here approximately 4 m thick.
The third flow (Rudno 3) 6— 8 m thick is poorly exposed, with a basal breccia of 2— 3 m in thickness. No samples were collected.
— 231 —
The fourth flow (Rudno 4) represented by samples P p95-98 is 10— 12 m thick. Its basal breccia fills the uneven surface of the 3rd flow, evidently an erosion surface; thus its thickness varies from 4 to 6 m.
The fifth and last flow (Rudno 5) represented by samples P p99-102 is over 5 m thick. Its basal breccia is 1.5 m thick. The upper vesicular
Fig. 3. O dsłonięcie m e la firu w R udnie. 1 — zlep ień ce m y ślach o w ick ie; 2 — m e la fir;
3 — k o le jn e w y lew y law o w e; 4 — k am ien io ło m y ; 5 — zam ek w T en czy n k u Fig. 3. O utcrops of m e la p h y re a t R udno. 1 — M yślachow ice C o n g lo m erate; 2 —
M e lap h y re ; 3 — Successive la v a flew s; 4 — Q u a rrie s; 5 — T en czy n ek C astle
B e l w e d e r
A t Belweder near Poręba Żegoty there occurs only one Lower Permian melaphyre lava flow tilted 110° NNE 15°. Its bottom breccia and contact with the Kwaczała Arkose (Middle Stephanian) were well exposed some time ago (cf. B i r k e n m a j e r 1952). The minimum thickness of the flow may be established as 15 m (of this 1— 2 m is represented by the basal breccia). The melaphyre is covered by Quaternary deposits. The samples (P p72-75) were taken from massive, vertically or obliquely jointed melaphyre exposed in the quarry.
O r l e j a n d Z a l a s
The outcrops of quartz porhyry at Orlej (Głuchówki) and at Zalas belong to one laccolith which is some 100 m thick (cf. D ż u ł y ń s k i 1955).
The porphyry is intruded into uppermost Visean-Namurian sediments (cf. D ż u ł y ń s k i o.c.; C z a r n i e c k i 1955) and hence is of post-Namu- rian age. It is not clear whether the porphyry was intruded during the Upper Carboniferous or during the Lower Permian (S i e d l e c k i 1952).
However, K o z ł o w s k i (1955, p. 83) is inclined to believe that it is related to the Asturic phase.
A t Zalas samples (P p64-67) were taken from the first quarry to the east of the road leading from Zalas to Sanka (see G r a d z i ń s k i 1960, p. 120, No. 42). The rock is here mostly greenish, but reddish if slightly altered.
— 23 2 —
— 23 3 —
A t Orlej the samples (P p68-71) were taken from greenish and reddish porphyry exposed in the southern part of the quarry, about 50 m from the contact with thermally altered Carboniferous sediments.
In general the rocks mentioned above were stably magnetized (Tab. 1) though of low intensity of magnetization, for demagnetization in A.C.
fields never significantly altered the direction of magnetization in the majority of cases (typical demagnetization curves are shown in Fig. 6).
It made very little difference whether the site mean was based on sample means of four measurements or upon single measurements and the latter method was consequently generally applied.
H
Fig. 5. S tere o g ra m k ie ru n k ó w m a g n ety za cji p e rm sk ic h la w w rejo n ie k rak o w sk im . N u m e ry o d p o w iad ają n u m e ro m w y lew ó w ja k n a ta b . 1. N u m ery 10 i 11 p o ch o d zą
z in tru z y w n eg o la k k o litu w O rlej u i Z alasie
Fig. 5. S te reo g ra m sh o w in g th e d irec tio n of m a g n etiz atio n of P e rm ia n la v a s fro m th e K ra k ó w d istrict. T h e n u m b e rs co rresp o n d to th e n u m b e rs of flow s as in T ab. 1.
N ote th a t 10 a n d 11 a r e fro m a n in tru s iv e lacco lith sam p le d a t O rlej a n d Z alas resp ectiv ely
PermianVolcanics,KrakówDistrict
— 234
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— 23 5 —
A t only one site (Orlej) were some samples too weakly magnetized for measurement (two out the four collected), the remaining two only gave a measurement in a field of 170 oe. The mean, as in the case of the Zalas samples, despite the very large circle o f confidence agreed very w ell with the mean of the remainder (excluding the Zalas samples). This distinction of the Zalas and Orlej sites in an intrusive laccolithic body, separates them from all the remaining sites which were in lava flows and indicates some marked difference in their ferromagnetic mineral
H. oe
Fig. 6. Z n o rm aliz o w a n e k rzy w e d em ag n ety z acji la w z R u d n a i R egulic (m elafiry), p o la zm ien n e do 250 oe. 1 — Regulice, w y lew 1; 2 — R udno, w y lew 5; 3 — R udno, w y le w 4; 4 — R udno, w y le w 5; 2 i 4 s ą k rzy w y m i z p ró b e k p o b ra n y c h w ty m
sam y m m iejscu
Fig. 6. N o rm alized d em ag n etizatio n cu rv es of R u d n n a n d R egulice la v as (m elaphyre), a lte r n a tin g field s u p to 250 oe. T h e cu rv es a r e n u m b e re d as follow s. 1 — Regulice, flo w 1; 2 — R udno, flo w 5; 3 — R udno, flo w 4; 4 — R udno, flow 5; 2 a n d 4 a re
cu rv es fro m d iffe re n t sam p les collected a t th e sam e site
content. That some difference exists is borne out by measurements on the Chevallier balance. Thermo-magnetic curves did not reveal the presence of a second magnetic phase in any of the lavas examined. Typical curves, tracings of photographic records, shown in Fig. 7 indicate a Curie point close to that of magnetite. Three of the curves in Fig. 8, however, do indicate the presence of a material with a Curie point of about 350 °C, a material which would appear to be destroyed by heating since it does not reappear in the cooling curve, in addition to magnetite. Two of the curves (a, b) came from samples collected at Zalas, the other two (c, d) were obtained from Orlej samples.
Overall site means have been calculated (see Tab. 1) including and excluding the two results (Zalas and Orlej), and from these means the position of the ancient pole has been calculated ł. It is felt that the better
1 M in eralo g ical an aly sis w o u ld be in te re s tin g to see w h e th e r ilm e n ite sh o w in g e x s o lu tio n w as p re s e n t in th e Z alas a n d O rlej sam ples.
— 236 —
representation of the ancient Permian pole excludes the Zalas and Orlej results. The ancient pole so obtained fits in remarkably well with other determination made in western Europe (see N a i r n 1960).
Individual flow directions are plotted in Fig. 5 in which the distribu
tion appears somewhat elongate although representing measurements which are magnetically stable from the A.C. point of view. The omission
Fig. 7. K rzy w e te rm o -m a g n e ty c z n e o trz y m a n e z a u to m aty c zn ej w agi s k rę c e ń z w y lew ó w law o w y ch (m elafirów ) z R udna. W ylew y p o n u m e ro w a n e ja k n a tab . 1.
G w a łto w n y sp ad ek in ten sy w n o ści zachodzi w p u n k c ie C urie. N a osi p io n o w ej w y znaczono in ten sy w n o ść, n a osi poziom ej te m p e ra tu rę . P rz e rw y w p rzeb ieg u k rzy w ej w y s tę p u ją w o d stęp ach 100°, k rz y w a g ó rn a je s t k rz y w ą o grzew ania, d o ln a —
o zięb ian ia
Fig. 7. T h e rm o -m ag n etic cu rv es o b ta in ed fro m a n a u to m a tic to rsio n b a la n c e of la v a flow s (m elap h y re) fro m R udno. T h e flo w s a r e n u m b e re d as in Tab. 1. T h e sh a rp fa ll in in te n s ity occurs a t th e C u rie p o in t. A r b itr a r y a x e s a r e d r a w n fo r co n v en ien ce:
in ten sity — v ertically , te m p e r a tu r e — h o rizo n tally . B reak s in th e tr a c e o ccu r a t 100° C in te rv a ls, th e u p p e r c u rv e b ein g th e h e a tin g curve, th e lo w e r th e cooling c u rv e
— 237 —
of the Zalas and Orlej results from the calculations can be justified on the basis of their very 'large circles of confidence.
N i e d ź w i e d z i a G ó r a
Within the same area, three samples (Pp58-60) were collected from a single diabase sill intruded into Upper Carboniferous rocks at Nie-
Fig. 8. K rzy w e z p ró b e k p o b ra n y c h z la k k o litu p o rfirow ego, a, b — Z alas; c, d — O rlej, in n e o znaczenia ja k n a fig. 7
Fig. 8. C u rv es fro m p o rp h y ry lacco lith sam ples, a, b — T w o sam p les fro m Z alas;
c, d — T w o sam p les fro m O rlej. F o r o th e r e x p la n a tio n s see Fig. 7
dźwiedzia Góra (western part of the quarry), and itself believed to be of Upper Carboniferous age (cf. S i e d l e c k i 1951, 1952), related to Asturic phase. Two samples (Pp61, 62) were also obtained of the lower contact
1 B elow th e sill th e re occur U p p e r C arb o n ife ro u s san d sto n es a n d arkoses. T h e c o n ta c t p la n e ex p o sed in th e w e s te rn p a r t of th e q u a r r y d ip s 120— 135° SW 21—30°.
— 238 —
and these together with A.C. demagnetization establish with reasonable certainty the magnetic stability of rock in question.
The study of the rock raises several problems: whether, in the absence of the upper contact, it is a genuine still or a possible lava flow, or whether intrusion or extrusion post-dated or pre-dated tilting. A case could also be made for a Permian age of the rock which is not different in chemical composition from the Permian extrusives (melaphyres) of the district.
In the absence of precise information as to the attitude in which the rock cooled, directions and pole positions have been computed with respect to the present bedding and with respect to the horizontal (see Tab. 2).
T a b l e 2 D iabase of N iedźw iedzia G óra, K rak ó w D istric t
M ean D e c lin a
tio n
M ean In c lin a
tion
a K N R A n cien t
P ole
C om puted w ith r e sp ect to b e d d in g . C om puted w ith r e s p ect to h o rizo n tal
212.0 212.5
+ 8.0
— 15.8
10 59.6 5 4.9329
28.9N 162.9E 40.IN 155.9E
It is not possible to draw any definite conclusion from the above data, for the rock from our initial considerations must be considered as affected by secular variation. If intruded or extruded and then tilted a Carboni
ferous age is possible; if intruded into tilted beds, then a Permian age is equally possible.
2. P a l a e o z o i c I g n e o u s R o c k s f r o m B a r d o , H o l y C r o s s Mts.
Measurements were attempted on four of five samples (P p124-128) collected near the outlet of Prqgowiec creek from natural outcrops of an augite- and spilite diabase dyke intruded subparallel to the contact of the Lower and Middle L u d low1. Two, of what appeared fresh material came from near the upper (southern) contact, and the remainder from a poorer outcrop some 10 m distant, near the lower (northern) contact. Two sam
ples were not measurable; whilst the remaining two gave measurements of reasonable internal consistency, there was little agreement between samples. Demagnetization in alternating fields up to 250 oe does not produce any better agreement, consequently no further work was carried out on this material. It is possible that with good exposures and fresh material, satisfactory results might be obtained.
1 T h e re a re no d ire c t ev id en ces of th e age of th e diabase. A t a n y r a te i t is y o u n g er th a n M id d le L udlow . O n co m p ariso n s w ith an alo g o u s rocks in th e H oly Cross Mts., w h e re th e p h ases of te cto n ic d efo rm a tio n s a r e d a te d m o re p recisely a C a rb o n ifero u s ag e (S udetic ph ase?) is su g g ested (cf. R y k a 1957, 1958).
— 2 3 9 —
3. T r i a s s i e B u n t s a n d s t e i n f r o m t h e H o l y C r o s s Mts.
Five sites were visited of which three were quarries and two were road cuttings.
G a ł ę z i c e
The samples were collected from the Low er Buntsandstein (cf. C z a r n o c k i 1938) exposed in a small quarry east of hill 312 m a.s.l. (samples
N
Fig. 9. S te re o g ra m k ie ru n k ó w m ag n e ty za cji p streg o p iask o w ca z G ór Ś w ięto k rz y skich. P ró b k i z ty c h sam y c h m iejsc zo stały połączone razem . W szy stk ie p ró b k i
z w y ją tk ie m je d n e j są n o rm a ln ie n a m a g n e ty z o w a n e . 1 — G ałęzice; 2 — J a w o r z n ia ; 3 — W y stęp a; 4 — T u m lin ; 5 — W y k ień
Fig. 9. S te re o g ra m sh o w in g th e d ire c tio n s of m a g n etiz atio n of T riassic B u n ts a n d s te in sam p les fro m th e H olly Cross M o u n tain s. S am p les fro m th e sam e s ite a r e lin k e d to g e th e r. N ote a ll sam p les w ith a sin g le e x c e p tio n a r e n o rm a lly m a g n e tiz e d a n d a r e in d ic a te d b y solid sym bols. T h e p r e s e n t d ip o le fie ld is in d ic a te d b y a n a s te risk . T h e sites a r e as follow s: 1 — G ałęzice; 2 — J a w o rz n ia ; 3 — W y stęp a; 4 — T u m lin ;
5 — W y k ień
— 240 —
B u n ts a n d s te in of
S ite S am p le
No.
In te n sity of m a g n etiz atio n
x 10-6
M ean D eclin atio n
M ean In clin atio n
G al^zice 108 12.165 ± 2.77 20.9 + 39.8
109 37.925 ± 7.13 0.9 + 43.8
110 8.623 + 1.88 3.9 + 38.9
111 10.323 + 1.63 20.7 + 28.6
site m e a n 12.1 + 38.1
J a w o rz n ia 103 1.770 + 0.30 358.2 + 61.3
104 1.175 + 0.24 237.9 + 28.4
105 2.178 db 0.60 333.5 + 47.4
106 6.240 + 0.88 229.0 — 6.5
107 8.99 ± 0 .1 1 165.7 + 6.7
site m e a n 237.6 + 51.3
, W y st^p a
112 1.890 ± 2.317 12.5 + 49.4
113 2.385 + 2.147 141.7 + 18.5
114 1.038 + 0.459 153.7 + 34.8
115 0.627 ± 0.229 127.2 + 69.2
s ite m e a n 127.6 + 56.1
T u m lin
116 0.808 + 0.382 328.9 + 74.1
117 0.965 + 0.492 326.9 + 51.2
118 1.365 + 0.167 27.9 + 62.7
119 1.298 ± 0.283 31.7 + 49.3
site m e a n 2.4 + 63.1
W ykien
120 1.748 + 0.557 3.0 + 59.1
121 1.308 + 0.755 51.2 + 74.3
122 1.690 + 0.373 40.1 + 70.7
123 1.858 ± 0.771 12.8 + 61.6
site m e an 21.7 + 67.6
— 241 —
th e K ielce D istric t
T a b l e 3
a K N R A n cien t Pole
6.0 238.8 4 3.9874
4.6 393.2 4 3.9924
13.2 49.4 4 3.9393
16.1 59.6 3 2.9665
12.1 58.6 4 3.9488 58.9N 178.8E
58.9S 1.2W
14.5 41.3 4 3.9274
50.6 4.3 4 3.2964
48.8 4.5 4 3.3349
— — 2 —
13.8 81.4 3 2.9754
76.2 2 5 2.9704 7.2N 25.2W
7.2S 154.8E
99.9 1.8 4 2.3754
64.4 3.0 4 3.0043
53.9 3.9 4 3.2276
176.7 1.8 3 1.9041
59.3 3.4 4 3.1115 9N 61E
9S 118.9W
26.0 13.4 4 3.7767
81.4 2.3 4 2.6733
30.2 10.2 4 3.7058
52.0 4.1 4 3.2678
24.5 15 4 3.800 83.4N 174N
83.4S 6E
26.2 13.3 4 3.7743
101.7 1.8 4 2.3507
19.2 23.9 4 3.8743
36.7 7.2 4 3.5855
12.8 52.6 4 3.9429 76.3N 104.6E
76.3S 75.4W
16 Rocznik PTG t. X X X IV z. 1—2
— 24 2 —
Pr108,109), and from a road cutting in the western part of the hill (samples P R110, 111). Dip of the beds ± 30° NNE.
J a w o r z n i a
The samples (P R103-107) were collected from the Lower Buntsand- stein (cf. C z a r n o c k i o.c.) in the western part of the quarry near point 313.0 m a.s.l., 1— 5 m above the contact with the Givetian limestones.
Mean strike and dip of the Buntsandstein: 95° NNE 20°.
W y s t ^ p a
The samples (P R112-115) were collected from the Low er Middle Bunt
sandstein (cf. C z a r n o c k i o.c.) in a road cutting, about 500 m NW of the main road (Kielce— Radom). The strike and dip of ripple-marked sandstones were 65° NW 4°.
T u m ' l i n
The samples (PR116-119) were collected from the Lower Middle Bunt
sandstein (cf. C z a r n o c k i o.c.) in an old (eastern) quarry. Mean strike and dip of cross-bedded sandstones: 95° NNE 2 1°.
W y k i e n
The samples (P R120-123) were collected from Lower Middle Bunt
sandstein (cf. C z a r n o c k i o.c.) in a working quarry at Wykien (Cminsk).
SW of Tumlin. Mean strike and dip of cross bedded sandstones: 80°
N N W 15°.
The rock in general was a fine grained reddish sandstone; only in the Jaworznia quarry, immediately above the Devonian unconformity did it prove possible to obtain deep red coloured siltstones.
As can be seen from the accompanying stereogram (Fig. 9), the results are in general clustered around the dipole field (cf. Tab. 3). The presence of occasional samples in the south-west quadrant suggests that some at
least of the samples may have been initially of reversed magnetization.
A t only one site, the one showing also the best grouping was the mean intensity of magnetization greater than 3 X 10-6 e.m.u./c.c. On the basis of the observed scatter and the low intensity of magnetization, these rocks were concluded to be unsuitable for the investigation of the direc
tion of the ancient magnetic field, and no further work was carried out of them.
Laboratory of Geology, Polish Academy of Sciences, Kraków, Sławkowska 17
Department of Physics K in g ’s College,
Newcastle upon Tyne, 1
— 243 —
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1 6*
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