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Trace element distribution in some British Carboniferous sediments
Qeochimica et Coemochhnica Aota, 1969, Vol. 33, pp. 619 to 623. Perylamon Press. Printed in Northern Ireland
NOTES
Trace element distribution in some British Carboniferoussediments C. D. &RTIS of Geology, The University,
Department
(Received 21 May 1968;
Sheffield Sl 3JD
accepted in revieed fern 21 October 1908)
Ati&-Traoe element concentrations in a sequence of Westphalirm sediments are reported. The date are disoussed in light of previously published palaeoecological and geoohemioal inform&ion for the same sediments. Distribution patterns are concluded to be much a%cted by early diagenetio processes. PFLE~IOUSreports (SPEARS 1964a, b; SPODE 1904; CURTIS, 1967) have described the mineralogy, major-element geochemistry and fauna1 and floral distribution within a sequence of Westphalian sediments penetrated by 8 British National Coal Board boring in the Yorkshire Coalfield (44/628168). This accumul&ed information was thought to make the sequenoe ideal for trace-element study. In partioular, much can be deduced concerning environmental fluctuations during deposition. Analytical data were obtained by optioal spectrography and are listed in Table 1. The analytical saheme followed olosely that suggested by AIIRENS and TAYLOR (1961). Coeaaients of Variation for each element were callculated for determinations from multiple burns on selected samples. The listed figures are means of triplicate determinations. The Standard Error of the Table 1. Spectrographic
trace element data
Sample
Depth (ft)
GE
B
Cr
V
Co
Ni
Cu
Pb
Mn
Sr
Ba
5937 948 960 962 2 4 6 8 12 14 16 18 20 22 24 26 28 30 32 969 970
937 948 960 962 953.5 954.6 955.5 956.5 958.6 959.5 960.5 961.5 962.6 963.6 964.5 965.6 966.5 967.6 968.6 969 970
30 38 36 35 31 27 35 27 29 33 35 34 31 35 34 34 39 13 40 17 28
78 ad. ad. n.d. 88 86 86 86 92 92 101 101 100 94 85 82 70 22 68 40 64
77 109 121 123 118 119 129 121 124 124 143 122 117 128 108 121 105 69 90 39 100
188 266 258 245 258 245 282 280 266 278 310 266 265 286 330 300 300 185 280 140 208
22 24 24 23 27 21 23 21 22 22 22 24 26 26 31 31 28 17 20 10 14
53 66 64 61 72 63 71 66 60 63 62 99 77 67 77 79 87 64 56 27 39
59 62 60 64 36 30 68 48 38 43 74 84 73 77 132 142 159 88 87 15 24
22 38 40 30 29 18 23 21 21 23 22 73 66 87 164 60 39 10 66 10 25
970 1116 1205 825 420 618 496 550 490 476 610 1046 1086 1160 1016 376 2300 2440 426 810 1180
88 99 136 126 118 122 119 111 116 134 144 135 124 132 120 120 96 368 66 32 70
690 465 466 496 465 666 606 466 440 666 485 610 666 660 630 685 7000 400 88 316
Note:
All values in ppm.
n.d. = not determined.
619
-
520
Notes Table 2. Selected major element analytical data* Total alkalis Sample
A’#,
S937 948 950 952 2 4 6 8 12 14 16 18 20 22 24 26 28 30 32 969 970
20.35 22.39 23.68 22.80 23.00 21.17 23.04 22.71 21.89 23.23 23.62 22.35 22.12 22.14 21.37 23.16 18.92 5.56 17.46 8.24 16.08
(= K,O)
Total diagenetic Fe as Fe,O,
Acid soluble nulphur
Organic matter
5.26 5.16 5.45 5.24 5.54 5.41 5.56 5.33 5.20 5.84 5.64 5.35 5.29 5.17 5.18 4.79 3.89 1.43 3.91 1.27 2.54
3.88 5.94 2.85 1.98 l-03 1.06 2.09 1.41 0.78 0.93 1.01 4.44 4.36 5.32 6.17 1.37 12.16 6.06 6.17 25.40 6.07
0.03 0.01 0.03 0.02 0.56 0.44 1.59 0.69 0.09 O-64 0.66 3.54 3.48 4.24 4.91 0.98 3.00 0.53 4.90 0.11 1.49
2.34 4.00 3.01 2.68 1.02 1.20 0.88 1.10 1.21 1.05 1.11 1.55 1.47 1.50 2.23 2.16 1.36 1.33 10.00 5.72 7.52
* Teken from SPEARS (1964), Cumrs (1966, 1967). All values wt. %.
Table 3. Major/trace element correlationcoeffiaientsaccepted at the 95% level in the total sample population
4%
Total alkalis Organic matter Total diagenetic Fe Sulphur
Ga
B
Cr
V
Sr
Ba
Co
Ni
+
+
+
+ + -
+ + -
+ +
+ +
-
-
-I+
+++
+
+
Cu
Pb
&In _ --
+
+
Coefficientof Variation (v = 1008/Z(2n), 1/Zwhere 6’ = Standard Deviation, I = mean and n, the number of determinations, = 3 in each case) proved to be approximately f15%(Sr), f 12 %(Ba) and f 10 % or better for the remaining trace elements studied. A number of major element analyses taken from previous reports are utilised in the data analysis. These are listed in Table 2. The prinoiplesediment components are quartz, clay minerals (illite with subsidiary chlorite and kaolinite), organic matter and diagenetio iron minerals [siderite, pyrite and, in sample 530, ankerite; this is thought to be the alterationproduct of calcite accordingto TAYLOR and SPRIARS (1967)]. AlsOs documents total clay variation whilst “total alkalis” (KpO plus NasO converted to equivalent KsO) is indicative of illite content. Acid soluble sulphur is a direct measure of pyrite. “Total diageneticFe” is the sum of Fe equivalent to sulphur (pyrite) and CO, (siderite)and is a measure of the non-detrital oomponent of these sediments. Covariation of traoe-elementswith major sediment constituentsis convenientlysummarised by the identificationof significantoorrelationcoefficientsin Table 3. All samples are considered for all possible relationships. It is apparent that Ga, B, Cr, V, Sr, Ba, Co and Ni vary sympathetically with olay content and antipatheticallywith organic matter and the total diagenetic fraction. Suoh a situation would be expected if these trace elements were olay located: the relationshipsbeing a simple consequenceof dilution of the clay fraction by orgrrnicmatter and diageneticminerals (and quartz). Mn behaviour is distinctive in being the converse. Cu and Pb seem to vary quite independentlyof clay content. Aoid soluble sulphurvaries sympath&ia&Iy
621
Notee
with V, Ni, Cuand Pb. This suggests pyrite location but several alternative explanations are available. Some brief summar~yof p8l8eoecologic8l information is necessary 8t this stage. The samples may be divided into two groups on the basis of fossil aontent. Samples S2 to 530 inclusive are marine. Samples S937, 948, 960, 962, 32, 969 and 970 constitute the nonm8rine population. The b8sal sediments of the sequence (samples 8970, 969 and 32) were deposited from non-marine waters and contain much coaliiled plent material. During early diagenesis, however, effective contact with marine waters was maintained vi8 diffusion and the diegenetic assemblage contains both pyrite and siderite. The marine sequence starts abruptly Table 4. Major/trace element correlation coefficients accepted at the 96 % level in the marine sample population GS
a&3
Total alkalis Organic matter Total diegenetic Fe Sulphur
+++ +++
B
Cr
V
Sr
-t
+
-I-
Ba
Co
Ni
Cu
Pb
+
+ +
+ + +
Mn -
+
+ +
+
+ +
and the lower pert wae deposited slowly in fully marine (shelf) waters. Towards the top of the marine succession (the unit is known locally 8s the Mansfield Marine Band, occurring at the Westphalian B/C junction), a goniatite assemblage is replaced by Ling&: an increasing breakish water component is indicated. The top of the marine sequence is marked by nonmarine lamellibranahs in sample 5962. The marine sequence thus passes from fully marine at the base through progressively more brackish waters until the marine element is ti8lly lost. This trend is accompanied by steadily increasing depositional rates. Of geochemical signi&ance in the present context is the concomitant decrease in organic matter and pyrite content. In more general terms, the environment of deposition of the basal non-marine sediments was dr8stically mod&d by 8 sharply transgressive marine episode. Thereafter, the geographio setting appears to have been st8ble: the remainder of the sequence accumulating from progressive silting of a shelf-sea. Gradually increasing depositional rates are readily equated with advanoe of the original shoreline. Provided, therefore, that attention is confined to the marine sequence, changes in palaeoenvironments can be sesegsed fairly accurately. The major variable ~8s rate of deposition (latterly with slight reduction in salinity) and this is presently reflected by systematic variation in overall sediment composition. These considerations suggest that analysis of variation within the marine sample alone might simplify interpretation of trace-element results. Significant major/trace correlation coeftlcients are identitled in Table 4. Neither organic matter nor siderite is a major sediment component within this population. It is not surprising to find that organic matter and total disgenetic Fe no longer correlate negatively with 8 number of traoe elements. Elimination of these dilution effects allows three fairly distinctive behavioural trends to be recognized. These are: (a) Be, Co, Ni, Cu and Pb are concentrated in the basal marine sediments together with organic matter and pyrite (total diagenetic Fe largely reflects pyrite content). It is unreasonable to conclude that either phase was directly responsible for concentration; this trend parallels depositional rate fluotuation. Sorption by clay minerals, for example, would equally lead to maximum concentration in the most slowly deposited basal sediments. (b) M.n correlates negatively with 018y content and positively with total d&genetic Fe. It is evident that diagenetic processes were all-important in governing final distribution. (a) Ga, B, Cr, V and Sr simply reflect clay content and show no tendency to covary with those parameters known to reflect environmental variation. It is difllcult to envisage any alternative to the simple explanation that these elements arrived at the site of deposition tlrmly bound in detrital olay lattices (as Gas+ Bs+ CrsCand Vs+ proxying for Ale+, S9+ possibly present in interlayer K+ sites) and that the initial concentrations were insignificantly 8Ugmented by sorption from solution.
522
Notes
Some further insight into probable incorporation mechanisms may be obtained from the results of experimental work and of recent sedimentation studies. It should be noted, however, that such information usually applies to pre-diagenetic distribution. TUREKIAN and IMBRIE (1966) described the distribution of Ba, Co, Cu, Iii, Pb, Cr, Mn and Sn in the tops of deep-sea cores from the Atlantic Ocean. Mn, Co and Ni showed a marked tendency for concentration in areas of low detrital deposition whilst a not dissimilar distribution of Cu was shown to be closely related to carbonate content. These elements can be said to show response to environmental factors whereas the distribution of Cr (radically different from the above) probably reflects detrital deposition and the mineralogy of the source area. In very general terms, these different behavioural patterns are broadly similar to those observed in the ancient sediments described here. Other researchers have concentrated on experimental methods (KRAUSKOP~, 1956) and on specific components within present day sediments (GOLDBERG and ARRHEMUS, 1958; HIRST, 1962; CHESTER and HUUHES, 1966; MANHEIM, 1966; PRICE, 1967). All tend to emphasise the importance of limonitic material or Fe-Mn oxides as scavengers of trace-elements from depositional waters. Upon burial, these oxidate phases would be rendered unstable in the chemically (and biochemically) active porewater environment. This dramatic change of chemical environment with burial has been emphasised by STRAI(HOV (1953). Final distribution of trace elements released by dissolution of limonitio material would be governed by partition between solution and sorbent phases (clay minerals and organic matter) or by coprecipitation with diagenetic sulphides and carbonates. This communication emphasises the problems of ancient sediment geochemistry: problems only superficially solved by extensive investigations of recent sediment geochemistry. The early diagenetio stage requires systematic investigation since this is the stage which appears to be most important in fixing trace-element distribution in argillaceous sediments. In the final analysis, it must be remembered that many ancient sedimentary basins (the European Carboniferous is but one) have no present day analogue. Ack~owledgemetis-Thanks are due to the British National Coal Board for making borehole material available, to Professor L. R. MOORE for his continued interest in the project and to Mrs. S. M. RHODES for invaluable assistance with analytical work. RE~RENCES AHRENS L. H. and TAYLOR S. R. (1961) S~ect~ochemicalAnaEysk (2nd edition). Pergamon. CHESTER R. and HUGHES M. J. (1966) The distribution of manganese, iron and niokel in a North Pacific deep-sea clay core. Deep-Sea Rea. 13,627-634. CURTIS C. D. (1965) A spectrographio study of the Mansfield Marine Band. Unpublished Ph.D. Thesis, University of Sheffield. CURTIS C. D. (1967) Diagenetic iron minerals in some British Carboniferous sediments. Beochim. Comchim. Acta 31,2109-2123. GOLDBERGE. D. and ARRHWNIUSG. 0. S. (1958) Chemistry of Pacifio pelagic sediments. Cfeochim. Cosmochim. Aota 13,153-212. Hms~ D. M. (1962) The geochemistry of modern sediments from the Gulf of Par&--II. The location and distribution of trace-elements. Qeochim. Co8mochim. Acta as, 1147-l 187. KRAUE)KOPFK. B. (1966) Factors controlling the concentration of thirteen rare metals in sea water. Qeochim. Cosmochim. Acta 9, l-32. fi-1~ F. T. (1966) Manganese-iron accumulations in the shallow marine environment. Narragansett Mar. Lab. Occaa. Publ. 3, 217-276. pRICa: N. B. (1967) Some geochemical observations on manganese-iron oxide nodules from different depth environments. Mar. Beol. 5, 611-638. &Ems D. A. (1964a) The radioaotivity of the Mansfield Marine Band, Yorkshire. Geochim. Cosmachim. Acb aS, 673-681. SPEW D. A. (196413)The major-element geoohemistry of the Mansfield Marine Band in the Westphalian of Yorkshire. Geochim. Co8mochim. Acta m 1679-1696. Spon~ F. (1964) A new record of Hystrichospheres, from the Mansfield Marine Band, Westphalian. Proc. Yorks. Geol. Sot. 84, 357-370.
Notes Srn~ov
N. M.
523
(1963) Disgenesis
8nd its importance in sedimentary ore formation. Izw. (British Government Dept. Education and Science Russian Transl8ting prognunme, R.T.S. 2763, pp. l-74, 1965.) TAYLOR R. K. snd Srcraas D. A. (1967) An unusual carbonate band in the East Pennine Coalfield (England). Ss&nentoZogg 9, 55-73. TU~EKLW K. K. and 1116srzm J. (1966) The distribution of trace elements in deep-se8 sediments of the Atlantic Ocean. Earth Pkmet. Sci. Lett. 1, 101-108.
Akad. Nauk S.S.S.R. Ser. &ol. 5, 1249.
&ochhnics
et Ccsmcchimica Acta, 1969, Vol. 33, pp. 623 to 627. Pergamon Press.
Age
of the
Manicouagan and
Clearwater
Printed in Northern Ireland
Lakes
craters
R. L. FLEIBCHER, J. R. M. VIERTL and P. B. PRICE General Electric Research and Development Center Schenectady, New York
12301
(Received 9 September 1908; accepted in revised form 18 October 1968) Ab&&-Track dating of M8nicouagen Cr8ter gl8ss gives 208 ( f25) m.y. Partial track feding in 8 Cle8rwater Lakes sample yields results consistent with the K-Ar age: 290 ( f30) m.y. The Clearweter Lakes Craters 8re, therefore, not contemporaneous with 8ny known tektite fall. Track annesling studies are important to the determination of reliable fission track 8ges. INTRODUCTION THE C~DIILN shield bears a multiplicity of structures (BEALS et al., 1963), which 8re the remmmts from a series of energetic events spread over the last ~10~ yr. Most observers (BEAU et al., 1963; DENCE, 1964, 1965; INNES, 1964; BEALS and KALLIDAY, 1966) regard these “fossil craters” 8s evidence th8t the earth has been bombarded by mete0ritic, asteroidal, and/or cometary bodies. Although the inferred impact origin of these craters has been questioned (Cmtanr, 1966), it is clear that 8 measurement of the ages of known impact structures would 8110~ 8 lower limit to be measured for the integrated flux of cmter-forming objects in the vicinity of the earth over geological times. One immediate application of such information is to set 8 lower bound also on the fraction of lunar craters that were formed by impact events, since the flux of objects at the moon (when suitably adjusted for the different grrtvitational effect of the moon) would be indistinguishable from that at the earth. Alternatively if the identification of the major portions of the larger lunar craters 8s due to primary impact is accepted, ages of different portions of the lunar surface can be inferred (OPIK, 1960; KREITER, 1960; SHOEMAKER et al., 1961). With these ends in mind we have directed fission track studies toward measuring the ages of two of the largest “probable” (DENCE, 1964; DENCE et al., 1965) impact craters on the North American continent, the Manicouagan crater (40 miles in dia.) and Clearweter Lakes West (it is the larger-20 miles in diameter-of the two Clearwater Lakes craters). A previous Ossiontrack age of 33*4( h4.5) m.y. (FLEISCHER and PRICK, 1964) has been determined for Clearweter L8kes, as well as K-Ar whole rock ages of 300 (f 30) and 285 (&-30) m.y. (WAxmrsset al., 1966). A whole rock K-Ar age for Manicouagan (WANLESS et al., 1965) w8s given as 225 (f30) m.y. Of four optically glassy Manicouagan samples that were examined, two were found suitable for dating. Two of the four were supplied by K. L. Currie: 14K8,8 plagioclase glass, ~8s found to be too non-uniform to be useful; 16-G w8s found suitable for track etching. This sample w&s taken from a vein that was about 4 in. wide, and exposed over 8 vertical height of 60 ft. The vein cuts crumbly biotite gneiss, and was intruded into the position where it was found, about 300 yards from the outer ring f8ult bounding the structure. Two samples were supplied by M. R. Dence: M-l was found by X-ray examination to be microcrystalline; M-2 was suitable for dating. M-2 is from a glassy dyke which cuts the basement gneisses (which are of Grenville age) near the margin of the crater.
NOTES
Trace element distribution in some British Carboniferoussediments C. D. &RTIS of Geology, The University,
Department
(Received 21 May 1968;
Sheffield Sl 3JD
accepted in revieed fern 21 October 1908)
Ati&-Traoe element concentrations in a sequence of Westphalirm sediments are reported. The date are disoussed in light of previously published palaeoecological and geoohemioal inform&ion for the same sediments. Distribution patterns are concluded to be much a%cted by early diagenetio processes. PFLE~IOUSreports (SPEARS 1964a, b; SPODE 1904; CURTIS, 1967) have described the mineralogy, major-element geochemistry and fauna1 and floral distribution within a sequence of Westphalian sediments penetrated by 8 British National Coal Board boring in the Yorkshire Coalfield (44/628168). This accumul&ed information was thought to make the sequenoe ideal for trace-element study. In partioular, much can be deduced concerning environmental fluctuations during deposition. Analytical data were obtained by optioal spectrography and are listed in Table 1. The analytical saheme followed olosely that suggested by AIIRENS and TAYLOR (1961). Coeaaients of Variation for each element were callculated for determinations from multiple burns on selected samples. The listed figures are means of triplicate determinations. The Standard Error of the Table 1. Spectrographic
trace element data
Sample
Depth (ft)
GE
B
Cr
V
Co
Ni
Cu
Pb
Mn
Sr
Ba
5937 948 960 962 2 4 6 8 12 14 16 18 20 22 24 26 28 30 32 969 970
937 948 960 962 953.5 954.6 955.5 956.5 958.6 959.5 960.5 961.5 962.6 963.6 964.5 965.6 966.5 967.6 968.6 969 970
30 38 36 35 31 27 35 27 29 33 35 34 31 35 34 34 39 13 40 17 28
78 ad. ad. n.d. 88 86 86 86 92 92 101 101 100 94 85 82 70 22 68 40 64
77 109 121 123 118 119 129 121 124 124 143 122 117 128 108 121 105 69 90 39 100
188 266 258 245 258 245 282 280 266 278 310 266 265 286 330 300 300 185 280 140 208
22 24 24 23 27 21 23 21 22 22 22 24 26 26 31 31 28 17 20 10 14
53 66 64 61 72 63 71 66 60 63 62 99 77 67 77 79 87 64 56 27 39
59 62 60 64 36 30 68 48 38 43 74 84 73 77 132 142 159 88 87 15 24
22 38 40 30 29 18 23 21 21 23 22 73 66 87 164 60 39 10 66 10 25
970 1116 1205 825 420 618 496 550 490 476 610 1046 1086 1160 1016 376 2300 2440 426 810 1180
88 99 136 126 118 122 119 111 116 134 144 135 124 132 120 120 96 368 66 32 70
690 465 466 496 465 666 606 466 440 666 485 610 666 660 630 685 7000 400 88 316
Note:
All values in ppm.
n.d. = not determined.
619
-
520
Notes Table 2. Selected major element analytical data* Total alkalis Sample
A’#,
S937 948 950 952 2 4 6 8 12 14 16 18 20 22 24 26 28 30 32 969 970
20.35 22.39 23.68 22.80 23.00 21.17 23.04 22.71 21.89 23.23 23.62 22.35 22.12 22.14 21.37 23.16 18.92 5.56 17.46 8.24 16.08
(= K,O)
Total diagenetic Fe as Fe,O,
Acid soluble nulphur
Organic matter
5.26 5.16 5.45 5.24 5.54 5.41 5.56 5.33 5.20 5.84 5.64 5.35 5.29 5.17 5.18 4.79 3.89 1.43 3.91 1.27 2.54
3.88 5.94 2.85 1.98 l-03 1.06 2.09 1.41 0.78 0.93 1.01 4.44 4.36 5.32 6.17 1.37 12.16 6.06 6.17 25.40 6.07
0.03 0.01 0.03 0.02 0.56 0.44 1.59 0.69 0.09 O-64 0.66 3.54 3.48 4.24 4.91 0.98 3.00 0.53 4.90 0.11 1.49
2.34 4.00 3.01 2.68 1.02 1.20 0.88 1.10 1.21 1.05 1.11 1.55 1.47 1.50 2.23 2.16 1.36 1.33 10.00 5.72 7.52
* Teken from SPEARS (1964), Cumrs (1966, 1967). All values wt. %.
Table 3. Major/trace element correlationcoeffiaientsaccepted at the 95% level in the total sample population
4%
Total alkalis Organic matter Total diagenetic Fe Sulphur
Ga
B
Cr
V
Sr
Ba
Co
Ni
+
+
+
+ + -
+ + -
+ +
+ +
-
-
-I+
+++
+
+
Cu
Pb
&In _ --
+
+
Coefficientof Variation (v = 1008/Z(2n), 1/Zwhere 6’ = Standard Deviation, I = mean and n, the number of determinations, = 3 in each case) proved to be approximately f15%(Sr), f 12 %(Ba) and f 10 % or better for the remaining trace elements studied. A number of major element analyses taken from previous reports are utilised in the data analysis. These are listed in Table 2. The prinoiplesediment components are quartz, clay minerals (illite with subsidiary chlorite and kaolinite), organic matter and diagenetio iron minerals [siderite, pyrite and, in sample 530, ankerite; this is thought to be the alterationproduct of calcite accordingto TAYLOR and SPRIARS (1967)]. AlsOs documents total clay variation whilst “total alkalis” (KpO plus NasO converted to equivalent KsO) is indicative of illite content. Acid soluble sulphur is a direct measure of pyrite. “Total diageneticFe” is the sum of Fe equivalent to sulphur (pyrite) and CO, (siderite)and is a measure of the non-detrital oomponent of these sediments. Covariation of traoe-elementswith major sediment constituentsis convenientlysummarised by the identificationof significantoorrelationcoefficientsin Table 3. All samples are considered for all possible relationships. It is apparent that Ga, B, Cr, V, Sr, Ba, Co and Ni vary sympathetically with olay content and antipatheticallywith organic matter and the total diagenetic fraction. Suoh a situation would be expected if these trace elements were olay located: the relationshipsbeing a simple consequenceof dilution of the clay fraction by orgrrnicmatter and diageneticminerals (and quartz). Mn behaviour is distinctive in being the converse. Cu and Pb seem to vary quite independentlyof clay content. Aoid soluble sulphurvaries sympath&ia&Iy
621
Notee
with V, Ni, Cuand Pb. This suggests pyrite location but several alternative explanations are available. Some brief summar~yof p8l8eoecologic8l information is necessary 8t this stage. The samples may be divided into two groups on the basis of fossil aontent. Samples S2 to 530 inclusive are marine. Samples S937, 948, 960, 962, 32, 969 and 970 constitute the nonm8rine population. The b8sal sediments of the sequence (samples 8970, 969 and 32) were deposited from non-marine waters and contain much coaliiled plent material. During early diagenesis, however, effective contact with marine waters was maintained vi8 diffusion and the diegenetic assemblage contains both pyrite and siderite. The marine sequence starts abruptly Table 4. Major/trace element correlation coefficients accepted at the 96 % level in the marine sample population GS
a&3
Total alkalis Organic matter Total diegenetic Fe Sulphur
+++ +++
B
Cr
V
Sr
-t
+
-I-
Ba
Co
Ni
Cu
Pb
+
+ +
+ + +
Mn -
+
+ +
+
+ +
and the lower pert wae deposited slowly in fully marine (shelf) waters. Towards the top of the marine succession (the unit is known locally 8s the Mansfield Marine Band, occurring at the Westphalian B/C junction), a goniatite assemblage is replaced by Ling&: an increasing breakish water component is indicated. The top of the marine sequence is marked by nonmarine lamellibranahs in sample 5962. The marine sequence thus passes from fully marine at the base through progressively more brackish waters until the marine element is ti8lly lost. This trend is accompanied by steadily increasing depositional rates. Of geochemical signi&ance in the present context is the concomitant decrease in organic matter and pyrite content. In more general terms, the environment of deposition of the basal non-marine sediments was dr8stically mod&d by 8 sharply transgressive marine episode. Thereafter, the geographio setting appears to have been st8ble: the remainder of the sequence accumulating from progressive silting of a shelf-sea. Gradually increasing depositional rates are readily equated with advanoe of the original shoreline. Provided, therefore, that attention is confined to the marine sequence, changes in palaeoenvironments can be sesegsed fairly accurately. The major variable ~8s rate of deposition (latterly with slight reduction in salinity) and this is presently reflected by systematic variation in overall sediment composition. These considerations suggest that analysis of variation within the marine sample alone might simplify interpretation of trace-element results. Significant major/trace correlation coeftlcients are identitled in Table 4. Neither organic matter nor siderite is a major sediment component within this population. It is not surprising to find that organic matter and total disgenetic Fe no longer correlate negatively with 8 number of traoe elements. Elimination of these dilution effects allows three fairly distinctive behavioural trends to be recognized. These are: (a) Be, Co, Ni, Cu and Pb are concentrated in the basal marine sediments together with organic matter and pyrite (total diagenetic Fe largely reflects pyrite content). It is unreasonable to conclude that either phase was directly responsible for concentration; this trend parallels depositional rate fluotuation. Sorption by clay minerals, for example, would equally lead to maximum concentration in the most slowly deposited basal sediments. (b) M.n correlates negatively with 018y content and positively with total d&genetic Fe. It is evident that diagenetic processes were all-important in governing final distribution. (a) Ga, B, Cr, V and Sr simply reflect clay content and show no tendency to covary with those parameters known to reflect environmental variation. It is difllcult to envisage any alternative to the simple explanation that these elements arrived at the site of deposition tlrmly bound in detrital olay lattices (as Gas+ Bs+ CrsCand Vs+ proxying for Ale+, S9+ possibly present in interlayer K+ sites) and that the initial concentrations were insignificantly 8Ugmented by sorption from solution.
522
Notes
Some further insight into probable incorporation mechanisms may be obtained from the results of experimental work and of recent sedimentation studies. It should be noted, however, that such information usually applies to pre-diagenetic distribution. TUREKIAN and IMBRIE (1966) described the distribution of Ba, Co, Cu, Iii, Pb, Cr, Mn and Sn in the tops of deep-sea cores from the Atlantic Ocean. Mn, Co and Ni showed a marked tendency for concentration in areas of low detrital deposition whilst a not dissimilar distribution of Cu was shown to be closely related to carbonate content. These elements can be said to show response to environmental factors whereas the distribution of Cr (radically different from the above) probably reflects detrital deposition and the mineralogy of the source area. In very general terms, these different behavioural patterns are broadly similar to those observed in the ancient sediments described here. Other researchers have concentrated on experimental methods (KRAUSKOP~, 1956) and on specific components within present day sediments (GOLDBERG and ARRHEMUS, 1958; HIRST, 1962; CHESTER and HUUHES, 1966; MANHEIM, 1966; PRICE, 1967). All tend to emphasise the importance of limonitic material or Fe-Mn oxides as scavengers of trace-elements from depositional waters. Upon burial, these oxidate phases would be rendered unstable in the chemically (and biochemically) active porewater environment. This dramatic change of chemical environment with burial has been emphasised by STRAI(HOV (1953). Final distribution of trace elements released by dissolution of limonitio material would be governed by partition between solution and sorbent phases (clay minerals and organic matter) or by coprecipitation with diagenetic sulphides and carbonates. This communication emphasises the problems of ancient sediment geochemistry: problems only superficially solved by extensive investigations of recent sediment geochemistry. The early diagenetio stage requires systematic investigation since this is the stage which appears to be most important in fixing trace-element distribution in argillaceous sediments. In the final analysis, it must be remembered that many ancient sedimentary basins (the European Carboniferous is but one) have no present day analogue. Ack~owledgemetis-Thanks are due to the British National Coal Board for making borehole material available, to Professor L. R. MOORE for his continued interest in the project and to Mrs. S. M. RHODES for invaluable assistance with analytical work. RE~RENCES AHRENS L. H. and TAYLOR S. R. (1961) S~ect~ochemicalAnaEysk (2nd edition). Pergamon. CHESTER R. and HUGHES M. J. (1966) The distribution of manganese, iron and niokel in a North Pacific deep-sea clay core. Deep-Sea Rea. 13,627-634. CURTIS C. D. (1965) A spectrographio study of the Mansfield Marine Band. Unpublished Ph.D. Thesis, University of Sheffield. CURTIS C. D. (1967) Diagenetic iron minerals in some British Carboniferous sediments. Beochim. Comchim. Acta 31,2109-2123. GOLDBERGE. D. and ARRHWNIUSG. 0. S. (1958) Chemistry of Pacifio pelagic sediments. Cfeochim. Cosmochim. Aota 13,153-212. Hms~ D. M. (1962) The geochemistry of modern sediments from the Gulf of Par&--II. The location and distribution of trace-elements. Qeochim. Co8mochim. Acta as, 1147-l 187. KRAUE)KOPFK. B. (1966) Factors controlling the concentration of thirteen rare metals in sea water. Qeochim. Cosmochim. Acta 9, l-32. fi-1~ F. T. (1966) Manganese-iron accumulations in the shallow marine environment. Narragansett Mar. Lab. Occaa. Publ. 3, 217-276. pRICa: N. B. (1967) Some geochemical observations on manganese-iron oxide nodules from different depth environments. Mar. Beol. 5, 611-638. &Ems D. A. (1964a) The radioaotivity of the Mansfield Marine Band, Yorkshire. Geochim. Cosmachim. Acb aS, 673-681. SPEW D. A. (196413)The major-element geoohemistry of the Mansfield Marine Band in the Westphalian of Yorkshire. Geochim. Co8mochim. Acta m 1679-1696. Spon~ F. (1964) A new record of Hystrichospheres, from the Mansfield Marine Band, Westphalian. Proc. Yorks. Geol. Sot. 84, 357-370.
Notes Srn~ov
N. M.
523
(1963) Disgenesis
8nd its importance in sedimentary ore formation. Izw. (British Government Dept. Education and Science Russian Transl8ting prognunme, R.T.S. 2763, pp. l-74, 1965.) TAYLOR R. K. snd Srcraas D. A. (1967) An unusual carbonate band in the East Pennine Coalfield (England). Ss&nentoZogg 9, 55-73. TU~EKLW K. K. and 1116srzm J. (1966) The distribution of trace elements in deep-se8 sediments of the Atlantic Ocean. Earth Pkmet. Sci. Lett. 1, 101-108.
Akad. Nauk S.S.S.R. Ser. &ol. 5, 1249.
&ochhnics
et Ccsmcchimica Acta, 1969, Vol. 33, pp. 623 to 627. Pergamon Press.
Age
of the
Manicouagan and
Clearwater
Printed in Northern Ireland
Lakes
craters
R. L. FLEIBCHER, J. R. M. VIERTL and P. B. PRICE General Electric Research and Development Center Schenectady, New York
12301
(Received 9 September 1908; accepted in revised form 18 October 1968) Ab&&-Track dating of M8nicouagen Cr8ter gl8ss gives 208 ( f25) m.y. Partial track feding in 8 Cle8rwater Lakes sample yields results consistent with the K-Ar age: 290 ( f30) m.y. The Clearweter Lakes Craters 8re, therefore, not contemporaneous with 8ny known tektite fall. Track annesling studies are important to the determination of reliable fission track 8ges. INTRODUCTION THE C~DIILN shield bears a multiplicity of structures (BEALS et al., 1963), which 8re the remmmts from a series of energetic events spread over the last ~10~ yr. Most observers (BEAU et al., 1963; DENCE, 1964, 1965; INNES, 1964; BEALS and KALLIDAY, 1966) regard these “fossil craters” 8s evidence th8t the earth has been bombarded by mete0ritic, asteroidal, and/or cometary bodies. Although the inferred impact origin of these craters has been questioned (Cmtanr, 1966), it is clear that 8 measurement of the ages of known impact structures would 8110~ 8 lower limit to be measured for the integrated flux of cmter-forming objects in the vicinity of the earth over geological times. One immediate application of such information is to set 8 lower bound also on the fraction of lunar craters that were formed by impact events, since the flux of objects at the moon (when suitably adjusted for the different grrtvitational effect of the moon) would be indistinguishable from that at the earth. Alternatively if the identification of the major portions of the larger lunar craters 8s due to primary impact is accepted, ages of different portions of the lunar surface can be inferred (OPIK, 1960; KREITER, 1960; SHOEMAKER et al., 1961). With these ends in mind we have directed fission track studies toward measuring the ages of two of the largest “probable” (DENCE, 1964; DENCE et al., 1965) impact craters on the North American continent, the Manicouagan crater (40 miles in dia.) and Clearweter Lakes West (it is the larger-20 miles in diameter-of the two Clearwater Lakes craters). A previous Ossiontrack age of 33*4( h4.5) m.y. (FLEISCHER and PRICK, 1964) has been determined for Clearweter L8kes, as well as K-Ar whole rock ages of 300 (f 30) and 285 (&-30) m.y. (WAxmrsset al., 1966). A whole rock K-Ar age for Manicouagan (WANLESS et al., 1965) w8s given as 225 (f30) m.y. Of four optically glassy Manicouagan samples that were examined, two were found suitable for dating. Two of the four were supplied by K. L. Currie: 14K8,8 plagioclase glass, ~8s found to be too non-uniform to be useful; 16-G w8s found suitable for track etching. This sample w&s taken from a vein that was about 4 in. wide, and exposed over 8 vertical height of 60 ft. The vein cuts crumbly biotite gneiss, and was intruded into the position where it was found, about 300 yards from the outer ring f8ult bounding the structure. Two samples were supplied by M. R. Dence: M-l was found by X-ray examination to be microcrystalline; M-2 was suitable for dating. M-2 is from a glassy dyke which cuts the basement gneisses (which are of Grenville age) near the margin of the crater.