DISCUSSION·
Comment
1
(Comment on the paper 'Geochemistry of Trondhjemites from Sigegudda, . Hassan District, Karnataka ' By P. Rama Rao et al. in the Journal of the Geological
Society of India, Vol. 37, April 1991, pp. 351-358).
The authors have heavily relied upon only a fe:wparameters (e.g., Na20/K20 ratios) as constraints in support to the nomenclature: as trondhjemites. and ignored several vital criteria such as An-content of plagioc:lases, Si02,
AI
203 and Na20 abundances relative to one another, and most importantly, the low potash the trondhjemites are expected to contain. In the light of the deiined petrochemical characters of trondhjemites, a number of intermediate (Si02 < 66%) calc-alkaline units of Sigegudda which have >2% (up to 2.53%) of K 20, '" 10 to 14% normative Qrthoc1ase and '" 10% modal K-feldspars would pass into non-trondhjemites. It would benefit the readers if the authors critically re··examine the petrochemistry of the Sigegudda litho units, distinguish the tlondhjemites from the rest of the rocks, and discuss their interrelations.Precambrian Geology Division Geological Survey of India Band/aguda, Hyderabad 500660
Reply
We thank Sri Sarvothaman for his interest on our paper.
H. SARVOTHAMAN
Following are the criteria for considering the rocks under study as trondhjemites; (1) Rocks of tonalitic composition having less, than 10% mafic minerals are termed as trondhjemites. (2) Na20jK20 ratio is> 2. (3) Low K 20 content (all the samples except one contain < 2.5% and majority of the samples contain < 2% Ki». (4) Position of the rocks fall in the tonalitic/trondhjemitic field in the petrochemi-cal diagrams (Figs. I and 2 of our paper).
We feel that any individual analysis may no t be indicative of the overall composition of a suite as there are bound to be varic:~tions in a system. Therefore, a reasonably large number of samples has been taken to bring out details of chemi-cal variations in the suite.
National Geophysical Research Institute H)'derabad 500007
Comment 2
(Comment on the paper, 'Geology, Petrography and Systematic Stratigraphy of Pre-Ariyalur sequence in Tiruchirapalli District, Tamil Nadu, India '. By S.
Ramasamy and Ranjit K. Banerjee, Vol. 37, June, 1991, pp. 577-594).
J. The proposed new litho-unit' Terani Formation' seems to be similar to , Therani Formation' (U. Gondwana) of ONGC Madras brochure on 'Rock Stratigraphy of Cauvery Basin' published in 1983 (p. 4, Fig. 2 and p. 5). Authors might have overlooked this publication.
2. 'The lower part of the Uttatur Formation is found to be homotaxially . equivalent to the Dalmiapuram Formation' (Abstract, p. 577). In Table I,
legend of Figure I and in systematic stratigraphy (pp. 590-592), the latter has been lescribed as a distinctly lower horizon. It has been noted that the Uttatur Formation consists of a lower clay member and an upper sandy clay member with alternating argillaceous limestone bands in both sub-divisions (Table I, p. 577). Further,' the fossiliferous limestone bands of Uttatur Formation are the genetic continuation of the biostromal band originating from the reefoidal complex of the Dalmiapuram, hence partly homotaxial with the DaJmiapuram Limestone Member' (p. 592). . This has created much confusion since a 'Formation', the fundamental unit in litho-stratigraphic classification, is 'a genetic unit formed under essentially uniform conditions or under an alternative of conditions' (Dunbar and Rodgers, 1957, p. 259). It is debatable whether such differentiation of two Formations is possible where part of the upper unit has' genetic continua-tion' to part of the lower (Ref: Art. 7, p. 5 of Code of Stratigraphic
Nomenclature of India; G.S.I. Misc. Pub. 20, 1971).
3. The area covered under the present work has a fiat to undulating topo-graphy with patchy outcrops of subhorizontal to low-dipping Iitho]ogies~ This is, perhaps, the reason why no dip data are shown in the geological map (Fig. 1). In such a geological setting it is difficult to encounter a very large number of lithologies (Fig. 3) at one outcrop or in a small area with few exposures. But the thicknesses of different formations, obtained from traverse mapping (Table II) and as represented in Figure 3 and Tables I and II, are of very high order. What would be the geometry of lithounits if at the margin of a transgressive shelf (see Fig., location I to X the lithostratigraphic columns are so lengthy (up to 1200 m at location X) ? It seems tbat there is some relation with the length of columns in Figure 3 with that of traverses outlined in Figure 1. No available drill-core data in this area (from O.N.G.C., G.S.1. and several exploratory pits of private mines) indicate such huge thickness of the Pre-Ariyalur sequence in this area.
DISCUSSION
area even at higher horizons (Sillakudi Formation), rather than discordance or structural complexity at Archaean-sedim(mtary contact' (p. 577).
5. The log numbers and locations in Figure 4, where distribution of petro-graphic types and subtypes in the Pre-Ariyalur sequence are depicted, seems to represent the same series as in Figure 3. Though the different petro-graphic types are matters of interpretation, the unit (gastropodal calcareous arenite) is never that much thick and extensive along the western margin of the basin (e.g., Kallakudi, Neykulam and Uttatur). The occurrence of gastropods in Garudamangalam area, tYPf: area for such rock, is quite patchy; and, if the ecology of this group of organisms is to be considered, they cannot form such thick series (about 160 m at Neykulam, 110 m at Uttatur, etc.).
Department 0/ Geology & Geophysics
llT, Kharagpur 721 302 ASlT K. GUHA
References
Code of Stratigraphic Nomenclature oflndia. G.S.1. Misc. pubJ. No. 20, 1971. 28+ iv pp. 8 Figs.
DUNBAR, C. O. and RODGERS, J. (1957) Principles :of Stratigraphy. J. Wiley & SODS,
N. York and London, 356 p.
Rock Stratigraphy of Cauvery Basin, ONGC, Madras.
Reply
We express sincere thanks to Prof. Guha for taking keen interest and for offering specific comments on our paper on the pre-Ariyalur sequence of Tiruchira-palli.
1. We are sorry to have missed the specific information on the Terani Forma-tion contained in the ONGC Madras brochure.
2. There is a misprint in the abstract which has been inadvertently left in the print. Instead of the Uttatur Formation (of the present authors) it should refer to the famous Uttatur Group of Blanford's classification used till recently. The Dalmiapuram and the Uttatur Formation (of the present authors) are two distinct lithological units which can be in part homotaxial to each other.
3. The lithologs on Figure 3 are plotted on the basis of the outcrop pattern and width as recorded along each traverse. On account of low dips and almost a flat terrain, it is not possible to measure the thickness of units at anyone place. The total length of each litho]og thus represents the
maxi-mum development of pre-Ariyalur sequence in the respective traverse. The total thickness so computed cannot be detected at anyone point in the sub-surface (well sections) as the depocentres of different stratigraphic units differ in place with time in a transgressiveAregressive shelf model.
5. The distribution of various petrographic types are plotted in the framework of the major Iithologica1 units, hence, figures 3 and 4 look very similar but differ in contents and purpose. The gastropodal calcareous arenite is an important petrographic type which corresponds with the famous' Shell limestones' of Garudamangalam. The relative distribution of gastropod shelIs may vary from place to place on account of variable abundance of other groups of invertebrate fossils.
Indian Institute of Technology Powai. Bombay-400 076
S. RAMASAMY RANJlT K. BANERH
Comment 3
(Comment on paper, Granites of Petermann Ranges, East Antarctica and Implications on their Genesis, by A. Joshi, N. C. Pant and M.,L Parimoo, published in Journal of the Geological Society of India, VoL 38, No.2, pp. 169-181).
1. There appears to be some discrepancy in naming the rock at the northern part of Petermann I and II as 'A-type granite' which the authors have described from the Petermann Ranges (as shown in their map on p. 170). In the 'Geological map of Wohlthat Mountains, Central Queen Maud Land, East Antarctica' by Geological Survey of India published on p. 5·of the Souvenir for Workshop on ' Antarctic Studies' (D.O.D., and N.P.L., 1988) the same outcrop has been shown as silica-rich anorthosite, probably by the same authors who also happened to participate in the Expedition.
Ravich and Kamenev (1975) had described the same rock as grano-syenite, Further, Kaul et al. (1988) and Mukerji et
at.
(1988) have shown this rock as quartz-syenite in their maps on p. 61 and p. 127 respective1y. On the basis of mineralogical composition the same rock has been described in detail by Hussain (1989) as quartz alkali-feldspar syenite to alkali-felds-par granite. We wonder how a rock can be so divergent from silica-rich anorthosite to quartz-syenite and now to an A-type granite.2. The geological map given on p. 170 of the present paper does not bear any acknowledgement to the earlier version from which the present one has been compiled, as the names appearing on the map show that an earlier version was available which should have been proper1y acknowledged. Ravich and Kamenev have published as far back in 1975 the geological map of this area with considerab1e detai1, a part of which was reproduced by Hussain (1989). The map given by the authors seems to be a simplified version of Ravich and Kamenev. One expects an improved detailed map from the Geological Survey of India which was participating in the Expedi-tions from the beginning.
3. In the F-M-A ternary diagram (Fig. 7 of the authors) used for plotting the granite data F shou1d have been either FeO
+
Fel03 according to Kuno172 DISCUSSION
in the absence of FeO and almost below detection limits of MgO this diagram is not of much use for these granites.
4. While discussing the REE contents of the samples on p. 176 they have mentioned that there is higher middle REE in some samples (Pj40A) which is not true; it has the least middle REE contents.
5. The authors have used chemical classification for the Petermann samples which should be avoided as far as possible. The rock should be named preferably according to its mineral content (Strekeisen, 1976) supported by chemical parameters (if needed).
6. The authors have compared the Petermann rocks with the A-type granites of Gabbo suite from Australia (Collins et al. 1982) and have concluded the former to be anorogenic in nature. A-type granites usually are associated with alkaline complexes, biotite-granites, peralkaline granites, quartz syen-ites and nepheline syensyen-ites (Gerasimovsky et al. 1974; Upton, 1974) and (;ould be the products of fractional crystallisation from a syenitic magma. We have attempted to classify the same rocks using the chemical parameters on the lines suggested by Batchelor and Bowden (1985) [Rl =4Si - 11 (Na+
K)-2 (Fe+Ti) and R2=6Ca+.2Mg+AI] and it is observed that these
Petermann rocks do not fall in ' A-type granite' field, whereas, the Gabbo suite (G) which the authors have used for comparison falls in the • A-type granite' field.
National Geophysical Research Institute Hyderabad 500007
S. M. HUSSAIN
V. DIVAKARA RAO
References
BATCHELOR, R. A. and BOWDEN. P. (1985) Petrogenetic interpretation of granitoid rock series u:;ing multicationic parameters. Chern. Geo!., v. 48, pp. 43-55.
COLLINS, W. J., BEAMS, S. D., WHITE, A. J. R. and CHAPPELL, B. W. (1982) Nature and origin of A-type granites with particular reference to Southeastern Australia. Contr. Min. Petrol., v. 80, pp. 189-200.
0.0.0. and N.P.L. (1988) A Souvenir for Workshop on 'Antarctic Studies'. Department of Ocean Development and National Physical Laboratory, New Delhi, Spl. Publn., 54 p.
GERASIMOVSKY, V. L. VOlKOV, V. P,. KOGARKO, L. N. and POLYAKOV, A. L. (1974) Kola Peninsula. In: H. Sorenson (ed.). The alkaline rocks. John Wiley and Sons, London. PI'. 206-220.
HUSSAIN, S. M. (1989) The Nature of Bedrock at Peterma:nn, I, WohHhat Range. Antarctica. Jour. Geol. Soc. India, v. 33, pp. 429-436.
IRVINE, T. N. and BARAGER, W. R. (1968) A guide to the chemical classification of the common volcanic rocks. Can. Jour. Earth Sci.. v. 8, pp. 523-548.
KAUL, M. K., MUKERJI. S., SINGH, R. K.. SRIVASTAVA, D. and JAYARAM, S. (1988) Geo-logical set up of a part of Central Queen Maud Land. East Antarctica. Dept. of Ocean Development, New Delhi, Technical Publn. No.5. pp. 57-97.
KUNO, H. (1968) Differentiation of basaltic magmas. In: Hess and Polderevaart (Eds.) The Poldervaart Treatise on Rocks of Basaltic Composition. Interscience PubIs., v. 2, pp. 623-688.
DISCUSSION
RAVICH, M. O. and KAMENEV, E. N. (1975) Crystalline Basement of the Antarctic Platform. John Wiley and Sons, New York, 582 p.
UPTON, B. G. J. (1974) The alkaline province of South-West Greenland. In.' H. Sorenson
(ed). The alkaline rocks. John Wiley and Sons. London, pp. 221·237.
STREKEISEN. A. (1976) To each plutonic rock its proper name. Earth Sci. Rev., v. 12, pp. 1-33.
Reply
.
We would like to thank Hussain and Rao for critically going through our paper. We have following points to make:
1. To our mind there is no discrepancy in relating the rocks at Petermann I and II as A-type granite since we have presented enough field, textural and chemical parameters in .our paper, Hussain and Rao will agree that the Souvenir brought out by the DOD during the '¥lorkshop on Antarctic Studies' is a pUblicity brochure. In this workshop no paper was presented by present authors on the Petermann granite.
. In our paper (p. 169), we have referred to the nomenclature of Ravich and Kamenev (1975), Their nomenclature was tentative, based on limited field and analytical data and hence. open to refinement. The QAP classifi-cation is used by Hussain (1989) and our preference is to chemical classifica-tion of the Petermann rocks. Their resemblance to A-type is an interpreta-tion based on anhydrous, alkaline and anorogenic nature (p. 178).
2. As our paper was only on the Petermann granites, the main intention in the accompanying map was to show the distribution of these in the Petermann Ranges. Since then a geological map of the Schirmacher-Wohlthat Region (1: 2,50,000 scale) has been published by the GSI in August, 1991.
3. The Fin FMA diagram shows the total iron (Fe203t) which includes FeO+ Fe203 as obtained from the XRF analyses. We have successfully used this diagram to depict the iron enrichment trend of these granites (p. 172). The fields of Irvine and Barager (1971 ; wrongly referred as 1968 by Hussain and Rao) have been used only for reference and no interpretation is based on them.
4. We thank Hussain and Rao for pointing out the error. It should be read as Pj40 instead of Pj40A.
5. It is difficult to ascertain accurately the modal mineralogy of these rocks due to the reasons mentioned in our paper. In this context, we would like to quote two of the classification principles from Le Bas and Streckeisen (1991 ).
'The eighth principle is that classification should be based on modal mineralogy, as far as possible '.
'The ninth principle is that if the modal mineralogy of an igneous rock cannot be determined satisfactorily, then chemical analytical parameters should be the next property used'.
Polarforschung Glacier area, East Antarctica (Table II of our paper) Hence, mention of only one suite is misleading. It is beyond our compre-hension why the widely reported association of A-type granite with massif anorthosite in the high-grade metamorphic terrains has been overlooked by Hussain and Rao.
We have used field, petrographic, textural and chemical evidence to suggest affinity of the Petermann granites to A-type. Use of a single dis-crimination diagram to refute all these is unjustified.
Geological Survey of India Antarctic Division.
NH-5P, NIT, Faridabad
A. JOSHr N. C. PANT M. L. PARIMOO
References
GEOLOGICAL SURVEY OF INDIA (1991) Geology of Scoirmlch'~r-Wohlthat. Region, Central Dronn-ing Maud Land, Antarctica. Map 00 1 : 2,50,000 scale.
HUSSAIN, S. M. and RAO, V. D. Comment on the Granites of Petermann Ranges, East Antarctica and implications on their genesis. (submitted).
IRVINE, T. N. and BARAGER, W. R. (1971) A guide to the chemical classification of the com-mon volcanic rocks. Can. Jour. Earth Sci .• v. 8, pp. 523-548.
LE BAS, M. J. and STRECKEISEN, A. L. (1991) The lUGS systematics of igneous rocks. Jour. Oeol. Soc., v. 148, pp. 825·833.
RAVICH, M. G. and KAMENEV, E. N. (1975) Crystalline Basement of the Antarctic Platform. John Wiley and Sons, New York, 582 p.
Comment 4
(Comments on the paper, 'Constraints on the Evolution of the Purana Basins ·of Peninsular India' by Vivek S. Kale, pub:lished in the Journal of Geo-logical Society of India Vol. 38, No.3, 1991, pp. 231-252).
The envisaged concept further need support from the Paleotectonic as well as Paleogeographic 2 D and 3 D maps for substantiatin;g the hypothesis.
The recommendation of pOly-historic evolution of Purana Basin is a practical concept needing the analysis of Purana Basins where the earlier generalized strati-graphic aIlalysis only clubbed many vertical tectonic events in one tectonic basin called Purana. Nevertheless, will it be proper to call the total vertical sequences ils constitl;lting one basin (as enumerated in the paper) in the entire period of Pro-terozoic (Aphebian and Riphean) even when they have poly-history? Is it not a case of over-simplified tectonic and stratigraphic interpretation? Rewa and Bhander sequences of Vindhyan units of Madhya :t>radesh are considered to be (Cambrian).
'I
DISCUSSION 175
the deposition of its sedimentary sequences into two geological cycles. The older -cycle is an interrupted one, restricted to fluvio-marine sedimentation during the -earlier part of Paleozoic followed by a large hiatus till the commencement of second fuller unit with a wide spread Permo-Carboniferous glaciation (Bap Boulder of Badhaura Formation), Interspersed Mezo-Cenozoic fluvio-marine sub-cycles sand-wiched between several unconformities represent this cycle of stable platform facies .deposited as homoc1ines on a basement controlled checker-box of blocks. Such a Phanerozoic sedimentary tectonics would hardly fit in with the Poly-historic Purana Basin envisaged by the author.
·Oil & Natural Gas Commission B. P. SHRIVASTAVA
.226, Cathedral Road, Madras-600 086
References
:SHRIVASTAVA. B. P. (1971) Rock-stratigraphic Nomenclature for the sedimentaries of West-Central Rajasthan. Bull. Geo!. Min. Metal. Soc. India. v. 44, pp. 1-19.
- - (1973) Evolution of Phanerozoic sediments in space and Time. Abstract, seminar on Recent Advances in Geology of Rajasthan and Gujarat. Geological Survey of India, Jaipur, Oct. 22-23.
Reply
Dr. Shrivastava is to be thanked for his interest shown in the paper. Much more work is certainly required before one can start unscrambling the detailed evo-lutionary histories of the Purana basins. The paper in question was only a pre-liminary evaluation of the more obvious geotectonic controls which appear to have .governed the evolution of the seven Middle-Late Proterozoic Purana basins; as also ·an attempt to emphasise their uniqueness in space and time.
It is gratifying to find support for the concept that the 'Purana' is neither a singular basin nor is it an acceptable stratigraphic entity, as has been traditionally ·considered. This term can more aptly be applied to the loose conglomeration of seven independent, sup~acrustal, epicratonic basins, which are mutually compa-rable to each other in terms of their evolutionary histories, notwithstanding the ·differences in their sediment content and deformational-metamorphic features.
Within one single 'polyhistory' basin, diverse depositional systems, shifting ·depocentres, localised hiatuses and diverse subbasinal deformational events are to be expected. Thererore, the Kaladgi-as also the other six-is treated as an indivi-<iua1 basin. It is likely that Shrivastava's comment is directed at the stacking of :sediment thickness in the' sediment-accumulation-curves (Fig. 4). The SACs have
not been plotted as replacements of the' basin subsidence curves', but only as preliminary plots in that direction. It is not implied that in each of the basins the 'stacking of the sediments actually exists as is depicted in its SAC. They are only intended to highlight the polyhistory nature of each of the basins, as also possibly :some of the constituent' Groups' (=sub-basins) within them.
As pointed out by Shrivastava, there have been several reports of Early Phanerozoic biota from some of the sediments in these basins. However, these reports are unfortunately not only sparse but also, at times, of doubtful validity (see
li6 DISCUSSION
preservation. They also are almost identical to the: type of environments and sedi-· ments within which some of the best Early Palaeozoic life forms have been studied. Yet reports of any shelly fauna or equivalent Early Palaeozoic biota are not yet available. This cannot be attributed to either absence of biota or their non-preservability due to environmental stress. Therefore, [even though this is a , negative argument' ] the available record would indicate a strong likelihood of
an
the sequences in the Purana basins being entirely confined to pre-Cambrian (see also Kale, 1990; Kale and Phansalkar, 1991).This author is in agreement with the point raisl!d by Shrivastava, regarding the status of the' Trans-Aravalli Basin '. These sequences cannot be grouped under 'Purana basins'. The only purpose of outlining this basin in Figure I was to-· point out that this basin was triditionally included as a ' Purana sequence ' (Pascoe~
1965 ; and that the currently available data unequivocally shows that it needs to be-removed from the purview of the' Purana basins' completely .
• Dept. 0/ Geology Univ. 0/ Poona, Pune
References
V. K. KALE
KALE, V. S. (1990) Problems of the Purana basins. In: S. K. Tandon and K. R. GUpta (eds.). Goals for Earth Science Activities in the Nineties. Mem. Geol. Soc. India, no. 18~
pp.77-93.
KALE, V. S. aDd PHANSALKAR. V. G. (1991) Purana Basins of Peninsular India. Basin
Re-search, v. 3, no. 1, pp. 1-36.
PASCOE, E. H. (1965) A Manual of the Geology of India and Bmma. Govt. of India, Geologi-cal Survey, v. 1, (3rd edn.) pp. 1-485.
VENKATACHALA. B. S. (1987) Organic remains from Purana sedimentary basins. Mem. GeoL Soc. India, no. 6, pp. 383-391
Comment 5
(Comment on the paper, 'Sediment Transport Direction Derived from Grain-size Statistics on the Continental-Shelf off Mangalore, West Coast of India ,. by A. C. Narayana and K. Pandarinath, published in the Journal of Geological Society of India, Vol. 38, No.3, 1991, pp. 293-298.
The following comments are offered:
(A) The number of samples considered for analysis of on-shore, off-shore transport are less than t he minimum required, i.e., ' 8' samples for calculation of , Z-Statistic ' to evaluate transport direction adequately (McLaren and Bowels 1985,. p. 463).
(B) Some of the inferences drawn on the' Along shore sediment transport' are doubtful.
1. Except for the 50-75 m depth range the other depth ranges are inferred to-· exhibit transport of sediment in the opposite directions in each range.
DISCUSSION
3. The surface currents altering the transport of sediment into opposing -directions of high energy regime (Case C at 0.01 level of significance) seasonally at ·a depth range of 150-250 m is doubtful.
4. It is likely that the admixture of recent sediment with the relict sediment might have produced such spurious sediment transport trends.
5. However, the high energy southerly trend of sediment transport (Case C at -().Ol level of significance) may be the only dominant trend. The present uni--directional high energy regime of transport might have erased the trends of the relict
sediment in this zone.
-49-53-8/11, Sneha Apartments
Baiaji Hills, Visakhapatnam 530013 V. RA VI KUMAR
Reference
'McLAREN, P. and BOWELS, D. (1985) The effects of sediment transport on grainsize distributors., Jour. Sed. P.;:trol., v. 55 (4). pp. 457-470.
Reply
I thank Ravi Kumar for his valuable and interesting comments on my paper. 'My reply to the comments is as follows:
(A) Number of samples: As samples are less than the suggested number in -each transect of onshore-offshore direction, the study area was divided into three sectors for the investigation of onshore-offshore transport. The tracks of each sector show the similar trend with respect to the direction, and, therefore, the on-shore-offshore transport trends in the study area are considered ~ignificant. Other workers ha.ve also explained the onshore-offshore transport trends successfully with less number of samples elsewhere (Prithviraj and Prakash, 1989).
(B) Alongshore sediment transport: Sediments in all depth ranges except for the 50-75 m depth exhibit transport trend in both north and south directions with ·different energy regimes. The inference relating to the surface currents causing transport of sediments in both north and south directions is drawn for the samples -of 30-50 m and 75-150 m depth ranges. There is no doubt that the role of surface ·currents in transportation of sediments at 150-250·m depth range is negligible. It
is clearJy mentioned in the paper that as the depth increases the role of surface -currents in sediment transportation decreases and at greater depths the sediment transport direction depends mainly on the influence of waves. The processes and effects of waves, both shelf waves aed near-inertial internal waves, in transport of sediments, particularly fine sediments, in the outer shelf regions have been observed .and explained by various workers (Karl et al. 1983; Sahl et al. 1987). Although waves play a major role in causing sediment transport in opposite directions at .,great depths, the role of the admixture of modern and relict sediments cannot be ,ruled out as mentioned by Ravi Kumar.
DISCUSSION
of transport could erase the trends of the relict sediment.
Only
futher detai1ed~bottom current studies could throw more light on this aspect.
Departm~'nt of Marine Geology Mangalore University
Mangalagangotri~574 199
References
A. C. NARAYANA
KARL, H. E., CARLSON, P. K. and COCOHIONE, D. A. (1983) Factors that influence sediment. transport at the shelfbreak. In: D. J. Stanely and G. T. Moore (Eds.). The shelfbreak: Critical interface on continental margins. Soc. Econ. PaJeontol. Minera1., Spec. Publ.,. v. 33, pp. 219-232.
PRITHVIRAJ, M. and PRAKASH, T. N. (1989) Sediment distribution and transport studies of the· innershelf zone off the central coast of Kerala, India, Jour. Coast. Research, v. 5 (2)~
pp. 271-280.
SAHL, L. E .. MERREtt W. J., McGREIL, D. W. and WEBB, J. A. (1987) Transport of mud ODI continental shelves. Evidence from the Texas shelf. Mar. Geot, v. 76, pp. 33-43. .
CORRIGENDUM
Geological Significance of Magnetic Depth Estimates Over W(!stern part of Cuddapah Basin, South India, by V. Babu Rao, (Vo1. 38, December, 1991,. pp. 605 to 614).
Figure 2 of this paper • Geological Map of Western Part of Cuddapah basin and adjoining crystal1ines (After GSI, 1981)! should be read as (After GSI, 1981 and Murthy et al. 1987).
Further, the depth to the top of the magnetic: sources is in kilometres-below ground and not metres kilometres-below ground as givm in the legend for Figure!>
2 and 3.
The inadvertent emission by the author is sincc~rely regretted. Reference
