Petrology and Sedimentation Trends of the Bhander Group (Upper Vindhyan) in the Singoli (Madhya Pradesh)—Mandalgarh (Rajasthan) Area
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Petrology and Sedimentation Trends of the Bhander Group (Upper Vindhyan) in the Singoli (Madhya Pradesh)—Mandalgarh (Rajasthan) Area By Khurshed Akhtar THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY DEPARTMENT OF GEOLOGY ALIGARH MUSLIM UNIVERSITY, ALIGARH 1973 T1425 'T\^^^ '^. \ iVlV \^1^ "^<-i U:i C_aDJ.c^^ ^MFCXHI5 imm '-^]^2.5 ABSTRACT The ancient sediments of the uppermost stratigraphic interval (Bhander Group) of the Vindhyan Supergroup (?Pre>Cambrian) have been investigated in the western lobe of the main Vindhyan basin with a view to reconstruct their depositional environments? paleogeographyt dispersal patterns and sediment source. The Bhander Group of study areai 335 m thicki comprises four mutually conformable formations: Gannrgarh Shale* Bhander Limestone? Sirbu Shale and Bhander Sandstone in the ascending order. Each formation has been divided into two or more units on the basis of lithologic and sedimentary characters. The lower half of Bhander Group (Ganurgarh Shale* Bhander Limestone) Sirbu Shale) is characterized by fine clastic-carbonate mudstone lithologic association} paralleT laminations* mud cracks* and absence of large-scale current- and wave- formed structures. Small channel-fills occur in some units. Flaser- bedded sandstones and shales mark the transition from the lower half of Bhander Group to the upper half. The latter comprises Bhander Sandstone which occurs in two markedly different facies — sheet and channel facies. Petrographic study of the arenites has demonstrated their high textural and compositional maturity. They are generally fine grained* - 2 - well sorted and almost entirely composed of siliceous constituents. Glauconite occurs in some samples as glauconitized clay pellets. The carbonates comprise four main constituents: intraclastS) micrite) sparry calcite and carbonate silt . Nine environmentally significant microfacies have been recognized. Most microfacies contain early dolomite. The depositional environments have been interpreted by analogy with "process-response" models of modern environments» and on the basis of Walther's Bule of Fades. By and large? Bhander Group sediments were deposited in a seamarginal tidal environment as is attested by features indicating processes of evaporation) exposure and desiccationt and late- stage emergence ebb outflow. Other evidences of tidal activity include blraodal-bipolar dip orientation of cross-strata? multimodal frequency distribution of cross-stratification set thicknesses and graded bedding in algal mat carbonate mudstones. The marine influence on sedimentation is further indicated by the presence of glauconite in sandstones. The lower half of Bhander Group was deposited mainly from suspension in supratidal and high tidal flat environments. Small channel-fills were formed in gullies and small tidal channels of high tidal flats. The transitional flaser-bedded sandstone-shale sequence resulted from alternate deposition of clay from suspension and sand by bedload transport in the mid flat environment. The upper half (Bhander Sandstone) was deposited on low tidal flats? beaches and bars. The associated large channel-fills have been interpreted as tidal channel and inlet deposits. Tectonic stability seems to have prevailed throughout the deposition of - 3 - the entire sequence. Orientation of ripple crestst rill marks* elongate tidal channel sand bodies} and the general trend of Sirbu Shale isopachs together suggest an east-southeast - west-northwest oriented shore line. Lateral facies changes and a combination of criteria* such as transgressive relationship and "fining-shoreward" textural distribution interpreted for the Sirbu Shale-Bhander Sandstone sequence* and the slope of lithologic boundary betwe«.v\ the two formations evidence a north-northeast directed paleoslope. Sediment dispersal patterns have been interpreted by relating paleocurrents to the inferred shore line and paleoslope. Such interpre tations are* by and large* redundant in the case of the lower half of Bhander Group since it is mainly a suspension load deposit. However* the meagre paleocurrent data obtained from small channel-fills suggest that bedload sediment transport occurred in small channels mainly in the onshore and offshore directions* and to some extent across-slope. In the upper half of Bhander Group* the sediments were mainly dispersed by west-northwest directed longshore currents* onshore and offshore currents played a subordinate role. The predominant west-northwest directed sediment dispersal pattern* and a matching of the inferred source composition with the composition of pre-Vindhyan rocks suggest that the provenance consisted of low-grade meta- sediments of Bijawar and Gwalior Series* and Bundelkhand granite. DEPARTMENT OF GEOLOGY ALIGARH MUSLIM UNIVERSITY ALIGABH INDIA This is to certify that Mr. Khurshed Akhtar has completed his research under my supervision for the degree of Doctor of Philosophy of the Aligarh Muslim University. This work is an original contribution to our knowledge of the sedimentology of the Vindhyan (?Pre-Cambrian) rocks and has not been published anjrwhere in part or in full, Mr. Khurshed Akhtar is allowed to submit the work for the Ph.D. degree of the Aligarh Muslim University? Aligarh. Dr. V,K, Srivastava 11 September, 1973 M.Sc.(B.H.U.), M.A. (Hopkins)) Ph.D. (Alig.) Supervisor CONTENTS INTRODUCTION The Vindhyan "System" ... 1 Choice and location of investigated area 3 Aim and scope of investigation 4 Acknowledgements 6 CHAPTER I - STRATIGRAPHY AND SEDIMENTARY CHARACTERS OF BHANDER GROUP 8 Nomenclature and classification 8 Regional stratigraphic relationships 11 Mandalgarh-Singoli area 16 Ganurgarh Shale 17 Bhander Limestone 20 Sirbu Shale 25 Bhander Sandstone 31 CHAPTER II _ SEDIMENTARY STRUCTURES 39 Directional structures 41 Cross-stratification 41 Ripple marks 48 Flute cast and flute mark 55 Current-drag structure 57 Parting lineation ... 59 Swash mark 60 Rill mark 61 Groove cast 61 Non-directional structures 63 Load structure 63 Bal1-and-pillow structure 64 Convolute lamination 65 Mud crack 67 Alga] mat structure 69 CHAPTER ITT - PETROGRAPHY 70 Petrography of sandstones 70 Sampling ... 71 Methodology and presentation of data 72 (i) (ii) Texture (grain size and roundness) 74 Detrital components... 78 Diagenesis ... R3 Petrography of carbonates 87 Major petrographic constituents 87 Microfacies 90 Dolomitization ... 98 CHAPTER IV - DEPOSITTONAL ENVIRONMENTS 101 Concept of depositional environment 101 Model of nearshore marine sedimentation 102 Tidal flats and channels 103 Lagoons ... 107 Beaches 108 Environmental analysis of Bhander Group 110 Ganurgarh Shale 110 Bhander Limestone ... 116 Sirbu Shale 129 Bhander Sandstone ... 134 Environmental synthesis 139 Vertical relationships 139 Tectonic framework ... 143 CHAPTER V - PALEOGEOGRAPHY AND SEDMENT DISPERSAL PATTERN 145 -The problem and approach 145 Directional data 147 Directionals and their distribution 147 Sampling ... 148 Variability analysis 151 Scalar data (thickness and isopach map) 166 Paleogeographic reconstruction 167 Shore line orientation 167 Paleoslope ... 172 Dispersal patterns of sediments 175 Ganurgarh Shale ... 176 Bhander Limestone ... 177 Sirbu Shale 177 Bhander Sandstone ... 177 (ili) Environmental control on dispersal patterns 182 Provenance 184 CHAPTER VI - CONCLUSIONS '189 REFERENCES 196 APPENDIX I - Thickness data of cross-stratification units from Bhander Group i APPENDIX II - Inclination data of cross-stratification foresets from Bhander Group ii • in APPENDIX III - Average wave lengthj amplitude and ripple index of ripple marks from Bhander Group iv APPENDIX IV - Grain size frequency distribution (number per cent) of Bhander Group sandstones v APPENDIX V - Statistical parameters of grain size distribution of Bhander Group sandstones vi APPENDIX VI _ Directional data: cross-stratification azimuths from Bhander Group vii - XVlll APPENDIX VII- Directional data: ripple trend and ripple asymmetry azimuths from Bhander Group xix • XXI1 APPENDIX VIII- Directional data: average parting lineation azimuths from Bhander Group xxiii APPENDIX IX - Directional data: azimuths of misce llaneous directionals from Bhander Group xxiv LIST OF PLATES Facing page PLATE I Photographs showing lithologic and sedimentary characters of Bhandcr Limestone and Sirbu Shale. 22 PLATE II Photographs showing lithologic and sedimentary characters of Bhander Sandstone. 34 PLATE III Photograohs of cross-stratification, 44 PLATE IV Photographs of ripple marks. 51 PLATE V Photographs of miscellaneous sedimentary structures. ^ PLATE VI Photographs of mud cracks. 68 PLATE VII Photomicrographs of Bhander Group sandstones showing quartz types, "78 PLATE VIII Photomicrographs of Bhander Group sandstones showing heavy minerals and other detrital constituents. 82 PLATE IX Photomicrographs of Bhander Group sandstones showing pressure solution and cementation. 84 PLATE X Photomicrographs of Bhander Group carbonates showing characteristic features of micrite> clayey micrite and graded raicrite microfacies, 91 PLATE XI Photomicrographs of Bhander Group carbonates showing characteristic features of dolomitized micrite? interlaminated micrite-calcisiltite and intracalcisiltite microfacies. 93 PLATE XII Photomicrographs of Bhander Group carbonates showing characteristic features of Intras- parruditej intramicrudite and oosparite microfacies. 96 LIST OF FIGUHES Facing page FIGURE 1 Map of the main Vindhyan basin showing location of area of investigation. 1 FIGURE 2 Geological and