D f .f DIAPIR RECOGNITION AND MODELLING with examples from the LATE PROTEROZOIC ADELAIDE GEOSYNCLINE, CENTRAL FLINDERS RANGES, SOUTH AUSTRALIA. by NICHOLAS M. LEMON B.Sc. (Hons.) (Adelaide) Department of Geology and Geophysics The University of Adelaide This thesis is submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in Geology at the University of Adelaide. October, 1988. (Í) TABLE OF CONTENTS Page No. ABSTRACT (vi) STATEMB¡T OF ORIGINALITY (vii) ( ACKNOWLEDGEMENTS viii ) 1 CHAPTER 1 INTRODUCTION CHAPTER 2 DIAPIR RECOGNITION ANd MODELLING 4 CHAPTER 3 REGIONAL GEOLOGICAL SETTING 15 CHAPTER 4 STRATIGRAPHY 32 CHAPTER 5 ENORA}4À DIAPIR 58 CHAPTER 6 BLTNMAN DIAPIR 72 CHAPTER 7 ORAPARINNA DIAPIR 79 CHAPTER 8 DIAPIRS nOrth Of BLINI4AN B2 CHAPTER 9 WIRREALPA ANd ANGORIGINA DIAPIRS 84 CHAPTER 1O DIAPIRS along the NARINNA FAULT and extensions 88 93 CHAPTER 1 1 ThC BELTANA - PINDA LINE CHAPTER 1 2 Far northern FLINDERS and. WILLOURAN RANGES DIAPIRS 100 CHAPTER 1 3 TELFORD DIAPIR (NCW NAINE) 103 CHAPTER 14 GEOCHEI"IICAL SIGNATURE around DIAPIRS 107 CHAPTER 15 GEOPHYSICAL EXPRESSION Of DIAPIRS 112 CHAPTER 16 NATURE of the BRECCIAS and SOURCE BEDS 116 CHAPTER 1 7 SU¡,IÌ"IARY: MODELS for FLINDERS RANGES DIAPIRS 121 REFERENCES ....... 129 LIST OF FIGURES Figure No. TITLE on,/between page/s Adelaide Geosyncline: Diapirs and Localities 1-2 2 Change in diapir shaPes 6 3 Stages of salt movernent 8-9 (ii) Figure No. TITLE Onr/between page/s 4 Summary of Adelaidean Stratigraphy 17 5 Adelaide Geosyncline: Tectonic and sedimentary zones 17-18 (6, Facies distribution, Umberatana Group 20-21 7 Facies variation, Brighton Limestone equivalent, section 46 21-22 ,8 AdeLaide Geosyncline: W-E section, Umberatana Group 24-25 9 Sections 52 and 53, Pantapinna Trail- 32-33 10 Sections 39 and 53, Pantapinna Trail 36-37 11 Upper Etina Formation, section E of Dedmans Bore 38-39 12 Facies variation near Enorama Diapir, wundowie Limestone 39-40 13 Tidal bundl-e thickness variation, "Aldoona Band" 41 14a Isopach - "Patterton ShaIe" 43-44 14b Isopach - Wundowie Limestone 43-44 14c Isopach - "Al-doona Band" 43-44 14d Water depth index - Wundowie Limestone 43-44 15 Facies variation near Enorama Diapir, Enorama Shale 45-46 16 Facies variation near Enorama Diapir-, lxezorra Formation 46-47 17 Trezona Formation, depositional models 51 -52 18 Measured sections, Elatina Formation 53-54 19 Directions of tepoid crests, Nuccaleena Formation 56 20 Enorama Diapir, summary of influence 58-59 21 DetaiI of contact, Tapley HiII Formation - Enorama Diapir 59 22 Sketch section across Enorama - Oraparinna Diapirs 60 23 Geology around Dedmans Bore, Enorama Diapir 61 -62 24 Facies variation near Enorama Diapirr upper Etina Formation 62-63 25 Facies variation near Enorama Diapir, lower Enorama shale 63-64 26 Gravity slide, "Aldoona Band", l{ of Enorama Diapir 65 27a Section W of Enorama Diapir, upper Etina F¡n. and Enorama Shale 66-67 27b Detail of algal reef, W margin of Enorama Diapir 66-67 28 Bl-inman Diapir, summary of influence 72-73 29 Bfinman Diapir, structure controlling deposition 72-73 (iii) Figure No. TITLE on/between pager/s 30 Vl-E section, S of Blinman Diapir 73-74 31 w-E section, N of Blinman Diapir 74-75 32 Relationships within Tapley HiII Fm. r W of Blinman Diapir 75 33 Tectonic setting of Central Flinders Diapirs 81-82 34 Geol-ogical map, Oratunga Diapir 82-83 35 Palinspastic reconstruction, development of Oratunga Diapir 82-83 36 Hypothetical cross section, Wirrealpa Diapir A7 37 Thickness variation in the Cambrian sequence, Wirrealpa Diapir 85-86 38 Geological map, Patawarta Diapir and Nuccaleena Dome 88-89 39 Cross section over the Patawarta Diapir 89 40 Bel-tana Diapir 94-95 41 Geology around the Pinda and I'lucatoona HiIl Diapirs 97-98 42 Burr "Diapir" 1 00-1 01 43 Tectonic setting, C and D Lobes, Leigh Creek 103-104 44 Original surface mapping, C Lobe 'lO4 45 Geochemical variation, shales of the upPer Etina Formation 1 07-1 08 46 Dolomite variation in the Enorama Shale 1 09 47 Aeromagnetic map, total intensity 112-113 48 Bouguer gravity anomaly over the Blinman Diapir 113-114 49 Computer gravity modelling, Glasses Gorge traverse 114-115 50 Diapir families and ages 123-124 51 Leve1 of exposure of diapirs 125-126 52 Models for exposed diapirs 1 27-124 Enclosure 1 Geological map of the Blinman area in pocket at the back Enclosure 2 GeologícaI rnap of the Oraparinna area (iv) I,IST OF PLÀTES Plate No. TITLE on/between page/s 8-9 1 Sandbox modelling of a synsedimentary diapir 2 Views and rocks of the Etina Formation 40-41 3 Aerial view of the Trezona Formation 46-47 4 Trezona Formation rocks and sequences 49-50 5 Features around the Enorama Diapir, 1 64-65 6 Features around the Enorama Diapir, 2 68-69 7 Miscellaneous views and photographs 118-119 APPENDICES APPENDIX I The studY area APPENDIX II Reprint: Physical- modeling of sedimentation adjacent to diapirs and comparison with late Precambrian Oratunga breccia body in Central Flinders Ranges, South Australia. APPENDIX III petrographic descriptions (index, example plus microfiche) APPENDIX IV l"leasured section summaries APPENDIX V Reprint: Blinman to Enorama - A one day excursion. APPENDIX VI Preprint: Glacigenic sediments of the late Proterozoic Elatina Formation and equivalents, Adelaide Geosyncline, South Australia. (v) ABSTRACT A large number of irregular breccia bodies have been mapped in the Iate Precambrian and Early Cambrian sediments of the Adelaide Geosyncline. Although a diapiric origin was suggested in 1960, the complex internal history and varied settings of these bodies has lead to numerous interpretations as to their origin and the subject is still controversial. The interaction of a syn-sedimentary diapir with surrounding sediments creates a number of diagnostic features and a catalogue of these features has been assembled from literature studies. Sandbox modelling of the complete intrusive history of salt-type diapirs, a new technique applied to this study, has confirmed many of the previously recorded diagnostic features and added to the list. Detailed mapping and section measurement around seven breccia bodies in the Central Flinders Ranges, and comparison with more regional mapping, has found specific evidence of synsedimentary diapirism. In particular, the Bnorama Diapir shows facies irregularities throughout 4000m of adjacent sediments. Many of the features described in the literature were found and several new features added to the list. Reconnaisance mapping around another seven breccia bodies has confirmed that, while some cannot specifically be called diapirs, all are diapirically associated breccias. A geochemical signature has been found in sediments around several of the diapirs studied and this has led to the proposal of two models of sedimentation patterns around exposed diapirs at times of high and low sea level. Some of the diapirs in the Flinders Ranges have been grouped into "families" based on their mode of initiation and tectonic setting. Although there is no direct evidence as such, extensive circumstantial evidence suggests that the diapirism is related to widespread evaporite deposits near the base of the Adelaidean sequence. Shale movement may have also been associated with the salt diapirism. The salt moved during the deposition of the Adelaidean sequence, during the subsequent Delamerian Orogeny and in a few cases, has been remobiLized during the Mesozoic and may still be potentially mobile. It is suggested that, as diapirs are areas of relatively incompetent rock, they are the focus of 'later tectonic activity. ( vi) STATEMENT OF ORIGINALITY This thesis contains no material which has been accepted for the award or any other degree or diploma in any university and, to the best of my knowledge and belief , it contains no material previously published or written by another person, except where due reference is made in the text. N.M, Lemon. (vii) ACKNOWLEDGEMENTS I would like to thank my supervisor, Dr. Vic Gostin, for all his assistance and helpful discussions throughout my candidature. A free rein throughout the fieldwork was greatly appreciated. My work was supported by a University of Adelaide Scholarship for the initial two years of full time candidature and by a teaching fellowship for the following three years. An Esso grant to Dr. Gostin provided aerial photographic and LANDSAT coverage of the study area. I also acknowledge the granting of a permit by the National Parks and Witdlife Service of S.A. to work within the Flinders Ranges National Park and the access to aII other areas by the local leaseholders. The Etectricity Trust of South Australia provided aerial photo coverage of the Leigh Creek area. I greatly benefitted from continuous interaction with my fellow students, Peter Haines and Updesh Singh, and from discussions in the field with many of the people who I have shown around, such as the participants of the Twelfth International Sedimentological Congress Field Trip, Dr. Wouter Nijman and Dr. Grant Young. Previous workers on similar topics also provided assistance and suggestions on where to map. These i¡clude Ron Coats, Wolfgang Preiss, Bob Dalgarno and Trevor Mount. I would like to thank the following technical staff of the department: Sherry Proferes (draughting), Rick Barrett (photography), Geoff Trevelyan (thin section preparation), Phil McDuie (XRF and AA analysis) and John Stanley ( XRD and XRF analysis ) . In particular, I would like to thank my wife and mother for their support throughout the years. The assistance and accomodation in the field provided by Beryt and Gordon Mclntosh and BiII and Jane Mclntosh of Gum Creek Station was invaluable. t vrlr, CHAPTER 1 INTRODUCTION The Nature of the Problem Early geological workers in the Central and Northern Flinders Ranges recognized zones of brecciated rock which did not appear to be part of the general sedimentary sequence and were difficult to put into stratigraphic context.