Age and depositional environment of the Draa Sfar massive sulfide deposit, Morocco

Mineralium Deposita

Volumn 43, Issue 8, 2008, Pages 891-911

  Moreno, C ^a   Saez R ^a   Gonzalez F ^a   Almodovar G ^a   Toscano, M ^a   Playford, G ^b   Alansari, A ^c   Rziki, S ^d   Bajddi, A ^d  

^a UNIVERSITY OF HUELVA   (Spain)

^b UNIVERSITY OF QUEENSLAND   (Australia)

^c CADI AYYAD UNIVERSITY   (Morocco)

^d Compagnie minière des Guemmassa ^*  (Morocco)

Author keywords

Biostratigraphy; Black shales; Draa Sfar; Massive sulfide deposits; Morocco

Indexed keywords

BIOSTRATIGRAPHY; BLACK SHALE; DEPOSITIONAL ENVIRONMENT; GEOCHRONOLOGY; MASSIVE SULFIDE; MINERALIZATION; ORE BODY;

EID: 56049087529     PISSN: 00264598     EISSN: None     Source Type: Journal    
DOI: 10.1007/s00126-008-0199-x     Document Type: Article

References (115)

1. Aarab El, Beauchamp J (1987) Le magmatisme carbonifére pré-orogénique des Jebilet centrales (Maroc). Précisions pétrographiques et sédimentaires. Implications géodynamiques. CR Acad Sci Paris Sér II 304:169-175
2. Arthur MA, Sageman BB (1994) Marine black shales: Depositional mechanisms and environments of ancient deposits. Annu Rev Earth Planet Sci 22:499-551
3. Attar A, Fournier J, Candilier AM, Coquel R (1980) Étude palynologique du Dévonien terminal et du Carbonifére Inférieur du bassin d'Illizi (Fort-Polignac), Algérie. Rev Inst Fr Pét 35:585-618
4. Barker CE (1988) Geothermics of petroleum systems; implications of the stabilization of kerogen thermal maturation after a geologically brief heating duration at peak temperature. In: Magoon LB (ed) Petroleum systems of the United States. US Geol Surv Bull 1870:26-29
5. Barrakad A, Huvelin P, Laforet Cl, Péez S, Permingeat F, Picot P (1977) Minéraux de cobalt, d'étain, de bismuth, de sélénium, d'or et d'argent dans l'amas sulfuré a pyrrhotite de Sidi Embarek (Jebilet). Notes Serv Géol Maroc 37:129-138
6. Barrie CT, Hannington M (1999) Classification of volcanic associated massive sulfide deposits based on host-rock composition. In: Tucker C, Hannington M (eds) Volcanic associated massive sulfide deposits: processes and examples in modern and ancient settings. Rev Econ Geol 8:1-11
7. Barton PB (1984) Redox reactions in hydrothermal fluids. In: Henley RW, Truesdell AH, Barton PB, Whitney JA (eds) Fluid-mineral equilibria in hydrothermal systems. Rev Econ Geol 1:99-113
8. Beauchamp J, Izart A (1987) Early Carboniferous basins of the Atlas-Meseta domain (Morocco): Sedimentary model and geodynamic evolution. Geology 15:797-800
9. Belkabir A, Gibson HL, Marcoux E, Lentz D, Rziki S (2008) Geology and wall rock alteration at the Hercynian Draa Sfar Zn-Pb-Cu massive sulphide deposit, Morocco. Ore Geol Rev 33:280-306
10. Ben Aissi L (2002) Gisement de Draa Sfar Sud: Etude géologique et métallogénique des minéralisations et des altérations hydrothermales associées (Jebilet Centrales, Maroc). Mémoire de DESA, Universit́ Cadi Ayyad, Marrakech, 82 pp
11. Ben Aissi L, El Boukhari A, Hibti M, Elharfi M, Maacha L, Zinbi Y (2005) Altération hydrothermale et déformation ductile des roches volcaniques acides associées au gisement sulfure de Draa Sfar (Jebilet Centrales, Maroc). Est Geol 61:147-160
12. Bernard AJ, Maier OW, Mellal A (1988) Aperçu sur les amas sulfurés massifs des Hercynides marocaines. Miner Depos 23:104-114
13. Bhatia MR (1983) Plate tectonics and geochemical composition of sandstones. J Geol 91:611-627
14. Bhatia MR, Crook KAW (1986) Trace elements characteristics of graywackes and tectonic discrimination of sedimentary basins. Contrib Mineral Petrol 92:181-193
15. Bitterlli P (1963) Aspects of the genesis of bituminous rock sequences. Geol Mijnb 24:183-201
16. Bohacs KM (1998) Mudrocks sedimentology and stratigraphy - challenges at the basin to local scales. In: Schieber J, Zimmerle W, Sethi P (eds) Shales and mudstones I, E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, pp 13-20
17. Bordonaro M (1983) Tectonique et pétrographie du district à pyrrhotite de Kettara (Paléozoĩque des Jebilet, Maroc). Thèse 3éme cycle, Université Louis Pasteur, Strasbourg
18. Bordonaro M, Gaillet JL, Michard A (1979) Le géosynclinal carbonifíre sud-mésétien dans les Jebilet (Maroc); une corrélation avec la province pyriteuse du sud de l'Espagne. CR Acad Sci Paris Sér D 288:1371-1374
19. Bouabdelli M, Piqué A (1996) Du bassin sur décrochement au bassin d'avant-pays: Dynamique du bassin d'Azrou-Khénifra (Maroc hercynian central). J Afr Earth Sci 23:213-224
20. Calvert SE, Karlin RE (1998) Organic carbon accumulation in the Holocene sapropel of the Black Sea. Geology 26:107-110
21. Calvert SE, Bustin RM, Pedersen TF (1992) Lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the Gulf of California. Geology 20:757-760
22. Canfield DE (1989) Sulfate reduction and oxic respiration in marine sediments: Implication for organic carbon preservation in euxinic environments. Deep-Sea Res 36:121-138
23. Canfield DE (1994) Factors influencing organic carbon preservation in marine sediments. Chem Geol 114:315-329
24. Condie KC, Wronkiewicz DS (1990) The Ce/Th ratio in Precambrian pelites from the Kaapvaal Craton as an index of cratonic evolution. Earth Planet Sci Lett 97:256-267
25. Cook AC, Hutton AC, Sherwood NR (1981) Classification of oil shales. Bull Cent Rech Explor Prod Elf-Aquitaine 5:353-381
26. Crerar DA, Barnes HL (1976) Ore solution chemistry V: Solubilities of chalcopyrite and chalcocite assemblages in hydrothermal solution at 200 degrees to 350 degrees C. Econ Geol 71:772-794
27. Cullers RL, Basu A, Suttner LJ (1988) Geochemical signature or provenance in sand-mixed material in soil and stream sediments near the Tobacco Root batholith, Montana, USA. Chem Geol 70:335-348
28. Dagbert M, Harfi M (2002) Resource estimation for the Draa Sfar South polymetallic deposit. Explor Min Geol 11:99-112
29. Doyle MG, Allen RL (2003) Subsea-floor replacement in volcanic-hosted massive sulphide deposits. Ore Geol Rev 23:183-222
30. Eremin NI, Dergachev AL, Pozdnyakova NV, Sergeeva NE (2002) Epochs of volcanic-hosted massive sulfide ore formation in the Earth's history. Geol Ore Depos 44:227-241
31. Eremin NI, Dergachev AL, Pozdnyakova NV, Sergeeva NE (2004) Large and superlarge volcanic-associated massive sulfide deposits. Geol Rudn Mestoroz 46:107-128
32. Essaifi A (1995) Relations entre magmatisme, déformation et altération hydrothermale, l'exemple des Jebilet Centrales (Hercynien, Maroc). Mémoires Géosciences Rennes 66:340
33. Essaifi A, Hibti M (2008) The hydrothermal system of Central Jebilet (Variscan Belt, Morocco): A genetic association between bimodal plutonism and massive sulphide deposits. J Afr Earth Sci 50:188-203
34. Essaifi A, Lagarde JL, Capdevila R (2001) Deformation and displacement from shear zone patterns in the Variscan upper crust, Jebilet, Morocco. J Afr Earth Sci 32:335-350
35. Essaifi A, Potrel A, Capdevila R, Lagarde JL (2003) Datation U-Pb: âge de mise en place du magmatisme bimodal des Jebilet centrales (chaéne Varisque, Maroc). CR Geosci 335:193-203
36. Felenc J, Fournier M, Hmeurras M (1986) Contrôles géologiques des amas à pyrrhotine des Jebilet et Guemassa. Définition des guides de recherche. Rapp BRGM 86:54
37. Finlow-Bates T, Croxford NJW, Allan JM (1977) Evidence for, and implications of, a primary FeS phase in the lead-zinc bearing sediments at Mount Isa. Miner Depos 12:143-149
38. Gaillet JL (1979) Sur les relations entre les Schistes du Sarhlef et le Flysch de Kharrouba dans le massif hercynien des Jebilet (Maroc). CR Acad Sci Paris Sér D 288:791-794
39. Gentil L (1918) Notice sur les titres et travaux scientifiques de L Gentil. Larose, Paris, 132 pp
40. Gilligan LB, Marshall B (1987) Textural evidence for remobilization in metamorphic environments. Ore Geol Rev 2:205-229
41. González F, Moreno C, Playford G (2005) Upper Devonian biostratigraphy of the Iberian Pyrite Belt, southwest Spain. Part two: organic-walled microphytoplankton. Palaeontogr Abt B 273:53-86
42. González F, Moreno C, Santos A (2006) The massive sulphide event in the Iberian Pyrite Belt: Confirmatory evidence from the Sotiel-Coronada Mine. Geol Mag 143:821-827
43. Goodfellow WD, Franklin JM (1993) Geology, mineralogy, and chemistry of sediment-hosted clastic massive sulfides in shallow cores, Middle Valley, Northern Juan de Fuca Ridge. Econ Geol 88:2037-2068
44. Goodfellow WD, Lydon JW, Turner RJW (1993) Geology and genesis of stratiform sediment-hosted (SEDEX) zinc-lead-silver sulphide deposits. In: Kirkham RV, Sinclair WD, Thorpe RI, Duke JM (eds) Mineral deposit modeling. Geol Assoc Can Spec Pap 40:201-251
45. Graham JR (1982a) Wave dominated shallow-marine sediments in the Lower Carboniferous of Morocco. J Sediment Petrol 52:1271-1276
46. Graham JR (1982b) Transition from basin-plain to shelf deposits in the Carboniferous flysch of Southern Morocco. Sediment Geol 33:173-194
47. Hatch JR, Leventhal JS (1992) Relationship between inferred redox potential of the depositional environment and geochemistry of the Upper Pennsylvanian (Missourian) stark shale member of the Dennis Limestone, Wabaunsee County, Kansas, USA. Chem Geol 99:65-82
48. Hãussinger H, Okrusch M, Scheepers D (1993) Geochemistry of premetamorphic hydrothermal alteration of metasedimentary rocks associated with the Gorob massive sulfide prospect, Damara Oregon, Namibia. Econ Geol 88:72-90
49. Herron MH (1988) Geochemical classification of terrigenous sands and shales from core or log data. J Sediment Petrol 58:820-829
50. Hibti M (2001) Les Amas Sulfurés des Guemassa et des Jebilet (Meseta sud-occidentale, Maroc): Témoins de l'hydrothermalisme précoce dans le Bassin Mesetien. Thése de Docteur d'Etat Es-Sciences. Université Cadi Ayyad, Marrakech, 318 pp
51. Hoepffner C, Soulaimani A, Piqué A (2005) The Moroccan Hercynides. J Afr Earth Sci 43:144-165
52. Hoffman DL, Algeo TJ, Maynard JB, Joachimski MM, Hower JC, Jaminski J (1998) Regional and startigraphic variation in bottom water anoxia on offshore core shales of Upper Pennsylvanian cyclothems from the Eastern Midcontinent Shelf (Kansas), USA. In: Schieber J, Zimmerle W, Sethi P (eds) Shales and mudstones I, E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, pp 243-269
53. Holland HD (2003) Discussion of the article by A.C. Lasaga and H. Ohmoto on "The oxygen geochemical cycle: Dynamics and stability". Geochem Cosmochim Acta 67:787-789
54. Hollard H, Huvelin P, Mamet B (1977) Stratigraphie du Viséen supérieur des Jebilet et age de la mise en place de la nappe des Jebilet orientales (Maroc). Notes Mém Serv Géol Maroc 37:7-22
55. Houari MR, Hoepffner C (2003) Late Carboniferous dextral wrench-dominated transpression along the North African craton margin (Eastern High-Atlas, Morocco). J Afr Earth Sci 37:11-24
56. Huvelin P (1961) Sur l'age Viséen Supérieur des schistes de Kettara et de Djebel Sarhlef (Djebilet Centrales, Maroc). CR somm Soc Gél France 10:290-291
57. Huvelin P (1972) Carte géologique et des minéralisations des Jebilet au 1/200000 scale. Serv Géol Maroc
58. Huvelin P (1977) Etude géologique et gétologique du Massif hercynien des Jebilet (Maroc occidental). Notes Mém Serv Géol Maroc 232bis:1-307
59. Huyck HLO (1990) When is a metalliferous black shales not a black shale? In: Grauch RI, Huyck HLO (eds) Metalliferous black shales and related ore deposits. Proc 1989 US Working Group Meet, Int Geol Correl Prog Proj 254, US Geol Surv Circ 1058, Washington DC, pp 42-56
60. Jones B, Manning DAC (1994) Comparison of geochemical indices used for the interpretation of paleoredox conditions in ancient mudstones. Chem Geol 111:111-129
61. Kissin SA, Scott SD (1982) Phase relations involving pyrrhotite below 350 degrees C. Econ Geol 77:1739-1754
62. Koski RA, Lonsdale PF, Shanks WC, Berndt ME, Howe SS (1985) Mineralogy and Geochemistry of a sediment-hosted hydrothermal sulphide deposit from the Southern Trough of Guaymas Basin, Gulf of California. J Geophys Res 90:6695-6707
63. Koski RA, Jonasson IR, Kadko DC, Smith VK, Wong FL (1994) Composition, growth mechanisms, and temporal relations of hydrothermal sulfide-sulfate-silica chimneys at the northern Cleft segment, Juan de Fuca Ridge. J Geophys Res 99:4813-4832
64. Lagarde JL, Choukroune P (1982) Cisaillement ductile et granitoïdes syntectoniques: L'exemple du massif hercynien des Jebilet (Maroc). Bull Soc Géol Fr 24:299-307
65. Lagarde JL, Michard A (1986) Stretching normal to the regional thrust displacement in a thrust-wrench shear zone, Rehama massif, Morocco. J Struct Geol 8:483-492
66. Lagarde JL, Omar A, Roddaz B (1990) Structural characteristics of granitic plutons emplaced during weak regional deformation: Examples from late Carboniferous plutons, Morocco. J Struct Geol 12:805-821
67. Lanzoni E, Magloire L (1969) Associations palynologiques et leurs applications stratigraphiques dans le Dévonien Supérieur et Carbonifére Inférieur du Grand Erg occidental (Sahara algérien). Rev Inst Fr Pét 24:441-453
68. Lescuyer JL, Leistel JM, Marcoux E, Milesi JP, Thieblemont D (1998) Late Devonian-Early Carboniferous peak sulphide mineralization in the Western Hercynides. Miner Depos 33:208-220
69. Lofti F, Belkabir A, Marcoux E, Brown AC, Brunet S (2006) Géologie, minéralogie et signature isotopiques du gisement de sulfures massifs Hercynien de Koudiat Ächa (Zn-Cu-Pb), Jebilet Central, Maroc. In: Recueil des Résumés 10émes Journées de Launay: Nouvelles approches de la recherche et de l'exploration miniéres, Marrakech, p 86
70. Maier OW, El Hakkourt (1984) Les amas sulfures volcano-sédimentaires des Jebilet Centrales. Communication aux Journées Nationales du Soufre, Rabat 11-12 Octobre
71. Mamet B (1974) Une zonation par foraminifÉres du Carbonifére Inférieur de la Téthys Occidentale. In: Septiéme Congrés International de Stratigraphie et de Géologie du Carbonifére, Krefeld, 1971, 3:391-408
72. Marcoux E, Belkabir A, Gibson HL, Lentz D, Ruffet G (2008) Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane. Ore Geol Rev 33:307-328
73. Massa D, Coquel R, Loboziak S, Taugourdeau-Lantz J (1980) Essai de synthése stratigraphique et palynologique du Carbonifére en Libye occidentale. Ann Soc Géol Nord 99:429-442
74. Matte P (1986) Tectonics and plate tectonics model for the Variscan Belt of Europe. Tectonophysics 126:329-374
75. Matte P (2001) The Variscan collage and orogeny (480-290 Ma) and the tectonic definition of the Armorica microplate: A review. Terra Nova 13:122-128
76. Mayol S (1987) Géologie de la partie occidentale de la boutonniére paléozoéque des Jebilet, Maroc. Trav Lab Sci Terre Sér B 27:241
77. Mayol S, Muller J (1985) Mise en ́vidence d'une unité allochtone hercynienne précoce (antéschisteuse) dans les Jebilet occidentales (Maroc). Étude de la structuration de la zone de contact. CR Acad Sci Paris Sér II 300:369-372
78. McLennan SM (1989) Rare earth elements in sedimentary rocks: Influence of provenance and sedimentary processes. MSA Rev Min 21:169-200
79. McLennan SM, Taylor SR (1991) Sedimentary rocks and crustal evolution: tectonic setting and secular trends. J Geol 99:1-21
80. Menning M, Alekseev AS, Chuvashov BI, Davydov VI, Devuyst FX, Forke HC, Grunt TA, Hance L, Heckel PH, Izokh NG, Jin YG, Jones PJ, Kotlyar GV, Kozur HW, Nemyrovska TI, Schneider JW, Wang XD, Weddige K, Weyer D, Work DM (2006) Global time scale and regional stratigraphic reference scales of Central and Western Europe, East Europe, Tethys, South China, and North America as used in the Devonian-Carboniferous-Permian Correlation Chart 2003 (DCP 2003). Palaeogeogr Palaeoclimat Palaeoecol 240:318-372
81. Ministère de L'Energie et des Mines, Royaume du Maroc (1997) Synthése sur les amas sulfurés au Maroc. Min Geol En 56:15-72
82. Mrini Z, Rafi A, Duthou JL, Vidal P (1992) Chronologie Rb-Sr des granïtoides hercyniens du Maroc: Conséquences. Bull Soc Géol Fr 163:281-291
83. Müller PJ, Suess E (1979) Productivity, sedimentation rate, and sedimentary organic matter in the oceans. I. Organic carbon preservation. Deep-Sea Res A 26:1347-1362
84. Ortiz E, Roser BP (2006) Major and trace element provenance signatures in stream sediments from the Kando River, San'in district, southwest Japan. Isl Arc 15:223-238
85. Peter JM, Scott SD (1988) Mineralogy, composition, and fluid inclusion microthermometry of sea-floor hydrothermal deposits in the southern trough of Guaymas Basin, Gulf of California. Can Min 26:567-587
86. Peter JM, Scott SD (1999) Windy Craggy, northwestern British Columbia; the world's largest Besshi-type deposit. Rev Econ Geol 8:261-295
87. Piqué A (1975) Différenciation des aires de sédimentation au Nord-Ouest de la Meseta marocaine; la distension devono-dinnantienne. CR Acad Sci Paris Sér D 281:767-770
88. Piqué A (2001) Geology of Northwest Africa. Gebrüder Borntraeger, Berlin, 310 pp
89. Piqué A, Michard A (1989) Moroccan Hercynides. A synopsis. The Palaeozoic sedimentary and tectonic evolution at the northern margin of West Africa. Am J Sci 29:286-330
90. Piqué A, Jeannette D, Michard A (1980) The Western Meseta shear zone, a major and permanent feature of the Hercynian belt of Morocco. J Struct Geol 2:55-61
91. Playford G (2003) Acritarchs and prasinophyte phycomata: A short course. AASP Contributions Series 41:1-46
92. Potter PE, Maynard JB, Pryor WA (1980) The sedimentology of shale. Springer, New York, 306 pp
93. Powell WG, Johnston PA, Collom CJ (2003) Geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the Burguess Shale Formation. Palaeogeogr Palaeoclimat Palaeoecol 201:249-268
94. Price LC (1983) Geologic time as a parameter in organic metamorphism and vitrinite reflectance as an absolute geothermometer. J Pet Geol 6:5-38
95. Racki G, Wignall PB (2005) Late Permian double-phased mass extinction and volcanism: An oceanographic perspective. In: Morrow J, Over J, Wignall PB (eds) Developments in paleontology and stratigraphy. Understanding Late Devonian and Permian-Triassic biotic and climatic events. Elsevier, Amsterdam, 20:263-297
96. Raiswell R, Berner RA (1987) Organic carbon losses during burial and thermal maturation of normal marine shales. Geology 15:853-856
97. Rimmer SM (2004) Geochemical paleoredox indicators in Devonian-Mississippian black shales, central Appalachian Basin (USA). Chem Geol 206:373-391
98. Rimmer SM, Thompson JA, Goodnight SA, Robl T (2004) Multiple controls on preservation of organic matter in the Devonian-Mississippian marine black shales: Geochemical and petrographic evidence. Paleogeogr Paleoclimatol Palaeoecol 215:125-154
99. Séez R, Pascual E, Toscano M, Almodóvar GR (1999) The Iberian type of volcano-sedimentary massive sulphide deposits. Miner Depos 34:549-570
100. Sageman BB, Lyons TW (2004) Geochemistry of fine-grained sediments and sedimentary rocks. In: Mackenzie FT (ed) Sediments, diagenesis, and sedimentary rocks. Elsevier Pergamon, Oxford, pp 115-158
101. Sageman BB, Murphy AE, Werne JP, Ver Straeten CA, Hollander DJ, Lyons TW (2003) A tale of shales: The relative roles of production, decomposition, and dilution in the accumulation of organic-rich strata, Middle-Upper Devonian, Appalachian basin. Chem Geol 195:229-273
102. Schlutz RB, Rimmer SM (2004) Geochemistry of organic-rich shales: New perspectives. Chem Geol 206:163-165
103. Slack JF (1993) Descriptive and grade-tonnage models for Besshi-type massive sulphide deposits. In: Kirkham RV, Sinclair WD, Thorpe RI, Duke JM (eds) Mineral deposit modeling. Geol Assoc Can Spec Pap 40:343-372
104. Sperling H, Walcher W (1990) Die Blei-Zink-Erzlagerstätte Rammelsberg (ausgenommen Neues Lager). Geol Jahrb Reihe D 91:153
105. Stein R (1986) Organic carbon and sedimentation rate - further evidence for anoxic deep-water conditions in the Cenomanian/Turonian Atlantic Ocean. Mar Geol 72:199-209
106. Stein R (1990) Organic carbon content/sedimentation rate relationship and its paleoenvironmental significance for marine sediments. Geo-Mar Lett 10:37-44
107. Stow DAV, Huc AY, Bertrand P (2001) Depositional processes of black shales in deep water. Mar Pet Geol 18:491-498
108. Taylor SR, McLennan SM (1985) The continental crust: Its composition and evolution. Blackwell Scientific, Oxford, 312 pp
109. Törmänen T (2005) Ore mineralogy, geochemistry, and formation of the sediment-hosted sea floor massive sulfide deposits at Escanaba Trough, NE Pacific, with emphasis on the transport and deposition of gold. Acta Univ Ouluensis A 429:168
110. Van Hite JE (1978) Geohistory analysis - application of micropaleontology in exploration geology. AAPG Bull 62:201-222
111. Weaver CE (1989) Clays, muds, and shales. Developments in sedimentology, vol 44. Elsevier, Amsterdam, 819 pp
112. Wignall PB (1994) Black shales. Clarendon, Oxford, 130 pp
113. Wood GD, Gabriel AM, Lawson JC (1996) Palynological techniques - processing and microscopy. In: Jansonius J, McGregor DC (eds) Palynology: Principles and applications 1. AASP Foundation, Dallas, pp 29-50
114. Ziegler PA (1982) Geological atlas of Western and Central Europe. Elsevier (in collaboration with Shell International Petroleum), Amsterdam, 130 pp
115. Zierenberg RA, Koski RA, Morton JL, Bouse RM (1993) Genesis of massive sulfide deposits on a sediment-covered spreading center, Escanaba Trough, Southern Gorda Ridge. Econ Geol 88:2069-2098