Upper Precambrian (Eocambrian) Mineral Fork Tillite of Utah: A Continental Glacial and Glaciomarine Sequence: Discussion and Reply

Christie-Blick discussion abstract: The observations and interpretation of the Mineral Fork Tillite by Ojakangas and Matsch (1980) are most welcome. I concur with them and others that the formation is glaciogenic. However, I suggest that polish and striations on the underlying unconformity for the most part are not due to Proterozoic glacial activity, and I propose modifications to their over-all interpretation of the sequence in the Mineral Fork area. Ojakangas and Matsch reply abstract: We welcome Christie-Blick's comments, for they may serve to generate further interest in the excellent exposures of diamictite in the Big Cottonwood Canyon area of the Wasatch Range, exposures which may be among the best preserved late Proterozoic (Eocambrian) diamictites anywhere. Basically, he concurs with our major interpretation that the Mineral Fork Tillite is indeed of glacial origin, but his interpretation differs from ours in some important aspects

Information Circular 34. Precambrian Geology of the Southern Canadian Shield and the Eastern Baltic Shield

U.S.A.-U.S.S.R.-Canada Joint Seminar, August 21-23, 1990, Duluth, MinnesotaThe geologic histories of the Canadian and Baltic Shields in North America and Europe, respectively, are broadly similar, and the topic was discussed during a conference and field trip involving North American and Russian participants in the late summer of 1990. During a two-day meeting prior to the field trip, twelve North American and eleven Soviet geologists presented papers, and participants discussed a variety of problems and ideas in Precambrian stratigraphy, sedimentology, tectonics, magmatism, industrial minerals, and metallogeny. Special emphasis was placed on problems of correlation. All papers were simultaneously interpreted by Senior Translator and Interpreter Grigori Sokolov of the Institute of Geology, Karelian Branch, U.S.S.R. Academy of Sciences, who accompanied the Russian delegation. His ability contributed greatly to the meeting's success. In addition to the speakers, thirty-eight geologists attended the conference: four Canadians, two Finns, and thirty-two Americans, including eight graduate students. As a result of the seminar and field trip, exciting and promising opportunities for continued cooperation were identified. Specific proposed activities include meetings, field excursions, short courses, joint publications, individual research-oriented exchanges, and joint projects. Involvement of young geologists was especially encouraged to promote long-term cooperative relationships. Opportunities also were identified for cooperation with other international projects, such as existing bilateral programs and the International Geological Correlation Program. It was mutually agreed that in 1991-1992, the Institute of Geology, Karelian Research Center, and the Kola Research Center of the USSR Academy of Sciences will host conferences and field trips on Proterozoic and Archean geology and metallogeny in the eastern Baltic shield. In 1991, the field program will emphasize Proterozoic geology, and in 1992, Archean geology. Other joint activities in the future will depend on the outcome of the 1991 and 1992 meetings. It was the intent of the organizers to bring this joint activity to the attention of officials involved in relevant international programs. Toward that end this proceedings volume has been published by the Minnesota Geological Survey. The body of this report consists of two parts; the first is a series of short papers that provide an overview of the Precambrian geology in the Great Lakes Region; the second part consists of a similar overview of the eastern part of the Baltic Shield.Convened with the support of United States National Science Foundation (N SF-INT -9000365) Geological Survey of Canada University of Minnesota, Duluth, Department of Geology Minnesota Geological Survey Ontario Geological Survey Union of Soviet Socialist Republics Academy of Sciences Soros Foundation-Soviet Unio

Sedimentology of quartz-pebble conglomerates and quartzites of the Archean Bababudan Group, Dharwar Craton, South India: evidence for early crustal stability

The 3200 to 3000 Ma Bababudan Group, locally as thick as 1800 m, consists of a variety of rocks indicating deposition on a stable platform. U- and Au-bearing pyritiferous quartz-pebble conglomerate a few meters thick overlies a regolith at the basal unconformity with a gneissic basement. The bulk of the column consists of mafic volcanics, including subaerial flows, lahars, and sills. Ultramafic and felsic rocks, iron-formation, and pelites are minor lithologies in most of the sequence, but iron-formation forms a major unit at the top of the group. Quartzite units, intercalated with the volcanics, are generally less than 40 m thick and make up 25 to 50% of the column. They are mineralogically mature and texturally submature. Recrystallization generally obscures original textures, but units that were originally clayey quartz arenites have survived total recrystallization. Rounded zircons dominate the nonopaque detrital heavy mineral suite, verifying a history of extensive abrasion. Paleocurrent patterns based on 197 cross-beds and 145 trough axes show general current directions to the S, SE, and E. Variance calculations from outcrops and combinations of outcrops range from 1815 to 8696; the average is 4451. The suggested depositional environment is a dominant braided fluvial plain on a peneplaned granitic craton, perhaps passing into shallow marine. The source rocks appear to have been gneissic and/or granitic rocks, probably portions of the Peninsular Gneiss complex situated to the west, northwest, and north of the outcrop belts. The source terrane was probably a low-lying, deeply weathered surface upon which wind abrasion of the quartz sand was an important process. The stable platform upon which the sediment was accumulating was repeatedly rifted, as indicated by the dominantly mafic lavas; a rifted continental margin or an intracratonic basin are possible tectonic settings. This Archean sequence of continental flows and quartz arenites is one of the oldest extensive examples of rocks deposited on a stable cratonal platform

Detrital zircon provenance of Permo-Carboniferous glacial diamictites across Gondwana

Gondwana changed its high latitude location during the late Paleozoic (338–265 Ma), relative to the South Pole, and the style of glaciation evolved from localized alpine glaciers and ice fields to ~30 small ice sheets across the supercontinent. We report the analysis of heavy mineral populations (n = 2217) and the ages of detrital zircons (n = 2920 U-Pb LA-ICPMS results) from Gondwana diamictite deposits from eight landmasses: Africa (5 samples), Antarctica (5), Australia (8), the Ellsworth Mountains terrane (1, Antarctica), the Falkland Islands (2, diamictite plus U-Pb SHRIMP ages on granite clasts), India (1), Madagascar (1), Oman (3), the equatorial Lhasa terrane (2), the equatorial North Qiantang terrane (2) and South America (10). Heavy mineral separations (SEM-WDS analysis) identified one anomaly, pyrope garnets present only in Dwyka Group and Dwyka-equivalent samples suggesting an ultramafic Antarctic source. Statistical analysis of detrital zircon age distributions support the inference of local transport of sediment from many small ice centers with five examples of far-field ice transport (>1000 km; four with ice flow >2000 km), and three from ice fields located along coastal Antarctica. We propose that ice was distributed from five main ice-caps of different ages in southern Gondwana with ice flow away from central Gondwana. We also confirm that the Permo-Carboniferous detrital zircon populations of Euramerica (eolian and fluvial) and Gondwana (ash, detrital-glacial) are not mixed across the equator or seaway and ponder the possibility of a late Paleozoic snowball Earth