In central Wisconsin, Cambrian strata of the Elk Mound Group record deposition on open‐coast, wave‐dominated tidal flats. Mature, medium‐grained quartz arenite is dominated by parallel‐bedding with upper‐flow regime parallel‐lamination, deposited during high‐energy storms that also produced three‐dimensional bedforms on the flats. Abundant wave ripples were produced as storms waned or during fair weather, in water depths ≤2 m. Indicators of variably shallow water (washout structures and stranded cnidarian medusae) and subaerial exposure (adhesion marks, rain‐drop impressions and desiccation cracks, including cracked medusae) are abundant. Parallel‐bedded facies preserve a Cruziana ichnofacies, similar to other Cambrian tidal‐flat deposits. Flats were dissected by small, mainly straight channels, the floors of which were grazed intensely by molluscs. Most channels were ephemeral but some developed low levées, point bars and cut‐banks, probably reflecting stabilization by abundant microbial mats and biofilms. Channels were filled with trough cross‐bedding that is interpreted to have been produced mainly during storm runoff. The strata resemble deposits of open‐coast, wave‐dominated tidal flats on the east coast of India and west coast of Korea. Ancient wave‐dominated and open‐coast tidal flats documented to date appear to have been limited to mud‐rich strata with ‘classic’ tidal indicators such as flaser bedding and tidal bundles. The Cambrian (Miaolingian to early Furongian) Elk Mound Group demonstrates that sandy, wave‐dominated tidal flats also can be recognized in the stratigraphic record.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Robert H. Dott; Robert Nathan Ginsburg, carbonate sedimentologist (1925–2017). Earth Sciences History 1 January 2017; 36 (2): 385–386. doi: https://doi.org/10.17704/1944-6178-36.2.385 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search

Charles Darwin was a reputable geologist before he achieved biological fame. Most of his geological research was accomplished in southern South America during the voyage of H.M.S. Beagle (1831–1836). Afterward he published four books and several articles about geology and coral atolls and became active in the Geological Society of London. We have followed Darwin's footsteps during our own researches and have been very impressed with his keen observations and inferences. He made some mistakes, however, such as appealing to iceberg rafting to explain erratic boulders and to inundations of the sea to carve valleys. Darwin prepared an important hand-colored geological map of southern South America, which for unknown reasons he did not publish. The distributions of seven map units are shown. These were described in his books wherein he also documented multiple elevated marine terraces on both coasts of South America. While exploring the Andean Cordillera in central Chile and Argentina, he discovered two fossil forests. Darwin developed a tectonic theory involving vertical uplift of the entire continent, which was greatest in the Andes where magma leaked up from a hypothetical subterranean sea of magma to form volcanoes and earthquakes. The theory had little impact and was soon eclipsed by theories involving lateral compression of strata. His and other contemporary theories suffered from a lack of knowledge about the earth's interior. Finally with modern plate tectonic theory involving intense lateral compression across the Andean Cordillera we can explain satisfactorily the geology so carefully documented by Darwin.

Abstract Cambrian strata in Wisconsin compose a sheet of mostly marine sandstone, with minor dolomite, deposited during the fluctuating advance of the North American epeiric sea. Sedimentary features and fossils indicate that deposition took place in both shallower, current-dominated regimes and deeper quiet-water settings swept by episodic storm surges. The sand sheet surrounds inliers of Precambrian rocks in the Baraboo area. The Baraboo inliers are remnants of an elliptical ring of islands in a subtropical shallow sea, which were gradually buried by Cambrian and Ordovician sediments. Spectacular conglomerates composed of red quartzite clasts accumulated around the islands, which were pounded repeatedly by waves that we presume to have been generated by tropical storms. Paleomagnetic evidence places Cambrian Wisconsin in the southern tropics. Boulders up to 1.5 m in diameter are well rounded whereas larger ones (up to 8 m) are not. This suggests the possibility of estimating the magnitude of the Cambrian storm waves using knowledge from modern oceanography and from wave trough experiments by coastal engineers. Such analysis suggests waves necessary to tumble quartzite boulders 1.5 m in diameter were of the order of 7–8 m high at their point of breaking. Such magnitudes are not uncommon today during storms on many modern rocky coasts.

Chapter 26 Contrasts in Tectonic History Along the Eastern Pacific Rim R. H. Dott Jr., R. H. Dott Jr. Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706Search for more papers by this author R. H. Dott Jr., R. H. Dott Jr. Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706Search for more papers by this author Book Editor(s):George H. Sutton, George H. SuttonSearch for more papers by this authorMurli H. Manghnani, Murli H. ManghnaniSearch for more papers by this authorRalph Moberly, Ralph MoberlySearch for more papers by this authorEthel U. Mcafee, Ethel U. McafeeSearch for more papers by this author First published: 01 January 1976 https://doi.org/10.1029/GM019p0299Citations: 3Book Series:Geophysical Monograph Series AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary The histories of ocean basins prior to the Jurassic must be sought in their old convergent margins, but such margins are extremely complex due to compressional and transcurrent deformation, metamorphism, uplift, and erosion. Commonly several important tectonic events have been superimposed. Some events, however, have been more widespread and profound, in which case these serve to punctuate an otherwise rather chaotic record. The mobile eastern Pacific rim, while superficially homogeneous- appearing, is in fact a collage of many tectonic elements and segments that differ significantly in detail from their neighbors. Successions of dismemberments by extensional and transform motions and telescoping by convergence have left important marks. In early Paleozoic time, both western North and South America had tranquil, trailing-edge shelf-slope margins presumably rifted from some other, unknown continent(s). Subduction accompanied by calc-alkaline igneous activity began along the entire eastern Pacific margin at least by Permian time, and has continued along most of the margin to the present. Evidence for subduction is clearest for Mesozoic and early Cenozoic time; ophiolites, melanges, and blue schists of the Franciscan complex providing especially compelling evidence in addition to calc-alkaline magmatism. Opening of a late Paleozoic marginal basin in western North America, a late Mesozoic one in Tierra del Fuego, and doubtless others, accompanied subduction. But other areas are almost totally lacking in ophiolites, melanges, and blue schists. Moreover, late Mesozoic-early Cenozoic granitic batholiths, which are almost universal along the entire Pacific rim, lie inland in many places, but on the coast in others. Even more puzzling, in western Peru and Chile, an old Paleozoic or Precambrian metamorphic crystalline complex lies at the coast and extends offshore beneath the continental shelf almost to the trench. In mid-Cenozoic (Oligocene-Miocene) time, almost the entire circum-Pacific rim underwent profound tectonic changes, but of different sorts in different regions. Although by no means precisely synchronous, those changes do seem to be related somehow. Collision of North America with the East Pacific ridge resulted in the replacement of subduction by transform and accompanying block-fault deformation. The Cascade and Aleutian arcs were born, as was the volcanic Isthmus of Panama. In the central Andes, great vertical uplift was accompanied by block faulting and formation of the modern Andean volcanoes. In the Scotia Sea region, final dismemberment of South America from Antarctica occurred as here, too, the continent collided with an old ridge system. The South Georgia microcontinent separated from Tierra del Fuego and soon thereafter the South Sandwich arc formed. These events around the Pacific margin correlate in a very general way with a major ridge jump in the east-central Pacific beginning about 25–30 m.y. ago, the slightly earlier bend in the Hawaiian- Emperor chain, and the upheaval of the Indonesian-Himalayan-Alpine orogenic belt. Citing Literature The Geophysics of the Pacific Ocean Basin and Its Margin, Volume 19 RelatedInformation

Statherian siliciclastic sedimentary rocks in the southern Lake Superior region are key to understanding the evolution and stabilization of Paleoproterozoic crust in the midcontinent. Deposited during an important period of significant crustal growth, controversy exists regarding the conditions of sandstone deposition and the relations between magmatism and sedimentation. In central Wisconsin, the Hamilton Mounds inlier, although restricted in areal extent, is significant in that it reveals the existence of two separate Statherian units: an 1800–1760Ma immature meta-arkose and a post-1760Ma Baraboo Interval supermature quartzite. The meta-arkose is crosscut by 1762Ma granite and contains abundant Penokean age detrital monazite grains. The younger quartzite contains detrital monazite as young as 1750Ma and was deposited unconformably upon these older units. All units experienced 1630Ma low-grade recrystallization and isotopic disturbance associated with the Mazatzal Orogeny. In addition, the supermature quartzite experienced K-metasomatism and brecciation at 1470Ma, ascribed to regional-scale hydrothermal alteration related to the influence of the nearby 1470Ma Wolf River batholith. Collectively, these data suggest an early Statherian episode of arkosic deposition and magmatism during Yavapai orogenesis, followed by a longer interval of deposition of supermature quartz arenite associated with crustal stabilization. The existence of two separate Statherian units reconciles apparent conflicts in depositional models and provides a greater understanding of the Paleoproterozoic evolution of the midcontinent.

Pure quartz arenites are especially characteristic of lower Paleozoic and Proterozoic strata deposited in nonorogenic settings. A century‐long debate over the origin of these remarkably pure sandstones has remained unresolved, largely because they seem nonactualistic. The much greater importance of wind and fluvial processes prior to the Silurian appearance of macroscopic vegetation supported a physical origin, but it is now clear that both multicycling and intense chemical weathering can produce them. Multicycling seemed essential to account for their extreme textural maturity, with the exceptional rounding of many examples pointing to important eolian abrasion. Other attributes such as evidences of mixed sources, upward maturation, association with major unconformities, and an inverse relationship between labile grain content and grain size also were consistent with recycling. A single‐cycle origin proven in the modern humid tropics, however, is supported in the ancient record by examples with underlying mature paleosol profiles, chemical etching and lesser rounding of quartz grains, single populations of accessory minerals, downcurrent maturation, dissolution ghosts of labile grains, oversized pores filled with clay, and interstratified pelites composed of only kaolinite or illite. Post‐depositional diagenesis also can contribute to maturation either with or without multicycling and may even produce pure, diagenetic quartz arenites in extreme cases. Accounting for the compositional maturity of ancient quartz arenites chemically seems paradoxical without something to stabilize land surface areas long enough to allow intense weathering. Biological crusts or microbial mats composed of complex communities of cyanobacteria, algae, and lichens are here proposed as the likely means of stabilization. Although most familiar today in arid regions, such crusts are known in practically all climatic zones. Apparently they developed early in Precambrian time from marginal marine or lacustrine stromatolites and mats and were the first life forms to invade land long before the advent of vascular land vegetation.

Red, supermature quartzites of the Baraboo interval of the Lake Superior region contain detrital zircon that ranges in age from 1782 to 1712 Ma. Deposition clearly occurred after the geon 18 Penokean orogeny. These late Paleoproterozoic sedimentary rocks consist largely of quartz, kaolinite or pyrophyllite, and hematite; detrital feldspar and muscovite are rare or absent. Their Chemical Index of Alteration ranges from 96.8 to 98.6, among the most chemically mature clastic sediments in the geological record. The quartzites are underlain by mature, feldspar‐free paleosols, accounting for the absence of feldspar in the overlying sediments and indicating the presence of first‐cycle quartzose detritus. Such physical and chemical characteristics imply that late Paleoproterozoic deposition in the Lake Superior region occurred in a stable tectonic setting with subdued topographic relief in a warm, humid climate. Folding and low‐grade metamorphism of the quartzites is thought to reflect ∼1630 Ma foreland deformation related to the Mazatzal orogeny. Younger hydrothermal alteration is widespread in the Baraboo and Sioux quartzites and, based on 40Ar/39Ar dating of low‐temperature minerals, is attributed to the migration of fluids along permeable channels in response to the thermal effects of magmatism associated with the 1465 Ma Wolf River batholith. Much of the Paleo‐ and Mesoproterozoic crust of Proto–North America may have been affected by areally extensive, but stratigraphically restricted, hydrothermal alteration related to the influence of geon 14 transcontinental A‐type granitic magmatism.

Fossilized impressions of soft-bodied organisms are exceptionally rare in coarse-grained strata. Fossilized mass-stranding events of soft-bodied organisms are even rarer. The Upper Cambrian Mt. Simon–Wonewoc Sandstone in central Wisconsin contains at least seven horizons characterized by hundreds of decimeter-sized impressions of medusae; these represent one of only two fossilized mass-stranding deposits. Medusae exhibit features nearly identical to those observed in modern scyphozoan strandings, including impressions of subumbrellar margins and gastrovascular cavities. This deposit provides insights about soft-tissue preservation in Phanerozoic marginal marine sediments, and suggests that large soft-bodied pelagic organisms were abundant in Cambrian seas.

Fossilized impressions of soft-bodied organisms are exceptionally rare in coarse-grained strata. Fossilized mass-stranding events of soft-bodied organisms are even rarer. The Upper Cambrian Mt. Simon-Wonewoc Sandstone in central Wisconsin contains at least seven horizons characterized by hundreds of decimeter-sized impressions of medusae; these represent one of only two fossilized mass-stranding deposits. Medusae exhibit features nearly identical to those observed in modern scyphozoan strandings, including impressions of subumbrellar margins and gastrovascular cavities. This deposit provides insights about soft-tissue preservation in Phanerozoic marginal marine sediments, and suggests that large soft-bodied pelagic organisms were abundant in Cambrian seas.

Conventional wisdom long held that all important intellectual diffusion was from Europe westward to North America until the 1940s, but two examples of a reverse flow of fundamental concepts of structural geology during the 1920s challenge that dogma. Those concepts were products of the renowned Wisconsin school of Precambrian geology, and their transplantation also involved Princeton University. The first example of Wisconsin export concerns the use of sedimentary structures for establishing the original top facing or way-up direction within complexly deformed strata. Although this technique was recognized in nineteenth century Ireland, that insight was ignored and lost. Only after its reintroduction to Great Britain from Wisconsin in the 1920s was its importance gradually recognized in Europe. The second example concerns the recognition that small-scale deformational structures visible in isolated outcrops reflect larger regional structures, which are commonly not directly observable. This fundamental inference also had its roots in Wisconsin, where Englishman Gilbert Wilson learned it in 1925-1926 and then taught it at the Imperial College in London.These two key concepts of small-scale structural analysis, coupled with the use of the stereonet and insights from experimental deformation of rocks, became the basis for a revolution in structural geology during the 1950s to 1970s. After the triumphs of four generations of Wisconsin faculty members, who were outstanding both as scientists and administrators, the Wisconsin school faltered until the waves of that revolution washed back upon American shores during the 1960s.

The Middle Ordovician St. Peter Sandstone and Glenwood Formation (Ancell Group) represent a significant target for gas exploration at the base of the Tippecanoe sequence in the Michigan basin. Core and well log data show that the St. Peter-Glenwood interval contains numerous carbonate units that provide the basis for both regional correlation and subdivision of the section into at least 20 high-frequency sequences. The temporal resolution afforded by these sequences allows a detailed analysis of sediment partitioning as the basin evolved. The spatial distribution of the basal sequences illustrates the pronounced east-to-west onlap of the Wisconsin arch. An abrupt increase in sequence thickness upsection indicates that a major episode of basin-centered subsidence began during middle St. Peter deposition and continued through the deposition of the Glenwood Formation. The upper sequences show a significant beveling of the Glenwood Formation and the top of the St. Peter Sandstone in the north, south, and southeast areas of the basin prior to deposition of the overlying Black River carbonates. Although eustatic sea level changes were undoubtedly operating at several scales, the facies distribution of this mixed clastic/carbonate system also documents significant changes of local and regional tectonics.

Quite a few things of note happened in 1797: Franz Schubert was born; Napolean defeated the Austrians and was appointed to command forces to invade England; John Adams became the second President of the United States; chromium was discovered; the first copper pennies and pound notes were issued in Britain; and Merino sheep were introduced to Australia. None of these seems more important, however, than the geological coincidence that brought us together for this outstanding Bicentennial Conference. In attempting to summarize our proceedings, I feel like that political foe whom Winston Churchill once characterized sardonically as 'having much to be humble about'. I trust that all of the conferees join me in thanking the Royal Society of Edinburgh and the University of Edinburgh for being such gracious hosts. We owe a special debt of gratitude to Gordon Craig and his organizing committee, together with the Session Chairmen (Charles Waterston, Graham Shimmield, Barry Dawson, Tony Hallam and Dennis Dean), who helped the speakers to be most effective, and those who arranged the fine excursions (Norman Butcher, David Land, David McAdam, Donald Mclntyre, Stuart Munro, Ian Rolfe, David Stephenson and Leonard Wilson). I have a special gift of appreciation for Gordon by way of returning a favour he did me seven years ago. In 1990 1 had the pleasure of presiding when the Geological Society of America's History Division honoured Gordon. What did he do after I presented our award to him, but counter by awarding me with a copy of Charles Lyell's notes for a lecture to be given in Philadelphia on 2 March 1842. This diverting token hooked me into a research project on Lyell's lectures and travels in America from 1841 to 1853, which I only completed this ye a r j u s t in time to report briefly at the London portion of this conference. So, in return, I wish to award Gordon with a bottle of 'Piltdown Man Wine', which my wife and I obtained recently from the winery that now occupies the site of the famous Piltdown skull. One good hoax deserves another! If memory serves, this is my fourth visit to Edinburgh. I have a rather spectacular history of failures when visiting these parts in spite of the fact that my paternal greatgrandfather emigrated from just across the firth in Fife and that both of my wife's paternal grandparents came from near Kinnordy, seat of the Lyell family. During my first visit in 1963, after dining at the University Staff Club, my two hosts escorted me on a pilgrimage to Greyfriar's Churchyard to see HuRon's grave and a plaque, which I knew had been placed there in 1947 on the 150th anniversary of his death. It was about 10 o'clock at night, but in mid-summer at 56~ latitude it was still light. No amount of light nor of guides' confidence, however, was sufficient, for we failed to discover either grave or