Occurrence of a Ctenacanthoid Shark Spine from the Upper Devonian of North Central Iowa

Although a diverse, invertebrate fauna is characteristic of the Upper Devonian, Lime Creek Formation, in north central Iowa, fossil fish remains are sparse. A detached and incomplete shark spine with ctenacanthoid features is reported and described. The specimen is the best example of the first occurrences of its kind from Devonian of Iowa. Despite some asymmetry in shape, the spine is interpreted as the cutwater of a dorsal fin. Overall length of the shark is estimated at l-l.5m

Recurrent Community Patterns in Epeiric Seas: The Lower Silurian of Eastern Iowa

In eastern Iowa, the Llandovery Series (Lower Silurian) consists of the Edgewood and Kankakee formations as well as much of the Hopkinton Dolomite. Outcrops of these rocks provide fossil assemblages of marine benthic invertebrates well suited for reconstructing epeiric sea communities. Results of preliminary field studies in Dubuque, Jackson. Jones, and Delaware counties indicate that an initial Lingula Community at the base of the section is succeeded by recurrent patterns of Coral, Pentamerid, and Stricklandid communities. The patterns are interpreted as community response to fluctuations in sea level, estimated to vary between a few and 60 m. At least two repetitions of deepening to shallowing seas are represented, possibly linked to eustatic causes. The orderly sequence of communities, symmetric with respect to reversals in changing water depth, suggests that the local geologic record is reasonably complete. Beds of the Hopkinton Dolomite previously unrecognized as distinct units are described and the first occurrences of the brachiopods, Cyrtia and Ferganella, from the Lower Silurian of Iowa are reporte

New Member Names for the Lower Silurian Hopkinton Dolomite of Eastern Iowa

Previously divided primarily on the basis of paleontologic units, the approximately 60-80 m thick Hopkinton Dolomite in eastern Iowa also comprises a set of lithologically unique subunits. With the development of a new capability for inter-regional correlation of Lower Silurian strata based on the use of sea-level curves, it is especially appropriate to recognize these subdivisions of the Hopkinton Dolomite as formal member units. Locally, the relationships shown by these units may also contribute to a better understanding of the Plum River Fault Zone and its associated structures in Iowa and Illinois. Willman (1973) named the Sweeney and Marcus Formations for strata in northwestern Illinois that he physically correlated with the Syringopora and Pentamerus Beds of the lower Hopkinton Dolomite. It is recommended that these units receive wider application as the Sweeney and Marcus Members of the Hopkinton Dolomite. The names Farmers Creek, Picture Rock, Johns Creek Quarry, Welton, and Buck Creek Quarry are proposed as members of the remaining middle to upper Hopkinton Dolomite. These names supersede the Cydocrinites, Favosites, Bioherm, Cyrtia, and Pentameroides Beds, respectively (Johnson, 1975; 1980)

Early Geological Explorations of the Silurian System in Iowa

The development of geology as a scientific discipline in Iowa had an early and active history dating from pre-statehood. A high standard of geological observation mixed with pioneer ruggedness evolved from the first reconnaissance work of David Dale Owen in 1839 to the detailed, county survey work of Samuel Calvin at the turn of the century. Aspects of explorations made within this period are highlighted, particularly those with reference to the Silurian System. Strenuous journeys, rival personalities, and the influence of scientific controversy in Europe characterize the early geological explorations in Iowa

Storm-related rhodolith deposits from the upper pleistocene and recycled coastal holocene on Sal Island (cabo verde archipelago)

This project examines the role of tropical storms in the northeast Atlantic Ocean related to the post-mortem deposition of rhodoliths in coastal settings during Neogene to Holocene time with primary emphasis on Sal Island in the Cabo Verde Archipelago located 600 km off the coast of Senegal in northwest Africa. Fossil rhodoliths from 10 to 15 cm in diameter are equal in size to contemporary rhodoliths that survive for a century or more at water depths undisturbed by all but the most energetic storms. The shape of large rhodoliths makes them susceptible to rare disturbances with sufficient energy to export them beyond their preferred habitat into extreme environments that include supratidal settings. The methodology of this study gauges the relative sphericity of rhodoliths based on measurements across three axes perpendicular to one another, plots size variations on bar graphs, and considers whether or not individual nodules are nucleated around rock cores eroded from proximal rocky shores. Sal Island is impacted on a steady basis by wave swell generated from the Northeast Trade Winds, but Pleistocene and Holocene deposits with large rhodoliths on the Island’s windward coast are interpreted as the result of major storms of hurricane intensity. Comparison of Sal Island rhodoliths with Pliocene and Miocene examples from other insular localities in the Northeast Atlantic considers evidence for displacement of the Inter-Tropical Convergence Zone (ITCZ) into more northern latitudes as an influence on past hurricane tracks that are less common today

Intense hurricane transports sand onshore:Example from the Pliocene Malbusca section on Santa Maria Island (Azores, Portugal)

Southern cliffs on Santa Maria Island in the Azores archipelago (North Atlantic Ocean) feature submarine volcanic sequences inter-bedded with Pliocene coralline algal limestone, shelly coquinas, and mixed volcaniclastic-calcarenite sandstone. Within the 20-m sedimentary succession at Malbusca, a singular, 5-m sandstone bed is distinguished by dark and light laminae dominated alternately by heavy minerals and carbonate detritus. Carbonate grain-size varies between that of coarse silt and very fine sand. The basal part shows coarser and more poorly sorted sand in an upward transition to increasingly finer carbonates. Accessible over a lateral space of 34 m, the big bed is shouldered against and overlaps the remnants of a drowned rocky shore with a paleorelief of 4 m that preserves intertidal to shallow subtidal biotas. Extrapolated from the big bed's rock face (1830 m2) and the width of the eroded shelf on which it resides (8 m), calculations yield a projected volume of 14,500 m3. Unique to the island, the big bed is interpreted as a major hurricane deposit that moved sand from an offshore bar in an onshore path. Such an event fits the context of the Pliocene Warm Period, during which global El Niño conditions were more intense than today

On the rise and fall of oceanic islands:Towards a global theory following the pioneering studies of Charles Darwin and James Dwight Dana

The careers of Charles Darwin (1809–1882) and James Dwight Dana (1813–1895) are intimately linked to circumnavigations of the globe with the British mapping expedition on the H.M.S. Beagle (1831–1836) under Captain Robert FitzRoy and the United States Exploring Expedition (1838–1842) under Lieutenant Charles Wilkes. The former expedition mainly surveyed coastal South America, but also visited many volcanic islands in the Atlantic, Pacific, and Indian oceans. The latter expedition followed a similar path through the Atlantic, but devoted more time to Pacific Ocean islands. Remembered more today for his visit to the Galapagos Islands and its subsequent impact on understanding the mechanisms of biological evolution, Darwin was motivated early on during his stopover in the Cape Verde Islands to compile studies on the geology of volcanic islands. Better known for his theory of atoll development from the subsidence of volcanic islands stimulated by his visit to the Keeling Islands and published in 1842, Darwin also wrote a related volume published in 1844 with an equally strong emphasis on island uplift. Dana was influenced by Darwin's theory of atoll development, and published his own independent observations on coral reefs and island subsidence in 1843, 1849, and 1853. The work of both geologists matured from primary observations using inductive logic during fieldwork (i.g. unconformable position of limestone on and between basalt flows as an indicator of paleo-sea level) to the advancement of broader theories regarding the behavior of the Earth's oceanic crust. Notably, Dana recognized age differences among islands in Pacific archipelagos and was strongly influenced by the orientations of those island groups. The classic Hawaiian model that features a linear string of progressively older and subsiding islands does not apply easily to many other island groups such as the Galapagos, Azores, Canary, and Cape Verde islands. Geologists and coastal geomorphologists increasingly find that the original observations on island uplift covered in Darwin's, 1844 treatment provide an alternative pathway to understanding the complexities of island histories in oceanic settings. Original work by Darwin and Dana also led to ongoing studies on the trans-oceanic migrations of marine organisms, such as barnacles, corals and non-attached coralline red algae represented by rhodoliths. This work gives added importance to oceanic islands as way stations in the dispersal of biotas over time.</p

What Darwin did not see : Pleistocene fossil assemblages on a highenergy coast at Ponta das Bicudas, Santiago, Cape Verde Islands

Two distinct Pleistocene assemblages from SE Santiago Island are comparable to modern analogues elsewhere in the Cape Verde Islands. A low-diversity Siderastrea radians assemblage lived atop basalt knobs surrounded by sand on a slope below a cliff. A Millepora alcicornis–Megabalanus azoricus assemblage occupied the cliff. The latter was a typical rocky-shore assemblage from a high-energy setting belowthe tidal zone.Bioerosion structures in basalt produced by Circolites kotoncensis and Gastrochaenolites isp. also occur there. Despite extensive studies on local limestone deposits in 1832 and 1836, lack of exposure prevented Darwin from seeing these fossils.Funding for fieldwork on Santiago Island in June 2011 was provided under grant CGL2010-15372-BTE from the Spanish Ministry of Science and Innovation to project leader Eduardo Mayoral (University of Huelva). Financial support to A. Santos came from the Spanish Ministry of Science and Technology (Juan de la Cierva subprogram, Ref: JCI-2008-2431). Additional support by the Junta de Andalucia (Spanish government) to the Research Group RNM276 is also acknowledged. Partial funding to J. Ledesma-Vazquez on this project came from the Programma Integral de Fortalecimiento Institucional 2010. We thank Christopher K. Pham, Department of Oceanography and Fisheries, University of the Azores, Portugal, for help with identification of the fossil barnacles and Ricardo Ramalho, Institut fur Geophysik, Westphalishe-Wilhelms Universitat, Germany, for discussions about bioerosion by sea urchins on basalt surfaces