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

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

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

Geological Oceanography of the Pliocene Warm Period: A Review with Predictions on the Future of Global Warming

Atmospheric carbon dioxide reached a record concentration of 419 parts per million in May 2021, 50% higher than preindustrial levels at 280 parts per million. The rise of CO2 as a heat-trapping gas is the principal barometer tracking global warming attributed to a global average increase of 1.2 °C over the last 250 years. Ongoing global warming is expected to perturb extreme weather events such as tropical cyclones (hurricanes/typhoons), strengthened by elevated sea-surface temperatures. The melting of polar ice caps in Antarctica and Greenland also is expected to result in rising sea levels through the rest of this century. Various proxies for the estimate of long-term change in sea-surface temperatures (SSTs) are available through geological oceanography, which relies on the recovery of deep-sea cores for the study of sediments enriched in temperature-sensitive planktonic foraminifera and other algal residues. The Pliocene Warm Period occurred between ~4.5 and 3.0 million years ago, when sea level and average global temperatures were higher than today, and it is widely regarded as a predictive analog to the future impact of climate change. This work reviews some of the extensive literature on the geological oceanography of the Pliocene Warm Period together with a summary of land-based studies in paleotempestology focused on coastal boulder deposits (CBDs) and coastal outwash deposits (CODs) from the margin of the Pacific basin and parts of the North Atlantic basin. Ranging in age from the Pliocene through the Holocene, the values of such deposits serve as fixed geophysical markers, against which the micro-fossil record for the Pliocene Warm Period may be compared, as a registry of storm events from Pliocene and post-Pliocene times

Hurricane Kay (September 2022) Impacts Rocky Shores in the Loreto Area of Baja California Sur, Mexico

This project follows a tradition of survey work undertaken to appraise physical and biological damage in the aftermath of hurricane-strength winds and waves at a given locality where conditions were well documented prior to the arrival of a particular storm. The locality is the 12 m limestone terrace at Arroyo Blanco on the eastern shores of Isla del Carmen in Baja California Sur, Mexico. A study undertaken in February 2018 established that the surface of the terrace is covered by a coastal boulder deposit that features large slabs of limestone pealed from the outer edge by strong surf attributed to storms of hurricane intensity but unknown date. The largest slabs tend to be rectilinear in shape vulnerable to dislodgement along horizonal bedding planes and weaknesses in vertical joints. These blocks are sufficiently large and weigh enough that movement by humans without necessary mechanical equipment would be impossible. Hurricane Kay, rated as a Category 2 storm, struck the island on 8 September 2022 and an effort was made to visit the area for reconnaissance and detailed survey work soon afterwards. Although a Category 2 storm lacked the energy to remobilize the largest limestone slabs on the terrace, it was found that the storm was sufficient to disturb the adjacent seabed and redeposit as many as 44 sea fans onto the terrace by overwash; the sea fans belonged to the species Pacifigorgia adamsi. Moreover, a species of land plant common to the limestone terrace is the Gulf Star Violet (Stenotis mucronate); it suffered significant desiccation and death due to saltwater exposure. The occurrence of large potholes on the limestone terrace represents a style of physical erosion previously undocumented at the locality and rarely seen elsewhere on rocky shores

Evaluation of Boulder Deposits Linked to Late Neogene Hurricane Events

The Neogene is a globally recognized interval of geologic time that lasted from 23 until 1 [...