Boulder, CO, USA - GEOLOGY covers multiple aspects of life on Earth, including extinctions and diversifications, "tool" use by the first creatures to walk on land, sirenians (manatees) in the Tethys-Mediterranean, the last refuge of the woolly mammoth, and Edwards Aquifer development as seen through cave spider DNA. Other topics include glaciation, mineralization, mineral decomposition, degassing, climate change, tectonics, volcanics, current velocity and seafloor structure, and giant earth-surface wind ripples. GSA TODAY focuses on the Great Ordovician Biodiversification Event.
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Hermit arthropods 500 million years ago?
James W. Hagadorn and Adolf Seilacher, Dept. of Geology, Amherst College, Amherst, Massachusetts 01002, USA. Pages 295-298.
When animals first crawled onto land, one of the greatest obstacles they had to contend with was figuring out how to breathe. No longer bathed in oxygen-rich marine waters, their gills would surely have dried out. Hagadorn and Seilacher have analyzed fossils from 500-million-year-old rocks that show one way these early pioneers may have dealt with this problem--the first terrestrial animals carried a shell on their backs. Like modern hermit crabs, these ancient pioneers had a scorpion-like body, and could stuff their abdomen into a coiled snail shell. One advantage of doing this was that the shell may have acted as a humid chamber to keep their gills moist. This would have allowed brief forays out of the water, to explore the beaches and tidal flats, and to graze in environments where there was no competition from other animals or predators. These fossils represent the first usage of "tools," and provide insights into how some animals may have made the leap from living in water to living on land.
Large perturbations of the carbon and sulfur cycle associated with the Late Ordovician mass extinction in South China
Tonggang Zhang et al., CRC in Biogeochemistry, University of Quebec at Montreal, Montreal H3C 3P8, Canada. Pages 299-302.
The Late Ordovician mass extinction took place in the Hirnantian Stage (445.6-443.7 million years ago) and is the second largest of all great extinction events over the past 543 million years. During this biological crisis, it has been estimated that 26% of all families, or 49% of all genera, became extinct. The Late Ordovician extinction appears to coincide with the Late Ordovician glaciation that developed in high-latitude Gondwanaland. This has led many to propose that the glaciation and extinction were causally linked. In this study, Zhang et al. performed high-resolution carbon and sulfur isotopic studies on Late Ordovician sedimentary rocks from South China. Their geochemical data reveal large perturbations of the sulfur and carbon cycle accompanying the mass extinction, and their isotopic data suggest deep-water anoxia in South China, in contrast to the conventional view that the global oceans were oxygenated. Zhang et al. argue that anoxia may have contributed to the episodic and stepwise extinction in the Hirnantian Stage, in conjunction with harsh climate and temperature changes related to glaciation.
Circum-Pacific arc flare-ups and global cooling near the Eocene-Oligocene boundary
Brian R. Jicha et al., Dept. of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706, USA. Pages 303-306.
Explosive arc volcanism can have significant environmental impact because of the discharge of ash and volatiles directly into the atmosphere and oceans. Jicha et al. compile 2,814 age determinations from four circum-Pacific arcs and show that peak periods and subsequent lulls in arc magmatism over the past 50 million years are coeval with major fluctuations in global climate. Hundreds of intermediate-to-silicic eruptions occurred during an extremely vigorous period of circum-Pacific volcanism beginning in the late Eocene, about 34 million years ago, which likely led to the production of sulfur aerosols in the stratosphere and fertilization of surface waters of the Pacific Ocean. The findings suggest that abundant arc volcanism may be partly responsible for the climatic preconditioning that must have preceded and ultimately promoted the first widespread glaciation of Antarctica.
Evidence of Cenozoic environmental and ecological change from stable isotope analysis of Sirenian remains from the Tethys-Mediterranean region
Mark T. Clementz et al., Dept. of Geology and Geophysics, University of Wyoming, 1000 E. University Ave., Laramie, Wyoming 82071, USA. Pages 307-310.
Sirenians (sea cows; manatees and dugongs) have been primary consumers in tropical and subtropical shallow-water marine ecosystems for over 50 million years. Though fossils of the earliest sirenians have been recovered from the Caribbean, sirenians are thought to have originated in the Tethys-Mediterranean region, which experienced significant climate change over the course of the Cenozoic. Application of stable isotope analysis can provide new insight into how diet and habitat preferences were impacted by climate change and, in turn, how these ecological changes correlate with diversity patterns for this region. Tooth enamel was sampled by Clementz et al. from 57 specimens of sirenians from the Tethys-Mediterranean and adjacent seas spanning the Eocene to Pliocene. Enamel delta-13C values across this time interval were consistently high and indicative of diets composed mostly of marine seagrasses. In contrast, enamel delta-18O values showed significant change over time and across the region. Sirenians from southern sites (i.e., Egypt, Libya) had significantly higher mean delta-18O values than specimens from most European locations, suggesting variation in salinity within the Tethys-Mediterranean. The range in enamel delta-18O values increased from the Paleogene through the Neogene, but enamel delta-13C values remained steady, indicating that changes in environmental conditions did not necessarily coincide with major changes in dietary preferences. Declines in sirenian taxonomic diversity in the late Miocene were likely due to the rapid climate and oceanographic changes during the latter half of the Cenozoic and their impacts on available dietary resources. Elevated delta-13C and delta-18O values in Mediterranean sirenians during the Messinian Salinity Crisis corroborate the hypothesis of ecophenotypic dwarfing in these animals.
Seismic and geodetic evidence for extensive, long-lived fault damage zones
Elizabeth S. Cochran et al., Dept. of Earth Sciences, University of California-Riverside, Riverside, California 92521, USA. Pages 315-318.
Growing evidence suggests that the crust adjacent to active faults suffers an incredible amount of damage and cracking during earthquakes. Using seismic and geodetic data, Cochran et al. have found a wide, sustained damage zone along the Calico fault, located in the Mojave Desert, California. The damage zone extends for 1.5 km across the fault, with seismic velocities reduced by up to 50%. This zone of damaged rock has not recovered in the hundreds, or perhaps thousands, of years since the last large earthquake occurred on the Calico fault. The results suggest that earthquakes can affect rock properties at large distances from a fault and may result in persistent fault systems through localization of strain.
Role of non-mantle CO2 in the dynamics of volcano degassing: The Mount Vesuvius example
Giada Iacono-Marziano et al., Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo la Malfa 153, 90146 Palermo, Italy. Pages 319-322.
Mount Vesuvius, although quiescent since 1944, is currently characterized by elevated carbon dioxide (CO2) emissions of debated origin (about 300 tons of CO2 per day). The volcano is sited on a carbonate sedimentary sequence several kilometers thick. In this paper, Iacono-Marziano et al. show how Mount Vesuvius basaltic magmas coming into contact with the carbonate rocks of the basement assimilate them and liberate CO2, explaining CO2 emissions measured at the surface around the volcano. The assimilation of carbonate rocks by magmas probably contributes, to a certain extent, to the CO2 degassing of several other volcanic centers, dormant or active, located over sedimentary rocks. Magma-carbonate interactions could therefore have a major role in global CO2 emissions from volcanoes, which has been underestimated so far.
Climate changes caused by degassing of sediments during the emplacement of large igneous provinces
Clement Ganino and Nicholas T. Arndt, Laboratoire de Geodynamique des Chaines Alpines, Universite Joseph Fourier de Grenoble, CNRS, 1381 Rue de la Piscine 38400 Saint Martin d'Heres, France. Pages 323-326.
Some, but not all, large igneous provinces coincide with global warming episodes and mass extinctions. The Cretaceous-Tertiary mass extinction coincides with flood volcanism in the Deccan province of India; the Permian-Triassic extinction with the emplacement of the Siberian Traps. In contrast, the enormous oceanic plateaus and the continental Karoo flood basalts had lesser effects on the biosphere. The cooling effect of volcanic ash and sulphate aerosols injected into the stratosphere during Plinian eruptions may be the main cause of mass extinctions, but the volume of erupted basalt of each large igneous province does not correlate well with the extent of mass extinction. An alternative explanation is that the global climatic changes are related to the volatiles released during low-temperature contact metamorphism of the intruded rocks. Ganino and Arndt studied the Emeishan flood basalts that intruded a dolomitic basin, and calculated that the amount of sediment-derived carbon dioxide (CO2) was three times more than magmatic CO2 released from the Emeishan lavas and intrusions. The vented CO2 would have led to greenhouse conditions and intense global warming. Ganino and Arndt propose that the thermal decomposition of anhydrite, salt, limestone, hydrocarbons, and coal in other provinces provided a toxic cocktail that caused other mass extinctions. The Karoo and other provinces had little to no environmental impact because they were emplaced in sterile magmatic or sedimentary rocks.
Bedform-velocity matrix: The estimation of bottom current velocity from bedform observations
Dorrik A.V. Stow et al., IPE-ECOSSE, Heriot Watt University, Edinburgh EH14 4AS, UK. Pages 327-330.
Deep-ocean currents continuously sculpt the seafloor beneath their course. In places, they generate ripples, sand waves, and giant mud waves over the backs of huge sediment mounds, while elsewhere they erode deep furrows and broad channels. Stow et al. have synthesized a large amount of published data, together with their own observations, to clearly document the link between current velocity and the type of seafloor feature (or bedform) generated. This will allow other ocean scientists to better chart and understand the flow of deep-sea currents around the global ocean, which will in turn, improve our knowledge of the all-important ocean-climate link. It will further provide sub-sea engineers with additional tools for the better siting and management of submarine cables, pipelines, and other seafloor installations.
Syndepositional fault control on lower Frasnian platform evolution, Lennard Shelf, Canning Basin, Australia
Annette D. George et al., School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia. Pages 331-334.
Ancient reef complexes flourished in a large Late Devonian sea about 380 million years ago in northwestern Australia. This sea no longer exists but is now represented by marine deposits, including famous reef complexes that grew in shallow water along the margins of the sea. The northern part of this area, known as the Canning Basin, was tectonically active at that time (similar to the Red Sea today), and fault movements elevated some parts of the seafloor to provide ideal conditions for reef-building organisms. This has been well known for decades. Through their work on one of the major reef complexes, including being able to date more closely when deposition of carbonate sediments took place, George et al. are able to show that fault movements continued to strongly control sea-level changes in the region and, therefore, controlled the overall evolution of the reef complex. Understanding how ancient reefs evolved is very important economically because they are well-known petroleum reservoirs, as well as hosts for mineral deposits containing lead and zinc.
Hydrologic evolution of the Edwards Aquifer recharge zone (Balcones fault zone) as recorded in the DNA of eyeless Cicurina cave spiders, south-central Texas
Kemble White et al., Cave and Endangered Invertebrate Research Laboratory, SWCA Environmental Consultants, 4407 Monterey Oaks, Building 1, Suite 110, Austin, Texas 78749, USA. Pages 339-342.
The history of the Edwards Aquifer is written in the DNA of its endemic cave spiders. White et al. present the first interdisciplinary study of its kind linking the biological evolution of endemic cave fauna with the hydrologic evolution of their vadose-zone aquifer habitat. Techniques originally developed for endangered species management have been applied in a novel approach to vadose-zone hydrology and paleohydrology. By establishing the synchrony between the speciation of cave fauna and the activation of discrete segments of the aquifer recharge zone, White et al. present a new set of tools to hydrologists and to managers of an aquifer resource serving more than a million people.
Largest wind ripples on Earth?
Juan Pablo Milana, InGe-CONICET, Universidad Nacional de San Juan, 5401 San Juan, Argentina. Pages 343-346.
Strong wind action has been the theme for many popular movies. However, we still do not fully understand the complicated interaction between strong winds and Earth's surface. The largest wind ripples found on Earth, and perhaps the coarsest grained, are described in the study by Milana. The wind ripples are found in the southern Argentinean Puna Plateau and reach 43 meters of crest spacing, helping fill the gap between the previously largest ripples described on Earth (over 20 meters) and the huge wind ripples found on Mars, reaching over 60 meters wavelength. Large wind ripples, which form under fast winds and the presence of lightweight volcanic grains transported by the wind, may help in understanding the formation mechanisms of these large bedforms, which are also considered to be sisters of the small wind ripple commonly formed in beach sand and dunes. Continued study may help in the understanding of the effect of very strong winds on surfaces with movable materials.
Bioapatite 87Sr/86Sr of the last woolly mammoths—Implications for the isolation of Wrangel Island
Laura Arppe et al., Dept. of Geology, P.O. Box 64, 00014 University of Helsinki, Finland. Pages 347-350.
Wrangel Island, off of eastern Siberia, was the last refuge of woolly mammoths before their final extinction. A population of mammoths became trapped on the island during rising sea levels at the end of the last glacial age. The isolation of the island from the mainland is interpreted by Arppe et al. from a distinct increase in the 87Sr/86Sr ratios of the mammoth skeletal remains, reflecting a change in the feeding area of the animals, from the vast plains of the continental self to the more mountainous area of present-day Wrangel Island.
Renewed glacial activity during the Antarctic cold reversal and persistence of cold conditions until 11.5 ka in southwestern Patagonia
P.I. Moreno et al., Dept. of Ecological Sciences and Institute of Ecology and Biodiversity, University of Chile, Santiago, Chile. Pages 375-378.
Resolving the timing, direction, and magnitude of paleoclimate changes in the southern middle-latitudes is a prerequisite for determining the mechanisms underlying abrupt and widespread climate changes between the hemispheres during the Last Glacial-Interglacial Transition (LGIT). Yet, this issue is still in debate, with previous studies producing apparently discordant findings. Here, Moreno et al. show evidence for a glacial re-advance and a cold episode between about 14.8 and 12.6 thousand years ago in southwest Patagonia (50 degrees south), contemporaneous with the Antarctic cold reversal. This was followed by ice recession under cold, but relatively milder, conditions until about 11.5 thousand years ago, when paleovegetation records indicate the onset of warm interglacial conditions. These findings differ from those reported in northern Patagonia (about 40 degrees south), where deteriorating conditions before 13.5 thousand years ago were followed by the coldest part of the LGIT that lasted until about 11.5 thousand years ago. They interpret the apparent blend of "Greenlandic" and "Antarctic" cold phases as evidence for their co-occurrence in the southern middle latitudes in Patagonia, and hypothesize that the position of the Antarctic Polar Front modulated the strength of these cold events in regions to the north or south of it.
GSA Today Science Article
Understanding the Great Ordovician Biodiversification Event (GOBE): Influences of paleogeography, paleoclimate, or paleoecology?
Thomas Servais et al., Equipe "Paleontologie et Paleogeographie du Paleozoique," UMR 8157 du CNRS "Geosystemes," Universite de Lille 1, F-59655 Villeneuve d'Ascq, France
The Cambrian "explosion" of multi-cellular life is perhaps the most significant and best known of the major evolutionary events in Earth's history. But what transpired after the Cambrian explosion? Did the species and life forms that sprang out of the Cambrian evolve steadily throughout the remainder of the Paleozoic? The work of Thomas Servais and his international team of colleagues suggests that most of the fauna and flora that characterized the Paleozoic period owed their existence not to the Cambrian explosion, but to an equally abrupt and perhaps even more dramatic evolutionary event: The Great Ordovician Biodiversification Event, or GOBE. About 490 million years ago, at a time when many of the Cambrian fauna were already extinct or in decline, a massive, even catastrophic growth in the number and variety of marine species began. The previously largely uninhabited water column became thick with plankton and the predators that fed on them, while the lifeless substrate to the ocean floor suddenly teamed with burrowing fauna. It was the GOBE that provided Earth with the bulk of the fauna that were to thrive in and characterize the Paleozoic era. But what triggered the GOBE, why was it so much more productive than the Cambrian explosion, and why were the GOBE fauna so successful and long-lived? As shown by Servais and his colleagues, answering these fundamental questions about one of the most important evolutionary events in Earth's history will require much further research.
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Geology