Denali duck-billed dino tracks

(Press-News.org) Boulder, Colo., USA – A trio of paleontologists has discovered a remarkable new tracksite in Alaska's Denali National Park filled with duck-billed dinosaur footprints -- technically referred to as hadrosaurs -- that demonstrates they not only lived in multi-generational herds but thrived in the ancient high-latitude, polar ecosystem. The paper provides new insight into the herd structure and paleobiology of northern polar dinosaurs in an arctic greenhouse world.

The article, "Herd structure in Late Cretaceous polar dinosaurs: A remarkable new dinosaur tracksite, Denali National Park, Alaska, USA," was written for Geology by lead author Anthony R. Fiorillo, curator of earth sciences at the Perot Museum of Nature and Science, and co-authors Stephen Hasiotis of the University of Kansas and Yoshitsugu Kobayashi of the Hokkaido University Museum.

"Denali is one of the best dinosaur footprint localities in the world. What we found that last day was incredible -- so many tracks, so big and well preserved," said Fiorillo. "Many had skin impressions, so we could see what the bottom of their feet looked like. There were many invertebrate traces -- imprints of bugs, worms, larvae and more -- which were important because they showed an ecosystem existed during the warm parts of the years."

**FEATURED ARTICLE** Herd structure in Late Cretaceous polar dinosaurs: A remarkable new dinosaur tracksite, Denali National Park, Alaska, USA Anthony R. Fiorillo et al., Perot Museum of Nature and Science, 2201 North Field Street, Dallas, Texas 75201, USA. Published online 30 June 2014; http://dx.doi.org/10.1130/G35740.1

Other GEOLOGY articles (see below) cover such topics as 1. The beneficial effect of Saharan dust in the Bahamas; 2. Geochemical fingerprinting of 25 trans-Atlantic dust events from North Africa to Barbados; 3. Study of shark teeth from Banks Island, NWT, Canada, shows that in the Eocene Arctic Ocean, sharks were abundant even in lower-saline conditions; and 4. Sample analysis from the largest volcanic eruption of the 20th century: the 1912 Novarupta eruption, Alaska.

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The fertilization of the Bahamas by Saharan dust: A trigger for carbonate precipitation? P.K. Swart et al., Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149, USA. Published online 30 June 2014; http://dx.doi.org/10.1130/G35744.1.

It has long been known the dust from Africa causes hazy sunsets and dirty cars during certain periods of the year in the south-eastern United States. However, this same dust has a beneficial effect on the shallow waters of the Bahamas. Here it provides iron to photosynthesizing bacteria which in turn fix N2 from the atmosphere and provides nitrogen to all of the biological communities. Evidence for this is present in the ratio of 15N/14N of the sedimentary organic material which is virtually indistinguishable from atmospheric values. The photosynthetic activity of the cyanobacteria in turn induces the precipitation of calcium carbonate in the shallow waters producing large amount of carbonate mud which is swept into deeper waters where it accumulates building and expanding the platform towards the west. It might be speculated that periodic increases in the supplies of dust through time have in turn been responsible for increased deposition of carbonate sediments and enlargement of the Bahamas.

Geochemical fingerprinting of trans-Atlantic African dust based on radiogenic Sr-Nd-Hf isotopes and rare earth element anomalies Ali Pourmand et al., Neptune Isotope Laboratory, Dept. of Marine Geosciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA. Published online 30 June 2014; http://dx/doi.org/10.1130/G35624.1

Mineral dust is an important component of Earth's climate system and biogeochemical cycles on a global scale. In order to understand the relationship between climate processes in the source areas and the properties of aerosols at distant receptor sites, we must be able to identify the source provenance of dust. We studied the geochemical composition of 25 trans-Atlantic dust events from North Africa to the Caribbean island of Barbados between 2003 and 2011 to investigate the possibility of tracking aerosols to their source origin. We find systematic differences between the geochemical composition of individual dust events, and the first evidence for seasonal shifts in dust source activity and transport between the months of May-September compared with November-April over the decade of study. These results indicate that coherent geochemical source signatures of trans-Atlantic dust can be preserved even after transport across thousands of kilometers. In the absence of geochemical data in aerosols over potential source areas in North Africa, however, it is difficult to make a direct comparison between aerosols over Barbados and the source origins. Nevertheless, our data suggests that many aerosol samples from Barbados are lined to sources in Mali and sub-Saharan regions.

Evidence from shark teeth for a brackish Arctic Ocean in the Eocene greenhouse Sora L. Kim et al., Current Address: Dept. of Geophysical Sciences, University of Chicago , 5734 S. Ellis Avenue, Chicago, Illinois 60637, USA (also Dept. of Geology & Geophysics, University of Wyoming, 1000 E. University Drive #3006, Laramie, Wyoming 82071, USA). Published online 30 June 2014; http://dx.doi.org/10.1130/G35675.1.

Temperatures are rising in the Arctic at twice the global rate, affecting the sensitive hydrological cycle with increased freshwater inputs to the ocean. A deep-time analogue often used to understand and predict global warming impacts is the early to middle Eocene greenhouse (about 38 to 53 million years ago). Although the terrestrial Arctic during this interval is well documented, marine records are rare and largely based on one central Arctic Ocean site (Lomonosov Ridge). Kim et al. estimate a mean paleosalinity of ~13 PSU for coastal waters of the western Arctic Ocean by analyzing the oxygen isotope composition of Eocene shark teeth from Banks Island, NWT, Canada, and incorporated these values into a salinity model. This paleo-salinity is substantially lower than others for the Eocene central Arctic Ocean (21 to 25 PSU) and today's Arctic Ocean (32 to 35 PSU), but similar to Louisiana's Lake Pontchartrain. This is the first salinity estimate for the western Arctic Ocean during Eocene time and, when considered with prior results from the central Arctic Ocean, suggests a reduced surface salinity but larger salinity gradient (~10 PSU) across the Arctic Ocean during the Eocene greenhouse. From an ecologic perspective, while today's lamniform sharks (e.g., sand tigers, thresher, and great white sharks) are largely intolerant of low salinity, Eocene species were abundant in the brackish Arctic Ocean, suggesting their past environmental tolerances were much greater than today.

Explosive to effusive transition during the largest volcanic eruption of the 20th century (Novarupta 1912, Alaska) Chinh T. Nguyen et al., Dept. of Earth Science, Rice University, Houston, Texas 77005, USA. Published online 30 June 2014; http://dx.doi.org/10.1130/G35593.1

Silicic volcanic eruptions commonly show abrupt shifts between violently explosive episodes and a gently effusive lava dome. It has been a subject of debate whether the gas loss through inter-connected permeable networks (outgassing) controls these transitions. Sample analysis from the A.D. 1912 Novarupta eruption, Alaska, shows that the degree of vesicle inter-connectivity (measured as the ratio of connected to total vesicle volume fraction) decreases with phenocryst content and increases with eruption intensity. Permeabilities of explosive samples show a weak dependence on vesicle volume fraction. Dome samples are not significantly different in permeability, but are of lower vesicle volume fraction. Quantitative analysis indicates that outgassing alone was insufficient to affect the transition to effusive activity. Rather, the change from explosive to effusive activity was probably a consequence of high versus low magma ascent rates.

Ammonite extinction and nautilid survival at the end of the Cretaceous Neil H. Landman et al., Division of Paleontology (Invertebrates), American Museum of Natural History, New York, New York 10024, USA. Published online 30 June 2014; http://dx.doi.org/10.1130/G35776.1

One of the puzzles about the end-Cretaceous extinctions is why some organisms disappeared and others survived. A notable example is the differential extinction of ammonites and survival of nautilids, the two groups of co-occurring, externally shelled cephalopods at the end of the Cretaceous. To investigate the role of geographic distribution in explaining this outcome, we compiled a database of all the occurrences of ammonites and the nautilid genus Eutrephoceras in the last 0.5 m.y. of the Maastrichtian. We also included recently published data on ammonite genera that appear to have briefly survived into the Paleocene. Using two metrics to evaluate the geographic range of each genus (first, a convex hull encompassing all of the occurrences of each genus, and second, the maximum distance between occurrences for each genus), we documented that most ammonite genera at the end of the Maastrichtian were restricted in their geographic distribution, possibly making them more vulnerable to extinction. The geographic distribution of those genera that may have briefly survived into the Paleocene is significantly greater than that of non-surviving genera, implying that more broadly distributed genera were more resistant to extinction. This pattern is further emphasized by the broad distribution of Eutrephoceras, which matches that of the most widely distributed ammonites at the end of the Maastrichtian. However, even the most widely distributed ammonites eventually succumbed to extinction, whereas Eutrephoceras survived. Evidently, a broad geographic distribution may have initially protected some ammonites against extinction, but it did not guarantee their survival.

Persistent intermediate water warming during cold stadials in the southeastern Nordic seas during the past 65 k.y. Mohamed M. Ezat et al., Centre for Arctic Gas Hydrate, Environment and Climate (CAGE), Uit, The Arctic University of Norway, NO-9037 Tromsø, Norway, and Dept. of Geology, Faculty of Science, Beni-Suef University, 62111 Beni-Suef, Egypt. Published online 30 June 2014; http://dx.doi.org/10.1130/G35579.1.

Greenland ice core records reveal millennial-scale climate variability during the last glacial (~100,000 to 10,000 years before present), known as Dansgaard-Oeschger (DO) events. A typical DO cycle (~1500 years) is characterized by an abrupt atmospheric warming of 8 to 16 degrees C from stadial (cold) to interstadial (warm) conditions followed by a gradual cooling and eventually a sudden cooling back to stadial conditions. In the modern Nordic seas, conversion of inflowing warm Atlantic surface water to deep cold water ( END