Marine record of late quaternary glacial-interglacial fluctuations in the Ross Sea and evidence for rapid, episodic sea level change due to marine ice sheet collapse

Some of the questions to be addressed by SeaRISE include: (1) what was the configuration of the West Antarctic ice sheet during the last glacial maximum; (2) What is its configuration during a glacial minimum; and (3) has it, or any marine ice sheet, undergone episodic rapid mass wasting. These questions are addressed in terms of what is known about the history of the marine ice sheet, specifically in Ross Sea, and what further studies are required to resolve these problems. A second question concerns the extent to which disintegration of marine ice sheets may result in rises in sea level that are episodic in nature and extremely rapid, as suggested by several glaciologists. Evidence that rapid, episodic sea level changes have occurred during the Holocene is also reviewed

The Kufrah paleodrainage system in Libya: A past connection to the Mediterranean Sea?

International audiencePaillou et al. (2009) mapped a 900 km-long paleodrainage system in eastern Libya, the Kufrah River, that could have linked the southern Kufrah Basin to the Mediterranean coast through the Sirt Basin, possibly as long ago as the Middle Miocene. We study here the potential connection between the terminal part of the Kufrah River and the Mediterranean Sea through the Wadi Sahabi paleochannel, which may have constituted the northern extension of the lower Kufrah River paleodrainage system. New analysis of SRTM-derived topography combined with Synthetic Aperture Radar images from the Japanese PALSAR orbital sensor allowed the mapping of seven main paleochannels located west of the Kufrah River, each of which is likely to have formed a tributary that supplied water and sediment to the main paleodrainage system. The northernmost four paleochannels probably originated from the Al Haruj relief, a Pliocene alkaline basaltic intracontinental volcanic field, and potentially connected to the Wadi Sahabi paleochannel. The remaining three paleochannels are in the more southerly location of the Sarir Calanscio, North-East of the Tibesti mountains, and barely present a topographic signature in SRTM data. They end in the dunes of the Calanscio Sand Sea, forming alluvial fans. The most southern paleochannel, known as Wadi Behar Belama, was previously mapped by Pachur (1996) using LANDSAT-TM images, and was interpreted by Osborne et al. (2008) as representing part of an uninterrupted sediment pathway from the Tibesti mountains to the Mediterranean Sea. Processing of SRTM topographic data revealed local depressions which allow to connect the seven paleochannels and possibly the terminal alluvial fan of the Kufrah River to the Wadi Sahabi paleochannel, through a 400 km-long, south-north oriented, paleocorridor. These new findings support our previous hypothesis that proposed a connection between the lower Kufrah River in the region of the Sarir Dalmah and the Wadi Sahabi paleochannel, which connected to the Mediterranean Sea. Including the newly mapped paleochannels, the Kufrah River paleowatershed, at its maximum extent, would have covered more than 400,000 km2, representing close to a quarter of the surface area of Libya

Paleodrainage Insights Into the Fluvial and Glacial History of the Western Chukchi Margin, Arctic Alaska

Chirp subbottom data collected from the Chukchi shelf, offshore of northwest Alaska, revealed extensive paleodrainage networks that incised the margin during sea level lowstands. These features are cut into folded Cretaceous bedrock strata and represent multiple sea level cycles. Several large incised valleys, 10s of km wide and up to 54 m deep, as well as numerous smaller, individual channels were identified. Sources of fluvial input include several, smaller rivers on the northwest Alaskan coast, such as the Kokolik, Kuk, Kukpowruk, and the Utukok Rivers. Correlation of sediment infill patterns provided insight to paleochannels and paleovalleys as well as outlined potential paleodrainage networks. Sediment infill and erosion patterns were examined to assess whether some of the valleys were formed by non-fluvial (i.e. glacial) processes. Results indicate the presence of four paleodrainage networks across the eastern Chukchi shelf based on shape, size, and infill of the paleovalleys: The Southern Valley, Northern Valley, Borderlands Valley, and Barrow Valley. All of the paleodrainage valleys are oriented perpendicular to the western Alaska coast except for Barrow Valley, which follows the northwest Alaskan coastline. All of the paleovalleys contain fluvial infill although some locations, such as the Southern and Barrow Valleys, appear to contain marine infill as well. Barrow Valley also appears to have negative erosional relief of up to 4.5 m on the transgressive surface, possibly from an ice shelf or other glacial features. The presence of ice may have also obstructed Barrow Canyon, which would explain why Barrow Valley appears to bypasses the large, shelf-indenting submarine canyon that presumably should have captured much of the drainage from northern Alaska

Palynology of acid-saline lakes of western Australiabiostratigraphy and paleoenvironmental reconstruction

Lakes are excellent repositories of fossils and sedimentary features that provide clues to past climatic and geologic events. Sediments from four cores drilled in Lake Aerodrome (LA1-09, LA2-09) and Lake Brown (LB1-09, LB2-09), two of the hundreds of ephemeral lakes in southern Western Australia, were analyzed for their palynological contents to understand the geologic and climatic evolution of the depositional basin. Palynofacies assemblages defined by statistical analyses of dispersed organic matter suggested differences in the depositional conditions and probable correlations between Lake Aerodrome cores. Detailed identifications and quantification of organic-walled microfossils yielded two palynomorph assemblages that reflect a climatic turnover: (1) a wet hinterland (rainforest), freshwater and swampy assemblage found in situ in the basal lignites of LA2-09 (44.58-59.63 meters); and (2) a sclerophyllic and halophilic assemblage in all younger sediments. The first and last appearances of key palynomorphs in the lignites, which contain Aglaoreidia cyclops (documented for the first time in Australia and the Southern Hemisphere), correlate the assemblage with the Middle Nothofagidites asperus Zone of the Werillup Formation. While Myrtaceidites lipsis constrains the age of the sediments from 23.38 meters depth to the top of LA2-09 as Pliocene to Recent, the sequence between 23.38 and 44.58 meters has long-ranging palynomorphs and is likely not older than the Miocene. Above the lignites, the salt-tolerant alga Dunaliella is used as a proxy for saline conditions. Reworking has been established in post-Eocene sediments because well-preserved Eocene freshwater and marine palynomorphs co-occur with sclerophyllic and halophilic palynomorphs --Abstract, page iii

Geological Framework of the Continental Shelf of South Carolina Winyah Bay: Paleodrainage, Transgressions and Essential Fish Habitat

A regional geophysical survey of the inner continental shelf off central South Carolina was completed on a cooperative cruise between NOAA and Coastal Carolina University in July 2015. An integrated mapping suite comprised of subbottom echosounder, side scan, multibeam and split beam sonars was used to define the regional geologic framework, including paleodrainage patterns across the shelf and to identify potential fish habitat locations that will provide additional inputs to a thematic habitat mapping routine developed by NOAA. Results from the thematic mapper characterization suggest that large-scale framework elements such as paleochannel networks may play a role in determining benthic habitat distribution. A large paleo-fluvial valley associated with the ancestral Santee and Pee Dee River system has been observed in the subbottom data and correlates with broad topographic lows identified by the thematic habitat mapping routine. The collective dataset provides opportunity to locally evaluate and provide a basis to refine the regional habitat mapping routine. Overall, the thematic mapper generally picked inshore complex features but did not pick up smaller detailed areas. This is where sub bottom data can be used to refine the habitat modeling scheme. Additional geophysical surveys are needed to connect the onshore and offshore framework and to further refine channel fill geometries, bottom habitat and Holocene reworking of the shelf system

Detrital-zircon records of Cenomanian, Paleocene, and Oligocene Gulf of Mexico drainage integration and sediment routing: Implications for scales of basin-floor fans

This paper uses detrital zircon (DZ) provenance and geochronological data to reconstruct paleodrainage areas and lengths for sediment-routing systems that fed the Cenomanian Tuscaloosa-Woodbine, Paleocene Wilcox, and Oligocene Vicksburg-Frio clastic wedges of the northern Gulf of Mexico (GoM) margin. During the Cenomanian, an ancestral Tennessee-Alabama River system with a distinctive Appalachian DZ signature was the largest system contributing water and sediment to the GoM, with a series of smaller systems draining the Ouachita Mountains and discharging sediment to the western GoM. By early Paleocene Wilcox deposition, drainage of the southern half of North America had reorganized such that GoM contributing areas stretched from the Western Cordillera to the Appalachians, and sediment was delivered to a primary depocenter in the northwestern GoM, the Rockdale depocenter fed by a paleo–Brazos-Colorado River system, as well as to the paleo–Mississippi River in southern Louisiana. By the Oligocene, the western drainage divide for the GoM had migrated east to the Laramide Rockies, with much of the Rockies now draining through the paleo–Red River and paleo–Arkansas River systems to join the paleo–Mississippi River in the southern Mississippi embayment. The paleo–Tennessee River had diverted to the north toward its present-day junction with the Ohio River by this time, thus becoming a tributary to the paleo-Mississippi within the northern Mississippi embayment. Hence, the paleo-Mississippi was the largest Oligocene system of the northern GoM margin. Drainage basin organization has had a profound impact on sediment delivery to the northern GoM margin. We use paleodrainage reconstructions to predict scales of associated basin-floor fans and test our predictions against measurements made from an extensive GoM database. We predict large fan systems for the Cenomanian paleo–Tennessee-Alabama, and especially for the two major depocenters of the early Paleocene paleo–Brazos-Colorado and late Paleocene–earliest Eocene paleo-Mississippi systems, and for the Oligocene paleo-Mississippi. With the notable exception of the Oligocene, measured fans reside within the range of our predictions, indicating that this approach can be exported to other basins that are less data rich

Phylogeographic inference of Sumatran ranids bearing gastromyzophorous tadpoles with regard to the Pleistocene drainage systems of Sundaland.

Rivers are known to act as biogeographic barriers in several strictly terrestrial taxa, while possibly serving as conduits of dispersal for freshwater-tolerant or -dependent species. However, the influence of river systems on genetic diversity depends on taxa-specific life history traits as well as other geographic factors. In amphibians, several studies have demonstrated that river systems have only minor influence on their divergence. Here, we assess the role of the paleodrainage systems of the Sunda region (with a focus on the island of Sumatra) in shaping the evolutionary history of two genera of frogs (Sumaterana and Wijayarana) whose tadpoles are highly dependent on cascading stream habitats. Our phylogenetic results show no clear association between the genetic diversification patterns of both anurans genera and the existence of paleodrainage systems. Time-calibrated phylogenies and biogeographical models suggest that these frogs colonized Sumatra and diversified on the island before the occurrence of the Pleistocene drainage systems. Both genera demonstrate phylogenetic structuring along a north-south geographic axis, the temporal dynamics of which coincide with the geological chronology of proto Sumatran and -Javan volcanic islands. Our results also highlight the chronic underestimation of Sumatran biodiversity and call for more intense sampling efforts on the island