Marine Geology

Holocene mass-wasting events in Lago Fagnano, Tierra del Fuego (54°S): Implications for paleoseismicity of the Magallanes-Fagnano transform fault

by Nicolas Waldmann

Basin Research, 23, 2, 171-190, 2011.

High-resolution seismic imaging and coring in Lago Fagnano, located along a plate boundary in Tierra del Fuego, have... more High-resolution seismic imaging and coring in Lago Fagnano, located along a plate boundary in Tierra del Fuego, have revealed a chronologic catalog of Holocene mass-wasting events. These structures are interpreted as sediment mobilizations resulting from gravity spreading induced by loading of the slope-adjacent lake floor during mass flow deposition. More than 22 mass flow deposits have been identified combining results from an 800 km-long dense grid of seismic profiles with sediment cores. Successions of up to 6 m thick mass flow deposits pond the basin floor spreading eastward and westward following the main axis of the eastern sub-basin of Lago Fagnano. An age model on the basis of information from previous studies and from new AMS-14C ages allowed establishing a well-constrained chronologic mass-wasting event catalogue covering the last ~15000 years. Simultaneously-triggered basin-wide lateral slope failure and the formation of multiple debris flow and megaturbidite deposits are interpreted as the fingerprint of paleo-seismic activity along the Magallanes-Fagnano transform fault that runs along the entire lake basin. The slope failures and megaturbidites are interpreted as recording large earthquakes occurring along the transform fault since the early Holocene. The results from this study provide new data about the frequency and possible magnitude of Holocene earthquakes in Tierra del Fuego, which can be applied in the context of seismic hazard assessment in southernmost Patagonia.

The marine geology of Port Phillip, Victoria

by Stephen Gallagher

Controls on Seaspray Group sonic velocities in the Gippsland Basin a multidisciplinary approach to the canyon "seismic velocity problem

by Stephen Gallagher

GEOCHEMICAL AND PETROGRAPHICAL ANALYSES FOR SELECTING QUATERNARY MARINE SHELLS FOR RADIOMETRIC DATING AND PALEOCLIMATE RECONSTRUCTIONS: EXAMPLES FROM PATAGONIA

by Ilaria Consoloni

Ilaria Consoloni, Giovanni Zanchetta, Marina L. Aguirre, Ilaria Baneschi, Monica Bini, Gabriella M. Boretto, Luigi Dallai, Massimo D’Orazio, Anthony E. Fallick, Massimo Guidi, John C. Hellstrom, Ilaria Isola, Enrique Fucks, Francesco Mazzarini, Marta Pappalardo & Adriano Ribolini. Il Quaternario 24, 208-210.

ABSTRACT: Consoloni I. et al., Geochemical and petrographical analyses for selecting Quaternary marine shells for more ABSTRACT: Consoloni I. et al., Geochemical and petrographical analyses for selecting Quaternary marine shells for
radiometric dating and paleoclimate reconstructions: examples from Patagonia. (IT ISSN 0394-3356, 2011)
The selection of suitable samples is a fundamental target in order to obtain reliable results in the field of radiometric
dating and paleoclimate. Marine molluscs are particularly interesting in this respect in what different radiometric
methods (e.g. U/Th, ESR) can be applied coupled with chemical analyses to reconstruct past environment. For this kind
of material is imperative that the samples have not undergone any alteration. We present, as example, the study of
marine molluscs from Quaternary beach ridges from the Atlantic Patagonian coast. Multiproxy analyses show that the
degree of weathering is quite variable but not enough for undermining the paleoclimatic values of the stable isotopes
content and of some trace element, but enough severe to make problematic the application of U/Th dating methods.
However, the careful petrographic observation and trace element analyses can support the selection of suitable
samples for U/Th dating.

Active gas migration systems offshore northern Israel, evidence from seafloor and subsurface data

by Nicolas Waldmann

Continental Shelf Research (in press)

An active gas migration system across the eastern Mediterranean continental shelf, offshore northern Israel, is... more An active gas migration system across the eastern Mediterranean continental shelf, offshore northern Israel, is described for the first time. Seven vintages of industrial multi-channel seismic reflection and high-resolution single-channel data are integrated with data from a deep borehole, bathymetry and backscatter maps. Combined interpretation, aided by seismic attribute analysis, exhibits a variety of seismic gas signatures across the subsurface and seabed: acoustic blanking, bright spots, phase reversals, gas chimneys, reflector smearing, pockmarks and presumed gas release into the water column. Sub-seafloor gas stems from three main sources: (1) Mid-Pleistocene and (2) Last Glacial Maximum unconformities and (3) a series of incised channels in-between which are also related to glacial maxima. Close to the seafloor, gas accumulates across an area of 72 km2 at depths ranging from 37-112 m below sea-level, while ~720 pockmarks pierce the seafloor mainly at the gas front periphery. Active emission from one seep at the seafloor was recorded repeatedly over three years. We hypothesize that the well developed active gas system shown here for the first time is not unique to the continental shelf off northern Israel. Conversely, it represents the usually underestimated marine methane contribution from mid-latitude continental shelves into the marine environment and maybe into the atmosphere. This study suggests that global warming and sea level rise induces a negative, restraining feedback for gas emission across mid-latitude continental margins and thus being inverse to high latitudes, where this feedback is most likely positive due to the stronger impact of bottom water warming.

Stevenson et al., 2012 Madeira Channels

by Christopher Stevenson

Wynn et al., 2012 (SEPM99) gradient effects on flows

by Christopher Stevenson

The Moroccan Turbidite System is unique in that individual gravity-flow deposits can be correlated across distances of... more The Moroccan Turbidite System is unique in that individual gravity-flow deposits can be correlated across distances of several hundred kilometers, both within and between depositional basins. An extensive dataset of shallow sediment cores is analyzed here, in order to investigate the influence of gradient changes on individual siliciclastic gravity flows passing through this system in the last 160,000 years. The largest flows (deposit volumes > 100 km3) are capable of travelling for more than 1000 km across slopes of less than 0.1°. The deposits
of these flows display significant lateral heterogeneity as a consequence of changes in seafloor gradient. Increases in gradient can lead to sediment bypass and/or erosion, and unconfined flows may become channelized. Decreases in gradient can lead to significant changes in sand–mud ratio and the deposition of thick mud caps, while small-volume flow deposits may pinch out completely. One of the largest flows shows evidence for multiple transformations as it crossed the Agadir Basin, with the resulting deposits switching laterally from (1) a gravel lag and cut-and-fill scours (representing bypass and erosion across a slope of 0.05°), to (2) a thick linked turbidite–debrite bed containing a muddy sand debrite (in response to a decrease in slope to < 0.01°), to (3) a normally graded turbidite (following a subtle increase in slope to 0.02°). Although the changes in slope angle described here appear remarkably subtle, the relative changes in slope are significant, and clearly exert a major control on flow behavior. Such variations in slope would not be detectable in outcrop or subsurface sequences,
yet will generate significant complexity in deep-water reservoirs.

Wynn et al., 2009 largest turbidite on earth

by Christopher Stevenson

Sumner et al., in press facies of basin plain turbidites.x

by Christopher Stevenson

In press with Sedimentology

Understanding of submarine sediment density flows is based heavily on their deposits, because such flows are... more Understanding of submarine sediment density flows is based heavily on their deposits, because such flows are notoriously difficult to monitor directly. However, it is rarely possible to trace the facies architecture of individual deposits over significant distances. Instead, bed-scale facies models that infer the architecture of ‘typical’ deposits encapsulate the understanding of depositional processes and flow evolution. In this study, the distribution of facies in 12 individual beds has been documented
along downstream transects over distances in excess of 100 km. These deposits were emplaced in relatively flat basin-plain settings in the Miocene Marnoso Arenacea Formation, north-east Italy and the late Quaternary Agadir Basin, offshore Morocco. Statistical analysis shows that the most common series of vertical facies transitions broadly resembles established facies models. However, mapping of individual beds
shows that they commonly deviate from generalized models in several important ways that include: (i) the abundance of parallel laminated sand, suggesting deposition of this facies from both high-density and low-density turbidity current; (ii) three distinctly different types of grain-size break, suggesting waxing flow, erosional hiatuses and bypass of silty sediment; (iii) the presence of mud-rich debrites demonstrating hybrid flow deposition; and (iv) dune-scale cross-lamination in finemedium
grained sandstones. Submarine sediment density flows in basin-plain settings flow over relatively simple topography. Yet, their deposits record complex flow events, involving transformation between different flow types, rather than the simple
waning surges often associated with the distal parts of turbidite systems.

Ferromanganese nodules and micro-hardgrounds associated with the Cadiz Contourite Channel (NE Atlantic): palaeoenvironmental records of fluid venting and bottom currents

by F. Javier González Sanz

González, F. J., Somoza, L., León, R., Medialdea, T., Torres, T., Ortiz, J. E., Lunar, R., Martínez-Frías, J., Merinero, R. 2012. Ferromanganese nodules and micro-hardgrounds associated with the Cadiz Contourite Channel (NE Atlantic): palaeoenvironmental records of fluid venting and bottom currents. Chemical Geology (doi:10.1016/j.chemgeo.2012.03.030)

Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf... more Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf of Cadiz (850–1000 m). This channel is part of a large contourite depositional system generated by the Mediterranean Outflow Water. Ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals. We present a complete characterisation of these deposits based on submarine photographs and geophysical, petrographic, mineralogical and geochemical data. The genesis and growth of ferromanganese deposits, strongly enriched in Fe vs. Mn (av. 39% vs. 6%) in this
contourite depositional system result from the combination of hydrogenetic and diagenetic processes. The interaction of the Mediterranean OutflowWater with the continental margin has led to the formation of Late Pleistocene–Holocene ferromanganese mineral deposits, in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events. The diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons (δ13CPDB=−20 to −37‰) and organic matter within the channel floor sediments, promoting the formation of Fe–Mn carbonate nodules. High 87Sr/86Sr isotopic values (up to 0.70993±0.00025) observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep-seated fluid venting across the fault systems in the diapirs below the Cadiz Contourite Channel. Erosive action of the Mediterranean Outflow Water undercurrent could have exhumed the Fe–Mn carbonate nodules, especially in the glacial periods, when the lower core of the undercurrent was more active in the study area. The growth rate determined by 230Thexcess/232Th was 113±11 mm/Ma, supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka. Ca-rich layers in the nodules could point to the interaction between the Mediterranean OutflowWater and the North Atlantic DeepWater during the Heinrich events. Siderite–rhodochrosite nodules exposed to the oxidising sea-bottom waters were replaced by Fe–Mn oxyhydroxides. Slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds, which show imprints of the Mediterranean Outflow Water with low 87Sr/86Sr isotopic values (down to 0.70693±0.00081). We propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents. We also compare and discuss the generation of ferromanganese deposits in the Cadiz Contourite Channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting.

Texas Coastal Hypoxia Linked to Brazos River Discharge as Revealed by Oxygen Isotopes

by Josiah Strauss

From corals to canyons: the Great Barrier Reef margin

by Alex Thomas

New discoveries of mud volcanoes on the Moroccan Atlantic continental margin (Gulf of Cádiz): morpho-structural characterization

by F. Javier González Sanz

León, R., Somoza, L., Medialdea, T., Vázquez, J. T., González, F. J., López-González, N., Casas, D., Mata, M. P., Fernández-Puga, M. C., Giménez-Moreno, C. J., Díaz-del-Río, V. 2012. New discoveries of mud volcanoes on the Moroccan Atlantic continental margin (Gulf of Cádiz): morpho-structural characterization. Geo-Marine Letters, doi: 10.1007/s00367-012-0275-1

During the MVSEIS-08 cruise of 2008, ten new mud volcanoes (MVs) were discovered on the offshore Moroccan continental... more During the MVSEIS-08 cruise of 2008, ten new mud volcanoes (MVs) were discovered on the offshore Moroccan continental margin (Gulf of Cádiz) at water depths between 750 and 1,600 m, using multibeam bathymetry, backscatter imagery, high-resolution seismic and gravity core data. Mud breccias were recovered in all cases, attesting to the nature of extrusion of these cones. The mud volcanoes are located in two fields: the MVSEIS, Moundforce, Pixie, Las Negras, Madrid, Guadix, Almanzor and El Cid MVs in the western Moroccan field, where mud volcanoes have long been suspected but to date not identified, and the Boabdil and Al Gacel MVs in the middle Moroccan field. Three main morphologies were observed: asymmetric, sub-circular and flat-topped cone-shaped types, this being the first report of asymmetric morphologies in the Gulf of Cádiz.
Based on morpho-structural analysis, the features are interpreted to result from (1) repeated constructive (expulsion of fluid mud mixtures) and destructive (gravity-induced collapse and submarine landsliding) episodes and (2) interaction with bottom currents.

Formation processes of methane-derived authigenic carbonates from the Gulf of Cadiz

by F. Javier González Sanz

Magalhães, V.H., Pinheiro, L.M., Ivanov, M.K., Kozlova, E., Blinova, V., Kolganova, J., Vasconcelos, C., McKenzie, J.A., Bernasconi, S.M., Kopf, A., Díaz-del-Río, V., González, F.J., Somoza, L. 2012. Formation processes of methane-derived authigenic carbonates from the Gulf of Cadiz. Sedimentary Geology 243-244, 155-168

The Gulf of Cadiz, NE Atlantic, represents an area of extensive formation of methane-derived authigenic carbonates... more The Gulf of Cadiz, NE Atlantic, represents an area of extensive formation of methane-derived authigenic carbonates (MDAC), indicative of fluid seepage. These MDAC, that reach extraordinary length and thickness, were geophysically mapped and sampled and the recovered carbonate-cemented material has δ13C values as low as −56.2‰ VPDB, indicating methane as the major carbon source. The MDAC form two main lithologic
groups, one mainly comprising dolomite and the second dominated by aragonite. The dolomite-dominated samples were found along fault-controlled diapiric ridges, on some mud volcanoes and mud diapirs, all on the pathway of the Mediterranean Outflow Water, and along fault scarps. Aragonite pavements were found associated with mud volcanoes and along fault scarps, but are otherwise not restricted to the pathways of
the Mediterranean Outflow Water. Based on the results from this study, we propose that the two lithologic groups reflect different geochemical formation environments associated with a formation model based on their morphology, mineralogy and geochemistry. The aragonite-dominated samples represent precipitation of authigenic carbonates at the sediment–seawater interface or close to it, in a high alkalinity environment resulting from anaerobic oxidation of methane-rich fluids venting into sulphate-bearing porewaters. In contrast, the dolomite-dominated samples result from cementation along fluid conduits inside the sedimentary column with a somewhat restricted seawater ventilation. The dolomite chimneys form in places presently
swept by the strong flow of the Mediterranean undercurrent so that the unconsolidated sediments are eroded and the chimneys are exposed at the seafloor. The widespread and large abundance of MDAC is a direct evidence of extensive methane seepage episodes in the Gulf of Cadiz. The coincidence of the different lithologic types in close spatial and temporal association indicates a persistence of seepage episodes in some
structures over large periods of time.

Pulsed subduction accretion and tectonic erosion reconstructed from the tephra record offshore Costa Rica

by Peter Clift

Long-term subduction erosion along the Middle America Trench offshore Guatemala

by Peter Clift

The first paper on the Noah's Flood in the Black Sea Basin

by Yavor Shopov

This is the first paper suggesting that Noah's (Bible) Flood happened in the Black Sea Basin 7500-7600 years ago. It was published and presented at Climatic Change: The Karst Record International Conference in Bergen on 1st August 1996

Speleothem growth rate variations represent mainly rainfall variations. Speleothem luminescence visualizes annual... more Speleothem growth rate variations represent mainly rainfall variations. Speleothem luminescence visualizes annual microbanding we used to derive proxy records of annual precipitations for the cave site. In case of Rats Nest cave, Alberta, Canada we obtained good correlation (correlation coefficient of 0.57) between annual precipitations (from Banff station 50 km north of the cave) and annual growth rate of the speleothem (Fig. 1). We used obtained regression coefficients to reconstruct annual precipitations for last 280 years at the cave site with estimated error of 80 mm/ year. Annual speleothem growth rate was not dependent on intensly of luminescence, on annual temperature and solar luminosity for the same time span (zero correlation).

By "tuning" of the time scale of a luminescent record with a geomagnetic dipole intensity record (Mazaud et al., 1991) we obtained a reconstruction of growth rates and precipitations in Bosnek karst region near Duhlata cave, Bulgaria for the last 50000 years (Fig.2). This record show a very prominent peak at 7000- 8000 years B.P., when annual growth rate was over 53 times higher than today. Considering that cave site is located in the place of the oldest civilizations (Mediterranean basin) this event can be related to the Bibles "Deluge". The age of the recorded event is about the age of "The Creation of the world". The duration of the recorded event is of several hundreds years, because of the low resolution of the record. In case that the real flood happened for a short time span it suggests enormous rainfall. Present day precipitation at the cave site is 685mm/yr. This speleothem was dated with 8 TAMS 14C dates.
By "tuning" of the time scale of a luminescent record with the calibration 14C record (Stuiver and Kra, 1986) we obtained a reconstruction of growth rates and precipitations for the last 6400 years with averaged time step of 41 years for Iowa, near Cold Water cave, US (fig.2). It suggests higher speleothem growth rate and higher precipitations between 6400- 2500 years B.P. at the cave site. This speleothem was dated with 7 AMS U/Th dates.

Structure-forming deformations on Knipovich ridge (physical modeling)

by Andrey Kokhan

Co-authored with A.L. Grokholsky, A.S. Abramova, E.P. Dubinin, and S.Yu. Sokolov

Experimental study of structure-forming deformations in ultra-slow spreading Arctic and Polar Atlantic ridges

by Andrey Kokhan

Сo-authored with E.P. Dubinin, A.L. Grokholsky

Increased contribution of terrigenous supply from Taiwan to the northern South China Sea since 3 Ma

by Peter Clift