Geological Sciences

Two different and physically separated chemosynthetic communities of bacteria are responsible for the formation of the Beeri native sulfur deposit hosted in a Late Quaternary sandstone on the southern coastal plain of Israel. The enriched concentrations are distributed over an area of about 1 km 2, within a zone 2–3 m thick at 1–13 m below surface.

The Afiq submarine canyon was one of a series of canyons initially incised in a drowned shelf edge and slope of the eastern Mediterranean margins in early Oligocene times (P19 zone). During most of the Early Miocene submarine erosion or non-deposition prevailed. This was followed by deposition of pelagic marls and debris flows in early Middle Miocene (N8) times.

An updated compendium of δ13C data offer compelling evidence that δ13C positive excursions of unsurpassed magnitude in the recorded Earth history (> 8‰, and up to 18‰ PDB) occurred in the early Proterozoic (the Lomagundi event). Questions whether or not these unprecedented positive δ13C shifts were contemporaneous in various basins and represent local or global events remain unresolved.

Abstract Coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of Huon Peninsula, New Guinea. Seven coral reef units, I–VII from the coast landwards spaced at about 20-kyr interval, provide a rather complete record of sea levels, oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle.

Whereas the physical links between solar irradiance and terrestrial climate are still poorly understood, an increasing number of proxy climate records provide circumstantial evidence suggesting solar inputs as a dominant controlling factor of global climate changes. Here we report the results of an investigation of stalagmites from a mid-ocean island in the South Pacific located at the epicenter of oceanic ENSO that contains a detailed and continuous millennial record of rainfall and ENSO variability.

Abstract The driving forces of global climate change are poorly understood in part due to the lack of high-resolution terrestrial climatic records. The study of carbonate cave formations (stalagmites) often provides uninterrupted annual to millennial records of past terrestrial climate conditions. It is well documented that the growth and isotopic composition of stalagmites are primarily controlled by climatic factors including air temperature, soil microbial activity, and rainfall.

Abstract Recent studies have suggested that ENSO may have been switched off prior to 5 Ka raising the possibility that El-Niño waxes and wanes over the millennia. An understanding of ENSO past irregularity may give important clues to our climate future in a greenhouse world and therefore more proxy climate records are needed to test the suggestions of ENSO switch on/off events.

On the northern Gulf of Mexico slope, foraminiferal communities in surface sediments associated with methane-hydrate dissociation exhibit a reduced species diversity (compared to the diversity in isobathyal, non-seep sediments from the same general area) and a conspicuous presence of microaerophilic species. These methane-tolerant species of Foraminifera, unlike some macroinvertebrates, are not endemic to cold seeps, but represent a part of the background community.

Description/Abstract Documentation of O-18 variations imprinted on Late Quaternary marine carbonates leads to the inference that temporal and spatial redistribution of O-18/O-16 isotopes occurred episodically between the ocean and the expanded polar ice caps. If O-18 data of deep sea benthic foraminifera are simple recorders of ocean chemistry changes, then the ice volumes they reflect must agree with the paleosea levels from raised corals reefs.

Description/Abstract Barite chimneys and crusts recovered by submersible dives from hydrocarbon seeps at water depths of 510-670 m in the Gulf of Mexico offshore Louisiana are enriched in {sup 226} Ra and {sup 228} Ra at levels of 780 pCi/g and 470 pCi/g, respectively. These values are comparable to those found in barite scale associated with hydrocarbon production in the Gulf Coast.

Abstract Alkalinity, dissolved inorganic carbon (DIC), and 13 C profiles from seep sites on the northwestern Gulf of Mexico upper slope show anomalously negative 13 C values of up to–4.5 PDB, increased levels of DIC of up to 2.45 mmole/liter, and slight alkalinity rises of up to 2.54 meq/liter, relative to water column profiles from a seep-free site (0.63, 2.04 mmole/liter, and 2.39 meq/liter).

Microbial mats were collected from a variety of sites near hydrocarbon vents along the slope in the northern Gulf of Mexico and, for comparison, from Warm Mineral Springs, Florida, USA. A predominant microorganism in each of the mats was the giant bacterium, Beggiatoa. Diameters of the bacterial filaments ranged from about 6 µm to approximately 200 µm. The latter organisms are the largest prokaryotic organisms yet found.

A storm layer identified in Lake Shelby, AL, a freshwater lake positioned only~ 250 m from the Gulf shoreline, was deposited by a powerful hurricane in 1717 AD that changed the culture of the South. Known to historians as “Pénicaut's Storm,” this catastrophic hurricane disaster severely damaged the French harbor and capital of French Louisiana at Mobile, AL. The extensive damage resulted in the movement of the French capital first to Pascagoula, MS and subsequently to New Orleans, LA.

ABSTRACT Niue Island, a former atoll in the South Pacific, contains unusually well-resolved successions of dolomites recording repeated episodes of Late Cenozoic dolomitization. The massive Upper Dolomite unit consists of shoaling-upward depositional cycles of Pliocene age which have been thoroughly replaced by corresponding repetitive successions of crystalline mimetic (CM), transitional (CMS), and microsucrosic (MS) dolomite textures.

Stable carbon isotope values of organic carbon have proven useful in identification of the salinity regime of marsh deposits in the Mississippi Delta plain. Using a mixing model and empirical measurements of the of marsh sediments, we show that carbon isotope analysis could be a useful technique on other coastlines.

ABSTRACT Research submersibles are being used in a study of massive carbonate buildups on the Louisiana continental slope. Geohazard survey data (high resolution seismic profiles and side-scan sonographs) as well as submersible observations confirm the widespread occurrence of complex sea floor topography associated with areas overlying and on the flanks of salt diapirs that have penetrated to near the modern sea floor.

Substrates associated with active hydrocarbon vents in bathyal Gulf of Mexico support numerous foraminiferal species, with a few of them showing unusually high relative abundances. In the 584-to 695-m-depth range, Bolivina ordinaria, Gavelinopsis translucens, andCassidulina neocarinata strongly dominate the vent community, whereasBolivina subaenariensis andUvigerina laevis play this role around a vent at 216 m water depth.

Abstract. Two kinds of records preserve the imprints of microbial processes in submarine seep environments. One record tracks transient changes in pore fluid chemistry and is based on the fact that microbial activities leave indelible marks on the pore fluids, which serve as the transport media of microbial metabolic products.