Coordinated taphonomic, geochronologic, and geochemical studies of bivalve death assemblages and their sedimentary environments of San Blas, Caribbean Panama, permit us to identify the major factors controlling skeletal degradation in mixed carbonate-siliciclastic tropical shelf sediments. Ten sites were studied along environmental gradients including water nutrients, grain size, and sediment c...

The Ethiopian Rift System consists of basins that are in different stages of evolution. Some of the rift-related basins in southwestern Ethiopia are half-grabens that have not evolved to symmetrical rifts since the initiation of rifting here in the middle Miocene. These basins contain fossiliferous Pliocene–Pleistocene volcaniclastic sediments and volcanic rocks and have been occupied by early ...

Reconstructing paleoenvironmental change from glacial geologic evidence in the Himalayas has been difficult because of the lack of organic material for radiocarbon dating and the problems of correctly identifying the origin of highly dissected landforms. Studies of the contemporary glacial depositional environments, and ancient landforms and sediments in the Hunza valley (Karakoram Mountains), ...

Sequential extraction integrated with isotope analysis was carried out on a sediment core from Liaodong Bay, northeast China, for characterizing Pb in various extraction phases and its possible sources. Results show that in all extracted fractions Pb concentrations increased abruptly in the top part of the sediments that deposited after 1980, but remained lower and rather constant before 1980. ...

Examining the patterns of archaeal diversity in little-explored organic-lean marine subsurface sediments presents an opportunity to study the association of phylogenetic affiliation and habitat preference in uncultured marine Archaea. Here we have compiled and re-analyzed published archaeal 16S rRNA clone library datasets across a spectrum of sediment trophic states characterized by a wide rang...

prior to being transported into the lake system. The combinaThe accuracy of Arctic lake chronologies has been assessed by tion of these factors commonly leads to radiocarbon ages measuring the C activities of modern carbon sources and that are apparently too old. Discrete macrofossils are rarely applying these isotopic mass balances to dating fossil lake materifound in sufficient quantities for...

The atmospheres of solid planets exert a fundamental control on their surfaces. Interactions between atmospheric and geologic processes influence the morphology and composition of surfaces, and over the course of geologic time determine the historical evolution of the planet’s surface environments including climate. In the case of Earth, the origin of life likely occurred within surface environ...

O decades, there has been increased salinization of fresh water in many regions of the world. Salinization was previously thought to be an environmental problem restricted primarily to arid regions. However, it is now recognized as a global environmental concern impacting humid regions due to human inputs from road deicers, sewage inputs, and water softeners (Figure 1). In both arid and humid r...

The hydrogen isotopic compositions of sedimentary hydrocarbon molecules are now being used to address a range of scientific questions, from paleoclimate to environmental reconstruction to understanding of petroleum systems. Here I review the environmental, biological, and physical/chemical factors that influence the H isotopic compositions of sedimentary hydrocarbons. A hierarchy of four main c...

Nuclear magnetic resonance (NMR) relaxation-time measurements can provide critical information about the physiochemical properties of water-saturated media and are used often to characterize geologic materials. In unconsolidated sediments, the link between measured relaxation times and pore-scale properties can be complicated when diffusing water molecules couple the relaxation response of hete...