Wednesday, April 26, 2017

Highlights: Continental Carbonate Conditions

Continental carbonates are distinct from their marine cousins, but like them, contain numerous proxies for the environment in which they formed. Yet, continental carbonates can be of two general types: those formed ambient temperature from calcium bicarbonate–enriched waters and those associated with hyperalkaline thermal springs, from fluids commonly depleted in dissolved inorganic carbon. Both are favored under distinct conditions, yet how closely they each reflect their environment is unclear. To better understand these complexities, Leleu and others examined travertine forming at DIC-depleted hyper-alkaline springs with pH up to 12. Their multi-disciplinary approach ranged from macroscopic to microscopic scale, analyzing travertine samples to assess the relationship between the petrologic features and fabrics and the geochemical and isotopic signatures. The results illustrate the potential of these deposits as proxies of past climatic record and atmospheric CO2 sequestration.

Travertines associated with hyperalkaline springs: evaluation as a proxy for paleoenvironmental conditions and sequestration of atmospheric CO2 by Thomas Leleu, Valérie Chavagnac, Adélie Delacour, Catherine Noiriel, Georges Ceuleneer, Markus Aretz, Céline Rommevaux, and Sandra Ventalon

Friday, April 21, 2017

Highlights: Appalachian Sand Sources

In providing clues of since-leveled landscapes, the stratigraphic record records tectonic evolution. In this study, Uddin et al. integrate petrographic, detrital-geochronologic, and mineral-chemistry analyses of detrital minerals and lithic clasts of the Pennsylvanian Pottsville Formation, part of a clastic wedge in the foreland basin in Alabama and Mississippi.  This manuscript illustrates that this part of the foreland basins received detritus mostly from the Appalachians, rather than the Oucahitas, and draws an analogy to the modern Himalayan-Bengal system. The mineralogy and dates suggest an initial Blue Ridge Piedmont source, followed by a migrating steep erosional front that buried previously eroded terrains; alternatively, some of the variations may result from along-strike transport of detrital material in the foreland basin.

Tuesday, April 18, 2017

Highlights: Quality Deep-Water Sand

Porten and others show how reservoir quality of deep-marine sandstones is controlled by sediment composition, transport, and depositional histories in a range of sediment-gravity-flow deposits in a Maastrichtian submarine-fan in the Vøring Basin (Norwegian Sea, Norwegian continental shelf). In these strata, porosity increases with decreasing clay content, and permeability increases with increasing grain size, decreasing clay volume, and increasing porosity. Porosities of the different depositional bed types are similar, whereas permeabilities are distinct, with high-density turbidites having permeabilities approximately two orders of magnitude higher than clay-rich hybrid event beds. The results of this study emphasize the importance of the transport and depositional processes responsible for producing different bed types with characteristic composition and texture. This step is essential in reservoir evaluation, necessary for predicting most likely porosity and permeability evolution with sediment burial and for understanding reservoir quality distribution in potential deep-marine siliciclastic hydrocarbon reservoir targets.

Thursday, April 13, 2017

Highlights: Ode to Sand o Green

To expl're the genesis of the Gosp'rt Sand, an Eocene greensand deposit from the U.S. Gulf coastal plain, Pietsch and co-auth’rs integrateth sedimentology, the min'ralogy, taxonomic and ecological analysis, and taphonomic hist'ry o’ the mollusk fauna. The results bewray yond this glauconite-rich sand enwheels hyp'r-div'rse mollusk fauna, int'rpret'd to representeth deltaic inn'r shallow shelf to ope soundeth environments. Although glauconite-rich shell beds art int'rpret'd to beest fav'r'd by transgression, the ov'rall stratigraphy wast influenc'd by delta progradation, subsidence, and shifting sea-level. This w'rk may representeth analogs to oth'r glauconitic and fossil bearing h'rizons throughout the paleogene gulf and atlantic coastal plain, and oth'r greensand h'rizons throughout the geologic rec'rd.

Monday, April 10, 2017

Highlights: Alluvial Sand Bodies Can Cluster

Alluvial architecture includes describing stacking patterns, spatial density of fluvial channel-belt sandstone bodies, and connectivity, aspects shaped by influences of autogenic and allogenic processes. This study by Benhallam et al. attempts to understand the relative roles of allogenic and autogenic factors on the fluvial John Henry Member of the Straight Cliffs Formation (Cretaceous) of the southwestern Kaiparowits Plateau of Utah. To attempt to discriminate between local and regional controls, this study uses a suite of spatial algorithms to quantify and statistically discriminate clustered, uniform, or random channel-belt bodies in several outcrops. By comparison with predictions from various experimental and numerical models of alluvial architecture, the existence of different patterns at different spatial scales implicates avulsion reoccupation at the small scale, and avulsion-driven compensational stacking at a larger scale. This study suggests that specific types of channel stacking patterns provide insights into the underlying controls and depositional processes, such as compensational stacking and avulsion reoccupation.

Thursday, April 6, 2017

Highlights: On Sand and Sequences

Although that dastardly diagenesis plays a role, many of the same depositional factors that control sequence stratigraphy also influence the composition of sandy sediment within those sequences. Taking this concept as a starting point, Tentori and others unravel relationships between siliciclastic sediment composition (petrofacies) and sequence stratigraphic systems tracts of the Quaternary sedimentary succession of the Roman Basin. The results document different quartz/feldspar and quartz/lithic ratios, and textural changes, among systems tracts. These changes are interpreted to represent the influences of hydraulic sorting (by various processes among systems tracts) and post-depositional in situ weathering, and are linked to tectonics, volcanism, and relative changes in sea level. The data show how a sedimentary petrographic approach can be used to derive information on the stage evolution of a sedimentary succession through time. These results might be directly applicable to petroleum exploration and production in wave-dominated deltaic succession.

Saturday, April 1, 2017

Highlights: The Future of Carbonate Sedimentology(?)

Although recently some have lamented the “demise” of carbonate geology, practictioners in the field are not ones to let it die. Instead of re-hashing what he considers to be more mundane aspects of carbonate depositional systems, or argumentative aspects of cyclostratigraphy, Bruce Wilkinson starts from the premise that “so much of carbonate sedimentology is crap” to develop the concepts and applications of the future of carbonate geology—peloids and pelotherapy. The Medical Subject Headings (MeSH) database of the MEDLINE/PubMed defines pelotherapy as “The therapeutic use of mud in packs or baths taking advantage of the absorptive qualities of the mud. It has been used for rheumatism and skin problems.” Building on efforts of clay mineralogists, Wilkinson argues that pelotherapy can take three approaches: 1) Geophagy, which utilizes the healing power of the calcium carbonate-organic mix, but which can become addictive; 2) Psammotherapy (sand baths) useful for muscular-skeletal diseases; and 3) Cosmetics, providing for a strong skrabiruyuschy effect. The manuscript notes a niche (but growing) peloid travel destination, clear relevance for modeling, and a strong and growing market – after all, who doesn’t love a good peloidal mud bath?