Monday, March 27, 2017

Highlights: Differences between the EARSs

The East African Rift System (EARS) includes a northern segment that is more volcanically influenced than regions to the south. To explore the roles of climate, tectonism, and volcanism and the architecture of sedimentary deposits in rift basins, this manuscript by Mtelela and others provides a sedimentologic investigation of the Pleistocene–Holocene upper Lake Beds, the uppermost stratigraphic unit exposed throughout the Rukwa Rift Basin in southwestern Tanzania. Integrating geologic mapping, lithofacies analysis, petrographic microscopy, scanning electron microscopy, and radiocarbon dating reveal alternating stacking patterns of landward- and basinward-stepping alluvial to fluvial channel, deltaic, and profundal lacustrine strata, bounded by unconformities. Sequence development in this rift basin is interpreted to be controlled largely by base-level changes drive by interplay between climate change and sediment supply, but was influenced by episodic volcanism in the Rungwe Volcanic Province.  Understanding these types of linkages is central to efforts in evaluating the resource potential of rift basins; in this basin, it also provides a foundational context for interpretation of regional paleoclimate and paleoenvironmental setting of vertebrate fossils.

Wednesday, March 22, 2017

Highlights: The Skinny on Limestone Micropores

Although most agree that micropores are important for scientific and economic reasons, geologists and material scientists have diverse opinions on the very definition of microporosity and its possible origin(s). To explore the nature and genesis of micropores, Hasiuk and others examine bulk stable-isotope and elemental analyses from a range of microporous limestone hydrocarbon reservoirs and a compilation of geochemical data from previous studies of subsurface microporous limestones from the Phanerozoic. Results illustrate microcrystals are composed of low-Mg calcite, and geochemical data suggest most are abiotic origin, but modified by shallow-burial diagenesis. On this basis, the authors suggest a uniform, diagenetic origin during early burial for the micrite that hosts most microporosity in limestone oil reservoirs. This understanding is a first step in modeling the distribution of microporosity in reservoirs, enhancing accurate prediction of reservoir performance.

Diagenetic origins of the calcite microcrystals that host microporosity in limestone reservoirs by Franek J. Hasiuk, Stephen E. Kaczmarek, and Shawn M. Fullmer

Monday, March 20, 2017

AE Interview: Get to Know Bruce Wilkinson

Bruce (Bieber?) Wilkinson, Department of Earth Sciences, Syracuse University

Q: What’s your research? 

A: Before its demise, I used to profess expertise in the general field of carbonate geology; often focused on making light of folk who worshiped at the church of our mother of divine parasequence. More recent efforts are directed toward subjects that are a bit more quantitative in flavor; my last paper was on trying to understand the “Sadler Effect” when pretending that rainfall is meteoric sediment. Today I finished up my input on using multidimensional scaling to understand differences among ages of zircons in terrigenous samples, and am working on a paper trying to derive intra-annual growth rates of clams from stable isotope profiles.

Q: Where is your favorite field area (and why)?

A: There are a bunch (yes, I go to the field; at least I used to). I guess if I had to choose, it would be the Miocene-Pliocene lake deposits along the southwestern margin of the Snake River plain. Thick and extensive lake-margin oolite and algal bioherms; hard to beat.

Q: What do you enjoy about serving as JSR AE? 

A: The demise of carbonate geology (it’s the reason Rankey has time to write a JSR blog); that “death” means much less work (I am damn near unemployed as a “carbonate AE” for the Journal.

Q: What was your favorite JSR paper from “back in the day” (or a recent year)?  

A: I guess it would be Bob Folk’s “The natural historyof crystalline calcium carbonate; effect of magnesium content and salinity”; the man rather invented the field of carbonate geology.

Q: What are your hobbies? 

A: We live on this 50-acre hobby farm in upstate New York; horses, goats, cats, turkeys, guinea fowl, pea fowl, chickens, ducks, geese, pigeons; love my John Deere tractor.

Q: What’s on your favorite Pandora station? 

A: I spend a few bucks on Spotify; I clamp on those Sony noise-canceling headphones, and try and do science to the likes of Tompall and the Glaser brothers, Justin Townes Earl, the Gourds, and Mason Porter. 

Thursday, March 16, 2017

Highlights: Connections and Transfers in Canyons

The heads of submarine canyons represent a critical link in the transfer of sediment from terrestrial sediment sources to deep basin sinks. Data from modern canyons and submarine fans suggests the strength of this connection determines the proportion and caliber of sediment stored in shelfal environments relative to that which is transferred to deep-water. Sweet and Blum document data on grain size, bathymetry and geochronology from twenty-four modern submarine canyons that demonstrate this link to be very sensitive to the distance between the canyon head and the shoreline, and, to a lesser extent, wave energy. A surprising observation from these data is the close relationship between the transport of grains of sand-size and coarser clasts and the distance between the river mouth or shoreline and the head of the submarine canyon. These data show the width of this zone filters the caliber of sediment delivered into deep-water with important implications for understanding sediment budgets and reservoir and seal distribution.

Monday, March 13, 2017

Highlights: Caldera Sediment

Although sedimentary deposits record the history of Earth-surface processes, only infrequently they are used to understand volcanic systems. In this paper, Murphy and others study the lacustrine sedimentary rocks deposited within the Long Valley Caldera, California, to understand the evolution of the caldera. The results reveal the nature of the volcaniclastic, chemical, and biogenic sediment, from near the caldera margin (Gilbert-type delta) to distal (diatomite and marl). The interpretations suggest that deformation, volcanism, catchment area shifts, and climate change each played distinct roles in controlling the nature and extent of sediment accumulations. These data and insights provide unique perspectives on this volcanic system, understandings distinct from those offered by igneous petrology or volcanology alone, and refine the conceptual model for sedimentary processes in caldera lakes in general.

Thursday, March 9, 2017

A Look Back: 60 Years—In Bars, Size Matters

Every student in undergraduate sedimentary geology class knows that fundamental descriptors of sediment include attributes of size and sorting. Examining a sand and gravel bar in the Brazos River near Hearne, Texas, this paper by Folk and Ward is the classic text for describing means to quantify these sedimentologic characteristics, and for showing the interpretive value of the data (as opposed to qualitative interpretation). The locals of Robertson County still enjoy their grains, as do geologists: “If one may be permitted to extrapolate from a small study such as this one and enter the seductive field of generalization,” the study ends one of the more penetrating conclusions in sedimentologic history: “Once a relationship is established in an ideal case, where the changes are laid out before the observer in their most perfect form, one soon learns to recognize the same relationships in less ideal examples, where the changes are obscure. The obscure examples, hitherto unfathomable, are explained in the light provided by the ideal examples. So it has been with the Brazos bar study.” The undergraduates memorizing Folk and Ward’s equations for skewness and kurtosis to impress at the party Friday night clearly are appreciative for the illumination, even if the utility of size is intuitively easier to grasp.

Monday, March 6, 2017

Highlights: The Rise and Fall of Tides

Tidal-dominated systems include complex simple and compound dunes, impacted by tidal and non-tidal processes. To better understand a channelized lower intertidal zone, Jo and Choi document an integrated multi-year morphodynamic and hydrodynamic data set from the macrotidal Gyeonggi Bay, Korea. The data provide a means to explore how external processes such as waves, and rain-induced discharge fluctuation shape intertidal compound dunes in time and space, controlling their stratigraphic architecture. The results of the study highlight the complexity of intertidal dune architecture, and provide criteria that could be used to distinguish between intertidal dunes and subtidal dunes in the stratigraphic record.

Tuesday, February 28, 2017

AE Interview: Get to Know Greg Ludvigson

Greg Ludvigson, Kansas Geological Survey, Lawrence, Kansas

Q. What’s your research?

A. I work on the Mesozoic and Cenozoic terrestrial paleoclimatology of stacks of paleosols in the clastic deposits filling continental sedimentary basins. I do this using petrographic and stable isotope techniques to investigate the diagenesis and paleohydrology of terrestrial carbonates. A lot of effort in recent years has been devoted to improvements in chronostratigraphic resolution using carbon isotope chemostratigraphy and collaborative efforts with U-Pb geochronologists.
Q. Where is your favorite field area (and why?)?

A. I keep going back over and over again to the San Rafael desert in eastern Utah to investigate the paleopedology, paleoclimatology, and chronostratigraphy of the Early Cretaceous Cedar Mountain Formation. This work has been carried out in concert with a group of colleagues and students who are similarly drawn to this awesome landscape and set of allied scientific questions.

Q. What do you enjoy about serving as JSR AE?

A. Just from having been around long enough, I can quickly think of appropriate peer reviewers to tap in case the author’s suggested reviewers don’t work out. In those instances, that helps me accelerate the peer review process for the journal. My term has been long enough to get a good sense of the wide range in the quality of submitted manuscripts, and that has helped me to quicken the pace of making recommendations to the Editors. I have really enjoyed having the chance to monitor new developments in the field of sedimentary geology through AE service to JSR.

Q. What was your favorite JSR paper from “back in the day” (or a recent year)?

A. I think back to my early years as a Ph.D student, and the impact that Robert Berner’s 1981 paper “A New Geochemical Classification of Sedimentary Environments” (JSP, v. 51, no. 2, p. 359-365) had on me at the time. It was a simple, elegant paper that pulled together a framework on how to interpret the presence of redox-sensitive authigenic minerals, and what they indicated about depositional environments. I read that paper at just the right time to begin collating my own field experiences and develop a world view on how redox processes are encoded in the sedimentary rock record.

Q. What are your hobbies?

A. I plant trees. I live on a rural acreage with a lot of space, meaning that my long-standing impulse toward therapeutic silviculture is not very well constrained. I am tending to an embarrassingly large number of sapling trees, and I enjoy making daily to weekly visits to see how they are doing. They live in slow-motion time scales relative to our daily human experiences, but if you look closely, they offer lots of clues.

Q. What’s on your favorite Pandora station?

A. I let my involvement with Pandora lapse some time ago. I am drawn to American Roots and folk music, and my exposure to new material in this genre comes from listening to local NPR affiliates on FM radio. Pretty old school, I know.

Tuesday, February 21, 2017

Highlights: Shelf-Edge Delta Ichnology

As both represent aspects of their environment, sediment and organisms can be closely related. In deltaic systems, numerous studies have examined the range of delta types and subenvironments and characterized facies and icnology. Yet, these relations are less well characterized in outer shelf deltas, a niche that Dasgupta and co-authors fill. This paper characterizes and ranks ecologic stress factors on the interactions between animals and substrates in a shelf-edge delta environment of the Plio-Pleistocene Gelasian Mayaro Formation of Trinidad Island, Trinidad. The field observations of the equatorial paleo-Orinoco system reveal a diverse suite of sedimentologic and ichnologic attributes, interpreted to reflect an extremely variable and dynamic marine environment. These data lead to an exposition of a comprehensive ichno-sedimentological conceptual model for large-river, low-latitude, accommodation-driven, shelf-edge deltas.

Tuesday, February 14, 2017

Highlights: Fluid-Mud Prone Lacustrine Deposits

All things . . . are in flux like a river,” wrote the ancient Greek philosopher Heraclitus.  As many geologists know, it is not only rivers that change, but indeed many types of flow are in flux.  In this contribution, Hovikoski and others explore density flow deposits, and the nature and dynamics of hybrid deposits, in a lacustrine setting. Focusing specifically on the origin of potentially flow-transforming mud, the paper describes a 500-m-long core, offshore Vietnam, from a Paleogene, freshwater rift-lake system. The results show that hybrid beds of various scales develop in freshwater lakes, in bed motifs very similar to marine deposits.  The data also suggest that lake-bottom mud commonly was assimilated into density flows, which in turn played an important role in changing flow concentration. Given the common density stratification of lakes, conditions favorable to development and preservation of these facies may be more common than anticipated.

Density-flow deposition in a freshwater lacustrine rift basin, Paleogene Bach Long Vi Graben, Vietnam by Jussi Hovikoski, Jens Therkelsen, Lars H. Nielsen, Jørgen A. Bojesen-Koefoed, Hans P. Nytoft, Henrik I. Petersen, Ioannis Abatzis, Hoang A. Tuan, Bui Thi Ngoc Phuong, Cao Van Dao, and Michael B.W. Fyhn

Wednesday, February 1, 2017

Highlights: Marginal Evaporites

Although the sequence stratigraphic setting of saline giant evaporite systems is well-known, less clear is the context of extensive basin-margin systems. In this paper, Clement and Holland examine an extensive basin-margin evaporite system, the Middle Jurassic Gypsum Spring Formation of northern Wyoming. The Gypsum Spring Formation contains three depositional sequences, with evaporites within facies that were deposited in coastal salinas and sabkhas, as well as extensive desert mudflats, in the TST and HST of individual sequences. Given their vast extent, and lack of evidence for diachroneity, these regionally expansive evaporites are interpreted to be sourced by continental rather than marine brines. These results provide analogs for evaporite resources or laterally continuous seals of hydrocarbon reservoirs.

Tuesday, January 24, 2017

AE Interview: Get to Know Murray Gingras

Murray Gingras is a professor at the University of Alberta, Department of Earth and Atmospheric Sciences

Q. What’s your research?

A: Studying animal–sediment relationships and sedimentary geology in general.  I view my role in this field as someone who takes a specific dataset and integrates it into established sedimentological datasets that have included aspects of ichnology, and as a result my work is applied from the Precambrian all the way through to the Modern, usually with the intention of refining our understanding of what the sedimentary environment was—and by refining I mean inferring things that we can’t infer from normal sedimentology, things like very highly refined sedimentation rates, timescales that vary from minutes to days to months, which we can’t do with geochronology, and chemical aspects of the sedimentary environment including relative levels of oxygenation and relative salinities. This type of parameterization allows us to take sedimentary interpretations to a much higher level. The end goal of this is to understand the ancient world and the modern world better but it also helps us establish better sequence stratigraphic frameworks, to understand paleogeographic restorations better, and it has very practical applications in refining facies interpretations in the subsurface so that oil and gas exploration can be brought to another level with better sedimentological analyses.

Q: Do you think rocks without animals are boring?

A: No! As long as there is awesome stratification or cool surface features like microbial wrinkle marks, or nifty casts, I think that is all really interesting.  I must admit that unburrowed, planar bedded silts and shales are a little too tedious for me sometimes. I was really trained as a geologist, not a sedimentologists, so I don’t find rocks boring ever, at all. I like igneous rocks, I have a mineral collection…and metamorphic rocks are hard to beat.

Q. What is your favorite field area and why?

A: Willapa Bay [Washington State, U.S.A.]. I did my PhD there. It has everything I love! Every time I go there I learn something new, I find that something I thought was right becomes incorrect in the face on new information gleaned from Willapa Bay. I have never walked along the shorelines there and not had an idea for a paper. I suppose if I followed up on the we could have 300 papers on Willapa Bay. It’s just a remarkable place to work. The west coast food culture has gotten steadily so excellent that you can go out to Astoria or Long Beach peninsula and get salmon…or a nice oyster stew. I’ve been all over the world, I’ve worked Argentina, Spain, France, Australia, New Zealand, and they were all great but Willapa Bay still wins, for sure.

Q. What was your favorite JSR paper “back in the day” (or the last year)?

A: Traces in the dark: sedimentary processes and facies gradients in the Upper Shale Member of the Upper Devonian–Lower Mississippian Bakken Formation, Williston Basin, North Dakota, U.S.A., by Sven Eggenhoff and Neil Fishman. They took an important dataset and showed that what a lot of people were assuming was incorrect. A lot of these unbioturbated units actually had bioturbation and that’s not trivial because a lot of organic-rich deposits we tend to think of as euxinic deposits, meaning no oxygen and very sulphitic water conditions, i.e., animal life can’t exist, so ichnofossils can’t exist. If you show that’s wrong it implies that something really fundamental about the way we view some organic deposits is incorrect and we need to recalibrate how we view them.

Hyperpycnal rivers and prodeltaic shelves in the Cretaceous seaway of North America, by Janok Bhattacharya and James MacEachern. I like the breadth of the undertaking—they looked at scalar data regarding deltas, sedimentological models, they used rock pictures, schematics, they really built a beautiful interpretation of the distribution, occurrence, and importance of hyperpycnites that I think was the result of thinking about it for many years. It was areally well executed synthesis, because Bhattacharya is so creative in how he articulates himself and MacEachern is so capable of precise technical prose that to me was a writing match made in heaven.

Q. What are your hobbies?

A: I read a lot of science fiction. When I retire, I am going to form a "Sasquatch Research Group" and prove the existence of Sasquatch.

Q. Oooh, can I help with the Sasquatch research?

A: Yes!

I also like building things around the house---bunny frames, trellises, etc. I made a nice strawberry frame to keep the birds out! I have to admit geology is as much my hobby as it is my job.

Q. What is your favorite Pandora station?

A: What is Pandora?

Q: A streaming music service.

A: Oh! In Canada I use Deezer. D-e-e-zed-e-r. I think the channel I most use is the ELO playlist, and David Bowie, Led Zepplin. For new music I like Eminem, Bruno Mars. My favorite new indie group is Fun.

This interview was done via Skype and transcribed and edited semi-accurately by Melissa Lester on January 19, 2017.

Tuesday, January 17, 2017

Highlights: Permian Plants Provide Pangean Perspectives

Plants provide important insights into paleo-landscapes and -climate, yet commonly are not well preserved in the geologic record. This paper by Simon et al. describes a perplexing case where the features of the abandoned channel deposits, plant fossils and paleosol sections suggest that conditions were relatively wet, although the formation has been interpreted to have been deposited under semi-arid to arid conditions. Within the Leonardian (Permian) Clear Fork Formation of north-central Texas, the Colwell Creek Pond site represents an abandoned channel Integrated field, sedimentologic, mineralogic, paleobotanic, and taphonomic observations reveal the formative conditions and preservation of the laminated mudstone beds, as well as the types of plants preserved and biomineralization process. The findings of this paper broaden understanding of the conditions within the equatorial regions of Permian Pangea, providing perspectives on these unique systems without complete modern analogs.

Wednesday, January 11, 2017

Highlights: On Hybrids (Event Beds, not Cars)

Although hybrid event beds (HEBs) occur in many of deep-water systems, the mechanisms responsible for their formation remain ambiguous. Most workers agree that acquisition of mud or muddy material is a key factor, with many hybrid flow models favoring an origin for the mud in up-dip channels, channel-lobe transition zones or slope sectors. In this study, Fonnesu and others describe outer-fan-lobe and confined-basin-plain sheet deposits of the Cretaceous–Paleocene Gottero Sandstone cropping out on Mount Ramaceto and Mount Zatta (NW Apennines, Italy). The succession includes cm- to m-deep erosional scours below sheet-like HEBs, features which appear to provide the mud necessary for local flow transformation. Extensive substrate delamination in distal deep-water environments has not been described in detail before nor linked to the local formation of HEBs.This hybrid flow model may apply generally, with implications for the distribution and heterogeneity of HEB muddy divisions and hence hydrocarbon reservoir properties.

Marco Fonnesu, Marco Patacci, Peter D.W. Haughton, Fabrizio Felletti, and William D. McCaffrey

Monday, December 19, 2016

Highlights: Economic Mineralization—It’s The Fault’s Fault

Pressure and temperature are two fundamental controls on diagenesis and formation of economic minerals. To understand the possible influence of fault-related hydrothermal fluids on uranium mineral deposits of Carboniferous to Jurassic siliciclastic deposits in the Tim Mersoï Basin in Niger, Mamane Mamadou  and others examine the P-T conditions of diagenesis using petrography SEM observations and chemical analyses, supplemented thermometric approaches of chlorite compositions and fluid inclusions in quartz overgrowths. Chlorite thermometry indicates that all Carboniferous to Jurassic section was subjected to elevated temperatures of around 125°C (Carboniferous) and 115°C (Jurassic). These temperatures suggest a strong thermal disequilibrium between incoming fluids and reservoirs, reflecting burial temperatures in excess of those expected at maximum burial depth.  The fault-influenced fluid circulation affecting these strata are interpreted to to be linked to major geodynamic events related to the opening of the Atlantic Ocean, and likely have analogs elsewhere.

Hot fluid flows around a major faultidentified by paleothermometric studies (Tim Mersoï Basin, Niger) by Marah Mamane Mamadou, Michel Cathelineau, Franck Bourdelle, Marie-Christine Boiron, Agnes Elmaleh, and Marc Brouand