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.