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

Tuesday, December 13, 2016

Highlights: Tibetan Forearc Basin Evolution

Forearc basins are depositionally important tectonic elements of ocean-continent collision zones, and commonly contain strata influenced by subduction and magmatic arc evolution. However, detailed spatial and temporal understanding of the timing and mechanisms of forearc development is limited, in part because these basins are rarely exhumed and easily accessible on land. To better understand tectonics and sedimentation of forarc basins, Orme and Laskowski examine Albian–Santonian strata of southern Tibetan Xigaze forearc basin, a large and well-preserved forearc basins, and which records upper-plate processes active prior to and following the inter-continental collision between India and Asia. Using regional geologic mapping, detailed sedimentologic and facies analysis, modal petrographic characteristics, and U-Pb detrital-zircon geochronologic data, the study documents the relationship between the Yarlung-Tsangpo ophiolite and Xigaze forearc basin and reconstructs the sedimentary environments of the southern margin of Asia during the initial stages of forearc deposition. Results reveal details of the evolution of the southern margin of Asia prior to its collision with India, including diachronous development of the forearc basin prior to India–Asia collision.

Friday, December 9, 2016

Highlights: Ichnology—Mixing It Up

Mixed siliciclastic-carbonate depositional systems occur throughout the geologic record. Although their general sedimentologic aspects are well-constrained, substrate-controlled trace fossil assemblages that can represent discontinuities in these successions are less well understood. By integrating ichnological descriptions and facies analyses of the Baldonnel Formation at Williston Lake, B.C., Canada, Schultz and others explore the ichnological composition of paired Trypanites- and Glossifungites-demarcated discontinuity surfaces, the significance of these surfaces in regional stratigraphy, and the relationship of these two assemblages to each other in individual parasequences sets. Recognition of these surfaces, and an understanding of their character, is paramount to the stratigraphic evolution and architecture of this mixed carbonate–siliciclastic depositional system, and may have analogs in other mixed systems.

Wednesday, December 7, 2016

Highlights: Mud-Dominated Shelf-Edge Rollovers

Although fine sediment represents an important proportion of sediment transferred by rivers, many studies of basin margin progradation emphasize supply and accretion of sand at and beyond the shelf edge. To understand how and when basin margin clinothems prograde in the absence of coarse-grained sediment supply to the shelf edge, Poyatos-Moré and others examine clinforms of the Permian Waterford Formation, in the Karoo Basin (South Africa). In these strata, normal and inverse grading, erosion surfaces, and moderate to low intensity of bioturbation are common in low-gradient (< 0.7°) clinoforms of thick, outer-shelf to upper-slope mudstone overlain by thin sandy shelf topset strata. The study provides a depositional model for shelf-to-slope transitions in fine grained successions, illustrating how progradational mud-rich, shelf-confined deltaic clinothems with muddy shelf-edge rollovers develop.

Mud-dominated basin-margin progradation: processes and implications by Miquel Poyatos-Moré, George D. Jones, Rufus L. Brunt, David M. Hodgson, Richard J. Wild, and Stephen S. Flint