Highlights—Changing Depositional Regimes and Sandstone Variability

Marginal marine depositional systems vary markedly across strike, but along-strike variability is less commonly explored.  Painter et al. describe study of a 14-km long outcrop window of the Cretaceous Sego Sandstone Member (Mesaverde Group, Upper Cretaceous), and compare the sedimentology and stratigraphy with the well-studied Book Cliffs region.  The results illustrate three sequences of roughly similar thickness to the Book Cliffs, but that this area included more tidal and fluvio-deltaic systems.  The spatial and temporal changes in depositional systems are interpreted to reflect changes in paleogeography, and the authors suggests that comparable changes in subsurface analogs would lead to changes in reservoir quality, continuity, and geometry.

Sequence Stratigraphy of the Upper Cretaceous Sego Sandstone Member Reveals Spatio-Temporal Changes In Depositional Processes, Northwest Colorado, U.S.A. by Clayton S. Painter, Carly C. York-Sowecke, and Barbara Carrapa

Highlights: 2013 Honorary Member: Dale Leckie

In shelf regions, geostrophic currents, or flows in which the pressure gradient force is balanced by Coriolis forces, result in water motion at a low angle to the shoreline.  These currents have been interpreted to represent important mechanisms for cross-shelf transport.  In this paper, SEPM Honorary Member Dale Leckie and Krystinik (1989) summarized paleocurrent information from a number of ancient progradational shoreface successions to test the interpretation of the importance of these deposits.  Systematic analysis of 8 formations from North America and Europe revealed a predominance of currents oriented offshore at angles between 70-90 degrees,  a result interpreted to reflect a lack of record of geostrophic currents on the sedimentary record preserved in these successions.  So…the answer to the question in their title was interpreted to be… “no.”

Is there evidence for geostrophic currents preserved in the sedimentary record of inner to middle-shelf deposits? by Dale A. Leckie and Lee F. Krystinik, Journal of Sedimentary Research, v. 59, p. 862-870.

Highlights: 2013 James Lee Wilson Award: Kyle M. Straub

Many sedimentary systems include channelized bodies.  These channels can be distributed randomly or can preferentially fill topographic lows at the time of deposition (termed compensational stacking).  Exploring the stacking patterns of meter- to km- thick channelized packages from river delta to deep-water minibasins in six separate basins, award winner Kyle Straub and others (2009) described a suite of measurements that suggest that stacking patterns of channelized deposits are midway between the random and the compensational end-members.  They interpreted the results to reflect that channel depth is a fundamental length scale that controls stratigraphic architecture across a range of depositional environments, and hence can be used to better constrain geologic models.

Compensational stacking of channelized sedimentary deposits, by K.M. Straub, C. Paola, D. Mohrig, M.A. Wolinsky, and T. George, Journal of Sedimentary Research, v. 79, p. 673-688, DOI: 10.2110/jsr.2009.070.

Highlights: 2013 Pettijohn Medalist: J.A.D. (Tony) Dickson

Secular changes in seawater chemistry, including the Mg/Ca ratio, control the preferred abiotic carbonate precipitate from aragonite to calcite and back.  In this paper, Pettijohn Medalist winner Tony Dickson (2004) empirically tested hypotheses regarding these controls using the composition of Mg-calcite rich echinoderms through the Phanerozoic.  The data revealed low Mg/Ca ratios in the Jurassic and Cretaceous, and highs during the Cambrian, late Carboniferous to Triassic, and today; trends broadly follow proposed first-order Mg/Ca raios from geochemical models and fluid inclusions.  These results were interpreted to represent independent confirmation of the general first-order trends derived from other means.

Echinoderm skeletal preservation: Calcite-aragonite seas and the Mg/Ca ratio of Phanerozoic oceans by J.A.D. (Tony) Dickson. Journal of Sedimentary Research, v. 74, p. 355-365.

Highlights: 2013 Twenhofel Medalist, Paul Enos

Primary depositional intergranular pore systems markedly impact porosity and permeability, influence diagenetic processes and control recovery of resources in many reservoir and aquifer systems.  In this pioneering study, Twenhofel Medalist Paul Enos and Sawatsky (1981) explored the depositional aspects of porosity and permeability by documenting their change in different Holocene carbonate sediment textures.  The results indicated that carbonate mud-rich sediment (fine wackestone) includes the highest porosity (with up to 70%); mud-free grainstone includes 40-50% porosity.  The results provided information on the baseline initial conditions of sediment porosity, for comparison with changes in porosity with compaction and diagenesis.  

Pore networks in Holocene carbonate sediments by Paul Enos and L.H. Sawatsky

Journal of Sedimentary Petrology, v. 51, p. 961-985.

Highlights—Tufas and Paleoclimate

As rapidly precipitating freshwater carbonate accumulations that form in equilibrium with ambient water, tufas represent potential sources of high-resolution paleoenvironmental records.  To critically examine the use of tufa isotopic records in such reconstructions,  Osácar et al. examine a 12-year record of a modern tufa system, comparing water δ18O with δ13C and δ18O signatures in the precipitates.  The data illustrate that these tufas mimic seasonal temperature changes, but that the pattern is complicated by changes in the isotope record of precipitation.  These results are interpreted to illuminate the complex interaction of factors operative at several different type scales (seasonal and annual) that must be evaluated to accurately understand the isotopic record of ancient tufa systems.

Environmental Factors Controlling the δ13C and δ18O Variations of Recent Fluvial Tufas: A 12-Year Record from the Monasterio de Piedra Natural Park (NE Iberian Peninsula) by M. Cinta Osácar, Concha Arenas, Marta Vázquez-Urbez, Carlos Sancho, Luis F. Auqué, and Gonzalo Pardo

Highlights—Hydrographs and Hyperpycnites

Hyperpycnites are deposits of a distinct style of flow that represents a mix of sediment and water that is denser than the water into which the mix flows; these types of deposits commonly are interpreted in the context of fluvial discharge into standing bodies of water.  Here, Saitoh and Masuda test conceptual and experimental models of hyperpycnal flow deposits by exploring spatial variability in subaqueous flood deposits in cores from a lake in Japan with limited wave or tide reworking.  The results clearly indicate that a single flood event can produce multiple eposides of waxing and waning flow, and the nature and controls on spatial variability in the sedimentology of the resultant deposits.  The results suggest the absence of a direct correlation between paleo-flood frequency or intensity and the sedimentary record.

Spatial Change of Grading Pattern of Subaqueous Flood Deposits in Lake Shinji, Japan by Yu Saitoh and Fujio Masuda

Highlights—SEPM Medalists

Each year, SEPM honors a group of medalists for their outstanding contributions to sedimentary geology.  This week, we start a series to honor some of the recipients by providing “Highlights” of their contributions to JSR. 

The 2013 awardees include:

Twenhofel Medalist: Paul Enos. The highest award of SEPM Society for Sedimentary Geology. This award is in recognition of "Outstanding Contributions to Sedimentary Geology."

Shepard Medalist: J. Casey Moore. The Francis P. Shepard Medal for Marine Geology is awarded in recognition of "Excellence in Marine Geology."

Pettijohn Medalist: J.A.D. (Tony) Dickson. The Francis J. Pettijohn Medal for Sedimentology is awarded in recognition of "Excellence in Sedimentology."

Moore Medalist: Kenton Stewart Wall Campbell. The Raymond C. Moore Paleontology Medal is awarded in recognition of "Excellence in Paleontology."

James Lee Wilson Award: Kyle M. Straub. The James Lee Wilson Award is bestowed in recognition of "Excellence in Sedimentary Geology by a Young Scientist."

Honorary Member: Dale Leckie.  Honorary Membership in the SEPM Society for Sedimentary Geology acknowledges excellence in professional achievements and extraordinary service to the Society.

Medals and awards will be presented to the awardees at the 2013 President's Reception and Awards Ceremony, during the SEPM Annual Meeting held in Pittsburgh, PA on Tuesday, May 21, 2013 in the Omni William Penn hotel.

To all recipients, congratulations on your honor!

Highlights—Paleosols and Paleoclimate

To evaluate climatic conditions through the geologic past, the stable isotopes of carbon and oxygen in paleosols have been evaluated to assess ancient atmospheric CO₂ concentrations and paleo-atmospheric circulation patterns.  Yet, these records may be compromised if they do not precipitate in equilibrium with soil CO₂ and soil water.  Michel et al. assess this possibility by examining the isotopic record of modern Vertisols (a soil class) that include a range of material incorporated from underlying marine limestone, a potential contaminant.  The results indicate the roles that soil development, weathering, and topographic position can play in compromising the soil signal.  They suggest that inheritance (contamination) from precursor substrates can alter a “climate” signal in some cases, and should be assessed in application of geological soils for paleoclimate studies.

Stable-Isotope Geochemistry of Vertisols Formed On Marine Limestone and Implications for Deep-Time Paleoenvironmental Reconstructions by Lauren A. Michel, Steven G. Driese, Lee C. Nordt, Daniel O. Breecker, Dana M. Labotka, and Stephen I. Dworkin

Highlights—Brrrr…The Cold Facts about Cryogenic Cave Pearls

Cave pearls are a distinct form of loose, spherical mineral deposit precipitated in caves (speleothems).  This paper by Žák et al. describes a genetically distinct type of cave pearls found in seasonally frozen ice caves of Carpathian Mountains, termed “cryogenic cave pearls.”  Integrating petrographic, SEM, U-series and radiocarbon dating, and stable carbon and oxygen isotope analyses, they illustrate the essential role of seasonal freezing and frost action in the formation of cryogenic cave pearls.  The results provide unique insights into the genesis of these features, and into conditions necessary for cave pearls in general.

Cryogenic Cave Pearls In the Periglacial Zones of Ice Caves by Karel Žák, Monika Orvošová, Michal Filippi, Lukáš Vlček, Bogdan P. Onac, Aurel Perşoiu, Jan Rohovec, and Ivo Světlík

Highlights—Microbes Pumping Iron(stone)

Oolitic ironstones occur quite frequently in condensed sections in the stratigraphic record and can serve as important iron resources. In this paper, Barale et al. use a Cretaceous condensed section to explore the conditions in which mixed Fe-oxide / Ca-phosphate ooids form, why they usually show an ellipsoidal shape in spite of a sub-equidimensional nucleus, and why Fe-oxide cortical layers intimately alternate with Ca-phosphate layers. Their results, which integrate cathodoluminescence, EDS microprobe, backscattered electron imaging, epifluorescence, XRD, and micro Raman spectroscopy, reveal a complex history of prolonged alterations of oxic and post-oxic conditions, interpreted to be related to alternating accumulation and winnowing, and related stop-and-start microbial activity. Collectively, the results provide new insights into the sedimentological and paleoenvironmental conditions in which oolitic ironstones form, detailing the sedimentation, shallow burial, reworking and sea-floor exposure of sediment that ultimately is composed almost exclusively of authigenic grains. 

The Role of Microbial Activity In the Generation of Lower Cretaceous Mixed Fe-Oxide–Phosphate Ooids from the Provençal Domain, French Maritime Alps by Luca Barale, Anna D'atri, and Luca Martire

Highlights—Small Carbonate Platform Evolution—No Bull!

Small reefal platforms that form in response to both tectonic and sea level changes are features ubiquitous through the Phanerozoic.  Commonly, however, these small platforms are buried and limited data are available on spatial and temporal lithofacies heterogeneity.  This paper by McNeill et al. documents the formation and timing of a ~90 km² Pliocene-Pleistocene platform as it evolved in a tropical, convergent tectonic setting (backarc) from a siliciclastic foundation to a mixed system dominated by reefal carbonates.  The results reveal three depositional sequences defined using field relations and refined depositional ages using strontium-isotope stratigraphy, magnetostratigraphy, and coral stratigraphy. The spatial sedimentological patterns of the three sequences provide a near-modern analog that illustrates lithofacies variability that may be present in buried reefal platforms.

Depositional Sequences and Stratigraphy of the Colón Carbonate Platform: Bocas Del Toro Archipelago, Panama by Donald F. McNeill, James S. Klaus, Laura G. O'Connell, Anthony G. Coates, and William A. Morgan

Highlights—Marine Mudstone: Neither Homogeneous nor Isotropic

Mudstone-dominated marine successions are common in the geological record, but a full understanding of their depositional processes commonly is hampered by a lack of generally accepted diagnostic criteria to distinguish between hemipelagic settling and deposition from a flowing medium.  In this paper, Dall’olio et al. integrate sedimentologic observations with analyses of the anisotropy of magnetic susceptibility (AMS) in the Miocene Marnoso Arenacea Formation of Italy to explore the utility of this technique for evaluating depositional processes.  The results reveal that maximum susceptibility axes clustered within the depositional plane along the average palaeoflow direction inferred from flute casts at the base of the nearest turbidite beds. This fabric is interpreted as largely sedimentary in origin, due to the alignment within the bedding plane of paramagnetic/ferromagnetic grains; this result contrasts with the hemipelagic settling interpretation that is commonly invoked for this unit.  Collectively, the results illustrate the value of AMS analysis in study of depositional processes.

Magnetic-Fabric Analysis as a Tool to Constrain Mechanisms of Deep-Water Mudstone Deposition In the Marnoso Arenacea Formation (Miocene, Italy) by Eleonora Dall'olio, Fabrizio Felletti, and Giovanni Muttoni

Highlights—Random Rivers Stack in Stratigraphy

The two end-member models of the facies architecture of alluvial-coastal plain systems suggest that patterns are either predictable within unconformity-bounded sequences or that they are substantively overprinted by autogenic processes.   In this paper, Hampson et al. critically appraise these end-member models of fluvial stratigraphy using detailed architectural analysis of sandbodies developed at different positions within a regressive alluvial-to-coastal plain wedge in the Upper Cretaceous Blackhawk Formation of Utah. The results illustrate variations in the size and internal organization of fluvial sandbodies, and the relationship between these parameters and stratigraphic context; trends are broadly interpreted to reflect decreasing tectonic subsidence through time, with random distribution of sandbodies that represent large-scale avulsion (e.g., autogenic) processes.  These results can be applied to enhanced characterization of hydrocarbon reservoirs deposited in fluvial environments.

Modest Change In Fluvial Style With Varying Accommodation In Regressive Alluvial-To-Coastal-Plain Wedge: Upper Cretaceous Blackhawk Formation, Wasatch Plateau, Central Utah, U.S.A. by Gary J. Hampson, Thomas O. Jewell, Nawazish Irfan, M. Royhan Gani, and Bryan Bracken