Thursday, May 29, 2014

Highlights—Protean Permian Paleoclimate

Paleosols include potentially important paleoclimate indicators. Counts and Hasiotis document continental deposits in core from Lower Permian strata of western Kansas that contain a number of pedogenic features that suggest variable soil moisture during the development of cumulic paleosols. These paleosols are interpreted to have formed over fourth-order eustatic cycles, although climate change associated with fifth-order cycles resulted in close juxtaposition of pedogenic features that suggest both humid and drier climates. The study demonstrates how paleosols may be the net product of highly variable climate and climate shifts, and emphasizes that all pedogenic features should be taken into account when reconstructing paleoclimate.

Tuesday, May 27, 2014

Highlights—Delta Front Bars

It is a truism that sedimentary geologists like bars; some actually study them. In this paper, Ahmed et al. describe the sandy architectural elements that build deltaic deposit in an outcrop of the Cretaceous Ferron Sandstone in Utah. The study evaluates the character of sandy mouth bars and more distal detached bars, and interprets the features in the context of jet-plume concepts. Detached sand bodies are interpreted to be deposited by descending, inertial and hyperpycnal flows, whereas the cross-bedded sands in the upper delta front are interpreted as radial bars reflecting a greater degree of frictional deceleration. Shallow terminal distributary channels lie in the uppermost delta front topset. Aside from the concepts, the characterizations of grain size variation and shale dimensions provide data potentially useful for fluid flow modeling of analog subsurface reservoirs.

Wednesday, May 21, 2014

Highlights—Shifting Monsoons

Monsoonal climates are characterized by seasonal shifts in rainfall and wind direction and intensity, and can also be influenced by longer-term climate change. To better understand the East Asian monsoonal system, Du et al. integrate observations of sedimentary facies, age dates, and proxy paleoclimatic indices from a section in the Miaodao archipelago in the Bohai Sea coastal zone. The data illustrate rapid climate oscillations within Miaodao stratigraphical section (MDS) deposits of isotope substage 5e. Strata from the Eemain period, for which the MDS record is particularly well preserved, indicate that winter monsoon wind strength oscillated numerous times. This millennial-scale climate variability had a quasi-periodicity with cycles of ~1,470 year for the late glacial period, interpreted to be driven by changes in solar activity.

Rapid changes in the East Asian monsoon during the last interglacial in the Bohai Sea coastal zone, China by Shuhuan Du, Baosheng Li, Zhiwen Li, Muhong Chen, Rong Xiang, David Dian Zhang, Dongfeng Niu, and Lanlan Zhang

Wednesday, May 7, 2014

Highlights—Channels by Chopper

Unravelling the allogenic and autogenic influences on fluvial architecture is challenging because of the large scale of outcrops required to capture sufficient data to test conceptual models. Using a suite of lidar data collected from a helicopter, Rittersbacher et al. explore controls on the large-scale architecture of fluvial sediment bodies in the nonmarine Blackhawk Formation of eastern Utah. Helicopter-based laser scanning provide data to quantify the geometry and continuity of channel bodies on a scale large enough (>10 km) to account for migration and avulsion of a fluvial system.  The data reveal almost 400 independent channel bodies. The stacking patterns and spatial evolution the dimensions of the channel bodies are interpreted to represent a succession of deposits of a large prograding distributary fluvial system. Analyses reveal that the key control on channel architecture is the distance of a channel to the contemporary shoreline, contrasting with previous interpretations that accommodation rate of the floodplain was the main controlling factor on accumulation.

Sunday, May 4, 2014

Highlights—May the Force (errr…topography-driven flow expansion) Be with You

The details of how sedimentary processes ultimately create the stratigraphic record are the result of complex interactions among many influences. Here, Sittoniet al. investigate sediment transport processes and alluvial sedimentary deposits formed by topography driven flow expansions, a deposition mechanism which complements with the parallel and recognized research thread of jet driven deposits. In topographic flow expansions, coupled topography and flow (not only flow, as in jets expansions) determine the characteristics of the deposits. The flow regime over topographic expansions is unchannelized at large aspect (flow width to depth) ratio. The characteristic depositional body produced by topographic flow expansions is a relatively thin, tabular sand body with flat base and slightly convex top, comparable to some "sheet flood" deposits described in the stratigraphic record. This work improves understanding and predictive capabilities of occurrence and characteristics of these deposits, and may be significant for subsurface exploration.