Monday, July 25, 2016

Highlights—Generous Shellfish? Yes, Oysters Share Insights!

Secret, and self-contained, and solitary as an oyster,” wrote Dickens.  But he also knew that no oyster lives independent of his environment. In this contribution, Sælen and others use this concept to attempt to use  δ18O, δ 13C, 87Sr/86Sr and elemental analysis of oyster shells to unravel paleoenvironmental settings of carbonates and mixed siliciclastic-carbonates from Miocene strata in the Lorca Basin of Spain. The raw and modeling results expand on patterns derived from contemporaneous corals and reveal novel insights into paleosalinities of marginal marine water in this basin. More generally, the results highlight the use of the well-preserved, low-Mg calcite shells of oysters to assess short-term changes in sea water salinity and temperature.

Oyster shells as recorders of short-term oscillations of salinity and temperature during deposition of coral bioherms and reefs in the Miocene Lorca Basin, SE Spain by Gunnar Sælen, Ingelin Løkling Lunde, Kristin Walderhaug Porten, Juan C. Braga, Siv Hjorth Dundas, Ulysses Silas Ninnemann, Yuval Ronen, and Michael Richard Talbot

Monday, July 18, 2016

Highlights—Islands in the Stream (with no Vegetation)

Interpretation of fluvial strata in continental basins is contingent upon recognizing stratal architectures and climate change signals from fluvial strata, and provide insights into understanding how fluvial sedimentation interacts with basin topography. These aspects are difficult to assess in the pre-Devonian fluvial rock record, because comparisons to models based on vegetated modern rivers may not be suitable. In this paper, Lowe and Arnott carefully describe the architecture of braided and ephemeral facies in the Cambro-Ordovician Potsdam Group in the Ottawa Embayment and Quebec Basin in northeastern North America. The contribution reveals pre-Devonian fluvial architectures and processes, and how they relate to global orbitally-forced climate changes in the Late Cambrian. These aspects of pre-Devonian fluvial sedimentology are important to the Joe Geologist because they provide a framework to make basin-wide time-significant stratigraphic correlations, and understand variations in stratal architectures with varying degrees of interaction with basement topography, potentially important for groundwater and oil migration, and discerning climate change during this critical period.

Tuesday, July 12, 2016

Highlights—In the Backwater of Tidal–Fluvial Interactions

As noted by Elvis and Ecclesiates, rivers flow surely to the sea. Yet, exactly what happens to rivers just before they get there is not well constrained, but has been interpreted to control avulsion nodes, and therefore, distributary channel patterns. To test scenarios of backwater hydraulics (especially water-surface drawdown) on sedimentology and morphology of lower-delta plain distributary channels, Columbera et al. describe field observations of the Cretaceous Neslen Formation (Campanian, Mesaverde Group) of the Book Cliffs in Utah. The results reveal ribbon sand bodies with architecture, lithofacies, and bounding surfaces and strata that are broadly consistent with patterns that would be expected in the region of rivers where the streambed drops below sea level.  Nonetheless, the authors conclude by noting a need for additional research on these processes in the rock record, and the appropriate revision of sequence stratigraphic models.

Tuesday, July 5, 2016

Highlights—Probertite and glauberite: the most interesting minerals you’ve never heard of….

Compared to their sulfur-rich evaporitic relatives, the origin and significance of sedimentary borates is poorly constrained, yet these deposits can form economic resources. To better understand lacustrine borates, Ortí et al. describe the sedimentology, petrographic characteristics, and stratigraphy of cores from Miocene strata of three exploratory boreholes from Turkey. The results reveal a succession rich in several scales of cyclic alternations of primary (depositional to interstitial) glauberite (Na2Ca(SO4)2) and probertite (NaCaB5O7(OH)4·3H2O) (yes, those will be on the quiz).  These minerals and their varied textures are interpreted to vary according to lake levels, chemistry, and paleogeographic setting in the paleo-saline lake. The results emphasize the diversity of hydrogeochemistry that can influence lacustrine evaporite depositional systems.