“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.
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.
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.
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.
