Salinity indicators in sediment through the fluvial-to-marine transition (Fraser River, Canada).

Many sediment attributes have been proposed as proxies for determining salinity conditions under which sediment is deposited, and six attributes (Sr/Ba-HAc, Sr/Ba-NH4Ac, δ13Corg, C/N, and the relative abundances and concentrations of dinoflagellate cysts) are compared here. In this paper, sediment attributes from the Fraser River Delta, Canada and surrounding coastal areas are compared by depositional position along the fluvial-to-marine transition, by salinity, and by sedimentological characteristics. Along the fluvial-to-marine transition, most attributes exhibit distinct trends between parts of the river that experience sustained marine water (saltwater) influence over seasonal and tidal timeframes, and parts that experience only freshwater or periodic saltwater influence. No attributes are reliable indicators of depositional position where saltwater incursion is short lived or where water is fresh. Where marine influence is sustained, Sr/Ba-HAc and Sr/Ba-NH4Ac are the most reliable positional indicators along the fluvial-to-marine transition. When compared strictly to salinity, Sr/Ba-HAc, Sr/Ba-NH4Ac, and δ13Corg all correlate predictably except in delta front and prodelta settings. Our data show that all six sediment attributes are heavily impacted by river-derived sedimentation, and it is not appropriate to compare values from strongly river-influenced settings (e.g., deltas) with those from weakly river-influenced settings (e.g., bays and estuaries).

The 20-million-year old lair of an ambush-predatory worm preserved in northeast Taiwan.

The feeding behavior of the giant ambush-predator "Bobbit worm" (Eunice aphroditois) is spectacular. They hide in their burrows until they explode upwards grabbing unsuspecting prey with a snap of their powerful jaws. The still living prey are then pulled into the sediment for consumption. Although predatory polychaetes have existed since the early Paleozoic, their bodies comprise mainly soft tissue, resulting in a very incomplete fossil record, and virtually nothing is known about their burrows and behavior beneath the seafloor. Here we use morphological, sedimentological, and geochemical data from Miocene strata in northeast Taiwan to erect a new ichnogenus, Pennichnus. This trace fossil consists of an up to 2 m long, 2-3 cm in diameter, L-shaped burrow with distinct feather-like structures around the upper shaft. A comparison of Pennichnus to biological analogs strongly suggests that this new ichnogenus is associated with ambush-predatory worms that lived about 20 million years ago.

Insolation-paced sea level and sediment flux during the early Pleistocene in Southeast Asia.

Global marine archives from the early Pleistocene indicate that glacial-interglacial cycles, and their corresponding sea-level cycles, have predominantly a periodicity of ~ 41 kyrs driven by Earth's obliquity. Here, we present a clastic shallow-marine record from the early Pleistocene in Southeast Asia (Cholan Formation, Taiwan). The studied strata comprise stacked cyclic successions deposited in offshore to nearshore environments in the paleo-Taiwan Strait. The stratigraphy was compared to both a δ18O isotope record of benthic foraminifera and orbital parameters driving insolation at the time of deposition. Analyses indicate a strong correlation between depositional cycles and Northern Hemisphere summer insolation, which is precession-dominated with an obliquity component. Our results represent geological evidence of precession-dominated sea-level fluctuations during the early Pleistocene, independent of a global ice-volume proxy. Preservation of this signal is possible due to the high-accommodation creation and high-sedimentation rate in the basin enhancing the completeness of the stratigraphic record.

Resolving the Architecture and Early Evolution of a Forearc Basin (Georgia Basin, Canada) Using Detrital Zircon.

Convergent-margin basins (CMBs) are commonly associated with active arcs, and hence are rich in detrital zircon (DZ) whose ages closely reflect the timing of deposition. Consequently, maximum depositional ages (MDA) from DZ geochronology can be employed to resolve the stratigraphy and evolution of CMBs. Herein, we use DZ to revise the internal architecture of the lower Nanaimo Group, which partially comprises the fill of the (forearc) Georgia (or Nanaimo) Basin. Maximum depositional ages and multi-dimensional scaling of DZ age distributions are employed to determine chronologic equivalency of strata and assess sediment provenance variability within the pre-existing lithostratigraphic framework. The results are compared to a recently developed sequence stratigraphic framework for the lower Nanaimo Group. The basal lithostratigraphic unit of the Nanaimo Group, the Comox Formation (Fm), comprises strata that are neither time correlative nor genetically related. The three lithostratigraphic units directly overlying the Comox Fm (Haslam, Extension, and Protection formations) comprise strata with similar genetic affinities and MDAs that indicate deposition of these units was not always sequential and locally was contemporaneous. Through this work, we provide an example of how MDAs from DZ geochronology in CMBs can resolve basin-scale stratigraphic relations, and identify chronological changes in sediment provenance.