INTERTIDAL ANIMAL-SEDIMENT INTERACTIONS OF THE OUTER-MIDDLE TO EXPOSED SPIT REGIONS OF NETARTS BAY, OREGON, USA
Netarts Bay is situated along the north Oregon coast approximately 8km south of Tillamook Bay. It is a well-mixed, wave-dominated, tidally-influenced micro- to meso-tidal bay. The neoichnology and sedimentology of three specific bay regions were studied in order to resolve how marine invertebrates respond to changes in hydraulic energy caused by wave and tidal currents as well as variations in sedimentation rate. Burrow density via grid counts, sediment samples for grain size and total organic carbon (TOC) analysis, and polyvinyl chloride pipe core as well as sediment peels were taken to evaluate sedimentary structures, burrow density and burrow morphology within the subsurface. Grain size was consistent throughout the outer bay and foreshore areas with an average grain size of upper-fine grained sand. The highest grain size values were recorded in the outermost Exposed Shoreface-Recurved Spit study area while lowest values were recorded in the innermost Outer-Middle Bay Tidal Flat study area. Average TOC values ranged from 0.1% to 1.3% with highest values occurring within the Outer-Middle Bay Tidal Flat as well as areas with eelgrass. The lowest TOC values occurred within the Exposed Shoreface-Recurved Spit area. Highest organism diversity and burrow density values were observed within regions possessing eelgrass.
Previous research has described various animal and sediment distributions within the bay, but no extensive research has been done which assays how and why animals respond to various sedimentologically and hydraulically derived ecological parameters. Assessment of integrated animal-sediment relationships along an exposed beach-middle to outer bay ecosystem is vital in furthering our understanding of these types of paleoenvironmental systems in the rock record, thus providing additional information to aid in the interpretation of various depositional environments.