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The Sedimentological and Ichnological Characteristics of the Mud-Dominated Fluvio-Tidal Deposits, The Petitcodiac River Estuary, NB, Canada


More sedimentological and ichnological research in the mud-dominated reaches of estuaries is needed to better understand the rock-record expression of inner-estuary deposits. Mud-dominated estuaries are under-represented in the literature, perhaps because muddy locales are delicate and difficult to work on. Another reason for the lack of muddy estuary studies is the outdated concept that mud deposition is simple and unimportant. However, recent efforts by many workers show that understanding mud-bed sedimentation is important for interpreting the sedimentary record. The meandering 79 km Petitcodiac River Estuary is also known as the Chocolate River due to the abundance of fine-grained sediment in the water. The river is located in the province of New Brunswick, Canada and debouches into the Bay of Fundy. The Petitcodiac River Estuary is characterized by the highest tides in the world and represents a well-mixed macrotidal estuary. The mean tidal range measured at the estuary entrance is 10.2 m. The detailed analysis of the mud-dominated point bars and tidal flats in the Petitcodiac River Estuary indicate that Inclined Heterolithic Stratification (IHS) is the dominant style of bedding. The IHS consists of interlaminated silty and sandy mud. Low-angle, planar bedding and ebb-oriented current ripples predominate. IHS strata forming the point bars dips channelward between 10-220. Tidal flats comprise 4-13 cm of very soft mud cover underlain by a comparably firm substrate. Individual beds can be traced along the entire length of the point bar and are occasionally disturbed by large-scale slumping. Mud ripples, tool casts, erosional tongues, rip-up clasts, desiccation cracks, streams of flocculated mud, and sediment binding bacteria/diatoms with patchy distribution have been observed on the tidal flat surface: all of these features have distinctive physical appearances that can be identified in rock-record examples. Low water salinity and high turbidity impose high ecological stress on the fauna, and explains the paucity of bioturbation. Tidal and seasonal processes influence the sedimentary textures and structures wherein the alternation between silty mud and sandy mud are associated with high fluvial outflow and low fluvial outflow respectively. The emerging pattern of mud deposition IHS development in the inner estuary is complex: the influence of sediment sources, the tidal range and fluvial flux are all important factors in shaping these deposits.