Ichnological Characteristics of Brackish Water Deposits

Late Quaternary drainage dynamics in northern Brazil based on the study of a large paleochannel from southwestern Marajó Island

“…The highly bioturbated nature of the sands overlying the discontinuity surface, and, particularly, the types of burrows, including Thalassinoides, Ophiomorpha, Diplocraterion, Planolites, and possibly Teichichnus (?) and rare Skolithos, are similar to assemblages recorded in many high energy, shallow marine to marginal-marine environments (Ekdale et al 1984, Wightman et al 1987, Griffis and Suchanek 1991, Pemberton and Wightman 1992, Beynon and Pemberton 1992, Buatois et al 1998, Gingras et al 1999. The fact that these traces continue below the discontinuity surface, where they form an endured horizon having trace fossils characterized by hard walls, is consistent with firm grounds, typical of Glossifungites ichnofacies Frey 1985, MacEachern et al 1992).…”

“…In particular, the double mud drapes separating alternating thicker and thinner foreset packages their imprint in these sediments, which is probably due to the influence of strong fluvial inflow. The overall absence of bioturbation, commonly abundant in association with many tidal channels recorded in the literature (e.g., Pemberton and Wightman 1992, MacEachern and Pemberton 1994, Rossetti 2001, conforms to a stronger influence of freshwater input relative to marine flows. Structures eventually attributed to tidal reworking, added to the dominance of well-sorted and well-to sub-rounded sands, are features that assure a coastal location for these fluvial dominated paleochannels.…”

Paleosalinities in ancient brackish water systems determined by 87Sr/86Sr ratios in carbonate fossils: A case study from the Western Canada sedimentary basin

“…To substantiate brackish water deposition, a wide variety of indicators are used including: ( 1) inferences on the ecological affinities of various macrofauna or microfauna (Pickerill and Brenchley, 1991)) (2) palynology (Banejee and Davies 1988), (3) ichnology (Pemberton and Wightman, 1992), (4) identification of syneresis cracks (Plummer and Gostin, 1981), (5) basin geometry (Zaitlin et al, 1994), and (6) presence of tidal structures (Howard and Frey, 1973;Thomas et al, 1987). Even when ancient sediments can be shown to have brackish water affinities by these methods, what is implied is that neither fully marine nor fully freshwater conditions prevailed during sediment deposition.…”

A rich ichnofossil assemblage from the Frasnian (Upper Devonian) deposits at Andoma Hill, Onega Lake, Russia

“…In the palaeoenvironmental reconstructions, mixture of traces characteristic of both the Skolithos and Cruziana ichnofacies sometimes has been interpreted as brackish water fauna (Pemberton & Wightman 1992). Brackish water fauna can be considered an impoverished marine assemblage, with endobenthic forms more abundant than the epibenthic ones.…”