Spatial variability of palaeosols across Cretaceous interfluves in the Dunvegan Formation, NE British Columbia, Canada: palaeohydrological, palaeogeomorphological and stratigraphic implications

Abstract

A basic sedimentological and palaeopedological framework is now in place for non‐marine sequence models. The variability of interfluve palaeosols has not, however, been systematically documented, nor have the stratigraphic implications of that variability been incorporated into sequence models. Interfluve palaeosol variability in the deltaic Dunvegan Formation, NE British Columbia, Canada, is investigated, for which a detailed allostratigraphic and palaeogeographic framework has been developed, based on abundant well (> 2300 logs) and outcrop (> 60 sections) control. Regionally extensive valley fills and interfluves have been mapped in coastal plain deposits over an area of about 50 000 km2. This palaeogeographic framework permits interfluve surfaces exposed in outcrop to be located in terms of distance from the margins of coeval valleys. The micromorphological, geochemical and mineralogical characteristics of five representative sequence‐bounding palaeosols located from 250 m to more than 15 km from coeval valley margins are described. These interfluve palaeosols are similar to modern Alfisols and all record (i) aggradation on an alluvial/coastal plain; (ii) a subsequent static and/or degradational phase related to valley incision, non‐deposition and soil thickening; and (iii) a final aggradational phase related to valley filling and renewed sedimentation across the coastal plain. Within this overall template, however, variations in palaeosol thickness, redoximorphic features, illuvial clay content and geochemistry suggest developmental control by hydrological characteristics that were influenced by both the nature of the underlying alluvial sediments and distance from the valley margin. The presence of mature interfluve palaeosols with complex developmental histories suggests that landscape dissection may have been related to terrace development associated with valley incision. Palaeosols closer to valley margins are thicker, contain more illuvial clay and display characteristics suggesting better drained conditions relative to those palaeosols that developed further from valley margins. Subsequent deposition on interfluves also reflects distance from valleys, with those sites close to valleys accumulating cumulic soils with evidence of brackish groundwater, whereas far from valleys (> 10–15 km), groundwater was fresh and clastic supply minimal, encouraging peat formation. Variations in drainage and palaeotopography during landscape dissection resulted in different palaeosol development styles on interfluve surfaces that can be shown, on the basis of physical correlation, to have the same geomorphic age. These observations support the concept of the soil‐forming interval as a basis for pedostratigraphic correlation in ancient terrestrial deposits. Palaeosol variability on interfluves is to be expected, and recognition and documentation of this variability is an important prerequisite to palaeogeomorphological, palaeoclimatic and sequence stratigraphic interpretations.

Sedimentological, geochemical and paleontological insights applied to continental omission surfaces: A new approach for reconstructing an eocene foreland basin in NW Argentina

“…Ti and Zr are found in minerals that are resistant to alteration and therefore tend to accumulate as weathering progresses. In uniform parent materials, Ti/Zr should change gradually and uniformly with depth, without sharp inflections or reversals in trends (McCarthy and Plint, 2003). At the Alemania profile (Fig.…”

“…Molecular ratios of relatively inert geochemical indicators have been used in many studies to help locate discontinuities in soils and paleosols (Al-Gailani, 1980;McCarthy and Plint, 2003). Ti and Zr are found in minerals that are resistant to alteration and therefore tend to accumulate as weathering progresses.…”

Response of Soils and Soil Ecosystems to the Pennsylvanian–Permian Climate Transition in the Upper Fluvial Plain of the Dunkard Basin, Southeastern Ohio, USA

“…Paleosols can be used to reconstruct landscape properties such as paleotopography and proximity to fluvial channels which can subsequently be used to interpret alluvial paleoenvironments and subenvironments [2,[28][29][30][31][32]. Local paleohydrology, erosional landscapes, sedimentation rates, and the time of formation can be interpreted using such properties as rhizoliths and gleization, truncation surfaces, paleosol type (cumulative, composite, compound), and paleosol maturity [2,3,33,34].…”

Micromorphology of Paleosols of the Marília Formation and their Significance in the Paleoenvironmental Evolution of the Bauru Basin, Upper Cretaceous, Southeastern Brazil

“…Paleosols have been used both in analysis and paleoenvironmental reconstructions (Andreis, 1981;Catt, 1990;Retallack, 2001;Sheldon and Tabor, 2009;Nascimento et al, 2017) by forming themselves into open systems capable of recording environmental conditions during their training, as in stratigraphic correlation (Brown and Kraus, 1988;Wright, 1992;Marriott and Wright, 1993;Kraus 1997;McCarthy and Plint, 2003), indicating a stable surface and representing moments of pause in erosion and deposition.…”