Recognizing products of palaeoclimate fluctuation in the fluvial stratigraphic record: An example from the Pennsylvanian to Lower Permian of Cape Breton Island, Nova Scotia

Abstract

Tectonics and climate are the major extrinsic upstream controls on both the external and internal architectures of fluvial channels. While the role of tectonics has been well‐documented, the role of climate has received less attention. Because both tectonics and climate can produce similar stratigraphic architectures, the ability to recognize and differentiate these has major ramifications for the interpretation of fluvial stratigraphy. The Pennsylvanian to Permian succession of the Maritimes Basin complex on Cape Breton Island is ca 5 km thick, and is composed of predominantly non‐marine strata deposited within a series of depocentres characterized by different subsidence regimes. Basins in the west are transtensional depocentres characterized by episodic fault movement. In contrast, basins in the east were formed during prolonged periods of passive thermal subsidence. The stratigraphy is composed of four second‐order sequences (A to D), each 5 to 10 Myr in duration. These sequences are composed of amalgamated fluvial channel deposits that fine upwards into extensive mud‐dominated floodplain deposits with isolated fluvial channel bodies. A spectrum of fluvial styles is recorded within the study area including perennial, perennial/intermittent and ephemeral. Four stratigraphic intervals (E1 to E4) are recognized in which the deposits of strongly seasonal perennial/intermittent fluvial deposits are predominant. These intervals, 2 to 6 Myr in duration, are correlated across the study area between basins with differing tectonic regimes and do not correlate with a particular position in second‐order sequences. This suggests that climate exerted the dominant influence on the formation of these intervals and can be differentiated from tectonic imprints. While the tectonic regime of a particular basin exerted a fundamental control on the external architecture, a coherent record of climate change is recognized in the internal architecture of fluvial units. This study demonstrates that tectonic and climatic controls can be recognized and differentiated in vertical successions by evaluating the changes in fluvial architecture.

Morphodynamics of rivers strongly affected by monsoon precipitation: Review of depositional style and forcing factors

“…Some cases show downstream-tilted trunks and upstream anchoring root traces (Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014. Other cases preserve closely spaced groups of upright lycopsid or calamitid trunks and/or stems, together with their radially propagated, mainly horizontal root systems (Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014 (Fig. 14).…”

“…In-channel vegetation and vegetation-induced sedimentary structures have been suggested as another characteristic feature of seasonal river deposits, especially in sub-humid subtropics (Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014. In Table 1, 20% of the seasonal river deposits, mostly in monsoonal and sub-humid subtropical climates, are reported to contain in-channel vegetation (e.g., Singh and Bhardwaj, 1991;Singh et al, 1993Singh et al, , 2007Croke et al, 1998;Shukla et al, 2001;Fisher et al, 2008;Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014.…”

“…In Table 1, 20% of the seasonal river deposits, mostly in monsoonal and sub-humid subtropical climates, are reported to contain in-channel vegetation (e.g., Singh and Bhardwaj, 1991;Singh et al, 1993Singh et al, , 2007Croke et al, 1998;Shukla et al, 2001;Fisher et al, 2008;Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014. In-channel vegetation occurs as in situ and ex situ plant fossil adpressions and carbonaceous traces (Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014 (Fig.…”

“…4) have been linked to the transition from dune to plane bed deposition, related to Froude numbers just below what is needed for UFR plane beds (Bridge, 1981;Bridge and Best, 1988). Some seasonal river deposits contain a great variety of UFR structures (e.g., Abdullatif, 1989;North and Taylor, 1996;Fielding, 2006;Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014Plink-Björklund and Birgenheier, 2013) (Fig. 6).…”

“…14). Such intervals may be chaotically bedded or contain a variety of vegetation-induced sedimentary structures, such as centroclinal cross-stratification, bowl-shaped depressions, upturned beds around in situ tree stumps, scour-and-mound beds, and mudstone filled hollows with downturned beds (Rygel et al, 2004;Fielding et al, 2009;Allen et al, 2011Allen et al, , 2013Allen et al, , 2014 (Fig. 14).…”