Plan-form evolution of ancient meandering rivers reconstructed from longitudinal outcrop sections


SEDIMENTOLOGY, vol.61, no.4, pp.952-977, 2014 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 61 Issue: 4
  • Publication Date: 2014
  • Doi Number: 10.1111/sed.12081
  • Journal Name: SEDIMENTOLOGY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.952-977
  • Keywords: thalweg trajectory, Palaeogene, point-bar architecture, fluvial palaeochannel, Boyabat Basin, meander-bend transformation, Turkey, BRITISH-COLUMBIA, BLACK-SEA, POINT-BAR, HIMALAYAN FOREDEEP, PETROLEUM GEOLOGY, FLUVIAL SYSTEMS, BEATTON RIVER, DEPOSITS, MODEL, HISTORY
  • Akdeniz University Affiliated: No


The mode of channel-bend transformation (i.e. expansion, translation, rotation or a combination thereof) has a direct bearing on the dimensions, shape, bedding architecture and connectivity of point-bar sandstone bodies within a fluvial meander belt, but is generally difficult to recognize in vertical outcrops. This study demonstrates how the bend transformation mode and relative rate of channel-floor aggradation can be deciphered from longitudinal outcrop sections aligned parallel to the meander-belt axis, as a crucial methodological aid to the reconstruction of ancient fluvial systems and the development of outcrop analogue models for fluvial petroleum reservoirs. The study focuses on single-storey and multi-storey fluvial meander-belt sandstone bodies in the Palaeogene piggyback Boyabat Basin of north-central Turkey. The sandstone bodies are several hundred metres wide, 5 to 40m thick and encased in muddy floodplain deposits. The individual channel-belt storeys are 5 to 9m thick and their transverse sections show lateral-accretion bed packages representing point bars. Point bars in longitudinal sections are recognizable as broad mounds whose parts with downstream-inclined, subhorizontal and upstream-inclined bedding represent, respectively, the bar downstream, central and upstream parts. The inter-bar channel thalweg is recognizable as the transition zone between adjacent point-bar bedsets with opposing dip directions into or out of the outcrop section. The diverging or converging adjacent thalweg trajectories, or a trajectory migrating in up-valley direction, indicate point-bar broadening and hence channel-bend expansion. A concurrent down-valley migration of adjacent trajectories indicates channel-bend translation. Bend rotation is recognizable from the replacement of a depositional riffle by an erosional pool zone or vice versa along the thalweg trajectory. The steepness of the thalweg trajectory reflects the relative rate of channel-floor aggradation. This study discusses further how the late-stage foreland tectonics, with its alternating pulses of uplift and subsidence and a progressive narrowing of the basin, has forced aggradation of fluvial channels and caused vertical stacking of meander belts.