A mid to late Holocene history of floodplain and terrace reworking along the middle Delaware River valley, USA Gary E. Stinchcomb a, ⁎, Steven G. Driese a , Lee C. Nordt a , Peter M. Allen b a Terrestrial Paleoclimatology Research Group, Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798–7354, USA b Department of Geology, Baylor University, One Bear Place #97354, Waco, TX 76798–7354, USA abstract article info Article history: Received 12 December 2011 Received in revised form 16 April 2012 Accepted 17 April 2012 Available online xxxx Keywords: Holocene Alluvial stratigraphy Buried soils Avulsion Incision Climate This study tests and refines the traditional floodplain development model for the partly confined middle Del- aware River valley, which has shown that the main channel was relatively stable and flanked by a 6000–8000 year old, vertically accreting alluvial terrace. The Holocene alluvial processes and history pres- ented here in 6 fluvial phases were reconstructed using morphostratigraphy, 36 profile descriptions, 332 grain size analyses, and 82 14 C ages from soil trenches, auger borings, and archaeological excavations. Fluvial phases I–III largely validate previous reconstructions showing a late Pleistocene (I: > 10.7 ka) braided stream transition into an early Holocene wandering stream with prolonged floodplain stability (II: 10.7–8 ka), followed by early–middle Holocene erosion and then deposition (III: 8–5 ka). The early and middle Holocene changes in alluvial stratigraphy and sedimentology broadly correlate with climatically derived Holocene sub- divisions, suggesting climate change partly controls alluvial response along the middle Delaware River valley. This study documents for the first time a middle Holocene episode of channel incision occurring sometime between 6.0 and 5.0 ka. Although the results reconfirm that the majority of alluvial landforms are composed of vertical accretion deposits, we present here new evidence of oblique, abandoned channel, and lateral ac- cretion deposits inset to similar landforms with different formation histories (i.e., polycyclic terrace develop- ment), depicting a river valley that has experienced floodplain and terrace reworking. The majority of floodplain and terrace reworking occurs during the late–middle and late Holocene phases IV–VI (5.5–0 ka), following the middle Holocene incision event. These phases demonstrate floodplain reworking processes in the form of channel abandonment, stripping, flood channeling, and convex bank erosion. The subsequent space filled rapidly with evidence of multistory soil formation, and eventually resulted in alluvial fill terraces with heights comparable to older surfaces. The most recent fluvial phase, VI (1.0–0 ka), shows markedly faster sedimentation rates and coarser flood deposits associated with peak prehistoric population and the onset of Euroamerican settlement. The results presented here contribute newly documented evidence of ero- sion and depict a river valley that has undergone middle Holocene incision and floodplain and terrace reworking since the late–middle Holocene. Stream modelers, fluvial geomorphologists and geoarchaeologists working in the NE USA should consider floodplain reworking processes when examining alluvial history and predicting changes in stream dynamics. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Floodplains figure prominently as global resources because of their biological productivity, ecological diversity, and overall econom- ic importance (Tockner and Stanford, 2002). Understanding how cli- mate change and land use influences floodplain development will be useful for mitigating future impacts. Floodplain development models (based largely on alluvial stratigraphy, fluvial sedimentology, and various forms of absolute and relative chronology) are critical for understanding the fate of floodplains as sediment reservoirs and ecological resources. Early models of floodplain development suggested that floodplains consist mostly of lateral accretion deposits overlain by a veneer of vertical accretion deposits (Wolman and Leopold, 1957; Jackson, 1976; Nanson and Croke, 1992, references therein). Ritter et al. (1973) challenged these earlier models and showed that a portion of the Delaware River valley bottom was com- posed of a thick succession of vertical accretion deposits, with no ev- idence of lateral accretion deposits. The data also suggested that no distinct episodes of floodplain erosion were present and the channel had been flowing in its present course since the early–middle Holo- cene. Subsequent studies within the same river valley (Crowl and Stuckenrath, 1977; Vento et al., 1989; Stewart, 1991; Stewart et al., 1991) and elsewhere have shown that in stable channel settings many floodplains will aggrade by vertical and oblique accretion Geomorphology xxx (2012) xxx–xxx ⁎ Corresponding author. Tel.: + 1 254 710 2361; fax: +1 254 710 2673. E-mail address: gary_stinchcomb@baylor.edu (G.E. Stinchcomb). GEOMOR-03983; No of Pages 19 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2012.04.018 Contents lists available at SciVerse ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Please cite this article as: Stinchcomb, G.E., et al., A mid to late Holocene history of floodplain and terrace reworking along the middle Del- aware River valley, USA, Geomorphology (2012), doi:10.1016/j.geomorph.2012.04.018