Chronosequence development and soil variability from a variety of sub-alpine, post-glacial landforms and deposits in the southeastern San Juan Mountains of Colorado Bradley G. Johnson a, ⁎, Anthony L. Layzell b , Martha Cary Eppes c a Davidson College, Environmental Studies, 209 Ridge Rd., Davidson, NC 28036, USA b Kansas Geological Survey, University of Kansas, Lawrence, KS 66047, USA c Department of Geography and Earth Sciences, University of North Carolina — Charlotte, McEniry 324, 9201 University City Blvd., Charlotte, NC 28223, USA abstract article info Article history: Received 17 July 2014 Received in revised form 16 December 2014 Accepted 20 December 2014 Available online xxxx Keywords: Chronosequence Extractable iron Post-glacial San Juan Mountains Parent material Variability Sub-alpine Surficial processes acting on post-glacial alpine and sub-alpine landscapes vary at small temporal and spatial scales and are thus often difficult to conceptualize in the context of large-scale landscape evolution models. Soils developing in this setting can thus provide valuable information about landform genesis, sedimentology and age. Relatively few post-glacial chronosequences have been examined in these settings however, particularly for the variety of landforms and parent materials that exist within alpine and sub-alpine environments. Here, we examine a chronosequence of relatively young, post-glacial landforms with varying parent materials and climate histories. We dug and described 39 soil pits in the upper Conejos River Valley of Colorado on a variety of deposits and landforms, including alluvial fans, terraces, colluvium, glacial till, and terminal moraines, and compared soil properties with radiocarbon ages from the area. Our results suggest that some typical chronosequence soil prop- erties (e.g., pH, structure, color) do not correlate with time over short time scales. However, extractable iron ra- tios (Fe o /Fe d ) show a relatively strong correlation with age across late-Pleistocene and Holocene time scales and maximum profile clay content shows a weak but statistically significant relationship with age. Both of these trends are stronger when examined across a single parent material. Differences in initial parent material texture and dust inputs seem to be the most significant complicating factors over post-glacial time scales. Soil property development through time is most inconsistent in cumulic alluvial fan soils. This observation may indicate that alluvial fans are more responsive to sub-basin scale processes as opposed to fluvial terraces that are more likely respond to processes active across the entire basin. These differences would explain why stratigraphically similar alluvial fans are mantled by soils with varying development. Nonetheless, horizonation, clay content, and extract- able iron ratios provide a useful tool for correlating young deposits, assigning ages, and interpreting the geomor- phic history of complex post-glacial environments. © 2015 Published by Elsevier B.V. 1. Introduction Accurate chronologies are key elements of geomorphic mapping and the interpretation of surface morphology. Soil chronosequences have long been used to provide inexpensive relative ages of landforms and deposits, which in turn allows for the investigation of landscape evolu- tion where numerical age dating is limited. In addition, soils can yield important information relating to incision and sedimentation rates (e.g., Birkeland et al., 2003; Leigh and Webb, 2006), landscape response to climate change and anthropogenic impacts (Eppes et al., 2008; Johnson et al., 2013; Layzell et al., 2012b, e.g., McFadden and McAuliffe, 1997), as well as alluvial response to intrinsic variability (Eppes and McFadden, 2008). Despite their importance as tools for investigating and reconstructing the geomorphic history of landscapes, few soil chronosequences have been created for the post-last glacial maximum (LGM) deposits of alpine and sub-alpine environments in the Rocky Mountains (e.g., Birkeland et al., 1987). Developing soil chronosequences in alpine and subalpine environ- ments is complicated by the overall young age of soils (e.g., Birkeland et al., 1987), which have typically only begun forming in the last 15 cal. kyr BP, since glacial retreat. In fact, few existing alpine chronosequences have attempted to discern variability in soil develop- ment at sufficiently short time scales to differentiate post-LGM deposits. The lack of established chronosequences is likely because it is not clear if traditional indicators of soil age such as color change and the presence of illuvial clays can be sufficiently differentiated between these relative- ly young deposits. Additionally, post-LGM climates have been shown to be quite variable (e.g., Jiménez-Moreno et al., 2008; Johnson et al., 2013), which further complicates chronosequence development. Catena 127 (2015) 222–239 ⁎ Corresponding author. E-mail address: brjohnson@davidson.edu (B.G. Johnson). http://dx.doi.org/10.1016/j.catena.2014.12.026 0341-8162/© 2015 Published by Elsevier B.V. Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena