Fluvial system response to late Pleistocene-Holocene sea-level change on Santa Rosa Island, Channel Islands National Park, California

Fluvial sedimentary history of Arlington Canyon, Channel Islands National Park, California

“…Although we did not obtain a basal age for this section (it was covered by slumped bank material), we used the calibrated 14 C ages to determine an average aggradation rate of ~1.4 m ka ‐1 (for depths between 12.2 and 0.9 m) and project it downward to a depth of 14.5 m, the base of the section. This yields an estimate of ~18 ka for the onset of alluvial sedimentation at this site, which is consistent with the basal age determined for nearby Cañada Tecelote (Schumann et al , ). Combined with other basal ages obtained by Schumann et al (), these results indicate that the oldest post‐Last Glacial Maximum (LGM) alluvium on SRI is present in drainages in the northwest part of the island.…”

“…These horizons typically have sharp, but in some cases irregular, lower contacts, tend to grade upward from darker into lighter‐colored sediments, and may include gravel layers or lenses. We did not analyze these sediments for pollen due to its generally poor preservation in fluvial sediments, but an in‐stream wetland interpretation is supported by the presence of freshwater ostracodes in some of the darker layers (Schumann et al , ).…”

“…This yields an estimate of ~18 ka for the onset of alluvial sedimentation at this site, which is consistent with the basal age determined for nearby Cañada Tecelote (Schumann et al , ). Combined with other basal ages obtained by Schumann et al (), these results indicate that the oldest post‐Last Glacial Maximum (LGM) alluvium on SRI is present in drainages in the northwest part of the island. The uppermost alluvial sediments at section 47 are a dark‐colored, organic‐rich paleosol at 0.9 m depth that yielded an age of 8.43 ka, suggesting that floodplain aggradation in the downstream part of Arlington Canyon may have ceased around this time.…”

“…Because fluvial erosion and sedimentation is driven by autogenic as well as allogenic forcings, different processes can produce deposits that are similar in appearance but of different ages in disparate reaches of the drainage. This same pattern of localized differences in the sedimentary sequences was observed in other drainages on SRI as well (Schumann et al , ). Primary drivers of this phenomenon in Arlington Canyon include short‐term extreme events, e.g., floods; lateral migration of the channel across the floodplain; vertical incision of the channel; and local rejuvenation of tributaries.…”

Interpreting palaeofire evidence from fluvial sediments: a case study from Santa Rosa Island, California, with implications for the Younger Dryas Impact Hypothesis

“…This terrace sedimentary fill consists of fluvial and localized colluvial deposits that aggraded from the canyon base during the latest Pleistocene until the mid‐to late Holocene (Pinter et al , ; Schumann et al , ). This was followed by a cessation of deposition and reinitiation of incision that cut base level to the bottom of the canyon and exposed the Pleistocene to Holocene fill deposits in a narrow ‘slot canyon’ through the terrace (Schumann et al , ). The terrace fill sequence consists of several fluvial cut‐and‐fill packages, consisting of channel and floodplain deposits that pinch out laterally or grade into colluvial deposits at their margins.…”