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The geology of Cherokee Caverns
Published in Barry F. Beck, Felicity M. Pearson, Karst Geohazards, 2018
Cherokee Caverns appears short today owing to the effects of erosion through geologic time. As stream and river channels changed their courses through time, their downcutting cut off segments of the original river passage. The original river passage became truncated, often sealed by collapse against hillsides. As rivers and streams continued to downcut through the area, some sections of the original cave remained active, while others were totally abandoned. Other segments became plugged with mud. Look outward from the entrance of Cherokee Caverns and envision streams cutting down through the cave’s roof, removing sections of the cave, and carving the valley below. Further to the southwest, the Clinch River meandered (six times) across what may have been the former route of Cherokee Caverns, further truncating the down-river portion of the original cave.
Hundalee Fault, North Canterbury, New Zealand: late Quaternary activity and regional tectonics
Published in New Zealand Journal of Geology and Geophysics, 2023
David J. A. Barrell, Mark W. Stirling, Jack N. Williams, Katrina M. Sauer, Ella J. van den Berg
We consider that the high terrace landform set is no younger than ∼30 ka (onset of the most recent lowstand). We infer a likely representative age of ∼65 ± 5 ka for the highest parts of the landform set, associated with an incised low-stand channel inferred to have discharged into the Conway Trough at the location of the star in Figure 10 (also see Supplement). We attribute the flight of high terrace remnants to progressive incision due to uplift, under the generally low sea level conditions of MIS 3 (~70–30 ka; Figure 7) which would have maintained the shoreline at or below the shelf edge. We suggest that the low terrace landform set reflect terraces formed during episodic uplift following culmination of the Holocene sea level rise, perhaps with coastal erosion contributing to downcutting and terrace formation (Figure S3B). The 3.5 ka alluvial fan deposits in the Okarahia fault trench provide a minimum age for the underlying Okarahia Stream alluvium of the 8-m-terrace, part of the low terrace landform set. One possibility is that the ∼3.2 ka coastal uplift event registered just north of Haumuri Bluffs induced downcutting of Okarahia Stream and contributed to the abandonment of fluvial activity on the 8-m terrace at the Okarahia trench site.
The age and origin of Sydney Harbour and the Parramatta River: the Cenozoic history of the coastal rivers of central New South Wales
Published in Australian Journal of Earth Sciences, 2023
Second, rather than following a more straightforward route downstream of Drummoyne, the river cuts through the upland barrier of the Hornsby Plateau to reach the sea at Port Jackson. Three alternative mechanisms may be employed to explain discordant drainage patterns of this sort. The first is that the river has developed along a pre-existing line of weakness. The main part of Sydney Harbour is aligned parallel to a suite of local, east-southeast-aligned dyke and joint sets (Herbert, 1983a; Herbert, 1983b, pp. 105–106; Norman, 1968, p. 13, figure 44) and lies along the northern edge of the Lachlan Transverse Zone (Figure 8a), which appears to form a broad trough on the eastern side of the Cumberland Basin (Herbert, 1983c, p. 115). These features may have controlled the alignment of a downcutting stream or the location of a headwardly eroding river. It is unlikely, however, that they could have directed the course of a river across an established topographic barrier. Unless headward erosion captured an existing basin on the inland side of the obstacle, it is difficult to see how the catchment of the river could have become sufficiently enlarged to create a regional-scale drainage path. Significantly, there is no evidence in the landscape of either stream piracy or drainage re-routing to support the idea of an antecedent upstream basin whose discharge has been redirected along the lower Parramatta River.
Geochemical evolution of high-pH sodic salt pans in Central Otago, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2022
Dave Craw, Cathy Rufaut, Dhana Pillai, Gemma Kerr
The floor of the upper Clutha basin in the vicinity of Mahaka Katia reserve is dominated by a broad late Pleistocene gravel terrace (∼70 ka; upper terrace in Figure 2A–C; Turnbull 2000). Subsequent erosional downcutting has left progressively lower terrace levels above the modern Clutha River level at Lake Dunstan (Figure 2C). Most of the saline pans of interest in this study are located on a terrace level ∼10 m below the upper terrace level (middle terrace; Figure 2A–C) that is ∼200 m wide. This middle terrace is coated with loess of presumed Late Pleistocene-Holocene age, in a discontinuous deposit up to 1 m thick, with the thickest deposits immediately downslope of the upper terrace riser (Figure 2C). The loess has been extensively reworked by surface water since original aeolian deposition (Figure 2C). Extensive aeolian and surface water reworking may have occurred during the 1950s when the area was bare of vegetation (Figure 2B, C). An additional small area of loess pans occurs on the eastern edge of the middle terrace, and these pans have remained largely unchanged since the 1950s (Figure 2A, B; Figure 3A, B).