To access this Earth Cache it is best to use the local Trail Entrance, there is a trail fee payable but the company keeps the area clean and all the trails well marked. The Earth Cache is accessible from the short easier trail but will require a steep climb even from the more direct service routes.
You can pick your poison of doing it on foot or via Mountainbike. but take your time and enjoy the park as there is a lot to see and also a good place for the end of your excursion in the park.
While hiking the trail we stopped at the nearby Geocache for the group to find. As I had previously found it I was not focusing on the cache finding and instead stumbled upon a unique phenomenon on the ground.
These rings are known as Liesegang bands and are formed by Concretion
Strange as they may look these bands occur naturally within many sedimentary rocks and less commonly within igneous and metamorphic rocks. At some point after the rock formed it was buried and saturated with iron-rich groundwater and the bands, which are typically an iron-rich mineral such as limonite, precipitated within the rock in repeating rings. Later, it was exposed at the surface and the softer sandstone eroded away leaving the harder rings standing in relief on the rock.
Liesegang bands can form an array of visually stunning patterns. Sometimes they form near-perfect cylinders that resemble iron pipes.
The local Geological group known as Timeball Hill and Rooioogte Formations it is made up of Mudrock, quartzite (ferruginous in places), wacke, chert breccia, minor diamictite, conglomerate, shale, magnetic ironstone
The Timeball hill and Rooioogte Formations form part of the greater Transvall SuperGroup
In order to log this Earth Cache Please complete the following:
1) Post a defining photo of yourself, an identifiable object or paper with the date of your visiting to your log
2) Answer these questions in an email or message to me;
2.1) Which rock type would be present at this location showing the Liesegang bands?
2.2) What is the colour of this rock and why would it be this colour?
2.3) Describe why these rocks have this unique shape to them?
References:
Liesegang rings (also called Liesegangen rings or Liesegang bands) are colored bands of cement observed in sedimentary rocks that typically cut across the bedding. These secondary (diagenetic) sedimentary structures exhibit bands of (authigenic) minerals that are arranged in a regular repeating pattern. Liesegang rings are distinguishable from other sedimentary structures by their concentric or ring-like appearance. The precise mechanism from which Liesegang rings form is not entirely known and is still under research, but there is a precipitation process that is thought to be the catalyst for Liesegang ring formation, referred to as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle. Though Liesegang rings are considered a frequent occurrence in sedimentary rocks, rings composed of iron oxide can also occur in permeable igneous and metamorphic rocks that have been chemically weathered.
The process by which Liesegang rings develop is not completely understood. Liesegang rings may form from the chemical segregation of iron oxides and other minerals during weathering. One popular mechanism suggested by geochemists is that Liesegang rings develop when there is a lack of convection (advection) and has to do with the inter-diffusion of reacting species such as oxygen and ferrous iron that precipitate in separate discrete bands which become spaced apart in a geometric pattern. A process of precipitation known as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle is known by the geologic community as a probable mechanism for Liesegang ring formation in sedimentary rocks. In this process the "...diffusion of reactants leads to supersaturation and nucleation; this precipitation results in localized band formation and depletion of reactants in adjacent zones." As Ostwald suggests, there is a localized formation of crystal seeds that occurs when the right level of supersaturation is reached, and once the crystal seeds form, the growth of the crystals is believed to lower the supersaturation level of fluids in pore spaces surrounding the crystals, thus mineralization that occurs after the initial crystal growth in the surrounding areas develops in bands or rings. One classic example based on the Ostwald-Liesegang hypothesis is observed in water and rock interactions where iron hydroxide precipitates in sandstone through pore space.
Liesegang ring patterns are considered to be secondary (diagenetic) sedimentary structures, though they are also found in permeable igneous and metamorphic rocks that have been chemically weathered. Chemical weathering of rocks that leads to the formation of Liesegang rings typically involves the diffusion of oxygen in subterranean water into pore space containing soluble ferrous iron. Liesegang rings usually cut across layers of stratification and occur in many types of rock, some of which more commonly include sandstone and chert. Though there is a high occurrence of Liesegang rings in sedimentary rocks, relatively few scientists have studied their mineralogy and texture in enough detail to write more about them. Liesegang rings are referred to as examples of geochemical self-organization, meaning that their distribution in the rock does not seem to be directly related to features that were established prior to Liesegang ring formation. For instance, in certain types of sedimentary rocks such as carbonate siltstones (calcisiltites), Liesegang ring patterns can be misinterpreted for faults; the rings may appear to be "offset," however the laminae in the rock exhibit an unbroken pattern, therefore the observed offset is attributed to pseudo faulting. Pseudofaults are the result of Liesegang rings developing within areas of the rock that are adjacent to each other but at varying stratigraphic levels. Liesegang rings can have the appearance of fine lamination and can be mistaken for laminae when parallel or subparallel to the bedding plane, and are more easily differentiated from laminae when the rings are observed cutting across beds or lamination.