Cape Fold Belt

From Wikipedia, the free encyclopedia

Small (Klein) Swartberg Ranges, seen from the Laingsburg area
Small (Klein) Swartberg Ranges, seen from the Laingsburg area
 This article does not cite any references or sources. (October 2007)
Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.

The Cape Fold Belt is the folded sedimentary sequence of rocks in the southwestern corner of South Africa. It is related to the Ventana Mountains near Bahia Blanca in Argentina. The rocks are generally sandstones and shales, with shales forming the valleys and the erosion resistant sandstones forming the parallel mountain ranges, reaching a maximum height at Seweweekspoortpiek (Afrikaans: Seven Weeks Defile Peak) at 2325m.

The rocks were laid down as sediments in a coastal delta environment upon the Malmesbury unconformity in the Ordovician (450ma) period, with the folding subsequently occurring in the Carboniferous and Permian periods during the merging of the supercontinent Pangaea. Even though the mountains are very old by Andean and Alpine standards, they remain steep and rugged, owing to the resistant nature of the quartzitic sandstones of the Table Mountain Group. The famous Table Mountain is comprised of hard rocks of the Peninsula Formation of the Table Mountain Group. The geographic range of the Cape Fold Belt is from Cape Town in the west and the Cederberg Mountains in the northwest to Port Elizabeth in the east.

The mountains, although mediocre in height by world standards, remain extremely majestic and dramatic to the eye. This is due in part to numerous geological factors; The ranges usually have few to no foothills and rise directly from the valley floor. The mountain's base is usually at or near sea level. The ranges are generally steep and rugged, due to their quarzitic sandstone geology making them very resistant to weathering.

[edit] Oregeny

Rock formations of the Swartberg
Rock formations of the Swartberg

The mountains are not particularly young, despite their old-looking appearance. They are considered middle-aged in Geologic terms. They were created during continental collision when Pangaea, the supercontinent formed from the late Carboniferous to Permian periods. Their stature is mostly due to their weather-resistant rocks of quartzitic sandstone, with the shale formations generally forming the valleys, capped by alluvial deposits, which are generally Quaternary in age.

The mountains were folded during this period and were still buried beneath the earth's surface. Due to the extreme temperatures and lithic pressure at these depths, folding was not a brittle process, as the rocks retained a "plastic" constituency, making the Cape Fold Mountains spectacular in their exposed folded, faulted and twisted sedimentary strata. A number of parallel faults still runs roughly parallel with the coast, having formed during the Gondwanaland rifting when South America separated from Africa. Patagonia was to the west of Cape Town and the Falkland Islands were to the south during the Jurassic period prior to separation. This faulting has caused the Table Mountain Sandstone to be exposed closer to and above sea level close to the coast, but gradually becoming deeper embedded in the overlying strata further inland, excluding areas where folding has caused anticlines to expose the rocks higher up (eg. Swartberg Mountains north of the Oudtshoorn Fault.

The opening of Pangaea and subsequently Gondwanaland also aided in their "conservation" as a range, as the Cape Supergroup of rocks were capped by the deposition of the Karoo Sequence of sedimentary deposits, including the Dwyka Formation, which is compacted glacial till deposited during the late Permian southern ice age.

[edit] The Ranges

The largest individual ranges within the Cape Fold Belt include (translations in brackets) from west to east:

(berg is Afrikaans for mountain. Plural is 'berge')