IGU – CGE Stellenbosch Conference: GEOCONFERENCE FIELD TRIP

Monday 27th October 2025

Clarence Drive, Stony Point & Harold Porter Gardens (Betty’s Bay), Hermanus: Gearing’s Point & Sansa

The Field Excursion Guide provides an overview of the western and southern Cape geology, comprising +600Ma of Late-roterozoic/Paleozoic basement rocks of the Malmesbury Group, related Cambrian Cape Granites, extensive overlying Palaeozoic Cape Supergroup (Table Mountain Sandstones & Bokkeveld sediments), and cover rocks of the Cenozoic Bredasdorp Group.

Ancient erosional land-surfaces, well preserved and documented sea-level changes, including raised and drowned-beaches, complete the spectrum of exceptional geology and earth evolution that shape the southern Cape landforms.

The excursion along Clarence Drive, the flank of the Kogelberg Mountains, Aasbank and Harold Porter Botanical Gardens (HPG) at Betty’s Bay, Benguela Cove (on the Bot River Estuary), to Hermanus, offers exceptional insight into the basement and younger geology of the southern Cape Region, which is being continuously reshaped by robust recent and present-day geological processes.

At HPG, 4.6 Billion years of earth evolution is presented in a comprehensive Earth Age Display (EAD) with an emphasis on the evolution and geological events that shaped the southern African region.

Time permitting (or on another day), there are also excellent geological features and a wealth of

anthropological history along the Hermanus Cliff Path, Walker Bay margin, Hemel + Aarde Wine Valley, and the Kelders Caves on the eastern-edge of the Bay.

The important Hermanus + Fernkloof TMS aquifers, Steenbras aquifers, Sir Lowry’s Pass with its False Bay dolerite suite forming the historical Gantouw (Eland) Pass (cross-cutting Sir Lowry’s Pass), are further highlights that add to the geological journey around the area.

The geology of the Western Cape was in the past been dominated by the iconic Table Mountain

Sandstones, represented by the magnificent slab of rocks that tower above the City of Cape Town, and extensive blanket of younger rocks of the Table Mountain Group (TMG), or else concealed by soils and vegetation, buried in wheatfields, vineyards, and indigenous Fynbos vegetation. As Kisters noted in 2016, less than 2% of the surface area of the Western Cape exposes rocks that constitute ‘geological basement’, yet previously these older rock assemblages were the focus of wideranging geological studies and many scientific publications.

In the past 20 years extensive new field mapping, geochemistry, isotope and dating studies have led to a better understanding of the evolution of the basement rocks, overlying sequences, structural history, and younger events that have reshaped the southern-most part of the African continent. The fascinating TMG assemblages and TMS aquifers have likewise being reinterpreted. Detailed work and studies of younger land and marine geology, structural events and climate change dynamics of the western and southern Cape Coast are now leading the way.

Modern geoscience research, in particular of the coastal regions of the southern Cape and our Early Ancestors are reshaping prior geological notions and views, making this region one of the most revisited localities of modern geological and anthropological research and findings.

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20251027-OGG-Clarence Dve_Bettys Bay_HPG_Hermanus-Excursion Guide -7 October 2025.pdf

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