R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS SOUTH AFRICAN JOURNAL OF GEOLOGY 2024 • VOLUME 127.3 PAGE 641-664 • doi :10.25131/sajg.127.0033 641 Regional variance in alluvial sedimentation and revised stratigraphy of the Klipheuwel Group and Franschhoek Formation R.F. Raath Department of Earth Sciences, University of Stellenbosch, Stellenbosch 7600, South Africa TECT Geological Consulting, Unit 3 Metrohm House, 20 Gardner Williams Ave, Somerset West, South Africa e-mail: ruanraath.geo@gmail.com; 0000-0002-7758-8522 C.R. Penn-Clarke Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa e-mail: cameron.penn-clarke@wits.ac.za; 0000-0003-2054-4673 A.F.M. Kisters Department of Earth Sciences, University of Stellenbosch, Stellenbosch 7600, South Africa e-mail: akisters@sun.ac.za; 0000-0003-3246-3053 © 2024 Geological Society of South Africa. All rights reserved. Abstract The siliciclastic sediments of the Klipheuwel Group mark the transition from Pan-African tectonism and amalgamation of Southwest Gondwana to the shallow marine deposits of the Cape Supergroup in the Western Cape. The rocks are preserved in a number of seemingly isolated depositories and previous studies have mainly focused on selected occurrences. The lack of any integration of regional sedimentological or structural characteristics has, to date, resulted in only tentative stratigraphic correlations and subdivisions of the Klipheuwel Group. Lithological and structural data from the Klipheuwel Group indicate at least two separate depocentres that accommodated the post Pan-African peneplanation of the Saldania Belt and clastic detritus in distinctly different palaeoenvironments. A northern depocentre can be distinguished from a southern depocentre, each characterised by distinct architectural elements and facies associations that reflect topographic and structural controls. The northern depocentre, including Klipheuwel Group occurrences at Eendekuil, Redelinghuys and Elands Bay, show laterally persistent braided fluvial facies associations that developed multi-storey superimposed ‘braided sheet’ deposits. Here, the rocks show gentle dips and thicknesses range from 300 to 450 m. The southern depocentre, including the Klipheuwel and Klapmutskop localities, are characterised by much larger thicknesses (up to >2 000 m), steep dips of the rocks and laterally discontinuous braided fluvial facies associations that developed staggered channelised braided deposits. The lateral continuity of fluvial facies in the northern depocentre reflect sedimentation on a peneplained basement. The larger thickness, steep dips and strongly channelised deposits in the southern facies, in contrast, indicate deposition in actively subsiding half-graben structures that reactivated basement faults. The spatially closely associated Franschhoek Formation shares numerous characteristics with the Klipheuwel Group but preserves Pan-African strains similar to that of the underlying Malmesbury Group, that may indicate its formation as compressional piggyback basins with synorogenic sedimentation. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 https://doi.org/10.25131/sajg.127.0033 https://orcid.org/0000-0002-7758-8522 https://orcid.org/0000-0003-2054-4673 https://orcid.org/0000-0003-3246-3053 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 642 SOUTH AFRICAN JOURNAL OF GEOLOGY Introduction The Cambrian Klipheuwel Group is a coarse-grained siliciclastic succession preserved as small, northwest-trending and typically elongated, but isolated outcrops that can intermittently be traced over a distance of >100  km in the Western Cape Province (Figure 1). The succession unconformably overlies folded Ediacaran-Cambrian metasedimentary and granitic intrusive rocks of the Malmesbury Group and Cape Granite Suite and are in turn erosively overlain by the Ordovician Table Mountain Group (De Villiers, 1980; South African Committee for Stratigraphy, 1980; Theron et al., 1992) (Figure 1). As such, the clastic sequence is an important time marker that chronicles the transition from Pan-African tectonism and the amalgamation of southwest Gondwana to post-orogenic collapse (Tankard et al., 2009), initiating the shallow marine deposition of the Cape Supergroup in the early Phanerozoic (Shone and Booth, 2005). Herein lies the debated genesis of the Klipheuwel Group, namely that: the Klipheuwel Group being associated with the formation • of the Saldanian belt (Gresse et al., 2006), or that of the Klipheuwel Group being associated as an early • sedimentation phase of the Cape Supergroup depocycle (Tankard et al., 2009). The type locality of the Klipheuwel Group, the Klipheuwel quarry, between Stellenbosch and Malmesbury, manifests a steeply-dipping, up to 2 000 m thick succession that may be subdivided into a lower Magrug Formation and an upper Populiersbos Formation, although the formation-level status of the latter has not yet been approved by the South African Committee for Stratigraphy (SACS) (Figure 1) (SACS, 1980; Theron et al., 1992). The Magrug Formation comprises a lower conglomerate package that grades upwards into a 900 m-thick sequence of medium- to coarse-grained sandstone, interbedded with conglomerate and granulestone, followed by several hundred meters of fine- to coarse-grained sandstone with interbedded shale (SACS, 1980; Gresse et al., 2006). The Populiersbos Formation comprises the upper 50 m of the Klipheuwel Group and consists of purple- to red-coloured shales and mudstones which overlie the Magrug Formation (SACS, 1980; Gresse et al., 2006). Although this stratigraphic subdivision has been used to describe the Klipheuwel Group at its type locality (SACS, 1980; Gresse et al., 2006), its application to other occurrences is problematic. Studies on individual exposures assigned to the Klipheuwel Group show conflicting stratigraphies, sedimentological characteristics, total thickness variations and inconsistent structural controls compared to those at the type locality (SACS, 1980). This highlights the need for the integration of different sedimentary facies in different localities into regional depositional models and the formulation of a stratigraphic subdivision that is applicable on a regional scale. This also includes the integration of similarly old sedimentary sequences such as the Franschhoek Formation, which is compositionally akin to the Klipheuwel Group and in a stratigraphically similar position, sandwiched between the Malmesbury Group and the Cape Supergroup. However, the actual stratigraphic position of the Franschhoek Formation within either the older Malmesbury Group (De Villiers, 1980; Gresse et al., 2006; Kisters and Belcher, 2018) or forming part of the Klipheuwel Group remains controversial (Frimmel et al., 2013). The aim of this study is to conduct an integrated, in- depth facies analyses of several prominent Klipheuwel Group exposures which would create a foundation to establish regional lithological correlations and variations across known outcrops. An in-depth facies analysis will help to deduce likely palaeoenvironments that prevailed during the time of deposition. These descriptive and interpretive similarities and differences between outcrops will assist our understanding of the genesis of the Klipheuwel Group as well as provide a basis from which to proceed classifying and categorising the Klipheuwel Group. Previous work on the Klipheuwel Group and Franschhoek Formation The first to distinguish Klipheuwel beds from the younger Table Mountain Group was Du Toit (1926). He identified a northwest- trending corridor of outcrops made up of steep northeasterly dipping, coarse-grained siliciclastics, unconformably overlying folded Malmesbury shales between Klapmutskop and Klipheuwel, north of Stellenbosch (Figure 1). Du Toit (1926) also noted a close resemblance of these units in the south to clastic sedimentary, but near-horizontal rocks exposed in the upper parts of Heuningberg (‘Heuningberg beds’), some 65 km to the north (Figure 1). These exposures near Piketberg, Porterville and Riebeek-Kasteel consist of a basal conglomeratic unit, overlain by coarse-grained sandstone, wackes and minor shales clearly distinguishing the rocks from the steeply-dipping, underlying Malmesbury shales (Rabie, 1948, 1974). Haughton (1933) named the succession ‘Klipheuwel beds’, with the Klipheuwel quarry as the type locality and separated it from the underlying French Hoek beds (later Franschhoek Formation). Holmes (1953) distinguished three distinct stratigraphic units in the Klipheuwel quarry type section, namely a ‘Lower Arenaceous Horizon’ overlain by a ‘Shale Band’ and an ‘Upper Arenaceous Horizon’. De Villiers (1956) and De Villiers et al. (1964) broadened the classified Klipheuwel beds to include the Heuningberg beds, the French Hoek beds and portions of the underlying and deformed Boland Formation into what they termed the ‘extended Klipheuwel Formation’, only sub-dividing it into a weakly- deformed unit and a highly-deformed unit. Visser (1967) disapproved of this broadened definition of the Klipheuwel Formation as he had recorded distinct structural and lithological differences between the French Hoek beds and Klipheuwel beds. He estimated a total stratigraphic thickness of 2 000 m for the Klipheuwel Group at the type-locality and also mapped exposures at Elandsbaai in the far north as Klipheuwel-type successions, as well as outcrops near Redelinghuys (Visser, 1967) that were previously defined by Rogers (1904) as the Ibiquas Beds (Visser and Toerien, 1971). The Klipheuwel Group succession in the northern exposures is markedly reduced in Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 643 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS Figure 1. Simplified geological map of the southwestern Western Cape and a corresponding table, outlining the spatial distribution and stratigraphic position of the Pan-African metasediments, Cape Granite Suite, Franschhoek Formation, Klipheuwel Group, Piekenierskloof Formation and Cape Supergroup. Map modified from Gresse et al. (2006) and Kisters and Belcher (2018). Stratigraphic table is modified from descriptions, maps and stratigraphic columns of De Villiers (1980), Dunlevey (1982), Hiller (1992), Thamm (1993) and Gresse et al. (2006). Thicknesses of the stratigraphic units are not to scale. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 644 SOUTH AFRICAN JOURNAL OF GEOLOGY thickness compared to those at the type locality, ranging from 488 m near Redelinghuys (Visser and Schoch, 1973) to 300 m at Eendekuil (Visser and Toerien, 1971). Vos and Tankard (1981) conducted a lithological study on the Piekenierskloof Formation as well as studied the lithological transition and facies of the underlying Klipheuwel Group at Elands Bay and Redelinghuys. Here they established three main facies for the Klipheuwel Group that differ from that described at the type locality. A ‘lower marine shelf facies’ is overlain by a ‘distal alluvial plain/fan delta facies’ and topped by a ‘distal, braided alluvial plain facies’. There is wide consensus that the deposition of the Klipheuwel Group was significantly influenced by tectonic activity, particularly in the southern, steeply dipping exposures (Holmes, 1953; Rust, 1973; Vos and Tankard 1981). Tectonic uplift and rapid basin subsidence are also interpreted to account for the abundance of feldspar, poor rounding and sorting and widespread conglomerates that point to a proximal derivation of detrital material. Northern Klipheuwel exposures at Elands Bay, Redelinghuys and Eendekuil show only very gentle dips and are interpreted as integrated alluvial fan deposits representing southward progradation of a distal braided alluvial plain environment (Rust, 1973; Vos and Tankard, 1981). The continual reclassification of the Klipheuwel Group also underlines the uncertainties in the regional correlation of individual exposures owing to the isolated occurrence of the rocks, thickness variations, orientation, and range of facies. At present, and in most recent stratigraphic classifications (SACS, 1980), rocks of the Klipheuwel Group are recorded at eight localities in the Western Cape Province, including, from north to south, Elands Bay, Redelinghuys, Klein Tafelberg, Eendekuil, Heuningberg, Slanghoek Valley, Klipheuwel quarry as the type locality, and Klapmutskop (Figure 1). The stratigraphic position of the Franschhoek Formation is even more problematic than that of the Klipheuwel Group. The Franschhoek Formation is exposed as a series of isolated, northwest-trending outcrops that are aligned along a narrow corridor from Franschhoek to Agter-Paarl, where the outcrops separate into two branches that pinch out (Figure 1) (De Villiers, 1980; SACS, 1980). Steep opposing dips to the northeast and southwest seem to indicate that the rocks are preserved in the core of a gently plunging, northwest-trending synformal structure (De Villiers, 1980). Where exposed, the contacts of the rocks against the underlying Malmesbury Group are strongly sheared and seemingly fault-bounded (Viljoen, 2016). Despite the unconformable contacts against the underlying Malmesbury Group and, in places, granites of the Cape Granite Suite, Hartnady (1969) noted a strong cleavage development in rocks of the Franschhoek Formation, more or less parallel to the foliation in the underlying Malmesbury Group. Conglomerate pebbles are flattened and stretched, parallel to fabrics in the underlying Malmesbury Group (Dunlevey, 1982; Theron et al., 1992). This metasiliciclastic succession comprises quartzite, feldspathic conglomerates, coarse-grained sandstone, phyllite, and black slate, with minor graded bedding and crossbedding (Dunlevey, 1981; SACS, 1980; Theron et al., 1992). The conglomerates are polymictic with extraclasts of vein quartz, quartzite, phyllite, chert, jasper, greywacke, quartz porphyry, and granite (Theron et al., 1992). Despite the compositional similarities and comparable stratigraphic position between the Franschhoek Formation and Klipheuwel Group, Dunlevey (1982) suggests the Franschhoek Formation to be grouped together with the Malmesbury Group (see also Gresse et al., 2006, Kisters and Belcher, 2018). In contrast, Frimmel et al. (2013) suggested a closer affinity to the Klipheuwel Group (Figure 2). Facies analysis Below, we present a summary of the sedimentological characteristics and sedimentary features of the Klipheuwel Group based on the selected study areas. Characteristics of the 16 different facies types, eight recognised architectural elements and six facies associations are summarised in Table 1, Table 2 and Table 3 and illustrated in Figure 3A to P. Descriptions, interpretations and analyses were conducted according to established fluvial sedimentological frameworks and previous studies by Miall (1985, 1987, 1996, 2006, 2022), Bridge (2006), Davies and Gibling (2010) and Colombera et al. (2013). A preliminary study on two localities of the Franschhoek Formation is also included, describing the dominant lithological characteristics. In this study, we explored the characterisation of the Klipheuwel Group and Franschhoek Formations in terms of their sedimentology and stratigraphy to determine likely depositional environments and whether a distinction can be made between northern and southern Klipheuwel exposures. At each exposure considered in this study, the sedimentology of the Klipheuwel Group has been described both in terms of its lithofacies and Figure 2. Contrasting lithostratigraphic subdivisions and position of the Klipheuwel Group and Franschhoek Formation according to Gresse et al. (2006), Frimmel et al. (2013), and Kisters and Belcher (2018). Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 645 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS Fa ci es C o d e Fa ci es D es cr ip ti o n In te rp re ta ti o n G cm C la st -s u p p o rt ed , m as si ve o r cr u d el y b ed d ed g ra ve l M as si ve , c la st s u p p o rt ed b re cc ia -c o n gl o m er at e w ith v ei n q u ar tz , q u ar tz ite , v o lc an ic s, s an d st o n es , b la ck s h al e an d in tr af o rm at io n al m ar o o n m u d st o n es u p t o 2 0 cm a cr o ss . Po o rl y so rt ed , u n gr ad ed , cr u d e b ed d in g w ith s im ila r si ze d c la st s w ith in b ed s, b u t va ry in g si ze d c la st s b et w ee n e ro si ve b ed s P se u d o p la st ic d eb ri s flo w (i n er tia l b ed lo ad , tu rb u le n t flo w ) G m m M at ri x- su p p o rt ed m as si ve o r cr u d el y b ed d ed g ra ve l M as si ve , m at ri x su p p or te d co ng lo m er at e w ith v ei n qu ar tz ( >8 0% ) an d va ri ou s se di m en ta ry c la st s (< 20 % ) su ch a s q u ar tz ite , s an d st on es , a n d m u d st o n es u p t o 1 5 cm a cr o ss . Po o rl y so rt ed , u n gr ad ed w ith s u b -a n gu la r to s u b -r o u n d ed c la st s su sp en d ed w ith in a c o ar se -g ra in ed t o g ri tt y m at ri x P la st ic d eb ri s flo w ( h ig h -s tr en gt h , vi sc o u s) G m g M at ri x- su p p o rt ed g ra d ed gr av el N o rm al ly g ra d ed , m at ri x su p p o rt ed c o n gl o m er at e, u su al ly l en ti cu la r b ed s, w it h v ei n q u ar tz , q u ar tz it e, v o lc an ic s, s an d st o n es , b la ck s h al e, in tr af o rm at io n al m ar o o n m u d st o n es u p t o 1 0 cm a cr o ss . Po o rl y so rt ed , ro u n d ed t o s u b -a n gu la r cl as ts d ec re as in g in s iz e an d a b u n d an ce u p w ar d s, su sp en d ed w ith in a c o ar se -g ra in ed t o g ri tt y m at ri x P se u d o p la st ic d eb ri s flo w ( lo w st re n gt h , vi sc o u s) G h C la st - o r m at ri x- su p p o rt ed , h o ri zo n ta lly b ed d ed g ra ve l H o ri zo n ta lly b ed d ed , cl as t- o r m at ri x su p p o rt ed c o n gl o m er at e w ith v ei n q u ar tz , q u ar tz ite , sa n d st o n es , b la ck s h al e an d i n tr af o rm at io n al m ar o o n m u d st o n es u p t o 6 c m a cr o ss . Po o rl y so rt ed , an gu la r- t o s u b -r o u n d ed c la st s, w ith in a v er y co ar se -g ra in ed m at ri x, b ed d ed a s st ri n ge rs o r b ed s o f < 30 c m t h ic k Lo n gi tu d in al b ed fo rm , la g d ep o si t, si ev e d ep o si t G t Tr o u gh c ro ss -s tr at ifi ed g ra ve l Tr o u gh c ro ss -b ed d ed , m at ri x su p p o rt ed c o n gl o m er at e w ith v ei n q u ar tz , q u ar tz ite , s an d st o n es , b la ck s h al e an d i n tr af o rm at io n al m ar o o n m u d st o n es u p t o 5 c m a cr o ss . Po o rl y so rt ed , an gu la r- t o s u b -r o u n d ed c la st s, w ith in a v er y co ar se -g ra in ed m at ri x, b ed d ed a s st ri n ge rs o r b ed s o f < 1 m t h ic k M in o r ch an n el fi lls G p P la n ar c ro ss -s tr at ifi ed g ra ve l P la n ar c ro ss -b ed d ed , m at ri x su p p o rt ed c o n gl o m er at e w it h p re d o m in an tl y ve in q u ar tz , b u t al so s o m e q u ar tz it e, s an d st o n es , b la ck s h al e an d in tr af o rm at io n al m ar o o n m u d st o n es u p t o 8 c m a cr o ss . P o o rl y so rt ed , an gu la r- t o s u b -r o u n d ed c la st s, w ith in a v er y co ar se -g ra in ed m at ri x, b ed d ed as b ed s o f < 1. 5 m -t h ic k Tr an sv er se b ed fo rm s St Tr ou gh c ro ss -s tr at ifi ed s an d, m ay c on ta in p eb bl es M ed iu m - to v er y co ar se - gr ai n ed s an d st o n e w ith t ro u gh c ro ss -s tr at ifi ca tio n w h er e th e lo w er b o u n d in g su rf ac es a re c u rv ed a n d t ru n ca te o th er f ac ie s o r co se ts . C o se ts r an ge i n t h ic kn es s fr o m 1 0 to 8 0 cm d ep en d in g o n t h e fa ci es a ss o ci at io n ( FA ) Si n u o u s- cr es te d a n d l in gu o id (3 -D ) d u n es Sp Pl an ar c ro ss -s tr at ifi ed s an d, m ay c on ta in p eb bl es M ed iu m - to v er y co ar se - gr ai n ed s an d st o n e w ith p la n ar c ro ss -s tr at ifi ca tio n w h er e th e fo re se t d ip r an ge s b et w ee n 1 5° a n d 3 0° d ep en d in g o n t h e FA Tr an sv er se a n d l in gu o id b ed fo rm s (2 -D d u n es ) Se Sa n d st o n e w ith i n tr ac la st s C o ar se -g ra in ed t o g ri tt y sa n d st o n e w ith s o m e gr an u le - to p eb b le -s iz ed e xt ra cl as ts a n d i n tr af o rm at io n al m ar o o n m u d st o n e cl as ts r ea ch in g si ze s < 25 c m a cr o ss Ss Sc o u r- fi ll sa n d , m ay c o n ta in p eb b ly M ed iu m - to v er y co ar se -g ra in ed s an d st o n e th at m ay c o n ta in g ra n u le - to p eb b le s iz ed i n tr ac la st s an d e xt ra cl as ts . Sc o u rs c an b e b ro ad a n d s h al lo w o r n ar ro w a n d s h al lo w d ep en d in g o n t h e FA . U su al ly o cc u rs a t th e b as e o f ch an n el s Sc o u r fi ll Sl Lo w -a n gl e cr o ss b ed d ed o r la m in at ed s an d st o n e Fi n e- t o c o ar se -g ra in ed s an d st o n e w ith l o w -a n gl e cr o ss l am in at in g, e xh ib iti n g fo re se t d ip a n gl es < 10 °. C an b e b ed d ed o r la m in at ed H u m p b ac k o r w as h ed -o u t d u n es , an tid u n es Sh H o ri zo n ta lly s tr at ifi ed sa n d st o n e M o d er at el y so rt ed , fi n e- t o c o ar se -g ra in ed , h o ri zo n ta lly l am in at ed a n d b ed d ed s an d st o n e P la n e- b ed fl o w ( su p er -c ri tic al fl o w ) Sr R ip p le c ro ss -l am in at ed sa n d st o n e M o d er at el y so rt ed , fi n e- t o c o ar se -g ra in ed , ri p p le c ro ss -l am in at ed s an d st o n e R ip p le s (l o w er fl o w r eg im e) Fl La m in at ed s ilt st o n e H o ri zo n ta lly l am in at ed s ilt st o n e, b ed d ed i n s u cc es si o n s o f 0. 4 to 1 .5 m -t h ic k O ve rb an k, a b an d o n ed c h an n el , o r w an in g flo o d d ep o si ts Fm M as si ve c la y Le n tic u la rl y b ed d ed , m as si ve m u d st o n e th at c an b e sl ig h tly l am in at ed w ith s ilt y cr ea m -c o lo u re d l am in ae o r le ss l ik el y, d ar ke r ch ar co al -c o lo u re d la m in ae . O cc u rr en ce s o f so ft s ed im en t d ef o rm at io n ( sl u m p s tr u ct u re s) a n d c ro ss r ip p le l am in at io n i s p re se n t o n l itt le a cc o u n t O ve rb an k, a b an d o n ed c h an n el , o r d ra p e d ep o si ts P Pe d o ge n ic c ar b o n at e M u d d y si lts to n e (F sm ) w ith c ar b o n at e co n cr et io n s p re se rv ed a s p ed o ge n ic n o d u le s u p t o 4 c m a cr o ss A n ci en t so il w ith i n -s it u c h em ic al p re ci p ita tio n T ab le 1 . D es cr ip tio n s an d i n te rp re ta tio n s o f lit h o fa ci es t yp es ( m o d ifi ed a ft er M ia ll, 1 98 5, 1 98 7, 1 99 6, 2 00 6, 2 02 2) f ro m t h e st u d ie d s tr at ig ra p h ic i n te rv al s o f th e n o rt h er n a n d s o u th er n K lip h eu w el G ro u p o u tc ro p s. T h e co lo u r o f w ea th er ed a n d u n w ea th er ed o u tc ro p w as r ec o rd ed u si n g th e M u n se ll C o lo u r C h ar t (2 01 1) . A ls o s ee F ig u re 3 f o r fie ld p h o to gr ap h s o f th e lit h o fa ci es t yp es . Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 646 SOUTH AFRICAN JOURNAL OF GEOLOGY facies associations (FA), as well as their three-dimensional morphology and relationships as architectural elements (AE). Collectively, these data are useful in determining sedimentary processes particular to certain depositional environments and systems (Collinson, 1969; Walker, 2006; Miall, 2010). In our study we interpret sedimentation in the Klipheuwel Group to have predominantly occurred in high energy fluviatile conditions, most likely in a broad alluvial fan and braidplain environment. Further, a distinction can be made between northern and southern exposures with the former showing a greater predominance of laterally extensive blanket deposits, as opposed to highly variable, laterally limited deposits in the south. The Klipheuwel Group Deposits of the Klipheuwel Group show a regional north- south dissimilarity in their sedimentology and their inferred palaeoenvironment (Figure 4A to E). As such, these will be presented separately. Northern Klipheuwel Group The northern exposures of the Klipheuwel Group are present in steep cliffs along mountainous sections from the west coast at Elands Bay past Redelinghuys to Eendekuil that can be traced for 65 km along a distinctly northwest-southeast trend. At all localities, the Klipheuwel Group unconformably truncates Malmesbury Group metasediments and is in turn overlain by the Piekenierskloof Formation of the Cape Supergroup. The maximum thickness of the Klipheuwel Group in this area is around 400 m with bedding dipping 10° to 15° southeast (Figure 4C). The northern Klipheuwel Group is characterised by three facies associations (FA1, FA2 and FA3) that are interpreted to be representative of weakly channelised ‘sheet braided’ stacks, unconfined streamflood and floodplain or overbank deposits respectively. At exposures in the vicinity of Eendekuil (farms Geelvlei, Meerlandsvlei and Spaarkloof) only FA1 and FA2 are developed whilst exposures at Elands Bay (main street T-junction) manifest entirely as FA3. Facies associations Facies association 1 (FA1) (distal braidplain - weakly channelised ‘sheet-braided’ stacks) Description: Facies association 1 comprises lithofacies St, Sp, Sh, Sl, subordinate stringers of Gh and Gt and remnants of Fm, ultimately forming multi-storey sandstones up to >30 m-thick (Figure 5A to E). Sandstone facies are moderately sorted, very- coarse grained and typically weather in colour to pale red Figure 3. Lithofacies of the Klipheuwel Group (adapted from Miall, 1985, 1987, 1996, 2006, 2022). The colour of weathered and unweathered outcrop was recorded using the Munsell Colour Chart (2011). Facies codes: G=Gravel; S=Sand, F=Fines; P=Pedogenic nodules; c=clast supported; m=matrix supported; t=trough cross bedding; p=planar cross bedding; e=intraclasts; s=scour; l=low-angle; h=horizontal bedding; r=ripples; m=massive. Scales: field book is 19.5 cm long and 13.5 cm wide; Canon camera lens is 6 cm in diameter. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 647 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS (A E ) A rc h it ec tu ra l el em en t D es cr ip ti o n In te rp re ta ti o n G eo m et ry Fa ci es c o m b in at io n s O th er c h ar ac te ri st ic s C H -a gg ra d at io n al c h an n el fi ll Fi n ge r, le n s, sh ee t A n y co m b in at io n , d o m in an tly g ra ve l an d sa n d y fa ci es V er tic al ly s ta ck ed , co n ca ve u p d ep o si tio n al i n cr em en ts d is p la yi n g in te rn al h o ri zo n ta l b o u n d in g su rf ac es . C H e le m en ts a re c o m p o se d o f sm al l- sc al e d o w n st re am - an d /o r la te ra l ac cr et io n e le m en ts w ith s ig n ifi ca n t ch an ge s in l at er al b ed d in g gr o w th A gg ra d at io n al i n fi ll o f ac tiv e ch an n el b el ts D A -d o w n st re am a cc re tio n b ar fo rm Sh ee t St , Sp , Sh , Sl , G m m D o w n st re am s ta ck ed d ep o si tio n al i n cr em en ts a t a lo w a n gl e w ith r es p ec t to t h e p al ae o flo w , d is p la yi n g su b h o ri zo n ta l to s lig h tly c o n ca ve -u p w ar d s an d o ft en e ro si o n al b as es In fi ll o f ac tiv e ch an n el b el ts b y d o w n st re am m ig ra tin g b ar s G B -g ra ve l b ar fo rm Ta b u la r, le n s G t, G p , G h , G m m , G m g, G cm C o ar se -g ra in ed d ep o si tio n al i n cr em en ts ( w ith g ra ve l si ze c la st s) w ith b ed s o f 0. 3 to 2 m -t h ic k an d 1 t o 1 2 m -w id e, t h at o ve rl ie i rr eg u la r o r co n ca ve -u p w ar d s er o si o n al b as es D ep o si ts f ro m h ig h e n er gy e ve n ts , in c h an n el m ig ra tin g d u n es o r gr av el b ar s SB -s an d y b ed fo rm Le n tic u la r, ta b u la r St , Sh , Sl , Se , Sr T h in t o t h ic k ve rt ic al ly s ta ck ed o r is o la te d d ep o si tio n al i n cr em en ts t h at i s sa n d st o n e- d o m in at ed , w ith s h ar p , p la n ar t o i rr eg u la r b o u n d in g su rf ac es t h at c an b e sl ig h tly e ro si ve O cc u rs a s ch an n el fi lls a n d m in o r b ar s SG -s ed im en t gr av ity -fl o w R ib b o n , sh ee t St , Sl , G t, G p , G h , G m m Sa n d y an d g ra ve lly d ep o si tio n al u n its w ith i rr eg u la r an d s h ar p b u t o ft en n o n -e ro si o n al b as e. In te rn al ly o ft en s tr u ct u re le ss , o th er w is e co m p o se d o f in te rb ed d ed G B a n d S B e le m en ts M as s m o ve m en t (h yp er co n ce n tr at ed fl o w s) ; la rg e d is ch ar ge e ve n ts A C -a b an d o n ed c h an n el fi ll Le n s, r ib b o n Fm , Fs m , Fl , Sh C h an n el is ed , ve rt ic al ly a cc re te d d ep o si tio n al i n cr em en ts t h at fi n e u p w ar d s as a r es u lt o f su sp en si o n s et tli n g C h an n el a b an d o n m en t le ad in g to p o n d ed w at er b o d ie s an d s u sp en si o n s et tli n g o f m u d -s iz e p ar tic le s C R -c re va ss e ch an n el Le n s, r ib b o n St , Sh , Sl , Ss C h an n el is ed s an d y fa ci es a gg ra d at io n w ith c o n ca ve -u p w ar d s er o si o n al b as e. A lw ay s as so ci at ed w ith o th er fl o o d p la in A E s su ch a s C S an d F F In fi ll o f m in o r ch an n el s em an at in g fr o m t h e m ai n ch an n el i n to t h e ad ja ce n t fl o o d p la in ; ac ti ve d u ri n g flo o d s C S- cr ev as se s p la y Ta b u la r Fl , St , Sh , Sl Sa n d y u n it th at t h in s aw ay f ro m t h e b o rd er in g ch an n el m ar gi n s an d g ra d es l at er al ly i n to o th er e le m en ts F F. T h ey t en d t o h av e fl at , sh ar p a n d s lig h tly e ro si ve b as es P ro gr ad at io n a n d a gg ra d at io n d ep o si ts t h at f o rm in o ve rb an k ar ea s w ith fl o w e m er gi n g fr o m t h e cr ev as se c h an n el s FF -o ve rb an k fi n es Ta b u la r, le n tic u la r Fm , Fl , Sh , Sr , P T h in t o t h ic k, v er tic al ly s ta ck ed , la te ra lly p er si st en t, fi n e- gr ai n ed s ilt st o n e o r m u d st o n e u n its th at c an c o n ta in p ed o ge n ic a lte ra tio n s A gg re ga tio n al d ep o si ts f ro m s u sp en si o n s et tli n g d u ri n g u n co n fi n ed fl o w s o n t h e flo o d p la in T ab le 2 . D es cr ip tio n a n d i n te rp re ta tio n o f th e ar ch ite ct u ra l el em en ts o f th e K lip h eu w el G ro u p i n t h e W es te rn C ap e, S o u th A fr ic a. M o d ifi ed a ft er M ia ll, 1 98 5, 1 98 7, 1 99 6, 2 00 6, 2 02 2 an d C o lo m b er a et a l., 2 01 3. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 648 SOUTH AFRICAN JOURNAL OF GEOLOGY Figure 4. Simplified geological map of the southwestern Western Cape outlining the main areas of focus for this study. The northern Klipheuwel Group localities, outlined in red, exhibit consistent characteristics and trends across outcrops which are highlighted in the red outlined insert. The southern Klipheuwel Group localities, outlined in green, display consistent characteristics and trends across outcrops which is highlighted in the green outlined insert. The Franschhoek Formation localities are outlined in brown. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 649 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS (5R 6/2) (Figure 5C). Throughout these deposits occasional gravel stringers (Gt and Gh) occur at the base of trough cross- (St) and planar bedded (Sh) bedsets. Clasts contained in lithofacies Gt and Gh are typically oligomictic comprising sub- rounded to angular extraformational vein quartz clasts, that are <40 mm in size (Figure 5C). Facies association 1 manifests as a stacked multi-storey sandstone composed of 10 to 40 cm-thick, undulatory St, Sp, and Sh bedsets, forming 1 to 2 m-thick superimposed cosets of trough-, planar- and horizontally bedded sandstone identified as downstream accretion barforms (DA) elements (Figure 5C). These laterally continuous sandstones display cosets separated by erosive 3rd- and 4th- order bounding surfaces, whereas the internal bedsets exhibit sub-planar undulatory 2nd- and 3rd- order bounding surfaces (Figure 5C). The simplicity of contained architectural elements and continuous lateral extent of FA1 produces extensive, stacked, monotonous sand bodies as steep cliff faces at Eendekuil and Redelinghuys as the upper-most stratigraphic section of the northern Klipheuwel Group, directly underlying the Piekenierskloof Formation (Figure 5B). Facies association 2 (FA2) (medial fan – unconfined streamflood deposit) Description: Facies association 2 is characterised by a combination of gravel-rich lithofacies, Gmm, Gh, Gt, and Gp, collectively arranged as gravel bars (GB) with minor amounts of sandy lithofacies such as Sh, Sl, and St that are collectively arranged as sandy bedforms (SB) (Figure 6A to C). The gravel facies are mostly massive but can be normally graded. Extraclasts associated with these deposits typically comprise sub-angular to rounded vein quartz with lesser quartzite and sandstone that are on average 65 mm in diameter. Extraclasts are hosted in a poorly sorted, coarse- to very coarse-grained, moderate reddish brown (10R 4/6) coloured sand-supported matrix (Figure 6B). The GB elements (Gmm, Gt, Gp, Gh) are interbedded with 3rd- and 4th- order bounding surfaces and display rapid lateral terminations for lithofacies Gt, Gp, and Gh, whereas the ungraded, massive Gmm lithofacies homogenously percolates throughout FA2 grading with adjacent gravel lithofacies. FA 2 comprises of various stacked, tabular Gmm lithofacies of 1 to 2.5 m-thickness, which is intercalated with several other gravel lithofacies (Gt, Gp and Gh) of 0.2 to 1  m-thick. These stacked GB are sometimes separated with interbedded SB of 0.2 to 0.5 m-thickness displaying 3rd- and 4th- order bounding surfaces (Figure 6B and C). Collectively this combination of GB and SB elements presents a 10 to 15 m- thick, laterally continuous, sheet-like deposit in the lower stratigraphy of the northern Klipheuwel Group, exposed at Eendekuil (Figure 6A). FA2 could be present at Redelinghuys and Elands Bay but remains unknown as the lower portion of the Klipheuwel Group is obscured here. Facies association 3 (FA3) (floodplain fines and overbank deposits) Description: Facies association 3 comprises lithofacies St, Sl, Sh, and Ss, in various groupings as well-sorted, medium- to coarse grained, moderate orange pink (5Y 8/4) and moderate red (5R 4/6) coloured sandstone forming crevasse splays (CS) and crevasse channels (CR) (Figure 7A to E). CS are distinguished from CR as the former is thinly bedded, 10 to 40  cm-thick, displaying laterally continuous planar beds, whereas the latter is thickly bedded, 1 to 2 m-thick, and is usually marked with Ss lithofacies (Figure 7). These sandy lithofacies alternate with moderate red (5R 4/6) coloured siltstones comprising lithofacies horizontally laminated (Fl) and pedogenic carbonate (P), which is classified as floodplain fines (FF) (Figure 7B and D). These architectural elements (FF, CR and CS) each represent distinct beds that are separated by 4th- order bounding surfaces (Figure 7B and C). Prominent FA3 exposures are showcased at Elands Bay at the northern-most edge of the mapped Klipheuwel Group outcrops (Figure 7A). Here the 5 to 15 m-thick FA3 unit exhibits a repetitive alternation of 10 to 40 cm-thick beds, between FF elements and sandy CS elements that is over- and underlain by 1 to 2 m-thick CR elements (Figure 7B and C). These layers are FAs AEs Lithofacies Description of geometry and architectural element content Locality Illustration FA1 DA, GB, AC St, Sp, Sh, Sl, Gh, Gt Multiple vertically stacked, DA-dominated, sheet-like channel belts. Laterally extensive, 100s of meters in width; thickness of 20-50 m North Figure 5 FA2 GB, SB St, Sh, Sl, Gmm, Gh, Gt, Gp Laterally extensive, sheet-like, superimposed GB elements with minorly interbedded, thin SB element depositing during low water stages. Width: >300 m; thickness: 10 to 20 m North Figure 6 FA3 FF, CR, CS P, Fl, St, Sh, Sl, Ss Ribbon/sheet-shaped floodplain fines and floodplain channel deposits, containing FF, CR and CS elements. Width: >50 m; thickness: 12 m North Figure 7 FA4 CH, GB, DA, SB, AC Fm, Fl, St, Sp, Sh, Sl, Se, Sr, Gcm, Gmg, Gh, Gt Sheet/lensoidal-shaped CH-dominated deposits truncating each other during vertical aggradation. This deposit mainly contains GB, DA, AC and FF elements. Width: 100s of meters; thickness: >250 m South Figure 9 FA5 SB, LS, AC Fm, St, Sh, Sl, Se, Sr Sheet-like LS and SB elements overlain by lensoidal, laterally limited, AC elements. Width: 100 to 150 m; thickness: 25 to 50 m South Figure 10 FA6 GB, SB St, Sh, Sl, Gcm, Gmg, Gh Stacked channelised GB elements accumulating through vertical and lateral aggradation, interbedded with SB elements as slack deposits. Width: 150 m; thickness: 35 m South Figure 11 Table 3. Description of facies associations (FAs) observed throughout the stratigraphic interval of the Klipheuwel Group. The individual FAs are illustrated in Figures 5 to 7 and 9 to 11. For their spatial and stratigraphic distribution of the respective FAs, see Figure 4. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 650 SOUTH AFRICAN JOURNAL OF GEOLOGY Figure 5. Facies association 1 (FA1) exposed at Eendekuil and Redelinghuys. (A) Overview of the Klipheuwel Group at Eendekuil with the spatial and stratigraphic position of FA1 and FA2 in relation to each other. (B) FA1 outcrop directly underlying the Piekenierskloof Formation with an angular unconformity. (C) Accretion barform (DA) element composed of multiple 10 to 40 cm-thick beds, which displays slightly erosive and slightly dipping 3rd order bounding surfaces with predominant trough cross-stratified sandstone (St) that constitutes FA1. (D) FA1 at Redelinghuys displaying horizontally stratified pebbly sandstone beds separated by 3rd order bounding surfaces. (E) Example of ex-situ massive mudstone (Fm) displaying ripple marks, likely from an abandoned channel (AC) element. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 651 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS tabular and stretch laterally for >50  m (Figure 7A). The FF element comprises Fl or massive siltstone that contains carbonate nodules of up to 4 cm in diameter, that may be pedogenic (P) in origin (Figure 7D). Stratigraphy Stratigraphic sections logged at and presented for the Elands Bay (32°18’57”S; 18°21’19”E), Redelinghuys (32°28’00”S; 18°30’05”E) and Eendekuil (32°34’00”S; 18°53’30”E) localities Figure 6. Facies association 2 (FA2) exposed at Eendekuil. (A) Overview of the laterally extensive, sheet-like FA2 exposures observed at Eendekuil, lower down in stratigraphy in relation to FA1. (B) FA2 outcrop exhibiting gravel bar (GB) elements, interbedded with sandy bedform (SB) elements. (C) FA2 outcrop displaying a combination of varying gravel lithofacies and subordinate amounts of sandy lithofacies. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 652 SOUTH AFRICAN JOURNAL OF GEOLOGY were deemed as being most representative for the northern Klipheuwel Group. These sections are considered type sections for this area (Figure 8A to E). Southern Klipheuwel Group Southern exposures of the Klipheuwel Group considered in this study are at Klapmutskop and the Klipheuwel quarry along the Mosselbank River. At these exposures, the total stratigraphic profile of the Klipheuwel Group is thicker than in northern localities. Here, some 900 to 2 000 m of stratigraphy is present, preserved in a number of narrow northwest-trending exposures that consistently dip 45° to 65° northeast (Figure 4D). These exposures can be traced more or less uninterruptedly for 22 km along strike from the Klapmutskop in the southeast to the Klipheuwel type locality in the northwest (Figure 4). The lower Figure 7. Facies association 3 (FA3), best exposed at the Elands Bay type locality. (A) Overview of the extent of FA3 of the Klipheuwel Group, directly underlying the Piekenierskloof Formation. (B) and (C) exhibits tabular, sheet-like floodplain elements such as crevasse splays (CS), flood plain fines (FF) and crevasse channels (CR). (B) and (C) cross correlates with the Elands Bay stratigraphic log in Figure 4A. (D) Close-up of the intercalated FF and CS elements, the respective lithofacies types composing these elements as well as the bounding surfaces separating them. (E) Close-up of CR element, predominantly exhibiting trough cross stratified medium- to coarse-grained sand. Abbreviations: FA=facies association, EB=Elands Bay. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 653 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS contact in the southwest between the Klipheuwel Group and the Malmesbury Group and/or Cape Granite Suite is marked by a locally well-exposed nonconformity. The upper contact of the Klipheuwel Group in the northeast, in contrast, is fault bounded against the trace of the Colenso Fault and related fault strands. The southern Klipheuwel Group is characterised by three facies associations (FA4, FA5 and FA6) that are interpreted to be representative of deeply channelised laterally variable proximal- and medial braidplain, as well as distal braidplain flood deposits respectively. At exposures in the Klipheuwel quarry and on Klapmutskop all three FAs (FA4, FA5 and FA6) are developed with a dominant FA4 fraction. Figure 8. Sedimentary logs of the northern Klipheuwel Group localities. Each stratigraphic column is considered a type section. Note the predominance of trough cross bedded sandstones and the correlation between (A) and (D) as well as (C) and (E). (A) Upper Klipheuwel Group, Elands Bay. (B) Lower Klipheuwel Group, Eendekuil. (C) Upper Klipheuwel Group, Redelinghuys. (D) Middle Klipheuwel Group, Redelinghuys. (E) Upper Klipheuwel Group, Eendekuil. For stratigraphic column abbreviations refer to Table 1 and Table 2. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 654 SOUTH AFRICAN JOURNAL OF GEOLOGY Figure 9. Examples of Facies association 4 (FA4) of the Klipheuwel Group observed at Klipheuwel. (A) Overview of FA4 directly and unconformably overlying a granitoid of the Cape Granite Suite (CGS). (B) Annotated overview of some of the architectural elements (AE) composing FA4 and their relationships with each other. (C) Trough cross (St) stratified bed situated in the middle of a cyclic channel fill (CH) element. (D) Annotated St stratified bed of Figure 9C. (E) Massive mudstone (Fm) exhibiting soft sediment deformation in the form of a slump structure. (F) Close-up of a siltstone bed (Fl) from Figure 9A, representing an abandoned channel (AC) element or in-channel fines. (G) Normally graded polymictic paraconglomerate (Gmg), representing a basal conglomerate (GB) within a larger CH element, cross cutting into a horizontally bedded sandstone (Sh) from a stratigraphically lower CH element. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 655 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS Facies associations Facies association 4 (FA4) (medial braidplain – channelised deposits) Description: Facies association 4 comprises lithofacies Gcm, Gmg, Gh, Gt, St, Sp, Sl, Se, Sh, Sr, Fl, and Fm arranged as typical repetitive vertical aggradation cycles from basal GB, succeeded by downstream DA, then SB and finally capped by abandoned channel fills (AC), morphologically resembling channel fill (CH) AEs (Figure 9A to G). These CH elements are 5 to 12 m-thick cross cutting each other up stratigraphy and laterally with relative lithological discontinuities along strike (Figure 9G). The GB elements are 0.2 to 2 m-thick and predominantly comprises polymictic matrix-supported conglomerates (Gmg) containing rounded to sub-angular clasts ranging between 20 to 100 mm in diameter (Figure 3C and Figure 9G). The clasts are composed of vein quartz, quartzite, sandstones, black shale, volcanics and mudstone rip-up clasts (Figure 3C). The sandy lithofacies (DA and SB) ranges between 2 to 8 m in thickness and varies laterally and up stratigraphy, but is predominantly composed of trough-, planar- and horizontally stratified, very coarse-grained pebbly beds (Figure 9A and C). The finer-grained lithofacies AC ranges between 0.4 to 1.5  m-thick and either occurs as moderate orange pink (5Y 8/4) coloured siltstone or as massive to laminated moderate red (5R 4/6) coloured mudstones displaying very rarely soft sediment deformation (Figure 9E) and on occasion ripple cross laminations. Internal sedimentary features (bed thickness, main lithofacies type) and matrix to pebble ratio can vary laterally and up stratigraphy, obscuring distinct channel margins. The cyclic units are marked with, usually concave-up, 5th- order bounding surfaces, whereas the varying Figure 10. Examples of FA5 of the Klipheuwel Group at Klipheuwel. (A) Overview of superimposed sandy bedforms (SB) elements composing FA5, dipping moderately to steeply (55°) northeast. (B) Close-up of horizontally laminated and low-angle cross laminated sandstone, representing the dominant lithofacies for FA5. (C) Ripple cross laminated sandstone, which is rarely preserved, in the upper parts of bedded sandstone (Sb) elements. (D) Maroon mudstone (Fm), representing abandoned channel fines (AC), directly overlying, with a sharp contact, horizontally stratified sandstone (Sh) of a larger SB element. (E) Medium- to coarse-grained sandstone hosting multiple sub-rounded to angular intraformational mudstone clasts, <15 cm. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 656 SOUTH AFRICAN JOURNAL OF GEOLOGY Figure 11. Examples of Facies association 6 (FA6) exposures. (A) Top-down drone image of FA5 overlying channel-like conglomerates of FA6. (B) Annotated top-down drone image of Figure 11A, exhibiting FA6 composed of multiple superimposed gravel bars (GB) elements, hosting various intercalated sandy barform (SB) elements. FA6 is overlain by FA5 which is composed by various SB elements, preserved in a sheet-like manner with minor amounts of interbedded channel fine (AC) elements. (C) Looking southwest, along strike, displays positively weathered GB elements interbedded with various, negatively weathered SB elements. (D) Low-angle cross bedded sandstone from a SB element from FA6. (E) Example of matrix supported horizontally stratified gravel (Gh) of FA6. (F) Displays various clast supported gravel beds (Gcm), overlying each other with erosive 3rd-order bounding surfaces forming a larger GB element. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 657 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS Figure 12. Sedimentary logs of the southern Klipheuwel Group localities. Each stratigraphic column is considered a type section. Note the dominance of trough cross (St) bedded sandstones and the correlation between (A), (B) and (C) as well as (D) and upper (E). (A) Middle to lower Klipheuwel Group, Klipheuwel. (B) Lower Klipheuwel Group, Klipheuwel. (C) Lower Klipheuwel Group, Klapmutskop. (D) Middle to upper Klipheuwel Group, Klipheuwel. (E) Lower to middle Klipheuwel Group, Klapmutskop. For stratigraphic column abbreviations refer to Table 1 and Table 2. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 658 SOUTH AFRICAN JOURNAL OF GEOLOGY Figure 13. Outcrops examples of the Franschhoek Formation. (A) Massively bedded cream-grey medium-grained sandstone showing a well-developed cleavage dipping steeply East. (B) Ungraded cream-grey coloured polymictic conglomerate. (C) Ungraded polymictic conglomerate hosting cobbles sized clasts of underlying Pan-African rocks. (D) Pebble-sized polymictic conglomerate displaying a mineral stretching lineation of elongated pebbles within the foliation plane. AE’s and bedsets are separated with 4th- order surfaces displaying 3rd- order internal surfaces between cosets (Figure 9D, F and G). Facies association 5 (FA5) (distal braidplain – flood deposit) Description: Facies association 5 comprises lithofacies St, Se, Sl, Sh, and Sr collectively arranged as SB with occasional isolated AC elements, comprising lithofacies Fm, surmounting these Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 659 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS upward-fining SB elements (Figure 10A to E). The SBs are medium-grained, well-sorted and moderate orange pink (5Y 8/4) coloured, composing 0.5 to 3 m-thick tabular sandstone beds consisting of a cyclic sequence with Se at the base (Figure 10E), transitioning to Sh, Sl, St and Sr, in that order (Figure 10B and C). The overlying AC elements are moderate red (5R 4/6) in colour, massively bedded, and laterally discontinuous, preserved as 0.3 to 2 m-thick lens-like beds (Figure 10D). SB and AC elements are separated by 4th order bounding surfaces (Figure 10A and D) with internal contacts throughout SB bedsets display 2nd- and 3rd- order bounding surfaces (Figure 10B). FA5 comprises various stacked, tabular, upward-fining SB elements, occasionally succeeded by massive, lenticular AC elements (Figure 10D). Exposures at Klapmutskop of FA5 directly overlies FA6 and are surrounded by FA4 deposits. At Klipheuwel, FA5 is stratigraphically confined within deposits of FA4, with no distinct contact. The exposures of FA5 at both localities are compiled of beds 1 to 3 m-thick that persist laterally for 100 to 150 m with a total thickness of 25 to 50 m. Facies association 6 (FA6) (proximal fan – channelised gravel deposit) Description: Facies association 6 comprises lithofacies Gcm, Gmg, and Gh, collectively arranged as GB’s with indistinct internal relationships complicated by irregular, erosive, 3rd- order contacts between crudely bedded lithofacies (Figure 11A to F). These GB elements are sporadically interbedded with lesser SB’s comprising lithofacies St, Sl, and Sh (Figure 11B and D). The gravel facies contain 10 to 120 mm sub-rounded to sub-angular extraclasts of vein quartz and quartzite as well as intraclasts of sandstone, shale and mudrock, and may be clast-, or matrix-supported (Figure 3A). The GB elements are crudely superimposed within a channel-like concave-up geometry extending a distance of 140 m that pinches out laterally and reach a maximum thickness of 30 m (Figure 11B). The sandy facies are 0.5 to 5 m-thick, medium-grained, and moderately sorted with sharp erosional contacts with GB elements, displaying 4th- order bounding surfaces (Figure 11B, C and F). FA6 manifests as a crudely bedded, massive polymictic conglomerate sequence with indistinct internal architecture, hosting several isolated sandy beds. FA6 has two exposures at the northern edge of Klapmutskop where it is surrounded by FA4 and directly overlain by FA5 with a 5th- order bounding surface (Figure 11B). Stratigraphy Stratigraphic sections logged at and presented for the Klipheuwel (33°41’40”S; 18°41’20”E) and Klapmutskop (33°49’00”S; 18°51’00”E) localities are deemed as being most representative for the southern Klipheuwel Group. These sections are considered type sections for this area (Figure 12A to E). The Franschhoek Formation Past disagreements regarding the relationship between the Klipheuwel Group and the Franschhoek Formation mainly exist as a result of similarities in lithological descriptions and spatial proximity of preserved outcrops. Figure 4 outlines the known spatial distribution of the Franschhoek Formation in relation to the Klipheuwel Group. The Franschhoek Formation is poorly exposed and preserved as fragmented outcrops, making it difficult to map the continuity of outcrops or marker horizons. This also hinders the possibility to establish a complete stratigraphic section as each outcrop presents an isolated section, likely unrelated to other outcrops. Below two Franschhoek Formation localities, confirmed by De Villiers (1980) and Theron et al. (1992), are briefly described to delineate the general characteristics and variability across exposures. Delta Valley Farms The outcrops at Delta Valley Farms (piggery), 9 km west of Paarl, are heavily weathered and covered in lichen. At this locality the beds are pale red (10R 6/2) in colour and comprise medium- to very coarse-grained sandstone often manifested as lithofacies Sm (Figure 13A). Some sandstone beds contain pebbles with minor conglomerate horizons. The limited outcrops are well sorted and homogenous, making it difficult to clearly distinguish bedding resulting in a massive appearance with unclear upper- and lower-bounding surfaces. Some beds, however, display a north-south trend with beds dipping 60° east (Figure 4E), confirming findings of De Villiers (1980). These coarse-grained sandy beds display a foliation oblique to bedding, dipping steeply to subvertical, east-southeast (Figure 4E and Figure 13A). Morgenhof Wine Estate The outcrop observed at Morgenhof Wine Estate, 4 km north of Stellenbosch, is poorly preserved and comprises a single road cutting as well as three farm tracks that expose extensively weathered sections. This locality is dominated by conglomerates with minor amounts of very coarse-grained pebbly sandstone displaying a moderate orange pink (5Y 8/4) colour (Figure 13B). The conglomerates are polymictic, poorly sorted and exhibit no distinct grading (Gmm). The clast size ranges from 2 cm to 15 cm in diameter, they are mostly sub-rounded and consist of, in order of abundance, sandstone, shale, granite, quartzite and vein quartz (Figure 13C). These rudaceous rocks lack internal bedding and grading structures. A well-developed foliation (fracture cleavage) in the rocks shows northerly strikes and steep (70°) dips to the east. A shallowly plunging, north-south trending mineral stretching lineation is developed in the foliation plane. The lineation is most prominently defined by the elongation of pebbles (Figure 13D). Discussion Klipheuwel Group The sedimentary architecture and AE’s of the Klipheuwel Group are characteristic for the deposition of sediments in a high- energy fluvial system (Collinson, 1996; Miall, 2022). Given the likely Cambrian age of the rocks and the absence of any terrestrial vegetation at that time, Klipheuwel deposits compare Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 well with pre-vegetation alluvial systems described by, inter alia, Schumm (1968) and Cotter (1978). Pre-vegetation alluvial systems mainly develop bed-load channels transporting coarse- grained sediment resulting primarily in the formation of widespread braided framework river systems. The absence of any vegetation also results in low soil stability, where surface runoff is high, leading to high rates of erosion (Went, 2005). In Klipheuwel times, this would imply a fluvial setting with rapid channel switching and lateral migration of channels over tens of kilometres (Rainbird, 1992; MacNaughton et al., 1997). This results in poorly channelised AE’s (Cotter, 1978, 1983; Long, 2004) and adverse conditions for the preservation of finer- grained deposits (Went, 2005). Also, gravel-bed and sand-bed braided rivers have broad channel systems. This leaves relatively small areas for overbank environments resulting in a minor floodplain component in the total fluvial assemblage (Reinfelds and Nanson, 1993). Both the northern- and southern Klipheuwel Group exposures exhibit braided fluvial lithofacies, AE’s and facies associations that grade from a proximal and medial setting to a distal braided fluvial environment. Although the Klipheuwel Group in its entirety displays large-scale architectural features and depositional environments representative of an alluvial plain-fan complex, there is a clear sedimentological difference between Klipheuwel Group exposures north of Piketberg (‘northern’ Klipheuwel depocentre) and Klipheuwel Group exposures south of Malmesbury (‘southern’ Klipheuwel depocentre) (Figure 4). Northern Klipheuwel Group Braidplains for the northern Klipheuwel Group, at the time of deposition, can be envisaged to have had little relief and to consist of very high width: depth ratios that could have varied from 20:1 and upwards of 1000:1 (Schumm, 1968; Cotter, 1978; Fuller, 1985; Fedo and Cooper, 1990; Rainbird, 1992; MacNaughton et al., 1997). Modern braided river analogues such as the ‘Trollheim Type’ closely resembles FA2 with the ‘South Saskatchewan Type’ mimicking FA1 (Miall, 1977; 1978). FA1 is interpreted to represent extensive, weakly channelised fluvial deposits that accumulated across a distal braided fluvial environment resembling multi-storey ‘sheet-braided’ stacks (Cant and Walker, 1976; Cotter, 1978; Rust, 1978a, 1978b; Fedo and Cooper, 1990; Deckelman, 1991; Sønderholm and Tirsgaard, 1998). FA2 is interpreted as unchanneled, wide-spread, streamflood deposits accumulating during peak runoff on all active sectors of the proximal- and medial braided fluvial alluvial fan (Olsen, 1987; Abdullatif, 1989; Went, 2005). FA3 is interpreted as terrestrial floodplain deposits, forming near the main channel margins (Bown and Kraus, 1987; Miall, 2006). These facies associations suggest that the northern Klipheuwel Group was deposited as multiple superimposed shallowly- channelised laterally persistent deposits, that originally were laterally far more extensive, likely blanketing an area in excess of 10 000 square km (Figure 14A). This resembles deposits of a pre-vegetation alluvial system. The reduced thickness and lateral persistent facies of the northern depocentre compared to the southern Klipheuwel depocentre can likely be attributed to two factors, namely: originally northern deposits developed, and are preserved • as, widespread thin (400 m) successions as a result of high width: depth ratio fluvial sedimentation with non- depositional areas in between outcrops; northern deposits developed as wide-spread deposits of • multiple thin superimposed beds, but these have extensively been denuded and reworked by the overlying Table Mountain Group, only preserving isolated erosional relics of the original extent of the Klipheuwel Group. This would account for the distinctly patchy and isolated occurrences of the rocks. Southern Klipheuwel Group The southern exposures, in contrast, are characterised by FAs displaying incised channels of a braided fluvial style, migrating laterally over a large area with high lateral variability. Consequently, there is a lack of marker horizons. FA4 is interpreted as superimposed channelised deposits developing on the medial to distal braidplain by cross-cutting other channel sediments and reworking slack deposits in AC’s during channel migration (McGowen and Groat, 1971; Smith, 1970, 1972, 1974; Miall, 1977, 1978; Hein and Walker, 1977). FA5 is interpreted as deposits accumulating on the distal braidplain during flooding events as broad sheets of sand that do not conform to channel parameters (Miall, 1977, 1984; Tunbridge, 1981, 1984; Sneh, 1983). FA6 is interpreted as diffuse sheets and longitudinal bars accumulating in channels with steep gradients and high runoff, characteristic of proximal- to medial-braided alluvial-plain environment (Rust, 1972, 1978; Smith, 1974; Boothroyd and Ashley, 1975; Boothroyd and Nummedal, 1978). These FAs resemble modern braided river analogues such as the ‘Scott Type’ for FA6, near the base of the stratigraphy, and the ‘Donjek Type’ for FA4, persisting throughout the stratigraphy (Miall, 1977; 1978). Despite the channelised AE’s, the southern Klipheuwel Group shows many of the characteristics of a pre-vegetated Cambrian environment. Bed-load channels transported coarse- grained sediment and the crosscutting of channels indicates rapid channel switching and lateral migration (Schumm, 1968; Cotter, 1978; Rainbird, 1992; MacNaughton et al., 1997; Went, 2005). Also, there is also no evidence of overbank deposits. This channelised characteristic can be as a result of changes in discharge and other external influences, such as channel confinement (Montgomery and Buffington, 1998). Channel confinement causes increased basal shear stress, deepening of channels (Montgomery and Buffington, 1998) and results in the constant reworking of overbank fines, mimicking depositional characteristics of the southern Klipheuwel depocentre. A confined depository is further supported for the southern Klipheuwel Group by a lower-bounding unconformable contact in the southwest with uniformly northeasterly dips of Klipheuwel beds terminating against the Colenso Fault trace trending northwest, inferring deposition of the southern Klipheuwel Group in a half-graben structure during progressive normal faulting along the Colenso Fault (Figure 14B). Synsedimentary normal faulting REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 660 SOUTH AFRICAN JOURNAL OF GEOLOGY Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 SOUTH AFRICAN JOURNAL OF GEOLOGY 661 R.F. RAATH, C.R. PENN-CLARKE AND A.F.M. KISTERS Figure 14. Interpretive palaeoenvironmental models for the respective depocentres. (A) Palaeoenvironment responsible for the northern Klipheuwel depocentre. (B) Palaeoenvironment responsible for the southern Klipheuwel depocentre. (C) Palaeoenvironment responsible for the Franschhoek Formation. Downloaded from http://pubs.geoscienceworld.org/gssa/sajg/article-pdf/127/3/641/7008945/641_0033_raath_et_al.pdf by University of the Witwatersrand user on 24 October 2024 REGIONAL VARIANCE IN ALLUVIAL SEDIMENTATION AND REVISED STRATIGRAPHY OF THE KLIPHEUWEL GROUP AND FRANSCHHOEK FORMATION 662 SOUTH AFRICAN JOURNAL OF GEOLOGY may not only account for the lateral confinement of channels on the downthrown block of the half graben, but also for the much thicker original and/or preserved thickness of the southern Klipheuwel exposures. Franschhoek Formation The two Franschhoek Formation localities are spatially separated and importantly exhibit distinctly variable lithological characteristics. The homogeneous, massive sandy beds (Sm) observed at Delta Valley Farms likely developed from sediment gravity flows or as a result of recurring bank collapses in an unstable environment (Miall, 2006), whereas the ungraded polymictic conglomerate (Gmm) from Morgenhof Wine Estate characteristically reflect high-strength debris flows passively following preexisting topography (Miall, 2006). The observed facies, sediment gravity flows and high-strength debris flows, usually develop as abrupt deposits on steep gradients forming irregular topography (Miall, 2006). These close to source depositional processes in conjunction with the presence of intraformational clasts, derived from the underlying Malmesbury Group and Cape Granite Suite, infers locally derived detritus. The coaxial folding of the Franschhoek Formation with rocks of the Malmesbury Group and the north-south trending foliation and stretching of pebbles and clasts in the foliation plane indicates that the Franschhoek Formation experienced east-west shortening, similar to strains in the folded and underlying Malmesbury Group (De Villiers, 1980). Given the similar strains, reworking of the Malmesbury Group and sheared yet unconformable contacts against the underlying Pan-African basement, the Franschhoek Formation is interpreted to have been deposited in a piggyback basin environment (Figure 14C). The basins record Pan-African strains and likely formed during the progressive shortening, folding, uplift and erosion of the Malmesbury Group that shed erosional detritus in structurally controlled depressions ahead of the uplifted basement rocks (Figure 14C). Conclusion This study describes the lithological characteristics and sedimentation controls for the Klipheuwel Group, on local and regional scale, inferring prevailing palaeoenvironments at the time of deposition. Based on the variation of AEs and FAs, two distinct and separate depositories of the Klipheuwel Group are distinguished. It is suggested that these depositories, the northern- and southern Klipheuwel Group, are individually treated and classified in future stratigraphic and sedimentological studies given their distinctiveness. Attempting to classify units across these two depositories results in a broad generalisation of layers, creating confusion and a general misunderstanding of the Klipheuwel Group. The individual classification of depocentres brings into question the validity of having one type locality for the entire Klipheuwel Group. The abundance of similar intra- and extraclastic material throughout the northern and southern Klipheuwel Group suggests the underlying Pan- African metasediments as the primary source of detritus for both depositories. Similar pre-vegetation fluvial sedimentation characteristics occur at both depocentres, but distinct variation in the facies association assemblage exists due to topographical controls on the respective depocentres. The laterally persistent facies assemblages and extensive northern depocentre are attributed to pre-vegetation braided fluvial characteristics prevailing on the peneplained Pan-African basement but are now only preserved as erosional isolated relics due to extensive reworking and denudation from the overlying Cape Supergroup. In contrast, the distinctly channelised southern Klipheuwel depocentre, with rapid lateral facies changes, is controlled by active subsidence and faulting due to localised reactivation of basement faults (Colenso Fault), developing a topographically confined braided fluvial environment. These basinal controls explain the preserved thickness variation for each Klipheuwel depocentre, with the north being exposed and severely reworked and the south being downthrown and preserved. These findings are in contrast to lithological and structural fabrics within the Franschhoek Formation, that indicate the stratigraphic separation of the two units. The rudaceous nature and Pan-African strains throughout the Franschhoek Formation suggests that synorogenic sedimentation in a compressional piggyback basinal setting. Acknowledgements We are grateful to the postgraduate support program (PSP) at Stellenbosch University for funding. 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