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In order to fully address the research questions proposed in Chapter 1, this study examines all Units in the Laingsburg and Fort Brown formations, as well as more detailed studies on Unit E and on the less extensive, smaller Units A/B, B/C and D/E for the first time in detail (Fig. 3.7).

3.3.1 SLOPE, SLOPE 2, SLOPE 3 and LOBE project databases

Detailed mapping and correlation of all units utilizes regional correlation work undertaken in previous studies across the Laingsburg depocentre (Appendix D.1-D.7) (Grecula et al., 2003;

Hodgson, 2009; Prélat et al., 2009; Di Celma et al., 2010; Figueiredo et al., 2010, 2013; Flint et

al., 2011; Hodgson et al., 2011; Kane and Hodgson, 2011; Brunt et al., 2013a, b; Morris et al., 2014a,b; van der Merwe et al., 2014; Spychala et al., 2015, 2017a,b).

Previous work in the Laingsburg depocentre includes sedimentary facies patterns and architectural descriptions recorded in seven regional scale (60–90 km long) depositional dip–

parallel correlation panels. From south to north, these are Floriskraal South, Floriskraal North, Baviaans South, N1 Dome South, Baviaans North, Faberskraal South, Faberskraal North) (Appendix D.1-D.7). The database includes more than 1000 measured sections that were correlated by walking out key surfaces and units (typically the mudstones between each sand-prone unit). The correlation panels follow the west-east–trending limbs of the main post-depositional folds, and careful tracing of markers around the closures of these folds provides high confidence correlation between fold limbs.

3.3.2 Fieldwork- This study

This study included the collection of over 400 measured sections, totalling 14 km in thickness (Fig. 3.8; Appendix A) and the revisiting and relogging of over 250 others throughout the Laingsburg depocentre (Figs 3.8 and 3.9). These were logged at mm-cm scale to create detailed panel sections, over 10s of kilometres in dip and strike section. Logged sections document the lithology, grain size, sedimentary structures and stratal boundaries. The correlation framework was established by walking stratigraphic surfaces between sections, with the aid of regional mudstone units for long distance correlations. Correlation panels are augmented by helicopter, unmanned aerial photography and other photopanels. Logged sections are used to create isopach and palaeogeographic maps (Section 3.3.3). The Chapter 4 dataset contains 20 logged sections (Fig. 3.8; Appendix A). The Chapter 5 dataset contains 311 logged sections (Fig. 3.8;

Appendix A) new and revisited (partially re-logged). Lastly, the Chapter 6 dataset contains 341 logged sections (Fig. 3.8; Appendix A) new and revisited. Locations of farms, roads and rivers are shown in figure 3.9.

Figure 3.8 Location of logged sections new and revisited/ relogged in this study colour coded by chapter in which dataset is used. Grid references in Appendix A.

Figure 3.9 Location of roads, tracks, rivers and farms within the Laingsburg depocentre.

3.3.3 Isopach and palaeogeographic maps- This study

Thickness distributions were created by fitting a surface to thickness values from logged sections. Input data were collected and prepared in Excel (Table 3.1).

Table 3.1 Representative chart of thickness data preparation for the creation of isopach maps in ArcGIS.

The surface operation was conducted in ArcGIS using the simple kriging tool within the

Geostatistical Wizard (http://resources.arcgis.com/en/home/). Maps are extended beyond the extremities of the input data by the surfacing algorithm, with unrealistic values removed. An example of an output is shown in figure 3.10.

Figure 3.10 Representative chart of thickness data preparation for the creation of isopach maps in ArcGIS.

Palaeogeographic maps were created by using panels to reconstruct broad depositional environment for a given interval and overlaying this with isopach contours modified in CorelDraw. Data have been used from previous studies in the Karoo (Grecula et al., 2003;

Figueiredo et al., 2010, 2013; Di Celma et al., 2011; Flint et al., 2011; van der Merwe et al., 2014; Spychala et al., 2015, 2017a,b) with some palaeogeographic maps modified from van der Merwe et al. (2014). Restored palaeocurrent data presented on maps were collected from ripple lamination and tool marks.

Obect ID Log_code X_Base Y_Base Y_BaseStretch17.2 DE_Total E2_Total E3_Total

1 WFN201410 521025 6331025 6331728.432 0 1.45 4

2 WFN20132 521359 6330383 6330976.008 0 1.5 4.6

3 WFN20144 521730 6330901 6331583.104 0 1.4 3.8

4 WFN20146 522090 6330877 6331554.976 0 1.2 4.9

5 WFN20149 522313 6330984 6331680.38 0 0.8 2.2

6 WFN20149 522571 6330965 6331658.112 0 1.05 3.5

7 WFN20132 522767 6330960 6331652.252 0 1.1 4.45

3.3.4 Datacube and surface maps – SLOPE 4 collaboration

The datacube was collated by Dr Rachel Harding at Manchester University and utilises outcrop logs collected in all 4 phases of the SLOPE project, which were used to create two

Schlumberger Petrel 2015 projects in order to visualize complete basin floor-to-slope-to-shelf systems of the Laingsburg depocentre interactively in 3D. My contribution to this project was supplying field datasets and panels as well as verification of correlations and surfaces. The main focus of the Laingsburg datacube is the outcrop sedimentary logs and correlations of the submarine slope deposits of the Fort Brown Formation, (Units C-G) from SLOPE Phase 3 (Flint et al., 2011) plus the Waterford Formation upper slope to deltaic section (Waterford

Clinothems WfC1-8; Jones et al., 2013, 2015; Poyatos-Moré et al., 2016). The structural framework of the Fort Brown Fm. covers 2265 km² (Data: Appendix C). Surface maps (tops and bases) of the main sand prone units/subunits have been constructed, along with a map for Top Vischkuil Fm. Thickness maps between these surfaces represent the thickness of sand prone units and inter unit claystones.

The Datacube was created in Petrel by importing composite logs consisting of the complete Whitehill to Waterford stratigraphy as wells, with the top Whitehill used as a basal datum.

Tops and bases of key units were selected using the well top function, and additional data were used to interpret polylines to add datapoints between outcrop logs. Depth structure maps were created for each key surface using the ‘make a surface’ function and thickness maps were created between key surfaces. Post depositional tectonic shortening was corrected for by stretching 13% in the Y direction, according to a mean value for palinspastic restoration derived by Spikings et al. (2015).