The Late Proterozoic Wonoka Formation of the Adelaide Geosyncllne, South Australia, is a regressive mixed carbonatezsiiiclastic sequence of marine origin. Outside the academic sphere, I gratefully acknowledge the support and encouragement of many personal friends, especially Simon, Kathy, Pru.
OPENING REMARKS
Hummocky cross-stratification
Dott and Bourgeois (1982) consider that HCS is “the result of a combination of consequences and .
FTGI-IFÈE L.4
This study of the Wonoka Formatlon has been largely confined to the study area outlined in fig. Map of this study's main area within the Flinders Ranges showing the distribution of the Wonoka Formation and.
MAIN STUDY
CEI\T'TTÈAI- AI\ID SOTJTI{ FI-II\TDEFÈS ZOIVES
The best exposure of the Wonoka Formation that is both fault-free and easily accessible is the 690 m thick Bunyeroo Gorge section in the Heysen Range (Fig.2.1). Most units were found to be throughout the CFZ and northern South Flinders Zone (SFZ).
T3'IGT-JFÈE 2 .I
ÉEF
Diseussion
UNIT 1
- Llthofecles of Unit I
In the Parachilna Gorge section, the exposures of the upper layers are exposed to extensive erosional scratching which is. In sections north of the areas described above, unit I is generally restricted to a thin (5–10 cm) allochthonous layer with a sharp base.
UNIT I
- UNIT 3
- Dlscussion of Unit I
- UNIT 2
- is eharacterized by the alternation of brown fine-grained calcareous and dolomitic sandstones and coarse siltstones, with maroon
- PLATE 2.1
- Unit 6 ,.'" o
- Unit 2....' r
- In the SFZ unit 2 displays a steady decrease in thickness to the east
- UNIT 2 PALAEOTURRENTS
It defines an abrupt regional change in sedimentation style, separating the uniform shales of the Bunyeroo Formation. The most common sole marks are fluted moulds, which can reach a considerably larger measured size: 60 cm long and 6 cm deep - see Plate 2.2Á)l below the thicker beds in the top of the unit.
III 72
- Discussion of Unit 2
- FTGTTFÈE 2 .6
- UNIT 2 - BUNYEROO
- UNIT 1
- UNIT 3
- is the most widely distributed, yet conservative of all unlts,
- PLATE 2.2
- UNIT 4
- is 150 m thick at Bunyeroo Gorge, and the base is taken at the first major occurrence of greenish limestones in the section. This may be a
- Lithofacies of Unit 4
- is characterized by the cyclic alternation of packets of thin-
In the CFZ and SFZ, the isopachs generally increase steadily to the east complementing the continuous decrease in thickness of unit 2. Following the abrupt cessation of sand supply at the top of the unit represents a return to dominant pelagic mud deposition. The base of unit 4 is particularly captured as indicated by the frequent association of malachite staining and nodules.
FTGIJR,E 2.7
Discussion of unit 4
In most areas, most of unit 4 was apparently deposited below storm wave base in an outer shelf environment, with increased impact of incident waves. The green color of the calcareous turbidite packages suggests reducing conditions in the source area higher on the shelf. Thls is a variation of the more common situation of oxidizing conditions in shallower waters and reducing conditions at depth.
PL,AITE 2.3
PLATE 2.3
- UNIT 6
- Carbonate lithofacies of unit 5
- Cyclic lithofacies of unit 5
They are well visible on large-scale aerial photographs, demonstrating that individual cycles can be traced with small changes in thickness of at least 10 km in a continuous outcrop. About 18 cycles can be recognized in the Mernmerna section, which is one of the best continuous outcrops. Three cycles from the Mayo Gorge section are shown in detail on the right (R = red horizon).
3 CYCLES
Diseussion of unlt 6
The cycles thus appear to be largely related to changes in the supply rate of. Such is the case in Mexico's eastern GuIf, one of the world's least modern carbonate shelves. Such climate change may be caused by Milankovitch cycles, which are periods of solar radiation associated with periodic changes in Earth's orbital parameters.
Lithofacles of Unit 6
Discussion of Unit 6
A thick unit of dark red limestone comprises the dark unit extending from the lower right corner (the top of unit 5. This is probably a relative)/thin subsurface of the pical unit 6,. These are interconnected beds of an inch thick swamp. in this case a distance of about 6 m. E'F Photo including the lower cycle shown in figure F) is a close-up of the lower part of (E) showing the red limestone at the bottom of the central rock in 2.10.
PLATE 2.4
- UNIT 7
- Lithofacies of Unit 7
Intraformational conglomerates, either as continuous beds or containing pot and gutter molds are common and increase in abundance toward the top of the unit lPlate 2.6 (C,F)], Abundance i. The base of the hammer rests on a lenticular red horizon, which divides the bed, of the first order. Weather hiehlieht laminae siltier and stylonodular quality at the top and bottom of.
PLATE 2.5
The stromatolites are usually confined to a single bed, usually not more than 30 cm thick, but at Brachina Gorge they occur in several beds over a 4 m interval and at the Mernmerna and Yappala sections they occur over a shallow water interval of 12 m. unit 7. Red hematitic limestone beds (dark red in outcrop, lighter when fresh), occur in units 6 to 7, but are generally most prominent in unit 7.
UNIT 7
PLATE 2.6
- Discussion
On a larger scale, the occurrence of red HCS limestones also appears to be cyclical in the middle of the unit. 2.10, Plate 2.4 (E-G)|, Most of the red HCS limestones at this locality are less than 1 m thick, but a 3 m bed is present with a distinct jointed character, including interbedded lenses of shale. To discover the reason for the alternation between red and green carbonates and their different sedimentary structures, it is useful to first look at.
PLATE 2.7
Letolle, 1980), but the close association of the two minerals observed here has only rarely been described (Bailey & Atherton, f969; Birch, 1979). The fact that the red limestones do not develop stylonodular textures and are generally not reworked into intraclasts like the associated gray-green limestones suggests. The formation of the red limestone, mainly in situ by ash entry into the active carbonate environment of the shelf, followed by seafloor oxidation and other changes, seems unlikely.
2.IO UNIT 8
Lithofacies of unit
Palaeopascichnus (see 5, 2) often occurs within such facies. Note the rotation of bedding laminae in the concretions relative to that in the host siltstone.
PLATE 2.8
- o.2 Discussion of unlt 8
The base of unit 8 appears to record a slight deepening after the very shallow conditions represented by stromatoles at the top of unit 7. The thin but widespread purple marker horizon may be related to contemporary volcanism and is considered a timeline.
2.II UNIT 9
PLATE 2.9
Wllkawillina Gorge pebble lenses occur near the middle of the unit. reworked in a(iacent sediments.
2.I2 UNIT IO
- Lithofacies of unit 10
- Discussion of Unit 10
The green shale unit at the top of unit 1O is widespread and is absent only in the northern CFZ and Wilkawillina Gorge section. During unit 10 time, this "red bed" facies prograded from the west over large areas of the CFZ and SFZ, but did not. As noted above, the facies developed in Unit 10 are very similar to some of the facies found in the Bonney Sandstone.
- is 16 m thick at the Bunyeroo Gorge referenee section. It generally
- UNIT 11
- Ooids of unit 1l
- PLATE 2.10
- Microstructures: Unit 11 contains normal ooids (composed of
- PLATE 2.11
- Calcrete-like material is also present. Of particular interest is
- g.2.2 Discussion: Brick textures were first described bV nþefto and
- FTGIJTÈE 2.L2
- Chapter 2 described the laterally persistent ('layer cake')
- UNITS 1 AND 2
Within unit 1l, the majority of the ooids are found in the areas south of the Parachilna Gorge and. More rarely, ooids may be composed of fine-grained doimite, which retains varying degrees of the original material. The well-developed olite-encapsulated cycles in the lower part of the unit resemble the granular ones.
FTGIJF¿E 3.2
BUNYEROO PARACHILNA WARRAWEENA GODDARD
UNIT 3
Goddard Syncline unit 3 is much thicker and has a much lower carbonate/shale ratio, similar to the typical development in the CFZ and SFZ. The lateral equivalents of units 4 and 5 in the extreme northern CFZ and equivalents of units 4 to 7 across the C/NFZ boundary, consist of. In most places the surface is overlain by mudstone, except in the deepest part of the eut, which is filled with debris flows.
PLATE 3.1
Bounding surfaces of the limestones are commonly planar, but in some sections, particularly in the northern part of the CFZ (i.e. Old Warraweena section), the lower bound carbonates are thinner. Intraformational truncation surfaces occur at several different scales within equivalents of units 4 and 5 along the Mt. The B channel filled with overlapping intraciaster (outline inked .. in) incised into the top of a collapsed mudstone rvith sparse. platl' earbonate clasts, Note overl)'ing limestone turbidites.
PLATE 3.2
- To the north this interval ls replaced by approximately 20 m of
- EQUIVALENTS OF UNITS 9 TO 1I
At the Black Range Spring partial section, at the southern edge of the boundary zone, unit 9 is 42 m thick. Northwest of the Pinda Diapir, the Wonoka Formation is also clearly visible. Coates (1973) indicates that the Pinda Diapir was active from the center. A detailed discussion of the Wonoka Formatlon in the NFZ is beyond the scope of this thesis.
PAI..AE O GEO GFÈAPHIC SIGI\ITFICAI\ÏCE
However, the purpose of this chapter is to describe several newly discovered occurrences of canyon deposits in the northern part of the study. Von der Borch et al. 1982) mapped Patsy Springs Canyon, which is perhaps the best preserved example of one of these structures. The canyon is exposed within the hinge of the tightly folded Angepena syncline and is cut through the Bunyeroo Formation, ABC Zone quartzite and part of the Brachina. Creation. Structure unfolding by von der Borch et al' (1982) indicates steep (60o) canyon walls and.
Ç 0 FIG. 4
Southern Flinders Ranges
Some of these were noted by Plummer (1978) who mapped part of one of the structures near Buekaringa Gorge. The bedding dips vertically near the bottom of the incision and steeply to the south higher up in the sequence. The lower part of the Wonoka Formation (Units 1, 2, and at least part 3) is truncated, so the canyon is an intraformational feature relative to the time of filling.
I Canyon fill sequence
- Unit B: Unit B outcrops very poorly and is about 400 m in
Near the base of the section, debris flows contain recognizable groups of ABC Range Quarztite, Brachina and Bunyeroo Formatlons, as well as abundant pink and green carbonates showing typical lower Wonoka. 4.3) is clearly unimodal with an average reading of 0300, which is the direction of Patsy Springs Canyon. Near the top of the unit, storms become common and there is a gradation to a sequence of white calcareous and dolomitic HCS sandstones and minor conglomerates (unit D), corresponding to.
PUTTAPA CANYON
- Canyon fill sequence
- Unit A: Unit A of the Puttapa Canyon is very similar to unit A
- Canyon fill sequence
A small coarse debris flow is exposed near the base of the cut, but the debris flows are much higher. Outcrops are mainly limited to the Bobmooney Creek bed and a few areas along the north shore. Unit B lies on the canyon wall northwest of the deepest point of the cut.
A normal section through the Wonoka Formation is visible along the southern edge of the map in Fie.4.6. This is clearly visible just west of the main road, where it bends at an angle of 15o to the north and is clearly truncated. Further debris layers higher in the range have been observed north of the map area.
C 1.5 m thick debris flow containing large angular blocks of canyon sediments and wall rocks of the lower Wonoka Formation, Bunyeroo Formation and euarchite of the ABC area.
PLATE 4.1
- DISCUSSION
- Are they really submarine canyons?
- CHAPTER SUMMARY
Recent unpublished observations (l2tt' International Sedimentological Congress Excursion) indicate that the fill of Patsy Springs Canyon contains evidence of tidai bundles, This may initially occur. In this respect, Patsy Sprlngs Canyon could be similar to lnclslons 3 and 4 of the Fortress Hill Canyon Complex (see von der Borch eú. Formation indicates the presence of oceanic depths ()l km) north and southeast of the Flinders Ranges at the time of deposition.
CHAPTE.FÈ 6
