Mineralogy and geochemistry of pattern formation in zebra rock from the East Kimberley, Australia
Bibliographic record
Abstract
Rhythmic patterns are widespread in geological materials. A particularly striking, macroscale example is zebra rock from the East Kimberley region of northwestern Australia. The rock is famous for its distinctive, rhythmically ordered, iron-oxide pattern, which transforms an Ediacaran-aged siltstone into an attractive semi-precious gemstone. Several different formation mechanisms of this pattern have been proposed in previous studies, with the two most prominent being redoximorphic banding in acid-sulfate soils and Liesegang banding in an acidic hydrothermal system. Using a combination of mineralogy, geochemistry and geological context, this study attempts to confirm both the occurrence and relative timing of acid-sulfate fluid rock interactions in zebra rock and seeks to determine whether pedogenic processes or hydrothermal alteration can better explain the origin of these patterns. We present the first evidence that the iron-oxide banding developed simultaneously with a period of aluminosilicate dissolution, clay precipitation, and fluid flow, consistent with the infiltration of an acidic fluid. This conclusion was evidenced through the hexagonal-platelet morphology of the hematite pigment, kaolinite-hematite textural relationships, and a paleoflow direction preserved in the asymmetric intensity of the hematite concentration. However, while the mineralogy of zebra rock strongly suggests interactions with acid-sulfates, the origin and temperature of the fluid could not be conclusively determined. Supporting a hydrothermal origin, a thorough analysis of zebra rock mineralogy revealed a mineral assemblage consistent with advanced argillic hydrothermal alteration, wherein pyrophyillite, kaolinite, and dickite indicate minimum palaeotemperatures upwards of 120 °C and the presence of alunite and a svanbergite-woodhouseite solid solution suggests oxidising, acidic (pH <5) conditions. The low Rb/Sr ratio and relative immobility of rare earth elements in most zebra rock deposits are also consistent with an acidic hydrothermal origin. Further support was also observed in the mineralogical trends between examined outcrops, grading from alunite-type to kaolinite/dickite-type facies in a south-west direction. But despite this evidence, the acid-sulfate soil hypothesis could not be refuted and was itself supported by the large number of pyrite dissolution voids both underlying and within the patterned layer. Furthermore, the consistent compaction of reduction spheroids, dissolution voids, and pseudomorphic inclusions within the light banding of zebra rock are in agreement with near-surface supergene weathering, ruling out hypogene hydrothermal alteration. A mechanism of pattern formation is proposed whereby zebra rock banding is formed by the Liesegang phenomenon, driven by the oxidation of Fe2+ ions during the infiltration of an Fe2+-rich, acid-sulfate fluid into oxidising host sediments.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".