Detrital zircon <scp>U–Pb–Hf</scp> data from Cambrian sandstones of the Ougarta Mountains Algeria: Implication for palaeoenvironment
Bibliographic record
Abstract
We report new detrital zircon U–Pb ages and Hf isotopic signatures of detrital zircons in Cambrian sedimentary rocks from the Ougarta Mountains of Algeria in the West African Craton (WAC) in order to provide constraints on the palaeo‐catchments of the Early Palaeozoic river systems draining Gondwana. The Cambrian sedimentary samples from the Ougarta Mountains have near‐identical age spectra with a dominant age peak at 618 Ma and an additional age peak at 2,035 Ma. The oldest detrital zircon grain is 3,407 Ma. The εHf (t) values of the 618 Ma age peak spans from εHf (t) +12 to −25 with a dominant mode at −1; the εHf (t) of the Palaeoproterozoic zircon ranges from 6 to −27 with an average of −10; the pre‐2,300 Ma zircon Hf lie along a crustal evolution trajectory ( 176 Lu/ 177 Hf = 0.01) back to the depleted mantle at ~3,100 Ma. The maximum depositional age of the sandstones in the Sebkhet el Melah Formation is constrained by the youngest detrital zircon age of 559 ± 13 Ma and by the underlying volcaniclastic rocks dated at 555 ± 7 Ma (Late Ediacaran to the Early Cambrian). The 618 and 2,035 Ma age peaks are consistent with a proximal provenance from the WAC, and it is possible that recycling of eroded material from the Cadomian arc and Pan‐African rocks may have been a potential source of the Ediacaran detrital zircons analysed herein. There were four (0.9%) Stenian detrital zircons identified in this study, and our results are consistent with the lack of WAC Stenian detrital zircon noted in previous studies, except those reported from a single Middle Cambrian sample in Morocco. Correlative sedimentary successions further to the east contain ubiquitous ca. 1.0 Ga detrital zircon that was likely supplied from the Trans‐Gondwana Mountain chain. It is noteworthy that the WAC and Sahara Metacraton are surrounded on three sides by Neoproterozoic orogenic systems, with the Rokelide, Dahomeyide, Pharuside, Anti‐Atlas, and Brasiliano orogens (reconstructed position from Gondwana palaeogeography) around the WAC and the Dahomeyide, Pharuside, East African orogen, and Oubangides orogens around the Sahara Metacraton. We posit these orogenic belts acted as drainage divides that controlled sediment routing pathways. Additionally, the occurrence of Stenian detrital zircon in Morocco could be explained by longshore drift coming from the east (present‐day coordinates).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".