Sedimentologic and Diagenetic Analysis of Microbialite-bearing Lacustrine Rift Sequence in the Lower Cretaceous Yucca Formation, Indio Mountains, West Texas-An Outcrop Analog to Presalt Microbialite Reservoirs
Bibliographic record
Abstract
Microbial carbonate reservoir facies in Cretaceous rift basins along the South Atlantic margins are poorly understood regarding their spatial and temporal distribution and modes of diagenetic porosity enhancement and occlusion. In order to better understand controls on reservoir and trap architecture in these complex systems, we present an outcrop analog study of the depositional/diagenetic features and stratigraphic framework of the Lower Cretaceous Yucca Formation lacustrine microbialite facies (MF) deposited within a syn-rift basin on the eastern margin of the Chihuahua trough. The syn-rift succession was inverted during Laramide-age shortening and is exceptionally well-exposed within 3 thrust panels in the Indio Mountains of West Texas. Microbialite-bearing cycles were also evaluated as to proximity to faults (syndepositional?). Three distinctive types of MF are recognized: (1) gray to greenish microbial carbonate concretions within reddish, light purple or greenish siltstone to mudstone. Concretion interiors contain septarian-style fractures mainly filled by coarse-crystalline calcite (CCC), which is commonly partially silicified following local brecciation. Additionally, saddle dolomite, carbonate fans, spherulites and shrubby textured precipitates (microbialite?) are locally present within the concretions. Porosity networks are formed by dissolution or fracture. The surrounding mudstones show multiple phases of replacement including detrital quartz replaced by euhedral dolomite and dolomite replaced by authigenic quartz; (2) low-porosity stromatolitic bindstone with dark irregular chert nodules. Phreatic dolomite, silica and CCC cements progressively filled in the primary porosity of microbial framework; (3) greenish, slightly dolomitized thrombolite of low porosity in light purple siltstone to mudstone. The three facies are organized into 3 to 5m thick lacustrine cycles separated by fluvial facies. Each cycle progresses upward from concretions, to stromatolites, to thrombolites. The lacustrine cycles are commonly eroded laterally by the overlying fluvial channels that contain basal gravels including MF clasts. The MF are depositionally and diagenetically highly variable over short distances, possibly related to proximity to faults. Microbial reservoir quality is mainly improved by diagenetic dissolution and fracturing during burial diagenesis.
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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 | 0.001 |
| 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) | 0.001 | 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".