Controls on the architecture of Lower Ismay zone of the Honaker Trail Formation (Pennsylvanian), San Juan River, Utah, USA | Posted on:2016-09-22 | Degree:M.S | Type:Thesis | University:University of Kansas | Candidate:Lechtenberg, Karen S | Full Text:PDF | GTID:2470390017981011 | Subject:Geology | Abstract/Summary: | | This study of the Pennsylvanian Lower Ismay zone of the Paradox Formation, Paradox Basin, Utah, USA intends to improve understanding of build-and-fill processes and carbonate sequence stratigraphy. Closely spaced, centimeter-scale stratigraphic sections reveal lateral and vertical heterogeneities in phylloid algal bafflestone and packstone of a mound-building phase and in fossil-rich wacke-packstone of a topography-filling phase.;Ten lithofacies and one sublithofacies were documented through field study and petrographic analyses. Facies are organized into 10 units within 2 sequences distinguished by lateral geometries and surfaces representing changes in depositional environment. Sequence 1 comprises Units 1-5 and provides evidence of an overall relative shallowing from 50-100m depositional depth to subaerial exposure. A relative sea-level rise was recorded between Units 4 and 5. Sequence 1 consists of lithofacies 1 through 5: 1) Black Laminated Mudstone (BLM); 2) Spicule Mudstone (SM); 3) Crinoid Packstone (CP); 4) Algal Bafflestone (AB); and 5) Algal Packstone (AP). The algal facies (Lithofacies 4 and 5) created relief-building geometries. The sequence was exposed and 5-7m of the topographically highest beds were erosionally truncated to create the famous undulose geometries of the algal facies, commonly known as the "mounds." Sequence 2 comprises Units 6-10, and shows evidence of an overall relative rise and fall in sea level. Facies of Sequence 2 fill in and drape underlying topography created by Sequence 1. It consists of the following lithofacies: Fusulinid Packstone (FP; 6); Skeletal Wacke-Packstone (SWP, 7); Skeletal Wacke-Packstone-Chaetetes (SWP-C, 7a); Peloidal Mudstone (PM, 8); Quartz Sandstone (QS,9); and Quartz Siltstone (QSt, 10).;The build-and-fill model is an enhancement of sequence stratigraphic models. It applies where carbonate strata exhibit subtle paleotopography, were subject to non-optimal carbonate productivity and high-amplitude sea-level changes. The stratigraphic succession in the Lower Ismay algal mounds shows evidence of relative shallowing and deepening during a relief-building phase. A subaerial exposure surface on the top of the algal facies indicates relative deepening was followed by shallowing during a relief-filling phase. The Lower Ismay zone provides an example of build-and-fill geometries that underwent different conditions than typical build-and-fill sequences, ultimately adding to our understanding of the processes that yield build-and-fill geometries. | Keywords/Search Tags: | Lower ismay zone, Sequence, Geometries, Build-and-fill | | Related items |
| |
|