Submarine lobe deposits of the Point Loma Formation, California: Quantifying event‐bed architecture and lateral heterogeneity. (28th July 2021)

• Record Type: Journal Article
• Authors: Fryer, Rosemarie C.; Jobe, Zane R.; Laugier, Fabien; Pettinga, Luke A.; Gilbert, J. Clark; Shumaker, Lauren E.; Smith, James E.; Sullivan, Morgan
• Is Part Of: Depositional record. Volume 7:Number 3(2021)
• Page Start: 374
• Page End: 391
• Publication Date: 2021-07-28
• Subjects: hybrid event bed -- pinchout -- submarine fan -- thinning rate -- turbidite; Sediments (Geology) -- Periodicals; Sedimentology -- Periodicals; Sedimentation and deposition -- Periodicals; 552.5
• DOI: 10.1002/dep2.156
• Languages: English
• ISSNs: 2055-4877

Abstract

Abstract: Over the last several years, numerous outcrop localities have been revisited to add quantitative detail to submarine lobe facies models that previously focussed on facies relationships in a qualitative sense. This study utilises well‐exposed submarine lobe deposits of the Point Loma Formation in Cabrillo National Monument (San Diego, CA) to provide quantitative and statistical insights into the lateral variability of event‐bed (i.e. turbidite) architecture within and between lobe elements. Within a lobe element (defined as a surface‐bounded, genetically related package), event beds compensationally stack, thinning over subtle sea floor topography created by the previous event bed. Between lobe elements, larger‐scale compensation is observed, with clearly defined stratal surfaces and facies architecture distinguishing the four lobe elements. A lateral facies transition is observed for one lobe element, where sandstone beds pinch out and the element thickness halves over a distance of 100 m. However, architectural parameters of event beds (e.g. bed thickness, thinning rate, fining rate) are not appreciably different between these elements, suggesting that the observed stratal architecture does not readily translate into vertical bed thickness (i.e. stacking) patterns that could be easily recognised in common subsurface data types like borehole‐derived core. While the data derived from this outcrop study are valuable for improving the construction of realistic geological and reservoir models, caution is necessary when interpreting lobe element boundaries from borehole data. The lobe deposits measured in this study have event‐bed thicknesses and thinning rates most similar to semi‐confined proximal lobes, suggesting a more proximal position and more confined than previously interpreted. Based on the relationships between sandstone and mudstone thicknesses and thinning rates, bed and lobe‐element compensation and minimal evidence of erosion, the Point Loma Formation at Cabrillo National Monument is reinterpreted as a medial lobe environment with some degree of lateral and/or frontal confinement. Abstract : Using exceptional exposures of submarine lobe deposits of the Point Loma Formation in San Diego, California, this study provides quantitative and statistical insights into the lateral variability of turbidite event‐bed architecture within and between lobe elements. The rich data set produced by this study provides insights for analysing lateral heterogeneity in submarine lobe deposits, especially in data‐limited settings where lateral facies variability at the bed scale is not observable. This study shows that the observed stratal architecture caused by event‐bed to event‐bed interaction and compensation does not readily translate into vertical event‐bed stacking patterns that could be recognised in common subsurface 1D data types (e.g. well‐log, core).