--> Supercritical Flow Signatures and Erosional Features in Juncal Formation Basin Floor-Fans, California, US
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Rocky Mountain Section Meeting:
2020 Vision: Turn Hindsight to Foresight

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Supercritical Flow Signatures and Erosional Features in Juncal Formation Previous HitBasinNext Hit Previous HitFloorNext Hit-Fans, California, US

Dessy Sapardina1 and Piret Plink-Bjorklund1


1Colorado School of Mines


September 13-15, 2020 (CANCELLED) – Rocky Mountain Section Meeting: 2020 Vision: Turn Hindsight to Foresight, Grand Junction, Colorado

Posted: September 16, 2020

Abstract

A drone datasets from the Juncal and Point Loma Formation Previous HitbasinNext Hit Previous HitfloorNext Hit fans in California suggests a large degree of channelization even in the outer Previous HitfanNext Hit. The Juncal formation dataset further shows a significant deposition from Froude supercritical flow in the outer Previous HitfanNext Hit. Outer Previous HitfanNext Hit channels and a lower volumetric proportion of lobes has been suggested from some modern and recent systems. For example, the Navy and the Congo Previous HitfanNext Hit datasets suggest that submarine fans consist of a multitude of channels and related smaller heterolithic lobes, with sands dominantly deposited in channels, even on outer Previous HitfanNext Hit. Sedimentary structures originating from supercritical flow conditions have been identified in other ancient and modern submarine fans. Therefore, these findings raise questions about our understanding of Previous HitbasinNext Hit Previous HitfloorNext Hit Previous HitfanNext Hit deposits. The objective of this study is to test the hypothesis that a high degree of channelization and supercritical flow deposits are a common feature even in more distal parts of the Previous HitbasinNext Hit Previous HitfloorNext Hit fans. We further aim to document the relationship between channels and lobes in Previous HitbasinNext Hit Previous HitfloorNext Hit fans.

Drone photography survey of the Middle Eocene Juncal Formation in in Alyson Canyon in Los Padres National Forest, Santa Barbara, Ojai and in Ojala, California, was motivated by a previous study of approximately coeval slope succession in the Frazier Park area that identified a high proportion of supercritical flow deoposits in the slope section. Previous studies interpreted the Alyson Canyon area as proximal depositional lobe complexes in a Previous HitbasinNext Hit-Previous HitfloorNext Hit Previous HitfanNext Hit (Thompson, 1987), and the Ojala area along Highway 33 as outer-Previous HitfanNext Hit setting of depositional lobes (Obligado, 2003). In the Alyson Canyon area the facies are sandstone dominated and the sandstone facies occur as amalgamated, erosionally bound lenticular deposits. The Ojai outcrops are also sandstone prone but the small size of the outcrop does not allow to observe larger bounding erosion surfaces. In the Ojala area a proportion of heterolithic facies is larger and some heterolithic facies have a tabular architecture suggesting deposition in sheets or lobes, whereas sandstone-prone facies occur as erosionally bound lenticular deposits. Comparison to Froude supercritical flow experimentally produced data suggest that Froude supercritical flow deposits are common in the Juncal Formation Previous HitbasinNext Hit Previous HitfloorNext Hit fans. The erosion surfaces and the association of sandstone prone facies with the erosionally bound deposits suggest that the proportion of channelized deposits is high, and present even in outer-Previous HitfanNext Hit setting. Drone photography survey of the Point Loma Formation in the Sunset Cliffs confirm the latter observations and further documents considerable lithological variability in the outer Previous HitfanTop succession, with mudstone-prone and thinly bedded facies occur as interbedded repeated packages that culminate with lenticular sandstones. This stratigraphic architecture suggest presence of relatively small heteroliyhic lobes and sand-prone channels.

AAPG Datapages/Search and Discovery Article #90374 © 2020 AAPG Rocky Mountain Section Meeting, 2020 Vision: Turn Hindsight to Foresight, Grand Junction, Colorado, September 13-15, 2020 (CANCELLED)