Halokinetic-sequence stratigraphy, fluvial sedimentology and structural geometry of the Eocene Carroza Formation along La Popa salt weld, La Popa Basin, Mexico

Abstract

AbstractThe Eocene Carroza Formation in La Popa Basin, Mexico, represents fluvial sedimentation in a shortening-influenced salt-withdrawal minibasin, termed the Carroza Syncline. The Carroza Syncline lies adjacent to the La Popa salt weld, which was formerly a passively-rising salt wall that was shortened during the Hidalgoan Orogeny in Late Cretaceous and Palaeogene time. The Carroza Formation displays distinct upsection changes in fluvial facies distribution and geometry of halokinetic drape folding. Fluvial channel distribution changes upwards from widespread thin, broad channels with variable palaeocurrents in the lower part of the formation to thick, stacked channels concentrated in the hinge of the Carroza Syncline with weld-parallel palaeocurrent directions in the upper part. The upper and middle members of the Carroza contain debris-flow facies derived from diapir roof strata and the diapir itself. The style of halokinetic drape fold upturn and thinning towards the weld changes upsection from a broad (800–1500 m) to a narrow (50–200 m) zone, where upper Carroza strata are overturned and in direct contact with remnant gypsum along the weld. The upsection changes in fluvial facies distribution and geometry reflect an overall decrease in local sediment-accumulation rates relative to salt-rise rates controlled by both Hidalgoan shortening and passive diapirism.