Skip to Main Content

Abstract

The deposition of the late Turonian-early Coniacian Upper Ferron Sandstone Last Chance Delta occurred during a long slow relative rise in sea level, interrupted only by three minor 4th-order relative falls in sea level. An analysis of stratigraphic, geometric, and architectural data, for both near-marine and non-marine facies indicate that Last Chance Delta architecture was controlled by changes in sediment supply. The systems tract style and parasequence set stacking pattern within deposition-al sequences reflect the relationship of the rate of sedimentation to the rate of relative change in sea level.

The Upper Ferron Sandstone Last Chance Delta was deposited along the western margin of the Cretaceous Western Interior Seaway between 90.3-88.6 Ma, as a wave-modified, river-dominated fluvial-deltaic system. Detailed stratigraphy and quantitative cross sections based on volcanic ash layer correlations and coal-zone stratigraphy have been used to delineate the depositional sequence stratigraphy of the Last Chance Delta clastic wedge exposed in Castle Valley of east-central Utah. Relative sea level and local subsidence curves, and sedimentation rates have been determined from analysis of these cross sections.

Within the Last Chance Delta, at least 42 parasequences organized into 14 parasequence sets form four 4th-order depositional sequences (denoted FS1 through FS4). In the non-marine to transitional near-marine facies associations, the upper boundaries of parasequence sets, when not coincident with sequence boundaries or transgressive ravinement surfaces, are coal zones. Laterally extensive unconformities, with 20–30 m (66-98 ft) of erosional relief, locally mark the lower boundaries of sequences FS2, FS3, and FS4. These unconformities are interpreted as type-1 sequence boundaries that record basinward shifts of paleoshorelines by up to 3-7 km (2–4 mi) and the development of incised-valley systems ranging up to 6-10 km (4-6 mi) wide.

The lower boundary of sequence FS1 is a correlative conformity immediately below a condensed section within the underlying Tununk Shale. The upper boundary of FS4 is a correlative conformity stratigraphically above a concretion-bearing condensed section a few meters above the uppermost sandstones of sequence FS4. FS1 is a 4th-order highstand sequence of the 3rd-order Hyatti Composite Sequence. FS2 and FS3 are the progradational (early lowstand) to aggradational (late lowstand) sequences of the Ferron Composite Sequence; FS4 is the transgressive sequence. Lowstand sequence FS2 contains well-defined forced regression deposits and higher-order sequence boundaries. The highstand deposits of the Ferron Composite Sequence are represented, within Castle Valley, only by offshore marine shale deposits.

You do not currently have access to this chapter.

Figures & Tables

Contents

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal