Stratigraphic Analysis of Eolian Interactions with Marine and Fluvial Deposits, Middle Jurassic Page Sandstone and Carmel Formation, Colorado Plateau, U.S.A.

Abstract

ABSTRACT The eolian Page Sandstone (Middle Jurassic) in south-central Utah and adjacent Arizona consists of multiple mostly eolian and sequence-bounding unconformities (super surfaces). The super surfaces are a powerful correlation tool that provide the basis for a detailed regional stratigraphic analysis of the Page Sandstone and coeval parts of the marine and coastal-plain Carmel Formation. Some Page Sandstone super surfaces correlate with sharp lithologic breaks in the Carmel Formation that are interpreted as marine flooding surfaces. Others correlate with fluvial surfaces in the Carmel Formation. The lower part of the Page-Carmel interval encompasses seven onlapping accumulation bounded by marine flooding surfaces. The uppermost two represent the Middle Jurassic marine high-water mark. These seven units comprise marine transgressive and marine highstand system tracts. Each interval is composed of progradational eolian deposits over marine deposits. Major tectonic and sedimentologic changes affected accumulation 8 and 9. The two intervals are continental in origin, fluvial to the west and eolian to the east. A major slightly angular regional unconformity marks the top of accumulation 9. The unconformity reflects regional tilting, up to the northeast, and ensuing erosion of older units in the Page Sandstone. Accumulation 10, the top of the s udy interval, displays complexly juxtaposed continental and marine facies that buried the unconformity as regional subsidence continued. The broad patterns described above can be correlated with thick marine carbonate and minor siliciclastic deposits of the Twin Creek Limestone 400 km north of the study area. The resulting depositional patterns define three broad depositional events. The oldest of these sequences defines a regional marine transgression and highstand. The second sequence reflects strong siliciclastic influx and slight regional tilting that resulted in widespread continental deposition. Regional tilting and erosion closed out this event. The youngest sequence indicates a partial return to marine transgressive conditions but was complicated by regional uplift and tilting related to are tectonism. This study demonstrates that a stratigraphic framework can be applied to sparsely fossiliferous eolian, sabkha, and restricted marine deposits in a marine-coastal setting. Using detailed sedimentologic and stratigraphic studies, tectonic, eustatic, and possibly climatic signals can be differentiated within the complex, cyclic facies patterns displayed in the Page Sandstone and Carmel Formation.