Sedimentology and stratigraphy of Tropic Shale and Tununk Member of Mancos shale (Cenomanian-Turonian), southern Utah

Conference · Mon Feb 01 04:00:00 EST 1988 · AAPG Bull.; (United States)

OSTI ID:5792475

Zelt, F B

The Tropic Shale and Tununk Member of the Mancos Shale in southern Utah comprise a tongue of marine mudrock that was deposited during the Cenomanian-Turonian eustatic highstand. Seventeen outcrop sections and numerous geophysical well logs were used to correlate marker beds and identify lithofacies in the Tropic and Tunuck. The lower part of the study interval consists of a condensed section of bentonite and smectitic, calcareous claystone that was deposited during widespread transgression in the latest Cenomanian and earliest Turonian. To the west, the overall stacking pattern of coeval shoreline deposits is retrogradational. In sections that are more than 70 km from the coeval paleoshoreline, the smectitic claystone facies is overlain by rhythmically interbedded calcareous claystone and calcareous clayshale. The calcareous claystone-clayshale couplets correlate bed-by-bed with the well-known limestone-calcareous clayshale couplets of the Greenhorn Limestone in central Colorado, which have been interpreted to record 40,000 year Milankovitch cycles. These rhythmites were deposited during the early Turonian eustatic highstand, when the previous, retrogradational stacking pattern of shoreline deposits in southern Utah gave way to aggradational and then progradational stacking. As a result of the lowering of relative sea level in the middle Turonian, typical sections of the Tropic and Tununk are capped by two additional lithofacies. These more proximal facies are a black non-calcareous claystone facies (70-35 km from paleoshoreline) and a siltstone-mudstone facies (< 35 km from paleoshoreline) that includes distal prodelta/lower shoreface turbidites.

• Research Organization: Exxon Production Research Co., Houston, TX (USA)
• OSTI ID: 5792475
• Report Number(s): CONF-880301-
• Conference Information: Journal Name: AAPG Bull.; (United States) Journal Volume: 72:2
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
&amp; Exploration
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
BENTONITE
CARBONATE ROCKS
CLAYS
COLORADO
FEDERAL REGION VIII
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
LIMESTONE
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
SHALES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SMECTITE
STRATIGRAPHY
USA
UTAH