Structural and depositional history, Jefferson and Madison basins, southwestern Montana

Conference · Mon Aug 01 04:00:00 EDT 1983 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6404372

Rasmussen, D L; Fields, R W

Recent seismic and gravity data from the Cenozoic Jefferson and Madison basins provide new information concerning their structural and depositional histories. Both basins are north-south elongated structural basins formed as a result of horizontal extension after Laramide horizontal thrusting. Gravity data show that each basin in the subsurface is asymmetric with a large steep west-dipping fault on the east flank, and one or more east-dipping fault(s) of smaller magnitude on the west flank. The deep axis of each basin runs parallel to the east mountain front and lies east of the surface geographic central axis. Jefferson basin has two deep, closed, structural lows (one east of Silver Star and one east of Twin Bridges), which are separated by a structural arch. Seismic data confirm or support the gravity data. Seismic also shows the folded and thrusted rocks of the east mountain footwall block dipping steeply westward to where they gradually disappear beneath the thick Tertiary sediments. Tertiary strata lying directly against the large west-dipping basin fault show dip reversal caused by drag-folding during basin subsidence. Strata seen in the seismic sections can be subdivided into a lower set which forms the bulk of the basin fill (possibly equivalent to the Renova Formation, late Eocene to early Miocene); a thinner middle set unconformably overlying the lower set (equivalent to the Sixmile Creek Formation, Miocene and Pliocene); and an upper set composed of west-dipping Quaternary alluvial fan deposits. Each set thickens toward the east basin-bounding fault.

• Research Organization: Davis Oil Co., Denver, CO
• OSTI ID: 6404372
• Report Number(s): CONF-8309274-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 67:8
• Country of Publication: United States
• Language: English

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