Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Control of Thrust-Belt Transverse Zones on Sedimentation Patterns Revisited: Implications for Exploration Strategies in Fold-Thrust Belts and Their Adjacent Foreland Basins
(1) Geology and Geological Engineering, Colorado School of Mines, Golden, CO.
(2) Southwestern Energy, Houston, TX.
Our two-part investigation examines the affect of transverse zones on modern depositional systems, and the tectono-stratigraphic development of an ancient transverse zone in the Sevier Fold-thrust belt (South Provo Salient, UT). Results highlight the utility of exploration strategies that integrate regional structural and stratigraphic analysis. Along-strike partitioning of thrust belts occurs at a range of spatial scales from crustal-scale salients and reentrants to sinuosity along individual thrusts. Transverse zones (TZ’s) accommodate this partitioning through suites of small-scale structures and/or fractures that are oriented oblique-perpendicular to the thrust-front. TZ’s can influence sedimentation and foreland basin fill through: (1) structural weaknesses that focus erosion and deposition; (2) deflection of depositional systems due to uplift of structures within the TZ; (3) variation in thrust-belt load across a TZ that augment flexural subsidence and accommodation patterns; (4) changes in the rock-type exposed that can shift sediment provenance across the TZ. Analysis of 116 modern transverse zones in Asia and South America through remote sensing indicates a strong correspondence between the location of TZ’s and hinterland-derived, through-going drainages. 68-75% of the South Asian TZ’s affect drainage location and deposition (i.e., style, orientation and/or provenance), yet this decreases to just 54% in South America. The difference may be due to changes in stream power, perhaps because of contrasting climates of these two regions. In the ancient, detailed analysis of upper Cretaceous, synorogenic outcrops within the southern Provo Transverse Zone delineate its structural evolution and influence on sedimentation patterns in the Cordilleran Foreland basin. As suggested by previous workers, this transverse zone was a long-lived sediment point-source; however, the TZ also affected the types and distribution of facies. Initially, small-scale folds within the TZ focused deltaic deposition and increased wave-influence within delta lobes that were proximal to structures. Later, fluvial systems were focused through the TZ, but were locally deflected by the small-scale folds within the TZ’s; this followed by southward expansion of thrust deformation and alluvial fan development. In summary, TZ’s can control the location of long-lived sediment point-sources, but can also affect the distribution and quality of reservoir facies at a basin-scale.