VICTORIA ISLAND STRUCTURE

VICTORIA ISLAND STRUCTURE

by: Charles O’Dale

  • Type: Complex
  • Location: N 37° 53’24″ W 121° 32’06″
  • Age Ma: 37 – 49a
  • Diameter: 5.5 km

a Supplemental cuttings and well log data may also further constrain the stratigraphic age of the structure within the Domengine-Nortonville interval. (Spevack et al 2007).

3-D SEISMIC AND WELL LOG ANALYSES OF THE VICTORIA ISLAND STRUCTURE, A POTENTIAL BURIED IMPACT CRATER, SAN JOAQUIN COUNTY, CALIFORNIA.
C. Spevack, J. R. Morrow, and B. Z. Spevack

Introduction: Analyses of a 3-D seismic survey and well logs in the southwestern Sacramento basin, San Joaquin County, California, have revealed a subsurface, circular, ~5.5-km-diameter anomaly that may represent a previously unrecognized complex impact crater (Figs. 1–3). This unique anomaly, buried 1,490–1,600 m below sea level under the southwestern part of
the Sacramento-San Joaquin Delta, is provisionally named the Victoria Island structure for an overlying surface geographic feature.

Figure 1. The Victoria Island structure is characterized by a concentric, annular, terraced rim and trough surrounding a structurally uplifted central peak. Contour lines of equal thickness over an area (Isopach map) of interval between upper Nortonville Shale marker and lower Domengine Formation marker, showing series of concentric circular ridges and troughs, together with positions of several major, curvilinear normal faults that surround the structure and cut the lower part of the isopached interval. (Spevack et al 2007)
I took this image in 1996 while flying over the Golden Gate Bridge, the peak of the bridge is just visible in the lower left. San Francisco is in the foreground and looking east, the position of the Victoria Island Structure is visible in the far distance of the image centre.

 The 5.5km-wide bowl of the Victoria Island Structure is buried under shale sediments west of Stockton, in San Joaquin County, and is thought to be between 37 and 49 million years old.
Figure 2. Contour lines of equal thickness over an area (Isopach map) of potential crater infill, between upper Nortonville Shale marker and base Nortonville Shale/top Domengine Formation marker. (Spevack et al 2007)

Analyses of a 3-D seismic survey and well logs in the southwestern Sacramento basin, San Joaquin County, California, have revealed a subsurface, circular, ~5.5-km-diameter anomaly that may represent a previously unrecognized complex impact crater (Figs. 1–3). This unique anomaly, buried 1,490–1,600 m below sea level under the southwestern part of the Sacramento-San Joaquin Delta, is provisionally named the Victoria Island structure for an overlying surface geographic feature. (Spevack et al 2007)

Figure 3. Oblique, inverted 3-D-view isopach map of potential crater infill. Map is based on same isopach interval as in Figure 2, between upper Nortonville Shale and base Nortonville Shale/top Domengine Formation markers. Vertical exaggeration is 20X. Isopach colors and thicknesses are the same as in Figure 2. Note the image is looking west to east. (Spevack et al 2007)
Figure 4. West-east seismic profile across structure (A–A’, Figs. 1–2). Stratigraphic markers: Blue– upper Nortonville Shale; red– base of Nortonville Shale/top of Domengine Formation; green– lower Domengine Formation; yellow– approximate base of Capay Formation/top of Mokelumne River Formation. Selected major, concentric normal faults (Fig. 1) that intersect the profile are shown schematically by black lines. (Spevack et al 2007)

ABSTRACT

The middle Eocene Domengine Formation crops out in the Coast Ranges along the structurally complex westernmargin of the basin and forms an economically important gas reservoir in the Sacramento basin, California. Previous studieshad interpreted the Domengine Formation as a conformable succession of barrier-island sandstone with tidal channels andcoastal-plain deposits or a delta, tidal shelf, marsh complex located along a north–south-trending shoreline bordering the shelf.Integration of outcrop and subsurface data, however, indicate that the Domengine Formation can be regionally subdivided intotwo sequences. The bases of each sequence consist of fluvial and estuarine sandstones that were deposited in northeast– southwest-trending incised-valley systems that are interpreted to have been formed by fluvial incision. Shelfal shales andshoreline sandstones overlie the incised-valley fills and reflect flooding of the shelf. This cyclicity is interpreted to have beenproduced by the interplay of tectonism and eustasy. Tectonism is interpreted to have controlled the location of the incisedsubmarine canyons and the fluvial estuarine systems throughout the early Tertiary as they stack vertically and trend southwesttoward the structurally controlled depocenter. Eustasy appeared to have controlled the timing of the transgressive–regressivedepositional cyclicity present in the lower Tertiary succession due to the strong correlation of available biostratigraphic dataconstraining the timing of these major periods of incision to the global coastal-onlap curves. Thickness trends observed in theDomengine Formation are interpreted as a product of variable incision, and not the result of depositional thinning in anorthwesterly direction suggested by the previous models. The importance of this reinterpretation of the Domengine Formation,within a sequence stratigraphic framework, is that it provides a predictive model for both understanding the thickness trendsand facies distributions of the Domengine Formation. It also potentially provides a more accurate depositional model for exploration and development of this important hydrocarbon reservoir. (SULLIVAN et al 2012).


References

Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education

Grieve R.A.F., Robertson P.B., IMPACT STRUCTURES IN CANADAthe Journal of the Royal Astronomical Society of Canada, February 1975

S. C. Spevack, J. R. Morrow, and B. Z. Spevack 3-D SEISMIC AND WELL LOG ANALYSES OF THE VICTORIA ISLAND STRUCTURE, A POTENTIAL BURIED IMPACT CRATER, SAN JOAQUIN COUNTY, CALIFORNIA. Lunar and Planetary Science XXXVIII (2007)

R. Sullivan AND M.D. Sullivan; SEQUENCE STRATIGRAPHY AND INCISED VALLEY ARCHITECTURE OF THE DOMENGINE FORMATION,BLACK DIAMOND MINES REGIONAL PRESERVE AND THE SOUTHERN SACRAMENTO BASIN,CALIFORNIA, U.S.A. Journal of Sedimentary Research, 2012, v. 82, 781–800

University of New Brunswick, 2012.