Abstracts

AAPG 2010 New Orleans

Growth Faults and Relay Ramps: A High-Resolution Seismic Survey, Livingston Parish, Louisiana

Erin Elliott and Juan M. Lorenzo
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana
eellio4@tigers.lsu.edu

The United States Gulf of Mexico Coast is home to several east-west trending listric normal fault systems. One such system, the Baton Rouge–Tepetate Fault System, Louisiana, comprises a contemporaneous series of growth faults and relay ramps. There is evidence of recent movement in surficial fault line scarps, offset roads, and sedimentation patterns throughout the area. In order to study this soft sediment system, two near-surface (0 - 300 m), high-resolution (10 - 300 Hz), 300-m-long, continuous seismic reflection profiles (3 m geophone spacing; 24-channel) were collected across a growth fault and a portion of a relay ramp in Livingston Parish, Louisiana. The seismic source is a Down-hole Betsy Seisgun using 200 grains FFFF Black Powder and source-to-receiver offsets range from 4 m to 73 m. One seismic line crosses the tip of a growth fault. The other line crosses where the fault has a noticeable vertical offset. Through close evaluation of these data, correlated with well logs and gravity surveys across the fault and in the ramp area, this study proposes to investigate the link between (1) observed width and distribution of strain within the expected broad, fault deformation zone, and (2) sediment density distributions previously inferred from gravity studies.

AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in

• Fall AGU, 2004

• Gulf Coast Association of Geological Societies Meeting, 2004. San Antonio Texas

Relation between Holocene and Tertiary normal faults: A comparison of shallow seismic and gravity data with deep well data across the Baton Rouge fault system, northern Gulf of Mexico coast, Louisiana, USA.

Juan M. Lorenzo, ¹ Carrie Cazes, ¹ Clay Westbrook, ¹ Allen Lowrie, ² and Ivor Van Heerden³

¹Department Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803-4101

²Consultant, 238 F. Z. Goss Road, Picayune, Mississippi 39466

³Louisiana State University Hurricane Center, Louisiana 70803-4101

Extended Abstract

The Tepetate-Baton Rouge fault system traverses Louisiana from west (Tepetate system) to east (Baton Rouge system), and continues east and south of the Pearl River. This fault system is part of a larger, regional, down-to-the-basin fault system along the northern Gulf of Mexico that extends into eastern Mexico (Murray, 1961). Within our study area (Fig. 1) productive hydrocarbon accumulations occur principally south of the Baton Rouge fault-line scarp in deep (~5-10,000 feet) rollover structures, downthrown to the fault. Immediately to the north of the fault there are no equivalent structural traps. Shallow (<1000 ft) hydrogeology studies suggest that fluids can migrate across the fault zone.

Extensive, but unpublished well data from oil and gas exploration has generally suggested the existence of E-W striking subsurface growth fault trends but correlation with much lesser studied near-surface faults is lacking. By comparison, the location of shallow (< 1500 ft) growth faults, their geophysical characterization and the natural moderators that control their rates of movement in the southern Gulf Coast region are poorly known. We show for the first time that fault-line scarps are parallel to subsurface growth fault traces that are mapped within productive hydrocarbon intervals. At depth, this fault system exhibits late Eocene to Oligocene synextensional growth strata. Maps of surface, fault-line scarps (McCulloh, 1991 and 1996) indicate reactivation of these growth faults during at least the Quaternary. New laser altimetry data (www.atlas.lsu.edu) (Fig. 1) helps verify and modify prior interpretation of fault-line scarp locations.

Overlapping normal fault segments along the central Baton Rouge fault system, in Livingston Parish, may develop ramps that serve to divert local stream flow from a general N-S direction into a more NW-SE direction. We use new, high-resolution gravity data (+/- .01 milligal), digital elevation models (LiDAR, +/- 1 ft; Light Detection and Ranging), and borehole data (<100 ft depth), to investigate the effects of ramp evolution on sediment history. Associated shallow (<300 ft) sedimentary bodies can be discerned in gravity models. Gravity data reveals there is no consistent spatial relation between the northern limits of Bouguer gravity anomalies and location of the fault-line scarp. However, gravity anomalies are probably associated with denser (sand) elongated units oriented parallel-to-subparallel to the strike of the fault-line scarp and within the overlap zone. Interpreted sand bodies increase in width (~500-3,000 ft) and thickness (~150-250 ft) toward the east where the fault offset is expected to be greater and accommodation created by the rollover larger. A fault zone ~300 ft-wide extends from the northern fault-line scarp southward, as interpreted from high-resolution (~100-350 Hz), seismic data. Together with forced folds and late-stage multiple fracture directions that are expected from competent rock models of overlapping normal fault zones (Peacock and Sanderson, 1991), a complex sediment distribution pattern is predicted.

References

• South-Central Geolocial Society of America meeting, Texas A&M University 2004

Paper No. 8-3

Presentation Time: 2:00 PM-2:20 PM

INFERRED FRACTURE PATTERNS WITHIN OVERLAPPING NORMAL FAULT ZONES FROM SHALLOW, HIGH-RESOLUTION GRAVITY, SEISMIC, AND LASER ALTIMETRY (LIDAR) DATA SETS: NEOTECTONICS ALONG NORTHERN GULF OF MEXICO COAST, LOUISIANA, USA

LORENZO, Juan M.1, LANDRUM, Jeffrey T.2, CAZES, Carrie1, WESTBROOK, Carroll1, and VAN HEERDEN, Ivor3, (1) Louisiana State Univ, E235 Howe-Russell, Baton Rouge, LA 70803-4101, juan@geol.lsu.edu, (2) Dept. Geology and Geophysics, Louisiana State University, Howe-Russell Building, E235, Baton Rouge, LA 70803, (3) LSU Hurricane Center, Louisiana State Univ, Suite 3221 CEBA Building, Baton Rouge, LA 70803 Holocene, normal fault reactivation of Tertiary growth faults at and south of ~30.5 degrees, Louisiana generates linear, arcuate and splayed surface fault traces with overlap zones hundreds of meters to 10 km wide. Within overlap zones detailed, surface and subsurface data provide snapshots of the different stages of complex fault deformation within soft sediments, and aid in developing kinematic models for fracture growth and orientation. Based on high-resolution seismic data (80-300 Hz, 1.5 m CDP spacing) and gravity (+/- .01 mGal per measurement error) simple interpreted cross-sections highlight a (1) broad ~100-m-wide brecciated fault zone and (2) antithetic reverse secondary faulting. LiDAR DEM’s (at least ~25 cm vertical accuracy) available from the Louisiana Oil Spill Coordinator's Office, show reorientation of Holocene meander belts with older regional stream directions changing from NW-SE to N-S directions over time in response to growth and breaching of structural ramps in overlap zones. We infer that during normal fault growth, within overlap zone, both E-W as well as ~N-S striking fractures interact to produce ‘chocolate-tablet’ fracture sets which divert surface drainage and complicate subsurface fluid pathways. We recommend 3-D seismic data seismic anisotropy measurements for P and S waves to test confirm subsurface orientations.

South-Central - 38th Annual Meeting (March 15–16, 2004) General Information for this Meeting

Session No. 8 Engineering Geology and Hydrogeology Texas A&M University: Geology Builiding, Room 104 1:00 PM-5:00 PM, Monday, March 15, 2004 Geological Society of America Abstracts with Programs, Vol. 36, No. 1, p. 23

Van Heerden, I., Binselam, S.A., Lorenzo, J.M., Cazes, C., and C. Westbrook, 2003 Application of LiDAR data to fault detection and mapping: Northern Gulf Coast of Mexico, Louisiana, USA. LaGIS 19th Annual Louisiana Remote Sensing and GIS Workshop April 29-May 1,2003 Cajundome Conference Center Lafayette, Louisiana.

Binselam, S.A. van Heerden, I., Streva, K., Lorenzo, J.M. Cazes, C. and C. Westbrook. Natural Geologic Hazard Mapping in Louisiana Utilizing LIDAR. 28^th Annual Workshop on Hazards Research and Applications. July 13^th – July 16, 2003, Boulder, Colorado.

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• Geological Society of America Meeting, Reno, NV  2000

  2000 GSA Annual Meeting -- Reno, Nevada

  Abs. No. 51962

  NEOTECTONICS IN THE LOWER MISSISSPPI VALLEY: HIGH-RESOLUTION GRAVITY AND SEISMIC CHARACTERIZATION OF ACTIVE SHALLOW-SUBSURFACE NORMAL FAULTS

  Author(s): LORENZO, Juan M., YUVANCIC, Beth, LATHAM, Hallie, BOULLION, Andre and CAZES, Carrie. Dept. Geology and Geophysics, Louisiana State University, Baton Rouge 70803-4101, juan@geol.lsu.edu

  Keywords: growth fault, Mississippi, gravity, seismics

  Few, shallow (< 0-500 m), active, faults in the lower Mississippi Valley have been surface-mapped. Interpretation of the fault trace from surface expression is ambiguous. Erosion displaces the fault scarp away from the fault trace and terrace and fault scarps can coincide. Subsurface geophysical imaging helps locate and characterize rates of fault movement through time. Fault movement may correlate with (1) regional stress induced by sedimentary loads and sea-level rise and/or (2) local stress associated with differential compaction, a process we deem secondary. Near Baton Rouge/Livingston Parish, Louisiana, a 30 km-long E-W fault system is interpreted from the alignment of high topographic gradients, damaged buildings and roads. Two N-S high-resolution gravity profiles and one high-resolution seismic reflection profile sample localities with high (6m), and low (1m) scarp relief. The high-scarp area corresponds to a 1.5 mGal Bouguer gravity anomaly, tens of meters wide-- an interpreted zone of reduced porosity. The low-scarp zone shows a ~0.5 mGal minima that can be modeled as a low-density, ~300 m wide, half-graben which is observable in seismic images (24-fold, 1-s, 1.5-m CDP spacing, 40-Hz geophones). Layers visible in the seismic section, in both low- and high-resolution seismic data, do not thicken toward the fault and there appears to be no syntectonic growth. Where observed, fault offsets are constant throughout the Recent section. Faulting probably occurred over a relatively short period of time. Further south along Bayou Lafourche, Louisiana, near the town of Golden Meadow one N-S high-resolution gravity profile and one high-resolution seismic reflection profile imply spatial correlation between river meanders correlate and fault zones.

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• American Association of Petroleum Geologists Meeting, New Orleans 2000

   Neotectonics in the Lower Mississppi Valley: High-Resolution Gravity and Seismic Characterization of Active Shallow-Subsurface Normal Faults
  
  Beth Yuvancic, Hallie Latham, Juan Lorenzo, Ivor Van Heerden*
  Dept. Geology and Geophysics, Louisiana State University, Baton Rouge 70803-4101
  e-mail: juan@geol.lsu.edu, * Louisiana State Geological Survey.
  
  Shallow (< 0-500 m), active, growth faults in the lower Mississippi Valley have been surface-mapped only near urbanized zones, hindered by high rainfall and associated erosive processes. The geophysical character of these faults and their rates of movement in the Quaternary remain virtually unknown. At present, the lack of knowledge of such fault systems affects the ability to manage waste disposal ground water for drinking purposes. Fault movement may correlate with (1) regional stress induced by sedimentary loads and sea-level rise and/or (2) local stress associated with differential compaction, or (3) extraction of subsurface brine or fresh water.
  
  At the latitude of Baton Rouge, Louisiana, we study a 30 km-long E-W fault system interpreted from the alignment of high topographic gradients., damaged buildings and roads. Three N-S high-resolution gravity profiles and one high-resolution seismic reflection profile sample localities with high (10m), intermediate (6m) and low (1m) scarp relief. Interpreted zones of reduced porosity correlate with 1mGal Bouguer gravity anomaly peaks, tens of meters in wavelength. Half-grabens, ~300 m wide are testable in seismic images (24-fold, 1-s, 1.5-m CDP spacing, 40-Hz geophones).
  
  Seismic surfaces which correlate to existing water-well bore logs permit determination of changes in the rate of fault movement. Stratigraphic patterns across the fault that show acceleration in fault movement above the Pleistocene regional surface are interpreted to result from greater subsidence induced by the depletion of local aquifers. Fault movement would be greatest below the Pleistocene surface as a result of regional sedimentary loads, which are greatest during glacial times.