Browsing by Subject "Seismic stratigraphy"

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Late Quaternary seismic stratigraphy and structure of the western insular shelf margin of Puerto Rico
(2006-05) Hanzlík-Valentín, Martín; Mann, Paul, 1956-
The modern insular shelf and slope of western Puerto Rico is characterized by reef carbonate and siliciclastic sedimentary environments controlled by the complex interplay of tectonic arching and faulting, vigorous erosion of the elevated island of Puerto Rico, fluvial incision and sedimentation pulses, reef growth, and rapid late Quaternary eustatic sea-level changes. For this study, I interpret 725 km of high-resolution, single-channel seismic lines that were collected over the western insular shelf and slope by the RV Isla Magueyes in 2000 to better understand tectonic, erosional, and eustatic controls on late Quaternary history. The seafloor geology of the western shelf and slope area of Puerto Rico has been well studied and mapped mainly from grab and short cores collected by geoscientists at the U.S. Geological Survey and at the University of Puerto Rico at Mayagü̈ez. Because of low tectonic uplift rates from the western coast of Puerto Rico, the onland late Quaternary sedimentary history is not recorded in Quaternary coastal outcrops. The results of my seismic interpretation and correlation with multi-channel seismic data collected in 1972, reveal four main units defined by characteristic stratal reflection terminations and seismic facies. These units include: Unit 1 (basement) - a gently folded and faulted basal section correlated to the Oligocene-early Pleistocene carbonate shelf of Puerto Rico; deeper penetration, industry multi-channel seismic lines show that these rocks are deformed in a broad east-west-trending arch; Unit 2 (lowstand systems tract, LST) - chaotic channel fill deposits filling deep (~ 30 meter) incisions formed during the Last Glacial Maximum about 20 ka; Unit 3 (transgressive system tract, TST) - poorly stratified deposits truncating the top of Unit 2 and deposited during early Holocene transgression of the shelf margin; Unit 4 (highstand system tract, HST) - late Holocene, highly stratified deposits related to aggradation as the Holocene transgression began to slow. The base of unit 4 is a downlap surface interpreted as a maximum flooding surface likely formed about 8 ka. East-northeast-striking faults are observed that offset the late Quaternary units in three separate zones off the west coast of Puerto Rico. Because of a lack of wells and long cores from the shelf and slope area, age estimates for the four units are based on correlations with sea-level curves derived from dated coral samples in the Caribbean and western Atlantic region. All four units are deformed by faulting that should be considered active and possibly hazardous for the rapidly developing west coast of Puerto Rico. In one area, a large, late Holocene-slump (~ 0.016 km³) is mapped using seismic, sidescan sonar and bathymetric data. Onland continuations of these faults are likely, but have not been identified due to cultural overprint of natural scarps on late Quaternary floodplains.
Seismic chronostratigraphy for reservoir characterization : modeling and applications
(2017-05) He, Yawen; Kerans, C. (Charles), 1954-; Zeng, Hongliu, 1957-; Fisher, William; Fomel, Sergey; Janson, Xavier
The assumption of the chronostratigraphic significance of seismic reflections serves as a fundamental premise in interpreting stratigraphy from seismic images. This hypothesis proposed in 1977 was initially applied to delineate depositional sequences as the basic interpretive unit, and then to reconstruct Wheeler Diagram and regional sea level curves. After a further comparison against with global eustatic events, these regional curves can further facilitate predicting the age, distribution, and facies of depositional sequence before drilling in a seismic-covered area during petroleum exploration. With a boom in reservoir-level seismic applications, for obtaining significant high frequency sequence (HFS) surfaces as the bounding surfaces in static reservoir model construction, this fundamental assumption was inevitably extended to characterize HFS and even high-frequency cycles (HFC) during seismic reservoir characterization. For an ultimate improvement in constructing reservoir-bounding surfaces, the author targeted at evaluating the validity of this fundamental assumption as applied to high-order seismic stratigraphy. The author conducted the entire project via the forward seismic modeling upon geologic models with known chronostratigraphic relationship. Besides, these input models carefully honor the reservoir geology for meaningful discussions on (1) shallow marine siliciclastic reservoirs in Starfak Field, GoM, (2) shallow-water mixed carbonate/clastic Upper San Andres-Grayburg reservoirs in Permian Basin, and (3) shallow-water carbonate Abo shelf margin-Clear Fork platform in Permian Basin. This study has achieved three-fold contributions. On the aspect of realistic geocellular, property and seismic modeling at the reservoir scale, the author integrated high-resolution sequence stratigraphic framework, published 3D depositional model, intra-facies heterogeneity in 3D modeling to selectively apply advanced geostatistical methods to model hierarchical heterogeneity. Subsequently, the author proposed an evaluation scheme with a defined parameter ('time-correlation error/TCE') to assess HFS-scale reservoir-bounding surfaces. These assessments revealed an interactive influence from (1) stratal geometry, (2) lateral lithofacies variation, (3) lithofacies-sonic velocity relationship in pure- versus mixed-lithology successions, (4) intra-facies heterogeneity, and (5) seismic frequency. Finally, based on these forward modeling results, the author proposed a decision tree to determine valid interpretation strategy in seismic chronostratigraphic correlation in scenarios with geoscientists’ expert knowledge and recommended an attribute-driven volumetric picking scheme to improve published algorithms for scenarios without prior knowledge.
Seismic stratigraphy and paleo-glaciology of Sabrina Coast, East Antarctica and Bering Trough, Gulf of Alaska
(2015-05) Montelli, Aleksandr; Gulick, Sean P.S.; Blankenship, Donald; Mohrig, David
Examination of the sedimentary record in areas occupied by fast flowing outlet glaciers and ice streams is critical for understanding ice sheet dynamics on millennial timescales. We use high-resolution seismic data together with log data and foraminiferal- based radiocarbon and isotope data from Integrated Ocean Drilling Program (IODP) Expedition 341 cores to examine the evolution of the Cordilleran Ice Sheet (CIS) in southeast Alaska. Evidence for at least seven advances of the Bering Glacier to the shelf break since the end of Middle Pleistocene Transition (MPT) are interpreted from the seismic data. Seismic data demonstrate two distinctive patterns of slope sedimentation, which are: (1) dominated by sediments bypassing a steep paleo-slope or (2) dominated by glacigenic debris flows (GDFs) that form a trough mouth fan (TMF) on a lower slope. Integration of seismic, well, and age data suggests that the TMF was formed as a result of three advances to the shelf break since ca. 140 ka, implying extreme (average > 4m/ka) rates of sediment delivery. Extraordinarily high sediment flux played a key role in the development of the margin architecture resulting from a temperate, highly aggressive Bering Glacial System and abundant source of erodible bedrock onshore (St. Elias orogeny). We use the first high-resolution seismic data acquired on the Sabrina Coast, East Antarctica, together with core data, to examine major transitions in glacial regime of East Antarctic Ice Sheet. Three large-scale megasequences represent changes in the dominant pattern of sedimentation: Megasequence I shows signs of Eocene fluvial and possibly glacio-fluvial sedimentation; Megasequence II provides evidence of Oligocene-Miocene polythermal glacial sedimentation with significant amount of meltwater; Megasequence III overlies the regional erosional surface that marks major Miocene ice sheet expansion and transition into polar (cold- based) ice sheet glacial regime with no significant evidence of subglacial meltwater preserved. Megasequence II exhibits preserved record of EAIS evolution starting from its first expansion. Seismic stratigraphic analysis suggests a dynamic glacial late Paleogene-early Neogene evolution including expansions of the EAIS across the shelf at least eight times, which is marked by erosional surfaces and chaotic acoustic character of overlying strata. We report on finding the first conclusive seismic evidence of deep, extensive tunnel valley systems incised into sedimentary substrate from Antarctic continental margins. The Sabrina Coast tunnel valley system was presumably formed during Oligocene as a result of the second major EAIS shelf expansion. Shallower erosion events observed in the upper part of Megasequence II suggest more extensive glaciations in the Oligocene compared to the Miocene.
Tectonic and depositional history of an active forearc basin, Sandino basin, offshore Nicaragua
(2014-05) Stephens, Jason Henry; Fulthorpe, Craig Stephen, 1954-; McIntosh, Kirk D.
High-resolution (20-250 Hz) multichannel seismic (MCS) reflection data with record lengths of 4-8 s TWT, totaling approximately 4620 line km on the shelf and slope of the Sandino forearc basin of offshore western Nicaragua, were acquired in November-December 2004 (cruise EW04-12) and subsequently processed at the University of Texas Institute for Geophysics. Seismic sequence interpretation was conducted using these MCS data in conjunction with deeper penetration (16-20. s TWT) MCS profiles from a previous survey (cruise EW00-05). Age estimates were based on cuttings from intersecting industry wells. Structure and isochron maps were created for 16 sequences and used to identify structural and depositional trends within the Sandino basin. The Tectonostratigraphic evolution of the basin varies considerably along-strike and is divided into five general stages from Late Cretaceous to recent. Evidence for multiple episodes of terrane accretion is observed from Late Eocene to Late Oligocene and potentially during Mid- to Late Miocene as well. Stratal stacking patterns suggest the Nicaraguan margin has not been dominated by subduction erosion during its history and extensional features beneath the slope are interpreted to have originated as a result of processes related to collision of allochthonous terrane of the downgoing plate, sediment underplating, and slab roll-back. With more precise age control, the stable northwestern region of the Sandino basin, where sediment is relatively undeformed since Late Oligocene and measures ≥ 16 km thick, offers a unique convergent margin setting for investigations of forcings on sequence development.
The Cretaceous-Paleogene boundary deposit in the Gulf of Mexico : oceanic basin response to the Chicxulub impact and geomechanics of reservoir-scale sand injectites, Panoche Hills, California
(2015-08) Sanford, Jason Charles; Flemings, Peter Barry, 1960-; Gulick, Sean P. S.; Snedden, John W
Hydrocarbon exploration in the last decade has yielded sufficient data to evaluate the Gulf of Mexico basin response to the Chicxulub asteroid impact. Given its passive marine setting and proximity to the impact structure on the Yucatán Peninsula, the Gulf is the premier locale in which to study the near-field geologic effect of a massive bolide impact. We mapped a thick (dm- to hm-scale) deposit of carbonate debris at the Cretaceous-Paleogene boundary that is ubiquitous in the Gulf and readily identifiable on borehole and seismic data. We interpret deposits seen in seismic and borehole data in the distal deepwater Gulf to be predominately muddy debrites with minor turbidites based on cores in the southeastern Gulf. Mapping of the deposit in the northern Gulf of Mexico reveals that the impact redistributed roughly 1.05 x 10⁵ km³ of sediment therein, and over 1.98 x 10⁵ km³ Gulf-wide. Deposit distribution suggests that the majority of sediment derived from coastal and shallow-water environments throughout the Gulf via seismic and megatsunamic processes initiated by the impact. The Texas shelf and northern margin of the Florida Platform were primary sources of sediment, while the central and southern Florida Platform underwent more localized platform collapse. Crustal structure of the ancestral Gulf influenced post-impact deposition both directly and indirectly through its control on salt distribution in the Louann salt basin. Nevertheless, impact-generated deposition overwhelmed virtually all topography and depositional systems at the start of the Cenozoic, blanketing the Gulf with carbonate debris within days. The Panoche Giant Injection Complex (PGIC) in central California is a complete injectite system. We measured hundreds of injectites over ~600 m of stratigraphic thickness in two locales in order to determine geomechanical controls on injection. We document an injectite architecture in the PGIC that we interpret to reflect a reversal in paleostress state from reverse to strike-slip or normal with proximity to the paleoseafloor. We demonstrate that injectite aperture and bulk strain decrease with distance from the injection source. We model this behavior with three hydraulic fracture geometries and conclude that injectites formed via radially propagating hydraulic fractures. We document a northeast-southwest paleo-orientation preference of subvertical injectites, which reflects the control of Farallon plate subduction on stress state at the PGIC. We estimate that the PGIC was complete and active for ~1 Ma and punctuated by ~20–150 ky-long periods of quiescence based on thickness and spacing of extrudites in the PGIC.