Active Growth Faults Research Articles

Active near-surface growth faulting and late Holocene history of motion: Matagorda peninsula, Texas

The structural framework of the northern Gulf of Mexico coastal zone includes numerous growth fault systems. Neotectonic processes in coastal environments here have been shown to be important contributors to subsidence and relative sea-level rise, as well as having significant influences on sedimentary accretion processes. One active growth fault at East Matagorda Peninsula, Texas was subjected to detailed study to address the hypotheses that (1) this fault was present and active before the peak of regional hydrocarbon recovery in the mid-20th century, and that (2) slip along this fault has been episodic over the resolved period of record. To characterize the late Holocene behavior of this fault, three core transects were established normal to the surface fault trace, and stratigraphic analysis was conducted with the use of radiocarbon (14C) for chronological control. Correlation of time-equivalent stratigraphic boundaries reveals a maximum total late Holocene offset of 0.7 m. The Matagorda fault was in place long before the peak of regional oil and gas extraction, but experienced a late Holocene rejuvenation, initiated between 2500 and 1500 years BP. The kinematic behavior of the fault expressed as temporally and spatially variable measures of expanded stratigraphic thicknesses on the downthrown extent suggest that sediment loading from the transgressive Matagorda barrier complex may have contributed to this rejuvenation, and that slip along the fault persists to the present. Radiocarbon chronology also revealed clear differences in the magnitude of fault throw during the late Holocene, with maximum displacement (0.7 m) occurring at the southwestern-most transect and minimum throw at the northeastern-most transect (0.2 m).

Sedimentation close to the active Medlicott Wadia Thrust (Western Himalaya): How to estimate climatic base level changes and tectonics

The Medlicott-Wadia Thrust (MWT) is one of the major active out-of-sequence thrusts in the Himalaya. Studies on Quaternary terraces in its vicinity have been performed using sedimentological, geomorphic and geochronological methods. We focus on the Riasi zone, south of the Pir Panjal range, in the Jammu and Kashmir region of India. The sedimentary units of Quaternary landforms have been mapped as a function of their location with respect to the thrust faults, their relative chronology, and their lithology. Three aggrading sedimentary units, five thin units above strath surfaces at the footwall of the fault system, and seven thin units above strath surfaces at its hangingwall are identified. The terraces have been dated by combining Optically Stimulated Luminescence (OSL) on fine-grained deposits and cosmogenic-nuclide dating (10Be) on sandstone pebbles sampled along depth profiles throughout the alluvial units. Three major allostratigraphic units were defined with upper surface ages estimated at ~4, ~15, and 36±3ka; the two older allostratigraphic units are encased terraces at the hangingwall but superposed sedimentary units at the footwall. They are related to phases of elevation of the river level (respectively 30 and 60m) at ~36–38 and 14–15ka and to a phase of extensive lateral incision before ~4ka. These units present vertical offsets induced by the MWT of 50, 190, and 375m, respectively. By taking the aggradation/incision rates at the footwall of the MWT into account, we found that the uplift of the hangingwall remains uniform since 36ka, with a value of ~10mm/yr. Therefore, the aggradation/incision events observed in the Riasi area cannot be ascribed to variations in the tectonic rates and are most likely driven by climatic fluctuations. The high uplift rate is possibly local and related to the Chenab recess, which affects the Himalayan frontal structure. Our results indicate that the MWT is an active growth fault, and one of the main emergences of the active Indian/Asian plate boundary in Western Himalaya.

Sequential growth of deformation bands in carbonate grainstones in the hangingwall of an active growth fault: Implications for deformation mechanisms in different tectonic regimes

Deformation bands in porous sandstones have been extensively studied for four decades, whereas comparatively less is known about deformation bands in porous carbonate rocks, particularly in extensional settings. Here, we investigate porous grainstones of the Globigerina Limestone Formation in Malta, which contain several types of deformation bands in the hangingwall of the Maghlaq Fault: (i) bed-parallel pure compaction bands (PCB); (ii) pressure solution-dominated compactive shear bands (SCSB) and iii) cataclasis-dominated compactive shear bands (CCSB). Geometric and kinematic analyses show that the bands formed sequentially in the hangingwall of the evolving Maghlaq growth fault. PCBs formed first due to fault-controlled subsidence and vertical loading; a (semi-)tectonic control on PCB formation is thus documented for the first time in an extensional setting. Pressure solution (dominating SCSBs) and cataclasis (dominating CCSBs) appear to have operated separately, and not in concert. Our findings therefore suggest that, in some carbonate rocks, cataclasis within deformation bands may develop irrespective of whether pressure solution processes are involved. We suggest this may be related to stress state, and that whereas pressure solution is a significant facilitator of grain size reduction in contractional settings, grain size reduction within deformation bands in extensional settings is less dependent on pressure solution processes.

Influence of growth faults on coastal fluvial systems: Examples from the late Miocene to Recent Mississippi River Delta

The details of how fluvial systems respond to spatial changes in land-surface subsidence produced by active faulting remain incompletely understood. Here, we examine the degree to which the positioning of individual channels and channel-belts is affected by local maxima in subsidence associated with the hanging walls of growth faults. The channel forms and faults are imaged using a seismic volume covering 1400km2 of Breton Sound and Barataria Bay in southern Louisiana, USA. We look at the consequences of interactions between channels, channel-belts, and faults in late Miocene to Recent strata. More than fifty individual channels that crossed the traces of active growth faults were examined. Of these channels, only three appear to have been redirected by the faults. There also appeared to be no systematic change in the cross-sectional geometries of channels or channel-belts associated with crossing a fault, though the orientation of the channel-belts appears to be more influenced by faulting than the orientation of individual channels. Seven out of ten mapped channel-belts appear to have been steered by growth faults. We propose that channel belts are more likely to be influenced by faults than individual channels because channel-belts are longer lived features, unlikely to shift their overall position before experiencing a discrete faulting event. In addition, the style of influence in the few cases where an individual channel is affected by a fault is different from that of larger systems. While downstream of a fault channel-belts generally become oriented perpendicular to fault strike, the individual channels are directed along the hanging wall of the fault, running parallel to the fault trace. We relate this to the ratio of the length-scale of fault rollover relative to the channel or channel-belt width. Fluvial-fault interactions with higher values for this ratio are more likely to be carried parallel to the fault trace than systems with lower ratio values.

Sediment supply systems of the Champion “Delta” of NW Borneo: Implications for deepwater reservoir sandstones

Middle Miocene to Pliocene sedimentation on the NW Borneo margin has been interpreted as the product of one relatively large deltaic system, the Champion Delta. However, several lines of evidence indicate that the Champion system was not a simple, large delta; its drainage basin was too small, fluvial outcrops indicate multiple, relatively small rivers and outcrop studies indicate the same facies associations as the diverse, modern depositional systems. The number and location of rivers reaching the shoreline changed as rapidly subsiding footwall synclines, episodically active inversion anticlines and growth faults created an evolving structurally-generated topography that not only controlled drainage pathways, but also segregated Champion strata into thick, wave-dominant and tide-dominant successions. Although the principal rivers within the Champion system, the Limbang, Padas and Trusan Rivers, transport significant loads of coarse sediment, the intermittent proximal ponding of sand in local basins, as is currently occurring in Brunei Bay, resulted in a variable delivery of sand to the shelf edge. The number and distribution of shelf edge canyons also changed with time. Consequently, the spatial and temporal distribution of deepwater sand accumulations sourced from the Champion system are not solely related to relative sea level fluctuations; such accumulations should be smaller and more scattered than those sourced from a large shelf edge delta. Because the catchments of the Champion system’s principal rivers represent different provenances, the system’s deepwater sands may carry the signal of specific rivers. For example, mineralogical contrasts between in the main reservoir sands of the deepwater Gumusut and Kikeh fields suggest that the relative contributions of the principal rivers shifted with time with the Trusan and Limbang Rivers dominating sand supply for the youngest reservoirs at Gumusut.

Active fault motion in a coastal wetland: Matagorda, Texas

Active growth faults contribute to the subsidence of deltaic basins around the world and can significantly augment local rates of relative sea level rise, which can inundate and drown wetlands. Little information exists on the temporal frequency and spatial magnitude of motion along these faults. Our objective was to quantify fault activity and displacement at multiple time scales in a salt marsh wetland on the East Matagorda Peninsula, Texas. We present evidence of this activity that includes remotely sensed aerial imagery, LiDAR data, ground penetrating radar data, shallow seismic data, lithostratigraphic and biostratigraphic evidence from core data, and sub-centimeter GPS and survey monitoring. The results support the interpretation that the Matagorda fault is currently active, and has been active in the past. Subsurface data to depths of ~150m displays evidence of disrupted strata at the fault plane, as well as thicker strata on the downthrown side of the fault. In the shallow subsurface down to ~3m of depth, vertical displacement in stratigraphic markers and surface deformation exhibits a sinusoidal pattern that runs perpendicular to the fault plane, which we interpret to represent fault-propagation folding. Maximum throw on this fault is estimated at ~0.75m over the last ~40–50years. We also recorded a vertical drop of −0.208m in the span of a single year, at a location close to the fault on its downthrown side. Records of yearly elevation change also show evidence of ongoing fault-propagation folding. We conclude that whereas the surface at the Matagorda fault moves intermittently up and down at the yearly time scale, fault displacement manifests as a sinusoidal pattern of displacement and deformation which has been integrated into the stratigraphic record at decadal-to-millennial time scales. This study presents a rare look into active motion and details its effects on the modern evolution of unconsolidated sedimentary surfaces.

Significance of active growth faulting on marsh accretion processes in the lower Pearl River, Louisiana

Neotectonic processes influence marsh accretion in the lower Pearl River valley. Active growth faults are suggested by groupings of ponded river channel sections, transverse and linear river channel sections, and down- and across-valley contrasts in channel sinuosity. Seismic profiles identified several likely, fault-induced structural anomalies, two of which parallel the axes of surface distributary networks. Lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the West Middle River, combined with 14C-based age control, yielded evidence of vertical offsets, indicating that this river section is on the plane of a growth fault. These data were used to estimate fault slip rates over two time intervals, 1.2mm/y over the last 1300yr, and 0.2mmyr−1 over the last 3700yr, and delineated a sinusoidal pattern of deformation moving distally from the fault, which we interpret as resulting from fault-propagation folding. Higher rates of sediment accumulation (of the order of cmyr−1 from 210Pbxs and 137Cs activity data) on the down-thrown side are consistent with sedimentary response to increased accommodation space, and mass-based sediment accumulation rates (gcm−2yr−1) exhibit a pattern inverse of that shown by fault-driven sinusoidal deformation. We contend that near-surface growth faults are critically important to driving accretion rates and marsh response to sea-level rise.

Geophysical mapping of the Hockley growth fault in northwest Houston, USA, and recent surface observations

Active growth faults cutting the land surface around the coast of the Gulf of Mexico represent a serious geohazard. Considering the average movement of these faults is a few inches per decade, the potential is high for structural damage to highways, industrial buildings, residential houses, and railroads that cross these features.

Integrated geophysical studies over an active growth fault in Houston

Active growth faults cutting the land surface in the Gulf Coast area represent a serious geohazard. Considering the average movement of these faults is a few inches per decade, the potential is high for structural damage to highways, industrial buildings, residential houses, and railroads that cross these features.

Volcanic degassing, hydrothermal circulation and the flourishing of early life on Earth: A review of the evidence from c. 3490-3240 Ma rocks of the Pilbara Supergroup, Pilbara Craton, Western Australia

New data gathered during mapping of c. 3490–3240 Ma rocks of the Pilbara Supergroup in the Pilbara Craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism. For most cherts, fossil hydrothermal fluid pathways are preserved as silica ± barite ± Fe-bearing veins that cut through the footwall and up to the level of individual bedded chert units, but not above, indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events. Silica ± barite ± Fe-bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units, and occurred under alternating high-sulphidation and low-sulphidation conditions. These veins provided pathways to the surface for elements leached from the footwall (e.g., Si, Ba, Fe) and volcanogenic emissions from underlying felsic magma chambers (e.g., CO 2, H 2S/HS −, SO 2). Stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of Warrawoona Group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and/or degassing of these magmas. Heat from these intrusions drove episodes of hydrothermal circulation. Listric normal faulting during caldera collapse produced basins with restricted circulation of seawater. Eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components, thereby providing habitats suitable for early life forms. Fossil stromatolites from two distinct stratigraphic units in the North Pole Dome grew in shallow water conditions, but in two very different geological settings with different morphologies. Stratiform and domical stromatolites in the stratigraphically lower, c. 3490 Ma, Dresser Formation of the Warrawoona Group are intimately associated with barite and chert precipitates from hydrothermal vents, suggesting that component microbes may have been chemoautotrophic hyperthermophiles. Evidence of shallow water to periodically exposed conditions, active growth faulting and soft sediment deformation indicates that the volcanogenic emissions were erupted into a shallow water, tectonically active caldera and concentrated therein to produce an extreme habitat for early life. Widespread conical and pseudocolumnar stromatolites in the c. 3400 Ma, Strelley Pool Chert at the base of the unconformably overlying Kelly Group occur in shallow marine platform carbonates. Silicification was the result of later hydrothermal circulation driven by heat from the overlying, newly erupted Euro Basalt. The markedly different morphology and geological setting of these only slightly younger stromatolites, compared with the Dresser Formation, suggests a diversity of microbial life on early Earth. The biogenicity of putative microfossils from this and younger hydrothermal silica veins in the Warrawoona Group remains controversial and requires further detailed study.

Present-day stress orientation in Brunei: a snapshot of ‘prograding tectonics’ in a Tertiary delta

The Baram Delta province of NW Borneo is unusual when compared with most other Tertiary deltas, as it has built up upon an active margin. Hence, structures observed in the Baram Delta province are the result of both margin-parallel gravity-driven deltaic tectonics and approximately margin-normal transpressive tectonics associated with the active margin. Image and dipmeter logs have been examined for breakouts and drilling-induced tensile fractures (DITFs) in 47 wells throughout Brunei. Breakouts and DITFs observed in 19 wells suggest that the maximum horizontal stress is oriented margin-normal (NW–SE) in the proximal parts of the basin and margin-parallel (NE–SW) in the outer shelf region. The margin-parallel outer shelf stress field is interpreted as a local ‘deltaic’ stress field caused by the shape of the clastic wedge. The margin-normal maximum horizontal stress in the inner shelf is interpreted to reflect basement stresses associated with the active margin. However, the maximum horizontal stress in the inner shelf is approximately perpendicular to the strike of Miocene–Pliocene normal growth faults, suggesting that maximum horizontal stress in the inner shelf has rotated from margin-parallel (‘deltaic’) to margin-normal (‘basement-associated’) over time. Hence, approximately the same stress rotation has occurred over time in the inner shelf as is currently observed spatially from the outer to inner shelf. The spatial and temporal stress rotations in Brunei are thus interpreted to be the result of ‘deltaic’ and ‘basement-associated’ tectonic regimes that are ‘prograding’ basin-wards. The proximity of the active margin has resulted in progressive uplift and inversion of the hinterland that has ‘forced’ the delta system to prograde rapidly. The zone of active deltaic growth faulting (and margin-parallel maximum horizontal stress) has shifted basin-wards (‘prograded’) as the delta system has rapidly prograded across the shelf. After uplift and delta progradation, the old growth faults of the inner shelf ceased being active and have then been successively reactivated by a similarly ‘prograding’ margin-normal inversion front.

Fluid transport by solitary waves along growing faults: A field example from the South Eugene Island Basin, Gulf of Mexico

The Red Fault system is one of the main growth faults found in the South Eugene Island Basin, a salt withdrawal minibasin located offshore Louisiana, in the Gulf of Mexico. This fault system corresponds to a lateral boundary between fluid overpressured compartments. In addition, there is a set of observations indicating that the Red Fault system exhibits rapid episodic migration of fluids. This fault represents an example of preferential pathway for the upward episodic migration of overpressured hydrocarbons from deep, heavily pressured, compartments on time scales of years. The migrations of fluids into active growing faults could take the form of propagating surges (solitary waves) that propagate upward along the fault planes in a wave-like manner at km/yr. Solitary waves represent a very efficient mechanism for the upward transport of fluids along growth faults in sedimentary basins generating its own permeability. In addition, this mechanism is compatible with the fact that the fault plane is observed to sustain a static pore fluid pressure difference between its two sides. The propagation of solitary waves in active growth faults appears as a fundamental mechanism to understand the nature of upward fast migration of fluids along active growth faults in compartimentalized sedimentary basins.

Evidence for Active Growth Faulting in the Terrebonne Delta Plain, South Louisiana: Implications for Wetland Loss and the Vertical Migration of Petroleum

Two regional growth faults, the Golden Meadow Fault and the Lake Hatch Fault, were mapped in Terrebonne and Lafourche Parishes, Louisiana, utilizing over 3000 line kilometers of seismic data. The subcropping location of these faults identify major vegetation biozonations, new areas of wetland loss, and the position of transgressive lakes. The proposed mechanism governing these fault-related manifestations of subsidence involves the venting of fluid (and gas) from geopressured shales vertically up fault planes. Saline fluids and gases exiting a basin via growth faults provide accommodation space at depth, resulting in active, fault-induced subsidence in the down-thrown block. By contrast, areas along the fault trend where no fluids or gases were migrating would not result in an increase of accommodation space and would be considered inactive regarding faultinduced subsidence. The model that emerges is a growth fault trace that does not act in concert but more closely resembles a key-stepping system with sections alternating between active and inactive. These findings are relevant to the role of growth faults in subsidence-related coastal land loss and the vertical migration of hydrocarbons.

Abstract: Seismic, electromagnetic, subsidence, and biozonation evidence for active growth faults in South Louisiana

Abstract: Seismic, electromagnetic, subsidence, and biozonation evidence for active growth faults in South Louisiana

Stratigraphy, palaeontology and correlation of the Vectis Formation (Wealden Group, Lower Cretaceous) at Compton Bay, Isle of Wight, southern England

A stratigraphie section of the Vectis Formation (Wealden Group, Lower Cretaceous) at Compton Bay, Isle of Wight is presented, including lithological and palaeontological data. The sequence is relatively thin, indicating either attenuation towards the faulted northern margin of the Wessex sub-basin or proximity to an active growth fault associated with this structure. The succession is closely comparable to the Atherfield ‘type’ section in terms of lithofacies and fauna, enabling recognition of intrabasinal marker horizons. The salinity tolerances of molluscan fossils from the section are discussed and storm-generated bioclastic marker beds are figured.

Episodic Migration of Natural Gas: A Worldwide Phenomenon of Dynamic Filling of Oil and Gas Fields: ABSTRACT

Natural gases form through bacterial and thermogenic conversion of organic matter over extended geological time. The isotopic properties of methane and C2+hydrocarbons are controlled by temperature dependent kinetic fractionation during maturation and mixing during migration and in reservoirs. Gas fields which are actively and repeatedly charged over extended periods of gas formation will receive compositionally and isotopically variable charges of natural gases that can mix in different proportions in single reservoirs. Episodic migration and multiple filling of reservoirs is a ubiquitous phenomenon observed in small and giant gas fields throughout the world. The following case histories from own research and from the literature will be discussed to illustrate this phenomenon: Gulf of Mexico: Pervasive mixing of bacterial and thermogenic gas charges results in large variations in isotopic signatures on a field and reservoir scale. Major formation and migration episodes are (1) Bacterial gases form in rapidly subsiding mini basins and migrate and accumulate around rising sell structures and active growth faults and (2) Following multiple charges of thermogenic gases mix in various proportions with bacterial gases. Angola: Giant oil fields off-shore Cabinda contain thermogenic gases with different isotopic signatures in the gas cap and the oil leg, indicating a multimore » phase migration of thermogenic; gases from mature to post-mature sources. The gas/oil columns are in some cases variable and suggest compartmentalization and/or unmixed oil hydrocarbon columns. Yacheng Gas Field: Gas composition and isotopic signatures of methane change from west to east in this giant field in the S. China Sea. Inert gas contents also vary vertically in the reservoir suggesting a late charge of a CO[sub 2] rich gas into the structure. South ltaly. Pliocene reservoirs in the Apulian Basin are mixtures of thermogenic and bacterial gases.« less

In-Situ Stress and Rock Strength in the GBRN/DOE Pathfinder Well, South Eugene Island, Gulf of Mexico

The authors present a relatively simple technique to constrain in-situ stress and effective rock strength from observations of wellbore failure in inclined wells. Application of this technique in the Global Basins Research Network (GBRN)/DOE Pathfinder well demonstrated that (1) the azimuth of S{sub h min} is {approx} N42{degree}E, perpendicular to a major growth fault penetrated by the well; (2) the magnitude of S{sub H max} is relatively close to the vertical stress; and (3) the effective in-situ compressive rock strength is 3,500 to 4,000 psi. They show that once they have estimated in-situ stress and rock strength, it is possible to compute the mud pressure required to inhibit failure for wells of any azimuth and inclination. Finally, they show how it is possible to estimate the magnitudes of both S{sub h min} and S{sub H max} in cases where independent knowledge of stress orientation is available (for example, from wellbore breakouts in nearby vertical boreholes).

Faults in the Purbeck—Isle of Wight monocline

Faults at Arish Meli and Corfe Castle in Dorset, and at Freshwater Bay and Shide, Newport, on the Isle of Wight cut the Purbeck-Isle of Wight monocline. Evidence for these hitherto unrecognized faults is based on outcrop displacements and differences in: (a) outcrop widths either side of the faults; (b) strike and dip of the strata; and (c) the direction of the axis of the monocline. The faults developed above offsets in large normal faults beneath the subsequent monocline and were active growth faults during deposition of the Chalk. During the later Alpine tectonic episode which formed the Purbeck-Isle of Wight monocline these faults were reactivated, so displacing the boundary between the Chalk and the Reading Beds. The faults locally weakened the chalk ridge and allowed south to north drainage to develop through the ridge.

Tectonic controls on Upper Jurassic to Lower Cretaceous reservoir architecture in the Jeanne d’Arc Basin, with some comparisons from the Porcupine and Moray Firth Basins

Abstract Seismic, wireline log and core data from three geographically separate basins in the North Atlantic provide an understanding of the regional dynamics of the basin system, and quantify the sedimentary geometry response to a composite rift episode. The response to the Late Cimmerian rift episode in the Jeanne d’Arc, Porcupine and Moray Firth Basins is broadly comparable, with an initial episode of clastic reservoir facies deposition associated with active growth faulting. This was followed by a mid-rift period where subsidence outstripped sedimentation, resulting in organic-rich source rocks and culminating in a mappable maximum flooding surface. During the final phase of the rift episode, the decrease in subsidence rate resulted in the return of reservoir-quality clastics. The reservoir-scale response to the initial rifting is illustrated in cored sequences from the Jeanne d’Arc Basin. These indicate the development of axial and lateral sandy and conglomeratic braided fluvial and alluvial fan systems, with periods of muddy lacustrine deposition. Pedogenic surfaces offer much potential for detailed correlation and the analysis of sandbody geometry. The onset of anoxic conditions conducive to source rock deposition during the mid-rift phase of Late Cimmerian tectonism, and the preferential development of reservoir facies at the base and top of syn-rift sediment fill, are characteristics of considerable importance to exploration of the North Atlantic borderland rift basins.

Latest Quaternary Outer Shelf and Slope Deposits, Northern Gulf of Mexico, USA: Industry Research Consortium

A consortium of oil companies is undertaking a multiyear shallow coring and high-resolution seismic investigation of the outer shelf-slope deposits of the northern Gulf of Mexico. The program's objective is to reconstruct the depositional, seismic stratigraphic, biostratigraphic, isotopic, and organic geochemical record of the latest Quaternary of a portion of the Gulf margin. Results will serve as an analog to deeper hydrocarbon reservoirs and to help in understanding sedimentation with glacial-interglacial sea-level changes. Nearly continuous cores up to 850 ft long from Main Pass Blocks 303, 242, 288 and Viosca Knoll Block 774 are being described and analyzed. Main Pass 303 core samples Holocene to Oxygen Isotope Stage 6 deposits and as old or older strata are expected to have been penetrated in the other boreholes. Three or four sea level cycles are represented. Seismic acquisition is planned for late 1990. The outer shelf and slope of the northern Gulf is an area of active growth faulting, high sedimentation rate, diapirism, and slumping. Recent work, including this study, shows that near-surface stratigraphy consists of coarse clastics alternating with carbonate-rich mud. Sands and gravels are inferred to have been deposited mostly during lowstands and rising sea level in deltas and valley-fillmore » systems. Delta clinoforms on high-resolution seismic may represent shelf-margin wedges, prograding wedges, or highstand systems tracts. Highstand deposits are characterized largely by thin, continuous intervals of bioturbated muds containing abundant diagenetic carbonate and pyrite. Precise dating and correlation of outer shelf-upper slope facies to magnitude and direction of sea level change is intended during the project.« less