Abstract The Madre de Dios Basin of Bolivia represents two distinct phases of tectonic development that illustrate the linked stratigraphic responses to a changing basin style. The first phase associated with the Paleozoic is characterized as an intracratonic setting. The second, which began during the late Mesozoic and persists today, is the development of the Sub-Andean Foreland Basin. Hydrocarbons occur primarily within stratigraphic traps, potential reservoirs and seals are Paleozoic to Late Mesozoic in age. Paleozoic depositional environments identified from core indicate major changes in climatic conditions have occurred and include fluvial/deltaic, eolian dune, coastal sabkha, and shallow marine carbonate facies. A Late Devonian marine source rock with total organic carbon (TOC) content of up to 18% also occurs within the basin. Cretaceous age sediments contain an incised valley system of 10 to 15 kilometers in width and 300 meters in depth. Valley fill facies represent low sinuosity, braided fluvial systems grading upwards into estuarine muds. Terracing of the valley margin formed in response to multiple cut and fill episodes (baselevel fluctuations) of valley formation. Recurrent movements of basement involved fault blocks related to migration of the advancing forebulge, controlled the location and magnitude of valley incision and drainage incisement patterns. Large-scale variations in depositional environments, duration of geologic time (450 to 60 MY) represented by the stratigraphic section within a changing tectonic style, provides the Madre de Dios Basin as an example of the process to response interplay between tectonics, eustasy, climate and sediment supply.

ABSTRACT Deltaic complexes, shelf, slope, and Mississippi fan in the northern Gulf of Mexico show differences in lithologies, depositional environment, and stratigraphy. Each province reveals vertical sequences that can relate to fluctuations in relative sea level, especially for the late Neogene. Shelf and upper slope deposition during periods of relatively high sea level is characterized by thin, laterally continuous, condensed clay-rich sections, with thin calcareous layers, showing well-defined, strong, and laterally continuous seismic reflections. During periods of relatively low sea level sediments reveal expanded sections with variable thicknesses and lithologies, with well-defined depositional trends, displaying a wide range of acoustical responses. The Mississippi fan consists of successive channel-levee-overbank complexes, while the intraslope basins reveal a cyclicity in seismic and lithological characteristics.

Cyclic sequences are extremely common in the geologic record; they are particularly well developed in marine deposits associated with large river systems. Superimposed on cycles attributed to shifting sites of deposition are those related to high-frequency sea-level changes. These latter cycles are well-developed in the near-surface sediments of the Northern Gulf of Mexico shelf. The large data base for this study (471 deep foundation borings, thousands of line kilometers of high-resolution seismic, and sedimentological and dating analyses) represents the most complete information on high-resolution lithostratigraphy that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics and spatial depositional patterns during several complete sea-level cycles over the entire continental shelf/upper slope of offshore Louisiana. Sedimentation during periods of high sea level is characterized by: 1) thin, slowly accumulated depositional sequences, referred to as condensed sections, 2) calcareous-rich deposits, including hemipelagic sediments and shell hashes, and 3) wide lateral continuity. Sedimentation during periods of low sea level is characterized by: 1) variable-thickness, rapidly accumulated sequences referred to as expanded sections, 2) coarse-grained clastic deposits, including abundant sands and gravels, and 3) well-defined depositional trends. Examination of high-resolution seismic records indicates that well-defined, high-amplitude, laterally continuous reflectors correlate with rising and highstand condensed sedimentary sequences and that the deposits laid down during falling and lowstand periods (expanded sections) are characterized by a wide range of acoustic responses. Discontinuous reflectors with high-amplitude variability, continuous parallel reflectors, and chaotic and amorphous zones are common acoustic responses. Even though the data set covers only a short period of geologic time (an estimated 240,000 years), these high frequency events are responsible for the deposition of excellent reservoir-quality facies in well-defined and predictable trends.

Abstract The Gulf of Mexico basin (Fig. 1) is the largest semi-enclosed depositional basin in North America and has been the site of extensive hydrocarbon exploration and exploitation since the turn of the century. Since Late Jurassic times, the drainage basin of the Mississippi River system has been delivering sediments to the Gulf of Mexico (Worzel and Burke, 1978; Chapter 8, this volume). Mesozoic and Cenozoic deposits are estimated to have attained a total thickness in excess of 15 km (Martin and Bouma, 1978; Bouma and others, 1978a). Thus, the river system has been operative over relatively long periods of time, constantly feeding sediments to the receiving basin and building a thick Jurassic, Cretaceous, Tertiary, and Quaternary sequence of interfingering deltaic, nearshore coastal brackish water, and marine sediments, which have prograded the coastal plain shoreline seaward. Relatively little sediment yield has occurred during the Quaternary from the southern rim of the Gulf of Mexico basin. Through time, depocenters have shifted within the northern flank of the basin, forming a relatively thick sequence of Tertiary and Quaternary clastic sediments. The zone of maximum thickness trends roughly east-west near the present-day coastal plain of Louisiana and west toward Texas. Rapid subsidence associated primarily with sediment loading and salt and shale diapirism has been responsible for unusually thick, localized sedimentary accumulations and for the complex bathymetry on the continental slope (Fig. 1; Plate I, this volume). Throughout the Tertiary and Quaternary, minor and major transgressions and regressions have occurred, although the major depositional component

Research in the modern delta of the Mississippi River has revealed short-term changes and processes that are of significant magnitude. Deltaic lobes, each lobe covering an area of 30,000 sq km and having an average thickness of 35 km, switch sites of deposition on an average of every 1,500 yr. Through short periods of geologic time, this process results in a relatively thick accumulation of stacked deltaic cycles covering extremely large areas. Within a single delta lobe, and operating on an even higher frequency, are bay fills and overbank splays. Bay fills, having areas of 250 sq km and thickness of 15 m, require only 150 yr to accumulate. Four major events have taken place in the modern Balize delta since 1838. Overbank splays are much smaller, covering areas of less than 2 sq km and having thicknesses of 3 m, but are associated with high floods on the river. At the river mouth, continued progradation of the distributary channel can form distributary mouth sand bodies that have dimensions of 17 km long, 8 km wide, and a thickness of 80 m in a period of only 200 yr. Differential sedimentary loading at the river mouth results in formation of diapirs that display vertical movements in excess of 100 m in a period of 20 yr. On the subaqueous delta platform, sediment instabilities operate nearly continuously, mass-moving large quantities of shallow-water deposits to deeper-water environments via arcuate rotational slides and mudflow gullies and depositional lobes. All of these changes and processes operate at differing spatial and temporal scales, but all result in deposition of large volumes of sediment over extremely short periods of time.

Abstract The Atlantic and Gulf Coastal Province differs from most other geomorphic provinces in North America in that it has a large suboceanic area (685 × 10 3 km 2 ) in addition to its subaerial segment (1,166 × 10 3 km 2 ; Table 1). The subaerial portion, usually referred to as the Coastal Plain * , extends from Long Island in New York (with outliers in Martha’s Vineyard and Cape Cod) to the Mexico border in Texas and includes all or part of 19 states. The suboceanic portion, which composes part of North America’s Continental Shelf, extends from the Canadian border south and west to the border with Mexico. The unifying character of this province stems mainly from a geologic history that has recorded alternating periods of submergence and emergence. Thus, all parts of the province have experienced coastal processes at one time or another, and most areas several times. However, over many parts of the province the surface expression of these processes has been destroyed or highly modified by erosion or burial. Most of the suboceanic portion of the province was subaerial as recently as 18,000 years ago, whereas parts of the subaerial portion of the Coastal Plain have not been submerged since the Cretaceous. The interface between the two divisions has been near its present elevational position for only some 5,000 to 6,000 years. During most of the province’s history, a number of geomorphic processes have been operative upon a relatively gently sloping surface consisting of rocks that generally increase in age upslope. In addition

ABSTRACT Large river systems deliver significant quantities of fine-grained sediment to continental shelf regions. In specific areas off deltas, deposition rates are rapid and the sediment may be involved in a variety of mass-movement processes on the subaqueous slopes (slumps and slides, debris flows, and mudflows), causing rapid sediment accumulation at shelfbreak depths and resulting in active progradation of the shelfedge. Seismically, the deposits appear as large-scale foresets and are commonly composed of in situ deep-water deposits alternating with shallow-water sediments transported by mass movement. On electric logs, sands within these units are sporadic and display sharp basal planes and blocky shapes. Progradation of the shelfedge deposits is generally accompanied by oversteepening and large-scale instability of the upper shelfbreak slopes. Deep-seated and shallow rotational slides move large volumes of sediments and deposit them on the adjacent slopes and upper rise. Extensive contemporaneous faults commonly form at the shelfedge. Continuous addition of sediment to the fault scarps, particularly by mass movement from nearby delta-front instability, causes large volumes of shallow-water sediment to accumulate on the downthrown sides of the faults, mostly forming large-scale rollover structures. Continued movement along the concave-upward shear planes commonly results in compressional folds and diapiric structures. Contemporaneous accumulation of shallow-water mass-movement deposits may occur in association with these structures. Massive retrogressive, arcuate-shaped landslide scars and canyons or trenches can also form at the shelfedge owing to slumping and other mass-movement processes. Such canyons and trenches can attain widths of 10–20 kilometers, depths of 800 meters, and lengths of 80–100 kilometers. The Mississippi Canyon probably originated in this manner. The creation of such features by shelfedge instability results in the yielding of exceptionally large volumes of shallow-water sediment to the deep basins in the form of massive submarine fans. The infilling of depressions by deltaic progradation is rapid, forming large foresets near the canyon heads. The low strength of the rapidly infilled, under-consolidated sediments causes downslope creep or reactivation of failure mechanisms, resulting in multiple episodes of filling and evacuation.