Stages Of Basin Evolution Research Articles

Strontium isotope trends during diagenesis in ore-bearing carbonate basins

Strontium isotope studies (120 analyses) were carried out on ore and gangue minerals from five ore districts in different carbonate basins. Most of the samples were separated from consecutive diagenetic generations. Even for diverse stratigraphic positions and mineralogies, very consistent trends are recognized. In all cases87Sr/86Sr ratios increase with advancing diagenetic stage. However, each district shows a different behaviour in the magnitude of increase over the first diagenetic generation, which ideally is close to contemporaneous seawater: The increase of the strontium ratios in the subsequent diagenetic generations is explained by equilibration during crystallization with fluids evolving towards more radiogenic compositions. This is interpreted as a consequence of the reaction of the fluids with Rb-bearing phases, mainly detrital clay minerals. Variation ranges of87Sr/86Sr ratios can constitute a sensitive tool for determining the stage of basin evolution in a similar way as vitrinite reflectance or illite crystallinity. This method has the disadvantage that the increase of radiogenic strontium depends not only on the evolution stage, i.e., temperature, pressure, and time, but also on the amount of Rb-bearing minerals present in the basin. On the other hand, this method has the important advantage that within a given basin this last parameter can be modelled. Each evolution stage is recorded in the cements or crystallization generations by its strontium isotope signatures, which tend towards increased radiogenic values with advancing diagenesis.

Mixed Siliciclastic-Carbonate Marine and Continental Syn-Rift Sedimentation, Upper Jurassic-Lowermost Cretaceous Todos Santos and San Ricardo Formations, Western Chiapas, Mexico

Initial Mesozoic sedimentation in western Chiapas, represented by the Upper Jurassic-lowermost Cretaceous Todos Santos and San Ricardo Formations, occurred over a horst-and-graben terrane formed during rifting in the ancestral Gulf of Mexico Basin. The Todos Santos consists of fluviolacustrine sequences deposited over block-faulted granodiorite. The San Ricardo overlies and interfingers with the Todos Santos, and consists of siliciclastics, carbonates, and evaporites deposited in arid tidal flat, beach, restricted back-barrier lagoon, barrier, shoreface, and shelf environments. San Ricardo facies distribution outlines three transgressive and regressive or still-stand sequences of Oxfordian, Kimmeridgian, and Tithonian-early Hauterivian age. The correspondence between the ages of these sequences and the age of eustatic cycles suggests that their development was primarily influenced by global sea-level changes. Superimposed on this eustatic pattern are stratigraphic features attributed to variable tectonic subsidence of basement blocks, including abrupt lateral thickening or thinning of facies, the localization of ooid grainstone deposition on horsts, and carbonate-platform drowning. Locally consistent patterns of thickening or thinning of both continental and marine facies indicates rift-related block faulting was active throughout Todos Santos and San Ricardo deposition. This style of rift-basin sedimentation contrasts with the Atlantic-margin type by including normal-salinity marine facies in addition to continental and restricted-marine facies. The identification of this style in the Gulf of Mexico is important for reconstructing and differentiating rift and postrift stages of basin development and for predicting the subsurface pattern of Upper Jurassic-Neocomian facies.

An extensional model of graben subsidence—the first stage of basin evolution

The formation of grabens in continental crust is generally associated with tensile faulting, crustal thinning, anomalously warm mantle below the rift zone and an updoming of the outer flanks of the rift zone. These features are also common to the initial stages of sedimentary basin formation and continental rupture (creating new sea floor). This similarity suggests that similar tectonic processes, but of varying duration, may be responsible for all three phenomena. In this study subsidence within continental grabens which have been formed by a sudden local stretching event is examined. Within the zone of extension two competing effects act to determine the sense (uplift or subsidence) and magnitude of initial epeirogenic movements: these are the thinning of the low-density crust and the upwelling of hot mantle material. On continental crust, depending on which effect is dominant, either rapid uplift or rapid subsidence may occur initially. Subsequently, thermally controlled subsidence occurs as the anomalously warm mantle below the rift cools. Due to lateral heat flow, subsidence occurs more rapidly in grabens than in basins and may be accompanied by a transient uplift of the graben flanks.

Evolution of the early Paleozoic deep-water basin of north Greenland—Aulacogen or narrow ocean?

A major lower Paleozoic deep-water sequence is exposed for more than 800 km along the coast of north Greenland. The maximum preserved width of the basin is about 200 km, and the thickness of the sedimentary sequence may reach 8 km. Nine evolutionary stages in basin evolution are recognized, each characterized by distinct sedimentary facies and structural style of the shelf-basin boundary: (1) the oldest sequence of unknown age is so deformed that inferences about the depositional environment are precluded; (2) late Precambrian(?)-Early Cambrian incipient basin; (3) Early Cambrian narrow turbidite basin; (4) Middle Cambrian-Ordovician basin expansion and initial starvation; (5) latest Ordovician-Early Silurian longitudinally filled turbidite basin; (6) Middle Silurian basin expansion and starvation; (7) Middle-Late Silurian wide turbidite basin; (8) Middle-Late Silurian Caledonian thrusting and conglomerate deposition; and (9) probably latest Silurian megasliding and advance of the Caledonian front. The basin evolution that came to an end during the mid-Paleozoic Ellesmerian orogeny was punctuated by events related to the closure of the Iapetus ocean and formation of the Caledonian mountain belt to the east. The basin may have been fully ensialic and formed during the early rifting stages preceding back-arc spreading, or it may have reached a narrow ocean stage. At present, however, we are inclined to favor an interpretation of the basin as being an aulacogen extending deeply into an old continent at a right angle to the Caledonian orogenic front to the east.

Geologic History of a Basin Depicted by Computer Mapping: ABSTRACT

Reconstructions of detailed geologic histories of basins have become an increasingly important part of the exploration process. However, a history that includes numerous stratigraphic horizons and several periods of orogeny and erosion usually involves handling such a great volume of data that use of a computer becomes necessary. A complete depiction of the geological history of a basin must include the geometric relationships between the various horizons (onlap, offlap, truncation, etc), the depths and thicknesses of the formations, and the effects of orogeny and erosion throughout the basin. Most computer mapping programs generate interpolated grids that are used for drawing contour maps. These grids and maps can show configurations of horizons at various stages of basin development, and can also show pre-erosional and pre-orogenic forms. The procedures are: (1) Interpret major geologic events. (2) Capture data at each selected control point (elevations of each mappable horizon and unconformity, estimates of loss in thickness due to erosion, estimate tectonic tilts and structures). (3) Construct grids (prepare data, construct grids of present stratigraphy, construct grids of pre-erosional forms). The resultant grids are used to depict present structure, paleostructure, map isopach units, and draw stratigraphic cross sections. End_of_Article - Last_Page 587------------

Correlations Between the Onshore and Offshore Santa Maria Basins -- A Dilemma: ABSTRACT

In an unexplored basin, extrapolation from known hydrocarbon-producing trends is ideal. However, along transform margins such extrapolations are difficult, owing to lateral displacement between individual blocks on both regional and local scales. An example of this is the relationship between the onshore and offshore Santa Maria basins, which are separated by the Hosgri fault. Stratigraphic packages have been used widely to approximate amounts of displacement. Lower Miocene volcanics in the offshore Santa Maria P-060-Oceano well may correlate with onshore outcrops, located across the Hosgri fault, 30 mi (48 km) to the east and 45 mi (72 km) to the south, near Point Arguello. Additionally, lower Miocene volcanics also are present in two exploratory wells across the Hosgri fault, 10 mi (16 km) to the east and 25 mi (40 km) to the north, near Point Buchon. These are the Honolulu-Tidewater U. S. L. Heller Lease 1, with 4,722 ft (1,440 m) thickness of volcanics, and the Tidewater Motadoro 1, with 3,873 ft (1,180 m) of lower Miocene volcanics. These wells provide two volcanic sections onshore to tie with the offshore volcanics. Originally, the lower Miocene volcanics now situated in the northern and southern extremities of the Santa Maria area, may have been joined near the midpoint of their present positions. As the onshore basin pulled apart, the volcanics were divided and transported in opposite directions. Synchronous pull-apart movements occurring in the offshore kept pace with the adjacent onshore. Alternatively, significant intrusive pathways may have opened in the later stage of basin development, allowing igneous material to migrate vertically. These pathways have been termed leaky transforms in the literature. Neither of these models necessitates significant lateral displacement once the onshore and offshore basins formed. Onshore the middle Miocene Monterey Formation and upper Miocene to Pliocene Sisquoc Formation correlate well with equivalent chronostratigraphic units in the offshore P-060-Oceano well, implying that relatively minor lateral displacement has occurred since the middle Miocene. If the offshore basin history is similar to that of the onshore its petroleum potential may approximate that of the onshore, which has been projected to produce 900 million bbl of oil. End_of_Article - Last_Page 1688------------

On basin hyposmetry and the morphodynamic response of coastal inlet systems

The exchange of water and entrained material between coastal basins and the inner continental shelf reduces to the problem of polarized transport (flood +, ebb —) in the conveyance channels routing flow through a coastal inlet. Here the net long-term movement of materials is largely a function of the fluid velocity and discharge — variables whose time history at-a-station contains both periodic and aperiodic elements. In this paper the importance of the major periodic elements in coastal inlet flows and their potential contribution to the net transport of bedload materials is discussed. With the aid of a numerical model featuring a closed hypsometric (area-height) representation of basin storage-volume—channel-flow relationships in a typical basin and inlet system at Wachapreague, Virginia, on the East Coast of the United States were studied to determine present mechanisms for inducing net flood or ebb bedload transport. The basin hypsometry and channel dimensions of the prototype system were then varied in the model to simulate other conditions that may have prevailed during earlier stages of basin evolution. Given a sine wave input to the model, the principal lunar semidiurnal constituent (M 2) and its first-harmonic overtide (M 4) respond in a predictable way to differences in basin hypsometry and channel configuration, and these constituents in turn account for distinctive rise and fall duration differences observed in the mean tide within the basin. These distortions in basin tides are also reflected at-a-station in the time histories of channel discharge and velocity in the form of greater peak magnitudes during ebb or flood depending upon which phase has the shorter duration, and depending in some instances on a further modulation by basin hypsometry and channel cross-sectional area. A consistent imbalance between peak flows of opposing direction is a plausible mechanism for long-term, net transport of bottom sedimentary materials. Thus it appears that a systematic contribution toward either flood or ebb dominance in channel flows can arise through complex periodic tides that exist as a result of specific morphological features in basin and inlet systems. The primary significance of these periodic mechanisms may lie in their apparent sensitivity to changes in basin hypsometry.

Transitional sedimentation styles in the Moodies and Fig Tree Groups, Barberton Mountain Land, South Africa: Evidence favouring an Archean continental margin

Lithologic and paleoenvironmental interrelationships within the ca. 3300 Ma old Fig Tree and Moodies Groups can best be accommodated within an evolving back-arc or passive margin geotectonic model. Associated with early rifting, banded iron formations at the base of the Fig Tree Group developed in localized grabens in response to volcanic exhalative activity. During initial spreading a ‘Steep Rift Type’ continental margin is considered to have developed, along which proximal high-concentration conglomeratic and distal low-concentration graywacke turbidites of the Fig Tree Group accumulated. A conformable transition into overlying fluvial conglomerates at the base of the Moodies Group indicates a narrow continental shelf at that stage of basin development. A subsequent rise in sea level, possibly associated with increased rates of spreading, coupled with the presence of the underlying turbidite sedimentary wedge, produced a widened continental shelf. The overlying Moodies Group sediments, including a well-developed assemblage of marginal marine facies, were deposited along this ‘Shelf Rise Type’ continental margin.

Quantitative Basin Analysis and Evolution of Deep-Marine Shale Basin, Middle Ordovician, Southern Appalachians: ABSTRACT

A quantitative portrayal of paleobathymetry, rate of sedimentation, age, and crustal subsidence of a deep-marine shale basin not only reveals the timing and magnitude of geologic events but also has potential practical application in petroleum geology, as marine shales commonly are a primary source for hydrocarbons. A quantitative basin analysis of the Middle Ordovician Sevier Shale basin in east Tennessee was made using: (1) lithofacies interpretation, (2) conodont-graptolite biostratigraphy, (3) paleobathymetry, (4) rate of sediment accumulation, and (5) sediment backstripping through time. This analysis indicates three main phases of crustal subsidence: (1) an early tectonic and sediment loading phase with a subsidence rate of 3 to 4 cm/1,000 years; (2) a second tectonic phase with a subsidence rate of 60 to 65 cm/1,000 years; (3) a final sediment-loading phase with a subsidence rate of 4 to 15 cm/1,000 years. Five stages of basin evolution were involved: (1) stable-shelf stage, (2) downwarping stage, (3) starved-basin stage, (4) turbidite-fill stage, and (5) contour-current stage. On the basis of morphologic, stratigraphic, sedimentologic, and tectonic similarities between DSDP site 262 (Pliocene-Quaternary) in Timor and the Sevier basin, it is proposed that Sevier basin evolution may be considered analogous to foredeep basin development in Timor. This development occurred by concomitant basin subsidence and uplift of adjacent tectonic land owing to basinward migration of a topographic wave. End_of_Article - Last_Page 525------------

Reversal of Basement-Block Motions in Cambay Basin, India, and Its Importance in Petroleum Exploration: DISCUSSION

The main stages in the paleotectonic profiles outlined in Chowdhary's Figures 4 to 8 (p. 90-94), that illustrate the reversal of basement-block motions are: (1) formation of grabens in the posttrap basement floor, (2) subsidence and accumulation of thick trap-derivative conglomerates in the grabens, (3) inversion of negative to positive movements and uplift of fault blocks, and (4) partial erosion before onset of early Eocene Cambay Shale deposition. Partial erosion of trap-derivative deposits occurred before deposition of the Cambay Shale. It is concluded that although differential movements along the Precambrian tectonic trends occurred in the various stages of basin evolution, there is hardly a case for reversal of basement block motions as envisaged in the paleostructural profiles of the Cambay basin described by Chowdhary. 1 figure (DP)

Simulation Model of Stream Capture

Because the importance of the process of capture, or piracy, in the formation of stream networks is difficult to evaluate by field or map studies, an indirect approach is used in this paper to investigate capture, through the use of a simulation model involving capture within rectangular stream networks on a square matrix. The simulation rules make the probability of capture of a stream by a lower adjacent stream proportional to the advantage in gradient of the potential path of capture between the streams compared to the present gradient of the higher stream. Stream elevations are assumed to be defined by the same type of pattern observed in natural stream networks, that is, a linear relationship between the logarithms of gradient and drainage area. The slope of this relationship, Z, is variable in nature and is the main adjustable parameter in the simulation model. Simulation of capture must start from assigned initial network patterns; random walk networks and parallel drainage are among those used for initial networks. For a given value of Z, the statistical properties of networks (for example, stream numbers, length and area ratios, and shape factors) formed after repeated captures are nearly the same for a wide range of assigned initial networks. However, when the value of Z changes during capture, the statistical properties of the resultant networks may depend upon the type of change, so that properties may be partially inherited from earlier stages of basin evolution. Both the networks simulated by capture and natural networks have similar slight deviations from topological randomness. The capture simulations more closely predict many properties of natural networks than do completely random methods of simulation, such as the random walk. In addition, several parameters in the capture-simulated networks exhibit a consistent trend with respect to the parameter Z that appears to occur also in natural networks. These correspondences between the capture model and natural networks suggest that capture may be an important natural process. However, capture should have its greatest relative importance in early stages of drainage basin evolution.

Geological Evolution of Assam and Cambay Tertiary Basins of India

Assam and Cambay sedimentary basins are the two major oil-bearing regions in India. Applying the principles of regional geotectonics, an attempt is made to correlate the structural and lithologic features of the Tertiary sedimentary sequence of Assam and Cambay with the stages in basin evolution. The Tertiary succession in Assam includes deposits in a geosynclinal belt including flysch stages, overlain by lower and upper molasse deposits, and Paleogene platform deposits overlain by Neogene molasse. The Disang-Naga thrust zone separates these two associations and determines the transition from platform to geosynclinal conditions. The Cambay basin represents platform structure of avlakogen type. It is characterized by predominantly negative movements controlled by basement faults until middle Eocene. Definite inversion during late Eocene-Oligocene is indicated by generally shallow-marine to lagoonal conditions of deposition and probable growth of structures. The Neogene was a period of regional uplift and encompassing both the source and depositional areas and resulting in change of drainage pattern. More arenaceous sediments were formed in the basin during this period with frequent changes from shallow marine to continental conditions. The sea gradually receded southward, forming the present Gulf of Cambay.