Regional Sea Level Changes Research Articles

Timing, style and sedimentary evolution of Late Palaeozoic-Mesozoic extensional basins of East Greenland

Abstract The late Palaeozoic-Mesozoic sedimentary basins of East Greenland record a complex series of events which eventually led to the successful opening of the Norwegian-Greenland Sea in the late Palaeocene. Major tectonic events and regional sea-level changes caused by plate movements and reorganizations, overprinted by the effects of local tectonics and associated sea-level changes are reflected in thick, unconformity bounded sequences. Caledonian crustal shortening and thickening culminated in the Silurian, and was succeeded by extensional collapse, vulcanism and intrusion of post-tectonic granites in the Devonian. Large, transtensional pull-apart basins were formed and became filled with continental red beds. Basin margins underwent repeated episodes of thrusting. A change to rifting took place in the latest Devonian. Rapid subsidence and continental deposition punctuated by episodes of igneous activity and contractional deformation continued from the Devonian until early Permian times for about 120 Ma leaving a record of alluvial fan and flood plain siliciclastics alternating with rhyolitic and alkaline basaltic intrusions and extrusions. Later basin subsidence reflected thermal cooling and contraction following the prolonged late Palaeozoic period of crustal thinning. Important phases of block faulting occurred at several intervals during Mesozoic times climaxing in the Volgian-Valanginian interval. Cenozoic basin inversions resulted in dramatic decoupled uplift and tilting of large blocks. The degree of Devonian extensional collapse, the position and orientation of Caledonian thrust planes, and the localization of mid- and late Palaeozoic transtensional strike-slip basins exerted a profound control on localization and style of the compartmentalized Mesozoic rift. The importance of pre-Mesozoic history, timing of Mesozoic tectonic events and the interplay of tectonism, and rates of subsidence, sea-level change and sediment influx have close parallels in the North Sea area. Examples from the exposed Mesozoic succession of East Greenland may thus serve as excellent predictive guides for subsurface geology around the British Isles.

The case for sea-level change as a dominant causal factor in mass extinction of marine invertebrates

A correlation between global marine regressions and mass extinctions has been recognized since the last century and received explicit formulation, in a model involving habitat-area restriction, by Newell in the 1960s. Since that time attempts to apply the species-area relation to the subject have proved somewhat controversial and promoters of other extinction models have called the generality of the regression-extinction relation into question. Here, a strong relation is shown to exist between times of global or regional sea-level change inferred from stratigraphic analysis, and times of high turnover of Phanerozoic marine invertebrates, involving both extinction and radiation; this is valid on a small and large scale. In many cases the most significant factor promoting extinction was apparently not regression but spreads of anoxic bottom water associated with the subsequent transgression. The sea-level-extinction relation cannot be properly understood without an adequate ecological model, and an attempt is made to formulate one in outline.

Phanerozoic Tectonic History of the Lands Bordering the Southeastern Mediterranean Basin: ABSTRACT

The part of the Arabo-African continental mass bordering the southeastern Mediterranean was stabilized by the Pan-African orogeny in the Early Cambrian. During most of the Phanerozoic it was a stable platform on which an extensive blanket of mature sediments accumulated in several phases of deposition, separated by periods of extensive erosion and controlled by regional tectonism and worldwide changes in sea level. The platform history comprises several stages with different tectonic regimes. During most of the Paleozoic the area was within Gondwanaland, some distance from any continental margin, and its long-wavelength vertical motions were not visibly related to the Mesozoic continental margin. After Late Permian time the pattern of vertical motions was characterized by subsidence increasing toward the Mesozoic continental margin. However, tectonism, volcanism, and deepwater sedimentation associated with its shaping are known only from Middle Triassic and early Liassic times when the Levant and the Zagros margins strongly subsided; in Egypt important subsidence began later. In Late Jurassic time the Levant basin was already about 2 km deep; farther west, deep-water conditions existed at least from the Early Cretaceous. A latest Jurassic-earliest Cretaceous hot spot produced widespread magmatism, uplifting, and erosion in the lands bordering the Levant basin, temporarily more » interrupting the regional subsidence. The Senonian plate covergence along the Alpine foldbelt produced mild compressional and shearing deformation in the northeast-southwest-trending Syrian arc, which modulated the sedimentation on the platform and along the continental margin. Following the Neogene, the area was affected by still-active rifting and continental breakup associated with widespread magmatism and uplifting which considerably modified the older regional structure. « less

Depositional History of Sunniland Limestone (Lower Cretaceous), Raccoon Point Field, Collier County, Florida: ABSTRACT

ABSTRACT The Sunniland Limestone (Lower Cretaceous), consisting of carbonate rick and anhydrite, has the distinction of producing the only oil and gas in southern Florida. Raccoon Point Field, Collier County, Florida, is one of thirteen fields discovered along the Sunniland trend, producing from paleotopographic highs associated with patch reefs and high-energy bioclastic deposits. Deposition of the Sunniland Limestone occurred in three transgressive-regressive sediment packages or sequences (Lower, Middle, and Upper Sunniland), each is related to regional or eustatic sea-level changes. Each sequence is further divided into successive shallowing-upward intervals or parasequences. The end of each sequence is marked by a basinward shift in coastal onlap, representing a major fall in relative sea-level. The end of the Middle Sunniland is marked by a prolonged fall in relative sea-level. During this lowstand, a restricted basin developed within the Florida Embayment where a thick subtidal anhydrite was deposited. The lowered sea-level at the end of the Middle Sunniland and the dominance of intertidal-flat and supratidal-sabkha environments in the Upper Sunniland are interpreted to have significantly influenced reservoir development at Raccoon Point Field through porosity and permeability enhancement of bioclastic deposits by leaching and dolomitization. The dolomite reservoirs at Raccoon Point Field occur at the top of the Middle Sunniland and within the Upper Sunniland. They are interpreted as high-energy deposits formed from bioclastic debris shed behind rudist mounds. Reservoir development in the Middle Sunniland is most likely because of diagenesis associated with restrictive hypersaline conditions under which an evaporite wedge was deposited when sea level fell at the end of Middle Sunniland deposition. Creation of the Upper Sunniland dolomitized bioclastic reservoir was probably influenced by restricted conditions associated with intertidal-flat and supratidal-sabkha environments. Anhydrite and dolomitized carbonate rock from these environments dominate the Upper Sunniland and therefore form a low porosity and permeability reservoir-seal.

Application of Soil-Stratigraphic Techniques to Engineering Geology

Soil-stratigraphic techniques are being increasingly applied to engineering-geological investigations for siting liquified natural gas (LNG) facilities, nuclear reactors, dams, and other critical structures. Soil (pedological) profiles in Quaternary sections are useful to ascertain the approximate age of site-area sediments, to reconstruct local geomorphic history, to date the last movement of faults, and in some cases to determine recurrence intervals of displacements associated with faults or large mass-movements. Soil stratigraphy includes the field of paleopedology, and generally employs the concepts and terminology of the soil scientist. Soil units particularly applicable to engineering geology are: the organic horizon of the modern solum and buried paleosol, frequently datable by radiocarbon assay; the albic horizon, sometimes indicative of local climatic and vegetative change; the argillic horizon, typical of strongly-developed profiles and useful as a regional stratigraphic marker; and the calcic horizon of arid and semi-arid regions, likewise often an indicator of climatic change. Exemplified in geo-technical investigations for a proposed LNG terminal near Point Conception (Little Cojo Bay), California, soil stratigraphy was employed to date last displacement of site-area faults, to estimate age of marine platforms, and to help reconstruct regional geomorphic history. Similarly, at the General Electric Test Reactor (GETR) site near Livermore (Vallecitos), California, soil stratigraphy was instrumental to date last displacement and recurrence of site-area slip surfaces engendered either by tectonic or by mass-wasting processes. Datable markers included four, strongly-developed buried paleosols, each of which marked epochs of regional landscape stability during the Quaternary. Soil-stratigraphic techniques are particularly effective when combined with geomorphic and other Quaternary studies. Many soils are also datable, either directly by radiometric assay, or indirectly by association with regional changes in climate, sea level, and landscape stability. These soils may thus well serve as important stratigraphic markers applicable to engineering-geological investigations in a wide variety of climatic and geomorphic settings.

Regional sea level, Southern Oscillation and beach change, New South Wales, Australia

Coastal erosion is a problem of increasing concern that affects 60% of the world's sandy coastline1. This erosion has been attributed to increased storminess, tectonic subsidence, eustatic sea-level rise, decreased shoreward sediment movement from the shelf, permanent longshore leakage of sediment from beach compartments, shifts in global pressure belts resulting in changes in the directional component of wave climates, and human interference2,3. No one explanation has worldwide applicability because all factors vary in importance regionally. Evaluation of factors is complicated by a lack of accurate, continuous, long-term erosional data. Historical map evidence spanning 100–1,000 yr has been used in a few isolated areas4–7; however, temporal resolution has not been sufficient to evaluate the effect of climatic variables. Air photographic evidence8 is restricted to the past 40 yr, and often suffers from insufficient ground control for accurate mapping over time. Ground surveying of beaches was rarely carried out before 1960 and is often discontinuous in time and space. I have resolved the problems of temporal and spatial continuity by studying change for the whole of Stanwell Park beach, New South Wales, Australia for the period 1895–1980 (Fig. 1). I report here that using the average high-tide wave run-up position measured accurate to ±2.5 m from oblique and vertical photographs, changes could be linked to regional sea-level variation and a globally significant climatic variable, the Southern Oscillation (SO).