High-frequency Sea-level Changes Research Articles

High-frequency sea-level changes recorded in deep-water carbonates of the Upper Cretaceous Dol Formation (island of Brač, Croatia)

High-frequency sea-level changes recorded in deep-water carbonates of the Upper Cretaceous Dol Formation (island of Brač, Croatia)The upper part of the Middle Coniacian/Santonian-Middle Campanian deep-water Dol Formation of the island of Brač is composed of countless fine-grained allodapic intercalations deposited in an intraplatform trough. Within the studied section 13 beds can be distinguished, each defined by its lower part built up of dark grey limestone with abundance of branched, horizontally to subhorizontally oriented burrows, and the upper part, in which the light grey to white limestone contains larger burrows, rarely branched, showing no preferential orientation. The lower, dark grey, intensively bioturbated levels are interpreted as intervals formed during high-frequency sea-level highstands, while the upper, light grey-to-white levels are interpreted as intervals formed during the high-frequency sea-level lowstands. Cyclic alternation of these two intervals within the fine-grained allodapic beds is interpreted as the interaction between the amount of carbonate production on the platform margin and the periodicity and intensity of shedding and deposition in the distal part of toe-of-slope environment, which is governed by Milankovitch-band high frequency sea-level changes.

Sea level changes revealed by cosmic dusts: A pilot study of the Upper Permian reefs in Guizhou, China

In this study, we test the hypothesis that the distribution of Co, characteristic of cosmic dusts, in platform carbonates may trace palaeo-environment changes. 23 samples collected from the Upper Permian reefs in the carbonate platform margin at Ziyun, Guizhou, have been measured by neutron activation analysis. The variation of Co in sedimentary rocks is used to calculate the variations in sedimentary rate and high-frequency sea level changes. The results are in good agreement with the integrated interpretation of sequence stratigraphy. Thus, the enrichment of Co from cosmic dusts may be useful for the analysis of high-resolution sequence stratigraphy.

Development of the Kura delta, Azerbaijan; a record of Holocene Caspian sea-level changes

Late Holocene deposits of the Kura delta indicate an alternating dominance of deltaic and shallow marine environments. These major environment shifts are controlled by the high frequency sea-level changes of the Caspian Sea. The level of the Caspian Sea, now at 27 m below Global Sea Level (GSL), changes at rates of up to a hundred times as fast as global sea level, allowing observation of sedimentary processes on a decadal scale that would take millennia in an oceanic environment. The modern Kura delta is a river-dominated delta with some wave action along its north-eastern flank, and without tidal influence. Morphological and hydrological changes have been monitored for over 150 years, continuing up to the present day using remote sensing imagery. Offshore sparker survey data, onshore and offshore corings, biostratigraphical analysis and radiometric dating enable a reconstruction of the Holocene Kura delta. Four phases of delta progradation alternating with erosional transgressive surfaces have been identified, representing just as many cycles of sea-level fall and rise. The first cycle is represented by lowstand deposits truncated by a transgressive surface (TS1) at ca. 80 m below GSL. TS1 is overlain by several metres of laminated clays and silts, deposited during a Late Holocene forced regression (H1). These deposits are truncated by the prominent reflector (TS2), corresponding to the Derbent lowstand around 1500 yr BP and subsequent transgression. This transgressive surface is overlain by prograding shallowing upwards deposits, H2, in turn truncated by a third transgressive surface (TS3), correlated with a lowstand of ca. 32 m below GSL. The last phase, H3, comprises an onshore progradational unit followed by an aggradational unit with an offshore veneer of clays and silts, corresponding to the formation of the modern Kura delta that started at the beginning of the 19th century.

High-Resolution Seismic Study as a Tool for Sequence Stratigraphic Evidence of High-Frequency Sea-Level Changes: Latest Pleistocene-Holocene Example from the Korea Strait

ABSTRACT Sequence stratigraphic analysis of high-resolution seismic reflection profiles and sediment data reveals that the latest Pleistocene-Holocene deposits in the Korea Strait shelf off the southeastern Korean Peninsula form a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 kyr) sea-level cycle. Eight depositional systems, each with different seismic facies, constitute the systems tracts. The lowstand systems tract, consisting of sandy mud, forms a deltaic wedge that pinches out updip near or at the relict shelf edge. The transgressive systems tract, consisting mainly of sands, includes six depositional systems: (1) inner-shelf transgressive layer, (2) transgressive estuarine-deltaic complex, (3) transgressive sand ridge, (4) mid-shelf transgressive layer, (5) incised-channel fill, and (6) beach-shoreface complex. Although the transgressive systems tract is widely distributed, it is much thinner than the lowstand and highstand systems tracts. The highstand systems tract is composed of a prodelta-shelf complex consisting almost exclusively of Holocene muds. The distribution and geometry of the systems tracts in the latest Pleistocene-Holocene sequence in the Korea Strait shelf is different from that of Vail's model in that: (1) the lowstand systems tract consists only of the lowstand deltaic wedge, which forms an elongated sediment body along the paleoshelf edge, and (2) the highstand systems tract is completely confined to the inner shelf and forms a nearshore belt parallel to the coastline. High-frequency (20 kyr), high-amplitude (magnitude of about 130 m) sea-level change, together with strong currents flowing northeastward along the southeastern coast of the Korean Peninsula and varying sediment supply, have resulted in this rather unusual stratigraphic architecture.

High-Resolution Seismic Study as a Tool for Sequence Stratigraphic Evidence of High-Frequency Sea-Level Changes: Latest Pleistocene-Holocene Example from the Korea Strait

High-Resolution Seismic Study as a Tool for Sequence Stratigraphic Evidence of High-Frequency Sea-Level Changes: Latest Pleistocene-Holocene Example from the Korea Strait

Mass extinctions and sea-level changes

Review of sea-level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions. The degree of certainty with which these eustatic oscillations are known varies considerably. Thus, the late Ordovician and end Cretaceous extinctions are associated with unequivocal, major regressions demonstrated from numerous, widespread regions. In contrast, the multiple, high frequency sea-level changes reported for the Frasnian–Famennian crisis (based on the supposed depth-preferences of conodont taxa) have little support from sequence stratigraphic analyses, which reveals the interval to be one of highstand. The end Permian mass extinction has long been related to a severe, first order lowstand of sea level [Newell, N.D., 1967. Revolutions in the history of life. Geol. Soc. Am. Spec. Pap. 89, 63–91.] based primarily on the widespread absence of latest Permian ammonoid markers, but field evidence reveals that the interval coincides with a major transgression. Newell's hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end Guadalupian and end Triassic extinction events but not for other crises. Rapid high amplitude regressive–transgressive couplets are the most frequently observed eustatic changes at times of mass extinction, with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive. The ultimate cause of the sea-level changes is generally unclear. A glacioeustatic driving mechanism can only be convincingly demonstrated for the end Ordovician and end Devonian events. At other times, it is speculated that they may relate to the widespread regional doming (and subsequent collapse) caused by the impingement of superplumes (and ultimate eruption) on the base of the lithosphere.

Post-Calabrian sequence stratigraphy of the northwestern Alboran Sea (southwestern Mediterranean)

The post-Calabrian sedimentary column of the northwestern Alboran Sea comprises three depositional sequences. The two older depositional sequences are defined by lowstand systems tracts (shelf-margin deltas, slope, base-of-slope, and basin deposits, and the Guadiaro channel-levee complex). In contrast, the most recent depositional sequence also includes transgressive (relict shelf facies) and high-stand (the Guadalmedina-Guadalhorce prodelta and hemipelagic facies) systems tracts. The stratigraphic architecture of these depositional sequences is controlled by the synchronism between high frequency sea-level changes, variations in sediment supply, and sedimentary processes. The configuration of the depositional sequences is variable and their distribution is complex, as a result of the relative importance played by sea-level changes and tectonism through the area. The sequence boundaries are represented by polygenetic surfaces in the proximal margin, and by monogenetic surfaces in the distal margin and basin. Each polygenetic surface results from the interaction between the sequence boundary with the lowstand erosional truncation surface and the transgressive surface, both developed during the previous sea-level cycle. The monogenetic surfaces correspond to unconformities and their correlative conformities, formed during sea-level lowstands. This pattern of depositional sequences developed in the margin and basin of the northwestern Alboran Sea shows differences with the Exxon Sequence Stratigraphy Model as traditionally applied: sea-level change control is essentially recognized through lowstand systems tracts, and sequence boundary coincides with lowstand erosional truncation surface and transgressive surface, both developed during the previous sea-level cycle.

Stratigraphical architecture at the muddy margin of the Cretaceous Western Interior Seaway, southern Utah

ABSTRACTThe Tropic Shale and correlative Tununk Shale Member of the Mancos Shale accumulated during Cenomanian‐Turonian time, within prodeltaic environments near the western margin of the Western Interior Seaway of North America. Stratigraphical and sedimentological analysis has revealed a detailed history of relative sea level change in the thick, fine grained succession. The Tropic and Tununk shales were deposited during the Greenhorn second‐order sea level cycle, over a time span of about 2–5 million years. In southern Utah, six depositional sequences are superposed upon the record of this long term sea level change. The sequences developed during third‐order relative sea level cycles of hundreds of thousands of years duration and are composed of at least 37 parasequences, arranged in retrogradational, aggradational and progradational parasequence sets.The Tropic Shale and Tununk Shale Member accumulated just basinward of the axis of maximum subsidence of a foreland basin. Stratal geometries and facies distribution patterns in the succession indicate that in southern Utah the Greenhorn cycle was tectonically controlled. During the Greenhorn transgression and highstand, rapid rates of tectonic subsidence trapped terrigenous sediment to the west of the study area, in the more proximal foreland. At this time, hemipelagic facies accumulated at relatively slow rates in southern Utah and type 2 sequences developed during third‐order sea level cycles. In contrast, during the Greenhorn regression rates of thrust‐induced subsidence in the proximal foreland basin evidently slowed, and deltaic clinoforms prograded across the study area. At least one forced regression occurred in southern Utah at this time, and type 1 sequences developed.The formation of type 1 sequence boundaries in the upper part of the Tropic Shale and Tununk Shale Member points to episodes of base level fall and indicates that the six third‐order sea level cycles recorded in the succession were not the result of changes in sediment supply alone. The third‐order cycles may have been a consequence of episodic tectonism. The timing of these cycles, however, suggests that development of sequences and parasequences in the Tropic Shale and Tununk Shale Member may have been related to orbital forcing in the Milankovitch band. Glacioeustasy or climatically related fluctuations in the amount of groundwater stored on continents may explain these high frequency sea level changes.

Sedimentary development of the Louisiana continental shelf related to sea level cycles: Part I—sedimentary sequences

Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well developed in marine deposits associated with large river systems. Superimposed on those cycles attributed to shifting sites of deposition are those related to high-frequency sea level changes. The large data base for this study (including 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 chronostratigraphy and lithostratigraphy that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics and spatial depositional patterns during three complete sea level cycles over the entire continental shelf/upper slope of offshore Louisiana.