Relative Sea Level Drop Research Articles

Carbonate platform depositional sequences, Upper Cretaceous, south-central Pyrenees (Spain)

The Upper Cretaceous (Cenomanian-Maastrichtian) of the south-central Pyrenees shows five carbonate platform sequences where the major parameters are tectonism, relative sea-level fluctuations and inherited depositional profile. Depositional geometries and basin analysis permit an understanding of the depositional history. Five depositional sequences have been recognized: (1) The Santa Fe sequence (Middle-Upper Cenomanian), a ramp to a skeletal rimmed shelf with an escarpment bypass margin. The lower boundary is an angular unconformity and the upper one records a sea-level drop. The platform location of the margin was determined by a listric normal fault. (2) An abrupt sea-level rise drowned the former platform. The Congost sequence (Turonian-Lower Coniacian), a distally steepened ramp with erosional distal deep slope. The depositional model was largely controlled by pre-existing basin morphology. Cessation of platform development was due to a relative sea-level drop. (3) The Sant Corneli sequence (Upper Coniacian-Lower Santonian), a mixed terrigenous-skeletal homoclinal ramp with upright margin, deep slope and dysaerobic basin. The slope results from the backstepping by 24 km of the previous margin and gentle basin tilting. The platform margin remained more or less at the same position, and relief between platform and slope increased indicating continuous relative sea-level rise. The upper boundary is an angular unconformity at the platform margin produced by an abrupt sea-level rise and platform drowning, and by listric normal faulting. (4) The Vallcarga sequence (Upper Santonian-Campanian), a distal-steepened skeletal homoclinal ramp, erosional escarpment and turbidite basin, which corresponds to the Mesozoic maximum marine expansion. A listric normal fault created two depositional areas: a more or less flat footwall block with a north-northwest prograding carbonate ramp.

Depositional Model for Submarine Fan Deposits of Vedder Sandstone, Eastern San Joaquin Basin: ABSTRACT

The Vedder sandstone is an informal subsurface term applied collectively to a series of offlapping clastic wedges of late Oligocene through early Miocene age that subcrop beneath the basal Saucesian unconformity along the southeastern flank of the San Joaquin basin. Although the Vedder has generally been accepted as a shoreface to shallow-water shelf deposit, such an interpretation is inconsistent with the sandstone body geometry, vertical and lateral sequence architecture, and inferred paleobathymetry of foraminiferal assemblages for the interval over the greater part of the northwestern subcrop trend. The Vedder sandstone in that region represents deposition in a series of small submarine fans that coalesced at the base of a fault-controlled slope along the eastern margin of the Zemorrian San Joaquin basin. The Vedder fans exhibit a relatively broad inner fan apron composed of amalgamated, channel-fill deposits that pass quickly downdip into a highly variable midfan belt of channel-levee complexes. The outer fan is characterized by thick, sand-rich depositional lobes with a narrow outer fan fringe. Three periods of fan progradation are recognized in the Vedder interval, each corresponding to a relative sea level drop related to local tectonic pulses in the active forearc setting. A subsequent lowstand coincident with majormore » uplift along the basin margin resulted in a regional unconformity that beheaded the Vedder fans and stripped off much of the equivalent slope and shelf facies. This unconformity juxtaposed the updip Vedder sandstones against an overlying transgressive sandstone, thus reducing the otherwise excellent stratigraphic trap geometries of the Vedder interval.« less

琉球列島南部における完新世の海岸地形および海水準

1. Marine terraces, marine notches, beachrock, in situ coral reef and emerged shellbeds are used as indicators of Holocene sea-levels in Kohama, Kuro and Hateruma Islands, the South Ryukyus. A sea-level slightly higher than the present one, about 1 m AMSL is found from ca. 3, 300 to 800yBP in Kohama and Hateruma Islands and about 1.5m AMSL at about 4, 200yBP in Kuro Island (Table 2). It is, however, difficult to distinguish local differences in these three islands, owing to the limited number of observations and some uncertainty in the value of some coastal features as indicators of former sea-level. Late Holocene emergence is very small. 2. Shorelines which records the culmination of Postglacial (Jomon) transgression at about 6, 000yBP have been found along many parts of the Japanese coastline. Such evidences of shorelines, however, have not been observed in these three islands. The buried notch in Kuro Island, covered by beachrock at ca. 4, 200yBP, may correspond to this early transgression. 3. The relative sea-level drop causing the emergence of marine features in several Ryukyu islands is a recent phenomenon. Slight emergence dated at ca. 800 to 600yBP occurs not only on Hateruma Island, but also on Yoron Island (DELIBRIAS and PIRAzz0LI, 1983), on central Okinawa Island (KAWANA and PIRAZZOLI, 1983) and on Tarama Island (PIRAZZOLI et al., 1984). 4. Deposits found on the southeast coast of Hateruma Island, can be interpreted as the result of a tsunami, which accompanied the great earthquake of 1771.