Rapid Sea-level Changes Research Articles

Eustatic Signals in Deep-Marine Sedimentary Sequences Recovered at ODP Site 978, Alboran Basin, Western Mediterranean Sea

ABSTRACT A continuous section of Pliocene marine sediments was recovered at Ocean Drilling Program Site 978, located in the Alboran Sea between Spain and Morocco. Three Pliocene subunits have been defined at Site 978: the lowermost (Subunit IC, 129.2 m thick) is characterized by alternating beds of lighter, more calcareous, and darker, less calcareous, claystone with bioturbated upper and lower contacts (Type 1 cycles); the middle (Subunit IB, 67.1 m thick) is composed of relatively homogeneous nannofossil claystone; and the uppermost (Subunit IA, 211.6 m thick) contains abrupt-based darker, terrigenous layers interpreted as turbidites that are interstratified with lighter nannofossil claystone (Type 2 cycles). The rhythmically bedded light and dark layers in Subunit IC correlate with those in the Rosello Composite Section of Sicily, a global reference standard for the Pliocene time scale. These sedimentary cycles are products of variations in precession and resulting continental runoff. Missing cycles occur during eustatic highstands. The shift to more homogeneous sedimentation in Subunit IB is represented in similar-aged sequences throughout the Mediterranean which display evidence of submarine mass wasting. Mediterranean-wide slope degradation was likely a response to rapid sea-level change at approximately 3 Ma. This change in sedimentation style was accompanied by an upsection increase in sediment accumulation rates associated with turbidite influx in Subunit IA. Turbidite frequency throughout the Pliocene section can be linked to eustatic changes in sea level, with turbidite maxima corresponding with mid-sequence downlap surfaces and their associated condensed sections.

Depositional sequences on a late Pleistocene–Holocene tropical siliciclastic shelf (Sunda Shelf, southeast Asia)

This study describes, and reviews, the stratigraphic architecture of the world's largest but least known tropical siliciclastic shelf using the sequence-stratigraphic concept. The Sunda Shelf provides conditions particularly suited for reconstructing its depositional history due to a low gradient and extreme width, the presence of huge paleo-valley systems and abundant filled channels, tectonic stability during the Quaternary, and high sediment input due to a large catchment area. We investigated the subsurface along the most prominent paleo-valley by shallow-seismic surveying and 36 gravity cores controlled by 80 radiocarbon dates. The deposits during sea-level fall prior to the last glacial maximum lowstand and the subsequent deglacial rise correspond to four systems tracts: (a) wide, partly detached prograding deltaic clinoforms indicate forced regression related to a regressive systems tract; (b) sparse shoreline deposits and widespread soil formation refer to a lowstand systems tract; (c) rapidly backstepping coastline-related deposits form a confined transgressive systems tract without stacking patterns and are mainly restricted to the paleo-valley system; (d) a thin marine mud cover extends as a condensed section over the whole shelf area (the base of a highstand systems tract). The stratigraphic architecture on the central Sunda Shelf strata over the past 50,000 years is the result of the interplay of three major factors: (1) rapid sea-level changes, (2) locally pronounced physiography and (3) changes in sediment supply that determined the distribution and accumulation pattern.

Malacological insights into the marine ecology and changing climate of the late Pleistocene – early Holocene Queen Charlotte Islands archipelago, western Canada, and implications for early peoples

The first intertidal species to colonize the Queen Charlotte Islands archipelago along the northeastern Pacific margin of Canada after the last glacial maximum (LGM) was Macoma nasuta at 13 210 ± 80 14C years BP. Prior to this time, molluscs were likely excluded where grounded ice extended from the 2 km thick Cordilleran ice sheet on mainland British Columbia. Low water temperatures, high sedimentation rates, high turbidity, dilution, and low primary productivity limited invertebrate colonization subsequent to the LGM, a period of rapid sea-level and climate change. As an adult, M. nasuta is a facultative deposit-suspension feeder that tolerates high turbidity and lowered salinity, and its pediveligers and early juveniles must also have been able to survive these conditions. Subsequently, in addition to M. nasuta, Macoma irus (inquinata), Saxidomus giganteus, Protothaca staminea, Protothaca tenerrima, Hiatella pholadis, Clinocardium nuttallii, and Mytilus trossulus constituted a typical intertidal bivalve assemblage. These findings are explained in terms of the physiology, feeding mechanisms, development, and sediment preferences of living molluscs. The disappearance of most bivalve species between ~11 000 and 10 000 14C years BP indicates the onset of a short interval of low sea-surface temperatures coincident with the Younger Dryas cooling event. Some cold-hardy species persisted, including Clinocardium californiense, Mya truncata, and Serripes groenlandicus. Bivalve species not previously reported as Pleistocene fossils were collected in sediments dating older than 10 000 14C years BP. They include Macoma incongrua, Musculus taylori, Mytilimeria nuttallii, and Tellina nuculoides. Fossil assemblages of intertidal molluscs are used to map ancient shorelines and indicate which species were available as a subsistence resource for early peoples from at least 13 210 ± 80 14C years BP. Intertidal food biomass densities may have reached present commercially harvested levels on southern Moresby Island by 8800 ± 70 14C years BP and on northern Graham Island by 8990 ± 50 14C years BP. When early peoples might have been migrating along the littoral zone, the molluscan productivity of the outer coast was much higher than it is at present.

Late Cretaceous chronology of large, rapid sea-level changes: Glacioeustasy during the greenhouse world

We provide a record of global sea-level (eustatic) variations of the Late Cretaceous (99- 65 Ma) greenhouse world. Ocean Drilling Program Leg 174AX provided a record of 11- 14 Upper Cretaceous sequences in the New Jersey Coastal Plain that were dated by in- tegrating Sr isotopic stratigraphy and biostratigraphy. Backstripping yielded a Late Cre- taceous eustatic estimate for these sequences, taking into account sediment loading, com- paction, paleowater depth, and basin subsidence. We show that Late Cretaceous sea-level changes were large (.25 m) and rapid (K1 m.y.), suggesting a glacioeustatic control. Three large d 18 O increases are linked to sequence boundaries (others lack sufficient d 18 O data), consistent with a glacioeustatic cause and with the development of small (,10 6 km 3 ) ephemeral ice sheets in Antarctica. Our sequence boundaries correlate with sea-level falls recorded by Exxon Production Research and sections from northwest Europe and Russia, indicating a global cause, although the Exxon record differs from backstripped estimates in amplitude and shape.

Links between climate and sea levels for the past three million years.

The oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on Earth -- the ice sheets and the oceans. Since the latest of these oscillations, the Last Glacial Maximum (between about 30,000 and 19,000 years ago), approximately 50 million cubic kilometres of ice has melted from the land-based ice sheets, raising global sea level by approximately 130 metres. Such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere, oceans, ice sheets and solid earth, all of which have different response timescales. The trigger for the sea-level fluctuations most probably lies with changes in insolation, caused by astronomical forcing, but internal feedback cycles complicate the simple model of causes and effects.

Small-scale stratigraphy in a large ramp delta: recent and Holocene sedimentation in the Volga delta, Caspian Sea

The Volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient (∼5 cm/km) and by being affected by the rapid sea-level changes of the Caspian Sea, at rates up to a hundred times the global sea-level rise. This paper reports (1) the morphological and facies development of part of the lower delta during the last full sea-level cycle between 1929 and 1995, as monitored using remote sensing and field mapping, and (2) the Holocene development of the delta from outcrop data and augered transects. During a sea-level fall of 3 m between 1929 and 1977, rapid progradation of levees, composed of fine sand, took place along over 800 distributary channels along the delta front. Smaller distributaries became filled with clay and organics. During the 3-m sea-level rise from 1977 to 1995, aggradation occurred, leading to deposition of silt and clay on the levees and minor filling of the flood basins. Sedimentation rates as established with 137Cs dating are up to 2–5 cm/year. Total thickness of Holocene deposits in the lower delta plain is 4–10 m. A coarsening-upwards sequence in the Damchik sandpit shows freshening-upwards mollusc assemblages dated around 1000 BP, and has been attributed to the Derbent regression at that time. Four transects with a total of 79 augerings down to 7 m depth show rapid lateral facies changes of: (a) lagoonal clays deposited in the palaeo relief between the dunes, (b) channel sands, (c) levee sands and silts, (d) laminated overbank and interdistributary bay deposits, (e) mouthbar deposits and (f) prodelta clays. Holocene depositional patterns are unrelated to the present drainage network, though the spatial variability is similar to that of the present highly segmented network. Seven 14C datings give a range of 6000–800 BP, and several phases of progradation seem to be present, but the lateral variability is too large and the age data too limited to make a solid correlation with known Holocene sea-level fluctuations. The Volga delta differs essentially from the classic river-dominated Mississippi delta because the offshore gradient is so gentle that no marine reworking takes place at the outlets, and the friction-controlled bifurcation continues basinward until a very fine maze of distributary outlets is produced. The Volga Holocene sequences more resemble those of the Atchafalaya and Saskatchewan lacustrine deltas. However, they differ from them in not being subsystems of a larger delta but the main depositional facies of the delta as a whole. Moreover, the recent Volga delta development shows that progradation is related to forced regression, not to avulsion triggered by base-level rise and/or subsidence. Thus, the Volga delta provides an excellent example of the impact of high-frequency sea-level changes on a ramp margin-type fluvio-deltaic system.

Modeling the development of marine terraces on tectonically mobile rock coasts

A mathematical model was used to study the effect of glacially induced fluctuations in sea level on the formation of wave-cut terraces on tectonically mobile rock coasts. Two deep water wave sets were used to calculate breaker height and depth, which, along with surf zone width, bottom roughness, and the gradient of the submarine slope, dictated the force exerted at the shoreline. An erosional force threshold was employed to represent the variable strength of the rocks. The model also considered tidal range, the time that the water level spent at each intertidal elevation, and the protective effect of debris accumulation at the cliff foot. Three hundred runs were made with constant sea level and with different rates of rising and falling relative sea level. Rates of erosion increased with the rate of rising and falling sea level, but eventually decreased in some runs with very rapid changes in relative sea level. Fifty-five longer runs were also made with a Quaternary sea level model that consisted of 26 glacial cycles representing the period from 2 million to 0.9 million years ago, and nine cycles, of approximately twice the amplitude and wavelength, in the last 0.9 million years. These runs were made on a landmass experiencing slow (0.11 mm yr −1) or fast (0.74 mm yr −1) positive or negative changes in the elevation of the land. It was found that on rising landmasses, erosional coastal terraces are formed during interglacial stages, and on subsiding landmasses during glacial stages. The number of terraces increased with the rate of uplift and subsidence, and with the slope of the hinterland. Terrace gradient increased with tidal range, and decreased with rock resistance. The was an inverse relationship between terrace width and the strength of the rock.

Rapid sea-level change and coastal evolution on the Pacific margin of Canada

Abstract A rapid regression occurred off the northern Pacific margin of Canada approximately between 14,600 and 12,500 14C years B.P., contemporary with the deglaciation of the continental shelf, primarily due to the rapid isostatic rebound. Sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12,400 14C years B.P., after which a rapid transgression occurred. At 12,500 14C years B.P., the shelf tilt across the northern Pacific margin of Canada ranged between 50 m of submergence at Prince Rupert on the British Columbia mainland to greater than 150 m of emergence on the western edge of the Queen Charlotte Islands. This regressive/transgressive cycle lasted only from 5200 to 5500 14C years, a result of the development and collapse of a glacioisostatic forebulge. Sediment supply, wave action and tidal-current energy are the primary factors that controlled the coastal response to these late Quaternary relative sea-level changes. Plate tectonics, on the other hand, played a secondary role in coastal evolution. During deglacial regression, extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break. During the transgression of the shelf, the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits, resulting in the formation of drowned wave-cut terraces, spit platforms and modification of estuarine environments, as the sea level rose in steps. The present unconsolidated coastline is mostly erosional. During the most recent ENSO event, the sea-level rise of up to 0.4 m resulted in as much as 12 m of coastal retreat.

Rapid sea level and climate change at the close of the Last Interglaciation (MIS 5e): evidence from the Bahama Islands

The geology of the Last Interglaciation (sensu stricto, marine isotope substage (MIS) 5e) in the Bahamas records the nature of sea level and climate change. After a period of quasi-stability for most of the interglaciation, during which reefs grew to +2.5 m, sea level rose rapidly at the end of the period, incising notches in older limestone. After brief stillstands at +6 and perhaps +8.5 m, sea level fell with apparent speed to the MIS 5d lowstand and much cooler climatic conditions. It was during this regression from the MIS 5e highstand that the North Atlantic suffered an oceanographic “reorganization” about 118±3 ka ago. During this same interval, massive dune-building greatly enlarged the Bahama Islands. Giant waves reshaped exposed lowlands into chevron-shaped beach ridges, ran up on older coastal ridges, and also broke off and threw megaboulders onto and over 20 m-high cliffs. The oolitic rocks recording these features yield concordant whole-rock amino acid ratios across the archipelago. Whether or not the Last Interglaciation serves as an appropriate analog for our “greenhouse” world, it nonetheless reveals the intricate details of climatic transitions between warm interglaciations and near glacial conditions.

Tidal changes in the Yellow/East China Sea caused by the rapid sea-level rise during the Holocene

Two-dimensional numerical simulations of M2 and K1 tides were performed in order to assess the effect of the rapid sea level change occurring during the last 20000 years in the Yellow/East China Sea (YECS). Results were interpreted by utilizing the difference of the dynamical nature inherited in diurnal and semi-diurnal tides. M2 tides at the coastal region south of Korea exceeded 2 m in amplitude when the sea-level was low, and decreased as the water depth become larger. In the Yellow Sea, on the other hand, tidal amplitudes were small at the low sea-level stages and increased along with the sea-level rise. The way of the increase was not monotonic but with fluctuations, which was due to the movement of the standing wave nodes. An additional experiment with closing the Taiwan Strait revealed that changing the sill depth of the strait not only affects the M2 tides around the southeastern Chinese coast, but also modifies the tides around the southwestern coast of Korea. This result recall us the significance of morphological condition on estimating the tidal field in the coastal ocean.

Sea‐level change and true polar wander during the Late Cretaceous

We demonstrate that rapid changes in the Earth's rotation vector can drive relative sea‐level (RSL) variations in excess of 100 m in as little as 1 m.y. Stratigraphic constraints on sea‐level change can thus be used as an independent test of true polar wander (TPW) events proposed on the basis of paleomagnetic evidence. Recent estimates of Late Cretaceous TPW include a period of rapid motion, however a corresponding period of large and rapid sea‐level change is not consistently evident in our preliminary examination of the geological record. This suggests that the magnitude of Late Cretaceous TPW may have been overestimated, although a definitive conclusion requires a comprehensive study of high‐resolution Late Cretaceous sea‐level records. (Index Terms: 1239, 1527, 4556, 8159).

Signature of hydrodynamic activity caused by rapid sea level changes in pelagic organic-rich sediments, Tarfaya basin (southern Morocco)

Abundant beds with calcareous tempestites, hummocky cross-stratifications ‘HCS’, bioclastic limestones ‘BL’ and limestone channels ‘LCh’ occur in the Late Cretaceous sequence (Middle-Late Cenomanian / Early Turonian) of the Tarfaya basin (SW Morocco) with a strongly erosive base. Results of the study have significant implications for sea level fluctuations in fine-grained basinal facies. According to the palaeoenvironmental reconstructions, the strata were deposited in the offshore area dominated by an upwelling system. The regular distribution of the ‘BL’, ‘HCS’ and ‘LCh’ throughout the section provides a constraint on palaeobathymetry. The water depth during deposition fluctuated frequently and ranged from below, but near, storm wave base.

Modern cool-water carbonates on a coastal platform of Northern Brittany, France: Carbonate production in macrophytic systems and sedimentary dynamics of bioclastic facies

The surficial sediments of the Baie de Morlaix, a large embayment at the rocky coast of northern Brittany (48°N), are predominantly composed of bioclastic carbonates. Several different macrophytic communities are the most prominent systems producing skeletal carbonate deposits within the euphotic zone of this shallow water environment. The distribution of these communities is controlled by the strength of the hydrodynamic energy. In the more exposed outer section of the bay, affected by episodically strong storm-wave impact, the rocky seabottom is densely colonized by extended kelp forests ofLaminaria hyperborea, L. digitata andSaccorhiza polyschides. The flexible thalli of the pseudoperennial phaeophytes contain numerous highly differentiated microhabitats, occupied by several carbonate-secreting organisms. Detachment and fragmentation of the epiphytic community generates coarse biogenic debris, mainly of balanids, bryozoans, serpulids and echinoids. In the sheltered parts of the numerous rocky shoals and small islands, which create a morphologically complex coastal platform, autochthonous coralline algal maerl-banks are developed. The biostromal framework of the maerl-banks is constructed by the small branched thalli of the coralline algaeLithothamnium corallioides andPhymatolithon calcareum. Depending on location and energy regime several characteristic parautochthonous to allochthonous subfacies can be recognized. Generally they are found in the deeper parts of the coastal platform whereas the autochthonous maerl-banks are restricted to the shallow (<8 m) environment. In contrast to the large, fast growing fronds of the kelp, annual growth rates of coralline algae are conspicuously low. The growth of the rhodoliths is predominantly controlled by extreme seasonal fluctuations of the environmental parameters, including water temperature, light and nutrient supply. The seasonality of growth is well documented by the alternating bright and dark bands inside the branches, corresponding also to alternating Mg-uptake into the skeletal calcite. To maintain metabolism and growth throughout the unfavorable photosynthesis periods in winter, the coralline algae utilize stored carbon resources which were produced during summer. The slow-growing coralline algae resist overgrowth and microfouling by attracting specific herbivores that graze upon the surface of the rhodolith branches. In addition to the macrophytic production centers of the coastal platform and their related sediments, fine grained bioclastic carbonates cover extended areas in the outer section of the bay. Most of the detrital material derives from the inner shelf where a benthic community, dominated by articulate bryozoans, colonize the gravely seafloor. Here in the aphotic zone, the carbonate production of the BRYOMOL-Facies is mainly controlled by phytoplankton production. Rapid sea-level changes during the late Pleistocene to Holocene have strongly influenced coastal morphology and the establishment of different carbonate production centers.

The geoarchaeological record of Holocene sea level change and human occupation of the Texas gulf coast

Geoarchaeological data from the central Texas coast suggest fundamental linkages between patterns of Holocene sea level change, evolution of estuarine environments, and human occupation. Three major periods of human occupation of estuary shorelines are identified, based on a series of calibrated radiocarbon ages from 47 stratigraphically discrete cultural components at 23 sites. These periods are separated by apparent hiatuses in occupation, intervals for which there is no chronometric or stratigraphic evidence of significant shoreline residence or of use of estuarine resources. Periods of occupation approximate times of sea level stillstand suggested by geologic data, while intervening periods correlate with proposed episodes of rapid sea level rise. During stillstand, the emergence of highly photosynthetic bay/lagoon shallows supporting nutrient-rich shoreline vegetation provided the basis for a rich, exploitable aquatic biomass. Rapid sea level change is likely to have adversely affected estuarine productivity through inundation of nutrient-rich shallows and through increases in salinity and water turbidity as protective barrier islands were breached by marine transgression. Geoarcheological study of estuarine environments under changing sea level conditions provides a long-term perspective on ecosystemic change relevant to concerns about the expectable effects of global change on the fragile biotic and economic productivity of shallow-water coastlines. ©1997 John Wiley & Sons, Inc.

The geoarchaeological record of Holocene sea level change and human occupation of the Texas gulf coast

Geoarchaeological data from the central Texas coast suggest fundamental linkages between patterns of Holocene sea level change, evolution of estuarine environments, and human occupation. Three major periods of human occupation of estuary shorelines are identified, based on a series of calibrated radiocarbon ages from 47 stratigraphically discrete cultural components at 23 sites. These periods are separated by apparent hiatuses in occupation, intervals for which there is no chronometric or stratigraphic evidence of significant shoreline residence or of use of estuarine resources. Periods of occupation approximate times of sea level stillstand suggested by geologic data, while intervening periods correlate with proposed episodes of rapid sea level rise. During stillstand, the emergence of highly photosynthetic bay/lagoon shallows supporting nutrient-rich shoreline vegetation provided the basis for a rich, exploitable aquatic biomass. Rapid sea level change is likely to have adversely affected estuarine productivity through inundation of nutrient-rich shallows and through increases in salinity and water turbidity as protective barrier islands were breached by marine transgression. Geoarcheological study of estuarine environments under changing sea level conditions provides a long-term perspective on ecosystemic change relevant to concerns about the expectable effects of global change on the fragile biotic and economic productivity of shallow-water coastlines. ©1997 John Wiley & Sons, Inc.

High-Resolution carbon isotope stratigraphy of the basal Silurian Stratotype (Dob's Linn, Scotland) and its global correlation

Since its designation as the Global Stratotype Section and Point (GSSP) for the base of the Silurian System, the choice of Dob's Linn, Southern Scotland, has received criticism due to the difficulties of relating its well-constrained graptolite biostratigraphy to shallow-water sequences elsewhere. Kerogen samples from across the Ordovician-Silurian boundary interval at Dob's Linn have yielded carbon stable-isotope signatures consistent with those recorded elsewhere, in particular showing a clear positive δ 13 C excursion in the terminal Ordovician. The architecture of the δ 13 C curve from Dob's Linn enables very high-resolution stratigraphic subdivision and direct correlation between the deep water Dob's Linn section and time-equivalent carbonate shelf deposits. An integrated stratigraphic scheme using isotope stratigraphy and biostratigraphy of graptolites, conodonts and shelly faunas has been constructed. This direct correlation shows that the shallow water successions, including the former stratotype candidate at Anticosti Island, are generally incomplete, with hiatuses related to the rapid sea-level changes during the Hirnantian stage. This confirms and greatly increases the global utility of Dob's Linn as a boundary stratotype.

Rapid sea-level changes at the close of the last interglacial (substage 5e) recorded in Bahamian island geology: Comments and Reply

Research Article| June 01, 1997 Rapid sea-level changes at the close of the last interglacial (substage 5e) recorded in Bahamian island geology: Comments and Reply James L. Carew; James L. Carew 1Department of Geology, University of Charleston, Charleston, South Carolina 29424 Search for other works by this author on: GSW Google Scholar John E. Mylroie; John E. Mylroie 2Department of Geosciences, Mississippi State University, Mississippi State, Mississippi 39762 Search for other works by this author on: GSW Google Scholar Paul J. Hearty; Paul J. Hearty 3Chertsey 112, P.O. Box N-337, Nassau, Bahamas Search for other works by this author on: GSW Google Scholar A. Conrad Neumann A. Conrad Neumann 4Marine Sciences Curriculum, University of North Carolina, Chapel Hill, North Carolina 27599-3300 Search for other works by this author on: GSW Google Scholar Author and Article Information James L. Carew 1Department of Geology, University of Charleston, Charleston, South Carolina 29424 John E. Mylroie 2Department of Geosciences, Mississippi State University, Mississippi State, Mississippi 39762 Paul J. Hearty 3Chertsey 112, P.O. Box N-337, Nassau, Bahamas A. Conrad Neumann 4Marine Sciences Curriculum, University of North Carolina, Chapel Hill, North Carolina 27599-3300 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1997) 25 (6): 572–575. https://doi.org/10.1130/0091-7613(1997)025<0572:RSLCAT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation James L. Carew, John E. Mylroie, Paul J. Hearty, A. Conrad Neumann; Rapid sea-level changes at the close of the last interglacial (substage 5e) recorded in Bahamian island geology: Comments and Reply. Geology 1997;; 25 (6): 572–575. doi: https://doi.org/10.1130/0091-7613(1997)025<0572:RSLCAT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Rapid sea-level changes at the close of the last interglacial (substage 5e) recorded in Bahamian island geology: Comment and Reply

Rapid sea-level changes at the close of the last interglacial (substage 5e) recorded in Bahamian island geology: Comment and Reply

Evidence for Glacial Control of Rapid Sea Level Changes in the Early Cretaceous

Lower Cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves. Strontium data from an interval spanning 7 million years in the Berriasian-Valanginian imply that global sea level fluctuated about 50 meters over time scales of 200,000 to 500,000 years, which is in agreement with the Exxon sea level curve. Oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes. If glaciation caused all the rapid sea level changes in the Cretaceous that are indicated by the Exxon curve, then an Antarctic ice sheet may have existed despite overall climatic warmth.

The Albian-Cenomanian boundary in northern California

There is no internationally agreed-upon stratotype for the Albian-Cenomanian (Lower Cretaceous–Upper Cretaceous) boundary. Type sections in France for the Albian and Cenomanian Stages are inadequate for this purpose. The proposed boundary stratotype sections in North Africa and Texas that were discussed in Copenhagen at the 1983 Third International Symposium on the Cretaceous System (Birkelund et al., 1984) are inadequately documented, facies restricted, or both. The widespread occurrence of the ammonites Stoliczkaia and Mortoniceras in the upper Albian and of Mantelliceras in the Cenomanian classically bracket the boundary and must be used until the boundary is formally defined. Recent work in North Africa (Robaszynski et al., 1993) promises an Albian-Cenomanian boundary definition based on lineages within these taxa. The ammonite-based Albian-Cenomanian boundary in northern California is between the last occurrence of the typically Albian genera Mortoniceras and Stoliczkaia and the entry of mantelliceratine juveniles (probably Graysonites) associated with Mariella. Pseudouhligella japonicum , heretofore regarded as a Cenomanian indicator in Japan, Alaska, and California, occurs in California in upper Albian and lower Cenomanian faunas. The boundary sequence in California is best exposed along Dry Creek in northern Tehama County, where an angular relationship within the Budden Canyon Formation, resulting from channel cutting on deep-sea fans, separates upper Albian ammonite-bearing rocks of the Chickabally Member from Lower Cenomanian ammonite-bearing rocks of the Bald Hills Member. Although angular relationships and coarse-grained strata of the lower Bald Hills Member are present in the boundary interval, no known ammonite zone is missing. These relationships are interpreted to mean that relatively continuous sedimentation occurred during the Albian–Cenomanian transition and reflect rapid uplift and erosion of a sedimentary, volcanic, and plutonic terrane to the north and east and, perhaps, accompanied by rapid sea-level changes. Collation of the ammonite biostratigraphy herein with previously established foraminiferal and radiolarian biostratigraphies for the Dry Creek sequence suggests that it is a prime Pacific-rim reference section for faunas in the Albian-Cenomanian boundary interval and that previous correlation of the uppermost Chickabally Member with the Cenomanian is incorrect, as Albian and Cenomanian stages are currently understood. This affects correlation and changes the dating of some units in California in the Franciscan Complex from Cenomanian to Albian.