Eustatic Sea-level High-stand Research Articles

Global evolution and paleogeographic distribution of mid-Cretaceous orbitolinids.

Members of the Larger Benthic Foraminiferal (LBF) family Orbitolinidae occurred from the Cretaceous to the Paleogene, however, they were most diverse during the mid-Cretaceous, and dominated the agglutinated LBF assemblages described from limestones of that period. Various orbitolinid species have been used to zone and date lithologies formed in the shallow, warm waters of the Aptian to the early Cenomanian, and many, sometimes inaccurate, generic and sub-generic nomenclatures have been proposed to differentiate the often-subtle morphological changes that orbitolinids exhibit over time. Also, until now, it has not been possible to develop an effective global overview of their evolution and environmental development because descriptions of specimens from Asia have been relatively rare. Following our recent study of over 1800 orbitolinid-rich thin sections of material from 13 outcrops of Langshan limestone, from the Southern Tibetan Plateau, and from the Barito Basin, South Kalimantan, Indonesia, it has been possible to compare the stratigraphic ranges of these orbitolinids with previously described Tethyan and American forms, based on the use of a planktonic zonal (PZ) scheme, itself tied to the most recent chronostratigraphic scale. This has allowed the reconstruction of the phylogenetic and paleogeographic evolution of the orbitolinids from their Valanginian origin in the Tethys. Although the Tethys remained the paleogeographic centre for the orbitolinids, it is inferred here for the first time that a bi-directional paleogeographic migration of some orbitolinid genera occurred from the Tethys to the Americas and also to the Western Pacific region. Our observations and dating suggest that global marine regressions in the Aptian were coincident with, and may well have facilitated, these orbitolinid transoceanic migrations. Migration stopped however after rising sea level in the early Albian appears to have again isolated these provinces from each other. Tectonic forces associated with the subduction of the Farallon Plate and further sea level raises led to the opening of the Western Interior Seaway in North America, which correlates with, and may have been the cause of, the middle Albian (top of PZ Albian 2) extinction of the American orbitolinids. The extinction of the orbitolinids revealed that the Western Pacific province was split into two sub-provinces, with extinction occurring at the end of the early Albian (top of PZ Albian 1) in the Northwest Pacific sub-province, and at the end of the Albian (top of PZ Albian 4) in the subprovince that is today South East Asia (on the margins and west of the Wallace Line). The final near extinction of the orbitolinids occurred at the end of the Cenomanian in the Tethyan province, which coincides with, and may have been caused by, global anoxic oceanic events that correlate with a near-peak Mesozoic eustatic sea level high-stand that led to the overall global collapse of the paleotropical reef ecosystem at that time.

Palynomorph evidence for tropical climate stability in the Gulf of Papua, Papua New Guinea, over the latest marine transgression and highstand (14,500 years BP to today)

Three sediment cores (MV-41, MV-46, and MD-50) from the Gulf of Papua (GoP), Papua New Guinea, were analyzed to assess changes in climatic, oceanographic, and sedimentological conditions over the last 14.5 kyr. Palynomorphs, which were isolated from sediment core samples, were collected at approximately 0.5-m intervals using a strong acid and oxidant (MD-50)/non-oxidant (MV-41, MV-46) procedure. Radiocarbon (14C) stable isotope geochronology, magnetic susceptibility, stable isotope analysis (MD-50 only; Oxygen-18 [18O] and Carbon-13 [13C]), and clay mineral maturity analysis were also completed for each core. Palynological data indicate that climatic conditions at sea level have remained warm, wet, and stable for the past 14.5 kyr with sea surface temperatures in the GoP above 14 °C. Potential decreases in vegetative cover marked the Younger Dryas interval (12.5–11.5 kyr BP), as indicated by reduced pollen and spore recovery. The end of the latest marine transgression (and the subsequent return to eustatic sea level highstand) is clearly delineated by increases in marine palynomorph recovery and decreases in mangrove pollen at approximately 5 kyr BP. An increase in seasonality and potential El Niño Southern Oscillation variability is observed in MD-50's oxygen isotope results at ∼5 kyr BP. This is not supported by the palynomorph record, likely because of the sampling interval and dilution by tropical pollen flora, which indicates stable climatic conditions throughout the last 14.5 kyr. Sediment transport pathways in the GoP remained fairly constant throughout the time interval, which is supported by the lack of major changes in palynomorph assemblage composition.

The Tethyan oyster Pycnodonte (Costeina) costei (Coquand, 1869) in the Coniacian (Upper Cretaceous) of the Iberian Basin (Spain): Taxonomic, palaeoecological and palaeobiogeographical implications

Abstract Oysters were among the most important groups of marine invertebrates in Late Cretaceous biotas of the Tethyan Realm. During the major eustatic sea-level highstands of this interval, large areas of northern Africa and southern Europe were characterized by carbonate shelf environments with conditions favourable for the widespread dispersal of highly diverse marine ecosystems, which included many ostreid bivalves. In this palaeoecological setting, Pycnodonte (Costeina) costei (Coquand, 1869) is one of the most widespread representatives of the subfamily Pycnodonteinae, extending from Central Asia and Egypt to southern France and the Iberian Peninsula. This taxon is characterised by a strong convex left valve with an expanded posterior flange, suggesting that this species was a free-lying recliner on infralittoral soft substrates. The species is also remarkable due to its morphological plasticity, with ecophenotypes characterised by extremely variable left valve ornamentation. The assemblages of P. (C.) costei studied herein occur in middle to upper Coniacian outer-shelf facies within the northern and central sectors of the Iberian Basin (Spain), associated with transgressive and highstand system tracts. The species occurs mostly in autochthonous concentrations of several tens of individuals, cemented or oriented side by side and colonised by epizoans and borers. Endolithic sponges related to the ichnogenus Entobia were especially abundant, infesting many specimens to a great extent. These new finds in the Iberian Basin also improve the known palaeogeographic range of P. (C.) costei. Its distribution can be related to current circulation along the Tethys Ocean, firstly from its original area in Central Asia to North African shelves and then to the Iberian Basin and France, across the proto-Atlantic Lusitanian area. This dispersal model inferred by these currents also explains much of the Tethyan affinities found in the Late Cretaceous marine faunas of Iberia.

Latest Campanian and Maastrichtian palaeoenvironmental changes: Implications from an epicontinental sea (SE Poland and western Ukraine)

The Maastrichtian was a time of a high variability in the climate/ocean system. Most studies on Maastrichtian palaeoenvironment fluxes have been based on evidence from the open ocean realm or from outcrops in the Tethyan realm. We have investigated epicontinental carbonate-rich sediments of Maastrichtian age of the Lublin-Lviv Syncline (SE Poland and western Ukraine). Our study is focused on the population changes of planktonic foraminifers from 21 Maastrichtian outcrop successions and one borehole section. Quantitative and qualitative studies of planktonic foraminifers show long-term foraminiferal changes that make it possible to reconstruct climatic changes and a sea-level curve for the latest Campanian and Maastrichtian from the high-latitude epicontinental sea. A significant regression is inferred for the latest Campanian and earliest Maastrichtian. The highest sea level is noted in the earliest Late Maastrichtian. It coincides with a migration of the benthic and planktonic foraminiferal fauna that was probably triggered by a cooling episode. The cooler episodes correlated with a eustatic sea-level highstand during that time, suggesting that sea level was the most likely mechanism causing a change of global circulation; this temperature drop could be the cause of the mid-Maastrichtian event.

Coastal response to climate change: Mediterranean shorelines during the Last Interglacial (MIS 5)

The response of shorelines to climate change is controlled by fall and rise of the sea level and by the alteration of the coastal environment due to changing fluvial discharge and biological activity. In the Mediterranean this response is complicated by the geographic proximity of the North Atlantic and the African Monsoon climate systems, by a time and space specific interaction of eustatic and water-load components of sea level and by the mid-latitudinal time lag between orbital forcing and terrestrial response. Here, six Mediterranean coastal records are presented which contribute to our understanding of how mid-latitudinal coasts respond to orbital forcing. The sediment sequences show sharp switches between siliciclastic- and carbonate-dominated nearshore environments where carbonate-rich sediments are composed of oolitic grainstones. From modern analogues it is deduced that the oolitic sediments represent a period of relatively high annual sea-surface temperature and lack of fluvial discharge. The warm-arid period was recorded at ∼114 ka on the southeast Iberian coast, at ∼113 ka on the Levant coast, at ∼110 ka on the coast west of the Nile delta and at ∼83 ka on the north Saharan coast. It lasted 10–20 ka in east (Levant coast) and west (Iberian coast) and lasted 40 ka or more in the central-south of the east Mediterranean. Timing and duration of the coastal proxy allow inferring instantaneous and dominant response to external forcing in the east and west and delayed and prolonged response due to dominant regional forcing in the centre of the East Mediterranean. A 9 m eustatic sea-level highstand during MIS 5e is suggested with a start of the subsequent sea-level fall at ∼118 ka while evidence for multiple MIS 5e highstand and a highstand during MIS 5a remain elusive.

A tidal depositional model for the Carolina sand (Pliocene, Talparo Formation) of central Trinidad

A BSTRACT. — The Pliocene geological history of Trinidad’s Northern Basin is little known. The need for such knowledge is pressing; some rock units cropping out there yield hydrocarbons offshore in the Gulf of Paria, but the environments in which they were deposited have yet to be deciphered. As a first step towards unravelling this geohistory, this study examines the sedimentology of the Carolina sand, a small and informal member of the Pliocene Talparo Formation. From plan view the lenticular Carolina sand is concluded to comprise a tidal sand ridge that built up almost to sea level. This interpretation is supported by abundant sedimentary structures indicative of tidal influence (herringbone cross-bedding, mud couplets, clay drapes). Drape and ripple orientations show northward transport that is concluded to be indicative of ebb tide currents. For most of the succession, sediments alternate between two lithofacies (tabular cross-bedded sands with clay drapes, and interlaminated sands and silts). Comparison with tidal flats suggests these lithofacies indicate rapid cycling between different water depths. The depth changes are suggested to be related to outflow from the paleo-Orinoco River, which, like the present day Orinoco, is suggested to have raised sea levels around Trinidad during the annual rainy season. The cross-bedded sands were deposited as deeper-water megaripples on the tidal ridge surface during the rainy season, the interlaminated sands and silts under intertidal conditions when sea levels fell during the dry season. The Carolina sand was probably deposited during one of the eustatic sea level highstands hitherto noted farther east, in the offshore Columbus Basin. K EYWORDS. — tidal sand ridge , Orinoco , clay drapes , herringbone cross-bedding , mud couplets

Foraminifera in elevated Bermudian caves provide further evidence for +21 m eustatic sea level during Marine Isotope Stage 11

Two hypotheses have been proposed to explain the origin of marine isotope stage (MIS) 11 deposits in small Bermudian caves at +21m above modern sea level: (1) a +21m MIS 11 eustatic sea-level highstand, and (2) a MIS 11 mega-tsunami event. Importantly, the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments. After statistically comparing foraminifera in modern Bermudian littoral caves and the MIS 11 Calonectris Pocket A (+21m cave) to the largest available database of Bermudian coastal foraminifera, the assemblages found in modern littoral caves – and Calonectris Pocket A – cannot be statistically differentiated from lagoons. This observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone, where typical coastal processes (waves, storms) homogenize and rework lagoonal, reefal, and occasional planktic taxa. Fossil protoconchs of the Bermudian cave stygobite Caecum caverna were also associated with the foraminifera. These results indicate that the MIS 11 Bermudian caves are fossil littoral caves (breached flank margin caves), where the total MIS 11 microfossil assemblage is preserving a signature of coeval sea level at +21m. Brackish foraminifera (Polysaccammina, Pseudothurammina) and anchialine gastropods (∼95%, >300 individuals) indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase. The onset of sea-level regression following the +21m highstand would first lower the ancient brackish Ghyben-Herzberg lens (<0.5m) and flood the cave with brackish water, followed by drainage of the cave to create a permanent vadose environment. These interpretations of the MIS 11 microfossils (considering both taphonomy and paleoecology) are congruent with the micropaleontological, hydrogeological and physical mechanisms influencing modern Bermudian coastal cave environments. In conclusion, we reject the mega-tsunami hypothesis, concur with the +21m MIS 11 eustatic sea-level hypothesis, and reiterate the need to resolve the disparity between global marine isotopic records and the physical geologic evidence for sea level during MIS 11.

Reply to “Mega-highstand or megatsunami? Discussion of McMurtry et al. “Elevated marine deposits in Bermuda record a late Quaternary megatsunami”: Sed. Geol. 200 (2007) 155–165” by Paul J. Hearty and Storrs L. Olson

Our recent paper [McMurtry, G.M., Tappin, D.R., Sedwick, P.N., Wilkinson, I., Fietzke, J. and Sellwood, B., 2007a. Elevated marine deposits in Bermuda record a late Quaternary megatsunami. Sedimentary Geol. 200, 155–165.] critically re-examined elevated marine deposits in Bermuda, and concluded that their geological setting, sedimentary relations, micropetrography and microfaunal assemblages were inconsistent with sustained intertidal deposition. Instead, we hypothesized that these deposits were the result of a large tsunami that impacted the Bermuda island platform during the mid-Pleistocene. Hearty and Olson [Hearty, P.J., and Olson, S.L., in press. Mega-highstand or megatsunami? Discussion of McMurtry et al. “Elevated marine deposits in Bermuda record a late Quaternary megatsunami”: Sedimentary Geology, 200, 155–165, 2007 (Aug. 07). Sedimentary Geol. 200, 155–165.] in their response, attempt to refute our conclusions and claim the deposits to be the result of a +21 m eustatic sea level highstand during marine isotope stage (MIS) 11. In our reply we answer the issues raised by Hearty and Olson [Hearty, P.J., and Olson, S.L., in press. Mega-highstand or megatsunami? Discussion of McMurtry et al. “Elevated marine deposits in Bermuda record a late Quaternary megatsunami”: Sedimentary Geology, 200, 155–165, 2007 (Aug. 07). Sedimentary Geol. 200, 155–165.] and conclude that the Bermuda deposits do not provide unequivocal evidence of a prolonged + 21 m eustatic sea level highstand. Rather, the sediments are more likely the result of a past megatsunami in the North Atlantic basin.

Sea-level highstands over the last 500,000 years; evidence from the Ironshore Formation on Grand Cayman, British West Indies

ABSTRACT The Ironshore Formation (up to 19 m thick) in the Rogers Wreck Point area of Grand Cayman is divided into the unconformity-bounded units A, B, C, and D. The unconformities are highlighted by caliches and/or terra rossa. Th/U dates from aragonitic corals indicate that unit A formed at > 400 ka, unit B 346 ka, unit C 229 ka, and unit D 131 ka. These ages correlate with the highstands of the last four interglacial periods and probably represent marine isotope stages 5 (unit D), 7 (unit C), 9 (unit B), and 11 (unit A). The limestones in units A-D, which have similar biotic and lithologic characteristics, represent deposition in shallow water on a narrow coastal shelf. Unit A has a high faunal diversity and was deposited in open-marine conditions, whereas units B, C, and D were deposited in quieter-water lagoons that probably had fringing reefs along their sea-ward edges. Although Grand Cayman is located on the Cayman Ridge close to an active spreading center and transform fault, the island has undergone little or no vertical movement over the last 500 ky. Available evidence indicates that sea level at the time of deposition of each unit relative to present sea level was: unit A, -9.0 to -5.5 m; unit B, -3.0 to +0.5 m; unit C, -2.5 to +1.1 m; and unit D, +2.5 to +6.0 m. These data are good estimates of eustatic sea-level highstands over the last 500 ky.

Interaction of tectonic and depositional processes that control the evolution of the Iberian Gulf of Cadiz margin

This study provides an integrated view of the growth patterns and factors that controlled the evolution of the Gulf of Cadiz continental margin based on studies of the tectonic, sedimentologic and oceanographic history of the area. Seven sedimentary regimes are identified, but there are more extensive descriptions of the late Cenozoic regimes because of the larger data base. The regimes of the Mesozoic passive margin include carbonate platforms, which become mixed calcareous–terrigenous deposits during the Late Cretaceous–early Tertiary. The Oligocene and Early Miocene terrigenous regimes developed, in contrast, over the active and transcurrent margins near the African–Iberian plate boundary. The top of the Gulf of Cadiz olistostrome, emplaced in the Late Miocene, is used as a key horizon to define the `post-orogenic' depositional regimes. The Late Miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the Miocene Atlantic–Mediterranean gateways. The terrigenous drift depositional regime of the Early Pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the Mediterranean outflow currents that developed after the opening of the Strait of Gibraltar. The Late Pliocene and Quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels. Deposition of shelf-margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence. During the highstand regimes of the Holocene, inner shelf prograding deltas and deep-water sediment drifts were developed under the influence of the Atlantic inflow and Mediterranean outflow currents, respectively. A modern human cultural regime began 2000 years ago with the Roman occupation of Iberia; human cultural effects on sedimentary regimes may have equalled natural factors such as climate change. Interplay of tectonic and oceanographic controls dominated the evolution of the Cadiz margin during the Cenozoic. Depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional Atlantic inflow currents on the shelf and Mediterranean outflow currents on the slope. The entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the Betic and Rif gateways, which become closed during the Late Miocene, and after the Messinian by the opening of the Strait of Gibraltar. Strong current development during eustatic sea level highstands of the Pliocene and Quaternary has controlled deposition because of maximum sill depths at Gibraltar for water circulation. Lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf. More recently, the human industrial revolution has caused heavy metal contamination of sediment and water over the Cadiz margin. Human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed. Future research efforts will need to focus on: (1) the effect of increased Mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages; (2) assessments of geologic hazards for planning man-made shoreline structures, developing offshore petroleum resources and maintaining undersea communications cables; and (3) confirmation of the general geologic history of the Cadiz margin.

Age and isotopic constraints on Pleistocene pluvial episodes in the Western Desert, Egypt

Abstract North Africa has undergone drastic climatic changes over the past several hundred thousand years. The timing of humid intervals called pluvials was investigated by uranium-series disequilibrium dating of travertines from the Kurkur Oasis, Western Desert, Egypt. The youngest and best dated travertines (70–160 ka) are found in Wadi Kurkur and include spring and lacustrine units exposed as 2 to 3 m high terraces. Travertines having an age of approximately 191–220 ka are exposed by differential erosion as linear mounds produced by spring systems over fracture zones in ancient wadis. The oldest travertines, having ages >260 ka, are extensive, cap limestone units above the oasis, and were deposited in paludal and lacustrine environments. Oxygen isotope ratios were measured for the wadi travertines (δ18O values ranging from 16.7 to 19.1‰ SMOW) and for spring mound travertines (18.5–20.5‰). Equilibrium oxygen isotope fractionation calculations indicate that the Kurkur travertines were deposited from waters having δ18O values similar to ancient Western Desert groundwaters (∼ −11‰, Sonntag et al., 1978a,b; Thorweithe, 1990; Sultan et al., 1996). The ages of the travertines correspond to times of monsoonal maxima, eustatic sea level high stands and interglacial maxima. Rainfall producing these groundwaters (and travertines) was significantly fractionated during atmospheric transport, in contrast to modern meteoric waters (−2.09‰, Joseph et al., 1992), implying a distant source for the pluvial waters. Increased precipitation, recharge of Western Desert groundwaters, and resultant travertine deposition are interpreted to be consequences of Milankovitch insolation cycle forcing, through enhanced Atlantic and Indian Ocean monsoons during interglacial time periods.

Eustasy as a test of a Cretaceous superplume hypothesis

The mantle plume model has been used to explain a variety of geological and geodynamic events. For instance, a large plume, or ‘superplume’, under the Pacific basin has been proposed to account for a number of Cretaceous events, such as a global sealevel rise, an increase in global average temperature, and a pause in the reversals of the Earth's magnetic field [1,2]. The primary evidence for this hypothesis is a model for the rate of production of ocean ridge material and ocean plateaus, with a high from about 120-80 Ma, mostly due to activity in the Pacific basin, which is claimed to have been driven by the upwelling of a large plume from the core-mantle boundary. The hypothesis requires that a large part of the primary evidence for this high productivity has disappeared by subduction. Here, we test this hypothesis by comparing the Cretaceous eustatic sealevel highstand which would result from the superplume model with generally accepted values. Our model includes estimates of eustatic sealevel change resulting from phenomena explicitly specified for the proposed plume, such as the volume of ocean crust produced and the extent of lithospheric swelling associated with the plume head, as well as other events known to affect eustatic sealevel, such as glaciation and continental collision. The estimated Cretaceous highstand resulting from all the modeled effects is 220–470 m, compared to the observed value of 120–200 m. This discrepancy indicates a probable overestimate of the rate of seafloor and plateau creation and of the size of plume that could have existed. The breakup of the Pangean supercontinent is a more viable explanation of the Cretaceous sealevel rise.

Evidence for Sediment Fan Deposition on Outer Texas Shelf During Miocene Eustatic Sea Level Highstands: ABSTRACT

Four types of data were reviewed in an attempt to clearly define the environments of deposition for reservoir sands in the Matagorda 668 field; well log curve shapes, seismic amplitude responses, micropaleontology, and thin section sedimentary petrology. All four lines of evidence support the interpretation that these lower Miocene sands were deposited as fan complexes. The sands exhibit three distinctive curve forms: coarsening upward, fining upward, and cylindrical-serrate. These represent respectively fringe settings around the perimeter of the fan where deposition from turbid flow dominates, proximal fan settings where settling from suspension is the more dominant process, and a collection of environments in medial settings intermediate between the two end members just described.