Modern Sea Level Research Articles

Geoarchaeological context of Holocene subsidence at the Ferry Berth Lapita site, Mulifanua, Upolu, Samoa

The 1973 discovery of an underwater archaeological site during dredging for a ferry landing at Mulifanua on Upolu raised important unanswered questions about the prehistory of Samoa, particularly the evolution of Holocene shorelines and relative local sea levels. A cultural horizon yielding Lapita potsherds, the only decorated Lapita assemblage yet found in Samoa and dating to ca. 2.8 ka, lies at a depth of 2.25 m below modern sea level beneath a capping of cemented paleobeachrock. With fluctuating hydro-isostatic sea level taken into account, the sherd occurrence implies subsidence of a former coastline by ca. 4 m at a mean rate of 1.4 mm/yr. Shoreline features on both Upolu and nearby Savai'i are fully compatible with bulk Holocene subsidence. We attribute the observed subsidence to downflexure of the lithosphere from volcano loading centered on the Savai'i locus of historic volcanism, and conclude that any other Lapita sites that may exist in Samoa have subsided by a comparable amount. Although the Samoan linear volcanic chain resembles other Pacific hotspot tracks where active volcano loading is confined to their southeastern ends, the most voluminous Holocene eruptions in Samoa have occurred on Savai'i at the northwestern end of the exposed island chain. Samoan volcanism has evidently been influenced by lateral flexure of the Pacific plate as it moves past the northern extension of the Tonga subduction zone, and the active volcanism is apparently controlled by a longitudinal rift, which transects both Upolu and Savai'i and is superimposed upon older volcanic edifices that may record earlier hotspot volcanism. Early archaeological sites in American Samoa display a variable record of subsidence and possible uplift apparently related to volcano loading in the Manu'a Islands and possibly to the location of Tutuila in a position to be affected by uparching of lithosphere between downflexures beneath more active volcanic islands to the east and west. Bulk subsidence of Upolu and Savai'i may be the fundamental cause of damaging coastal erosion in modern Samoa. © 1998 John Wiley & Sons, Inc.

Late quaternary regional geoarchaeology of Southeast Alaska karst: A progress report

Karst systems, sea caves, and rock shelters within the coastal temperate rain forest of Alaska's Alexander Archipelago preserve important records of regional archaeology, sea level history, glacial and climatic history, and vertebrate paleontology. Two 14C AMS dates on human bone discovered in a remote cave (49-PET-408) on Prince of Wales Island document the oldest reliably dated human in Alaska to ca. 9800 B.P. A series of 14C AMS dates from cave deposits span the past 40,000 years and provide the first evidence of Pleistocene faunas from the northwest coast of North America. Other discoveries include sea caves and marine beach deposits elevated above modern sea level, extensive solution caves, and mammalian remains of species previously undocumented within the region. Records of human activity, including cave art, artifacts, and habitation sites may provide new insights into the early human colonization of the Americas. © 1997 John Wiley & Sons, Inc.

Tyrrhenian coastal deposits from Sardinia (Italy): a petrographic record of high sea levels and shifting climate belts during the last interglacial (isotopic substage 5e)

Abstract Detailed petrographic and sedimentological analysis of Tyrrhenian coastal deposits from four sites in Sardinia provides new data about climate and sea-level changes during the early part of the last interglacial (isotopic substage 5e) and shows that facies analysis is not only useful for the identification of ancient depositional environments, but also represents a powerful tool for evaluating past climatic conditions and sea-level forcing mechanisms. Two shallowing-upward sequences (sensu Ward, W.C., Brady, M.J., 1979. Strandline sedimentation of carbonate grainstones, Upper Pleistocene, Yucatan Peninsula, Mexico. Am. Assoc. Pet. Geol. Bull. 63, 362–369), commonly separated by an erosion surface and displaying complex geometric relationships, occur above modern sea level at several locations along the shorelines of Sardinia. These sequences include upper shoreface to backshore deposits and were formed during separate sea-level highstands attributed to isotopic substage 5e. Our recent revision of these deposits indicates that each sequence presents distinctive petrographic characteristics. The older succession essentially contains mixed calcarenites, rich in quartz grains and lithic fragments, whereas the younger sediments are dominated by carbonate bioclasts such as red algae, coral and mollusk fragments. Both units apparently accumulated in a similar depositional setting, but during different climatic regimes. The petrography of the lower unit reflects a temperate-humid period characterized by increased weathering and continental erosion, whereas the composition of the upper one suggests a dryer, and possibly warmer, climate favoring active carbonate production. The disparity in petrographic composition between sequences probably records the migration of atmospheric circulation cells, i.e. a shift of climate belts, before and after the ∼128-ka insolation maximum. Our climatic data are coherent with the calculated insolation curves for isotopic substage 5e and thus support the Milankovitch hypothesis for the origin of Pleistocene climates. In contrast, our sedimentological data clearly show the occurrence of two distinctive highstands of sea level during this time period, which does not agree with the hypothesis. It follows that the relation between orbitally induced insolation variations, climate and sea level is not necessarily straightforward.

Marine terraces of Western Sakhalin Island

Biostratigraphical and sedimentological studies of deposits of terraces with heights of 2–3, 3–4, 4–6, 8–10, 12–15, 20–30, 35–40, 60–80 and 100–120 m on Western Sakhalin Island have shown that they were all marine in origin. The upper complex of terraces (Q I–Q II) formed during a period of slow tectonic uplift (< 0.1 m ka − in this area to 120 m above modern sea level. The lower complex of terraces (Q III–Q IV) may have formed in response to sea level oscillations without any influence of tectonic uplift.

Origin of beach ridges: Reply

The important difference here is whether or not sea level can change by the right amounts and on the right schedule. Curray says “no”. However, various reports in the recent literature (cited below) show that he is mistaken. Likewise his concept of uniform global change is not supported by the published data. Sea level does change, at relatively short intervals (years, decades), by amounts that are adequate to produce individual sandy beach ridges, and this change is not uniform at all places. My citation of Curray (and others) for an 18.6-year period in one sandy beach ridge plain was an inadvertent error, and I apologize for it. My caveat that we do not know that his study area — in a well-known modern deformational belt — was completely stable throughout the Holocene, is still valid. The corollary: Data obtained from such areas may not be as useful as information from other areas; therefore the presumed 18.6-yr cycle is suspect ab initio. Curray's hypothesis that beach ridges are initiated by what is basically the suggestion of de Beaumont, does not provide a suitable model, as is discussed below. Finally, Curray disregards the detailed granulometric analysis which was the basis for most of my work. This modern analysis can stand alone, if necessary, and is not affected in any significant way by warping or other small deformation. However, the present availability of records of small modern sea level changes confirms the reasonableness of the timing and magnitudes which were deduced as part of the granulometric work.

Late Quaternary history of Henderson Island, Pitcairn Group

Henderson Island is an emergent limestone island. It rises to 33.5 m above modern sea-level (MSL) from a sea-floor depth of about 3500 m and conforms to the pattern of an elevated atoll, although no field evidence was found pertaining to the pre-atoll volcanic history of the island. The emergence of this coral atoll can be explained by lithospheric flexure processes subsequent to the emplacement of the Pitcairn Island volcano, built by two phases of volcanism (estimated at 855 and 540 kyr by K-Ar dating). U-Th dates obtained from Henderson Island indicate that the majority of the presently visible fossil corals have an age between 404-225 kyr. Henderson Island first became emergent above MSL when sea level dropped subsequent to 380 kyr, as the period 440-380 is thought to have been characterized by sea level at least several metres above MSL in the Central Pacific. As a result Henderson Island would have become subaerially exposed from 380 kyr onwards. The uplift rate of Henderson Island is approximately 0.093-0.10 mm/yr indicating that flexure-induced uplift component above MSL commenced between 360-335 kyr, 500 kyr after the initial, and 190 kyr after the last phase of construction of the Pitcairn volcano. The time-lag following the loading of the Pitcairn volcano and the present continuation of uplift on Henderson support the theory that the lithosphere behaves in a visco-elastic manner. Field relations and U-Th dates indicate three main periods of reef development: (1) A prolific reef-building period (440-380 kyr [Unit 1] and 330-300 kyr [Units 2 & 3]) dominated by large, stout branching coral colonies; (2) A shorter period of reef growth (285-275 kyr [Unit 4]) dominated by well-formed large in situ coral colonies and Tridacna maxima; (3) A less prolific period of reef growth (230-215 kyr [Unit 5]) dominated by platy corals enveloping the previous lithologies below 19.6 m. The absence of dateable material from the last interglacial, oxygen isotope substage 5.5 (= 5e) at Henderson Island is in marked contrast to the Late Pleistocene reefs in the southern Cook Islands where reefs of substage 5.5 age skirt older carbonate complexes.

Late Quaternary history of Henderson Island, Pitcairn Group

Henderson Island is an emergent limestone island. It rises to 33.5 m above modern sea-level (MSL) from a sea-floor depth of about 3500 m and conforms to the pattern of an elevated jyatoll, although no field evidence was found pertaining to the pre-atoll volcanic history of the island. The emergence of this coral atoll can be explained by lithospheric flexure processes subsequent to the emplacement of the Pitcairn Island volcano, built by two phases of volcanism (estimated at 855 and 540 kyr by K-Ar dating). U-Th dates obtained from Henderson Island indicate that the majority of the presently visible fossil corals have an age between 404–225 kyr. Henderson Island first became emergent above MSL when sea level dropped subsequent to 380 kyr, as the period 440–380 is thought to have been characterized by sea level at least several metres above MSL in the Central Pacific. As a result Henderson Island would have become subaerially exposed from 380 kyr onwards. The uplift rate of Henderson Island is approximately 0.093–0.10 mm/yr indicating that flexure-induced uplift component above MSL commenced between 360–335 kyr, 500 kyr after the initial, and 190 kyr after the last phase of construction of the Pitcairn volcano. The time-lag following the loading of the Pitcairn volcano and the present continuation of uplift on Henderson support the theory that the lithosphere behaves in a visco-elastic manner. Field relations and U-Th dates indicate three main periods of reef development: (1) A prolific reef-building period (440–380 kyr[Unit 1]and 330 300 kyr[Units 2 & 3])dominated by large, stout branching coral colonies; (2) A shorter period of reef growth (285–275 kyr[Unit 4])dominated by well-formed largein situcoral colonies andTridacna maxima; (3) A less prolific period of reef growth (230–215 kyr[Unit 5])dominated by platy corals enveloping the previous lithologies below 19.6 m. The absence of dateable material from the last interglacial, oxygen isotope substage 5.5 (=5e) at Henderson Island is in marked contrast to the Late Pleistocene reefs in the southern Cook Islands where reefs of substage 5.5 age skirt older carbonate complexes.

Quaternary tectonic stability of the Bahamian archipelago: evidence from fossil coral reefs and flank margin caves

Throughout the islands of the Bahamian archipelago fossil coral reefs are found from current sea level up to a maximum elevation of +4 m. 234 U 230 Th radiometric dates obtained from in situ corals from these reefs, by both alpha-count and mass-spectrometric techniques, indicates that they were all formed during Oxygen Isotope Substage 5e (ca. 125,000 years ago). Those data are consistent with a maximum sea-level highstand of +6 m during Substage 5e, and either no vertical motion of the Bahamas, or possible isostatic subsidence of up to 2 m during the past 120,000 years. No older in situ fossil corals, or other subtidal deposits, have been found subaerially exposed anywhere in the Bahamas. That finding suggests that late Quaternary (at least the past 300,000 years) isostatic subsidence has occurred at a rate of 1–2 m per hundred thousand years, and/or no pre-5e highstands were above modern sea level. An independent corroboration of the conclusions drawn about sea level amplitude and tectonic stability of the Bahamas from the coral reef data is available from examination of abundant flank margin caves (horizontal, phreatic dissolution caves) found above modern sea level throughout the Bahamas. These horizontally extensive air-filled caves have dissolutional ceilings with elevations that are restricted to +1 to +7 m, which is consistent with formation at the margin of a thin freshwater lens elevated by a past +6 m sea-level highstand. The restricted cave elevations, and the lack of stalagmites in these caves that are older than 100,000 years, are also consistent with cave formation during Substage 5e, and possible subsequent isostatic subsidence of a few metres. The subsurface geology of the southeastern Bahamas contains a long-term record (millions of years) that has been attributed to past tectonic activity along the North American/Caribbean plate boundary. While that record suggests differential subsidence across the Bahamas in the Tertiary Period, the data from fossil coral reefs (and subtidal deposits) and flank margin caves indicate that all Bahamian banks on which there are islands have been tectonically stable, and behaving similarly, for at least the past several hundred thousand years.

Late quaternary evolution of the French Guiana continental shelf: Evidence from 3.5 kHz data

Twelve seismic profiles (3.5 kHz) accounting for more than 1850 line kilometres over a 36,000 km 2 area were examined to evaluate the seismic stratigraphic framework of the French Guiana continental shelf. The high density of seismic data favoured a high-resolution seismic stratigraphy interpretation. Acoustic reflectors in the seismic profiles were related to sedimentological properties. The various acoustic reflectors observed in the area can be attributed to: (1) a substratum S which covers the entire area, (2) a formation A, which consists of sediments deposited in channels of fluvial origin, (3) a formation B, which is composed of coral clasts, and (4) two high sea-level sedimentary prisms C and D, which correspond to a near modern sea level, and are Holocene in age. The extent of these formations is controlled by the specific morphology of the acoustic substratum, which is asymmetrical on either sides of the shore-normal line extending northeast from Kourou. The influence of Amazon discharge is controlled by this feature.

Late Cenozoic flexural deformation of the middle U.S. Atlantic passive margin

Despite the century‐long recognition of regional epeirogeny along the middle Atlantic passive margin, relatively few studies have focused on understanding postrift uplift mechanisms. Here, we demonstrate that epeirogenic uplift of the central Appalachian Piedmont and subsidence of the Salisbury Embayment represent first‐order, flexural isostatic processes driven by continental denudation and offshore deposition. Our results show that regional epeirogenic processes, present on all Atlantic‐type passive margins, are best resolved by specific stratigraphic and geomorphic relationships, rather than topography. A simple one‐dimensional geodynamic model, constrained by well‐dated Baltimore Canyon trough, Coastal Plain, and lower Susquehanna River (Piedmont) stratigraphy, simulates flexural deformation of the U.S. Atlantic margin. The model represents the passive margin lithosphere as a uniformly thick elastic plate, without horizontal compressive stresses, that deforms flexurally under the stress of strike‐averaged, vertically applied line loads. Model results illustrate a complex interaction among margin stratigraphy and geomorphology, the isostatic response to denudational and depositional processes, and the modulating influence of exogenic forces such as eustasy. The current elevation, with respect to modern sea level, of fluvial terraces and correlative Coastal Plain deposits or unconformities is successfully predicted through the synthesis of paleotopography, eustatic change, and margin flexure. Results suggest that the middle U.S. Atlantic margin landward of East Coast Magnetic Anomaly is underlain by lithosphere with an average elastic thickness of 40 km (flexural rigidity, D = 4 × 1023 N m), the margin experiences an average, long‐term denudation rate of approximately 10 m/m.y., and the Piedmont has been flexurally upwarped between 35 and 130 meters in the last 15 m.y. Long‐term isostatic continental uplift resulting from denudation and basin subsidence resulting from sediment loading are accommodated primarily by a convex‐up flexural hinge, physiographically represented by the Fall Zone. Our results elucidate an inherent danger in using topography alone to constrain late‐stage passive margin deformation mechanisms. Only through careful synthesis of field stratigraphic and geomorphic elements such as fluvial terraces, Coastal Plain deposits, and offshore stratigraphy can age control be extended from the offshore depositional setting to the erosionally dominated continent. This study demonstrates that despite a relatively subdued topography, the middle U.S. Atlantic margin experiences progressive flexural isostatic deformation similar to that proposed for high‐relief margins characterized by great escarpments. Thus margin topographic diversity remains a function of other factors, such as lithospheric composition and/or structure, supracrustal stratigraphy and structure, degree of drainage integration, drainage divide migration, and climate.

Late pleistocene sea level change in the Bahamas from mass spectrometric U-series dating of submerged speleothem

The dating of sea level events by a method independent of orbital tuning techniques and the marine foraminiferal isotopic record provides a test of both the dating of the marine record and the strength and nature of the relationship between climatic change, sea level change and Milankovitch cycles. Dating of fossil corals and submerged speleothem provides such independent information. Results of thermal ionization mass spectrometric U-series dating on layers of flowstone speleothem from Lucayan Caverns, Grand Bahama Island indicate that multiple sea level events have passed through a depth of −10 to −15 m below modern sea level during the last 300,000 years. These data are used to constrain the magnitude and timing of sea-level fluctuations during the late Pleistocene. The new sea level curve constructed from these data correlates closely with the marine isotopic record: sea level peaks occurred at around 233, 215, 125 and 100 ka BP. There is no evidence at the depth from which this speleothem was retrieved of any high sea stands at 195 or 80 ka corresponding to the foraminiferal 7a and 5a oxygen isotope peaks. There is also no evidence of a double rise around the 125 ka (5e) peak, although such an oscillation could have occurred above −10 m leaving no record in the Lucayan Caverns speleothem.

Dynamic hydrology and diagenesis of a submerged Pleistocene fringing reef, Discovery Bay, Jamaica

In the Discovery Bay area of north Jamaica, a Pleistocene fringing reef grew and was subsequently planed off as sea level rose to and fell from a highstand approximately 5 to 10 m below modern sea level between 132,000 and 147,000 yrs BP. Dynamic movement of seawater through the reef today, evidenced by flow of water in and out of open core holes, has caused precipitation of cements which overprint previous diagenetic fabrics in certain zones. In the reef-flat and distal fore-reef facies, where porosity is diffuse, modern water movement is slow and has had little effect on pre-existing diagenetic fabrics, which are dominantly vadose in texture. In facies with conduit porosity, as in the reef crest and proximal portions of the shallow fore-reef, seawater is channelized and high flow rates have resulted in the precipitation of substantial amounts of Holocene sparry high-magnesian calcite cements (15–18 mol% MgCO 3) up to 250 μm thick, resulting in incorporation of significant amounts of 14C in the Pleistocene rocks. Smaller Mg-calcite crystals, having lower magnesium content, are characteristic of zones with diffuse porosity. The dynamic marine system apparently also favors the precipitation of dolomite. In zones of diffuse porosity, water motion within the reef results in the slow movement out of the man-made conduits. In zones of conduit porosity, such as in facies having highly localized permeability, water is sucked into open core holes in accordance with Bernoulli's Principle. It is not known to what depths such channelized flow occurs. Data from a recording current meter demonstrate that the driving force responsible for the dynamic hydrology has a strong tidal component. The tidal component is augmented by wind-driven waves and is probably superimposed on another, unidentified, current which contributes to the flow of water in the reef at all tidal stages.

Deltas, spits and littoral terraces associated with rising sea level: Late Quaternary examples from northern Iceland

Boomer records from Eyjafjördur, northern Iceland, reveal a major fossil delta with associated wave-built littoral terraces which formed when contemporary sea level was at about 40 m below the modern level and which post-date Late Weichselian glaciation of the site. The structure of these units, and a sequence of similar submerged deltas and spits which lie higher on the fjord side, are very instructive examples of the evolution of the structure of shallow-water sediment units formed on a rising sea level, and permit the nature of the transgression to modern sea level to be reconstructed. Simple approaches to the reconstruction of sea-level change from limited evidence are set out. In order to produce a sea level of −40 m in Eyjafjördur, it is necessary that the isostatic component of sea level change should have decayed before early Holocene eustatic sea levels rose above −40 m at 9000–10,000 yrs B.P. This may be explained either by a substantial early reduction in the local glacier load on the crust and associated early decay of the isostatic component of relative sea-level change, or by a low asthenosphere viscosity beneath Iceland permitting an anomalously rapid decay of the isostatic component.

The history of Post‐Miocene sea level change: Inferences from stratigraphic modeling of Enewetak Atoll

The history of post‐Miocene sea level change has been investigated using a quantitative, one‐dimensional stratigraphic forward model. The stratigraphic model produces synthetic stratigraphies, including mineralogy and sediment age versus depth, in response to changes in sea level, subsidence, sedimentation, and diagenesis. Model outputs, using sea level curves inferred from passive margin sequence stratigraphy and deep‐sea foraminiferal oxygen isotope stratigraphy, were compared to the post‐Miocene stratigraphy of Enewetak Atoll. Modeling results support high‐frequency (104 to 105 years) fluctuations of post‐Miocene sea level. Post‐Miocene sea level elevations significantly greater than modern sea level elevation are not easily reconciled with the stratigraphy of Enewetak Atoll. Model/data fit is maximized when a rapid subsidence rate for Enewetak Atoll is used. Alternatively, model/data fit may be maximized using a lower subsidence rate for Enewetak and having post‐Miocene sea level elevations significantly lower than modem sea level elevation. Given the present state of knowledge, much work is still needed to accurately decipher the record of post‐Miocene sea level change.

The evolution of a moderate energy coast in Holocene time, Pacific Harbour, Viti Levu, Fiji

Abstract In the absence of a fringing reef the Pacific Harbour coast of southern Viti Levu has evolved primarily under the influence of waves generated by the prevailing southeasterly trade winds. By c. 3800 yr B.P., a coastal embayment had been partially enclosed by the formation of a gravel storm beach ridge. Subsequent barrier progradation followed only when longshore sediment was transported into the area from the developing Navua/Deuba Delta to the east, resulting in the accretion of a sandy beach ridge sequence. The estuary/lagoon system enclosed by the barrier was converted into a freshwater swamp in which up to 4 m of peat accumulated. Evidence indicates that Holocene sea levels in the area are unlikely to have exceeded c. 0.6 m above the present level, which is consistent with most evidence from elsewhere in Viti Levu. However, hydro-isostatic processes may explain the apparent inconsistency between the attainment of modern sea level at c. 4000 yr B.P. in the Pacific Harbour and Labau areas of so...

High eustatic sea level during the middle Pliocene:Evidence from the southeastern U.S. Atlantic Coastal Plain

The middle Pliocene, {approximately}3.5-2.5 Ma, was a period of global warmth preceding the growth of major Northern Hemisphere ice sheets. The authors report on eustatic sea level for the middle Pliocene based on microspaleontologic study of marine deposits of the Duplin Formation of South Carolina and North Carolina. The Duplin was deposited during a middle Pliocene marine transgression that formed the Orangeburg scarp, a prominent wave-cut geomorphic paleoshoreline of the southeastern U.S. Atlantic Coastal Plain. They concluded that (1) the scarp in South Carolina was formed mostly during the middle Pliocene (3.5-3.0 Ma), (2) eustatic sea level was about 35 {plus minus} 18 m higher than modern sea level (the scarp has been uplifted about 50-65 m since the middle Pliocene), and (3) ocean-water temperatures along eastern North America were warmer when the scarp was formed that they are at present.

High-precision mass-spectrometric uranium-series dating of cave deposits and implications for palaeoclimate studies

CALCITE deposits in caves, known as speleothem, can provide valuable palaeoenvironmental information1–4. In particular, because speleothem are deposited only in air-filled caves, gaps in deposition in coastal caves record high-stands of sea level. Here we report the use of isotope-dilution mass spectrometry to date speleothem by the uranium-series method. The use of mass spectrometry in uranium-series dating was first applied to corals5, and has greatly improved the precision of this dating method. The speleothem dated here—a flowstone from 15 m below modern sea level in a Bahamian cave—records changes in sea level over the past 280,000 years. The dated hiatuses in deposition indicate high sea-level stands that are in general agreement with data from deep-sea oxygen isotope stratigraphy6 and other estimates for the timing of high-stands and glacial minima1–3,7.

Paleoclimates in Southwestern Tasmania during the Last 13,000 Years

Plant-sociological and climatic classification of the Australian Nothofagus cunninghamii rain forest provides the basis for a new, semiquantitative approach to interpretations of late-Quaternary paleoclimates from four pollen sequences in southwestern Tasmania. Varying proportions of rain-forest pollen types in the records were related to different modern rain-forest alliances and their specific climatic regimes, such as Eastern Rain Forest, Leatherwood Rain Forest, and sclerophyllous, Subalpine Rain Forest. According to this interpretation, early Holocene climates were characterized by 1,600 mm annual precipitation and 1 0?C annual temperature, conditions substantially warmer and drier than previously thought. Maximum precipitation levels of 2,500 mm annually were not reached until 8,000 years B.P. A short-term cooling episode between 6,000 and 5,000 years B. P. led to the establishment of modern rain-forest distribution in western Tasmania, characterized either by a precipitation gradient steeper than before, or by greater climatic variability. To interpret paleoclimates from before 12,000 years B.P., when non-arboreal environments dominated in western Tasmanian pollen records, various modern treeless environments were studied in search for analogs. Contrary to earlier interpretations, late-glacial environments were not alpine tundra with a treeline at modern sea level, but steppe, with marshes or shallow lakes instead of the modern lakes. Climate was characterized by 50% less precipitation than today, resulting in substantial summer droughts. To explain such drastic precipitation decrease, the westerlies that dominate Tasmanian climate today must have been shifted polewards. This suggestion is supported by climate models that take Milankovitch-type insolation differences into account as well as sea-surface temperatures. Paleolimnological information based on diatom analyses support the general paleoclimatic reassessment. INTRODUCTION

Nearshore fringing reefs in north Queensland

Increasing information on the internal structure of north Queensland fringing reefs shows that many have developed true reefal structures only since mid-Holocence times, over rapidly accumulated non-reefal sediments. The reefal veneer consists mainly of head corals and is generally less than 7 m in thickness. Early reef flat development may have been at a level slightly higher than modern sea level.

Tertiary Sea-Level Movements around Southern Africa

Sedimentological, micropaleontological and seismic-profiling data elucidate the history of Tertiary sea-level movements around southern Africa. These new data show that landward movement of the sea began in early Paleocene time and continued into the early Eocene. The sea probably reached its maximum Paleocene height during the early Eocene, and is today represented by outcrops up to at least 204 m, and probably as high as 360 m, above modern sea level. A brief regressive pulse occurred during the middle Eocene, with renewed transgression in the late Eocene. A major regression followed, probably spanning all of Oligocene and early Miocene times. This regression exposed much of the continental shelf and is clearly represented on seismic-reflection profiles by a widespread unconformity. The major Neogene transgression began in the middle Miocene and probably reached its greatest extent in the late Miocene or early Pliocene. The overall middle Miocene to early Pliocene transgression was interrupted by a brie...