Abstract Micropaleontology and biostratigraphy play vital roles for deciphering the stratigraphic record produced by changes in relative sea level, interpreting the history of global sea-level change, and testing models for the causes of sea-level fluctuations due to the variable influences of tectonics, glacio-eustasy, and climate. The stratigraphic architecture developed in response to changing eustasy, accommodation space, and sediment supply along continental margins, in epicontinental seas, and on carbonate platforms can be interpreted using the tools of marine micropaleontology. Microfossils provide chronostrati-graphic control and a wealth of paleoenvironmental information about depositional environments as well as postdepositional changes to those environments. Although industry micropal-eontology has taken a backseat to seismic stratigraphy as a fundamental exploration and correlation tool, academic micro-paleontology has stepped up to fill the void and provide valuable ground-truth data for the characterization and timing of sea-level change. At the national American Association of Petroleum Geologists (AAPG) meeting in 1999, held in San Antonio, Texas, the North American Micropaleontology Section (NAMS) of SEPM (Society for Sedimentary Geology) sponsored a full-day technical session entitled “Paleobiological, Geochemical, and Other Proxies of Sea-Level Change.” The purpose of the session was to highlight the application of micropaleontology to the study and interpretation of stratigraphic sequences deposited during changes in sea level. Many of the abstracts presented at that meeting have been developed into the research articles contained in this volume. Eighteen articles spanning late Paleozoic to modern times, and representing siliciclastic, mixed siliciclastic–carbonate, and carbonate-dominated depositional systems are presented in this volume. The studies range

Abstract Foraminifera of siliciclastic and mixed siliciclastic–carbonate continental margins are sensitive to changes in sea level because of the complex biological, chemical, and physical oceanographic variables that help to shape foraminiferal niche space. Data on foraminiferal distribution and abundance provide useful proxies for paleoenvironment. Here we emphasize the importance of salinity, temperature, seasonality, food supply (productivity), and dissolved oxygen in controlling the nature of marginal marine, neritic, and upper bathyal foraminiferal biofacies. We also elaborate on the paleoecologic significance and utility of using planktic:benthic ratios, diversity indices, and similarity coefficients for interpreting changes in relative sea level. The recognition and correlation of the systems tracts that define sequence stratigraphic architecture reliably hinge on multi-proxy micropaleontologic evidence, particularly that provided by benthic and planktic foraminifera, coupled with sedimentology and geochemistry.

Abstract Analyses of total abundance of dead foraminifera from a twelve-month study of surface samples (0–1 cm) from Cowpen Marsh shows no definite seasonal pattern, but significant seasonal variations are evident in the relative abundance of agglutinated and calcareous taxa. Agglutinated species are most dominant in the winter months whilst calcareous foraminifera reach their peak relative abundances during the summer. We identify three cluster zones: a high-marsh and middle-marsh zone of Jadammina macrescens and Trochammina inflata ; a low-marsh zone of Miliammina fusca and Jadammina macrescens ; and a mudflat zone of calcareous foraminiferal species, notably Elphidium williamsoni , Haynesina germanica , and Quinqueloculina spp. The variations of contemporary foraminiferal distribution across the intertidal zone during an annual cycle modify the elevation of the zonal boundaries by as much as 0.9 m. Consequently, a contemporary sample taken in one month can significantly underestimate (0.35 m) or overestimate (0.48 m) the elevation range of a zone. Hence, the value of cluster zones as indicators of former sea levels can be assessed only following a consideration of the elevation errors induced by the seasonal variability in saltmarsh foraminiferal distributions. We developed monthly and annual foraminifera-based transfer functions using weighted averaging regression and calibration. Results suggest that precise reconstructions of former sea levels are possible ( r 2 ≥ 0.82) but that the accuracy of these reconstructions varies during the course of the year. Greatest precision is achieved using samples collected in the winter months (± 0.29 m) and weakest during the summer (± 0.35 m) because the foraminiferal assemblages are dominated by agglutinated and calcareous species, respectively. We conclude that an investigation of contemporary saltmarsh foraminifera that recovers a complete set of samples in the winter, spring, summer, and autumn will provide the best-quality data for use in sea-level investigations (error = ± 0.21 m). If only one set of measurements can be obtained, sampling in the winter months may represent the most reliable alternative.

Abstract Foraminiferal assemblages of Bombay Hook National Wildlife Refuge (Smyrna, Delaware, U.S.A.) exhibit substantial variation in spatio-temporal test inputs to marsh sediment and are strongly overprinted by seasonal changes in porewater chemistry. Seasonal surface and near-surface samples are typically not representative of foraminiferal inputs at depth (60 cm). Long-term ecological signals are detected using artificially time-averaged (ATA) assemblages, in which dead and live counts of foraminifera are summed separately for an entire two-year sampling period. Unlike seasonal assemblages, cluster analysis of ATA assemblages reveals a distinct change in assemblages at ∼ 20 cm depth. Differential preservation of foraminifera in the upper 60 cm—and especially the upper 20 cm—of sediment mimics a sharp paleoenvironmental change that could potentially be interpreted as a rapid fall in sea level during a time of documented transgression over the last ∼ 100–200 years.

Abstract Detailed stratigraphic study, paleoenvironmental interpretation of tidal wetland facies based on macroflora and agglutinated foraminiferal assemblages, radiocarbon dating, and modern marsh accretion rates are used to reconstruct the late Holocene sea-level history of the Leipsic River valley. Transgressive valley-fill deposits of the Leipsic River valley consist of brown peat, olive-gray mud, and gray-brown muddy peat. These facies were deposited in brackish wetland environments, open-water subtidal environments, and modern salt-marsh environments, respectively. In the early Holocene the Leipsic River was a tributary to a major fluvial system, possibly the paleo–Delaware River. The Holocene transgression reached the area about 5,000 yr BP, when fringing tidal wetlands began to develop in both valleys, depositing brown peat. Rapidly rising sea level flooded the valley of the Leipsic River by 3,000 BP, turning it into an open-water estuarine environment. After 3,000 yr BP, the rate of the sea-level rise decreased, resulting in wide expansion of brackish wetlands in the Leipsic River valley and along the Delaware Bay coast. Tidal creeks migrating on the marsh paleosurface were eroding brown peat and depositing mud units at different depths. The brackish conditions persisted in the area until about 1,000 yr BP. One thousand years ago a change in the environments occurred when modern salt marshes began to replace the brackish wetlands. Sea level was approximately 12 m below modern MHW when the first emergent tidal wetlands were developed in the valley. By 4000 yr BP, rapidly rising sea level reached an elevation of 9 m below MHW. From 4000 to 2000 yr BP, sea level rose to an elevation of 3.5 m, and by 1000 yr BP it reached an elevation of about 3 m below the modern marsh surface. Salt marshes developed in the valley during the last 100 years with a vertical marsh accretion rate of 0.29 cm/yr. Twenty years ago, the marsh vertical accretion rate increased up to 0.46 cm/yr. These rates are comparable to the average rate of sea-level rise of 0.33 cm/yr measured by the tide gauge at Breakwater Harbor, Delaware. Thus, the salt marshes at Bombay Hook National Wildlife Refuge are in a dynamic equilibrium with rising sea level.

Abstract Examination of the benthic foraminifera from the northwestern Gulf of Mexico slope (90–95 o W; 283–1341 m) reveals widespread changes in their assemblages during the transition from the most recent sea-level lowstand (last glacial maximum) to the current highstand (interglacial). These glacial assemblages are defined by Q-mode cluster and R-mode principal component analyses of both relative abundance and presence/absence data from 61 samples dated at 15 ka. Distinct bathymetric positions can be assigned to the assemblages, except in the case of a deltaic outflow assemblage. They are interpreted to be associated with water masses, and basin-wide changes in water-mass position and chemistry at the glacial–postglacial transition are reflected in assemblage changes. Most important is the switch from North Atlantic Intermediate Water (NAIW), which was found in the Gulf during the last glacial maximum, to Subantarctic Intermediate Water (SAIW), which is found in the modern Gulf. This water-mass shift allowed several species associated with SAIW (e.g., Bulimina alazanensis and Osangularia culter ) to reenter the Gulf after the last glacial interval. The position of several water-mass boundaries were found to differ between the two time periods, causing the upper depth limits of some species to change with time. The benthic foraminiferal record in a core (water depth 726 m) shows three faunal events during and after the deglaciation; apparently, these events are related to water-mass shifts at 13 and 11 ka and a change in the substrate organic matter at 4.5 ka.

Abstract Biostratigraphic signals have been utilized in allostratigraphic studies in conjunction with wire-line log analysis and seismic stratigraphy. In particular, systematic variations in abundance and diversity (simple species diversity and the Shannon–Weiner information function ( H ) of planktonic and benthonic foraminifera have been shown to characterize critical surfaces and individual systems tracts. Species diversity is a measure of both species richness and evenness. However, diversity values can vary greatly when evenness is constant and species richness varies. Diversity is, therefore, not necessarily an easy tool to interpret. The inability to partition diversity into its two components, richness and evenness, was addressed by Buzas and Hayek (1996) , who demonstrated the utility of their new diversity measure (SHE) for biofacies identification along a depth transect in the Gulf of Mexico ( Buzas and Hayek, 1998 ). SHE analysis should, therefore, be of use in bio-sequence stratigraphic studies, a hypothesis that is explored. The SHE plot used shows species richness ln( S ) and H on the same plot. Evenness ln( E ) is represented by the envelope formed by the H and ln( S ) curves. Variations in the SHE plot are used to characterize systems tracts and critical surfaces. Within a depositional sequence the decrease to a minimum of ln( E ) that coincides with decreasing ln( S ) and H characterizes the candidate sequence boundary. An increase in ln( E ) to a maximum in conjunction with increasing ln( S ) and H characterizes flooding surfaces, and the maximum flooding surface in particular.

Abstract An unconventional application of traditional similarity coefficients, the similarity curve, is presented to assist in the identification and interpretation of stratigraphic discontinuities. Similarity curves are generated for an entire stratigraphic sequence by comparing each sample to the sample immediately above it in stratigraphic sequence. Similarity coefficients are calculated for each sample pair on the basis of their contained foraminiferal assemblages, and a similarity curve is then generated for the stratigraphic section. By examining the breaks in these curves and comparing the total assemblage similarity curve to similarity curves generated individually for planktonic and benthic groups, we interpret candidates for discontinuities from a well in the Gulf of Mexico. Furthermore, we discuss these discontinuities and relate them to factors such as potential sea-level change, changes in sedimentation locus, and dissolution effects.

Abstract Analysis of biostratigraphic information from 31 industry wells in the Qiong Dong Nan and Ying Ge Hai Basins in the South China Sea establishes a chronostratigraphy for the area. Microfossil biostratigraphy of the wells permits recognition of individual regressive sequences and overlying marine flooding events. Dating of the sequences and unconformities shows a definite correlation of the transgressions and regressions to those depicted on published global sea-level curves. This tie indicates the influence of sea level on sediment dispersal enhancing local rift-related deposition. Age control developed for the basins in this study has improved stratigraphic correlations by verifying seismic-to-well ties and providing bracketing ages across hiatuses. Wells in the basins penetrate a thick Holocene–Pliocene clastic interval to reach an Upper Miocene deep-water clastic reservoir in offshore downdip wells or a Lower Miocene–Upper Oligocene shallow-water clastic reservoir horizon on structural highs. Although the hydrocarbon source is assumed to be local Lower Tertiary (Eocene or older) nonmarine coals, these units have not yet been reached by drilling. The regional seal is an upper Middle Miocene marine flooding event. Paleoecology and paleobathymetry were determined on the basis of foraminiferal analyses. Biostratigraphic dating with foraminifera and calcareous nannofossils permits construction of time-slice maps to show the basin configuration at correlative horizons. Synthesis of many individual well paleobathymetry curves yields a general sea-level curve for the basins. The overall shape of this sea-level curve compares favorably with published global curves.

Abstract Palynomorphs are acid-resistant organic particles which behave aerodynamically and hydrodynamically like silt, and which resist degradation except in oxidizing or highly alkaline conditions. They are present in virtually all marine sediments, from the tropics to the poles and from estuarine to abyssal environments. Reconstructions of Quaternary sea level in cores from the New Jersey shelf (ODP Hole 1072A) and slope (ODP Hole 1073A) based on the modern distribution of palynomorphs across the New Jersey margin as well as the taphonomic alteration of palynological samples agree fairly well with data from other available proxies (e.g., oxygen isotopes). The palynological signatures of sediments on continental margins also provide information about the generation of sequences and sequence boundaries. The palynological character of surfaces identified as sequence boundaries from seismic reflection profiles records the generation of erosional unconformities during extreme lowstand events that altered the geometry of the margin. Very low palynomorph concentrations and presumably oxidized palynological assemblages (containing few protoperidinioid dinocysts or thin-walled pollen grains) characterize erosional unconformities. The strong seismic reflection associated with sequence boundaries results from physical contrast between the transgressive/highstand sediments (with very high palynomorph concentrations, P:D values declining rapidly upcore, and Pinus -dominated pollen assemblages) and underlying the lowstand sediments (with low palynomorph concentrations, high P:D values, taphonomically altered and ecologically mixed palynological assemblages). The palynological content of Quaternary sediments at ODP Sites 1072 and 1073 thus supports the role of eustasy as an important factor in shaping the New Jersey margin.

Abstract We evaluate late Miocene–Recent paleoenvironments, paleobathymetry, and depositional facies recovered at two sites drilled by Ocean Drilling Program Leg 174A on the New Jersey continental shelf. Based on seismic stratigraphy, previous studies suggested that the New Jersey margin sequences are primarily either highstand deposits or lowstand systems tracts. However, benthic foraminiferal biofacies and planktonic foraminiferal abundances proved to be key to deciphering systems tract development. By integrating foramin-iferal, lithologic, and downhole logging evidence within a seismically defined sequence stratigraphic framework, we show that Pleistocene sequences cored by Leg 174A are characterized by transgressive and highstand deposits, whereas Miocene sequences consist of lowstand, transgressive, and highstand deposits, with repeated flooding surfaces indicating parasequences. We propose that the erosion responsible for the shelf sequence boundaries can be attributed to mean lowerings of base level in response to changes in the mean states of glaciation that marked: (1) the Miocene increase in ice volume and glacioeustatic lowering; (2) the transition to Northern Hemisphere–dominated glaciation; and (3) the transition to the large eustatic fluctuations of the middle–late Pleistocene.

Abstract The physical packaging into unconformity-bounded units of the upper Oligocene and lower Miocene neritic strata in southeastern Australia is chronologically consistent with third-order putative global sequences and glaciations. Foraminiferal biofacies data show both recurrence and progression. Species used as proxies for inner-neritic and outer-neritic environments display recurring fluctuations in close harmony with stratal packaging. In contrast to this recurrence or cycling, biofacies cluster groups are strongly sequential or “progressive” at the third-order, 10 6 -year scale, with very little overlap between the successional assemblages named Angahook, Jan Juc-1, Jan Juc-2, and Puebla. The Angahook–Jan Juc-1 and Jan Juc-2–Puebla biofacies boundaries, implying some turnover in communities, fall respectively at sequence boundaries Ru4–Ch1 and Ch4–Aq1 and glacioeustatic perturbations OCi-1 and MAi-1 (= Mi1), but the Jan Juc-1–Jan Juc-2 boundary within the Jan Juc Formation falls close to the flooding surface of sequence TB1.2. These third-order patterns of recurrence and sequential change were largely sustained at higher frequencies in the study of an interval approaching a glacial within the Jan Juc-1. Samples at the centimeter scale (about 2–4 cm spacing) over one meter of alternating soft and hard (lithified) layers yield four biofacies groups mainly on abundance variations of individual species and species groups. The clusters are cleanly separated superpositionally (thus, strongly successional), reflecting environmental cycles at 10 4 -year scale, perhaps in the Milankovitch band of 41,000 years. Shallower-water species dominate clusters B and D from hard layers, whereas deeper-water species are more abundant in clusters A and C from soft layers. The differences suggest paleodepth change of 50–70 m, with maxima in the soft layers and minima at the tops of hard layers. The high abundance of infauna and a stronger mixing between shallower-water and deeper-water species indicates an oxygen-poor environment coupled with bioturbation. Similarities between faunas of third-order and Milankovitch scales include: (i) coincidence of biofacies with lithofacies or lithostratigraphy is due largely to abundance variations of the prominent species, (ii) recurring biofacies signals of sea-level change are chronologically consistent with other published proxies of glacioeustasy, and (iii) clustered assemblages of benthic foraminifera are distinct and strongly successional.

Abstract Quantitative analysis of Oligocene assemblages in cool-water carbonates suggests a two-tiered response by benthic, neritic foraminiferal faunas to a succession of glacioeustatic fluctuations. One response appears at lower-frequency or second-order cycles and is marked by more substantial, nonreversible, taxic change at the Eocene–Oligocene boundary, at the Rupelian–Chattian (Early–Late Oligocene) boundary, and during a Late Oligocene transgressive phase. These faunal changes were responses to climatic changes forced by glaciations signaled by oceanic oxygen-isotope maxima. The second response is seen in fluctuations in the abundances of benthic neritic taxa. Rapid changes in infaunal-to-epifaunal ratios appear to chronicle reversible “short-term” local paleoenvironmental shifts forced by third-order cycles. Sequence stratigraphic packages and bounding surfaces are easier to decipher in sequences characteristic of the warmer and more sluggish Priabonian ocean than in the cooler and better-ventilated Rupelian ocean. The major (second-order) physical event at the Rupelian–Chattian boundary is recorded faunally but shows a relatively muted impact on the regional succession of neritic foraminifera compared to the sequence boundary coinciding with glaciation Oi1 in the very earliest Oligocene. We interpret, from graphic correlation and cluster analysis, that patterns of faunal change reflect endemism that developed on a broad neritic zone with wide variation in intensity of oceanic influence.