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Abstract Incised-valley fills provide the greatest potential for preservation of sediments in a transgressive system. We compare examples from the coastal plain of Delaware and the glaciated bedrock terrain of Maine. Facies models developed in these areas suggest that 1/2 to 2/3 of the initial phases of transgression may be preserved below the shoreface ravinement surface in coastal-plain settings, recording initial fluvial, estuarine, lagoon, and some flood-tidal delta deposits. Coastal-plain systems are controlled by processes of open-ocean wave energy and back-barrier tidal systems. Lithosomes are irregular and may be disconnected lenses, 10–30 m maximum thickness, 1–5 km normal to the shoreline, and 10's of kilometers alongshore extent. Shoreface incision to a wave base of 10 m creates a ravinement unconformity. Incised-valley fills along the margins of a major estuary, Delaware Bay, record a similar sequence, but shoreface incision is smaller, approximately 1 m. In Maine, embayments are framed by bedrock, and cut into glaciomarine sediments. The tide-dominated system accumulates sediment in the inner reaches but becomes progressively truncated by tidal-channel erosion at mid-embayment, creating an estuarine, tidal-ravinement surface. The outer, less geographically sheltered reaches are dominated by wave erosion, which removes the majority of the sequence. Lithosomes are disjunct lenticular pods of a few meters to 10 m thickness and kilometer scale in lateral and longitudinal extent. In both cases, maximum preservation may occur as sea level reaches highstand, producing a prograding sequence that caps the earlier transgressive units.

Abstract Sea-level changes have had an important influence on the distribution of late Quaternary inner continental-shelf sediment in the western Gulf of Maine. Previous stratigraphic models of sea-level change in the region were based on terrestrial observations and a large quantity of offshore high-resolution seismic-reflection data. These models, however, were not constrained by core data. Integration of new vibracore data with earlier observations indicates that nearshore regions were (1) probably deglaciated and subjected to glacio-marine conditions around 13.5 ka, (2) subaerially exposed by a fall in sea level sometime after 11 ka, and (3) flooded by a transgressing sea following an inferred lowstand of sea level between 11 and 9 ka. The greatest amount of sediment accumulated on the shelf during the initial transgression, under glacio-marine conditions. Sandy fluvial sediment accumulated in large quantities during the following regression and early Holocene transgression. Sediment influx from eroding bluffs of glacial origin was significant throughout the Holocene transgression, especially in regions lacking a fluvial source.

Glacial marine sedimentation dominated the inner shelf and coastal lowlands of Maine between ca. 14,000 and 11,000 B.P. Three major seismic facies interpreted as glacial marine deposits beneath the inner shelf are identified by recent high-resolution seismic reflection profiling. These are: (1) GM-M, massive glacial marine sediment, a uniform, draping blanket with abundant ice-rafted detritus, either mud or diamicton; (2) GM-D, conformable glacial marine mud, with a distinct draping geometry, usually well stratified; and (3) GM-P, less well-stratified glacial marine mud with a distinctly ponded, variable geometry. These glacial marine facies are associated with underlying seismic facies interpreted as till, stratified drift and bedrock, and overlying seismic facies interpreted as Holocene littoral and marine facies. The glacial marine facies are contained within one of two seismic stratigraphic sequences, which record rapidly changing sea levels and sedimentary environments. Sequence G is composed of till, stratified drift, and glacial marine mud. It records the deglaciation of the northern Gulf of Maine and Maine coast. It is overlain by a distinct unconformity above the −60-m sea-level lowstand, which grades to a conformity in deeper basins, further overlain by seismic sequence H. A critical issue concerning deglaciation of the area is identification of deglacial environments. A working hypothesis is that the initial deglaciation, ca. 18,000 to 14,000 B.P., was through a series of small, topographically buttressed, warm-based ice shelves, which were abundantly productive of poorly sorted sediment. These shelves may have formed and disintegrated in a sequential stepwise fashion, temporarily grounding on highs north of the major basins in the Gulf of Maine. After about 14,000 B.P., the ice front was a calving embayment, producing ice-rafted detritus, turbid suspensions, and subaqueous outwash. After 12,500 B.P., the ice margin was terrestrial, feeding melt-water streams and producing little ice-rafted detritus. The Maine inner shelf preserves this sequence in shelf valleys. Elsewhere, erosion during local relative sea-level changes has stripped bedrock highs of the majority of sediments, between the −60-m isobath and the inland marine limit (60- to 132-m elevation).

The aminostratigraphic relationships of approximately 150 coastal Quaternary sites from Nova Scotia to Florida and the Bahamas Islands are reviewed. The broad latitudinal range of the sites provides a useful perspective on the relative kinetics of racemization at substantially different temperatures. Local aminostratigraphic sections are presented for five regions in which present mean annual temperatures differ by 3°C or less. Correlation of these individual aminostratigraphies is accomplished by qualitative comparison of results for overlapping sections and by quantitative kinetic modeling. Correlations based on kinetic modeling with local calibration are compared with available U-series data for coastal plain sites. Using basic aminostratigraphic assumptions about the relationship of present and past temperature gradients, the amino acid data from most of the calibration sites follow logical trends. However, significant conflicts between U-series dates and aminostratigraphic age estimates are recognized for sites in South Carolina and for a group of sites in eastern Virginia (central Chesapeake Bay). Reconciliation of the aminostratigraphic data with all of the Atlantic Coastal Plain U-series coral dates is not possible without invoking extreme (and latitudinally variable) thermal effects on the racemization kinetics.

Abstract Most early studies of the U.S. Atlantic continental margin were dominated by the concept of 'layer-cake' stratigraphy with disruptions in continuity often explained by 'yo-yo' processes of basin faulting. Recent studies now demonstrate that these two concepts are not totally satisfactory in explaining the stratigraphic patterns of the past 24-million-year history of the Atlantic margin. During the past two decades, increasing sophistication of such tools as high-resolution seismic stratigraphy, biostratigraphic time zonations, and absolute dating techniques have provided a detailed basis for interregional correlations and environmental interpretations of upper Cenozoic lithostratigraphic units. The coastal plain and continental shelf are now recognized as parts of a coherent geologic province on a passive plate margin that have responded as an integral unit to complex sets of rapidly changing environmental conditions. The resulting upper Cenozoic sediment record is characterized by extremely variable lithologies with complex geometries and which are extensively dissected by unconformities.

Abstract: On the Maine coast, evidence of local relative sea level 12.5 ka is now exposed 60-80 m above present sea level. At that time, eustatic sea level was at least 70 m below present in most parts of the world. The difference is due to isostatic depression of the Maine coast by the weight of glacial ice. During deglaciation, the sea advanced inland in contact with the retreating margin of the marine-based ice sheet. Due to isostatic rebound and the contours of the land, the ice sheet grounded as much as 150 km inland of the present coast, glaciomarine deltas formed, and the transgression reached a stillstand at what is termed the upper marine limit. Due to differential tilting during rebound, this marine limit is now over 132 m in elevation at its farthest inlet extent. As rebound became dominant, sea level reached to 65 m below present at about 9.5 ka. At that time rebound slowed to about the same rate as that of eustatic sea-level rise. Shorelines were cut and deltas were formed at this lower marine stillstand position. Subsequently, eustatic rise became the predominant mode. Radiocarbon dates on fossil marine mollusks provide timing for this onlap and offlap. From 7.0 ka to the present, radiocarbon dates on wood and salt marsh peats provide a relatively precise sea-level curve. During the period 4.2--1.5 ka, sea level rose at 1.22 m/1,000 yrs. Before that period, it may have risen more than twice as fast. After 1.5 ka, it slowed to half the mid-late Holocene rate. Recent tide-gauge records show an acceleration in rate to 2--3 mm/yr for the past 40 yrs. Releveling, tide gauges, and other evidence (Anderson and others, 1984) suggest that the coast is being warped downward to the east, possibly due to non-glacially induced neotectonics.

Abstract: Transgressive barriers of the embayed Atlantic and Gulf coast are generally similar in overall form, processes, and landward migration in response to relative sea-level rise, but they vary greatly in potential sources and volume of sand supply. Delaware's transgressive barriers vary in thickness from 25 m to less than 5 m; dunes may rise to 20 m above sea level, whereas barrier-spit and inlet sand reach depths of 10–18 m below sea level. Widths vary between 0 m at eroding headlands and 4–6 km near tidal delta and spit complexes. A complete Holocene paralic sequence for Delaware includes a basal sand and/or gravel overlain by marsh, lagoon, and barrier lithosomes. Shoreface erosion, as the barrier lithosome moves landward, occurs to an average depth of 10 m, with about 50% of eroded sediment derived from Holocene and Pleistocene lagoonal mud outcrops. Since the suspended material is carried out of the shoreface, its removal requires a re-evaluation of the volumetric model commonly inferred from the Bruun mechanism. Also, the third dimension of longshore transport of coarse material needs to be considered. As transgression continues, the ravinement surface exposes lagoonal sediments, marsh mud, irregularly shaped basal remnants of the Holocene barrier lithosome, or varied Pleistocene strata. These are then blanketed by varying thicknesses of inner-shelf sand. Ultimately, the transgressive barrier and associated paralic environments migrate landward to peak interglacial positions where the entire transgressive record may be preserved. A relatively complete vertical sequence of transgressive coastal lithosomes might also be preserved at the outer edge of the continental shelf at glacial sea-level minima. Thus, the optimal chance for total preservation of a transgressive coastal lithosome sequence lies at the extremes, landward at the peak interglacial when eustatic sea-level rise stops and the coastal lithosome sequences become stranded, and possibly on the outer edge of the shelf as deglaciation begins and there is rapid rate of sea-level rise.