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Notes: Stratigraphy presupposes a hierarchy of scales of spatial organization supplemented at the small-scale end by sedimentological concepts (beds, bed sets and bed cosets) and, at larger spatial scales, by sequence-stratigraphic concepts (systems tracts, parasequences, sequences). Between these two end-members are intermediate-scale bodies described as ‘lithofacies’, or simply ‘facies’. A more restricted concept, granulometric facies, can be described in terms of horizontal grain-size gradients (‘facies change’) and cyclic vertical grain-size gradients (‘stratification’). Assemblages of facies so defined (also called depositional systems) are not random, but occur in a limited suite of patterns. Such assemblages may be linked to two classes of bounding surfaces, a source diastem (the immediate source of the sediment) and a surface of closure (if preserved), between which is sandwiched a transgressive or regressive, basinward-fining facies succession. Systems-bounding surfaces are notably more continuous than internal (gradational) facies boundaries. By thus restricting the definition of a facies assemblage (depositional system), it is possible to describe the Quaternary of the Virginia coast with as few as 12 systems. Depositional systems in the Quaternary of the Virginia coast are allometric, in that any system can be derived from any other by plastic expansion of one or more facies relative to another, or by simple symmetry operations. Self-similarity prevails across this intermediate scale of stratigraphic organization. Facies assemblages (depositional systems) consist of event beds, which themselves have erosional basal boundaries and internal successions of microfacies. At larger spatial scales, depositional systems are repeated, either autocyclic repetitions forced by processes within the basin of deposition or allocyclic repetitions, as ‘parasequences’ and high-frequency sequences. In the Virginia Quaternary, systems architecture is compatible with sequence architecture and nests conformably within its framework, but analysis of systems architecture reveals rules beyond those governing sequence architecture.

Notes: Grain-size distributions of sand samples by means of a Benthos Rapid Sediment Analyzer were determined, using SCHLEE'S (1966) fall times. The results were compared with analysis of the same samples by sieving. The Rapid Sediment Analyzer (RSA) consistently overestimated the mean diameter of fine samples and underestimated the diameter of coarse samples relative to sieving. Since we used a wider settling column and a smaller sample weight than did Schlee, we infer that the differences were due to weaker grain interaction effects in our analyzer. Thus, by using Schlee's fall times, we overcompensated for these effects. We conclude that the “new grain parameter” of fall velocity (SENGUPTA and VEENSTRA, 1968) is indeed valuable. MIDDLETON'S (1967) psi transform is more convenient than the analogous phi transform in that it yields Middle-ton sand classes of 0 to 5 psi, as compared to Wentworth-Krumbein sand classes of -1 to 4 phi. However, use of fall velocity does not completely obviate the need to determine grain diameter, since this is the most expedient criterion with which to correct fall velocity to standard fall velocity.

Notes: In order to evaluate a model of Holocene shelf sediment distribution requiring a nearshore modern sand facies and an offshore relict sand facies, we have undertaken a textural reconnaissance of the Virginia-North Carolina Coast between Capes Henry and Hatteras. Grab samples were subjected to grain-size analysis by means of a modified Woods Hole Rapid Sediment Analyser. Textural provinces were erected with the aid of factor vector analysis. These include medium-grained sands of the beach and surf zones; seaward fining, fine-grained sands of the shore face, and heterogenous sands of the sea floor. In this latter province, grain size is controlled by a ridge and swale topography, with coarser sand on the crests. Coast-wise grain-size trends on the beach and shore face can be explained by assuming that wave heights increase toward the south, and that the Pleistocene sediment source is exposed higher on the shore face in the north than it is in the south. The shore face is retrograding, except in the vicinity of Diamond Shoals. There is textural evidence for a former Albemarle River channel, which bisects the study area. A model for sediment fractionation on a retreating barrier coast with low sediment input is proposed, based on studies which indicate that on such coasts: (1) barrier superstructures retreat more or less continuously by upper shore-face erosion and storm washover; and (2) lower shore-face erosion results in an equal-volume aggradation of the adjacent sea floor, and forms the leading edge of the Holocene transgressive sand sheet. The nearshore “modern” sands and offshore “relict” sands are both present in the study area, but the terms are unnecessarily restrictive. Both are “relict” in the sense of being derived from a Pleistocene substrate, and both are “modern” in the sense of having undergone adjustment to a modern hydraulic regime. While modern and relict are useful general terms, it is convenient in this area to refer to a Holocene barrier sand prism, versus a Holocene transgressive sand sheet.