Abstract This four-day field trip will include 21 field stops along a 105-km reach of Maryland’s and Virginia’s barrier-island coast along the Delmarva Peninsula. Along the way, we will cover aspects of barrier-island and nearshore geology and of barrier-island and backbarrier marsh process-response morphodynamic systems in two hydrodynamic settings: (1) the wave-dominated Assateague Island along the northern Delmarva Peninsula and (2) the mixed-energy Virginia barrier islands along the southern Delmarva Peninsula. We will also examine anthropogenic impacts on barrier-island systems at Ocean City Inlet, Maryland, and the National Aeronautics and Space Administration’s (NASA) Wallops Island, Virginia.

Abstract Stage 5 deposits (unit Q2) have been identified along the inner shelf of Maryland. Peak sea-level substage 5e deposits (lower Q2) consist of (buried) shoal-forming sands on the inner shelf, analogous to modern shelf sands, and relict barrier facies onshore. Substages 5d-5a, however, are represented by geographically widespread, thick, fossiliferous muds (upper Q2), whose age range was determined by amino-acid racemization. The time frame of mud deposition was further subdivided into stage 5 substages. Ostracode assemblage zones in unit Q2 record a consistent, repetitive sequence of four rapid and distinct climatic fluctuations that follow the isotopic excursions in stage 5. Sea levels remained high for the duration of stage 5, fluctuating within a maximum range of 30 m. The first physical evidence of substage 5d sea levels being higher than -23 m mean seal level (MSL) is contained within ostracode zone 2 in unit Q2. An anomalous lithofacies such as a thick mud deposited in a relatively high sea level requires alternative sediment sources and shelf sedimentation processes than those operating on the present and substage 5e transgressive sandy shelves. Sea level during stage 5 along the Maryland coast consisted of a prolonged period (=45,000 yrs) of water covering the shelf at less than maximum sea levels, following the substage 5e peak highstand (+ 6 m MSL) spanning 11,000 yrs. Stage 5 may be modeled as follows: Early stage 5 transgressive facies migrated across the shelf and were deposited at their peak position during substage 5e (at 125 ka), when sea level reached +6 m MSL. Late stage 5 sea levels maintained a range of —23 (extreme minimum) to +0.1 (present) m MSL and deposited thick, laminated, unbioturbated muds containing numerous radiations of Mulinia lateralis (Say). Onshore facies of late stage 5 include a barrier system (substage 5c at +0.1 m MSL) and tidal flats and/or marshes (of substages 5d, 5b, and 5a). It is inferred that at slightly depressed late stage 5 sea levels the Chesapeake and Delaware estuaries became fluvially dominated, as the estuarine portion of the drowned river valley was expelled, or shifted seaward out of the basin. Muds were thereby exported from these major fluvial systems onto the inner shelf and redistributed by shelf currents. Sources of excess fine sediment could include pre-stage 5 glacial sediment, as well as sediment eroded from exposed coastal areas at lowered sea levels. Deposition appears to have been exceedingly high, as evidenced by intact laminae of fine sand-silt in the muds and by the in situ fossil assemblages and their relation to sedimentary characteristics of the unit. The 45,000-yr-long period of relatively high sea level during stage 5 was unique in Pleistocene history, and was the controlling factor in establishing sea-level-related processes resulting in the muddy shelf environment, which characterizes only stage 5.