Geology topics

D. J. Mallinson

Publications and source records attributed to D. J. Mallinson.

8 recordsLinked to original sources

USGS2017

Barrier island response to late Holocene climate events, North Carolina, USA

T he Outer Banks barrier islands of North Carolina, USA, contain a geologic record of inlet activity that extends from ca. 2200 cal yr BP to the present, and can be used as a proxy for storm activity. Optically stimulated luminescence (OSL) dating (26 samples) of inlet-fill and flood tide delta deposits, recognized in cores and geophysical data, provides the basis for understanding the chronology of storm impacts and comparison to other paleoclimate proxy data. OSL ages of historical inlet fill compare favorably to historical documentation of inlet activity, providing confidence in the technique. Comparison suggests that the Medieval Warm Period (MWP) and Little Ice Age (LIA) were both characterized by elevated storm conditions as indicated by much greater inlet activity relative to today. Given present understanding of atmospheric circulation patterns and sea-surface temperatures during the MWP and LIA, we suggest that increased inlet activity during the MWP responded to intensified hurricane impacts, while elevated inlet activity during the LIA was in response to increased nor'easter activity. A general decrease in storminess at mid-latitudes in the North Atlantic over the last 300 yr has allowed the system to evolve into a more continuous barrier with few inlets.

North Carolina↗

USGS2017

Rapid Holocene coastal change revealed by high-resolution micropaleontological analysis, Pamlico Sound, North Carolina, USA

Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000. yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500. cal. yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting. ?? 2011 University of Washington.

North Carolina↗

USGS2013

Quaternary geophysical framework of the northeastern North Carolina coastal system

The northeastern North Carolina coastal system, from False Cape, Virginia, to Cape Lookout, North Carolina, has been studied by a cooperative research program that mapped the Quaternary geologic framework of the estuaries, barrier islands, and inner continental shelf. This information provides a basis to understand the linkage between geologic framework, physical processes, and coastal evolution at time scales from storm events to millennia. The study area attracts significant tourism to its parks and beaches, contains a number of coastal communities, and supports a local fishing industry, all of which are impacted by coastal change. Knowledge derived from this research program can be used to mitigate hazards and facilitate effective management of this dynamic coastal system.

North Carolina↗

USGS2012

Standardizing texture and facies codes for a process-based classification of clastic sediment and rock

Proposed here is a universally applicable, texturally based classification of clastic sediment that is independent from composition, cementation, and geologic environment, is closely allied to process sedimentology, and applies to all compartments in the source-to-sink system. The classification is contingent on defining the term "clastic" so that it is independent from composition or origin and includes any particles or grains that are subject to erosion, transportation, and deposition. Modifications to Folk's (1980) texturally based classification that include applying new assumptions and defining a broader array of textural fields are proposed to accommodate this. The revised ternary diagrams include additional textural fields that better define poorly sorted and coarse-grained deposits, so that all end members (gravel, sand, and mud size fractions) are included in textural codes. Revised textural fields, or classes, are based on a strict adherence to volumetric estimates of percentages of gravel, sand, and mud size grain populations, which by definition must sum to 100%. The new classification ensures that descriptors are applied consistently to all end members in the ternary diagram (gravel, sand, and mud) according to several rules, and that none of the end members are ignored. These modifications provide bases for standardizing vertical displays of texture in graphic logs, lithofacies codes, and their derivatives- hydrofacies. Hydrofacies codes are nondirectional permeability indicators that predict aquifer or reservoir potential. Folk's (1980) ternary diagram for fine-grained clastic sediments (sand, silt, and clay size fractions) is also revised to preserve consistency with the revised diagram for gravel, sand, and mud. Standardizing texture ensures that the principles of process sedimentology are consistently applied to compositionally variable rock sequences, such as mixed carbonate-siliciclastic ramp settings, and the extreme ends of depositional systems.

Journal of Sedimentary Research↗

USGS2010

Regional seismic stratigraphy and controls on the Quaternary evolution of the Cape Hatteras region of the Atlantic passive margin, USA

Seismic and core data, combined with amino acid racemization and strontium-isotope age data, enable the definition of the Quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of North Carolina, U.S.A. Seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets, and enable an understanding of the evolution of this margin. Data reveal the progressive eastward progradation and aggradation of the Quaternary shelf. The early Pleistocene inner shelf occurs at a depth of ca. 20-40 m beneath the western part of the modern estuarine system (Pamlico Sound). A mid- to outer shelf lowstand terrace (also early Pleistocene) with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract, occurs at a deeper level (ca. 45-70 m) beneath the modern barrier island system (the Outer Banks) and northern Pamlico Sound. Seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle Pleistocene shelf. Middle to late Pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units, and contain numerous filled fluvial valleys that are incised into the early and middle Pleistocene deposits. The stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea-level fluctuations during the middle to late Pleistocene, expressed as falling stage, lowstand, transgressive and highstand systems tracts. Thick stratigraphic sequences occur within the middle Pleistocene section, suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north. Furthermore, the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system. ?? 2009 Elsevier B.V.

Marine Geology↗

USGS2009

Recognizing former flood-tide deltas in the Holocene stratigraphic record from the Outer Banks, North Carolina, USA

Foraminiferal and sedimentologic data were collected by vibracoring a small, relict, short-lived, migrating inlet (New Inlet) and its flood-tide delta on the Outer Banks, North Carolina. These data, placed in the context of geospatial data derived from ground penetrating radar, were developed into a stratigraphic model for this sedimentary environment. The model was applied to vibracores collected from two additional barrier island segments within which historic inlets had not been recorded to investigate whether inlets had existed in these segments in the past. Five foraminiferal biofacies were recognized within the three barrier island segments. Biofacies 1 through 5 are all associated with interior and back-barrier depositional environments but Biofacies 4 and 5 contained foram-inifera indicating a sediment source on the shoreface or shallow inner shelf. Biofacies 4 and 5 thus represent overwash or flood-tide delta depositional settings. Utilizing the model as an interpretive tool, we recognized a previously undocumented inlet and flood-tide delta that existed prior to 962-662 cal. yrs BP, a few kilometers north of Rodanthe, NC. However, at a barrier island segment between Avon and Buxton, NC., the lack of information on stratal geometry and foraminiferal assemblages meant that it could not be determined whether this sedimentary succession was influenced more by overwash or inlet dynamics. Given the similarity of foraminiferal assemblages in overwash and flood-tide delta sediments, it is clear that additional lines of evidence (lithologic and geospatial) are required to recognize small-scale flood-tide delta deposits in the subsurface.

Stratigraphy↗

USGS2008

Micropaleontologic record of late Pliocene and Quaternary paleoenvironments in the northern Albemarle Embayment, North Carolina, U.S.A.

Micropaleontological data provide a strong actualistic basis for detailed interpretations of Quaternary paleoenvironmental change. The 90 m-thick Quaternary record of the Albemarle Embayment in the mid-Atlantic coastal plain of the USA provides an excellent opportunity to use such an approach in a region where the details of Quaternary environmental change are poorly known. The foraminiferal record in nine cores from the northern Outer Banks, east of Albemarle Sound, North Carolina, indicates the deposition of subhorizontal, mostly open-marine early to late Pleistocene units unconformably upon a basement of late Pliocene reduced-oxygen, fine-grained, shelf-basin deposits. Pollen data record several warm–cool fluctuations within the early to mid-Pleistocene deposits. Diatom data indicate that some fresh and brackish-water units occur within the generally open-marine Pleistocene succession. A channel cut by the paleo-Roanoke River during the last glacial sea-level lowstand occurs in the northern part of the study area. Pollen indicates that the basal fluvial valley fill accumulated in cooler than modern climate conditions in the latest Pleistocene. Overlying silts and muds accumulated under cool climatic, estuarine conditions according to diatom and pollen data. Radiocarbon ages from the estuarine deposits indicate that the bulk of these sediments accumulated during the latest Pleistocene. The estuarine channel-fill deposits are overlain by Holocene open-marine sands deposited as the rising sea transgressed into the estuary approximately 8.5 to 9.0 kyr BP. Within the barrier island drill cores of this study, fully marine sedimentation occurred throughout the Holocene. However, immediately west of the present barrier island, mid- to late Holocene estuarine deposits underlie the modern Albemarle Sound. The islands that currently form a continuous barrier across the mouth of Albemarle Sound have a complex history of Holocene construction and destruction and large portions of them may be less than 3 kyr old. The barrier island sands overlie open-marine sands of Colington Shoal in the north and to the south overlie fluvial and marine sand filling paleo-Roanoke tributary valleys. The Pleistocene sediments underlying the northern Outer Banks study area are mainly of open inner to mid-shelf origin. If, as is likely, sea level continues to rise, a return to such environmental conditions is likely in the near future.

North Carolina↗

USGS2003

Sediment-starved sand ridges on a mixed carbonate/siliciclastic inner shelf off west-central Florida

High-resolution side-scan mosaics, sediment analyses, and physical process data have revealed that the mixed carbonate/siliciclastic, inner shelf of west-central Florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms. The sand ridges, mostly oriented obliquely to the shoreline trend, extend from 2 km to over 25 km offshore. They show many similarities to their well-known counterparts situated along the US Atlantic margin in that both increase in relief with increasing water depth, both are oriented obliquely to the coast, and both respond to modern shelf dynamics. There are significant differences in that the sand ridges on the west-central Florida shelf are smaller in all dimensions, have a relatively high carbonate content, and are separated by exposed rock surfaces. They are also shoreface-detached and are sediment-starved, thus stunting their development. Morphological details are highly distinctive and apparent in side-scan imagery due to the high acoustic contrast. The seafloor is active and not a relict system as indicated by: (1) relatively young AMS 14C dates (< 1600 yr BP) from forams in the shallow subsurface (1.6 meters below seafloor), (2) apparent shifts in sharply distinctive grayscale boundaries seen in time-series side-scan mosaics, (3) maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation, (4) sediment textural asymmetry indicative of selective transport across bedform topography, (5) morphological asymmetry of sand ridges and 2D dunes, and (6) current-meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded. Although larger sand ridges are found along other portions of the west-central Florida inner shelf, these smaller sand ridges are best developed seaward of a major coastal headland, suggesting some genetic relationship. The headland may focus and accelerate the N-S reversing currents. An elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf, allowing them to be more easily influenced by currents and surface gravity waves. Tidal currents, storm-generated flows, and seasonally developed flows are shore-parallel and oriented obliquely to the NW-SE trending ridges, indicating that they have developed as described by the Huthnance model. Although inner shelf sand ridges have been extensively examined elsewhere, this study is the first to describe them in a low-energy, sediment-starved, dominantly mixed siliciclastic/carbonate sedimentary environment situated on a former limestone platform. ?? 2003 Elsevier B.V. All rights reserved.

Florida↗