Geology topics

Lucy E. Edwards

Publications and source records attributed to Lucy E. Edwards.

At least 19 recordsLinked to original sources

USGS2026

Capitalization of positional (Lower/Middle/Upper) and temporal (Early/Middle/Late) adjectives in the names of formal chronostratigraphic and geochronologic units of the Phanerozoic

Many authors are understandably confused about the capitalization of the words “lower,” “middle,” “upper,” “early,” and “late.” Where these words are used simply as descriptive adjectives, they should be in lowercase; where they form the first word of a formal chronostratigraphic or geochronologic unit name, they should be in uppercase.

Professional Paper↗

USGS2026

Report 17—Revisions to the articles of organization and procedure of the Commission on Stratigraphic Nomenclature of the Americas

Several revisions to the Articles of Organization and Procedure for the North American Commission on Stratigraphic Nomenclature have been adopted following the 75th, 79th, and 80th annual meetings of the Commission in 2020, 2024 and 2025, respectively. Of these, the most substantial change was revision of Article III regarding membership composition of the Commission and the addition of new member organizations from Central and South America and the Caribbean region. As a result, the Commission also voted to change its name to be more inclusive of the expanding membership, with approval of the name: Commission on Stratigraphic Nomenclature of the Americas. A corresponding change to the Commission’s fundamental publication was also approved at the 2025 meeting as the Stratigraphic Code of the Americas (formerly the North American Stratigraphic Code). Additional revisions to the Articles include those aimed at ensuring gender neutrality of titles, permission to hold virtual meetings, and processes for designating new Commissioners. Article V was also modified to define quorum for meetings and the nature of a two-thirds majority vote, with the process for making amendments to the Articles modified to specify that a two-thirds majority vote is required. These revisions are reflected in the following bylaws, which otherwise are as adopted by the Commission under its former name (North American Commission on Stratigraphic Nomenclature) at its 62nd annual meeting in 2007 amended by mail ballot, and published by Owen et al. (2009). The amended bylaws printed below became effective at the close of the 80th annual meeting in 2025 and supersede all previous versions (Moore 1947; Hutchinson 1953; Owen et al. 1985; 2009)

Stratigraphy↗

USGS2023

Divisions of geologic time—Major chronostratigraphic and geochronologic units

Introduction Effective communication in the geosciences requires consistent use of stratigraphic nomenclature, especially divisions of geologic time. A geologic time scale is composed of standard stratigraphic divisions that are based on rock sequences and is calibrated in years (Harland and others, 1982). Over the years, the development of new dating methods and the refinement of previous ones have stimulated revisions to geologic time scales. Since the mid-1990s, geologists from the U.S. Geological Survey (USGS), State geological surveys, academia, and other organizations have sought a consistent time scale that can be used in communicating ages of geologic units in the United States. Many international debates have occurred over the names and boundaries of units, and various time scales have been used by the geoscience community in years past (for example, U.S. Geological Survey Geologic Names Committee [USGS GNC], 2007, 2010, 2018). However, the numerical ages assigned to geochronologic units frequently change as the science of stratigraphy moves forward. Once ratified, changes in numerical ages are recorded by the International Commission on Stratigraphy (ICS) on their website ( https://stratigraphy.org/chart ). In addition, such advances in stratigraphy and changes in geochronology require that any time scale be periodically updated. Therefore, the time scale presented in this report (hereafter referred to as “Divisions of Geologic Time”) is dynamic, and it is modified as needed to include accepted changes of unit names and boundary age estimates (USGS GNC, 2007, 2010, 2018).

Professional Paper↗

USGS2022

The Anthropocene as an event, not an epoch

Over the course of the last decade the concept of the Anthropocene has become widely established within and beyond the geoscientific literature but its boundaries remain undefined. Formal definition of the Anthropocene as a chronostratigraphical series and geochronological epoch following the Holocene, at a fixed horizon and with a precise global start date, has been proposed, but fails to account for the diachronic nature of human impacts on global environmental systems during the late Quaternary. By contrast, defining the Anthropocene as an ongoing geological event more closely reflects the reality of both historical and ongoing human–environment interactions, encapsulating spatial and temporal heterogeneity, as well as diverse social and environmental processes that characterize anthropogenic global changes. Thus, an Anthropocene Event incorporates a substantially wider range of anthropogenic environmental and cultural effects, while at the same time applying more readily in different academic contexts than would be the case with a rigidly defined Anthropocene Series/Epoch.

Journal of Quaternary Science↗

USGS2021

A practical solution: The Anthropocene is a geological event, not a formal epoch

The Anthropocene has yet to be defined in a way that is functional both to the international geological community and to the broader fields of environmental and social sciences. Formally defining the Anthropocene as a chronostratigraphical series and geochronological epoch with a precise global start date would drastically reduce the Anthropocene’s utility across disciplines. Instead, we propose the Anthropocene be defined as a geological event, thereby facilitating a robust geological definition linked with a scholarly framework more useful to and congruent with the many disciplines engaging with human-environment interactions. Unlike formal epochal definitions, geological events can recognize the spatial and temporal heterogeneity and diverse social and environmental processes that interact to produce anthropogenic global environmental changes. Consequently, an Anthropocene Event would incorporate a far broader range of transformative human cultural practices and would be more readily applicable across academic fields than an Anthropocene Epoch, while still enabling a robust stratigraphic characterization.

Episodes↗

USGS2020

North American commission on stratigraphic nomenclature report 14 – Revision of articles 25-27 of the North American stratigraphic code to formalize subseries and subepochs

At the 75th Annual Meeting of the North American Commission on Stratigraphic Nomenclature, 22 October, 2020, in connection with GSA 2020 Connects Online, the Commission voted unanimously to accept the revision of Articles 73, 81 and 82 of the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 2005 with subsequent updates), and concomitant changes to Table 2; specific revisions of the Code are indicated in red color. These replace all older versions of the specified Articles. An application for this revision (Aubry et al. 2019) was published in Stratigraphy more than one year prior to the meeting; thus, the vote on this application for revision follows Article 21 of the Code.

Stratigraphy↗

USGS2020

Cross section of the North Carolina coastal plain from Enfield through Cape Hatteras

Introduction The Atlantic Coastal Plain, the southeasternmost physiographic province in the United States, is underlain by strata that regionally dip gently eastward and gradually thicken toward the Atlantic Ocean basin. These strata, ranging in age from Middle Jurassic to Holocene, accumulated along the eastern margin of North America after the break-up of the supercontinent Pangaea during the Early Jurassic. In the east-central United States north of Florida, Cape Hatteras is the point of land that most closely approaches the eastern edge of the Atlantic Continental Shelf of the United States. In 1946, Esso (now part of ExxonMobil) drilled a deep oil exploration well to basement rock near the Cape Hatteras lighthouse. No oil or gas was found there, or in any of the other test wells that were drilled within the onshore North Carolina Coastal Plain. Recent work indicates that the top of the oil window lies at 9,000 feet near the base of the Cape Hatteras Esso #1 test well. Therefore, any mature petroleum source rocks that may be present in the North Carolina Coastal Plain are only likely to be found east of the present coastline. Although the Cape Hatteras test well did not produce oil or gas, it did produce a wealth of stratigraphic information about the outer portion of the onshore Atlantic Continental Shelf. Advances in global stratigraphic correlation, in tandem with our analyses of calcareous nannofossils and dinoflagellate cysts (dinocysts) from the Cape Hatteras test-well spot samples have produced significant advances beyond earlier interpretations of this well and other deep test wells inshore of Cape Hatteras. These results, when coupled with work done offshore of Cape Hatteras, have allowed us to create a more detailed cross section of the North Carolina Coastal Plain and adjacent continental shelf than previously possible.

North Carolina↗

USGS2020

North American Commission on Stratigraphic Nomenclature Note 70: Records of the Stratigraphic Commission 2014-2017

NACSN (North American Commission on Stratigraphic Nomenclature) Note 70 is a summary of the activities of the Commission from October 2014-October 2017. This note is condensed from the minutes of the 69th through the 72nd meetings of the NACSN held in conjunction with the Annual Meetings of the Geological Society of America. The 69th meeting of the NACSN was held October 20, 2014, in Vancouver, British Columbia; the 70th meeting on November 2, 2015, in Baltimore, Maryland; the 71st meeting on September 26, 2016, in Denver, Colorado; and the 72nd meeting on October 23, 2017, in Seattle, Washington. Members of the NACSN who served as officers during the period 2014-2017 serve as co-authors of this note and are listed with their roles in Appendix A. The mission of the NACSN is to develop statements of stratigraphic principles, recommend procedures applicable to the classification of nomenclature of stratigraphic units, review problems in classifying and naming stratigraphic and related units, and formulate expressions of judgement on these matters. Commissioners of the NACSN represent various geoscience professional organizations from Canada, Mexico, and the United States who have an interest in maintaining a stable stratigraphic nomenclature. Commissioners and their constituencies for 2014-2017 are listed in Appendix B.

Stratigraphy↗

USGS2019

Geology of the Hardeeville NW Quadrangle and parts of the Brighton and Pineland Quadrangles, Jasper County, South Carolina

Introduction This publication portrays the geology of the Hardeeville NW quadrangle and parts of the Brighton and Pineland quadrangles that are within Jasper County, South Carolina. The study area is located in the Atlantic Coastal Plain province, approximately 50 to 70 kilometers (km) inland from the coast. The data are compiled from geological field mapping, light detection and ranging (lidar) elevation data, cores, optically stimulated luminescence ages, radiocarbon ages, and biostratigraphic interpretations. Most of the study area is occupied by the valley of the Savannah River, and exposures of geologic units are very limited. Traditional geologic mapping in this area is difficult because of limited access, subdued topography, extensive swamps, and abundant vegetation. The Savannah River flows predominantly southeast, and forms most of the border between the States of South Carolina and Georgia. The river is approximately 483 km long and has a total drainage area of approximately 15,850 square km. Although upstream tributaries drain the southeastern side of the Appalachian Blue Ridge province, the Savannah River begins in the Piedmont province and then flows across the Atlantic Coastal Plain province to the Atlantic Ocean. For much of its extent, the modern channel of the Savannah River is located on the southwestern side of the river valley, and the southwestern bank of the valley is the active cut bank. Within the study area, the valley of the Savannah River trends southeast and is relatively straight. The valley has relatively low relief, although the southwestern valley wall is steeper and has greater relief than the northeastern valley wall. Elevations within the valley mostly range from 3 to 15 meters (m) above sea level, whereas elevations on the high terrace that forms the eastern margin of the Savannah River valley are 15 to 20 m above sea level. The width of the valley is 6 to 7 km in the northern part of the study area and expands to 10 to 12 km farther south. The modern river channel occupies the southwestern side of the valley, and some modern (active) creeks enter the river from the west. Sand hills and low-relief terraces are present to the east of the modern river channel, and the eastern side of the valley is characterized by abandoned meandering and linear channels. Fan-shaped deposits of sand and mud are present where relict (inactive) channels enter the eastern side of the valley. Abandoned meandering channels of low relief (<3 m) are also present to the east on the high terrace (>15 m elevation) that forms the eastern margin of the Savannah River valley. Within the study area, most of the Savannah River valley is covered by alluvial wetland community vegetation dominated by cypress and tupelo trees, although sand hills within the valley are covered by xeric sand community vegetation dominated by pine trees.

South Carolina↗

USGS2019

North American Commission on Stratigraphic Nomenclature Note 69 – Application for addition of subseries/subepoch to the North American Stratigraphic Code

Consistency in stratigraphic nomenclature enables communication among scientists both regionally and globally, thus requiring the North American Stratigraphic Code, as presented by the North American Commission on Stratigraphic Nomenclature, to follow international convention. The ratification of three subseries of the Holocene by the InternationalUnion of Geological Sciences (IUGS) in June 2018 warrants the integration of subseries among formal chronostratigraphic ranks in the Code. The purpose ofmaking subseries a formal rank is that it aligns the Code with the International StratigraphicGuide, and establishes the option of using the prefixes super- and sub- for other chronostratigraphic and geochronologic ranks. This is in accordance with the guiding principle of the Code to make it as consistent as possible with international usage and to foster innovations to meet the expanding and changing needs of earth scientists.

Stratigraphy↗

USGS2018

A fossiliferous spherule-rich bed at the Cretaceous–Paleogene (K–Pg) boundary in Mississippi, USA: Implications for the K–Pg mass extinction event in the Mississippi Embayment and Eastern Gulf Coastal Plain

We describe an outcrop of the Cretaceous–Paleogene (K–Pg) boundary exposed due to construction near New Albany, Union County, Mississippi. It consists of the Owl Creek Formation and overlying Clayton Formation. The Owl Creek Formation is rich in the ammonites Discoscaphites iris and Eubaculites carinatus, which, along with biostratigraphically important dinoflagellate cysts and calcareous nannofossils, indicate deposition occurred within the last 1 million years, most likely last 500 kyrs, of the Cretaceous. The base of the overlying Clayton Formation marks the K–Pg boundary, and consists of a 15-30 cm thick muddy, poorly sorted quartz sand containing abundant spherules representing ejecta derived from the Chicxulub impact event. Impact spherules range in size from 0.5 mm to 1 mm in diameter and are hollow and well preserved, with details such as smaller vesicular spherules enclosed within. The spherules are altered to clay minerals such as smectite and are typical of those found at K–Pg boundary sites in the Gulf of Mexico and beyond. Spherules are scattered throughout the bed, and surface counts suggest an average of 4 spherules per cm2. Macrofossils within the spherule bed represent a rich fauna of ammonites, benthic molluscs (bivalves and gastropods), echinoids, as well as crabs and sharks. Macrofossil preservation ranges from whole to fragmentary, with most fossils preserved as internal moulds. The infill of the fossils is lithologically identical to the matrix of the spherule bed, including impact ejecta preserved within phagmocones and body chambers of ammonites, and differs from the underlying Owl Creek Formation. This suggests that the animals were either alive or loosely scattered on the sea floor at the time of deposition. Grain size changes indicate multiple events were responsible for deposition, and together with taphonomic evidence are consistent with dynamic high energy post-impact processes. Later sea level change during the Paleocene is responsible for a sharp contact at the top of the spherule bed. Geochemical evidence from the Owl Creek and Clayton Formations at this locality indicate numerous local palaeoenvironmental changes affected the Mississippi Embayment at the time of the K–Pg boundary and mass extinction event.

Mississippi↗

USGS2018

The significance of dinoflagellates in the Miocene Choptank Formation beneath the Midlothian gravels in the southeastern Virginia Piedmont

The Fall Line (formally "Tidewater Fall Line") separates the more resistant igneous, metamorphic, and consolidated sedimentary rocks of the Piedmont from the typically unconsolidated deposits of the Coastal Plain of Virginia. Widespread but now discontinuous patches of a deeply weathered sand and gravel are found west of the Fall Line, capping the highest hilltops. Near the community of Midlothian, Virginia, the gravels are underlain by fine-grained marine silts that bear an informative assemblage of fossil dinoflagellate cysts (dinocysts). In situ dinocysts belong to middleMiocene zone DN7, which is calibrated to ~12-13 Ma. These deposits are assigned to the upper part of the Choptank Formation, which crops out ~ 25 km(15 mi) to the east at an elevation ~ 60m(200 ft) lower. The dinocyst assemblage suggests that the maximum extent of this Choptank transgression probably covered a significant expanse of the Virginia Piedmont. The Choptank marine silts constrain the age of the unconformably overlying Midlothian gravels to younger than the latter part of the middle Miocene. Previous work has indicated that these gravels also are older than the Pliocene Yorktown Formation. Rare, reworked dinocysts in these Choptank outcrops west of the Fall Line are sourced from older deposits of more than one age. The source could be older updip strata of the lower Eocene Nanjemoy Formation, now erosionally removed. Alternatively, the source could be material referable to the upper Eocene Exmore Formation that resulted from the Chesapeake Bay impact event.

Miocene Choptank Formation↗

USGS2017

Shallow marine response to global climate change during the Paleocene-Eocene Thermal Maximum, Salisbury Embayment, USA

The Paleocene-Eocene Thermal Maximum (PETM) was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale. Here we examine the sediments, flora, and fauna from an expanded section at Mattawoman Creek-Billingsley Road (MCBR) in Maryland and explore the impact of warming at a nearshore shallow marine (30–100 m water depth) site in the Salisbury Embayment. Observations indicate that at the onset of the PETM, the site abruptly shifted from an open marine to prodelta setting with increased terrestrial and fresh water input. Changes in microfossil biota suggest stratification of the water column and low-oxygen bottom water conditions in the earliest Eocene. Formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift, while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites. This proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12 C-enriched CO 2 . We conclude that the MCBR site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming.

Maryland, New Jersey, Pennsylvania, Virginia↗

USGS2017

Geology and biostratigraphy of the Potomac River cliffs at Stratford Hall, Westmoreland County, Virginia

The cliffs along the Potomac River at Stratford Hall display extensive exposures of Miocene marine strata that belong successively to the Calvert, Choptank, St. Marys, and Eastover Formations. Within the lower part of this sequence, in the Calvert and Choptank Formations, there is well-developed cyclic stratigraphy. Above the Miocene units lies the marginal marine to deltaic Pleistocene Bacons Castle Formation, which is the highest and youngest formation exposed in the cliffs. The goals of this field trip guide are to (1) show the Miocene formations exposed in the cliffs and discuss the paleoenvironments within which they formed, (2) demonstrate the cyclicity in the Miocene marine formations and discuss its origin, (3) compare and contrast the section exposed at the Stratford and Nomini Cliffs with the classic Miocene Calvert Cliffs sequence exposed to the northeast in Calvert County, Maryland, and the Miocene sequence recovered in the Haynesville cores to the southeast in Richmond County, Virginia, (4) discuss and explain why a detailed correlation among these three places has been so difficult to attain, and (5) show typical lithologies of the Bacons Castle Formation and discuss the paleoenvironments in which they formed.

Virginia↗

USGS2017

North American Commission on Stratigraphic Nomenclature Report 12 – Revision of article 37, lithodemic units, of the North American Stratigraphic Code

At the 71st Annual Meeting of the North American Commission on Stratigraphic Nomenclature, 26 September, 2016, in Denver, Colorado, the Commission voted unanimously to accept the revision of Article 37 of the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 2005), printed below. It replaces all older versions of this Article. An application for this revision (Easton et al. 2015) was published in Stratigraphy more than one year prior to the meeting; thus, the vote on this application for revision follows Article 21 of the Code.

Stratigraphy↗

USGS2016

A new specimen of Agorophius pygmaeus (Agorophiidae, Odontoceti, Cetacea) from the Early Oligocene Ashley Formation of South Carolina, USA

The holotype partial skull of Agorophius pygmaeus (the monotypic form for both the genus Agorophius and the Family Agorophiidae) has been missing for approximately 140 years. Since the discovery of Agorophius pygmaeus , many additional taxa and specimens have been placed in the Family Agorophiidae, only to be reclassified and removed later. This has created confusion as to what is and what is not an agorophiid and a lack of clarity as to what characteristics delimit the Agorophiidae. A newly discovered skull of an agorophiid recently collected from an underwater cliff face of the Ashley River, South Carolina, USA, is assigned to Agorophius pygmaeus . It derives from the base of the Ashley Formation (early Oligocene). The new specimen consists of most of the skull and periotics, which are well preserved and described for the first time in an agorophiid. The new specimen provides an opportunity to diagnose the Agorophiidae and place the genus and species within the phylogenetic context of the early odontocete radiation in the Oligocene, along with other taxa such as the Ashleycetidae, Mirocetidae, Patriocetidae, Simocetidae, Waipatiidae, and Xenorophidae. Based on this new understanding, Agorophiidae are known with certainty only from the early Oligocene of South Carolina, with other undescribed, potential agorophiid specimens from the Oligocene of the North Pacific region (Japan, Mexico, and Washington State).

South Carolina↗

USGS2016

Erosional and depositional history of the Atlantic passive margin as recorded in detrital zircon fission-track ages and lithic detritus in Atlantic Coastal plain sediments

Comparison of fission-track (FT) ages of detrital zircons recovered from Atlantic Coastal Plain sediments to FT ages of zircons from bedrock in source terranes in the Appalachians provides a key to understanding the provenance of the sediments and, in turn, the erosional and depositional history of the Atlantic passive margin. In Appalachian source terranes, the oldest zircon fission-track (ZFT) ages from bedrock in the western Appalachians (defined for this paper as the Appalachian Plateau, Valley and Ridge, and far western Blue Ridge) are notably older than the oldest ages from bedrock in the eastern Appalachians (Piedmont and main part of the Blue Ridge). The age difference is seen both in ZFT sample ages and in individual zircon grain ages and reflects differences in the thermotectonic history of the rocks. In the east, ZFT data indicate that the rocks cooled from temperatures high enough to partially or totally reset ZFT ages during the Paleozoic and (or) Mesozoic. The majority of the rocks are interpreted to have cooled through the ZFT closure temperature (∼235 °C) at various times during the late Paleozoic Alleghanian orogeny. In contrast, most of the rocks sampled in the western Appalachians have never been heated to temperatures high enough to totally reset their ZFT ages. Reflecting their contrasting thermotectonic histories, nearly 80 percent of the sampled western rocks yield one or more zircon grains with very old FT ages, in excess of 800 Ma; zircon grains yielding FT ages this old have not been found in rocks in the Piedmont and main part of the Blue Ridge. The ZFT data suggest that the asymmetry of zircon ages of exposed bedrock in the eastern and western Appalachians was in evidence by no later than the Early Cretaceous and probably by the Late Triassic. Detrital zircon suites from sands collected in the Atlantic Coastal Plain provide a record of detritus eroded from source terranes in the Appalachians during the Mesozoic and Cenozoic. In Virginia and Maryland, sands of Early Cretaceous through late early Oligocene age do not yield any old zircons comparable in age to the old zircons found in bedrock in the western Appalachians. Very old zircons yielding FT ages >800 Ma are only encountered in Coastal Plain sands of middle early Miocene and younger age. Miocene and younger fluvial-deltaic deposits associated with the major mid-Atlantic Coastal Plain rivers that now head in the western Appalachians (the Hudson, Delaware, Susquehanna, Potomac, James, and Roanoke) contain abundant clasts of fossiliferous chert and quartzite and other distinctive rock types derived from Paleozoic rocks of the western Appalachians. These distinctive clasts have not been reported in older Coastal Plain sediments. The ZFT and lithic detritus data indicate that the drainage divide for one or more east-flowing mid-Atlantic rivers migrated west into the western Appalachians, and the river(s) began transporting western Appalachian detritus to the Atlantic Coastal Plain, sometime between the late early Oligocene and middle early Miocene. By no later than late middle Miocene most if not all of the major rivers that now head west of the Blue Ridge were transporting western Appalachian detritus to the Coastal Plain. Prior to the drainage divide migrating into the western Appalachians, the ZFT data are consistent with the dominant source of Atlantic Coastal Plain sediments being detritus from the Piedmont and main part of the Blue Ridge, with possible input from distant volcanic sources. The ZFT data suggest that the rapid increase in the rate of siliciclastic sediment accumulation in middle Atlantic margin offshore basins that peaked in the middle Miocene and produced almost 30 percent of the total volume of post-rift siliciclastic sediments in the offshore basins began in the early Miocene when Atlantic river(s) gained access to the relatively easily eroded Paleozoic sedimentary rocks of the western Appalachians.

American Journal of Science↗

USGS2016

The “Anthropocene” epoch: Scientific decision or political statement?

The proposal for the “Anthropocene” epoch as a formal unit of the geologic time scale has received extensive attention in scientific and public media. However, most articles on the Anthropocene misrepresent the nature of the units of the International Chronostratigraphic Chart, which is produced by the International Commission on Stratigraphy (ICS) and serves as the basis for the geologic time scale. The stratigraphic record of the Anthropocene is minimal, especially with its recently proposed beginning in 1945; it is that of a human lifespan, and that definition relegates considerable anthropogenic change to a “pre-Anthropocene.” The utility of the Anthropocene requires careful consideration by its various potential users. Its concept is fundamentally different from the chronostratigraphic units that are established by ICS in that the documentation and study of the human impact on the Earth system are based more on direct human observation than on a stratigraphic record. The drive to officially recognize the Anthropocene may, in fact, be political rather than scientific.

GSA Today↗