Geology Reports⌕ Search

Geology topics

Carlton E. Brett

Publications and source records attributed to Carlton E. Brett.

11 recordsLinked to original sources
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↗
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

Revised perspectives on Devonian biozonation and environmental volatility in the wake of recent time-scale revisions

Revised time-scales for the Devonian Period have highlighted major discrepancies in the frequency of evolutionary, eustatic, carbon cycle, and biotic events. The number of conodont biozones per million years shows strong variation among stages. Using two alternative time scales, the lowest values are in the Emsian and highest in the Givetian, Frasnian, and Famennian stages. A similar result is obtained by dividing the Devonian time scale into 12 equal 5-million year bins and determining the number of conodont zonal subdivisions in each bin. The record of ammonoid biozones also shows interesting parallels. The acuity of biostratigraphic zonation and zonal subdivisions appears to be correlative with the frequency of environmental perturbations, including eustatic, positive carbon isotopic excursions, and hypoxic/anoxic related bioevents, and these are similarly unevenly distributed. All calculations of environmental volatility metrics show the late Eifelian through early Frasnian to be the most volatile interval of the Devonian, followed by the mid-late Famennian, while the Lochkovian through Emsian and mid-Frasnian through early Famennian are the least volatile. Furthermore, the majority of major bioevents occur in the Eifelian through early Frasnian, and late Famennian. The strong evidence for higher biotic and environmental volatility in the late Eifelian through early Frasnian and late Famennian rock record corresponds to the coolest paleoclimate conditions in the Devonian according to recent conodont apatite δ18O compilations, and the transition from an overall cooling to warming paleotemperature trend during the mid-Givetian. Regardless of mechanism, strong variations in volatility occurred during the Devonian Period. Intervals with greater biostratigraphic resolution also show much stronger environmental volatility including a series of relatively quasi-stable conditions punctuated by major turnovers with abrupt sea-level rise, widespread hypoxia, and changes in the carbon cycle. It was during these intervals that much net evolutionary and ecological change appears to have taken place.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
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

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

The rise of pinnacle reefs: Islands of diversity in seas of despair

Pinnacle reef tracts are geomorphic features of carbonate systems that originated in the early Silurian and display an episodic distribution into the Cenozoic. Detailed study of Silurian pinnacle reefs of the United States midcontinent demonstrates repeated motifs, but most enigmatic is the coincidence of carbonate carbon isotope (δ 13 C carb ) excursions and reef pulses. Silurian δ 13 C carb excursions were associated with environmental changes and extinctions, and reefs appear to mark a resurgence of conditions favorable to biomineralizers following those extinction events. Previous workers in the region identified six discrete reef origination events in the United States midcontinent during the Silurian. Our reevaluation of outcrops and cores, conodont collections, and the generation of considerable new chemostratigraphic data across the region are clarifying the age relations of these events and their relationships to perturbations of the global carbon cycle.

Book chapter↗
USGS2011

Sequence stratigraphy and a revised sea-level curve for the Middle Devonian of eastern North America

The well-exposed Middle Devonian rocks of the Appalachian foreland basin (Onondaga Formation; Hamilton Group, Tully Formation, and the Genesee Group of New York State) preserve one of the most detailed records of high-order sea-level oscillation cycles for this time period in the world. Detailed examination of coeval units in distal areas of the Appalachian Basin, as well as portions of the Michigan and Illinois basins, has revealed that the pattern of high-order sea-level oscillations documented in the New York–Pennsylvania section can be positively identified in all areas of eastern North America where coeval units are preserved. The persistence of the pattern of high-order sea-level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea-level oscillation, as opposed to autocylic controls, such as sediment supply, which would be more local in their manifestation. There is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to Milankovitch orbital variations, with the short and long-term eccentricity cycles (100 kyr and 405 kyr) being the dominant oscillations in many settings. Relative sea-level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism, given that the Middle Devonian appears to record a greenhouse phase of Phanerozoic history. These new correlations lend strong support to a revised high-resolution sea-level oscillation curve for the Middle Devonian for the eastern portion of North America. Recognized third-order sequences are: Eif-1 lower Onondaga Formation, Eif-2: upper Onondaga and Union Springs formations; Eif–Giv: Oatka Creek Formation; Giv-1: Skaneateles, Giv-2: Ludlowville, Giv-3: lower Moscow, Giv-4: upper Moscow–lower Tully, and Giv-5: middle Tully–Geneseo formations. Thus, in contrast with the widely cited eustatic curve of Johnson et al. (1985), which recognizes just one major transgressive–regressive (T–R) cycle in the early–mid Givetian (If) prior to the major late Givetian Taghanic unconformity (IIa, upper Tully–Geneseo Shale), we recognize four T–R cycles: If (restricted), Ig, Ih, and Ii. We surmise that third-order sequences record eustatic sea-level fluctuations of tens of meters with periodicities of 0.8–2 myr, while their medial-scale (fourth-order) subdivisions record lesser variations primarily of 405 kyr duration (long-term eccentricity). This high-resolution record of sea-level change provides strong evidence for high-order eustatic cycles with probable Milankovitch periodicities, despite the fact that no direct evidence for Middle Devonian glacial sediments has been found to date.

Wisconsin, Illinois, Michigan, Indiana, Kentucky, ↗
USGS2010

Paleobiogeography, high-resolution stratigraphy, and the future of Paleozoic biostratigraphy: Fine-scale diachroneity of the Wenlock (Silurian) conodont Kockelella walliseri

The Wenlock Epoch of the Silurian Period has become one of the chronostratigraphically best-constrained intervals of the Paleozoic. The integration of multiple chronostratigraphic tools, such as conodont and graptolite biostratigraphy, sequence stratigraphy, and ??13Ccarb chemostratigraphy, has greatly improved global chronostratigraphic correlation and portions of the Wenlock can now be correlated with precision better than ??100kyr. Additionally, such detailed and integrated chronostratigraphy provides an opportunity to evaluate the fidelity of individual chronostratigraphic tools. Here, we use conodont biostratigraphy, sequence stratigraphy and carbon isotope (??13Ccarb) chemostratigraphy to demonstrate that the conodont Kockelella walliseri, an important guide fossil for middle and upper Sheinwoodian strata (lower stage of the Wenlock Series), first appears at least one full stratigraphic sequence lower in Laurentia than in Baltica. Rather than serving as a demonstration of the unreliability of conodont biostratigraphy, this example serves to demonstrate the promise of high-resolution Paleozoic stratigraphy. The temporal difference between the two first occurrences was likely less than 1million years, and although it is conceptually understood that speciation and colonization must have been non-instantaneous events, Paleozoic paleobiogeographic variability on such short timescales (tens to hundreds of kyr) traditionally has been ignored or considered to be of little practical importance. The expansion of high-resolution Paleozoic stratigraphy in the future will require robust biostratigraphic zonations that embrace the integration of multiple chronostratigraphic tools as well as the paleobiogeographic variability in ranges that they will inevitably demonstrate. In addition, a better understanding of the paleobiogeographic migration histories of marine organisms will provide a unique tool for future Paleozoic paleoceanography and paleobiology research. ?? 2010 Elsevier B.V.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2008

Hierarchy of sedimentary discontinuity surfaces and condensed beds from the middle Paleozoic of eastern North America: Implications for cratonic sequence stratigraphy

Sedimentological analyses of middle Paleozoic epeiric sea successions in North America suggest a hierarchy of discontinuity surfaces and condensed beds of increasing complexity. Simple firmgrounds and hardgrounds, which are comparatively ephemeral features, form the base of the hierarchy. Composite hardgrounds, reworked concretions, authigenic mineral crusts and monomictic intraformational conglomerates indicate more complex histories. Polymictic intraformational conglomerates, ironstones and phosphorites form the most complex discontinuity surfaces and condensed beds. Complexity of discontinuities is closely linked to depositional environments duration of sediment starvation and degree of reworking which in turn show a relationship to stratigraphic cyclicity. A model of cratonic sequence stratigraphy is generated by combining data on the complexity and lateral distribution of discontinuities in the context of facies successions. Lowstand, early transgressive and late transgressive systems tracts are representative of sea-level rise. Early and late transgressive systems tracts are separated by the maximum starvation surface (typically a polymictic intraformational conglomerate or condensed phosphorite), deposited during the peak rate of sea-level rise. Conversely the maximum flooding surface, representing the highest stand of sea level, is marked by little to no break in sedimentation. The highstand and falling stage systems tracts are deposited during relative sea-level fall. They are separated by the forced-regression surface, a thin discontinuity surface or condensed bed developed during the most rapid rate of sea-level fall. The lowest stand of sea level is marked by the sequence boundary. In subaerially exposed areas it is occasionally modified as a rockground or composite hardground.

Conference Paper↗
USGS2007

Eo-Ulrichian to Neo-Ulrichian views: The renaissance of "layer-cake stratigraphy"

Classical notions of "layer-cake stratigraphy" have been denigrated as representing an antiquated "Neptunian" view of the geologic record with the American paleontologist-stratigrapher E.O. Ulrich vilified as its quintessential advocate. Some of the extreme "layer-cake" interpretations of E.O. Ulrich are demonstrably incorrect, especially where applied in marginal marine and terrestrial settings. However, close scrutiny of Ulrich's work suggests that the bulk was correct and demonstrated considerable insight for the time. Subsequent development of facies concepts revolutionized geologists' view of time-space relationships in stratigraphy, but rather than focusing on facies patterns within the established stratigraphic (layer-cake) frameworks many geologists in North America came to view strata as parts of diachronous facies mosaics. Recent advances in the development of event and sequence stratigraphic paradigms are beginning to swing the pendulum back the other way. Possible causes of "layer-cake" patterns are numerous and varied, including: (1) parallelism of depositional strike and outcrop belts, especially in foreland basins, (2) very widespread environmental belts developed in low-relief cratonic areas, (3) time-averaging homogenizes facies to a limited extent, resulting in a very subtle signature of lateral change, (4) condensed beds (hardgrounds, bone beds, ironstones, etc.) often form in responses to extrabasinal forces, thus they cross-cut facies, and (5) large events (i.e. hurricanes, floods, tsunamis, eruptions, etc.) are "over represented" in the rock record. A revised ("Neo-Ulrichian") layer-cake paradigm carries many of the original correct empirical observations of pattern, noted by Ulrich, recast in terms of event and sequence stratigraphy.

Conference Paper↗