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North American Land Mammal Ages
The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when referring to the rock strata of that age) and were established using geographic place names where fossil materials were obtained. System The North American land-mammal-age system was formalized in 1941 as a series of provincial land-mammal ages. The system was the standard for correlations in the terrestrial Cenozoic record of North America and was the source for similar time scales dealing with other continents. The system was revised into a formal chronostratigraphic system. This approach is nominally justified by international stratigraphic codes; it holds that first appearances of individual species in particular sections are the only valid basis for naming and defining the land-mammal ages. The basic unit of measure is the first/las ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geologic Time Scale
The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of geology that aims to determine the age of rocks). It is used primarily by Earth scientists (including geologists, paleontologists, geophysicists, geochemists, and paleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardised international units of geological time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to preci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Megaannum
A year is a unit of time based on how long it takes the Earth to orbit the Sun. In scientific use, the tropical year (approximately 365 solar days, 5 hours, 48 minutes, 45 seconds) and the sidereal year (about 20 minutes longer) are more exact. The modern calendar year, as reckoned according to the Gregorian calendar, approximates the tropical year by using a system of leap years. The term 'year' is also used to indicate other periods of roughly similar duration, such as the lunar year (a roughly 354-day cycle of twelve of the Moon's phasessee lunar calendar), as well as periods loosely associated with the calendar or astronomical year, such as the seasonal year, the fiscal year, the academic year, etc. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the planet, four seasons are gener ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Duchesnean
The Duchesnean North American Stage on the geologic timescale is a North American Land Mammal Age (NALMA), with an age from 42 to 38 million years BP, representing . It falls within the Eocene epoch. The Duchesnean is preceded by the Uintan and followed by the Chadronian NALMA. The Duchesnean falls within the Bartonian age of the geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochron .... References {{geochronology-stub Eocene life Eocene animals of North America ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chadronian
The Chadronian is a North American Land Mammal Age typically set from around 37,000,000 to 33,700,000 years BP, a period of . The Chadronian is preceded by the Duchesnean and followed by the Orellan NALMA stages. Relative to global geological chronology (the geologic time scale), it is usually considered to fall within the later part (Priabonian stage) of the Eocene epoch, ending around the same time as the Eocene-Oligocene boundary. The Chadronian is named after the Chadron Formation, a widespread component of the White River Group in Nebraska and South Dakota. The most well-studied examples of Chadronian strata in the White River Group/Formation are the Flagstaff Rim area of eastern Wyoming and the Toadstool Park area of northwest Nebraska. The beginning of the Chadronian is defined by the first appearance of '' Bathygenys'' (a merycoidodontid, or " oreodont"). Other mammals which first appear at the start of the stage include '' Merycoidodon dunagani'' (a merycoidodontid) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orellan
The Orellan is a North American Land Mammal Age typically set from around 33,700,000 to 32,000,000 years BP, a period of . The Orellan is preceded by the Chadronian and followed by the Whitneyan NALMA stages. Relative to global geological chronology (the geologic time scale), it is usually considered to fall within the earliest part (early Rupelian stage) of the Oligocene epoch, beginning around the same time as the Eocene-Oligocene boundary. The Orellan is named after the Orella Member of the Brule Formation, a widespread subunit of the White River Group. The Orella Member crops out most extensively in northwest Nebraska and eastern Wyoming. In the White River badlands of southwest South Dakota, an equally extensive Orellan component of the Brule Formation is known as the Scenic Member. Orellan strata of the Brule Formation can be found in more restricted exposures across northeast Colorado (Cedar Creek Member) and North Dakota. Certain sites in Montana preserve Orellan mammals: ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Whitneyan
The Whitneyan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 33,300,000 to 30,800,000 years BP, a period of . It is usually considered to fall within the Early Oligocene. The Whitneyan is preceded by the Orellan and followed by the Arikareean NALMA stages. The Whitneyan is interchangeable with the Rupelian The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ... age. References Oligocene life Oligocene animals of North America {{geochronology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arikareean
The Arikareean North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 30,600,000 to 20,800,000 years BP, a period of . It is usually considered to overlap the Oligocene and Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ... epochs. The Arikareean is preceded by the Whitneyan and followed by the Hemingfordian NALMA stages. The Arikareean can be further divided into the substages of: *late Late Arikareean: Lower boundary source, base of Geringian (approximate) *early Late Arikareean: base of Geringian (approximate). Upper boundary source: base of Hemingfordian (approximate). *late Early Arikareean: Lower boundary source of base of Geringian (approximate). Upp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemingfordian
The Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the latest Aquitanian and Burdigalian of the Early Miocene. The Hemingfordian is preceded by the Arikareean and followed by the Barstovian NALMA stages. The Hemingfordian can be further divided into the substages of: *Late/Upper Hemingfordian: Lower boundary source: base of Burdigalian The Burdigalian is, in the geologic timescale, an age (geology), age or stage (stratigraphy), stage in the early Miocene. It spans the time between 20.43 ± 0.05 annum, Ma and 15.97 ± 0.05 Ma (million years ago). Preceded by the Aquitanian (sta ... (approximate). *Early/Lower Hemingfordian (shares lower boundary) References Miocene geochronology Miocene North America {{geochronology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barstovian
The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 16,300,000 to 13,600,000 years BP, a period of . It is usually considered to overlap the Langhian and Serravallian stages of the Middle Miocene. The Barstovian is preceded by the Hemingfordian and followed by the Clarendonian NALMA stages. The Barstovian can be further divided into the substages of: * late Late Barstovian: Lower boundary source of the base of the Langhian (approximate) * early Late Barstovian: Base of the Langhian (approximate) * early/lower Barstovian: Upper boundary source: base of Clarendonian (approximate) Correlations The Barstovian (15.97 to 13.6 Ma) correlates with: * SALMA ** Colloncuran (15.5-13.8 Ma) [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clarendonian
The Clarendonian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 13,600,000 to 9,000,000 years BP, a period of . It is usually considered to overlap the Serravallian age of the Middle Miocene and the Tortonian age of the Late Miocene. The Clarendonian is preceded by the Barstovian and followed by the Hemphillian The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered t ... NALMA stages. Subdivisions The Clarendonian can be further divided into the substages of: * Late/Upper Clarendonian: Lower boundary source of the base of the Clarendonian (approximate) * Early/Lower Clarendonian (shares lower boundary) References Miocene life Miocene animals of North ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemphillian
The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered to overlap the Tortonian age of the Late Miocene and Zanclean age of the Early Pliocene. The Hemphillian is preceded by the Clarendonian and followed by the Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of . [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blancan
The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of . Blancan North American Stage GeoWhen Database. Version 1.1.0. Retrieved 2017-June-26. It is usually considered to start in the early-mid Epoch and end by the early . The Blancan is preceded by the Hemphil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
