USGS Science⌕ Search

Geology topics

R.H. Tschudy

Publications and source records attributed to R.H. Tschudy.

11 recordsLinked to original sources
USGS1986

Extinction and survival of plant life following the Cretaceous/Tertiary boundary event, Western Interior, North America

The palynological Cretaceous/Tertiary boundary is recognized in the northern part of the Western Interior by the abrupt disappearance of a few characteristic Cretaceous pollen genera, principally Proteacidites and Aquilapollenites . In the southern part, the boundary is recognized by the disappearance of a somewhat different group of pollen: Proteacidites , “ Tilia ” wodehousei , and Trisectoris . The abrupt change in both regions takes place precisely at the stratigraphic horizon at which boundary clay layers containing anomalously high concentrations of iridium (interpreted to be the result of an asteroid impact) are found. Although some characteristic Cretaceous taxa apparently became extinct, others were minimally affected by this boundary event and reappear in strata above. However, all the principal Cretaceous pollen genera (though not species) that disappear regionally have been reported from Tertiary rocks in other parts of North America. Differential apparent extinction and/or survival reflects a pronounced temporary disruption of plant life immediately after the event. Some Cretaceous plants must have persisted in refugia to have provided the propagules for the rapid recovery of the flora. No massive total extinction of plant genera at the end of the Cretaceous can be seen from the palynologic record.

Geology↗
USGS1984

Trace element patterns at a non-marine cretaceous-tertiary boundary

At the fossil-pollen-defined Cretaceous-Tertiary boundary in the Raton Basin of New Mexico and Colorado, an iridium abundance anomaly and excess scandium, titanium, and chromium are associated with a thin ash or dust fallout bed (now kaolinitic clay) that was preserved in freshwater coal swamps. ?? 1984 Nature Publishing Group.

Nature↗
USGS1984

Disruption of the terrestrial plant ecosystem at the Cretaceous-Tertiary boundary, western interior

The palynologically defined Cretaceous-Tertiary boundary in the western interior of North America occurs at the top of an iridium-rich clay layer. The boundary is characterized by the abrupt disappearance of certain pollen species, immediately followed by a pronounced, geologically brief change in the ratio of fern spores to angiosperm pollen. The occurrence of these changes at two widely separated sites implies continentwide disruption of the terrestrial ecosystem, probably caused by a major catastrophic event at the end of the period.

North America western interior↗
USGS1982

Iridium abundance measurements across the Cretaceous/Tertiary boundary in the San Juan and Raton Basins of northern New Mexico

During the past year we have been measuring trace element abundances and searching for anomalously high iridium (Ir) concentrations in continental sedimentary rocks that span the Cretaceous-Tertiary boundary in the Raton and San Juan Basins of northern New Mexico and southern Colorado. Using neutron activation and radiochemical separations, we have identified anomalous concentrations of Ir in samples from two sites in the Raton Basin: in a drill core at York Canyon, about 50 km west of Raton, New Mexico, and in a road cut near the city of Raton. In both cases the anomaly occurs essentially at the base of thin coal beds, across a thickness span of only a few cm and at the same level at which several species of Cretaceous pollen become extinct and the ratio of angiosperm pollen to fern spores drops sharply. The Ir surface density ranges from 8 to 40 × 10 −9 g cm −2 . In the York Canyon core the Ir concentration reaches a value of 5.6 × 10 −9 g/g of rock over a local background of about 10 −11 g/g; the Pt abundance distribution is similar to that for Ir, while Au reaches its maximum concentration about 10 cm below the Ir peak. Se, V, Cr, Mn, Co, and Zn are about two-fold more abundant at the anomaly zone than in adjacent zones, and mass spectrometric 244 Pu analysis showed the 244 Pu/Ir atom ratio ⩽ 1 × 10 7 . In the San Juan Basin we have located a small Ir spike (55 × 10 −12 g/g over a local background of 8 × 10 −12 g/g) that is accompanied by high concentrations of Co and Mn. It is thought to be due to geochemical enrichment processes.

Colorado, New Mexico↗
USGS1981

Geographic distribution and dispersal of normapolles genera in North America

Normapolles pollen have been found in North America in Cretaceous and Lower Tertiary rocks from the eastern Atlantic Seaboard, the Mississippi embayment region and from the states and provinces from western North America as far north as the District of Mackenzie, Northwest Territories. Previous postulates relating to the Normapolles floral province (western Europe-eastern North America) were re-examined in the light of new finds of Normapolles genera in rocks from west of the Cretaceous epeiric seaway which separated the Normapolles province from the western North American Aquilapollenites province. A study of published occurrences of Normapolles genera and U.S. Geological Survey Denver Laboratory Normapolles records revealed that of the approximately 60 Normapolles genera recognized from western Europe, only 26 of these have been recognized from eastern North America. These data suggest that Normapolles-producing plants originated in western Europe and migrated to eastern North America prior to the opening of the north Atlantic seaway. Ten of these 26 genera also have been found in rocks from west of the Cretaceous epeiric seaway, suggesting that these genera were the only ones able to cross this barrier. At least six genera having Normapolles characteristics occur in eastern North America but have not yet been recorded from Europe. Two additional genera with Normapolles characteristics have been reported only from the Aquilapollenites province of western North America. Several discrepancies in the record need resolution, such as the latitudinal restriction of Thomsonipollis and Nudopollis to areas south 40??N latitude, the absence of records of Thomsonipollis east and north of central Georgia, and the absence of records of Kyandopollenites and Choanopollenites west of eastern Texas. These data show that the known boundaries of the Normapolles province are somewhat hazy and that firm conclusions regarding the geographic distribution and history of dispersal of Normapolles genera are premature. ?? 1981.

Review of Palaeobotany and Palynology↗
USGS1981

An iridium abundance anomaly at the palynological Cretaceous-Tertiary boundary in northern New Mexico

An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.

New Mexico↗