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Judith T. Parrish

Publications and source records attributed to Judith T. Parrish.

6 recordsLinked to original sources
USGS1989

Thermal and cementation histories of Permian shelf-edge carbonate rocks in the Nanpanjiang Basin, South China

As of 1984, the Nanpanjiang Basin of South China has had almost no exploration by drilling although oil seeps exist among its margins and producing wells occur in adjacent basins. however, cooperative studies by petroleum geologists and geochemists of the United States and the People's Republic of China (1982-1984) show that calcite-cemented reef and fore-reef carbonate rocks near Ziyun contain bitumen in Upper Permian shelf-edge sediment. the cementation history consists of three episodes: (1)precipitation of syndepositional marine cement (formerly botryoidal aragonnite and fibrous magnesian calcite); (2)precipitation of post-depositional early cement (radiaxial calcite); and (3)precipitation of late burial cement (white calcite spar). Hydrocarbons were introduced into the rocks between cementation episodes 2 and 3. Fluid inclusion analysis of secondary inclusions in the burial cement indicates that the rocks were heated to nearly 200 C after hydrocarbon migration and cementation episode 3. Bitumen remains in the rocks as evidence of the earlier presence of liquid hydrocarbons. During this study, Ordovician through Permian carbonate rocks and Cambrian through Triassic clastic rocks were analyzed for total organic carbon (TOC) vitrinite reflectance (R 0 ), and extractable hydrocarbon (HC) content and composition. Within the basin, TOC values ranged from 0.02% to 3.91%, total HC ranged from 0.004 to 0.11 mg/g, and R 0 values were mostly greater than 2.0%. Previous studies by several groups of scientists in this region have found low TOC values and evidence of overmaturity. Our studies found higher TOC values, but otherwiese confirm the earlier findings. We conclude that portions of the basin have been heated beyond the level of liquid hydrocarbon generation and retention. Although our observations do not favor the occurrence of liquid hydrocarbons in the Paleozoic strata along the western maring of the basin, the possibility of significant gas accumulations in fractured reservoirs or of other hydrocarbon accumulations in the basin cannot be ruled out.

Nanpanjian Basin↗
USGS1988

Wind directions predicted from global circulation models and wind directions determined from eolian sandstones of the western United States - A comparison

Wind directions for Middle Pennsylvanian through Jurassic time are predicted from global circulation models for the western United States. These predictions are compared with paleowind directions interpreted from eolian sandstones of Middle Pennsylvanian through Jurassic age. Predicted regional wind directions correspond with at least three-quarters of the paleowind data from the sandstones; the rest of the data may indicate problems with correlation, local effects of paleogeography on winds, and lack of resolution of the circulation models. The data and predictions suggest the following paleoclimatic developments through the time interval studied: predominance of winter subtropical high-pressure circulation in the Late Pennsylvanian; predominance of summer subtropical high-pressure circulation in the Permian; predominance of summer monsoonal circulation in the Triassic and earliest Jurassic; and, during the remainder of the Jurassic, influence of both summer subtropical and summer monsoonal circulation, with the boundary between the two systems over the western United States. This sequence of climatic changes is largely owing to paleogeographic changes, which influenced the buildup and breakdown of the monsoonal circulation, and possibly owing partly to a decrease in the global temperature gradient, which might have lessened the influence of the subtropical high-pressure circulation. The atypical humidity of Triassic time probably resulted from the monsoonal circulation created by the geography of Pangaea. This circulation is predicted to have been at a maximum in the Triassic and was likely to have been powerful enough to draw moisture along the equator from the ocean to the west.

western United States↗
USGS1985

Carboniferous paleogeographic, phytogeographic, and paleoclimatic reconstructions

Two revised paleogeographic reconstructions of the Visean and Westphalian C-D stages are presented based on recent paleomagnetic, phytogeographic, stratigraphic, and tectonic data. These data change the positions of some continental blocks, and allow the definition of several new ones. The most important modifications that have been incorporated in these reconstructions are: (1) a proposed isthmus linking North America and Siberia across the Bering Strait; and (2) the separation of China and Southeast Asia in six major blocks, including South China, North China, Shan Thai-Malaya, Indochina, Qangtang, and Tarim blocks. Evidence is presented that suggests that at least the South China, Shan Thai-Malaya, and Qangtang blocks were derived from the northern margin of Gondwana. Multivariate statistical analysis of phytogeographic data from the middle and late Paleozoic allow definition of a number of different phytogeographic units for four time intervals: (1) the Early Devonian, (2) Tournaisian—early Visean, (3) Visean, and (4) late Visean—early Namurian A. Pre-late Visean—early Namurian A floral assemblages from South China show affinities with northern Gondwana floras suggesting a southerly position and provides additional support for our reconstruction of South China against the northern margin of Gondwana. There is a marked decrease in the diversity of phytogeographic units in the Namurian and younger Carboniferous. This correlates closely with the time of assembly of most of Pangaea. The general pattern of Carboniferous phytogeographic units corresponds well with global distribution of continents shown on our paleogeographic reconstructions. In addition, we have constructed paleoclimatic maps for the two Carboniferous time intervals. These maps stress the distribution of rainfall, as this should be strongly correlated with the floras. There is marked change in the rainfall patterns between the Visean and Westphalian C-D. This change corresponds with the closing of the Appalachian-Ouachita ocean between Laurussia and Gondwana, and reflects the removal of a low-latitude moisture source that probably gave rise to monsoonal conditions along the northern margin of Gondwana in the Visean and earlier times. As well, the presence of a substantial heat source at high elevation in the Late Carboniferous significantly influenced the distribution of climatic belts.

International Journal of Coal Geology↗