Dinoflagellate response to sea level change in the Cretaceous Western Interior.
Item
-
Title
-
Dinoflagellate response to sea level change in the Cretaceous Western Interior.
-
Identifier
-
AAI9432350
-
identifier
-
9432350
-
Creator
-
Li, Huan.
-
Contributor
-
Adviser: Daniel Habib
-
Date
-
1994
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Palynology | Paleoecology | Biology, Oceanography
-
Abstract
-
Detailed palynological analysis of depositional environments in carbonaceous shales and marlstones in the Cenomanian-Turonian(C-T) interval of the Western Interior Cretaceous Seaway indicates that (1) dinoflagellate species diversity, (2) ratio of Spiniferites to Cyclonephelium (S/C ratio) and (3) depositional organic facies are collectively useful for distinguishing cycles of marine transgression and regression. The increase in number of dinoflagellate species and of the S/C ratio within a matrix of abundant amorphous debris is interpreted to have resulted from the expansion of an epeiric seaway. The marked drop in species diversity in the interval of mixed amorphous debris and detrital inertinite adjacent the Sciponoceras-Neocardioceras zonal boundary and prior to or at the C-T boundary indicates two short periods of shoreline progradation. The S/C ratio increases in the offshore direction as well as in the transgressive intervals. The largest number of species occurs in the lower part of the transgressive intervals, and not in peak transgression. The successive decrease in species diversity from the early stage to late stage within the transgressive interval and into the next highstand interval is the result of shoreline progradation. The downlap surface (maximum starvation surface) which delimits the boundary between the transgressive and highstand intervals may be indicated by an inflection in the trend of decreasing species diversity. The position of the inflection point within the C-T transgressive sequence shows the same trend as the position of the condensed interval that shifts higher in the offshore direction.;The preservation of dinocysts in sediments is highly variable and closely corresponds to lithology, with best in calcareous shales and worst in limestones and marlstones. The concentration of dinocysts in the C-T sediments decreases semi-logarithmically with increasing percentages of carbonate fraction. The organic matter deposited in the C-T sediments is mostly marine amorphous fecal debris and there is little landplant detritus even within the interval of progradation. The amount of terrigenous inputs from the western highland may not be as large as other studies showed. The bottom condition in the coastal and nearshore areas may have been oxygenated or sub-oxygenated during transportation and deposition, providing the potential for oxidation and degradation of landplant material.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
