Microfossils of the Trinity River Delta
Brann, Bethany Celia
Lankford, Robert R.
Master of Arts
A study of the distribution of Poraminifera and other microscopic fossils in cores penetrating the modern Trinity Delta reveals three distinct foraminiferal assemblages. The assemblages encountered from the base of the cores to the delta surface include: 1) the river-influenced upper bay assemblage; 2) the delta-margin assemblage; and 3) the marsh assemblage. The above assemblages are defined not only on the qualitative presence or absence of species but also on percentage abundances and agglutinated-calcareous ratios. The river-influenced upper bay assemblage is characterized by relatively large numbers of calcareous Poraminifera, including the dominant species Ammonia beccarli (Linne). The delta-margin assemblage occurs in sediments indistinguishable from those of the river-influenced upper bay; the delta-margin assemblage is characterized by only two Poraminifera, the agglutinated species Ammotium salsum (Cushman and Bronnimann) and Miliarrmina fusea (Brady). The marsh assemblage contains a wholly agglutinated fauna of which the prevalent species are Trochammina macrescens Brady and Trochamminita irregularis Cushman and Bronnimann. Some species of Thecamoebina are associated with the marsh assemblage and characterize channel-fill deposits. Other microfossils occur in variable abundances and may be environmentally significant.