About This Item
Share This Item
Grain-size analyses and chert-to-quartz ratios were studied on Pliocene and Quaternary gravel fractions from the Florida parishes of southeastern Louisiana to differentiate between gravels of different ages. Gravels are found in the following units: (1) Pliocene-Pleistocene Citronelle Formation; (2) Prairie Formation (< 35,000 y.B.P.); (3) Deweyville terrace deposits (30,000 to 17,000 y.B.P.); and (4) Holocene channel and bar deposits.
Petrologic studies show that the Citronelle gravels are easily distinguished from the younger terrace gravels by their coarser grain size, low granule content and high chert-to-quartz ratios. Prairie and Recent gravels have similar textures and composition indicating they were deposited under similar conditions. Both Prairie and Recent gravels were derived directly from the Citronelle (Bogue Chitto valley), whereas in others (Tangipahoa valley) they were cycled through the Prairie Formation.
In the Pearl River valley, Prairie and Deweyville gravels are significantly finer and contain higher granule content and lower chert-to-quartz ratios than other gravels in the Florida parishes; this suggests that the late Pleistocene Pearl River was mature and had high discharges, possibly due to an enlarged drainage basin that contained quartz-rich sources which are not available to the modern Pearl River. Post-Deweyville climatic and hydrologic changes have resulted in a smaller drainage basin and less discharge for the modern Pearl River.
End_of_Article - Last_Page 1471------------