Rapid Facies Changes Research Articles

Formation Waters in Southwest Louisiana

In southwest Louisiana a relationship is found between the salinity of connate waters and the facies changes of the sediments from which they are derived. The geological setting of the area is discussed. Facies changes are important in determining the character and relative amounts of sand, shale, or limestone deposited. Seventy-two salinity determinations were made on waters from sixty-nine wells in twenty-nine oil or gas fields. From these data it appears that the salinity of formation waters from sand bodies is a function of the quantity and degree of compaction of adjacent shales. The important considerations and results of this reconnaissance study may be summarized as follows. 1. Cenozoic sediments in southwest Louisiana reflect, with lateral variations in their character and quantity, the rapid facies changes in their cyclic depositional history. 2. The saline content of the connate waters obtained for this study appears to be correlative with the relative percentages of sand and shale found in these sediments. 3. High salinities (up to 4½ times that of normal sea water) are found in younger sediments (Miocene-Pliocene) where the relative quantity of shale is small and its degree of compaction slight. Lower salinities (down to ½ that of sea water) are found in older sediments (Eocene-Oligocene) where the relative quantity of shale is large and its degree of compaction great. 4. In sediments of the same age, highest salinities mark the updip non-marine part, lower salinities the downdip marine equivalent. The transition between them is gradual.

Some Observations on Geological Structures in Eastern Nevada: ABSTRACT

The White Pine Range of east-central Nevada consists of a central dome of Lower Paleozoic sedimentary rocks and a small granodiorite intrusive, surrounded by sedimentary rocks of Devonian and Carboniferous age. The dome is bounded by arcuate normal faults with maximum vertical displacements of 15,000-18,000 feet. The evidence suggests that the dome has been pushed up, as a unit, into the younger rocks. The principal structures within the Upper Paleozoic rocks of the Range are folds and thrust faults. At least part of the folding occurred during Eocene time. No evidence of folding of these rocks during the down-warping of the Cordilleran geosyncline was recognized, although any structural traps of that era would be most desirable. Contained in these Upper Paleozoic rocks is a thick section of the Middle Mississippian White Pine formation, which, although there are rapid facies changes, often contains a considerable thickness of black carbonaceous shales. This formation is general throughout eastern Nevada and could well be a source rock for petroleum providing the structure and surrounding rocks furnish favorable reservoirs. Other observed areas throughout eastern Nevada have structures generally similar to those within the White Pine district. That is, the rocks are folded and the folds are broken by thrust faults. The thrust faults vary from minor breaks with a few feet of displacement to displacements of several or even tens of miles. The mountain ranges generally furnish some evidence of being bounded by a series of normal faults and there are commonly many normal faults within the ranges. The presence of volcanic flows need not discourage oil exploration as these have flowed many miles from the source. However, the intrusive rocks, including the dike feeders of lava flows, have altered and metamorphosed the surrounding rocks. The Upper Paleozoic rocks are probably the only potential source rocks for petroleum in eastern Nevada, although the Ordovician graptolite shales of central Nevada undoubtedly warrant examination, as well as the Triassic marine shales of southern Nevada. End_of_Article - Last_Page 2063------------