A 3-MILLION-YEAR RECORD OF CONTINENTAL CLIMATE A 3,050-foot core was recovered in 1967 from an area near the center of Searles (dry) Lake in southeastern California. A study, completed last year, shows that the core represents a detailed history of climate-controlled sediment deposition in this desert basin starting more than 3 million years ago. A surprising discovery is that the lake's record of climate history differs so conspicuously from the marine record of global glaciation, in that periods of major change occur at different times and the lengths of time that particular climatic patterns persisted differ by factors as large as four. The one similarity is that a marked resurgence of large continental ice sheets, according to studies of the marine cores, and the first establishment of a lake in this valley both began about 3.2 million years ago. The deepest and oldest sediments in the core, 728 feet of reddish-brown desert fan gravels, rest on granitic bedrock, and 2,275 feet of lake deposits (clay, silt, and salts) make up the remainder of the valley fill. Sedimentation rates in this lake averaged 117 years per inch of deposits. This rate is 10 to 50 times faster than sedimentation rates of most deep-sea sediments that are widely used for studies of Quaternary climate, so this record provides much better resolution of short climatic events. Regional climates are indicated by the sediment composition; salt beds and tan "dry" lake sediments indicate times of aridity when evaporation exceeded inflow of water into the lake; greenish silt and clay indicate times when perennial lakes occupied the valley, implying greater water accumulation as a result of increased regional precipitation. The upper 226 feet of lake sediments represent approximately the last 130,000 years. The underlying lake sediments have the following lithologies and ages and imply the indicated lake character and climate: The shift from alluvial fan to lake basin deposition in Searles Valley took place about 3.2 million years ago. It could have been an indirect result of a volcanic eruption at that time which diverted a large river system to the north or a direct result of worldwide climate change. Climatic reconstructions indicate a steady decrease over the 3.2-millionyear period in the regional precipitation that controlled the runoff that fed the lake. This was caused, in part, by the gradual uplift of the Sierra Nevada, which created an increasingly effective rain barrier, but climatically A POSSIBLE EXTENSION OF AN OIL AND GAS PROVINCE The Appalachian Mountains form a linear geologic system in the Eastern United States that extends for over 1,000 miles southward from New York to Alabama. Continuous research by State, Federal, university, and industry scientists has been an ongoing process since the early 1800's. Although it would appear that this amount of long-term research would have been adequate to provide a good understanding of the geology of the area, this is far from the truth. Much of the previous work has concentrated on an intense study of surface relations that provided a two-dimensional framework. Subsurface data, which adds the third dimension to the framework, have been available only for the western part of the mountain system where deep drilling and seismic surveys have been used in the search for oil and gas. Only recently has enough subsurface data become available to augment the surface data in the eastern part of the Appalachians. These new data require a reevaluation of many long-held concepts, based entirely on surface studies, concerning the distribution of possible oil and gas source rocks within the Appalachian Mountain system. In the past, geologists, basing their evidence on surface relations, believed that the Appalachian Mountain system could be divided into two main parallel parts, an eastern part, which includes the Blue Ridge and Piedmont and is composed of crystalline rocks (metamorphic and igneous), and a western folded and faulted part, which lately is called the Eastern overthrust belt and is composed of sedimentary rocks. Sedimentary rocks in the Eastern overthrust belt have been a source of natural gas for more than 100 years. In comparison, the Piedmont has not received much attention from petroleum geologists because its crystalline rocks are considered to be the "basement" below which no sedimentary oil and gas source rocks were believed to exist. Recent seismic surveys, utilizing refined geophysical methods for investigating deep in the Earth, have revealed that faulting has moved crystalline rocks of the Blue Ridge and Piedmont westward more than 100 miles and buried a large section of sedimentary rocks of the Eastern overthrust belt. From central Virginia southward, the main area for which subsurface data is available, the buried part of the overthrust belt is from 10,000 to more than 20,000 feet thick. This hidden and unknown part of the overthrust extends in the subsurface eastward for at least 60 miles and may even extend further. In Georgia, 150 miles southwest of the area covered by the Survey's data, seismic data acquired by others suggest that seismic reflections indicative of sedimentary rock extend in the subsurface perhaps completely across the Piedmont. If these initial seismic data are representative, then a concealed belt of sedimentary rock is buried under the Blue Ridge and Piedmont from at least central Virginia to Alabama (see the figure). Because this buried belt is about as wide as that exposed in the southern part of the Eastern overthrust belt, the area for possible natural gas exploration is about doubled in size. Of immediate interest to the petroleum geologist is the fact that the buried segment appears to be composed of sedimentary rocks similar to those currently being explored for natural gas in the exposed parts of the Eastern overthrust belt. However, like most unexplored frontier areas, data are not sufficient to assess the oil and gas potential of this hidden area. Because these sedimentary rocks occur beneath the Piedmont, where previous geologic concepts suggested such rocks would be unlikely, future exploration programs for oil and gas within the Appalachian region might well include this vast untested and unknown area. Perhaps an even more far-reaching effect is that these new seismic data require a major rethinking of how the Appalachian regional framework was formed. Previous models of the overthrust belt have served as guides for petroleum exploration in overthrust belts around the world. Changes in our understanding of the Appalachian overthrust belt will have an important effect on the future search for oil and gas in other areas that have a similar structure. Map showing the inferred regional distribution of the concealed sedimentary rocks of the Eastern overthrust belt beneath the metamorphic and igneous rocks of the Blue Ridge and part of the Piedmont. The interpreted seismic reflection section A-A' shows the continuity of sedimentary rocks of the Eastern overthrust belt eastward beneath the crystalline rocks of the Blue Ridge and Piedmont in Tennessee and North Carolina. |