GEOLOGIC STRUCTURE of PARTS of NEW MEXICO. by N. H. DAKTON. Although New Mexico Is Not Yet Producing Oil, Wide Areas of the Stat
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GEOLOGIC STRUCTURE OF PARTS OF NEW MEXICO. By N. H. DAKTON. INTRODUCTION. Although New Mexico is not yet producing oil, wide areas of the State are underlain by rocks of the same age as those which yield oil and gas in adjoining States to the east, and in many places the struc tural conditions are favorable for the accumulation of oil and gas if they are present. So far the only notable discovery of oil has been that made near Dayton, in Pecos Valley, where some artesian wells yield small amounts, but indications of oil have been reported in several parts of the State. Many deep holes have been bored for water and a few for oil, but most of them have been in places where the structure is not favorable for oil or gas or were not deep enough to test the possibilities of all the strata. This report is published in order to place in the hands of oil and gas geologists the information now in hand as to the structural fea tures of New Mexico. Many of the data are new and are by-products of investigations made with objects very different from those of the geologist in search of new oil fields. During the last four years I have studied the stratigraphy and depositional history of the "Red Beds" region of the Southwest, including a large part of New Mexico, with special reference to the determination of the centers of greatest salt deposition. The principal aim of the work was to discover areas in which potash salts also may have been locally deposited. In the course of these studies reconnaissance was extended over large por tions of New Mexico, especially in areas where the stratigraphy and structure were but little known. The results of this work, together with information previously available, are embodied in a forthcoming report on the geology of the "Red Beds" and associated formations of New Mexico, to be accompanied by a colored geologic map on a topographic base founded in large part upon original topographic sketches. On account of the great number of requests received by the Geo logical Survey for information relating to the general stratigraphy and structure of New Mexico, it has been decided to publish at this time the data on the character and thickness of the formations and the general structure for the special use of oil geologists in a report with simple maps that may be placed in the hands of the public in advance of the engraving of the more elaborate geologic map of the 173 174 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1921, PART II. State. Emphasis must be laid on the facts that the field examina tions were not made for the purpose of finding areas favorable for the occurrence of oil and that the work was done largely by methods less detailed than those required in the search for oil and gas, espe cially in the recognition and mapping of minor anticlines or domes that might be important centers of oil or gas accumulation. How ever, it is believed that this report will be of value as a guide to the regions in which the stratigraphy of the formations appears more favorable and as a presentation of the larger structural features. Doubtless it will also indicate some of the areas where minor folds are to be looked for. At the same tune many portions of the State are differentiated as offering no encouragement to prospectors for oil. In general, New Mexico has not been regarded with favor by most of the oil and gas geologists of the country, notwithstanding the fact that surface indications of oil are known at several points in the State and oil in small amounts has been found near Dayton and Seven Lakes. This disfavor is not without some foundation, for there are several adverse considerations, of which the following are perhaps the most important: (1) In New Mexico the Cretaceous formations, which are the sources of most of the oil in the Rocky Mountain States, are present only in relatively small areas, in many pf which their position and structure are not favorable for oil; (2) in the many wide areas where the Cretaceous formations are absent, particularly in the central and northern parts of the State, the Paleo zoic formations are of no great aggregate thickness, the Carboniferous lying directly on the pre-Cambrian crystalline rocks; (3) the Jurassic, Triassic, and Permian formations in general carry but little carbona ceous matter, the thick succession of these strata being singularly deficient in such organic debris as is generally regarded as the mother substance of petroleum; (4) through the central and southern portions of the State the folding and faulting are relatively pronounced, the pre-Cambrian crystalline rocks are brought up in the axes of the arches, the basins are comparatively narrow, and although minor folds undoubtedly are present, the marginal areas are in some places much faulted and cut by later lavas and many of the catchment areas are very small; and (5) finally, it is likely that in many areas, particu larly in the older rocks and toward the southwest, carbonization of the organic debris in the formations has progressed so far as to pre clude the survival of oil in commercial pools, though gas in consider able amounts may be present. The data on this fifth point are, however, very meager, so that it is not possible to state at the present time their bearing on the prospects in the different areas. The same condition exists in the Cretaceous rocks in some areas, notably in the Raton and Cerrillos coal fields. For the same reason also it seems probable that the Pennsylvanian rocks in the upper Pecos Valley east of Santa Fe and in a part of Bernalillo County may be too much TT. S. GEOLOGICAL SURVEY BULLETIN 720 PLATE XXX 0 10 2JO 30 4-0 50 60 70 80 Miles 1______l_-.. L. I 1______1______|______1______1 MAP OF NEW MEXICO. Showing areas covered by detailed maps. GEOLOGIC STRUCTURE OF PARTS OF NEW MEXICO. 175 altered to encourage the prospector for oil. On the other hand, it is probable that the Cretaceous rocks in the San Juan Basin, except possibly near the Colorado line, and the Carboniferous beds in the eastern third of the State are not too greatly altered. In general the oil geologist may find it advantageous to consider the state of car bonization of the combustible debris of the coals and carbonaceous shales in most areas in advance of testing by the drill. Although the "Red Beds" are nearly barren of oil-making mate rials they include sandstones which may be excellent reservoirs for the storage of oil that has migrated from more favorable strata, separated by considerable thicknesses of unproductive beds. The demonstrated presence of oil in the "Red Beds" of the Pecos Valley near Dayton encourages the hope that in some areas the sands in these unpromising rocks may be reservoirs for commercial deposits of oil, even where they are remote from strata rich in carbonaceous matter. On the whole, the Carboniferous and Cretaceous areas of eastern New Mexico and the Cretaceous areas of the northwestern portion of the State, west of the Nacimiento uplift, probably offer greater encouragement for the discovery of commercial oil fields than other portions of the State. Oil, gas, or asphalt are present in these areas; the sedimentary formations attain considerable thicknesses; some of the associated strata are sufficiently rich in carbonaceous debris; and the presence of stresses, indicated by the major folding, makes it almost certain that examinations in detail will reveal minor anti clines and domes of the type most favorable for oil and gas. SEDIMENTARY ROCKS OF NEW MEXICO. GENERAL SUCCESSION. The strata in New Mexico present a great thickness of beds from Cambrian to Recent in age, but portions of some of the geologic periods are not represented by deposits. The classification of most of the formations has been established by the work of several geolo gists, and this subject will be only briefly treated here, except as it is touched by my own investigations of the Triassic and Permian "Red Beds" and associated formations, for which some new classi fications must be introduced. It is necessary to consider these matters briefly at this time, because in this report many new facts are presented in connection with the distribution and structure of the formations of Jurassic, Triassic, and Permian age. A more detailed discussion will be given in the fuller report now in preparation. The following lists show the stratigraphic position, character, and thickness of the principal formations in different parts of New Mexico. It is not practicable to give them all in one table, because of the regional variations in the character of the deposits in this large State, which has an area of 122,634 square miles. 176 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1921, PART II. Formations in northeastern New Mexico. Average Age. Group and formation. Character and general relations. thickness (feet). Recent. Alluvium. Sand, gravel, and clay. 50 ± Pliocene and Mio cene. Santa Fe formation. Sand, silt, gravel, and conglomerate. 150+ Eocene. Eaton formation. Conglomerate and sandstone; local coal beds. 1,200-1,600 Sandstone and conglomerate. Relations to Eocene (?). Galisteo sandstone. Raton formation unknown. 700+ Vermejo forma tion. Sandstone and shale, with coal beds. 0-375 Montanagroup. Trinidad sand stone. Sandstone, gray to buff. 0-100 Shale, mostly dark colored; upper beds Plerro shale. sandy. (?) Apishapa shale. Shale, in part limy. Niobrara for 500 mation where Upper Cretaceous. not differen Timpas limestone.