New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/16 Early Paleozoic of New Mexico Rousseau H. Flower, 1965, pp. 112-131 in: Southwestern New Mexico II, Fitzsimmons, J. P.; Balk, C. L.; [eds.], New Mexico Geological Society 16th Annual Fall Field Conference Guidebook, 244 p. This is one of many related papers that were included in the 1965 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. 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One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. 112 EARLY PALEOZOIC OF NEW MEXICO ROUSSEAU H. FLOWER New Mexico Bureau of Mines and Mineral Resources INTRODUCTION mations have retained their apparent simplicity. The Early Paleozoic was a long time, extending roughly It was not too long ago that the Early Paleozoic of from 600 to 370 million years ago, and it is perhaps New Mexico was regarded as simple, with almost one too much to hope that the physical history in terms formation for each geological system. Even this was an of periods of deposition and erosion, was any simpler advance, for earlier work lumped the whole of the here than it has been found to be in other regions in Early Paleozoic into one formation, the Mimbres lime- North America. Eastern sections, which have been stone. For mapping on the scale then used, and in- longer under investigation, show quite complex his- deed, in many cases on scales in current use, the Early tories in each of the systems. Paleozoic shows such a narrow belt of outcrop that Figure 1 shows the development of the geologic finer division is impractical. While Kelley and Silver column of the Early Paleozoic of New Mexico. Col- (1952) made an important step in the recognition of umn 1 shows the old broad formations, roughly one to finer units, their units, new formations, had to be a system, which developed from 1906, and are found grouped together in mapping because of scale of the in Darton (1917). Column 2 shows divisions proposed map and the limited areas of outcrop. within these broad units up through 1952—Entwistle It has, however, been necessary to inquire more (1944) for the Montoya, Stevenson (1945) for the closely into the parts of systems represented by the Devonian, Kelley and Silver (1952) for El Paso and deposits in the Early Paleozoic of New Mexico, in Montoya. Column 3 shows the divisions used in this order to arrive at a clearer concept of the geological paper—both formation names and faunal zones are history in terms of periods of deposition alternating given. Column 4 shows the correlation of these divi- with intervals of elevation and erosion. It was necessary sions in terms of a general column for North America. to know what parts of systems were represented and This column is incomplete; major intervals not repre- how the New Mexico sections correlate with those of sented in New Mexico arc omitted. other regions. There are two realities in geology, the Figure 2 relates the Early Paleozoic sediments of actual geological history, and the succession of rocks New Mexico to a generalized column for North as we see them today, and the first is not always ob- America which includes the major divisions of systems vious from the second. A case is shown by the Mon- from Upper Cambrian through the Devonian. The toya Group of New Mexico. In some exposures, the thicknesses of these intervals have no time significance Second Value and the Aleman are distinct, and we and intervals unrepresented in New Mexico sediments have reason to believe that they are separated by a have been reduced in thickness to permit fuller repre- general period of uplift and erosion. Yet where, as in sentation of the New Mexico section. the Sacramento Mountains or in the Mud Springs Mountains, both show advanced dolomitization, lithic differences are obscured, only previously silicified fos- SEQUENCE OF EVENTS sils are retained, and the two units may be so fused "These things," the Golux said, "I hope are true." that it is difficult and in some sections impossible to Thurber—the 13 clocks point out the contact. 1. Deposition of Dresbachian sediments (earliest Interpretation has depended to a large extent upon late Cambrian) in the region athwart the southern the faunas, which have made possible correlations with New Mexico-Arizona border. It is not yet clear other regions. Yet there may be regional peculiarities whether this is a continuation of deposition which be- in zonation, and regions such as New Mexico, which gan earlier in Middle Cambrian time in southern Ari- may be invaded by faunas from both eastern and west- zona, or whether it marks a separate invasion of the ern geosynclinal belts, are particularly apt to show sea. Some complexity of events is suggested by the some zonal anomalies. In some cases established zona- presence of the Cedaria zone, absence of the Crepi- tions have held well. This is particularly true of our cephalus zone, and indications of the next two, the Cambrian. The Canadian, however, shows a faunal Aphelaspis and Dunderbergia zones. succession including mixtures of eastern and western 2. Early Franconian beds of the Elvinia zone, gen- elements, with some endemic features. erally widespread in North America, have been found With closer scrutiny, almost none of the older for- only in one locality, at White Signal, but may be rep- NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 1 1 3 resented by barren beds at Lone Mountain. This Hatchet Mountains, and continue eastward, being period of deposition is greatly restricted. represented largely by calcarenites. In the extreme east 3. Eoorthis zone. Deposition was possibly continu- at this position are dolomites with Apheoorthis cf. ous from the preceding interval into this one, but de- emmonsi. It is not yet certain whether these beds are posits cover a wider area ranging from the Silver City equivalents of the Kainella zone or whether they are region to the Hatchet Mountains. an initial phase of Middle Canadian deposition. 4. Apparent elevation in the succeeding interval, 10. Demingian deposition, comprising the sequence marked by the Conaspis zone (restricted) and the of first endoceroid, first piloceroid zones, oolite, Bridge- Taenicephalus zone. ites reef and gastropod beds above, is general in New 5. Late Franconian deposits of the Ptychaspis- Mexico. At El Paso the beds above the oolite are Prosaukia zone, divisible into three subzones. These wanting. are well developed in the Caballo, Mud Springs Moun- 11. Minor emergence in late Demingian time was tains and on the east side of the Black Range, are confined to the El Paso region and involved nondepo- represented by nearly barren, dominantly glauconitic sition or removal of beds above the oolite. beds in the Silver City region, and continue west into 12. Widespread deposition of Jeffersonian lime- Arizona. There is some indication that these beds may stones. Deposits are thick and contain many stro- be limy in the extreme southwest, in the Chiracahua matolitic beds, particularly well developed in eastern Mountains. sections. 6. Trempealeauan deposition is known only in the 13. A minor break, known only in the east, followed Silver City region. Seas were more restricted, and de- by Cassinian deposition. posits arc conspicuously cross-bedded, coarse sand- 14. Cassinian deposition continued locally to the stones. Presumably New Mexico was emergent east close of the Canadian. of the Black Range. 15. General emergence with warping, and erosion Question: Is the marked faunal change at the top of the El Paso. Warping makes depth of erosion some- of the Cambrian the result of uplift and withdrawal what irregular, but it penetrates increasingly lower of the seas, which then return, bringing in a new asso- levels to the west and to the north. Precise dating is ciation of organisms, or is this a general biological not yet possible. Erosion may have begun as early as change of continental or world-wide significance with- Whiterock and its end is probably no older than Black out a demonstrable cause? This is a question which River.