The Trans-Mexican Volcanic Belt has been recognized as a major volcanic arc, which crosses México from the Pacific Coast to the Gulf of México, that has displayed normal faulting and volcanism since the Miocene. In this work we present the deformation events that have been recorded N and S of the belt in order to establish when the crustal discontinuity originated and also to determine the deformation field precursor of the volcanic arc emplacement. In Mesa Central, the post-Laramide deformation occurred in three extensional events during the Eocene, Oligocene, and Miocene-Recent. The three events produced extension in two horizontal directions and shortening in a vertical direction. The direction of the principal extension in the Eocene is not well known. A 20% extension in an ∼ENE-WSW direction is recorded for the Oligocene event. The most recent event, active since the middle Miocene, has developed in the Trans-Mexican Volcanic Belt and along its northern boundary. In the Sierra Madre Oriental, Cenozoic deformation has been minimal. In the Taxco region, there were two post-Laramide deformation events, mainly a result of NW-SE and N-S lateral faults. The first one occurred in the late Eocene with a NNW-SSE horizontal extension direction. The second event was early Oligocene with a maximum extension to the NE-SW. It is concluded that since the Eocene, the deforma tion style has been different in Mesa Central and in the Sierra Madre del Sur, which implies the presence of a detachment zone between these provinces.

Abstract The Joya Honda maar (JHm) is located in central Mexico, 35 km NNE of the city of San Luis Potosí. It lies in the Plio-Quaternary alkaline Ventura-Espíritu Santo Volcanic Field located in the eastern part of Mesa Central province. The JHm eruption occurred at 311±19 ka (40 Ar/ 39 Ar) along a fissure that formed an elliptical crater (c. 1.3 × 0.9 km wide and c. 270 m deep) with a major axis oriented to the ENE–WSW. The eruption generated pyroclastic surge deposits that preferentially extended up to a distance of 7 km to the NW–NE of the crater, with a very limited distribution to the south. At the crater rim, the sequence is 60–80 m thick on the NE–NW wall and 1–15 m thick on the south–SW rim. The JHm sequence is divided into five units with different structures, textures, granulometry and components. The juvenile basanite clasts of these units display differences in vesicularity, density and morphology under scanning electron microscopy. These units correspond to the same number of eruptive phases as follows: Phase 1 occurred as a series of alternating strombolian and phreatomagmatic explosions that dispersed fall deposits and base surges; Phase 2 began with strombolian activity that emplaced basanite scoria with low contents of mantle xenoliths; Phase 3 continued with phreatomagmatic explosions that emplaced wet and dry pyroclastic surges; Phase 4 generated strombolian explosions rich in mantle xenoliths; and Phase 5 produced a violent strombolian phase that dispersed fallouts rich in mantle xenoliths and intermixed with discrete phreatomagmatic explosions that emplaced pyroclastic surges. These eruptive fluctuations during the genesis of JHm are a response to the relative proportions of magma–water interaction through time and complex faulting of the calcareous rocks underneath the volcano. The distribution and textural characteristics of the deposits suggest that simultaneous or alternating vents were active during the eruption, possibly following a fissure. These variations may have been subordinated to factors such as the availability of groundwater, the velocity of magma ascent, the discharge rate and degassing.

The Upper Cretaceous strata of the Gulf Coast region of México, Texas, and southwestern Arkansas contain rich, abundant, well-preserved, and, hitherto, poorly studied assemblages of planktonic foraminifera. The rapid evolution and cosmopolitan nature of these planktonic microfossils make them an ideal biostratigraphic tool for the development of detailed, long-distance systems of zonation. In the present report, the planktonic foraminifera have been utilized to subdivide the Upper Cretaceous of the western Gulf Coast region into the following biostratigraphic units: (1) The Rotalipora s.s. Assemblage Zone: Rotalipora evoluta Subzone to Rotalipora cushmani - greenhornensis Subzone. Late Washitian to early Eagle-fordian (early to late Cenomanian). (2) The Marginotruncana helvetica Assemblage Zone: Marginotruncana sigali Subzone to Whiteinella archaeocretacea Subzone. Middle to late Eagle-fordian (early to late Turonian). (3) The Marginotruncana renzi Assemblage Zone: Early Austinian (Coniacian). (4) The Globotruncana bulloides Assemblage Zone: Marginotruncana concavata Subzone to Globotruncana fornicata Subzone. Middle to late Austinian (early to late Santonian). (5) The Globotruncana fornicata—stuartiformis Assemblage Zone: Archaeoglobigerina blowi Subzone (Dictyomitra multicostata Zonule to Planoglobulina glabrata Zonule); Globotruncana elevata Subzone (Pseudotextularia elegans Zonule to Globotruncana calcarata Zonule); and Rugotruncana subcircumnodifer Subzone ( Globotruncana lapparenti s.s. Zonule to Rugotruncana subpennyi Zonule). Archaeoglobigerina blowi Subzone = early Taylorian (early Campanian); Globotruncana elevata Subzone = late Taylorian (late Campanian); and Rugotruncana subcircumnodifer Subzone = early Navarroan (early Maestrichtian). (6) The Globotruncana contusa — stuartiformis Assemblage Zone: Globotruncana gansseri Subzone to Abathomphalus mayaroensis Subzone. Middle to late Navarroan (middle to late Maestrichtian). This system of zonation is based (1) on the association of diagnostic taxa at given stratigraphic horizons; (2) the range zones and concurrent range zones of the various taxa; (3) the relative abundance of important taxa at various stratigraphic horizons; and (4) the phylogeny and evolution of Upper Cretaceous planktonic foraminifera. It has become established through the analysis of more than 1000 fossiliferous samples from the surface and sub-surface in both the western part of the Gulf Coast region and in the Caribbean region. Where possible, samples were collected within the framework of measured sections of the lithic units under study. Samples for planktonic foraminifera were collected as far south in the western Gulf Coast region as the approximate latitude of Tampico, México (22° north latitude) and as far north as Brownstown, Sevier County, Arkansas (34° north latitude). At a given stratigraphic horizon, such as the Globotruncana elevata Subzone, there are few species of planktonic foraminifera that do not occur in both the Tethyan faunal province and southern part of the Boreal faunal province. In most cases planktonic species that do not occur in both areas are new species, whose stratigraphic and geographic distribution are yet unknown. The present study indicates that the above-mentioned system of zonation is applicable at the zonule level at least as far north as the latitude of Brownstown, Arkansas. Furthermore, Olsson’s (1964) work in New Jersey and investigations in progress in California by the writer, Douglas, and others suggest that the system of zonation introduced here can be applied at the subzone level as far as 40° north latitude in eastern North America and as far as 34° north latitude in western North America. One of the chief by-products of this study is the creation of a regional correlation chart for the Upper Cretaceous of the western Gulf Coast region that is based on planktonic-foraminiferal zonation. Accurate biostratigraphic dating of lithic units in eastern México utilizing planktonic foraminifera indicates that a number of formational units are time transgressive from north to south. Units like the San Felipe Formation and Agua Nueva Formation are considerably older in northern México near Monterrey than they are in southern México near Tampico. The present study has yielded few radical changes in the dating of lithic units in Texas and Arkansas previously established on the basis of megafossils (Stephenson and others, 1942). Notable among these changes are Navarroan ages for the Upson Clay and San Miguel Formation of the Rio Grande area of Texas (approximate latitude of Eagle Pass) and all, but perhaps, the lowermost part of the Marlbrook Marl of Arkansas. Correlation with the type-European Upper Cretaceous stages is rendered difficult (1) by the imprecise and often obsolete definition of the stages in their type areas and (2) by a lack of accurate data concerning the stratigraphic distribution of planktonic foraminifera in the type sections of the stages. The first of these problems affects all Upper Cretaceous biostratigraphy irregardless of the group of organisms used for correlation. It can perhaps only be solved by an international stratigraphic commission chosen to modernize the definition of the European stages. The second problem can be solved by detailed sampling of strata included in the type sections of each European stage for planktonic foraminifera. Until a detailed reanalysis of the majority of the type-European stages is made, the writer prefers to use North American stage names — particularly those of the standard Gulf Coast section. European stage names are used in this report only in a tentative way. The Eaglefordian Stage of the standard Gulf Coast Upper Cretaceous section has been subdivided into 3 new substages: (1) the Lozierian; (2) the Bocian; and (3) the Sycamorian. The Boquillas Formation in Val Verde and Terrell Counties, Texas, has been subdivided into a lower unit termed the Rock Pens Member and an upper unit termed the Langtry Member. The terms Ateo Chalk and Bruceville Chalk Marl , first used informally by Durham (1957), have been formally introduced here.

Three brachiopod faunas discussed herein record different depositional and tectonic settings along the southwestern margin of Laurentia (North America) during Devonian time. Depositional settings include inner continental shelf (Cerros de Los Murciélagos), medial continental shelf (Rancho Placeritos), and offshelf continental rise (Rancho Los Chinos). Ages of Devonian brachiopod faunas include middle Early (Pragian) at Rancho Placeritos in west-central Sonora, late Middle (Givetian) at Cerros de Los Murciélagos in northwestern Sonora, and late Late (Famennian) at Rancho Los Chinos in central Sonora. The brachiopods of these three faunas, as well as the gastropod Orecopia , are easily recognized in outcrop and thus are useful for local and regional correlations. Pragian brachiopods dominated by Acrospirifer and Meristella in the “San Miguel Formation” at Rancho Placeritos represent the widespread Appohimchi Subprovince of eastern and southern Laurentia. Conodonts of the early to middle Pragian sulcatus to kindlei Zones associated with the brachiopods confirm the ages indicated by the brachiopod fauna and provide additional information on the depositional setting of the Devonian strata. Biostratigraphic distribution of the Appohimchi brachiopod fauna indicates continuous Early Devonian shelf deposition along the entire southern margin of Laurentia. The largely emergent southwest-trending Transcontinental arch apparently formed a barrier preventing migration and mixing of many genera and species of brachiopods from the southern shelf of Laurentia in northern Mexico to the western shelf (Cordilleran miogeocline) in the western United States. Middle Devonian Stringocephalus brachiopods and Late Devonian Orecopia gastropods in the “Los Murciélagos Formation” in northwest Sonora represent the southwesternmost occurrence of these genera in North America and date the host rocks as Givetian and Frasnian, respectively. Rhynchonelloid brachiopods ( Dzieduszyckia sonora ) and associated worm tubes in the Los Pozos Formation of the Sonora allochthon in central Sonora are also found in strati-form-barite facies in the upper Upper Devonian (Famennian) part of the Slaven Chert in the Roberts Mountains allochthon (upper plate) of central and western Nevada. Although these brachiopods and worm tubes occur in similar depositional settings along the margin of Laurentia in Mexico, they occur in allochthons that exhibit different tectonic styles and times of emplacement. Thus, the allochthons containing the brachiopods and worm tubes in Sonora and Nevada are parts of separate orogenic belts and have different geographic settings and tectonic histories. Devonian facies belts and faunas in northern Mexico indicate a continuous continental shelf along the entire southern margin of Laurentia. These data, in addition to the continuity of the late Paleozoic Ouachita-Marathon-Sonora orogen across northern Mexico, contradict the early Late Jurassic Mojave-Sonora megashear as a viable hypothesis for large-magnitude offset (600–1100 km) of Proterozoic through Middle Jurassic rocks from California to Sonora.

Abstract The coal deposits of México are located in the states of Sonora, Chihuahua, Coahuila, Hidalgo, Puebla, Oaxaca, and Tamaulipas. Particularly, the Sabinas Basin in Coahuila contains more than 5000 m of Upper Jurassic and Cretaceous rocks. The coal seams are at the top of the Upper Cretaceous section and occur from the present surface to a depth of about 900 m. They are identified on well logs by high resistivity, low density, and by lithology inferred from gamma-ray logs. Interpretation of logs from 12 wells in the Sabinas coal basin and 4 wells in the Río Escondido coal basin, all with thick Upper Cretaceous sections, allow regional identification of the Austin and Upson Formations, four units in the San Miguel Formation, the Olmos Formation, and a thick sandstone in the Escondido Formation. A preliminary interpretation of this study is that several coal seams assigned to the Olmos Formation likely are contained in the lower one-third of the Escondido Formation, although it is possible that coal seams may occur at other stratigraphic levels in other areas. Coal in the Sabinas Basin was deposited in regressive, high-frequency, deltaic sequences characterized by overall lenticular geometries. A concentration of higher plants led to the accumulation of type III kerogen favorable for the in situ generation of methane. Coal in the Sabinas Basin is bituminous, with high-to-medium volatility. It has 45% fixed carbon, 14% volatile material, 40% ash content, and 1% sulfur and other impurities. Its caloric content is 1300 to 1400 Btu with a vitrinite reflectance of about 0.5, which places it between the zones of diagenesis and catagenesis with a maximum burial depth that may have been between 800 and 1200 m. By drilling 60 shallow wells (average depth of 700 m) at a cost of $US 21.6 million, approximately 18 million ft 3 of gas per day could be produced with a payout of the investmentin 18 months calculated at a price of$2.15 per thousand ft 3 . This area could potentially produce coalbed methane commercially for nearly 20 years, considering production increase though time as the coal seams desorb.

Abstract A regional survey of emerged Pleistocene marine terraces, with emphasis on chronostratigraphic data, permits documentation of recent deformation in coastal areas adjacent to the plate boundary of northwestern Mexico. During the last million years, the eastern coast of the Gulf of California, on the North American plate, remained vertically “stable,” whereas the Baja California peninsula was subjected to a slow and fairly continuous uplift. As a whole, the peninsular block has been uplifted at a mean rate of approximately 100 mm/10 3 y in the past million years. However, uplift rates seem to have decreased, at least locally, based on the relative stability of the late Pleistocene terrace (ca. 125,000 years BP) in several areas of the northeastern, southern, and west central parts of the peninsula. During the late Quaternary, the most deformed and uplifted areas were located close to the main fracture zones—in north westernmost Baja California (between the Agua Blanca and Rose Canyon-San Miguel fault systems), in the westernmost Vizcaino region (along the Bahia Tortugas fault, related to the Tosco-Abreojos fault system), and in the Colorado delta region (along the Cerro Prieto fault system). Strong uplift and warping motions also occurred in the Santa Rosalia area, but these are controlled by volcano-tectonic events related to the La Reforma Plio-Quaternary caldera. The Baja California peninsula behaved as one large crustal block, in near-isostatic equilibrium, and was much less deformed than the California coast. This block has not been tilted westward since the Pliocene. This study supports the concepts that the peninsula is not completely attached to the Pacific plate, and that there is some plate motion along the western continental margin of Baja California.

Introduction The case histories presented in this chapter outline some of the interpretation techniques discussed in Chapter 6, and also illustrate how to estimate some of the rock parameters suggested in Chapter 3. Acquisition and processing of the data follows techniques outlined in Chapters 4 and 5. These case histories illustrate the use of multicomponent interpretation for various types of exploration and development problems. We discuss several applications to demonstrate the flexibility and diverse uses of multicomponent seismology. We begin with a simple study that confirms P-wave “bright spots” as an indication of gas and as an estimation of gas reservoir thickness (Putah Sink, northern California). A similar case history uses Vp/Vs as an indication of gas and estimation of gas reservoir thickness where no “bright spot” amplitude indicator is present (Jeffress Field, south Texas). Lithology estimation is illustrated, along with a measure of the limits of vertical resolution, in the San Miguel example of south Texas, while sandshale estimation, and isolation of channel sands, is demonstrated in the Empire-Abo Field of southeastern New Mexico. Identification of dolomite reservoir within a massive limestone is applied in the Scipio field trend of southern Michigan. Porosity variations in a unit of constant lithology are addressed in the Kingfisher, Okla. data set.