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    ABSTRACT: Fault linkage plays an important role in the growth of faults. In this paper we analyze a published synthetic model to simulate fault linkage. The results of the simulation indicate that fault linkage is the cause of the shallower local slopes on the length–frequency plots. The shallower local slopes lead to two effects. First, the curves of log cumulative number against log length exhibit fluctuating shapes as reported in literature. Second, for a given fault population, the power-law exponents after linkage are negatively related to the linked length scales. Also, we present datasets of fault length measured from four structural maps at the Cantarell oilfield in the southern Gulf of Mexico (offshore Campeche). The results demonstrate that the fault length data, corrected by seismic resolution at the tip fault zone, also exhibit fluctuating curves of log cumulative frequency vs. log length. The steps (shallower slopes) on the curves imply the scale positions of fault linkage. We conclude that fault linkage is the main reason for the fluctuating shapes of log cumulative frequency vs. log length. On the other hand, our data show that the two-tip faults are better for linear analysis between maximum displacement (D) and length (L). Evidently, two-tip faults underwent fewer fault linkages and interactions.
    Full-text · Article · Jan 2010 · Journal of Geodynamics
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    ABSTRACT: For exploration and development the geologists and engineers try to know the true stratigraphic thickness (t). The monoclinal and folded bed models are published methods for t calculation. Both models assume parallel beds which can lead to significant deviations. In order to calculate the values of t considering the effects of both folding and stratigraphic variation we propose the 'folded wedge model'. Three are considered: β<sub align="right"> 1 </sub>, the bed dip at the point where the well enters; β<sub align="right"> 2 </sub>, the bed dip at the point where the well leaves; and α, the deviated angle of borehole (angle between vertical and borehole). Three values of t can be obtained: the value measured normal to top (t<sub align="right"> 6 </sub>); the value measured normal to bottom (t<sub align="right"> 7 </sub>); the average value measured normal to bottom and top (t<sub align="right"> 8 </sub>). The folded wedge model is applied to the Cantarell oil field complex obtaining more reasonable values of t than using the existing methods. [Received: August 16, 2009; Accepted: February 10, 2010]
    Full-text · Article · Jan 2010 · International Journal of Oil Gas and Coal Technology
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    ABSTRACT: The processes that accompany asteroid impact and the roles they play in creating or destroying petroleum source rocks, reservoirs and traps are discussed. Most asteroids orbit the Sun in the asteroid belt, which lies between Mars and Jupiter but some come closer to the Earth. Excavation produces a bowl-shaped transient crater. Craters larger than a few kilometers in diameter usually have complex morphologies characterized by an uplift central area. The central high consists of shocked target rock that has been structurally uplifted by rebound. The bottom of the crater filled with melt brecias, mixtures of granite, carbonate, and dolomite in a spherulitic matrix. The impact that has drawn the most attention is the collision of the Chicxulub impactor with what is now the Mexican Yucatán Peninsula. A direct hit by an asteroid can also cause the demise of an hydrocarbon accumulation.
    No preview · Article · Dec 2009 · Oilfield Review
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    ABSTRACT: The Global Stratotype Section and Point (GSSP) for the Cretaceous/Paleogene (K/Pg) boundary was defined at the base of the boundary clay at a section near El Kef Tunisia, but the outcrop became quite deteriorated. In order to better characterize the boundary and to solve problems of correlation, several auxiliary sections are designed and described in detail including: Al'n Settara and Ellès in Tunisia, Caravaca and Zumaya in Spain, Bidart in France and El Mulato and Bochil in Mexico. These sections are the most continuous, expanded and representative of marine sedimentation in areas proximal and distal to the Chicxulub meteorite impact site. In addition, these sections are classical, very well known, physically accessible, have been exhaustively studied and allow a very detailed global correlation. The correlation criteria used were the meteorite impact evidence (Ir anomaly, Ni-rich spinel, etc.) and the mass extinction of planktic micro- and nannofossils. Furthermore, it was proposed that the K/Pg boundary is marked exactly by the moment of the meteorite impact, which implies that all the sediments generated by the impact belong to the Paleogene. While in distal areas to the impact site the K/Pg boundary coincides with a millimetre-thick rusty layer, in proximal areas the K/Pg boundary correlates to the base of a metre-thick Clastic Unit, including a thick calcareous breccia in the sections closer to the impact crater.
    No preview · Article · Jun 2009 · Episodes
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    ABSTRACT: Outcrops and offshore Campeche borehole data clearly document the presence of a carbonate facies succession, including calcareous breccia, on the western Yucatan Platform (Campeche Sound) and the Chiapas-Tabasco Platform. This carbonate sequence is associated with ejecta that contains altered glass, shocked minerals, and accretionary lapilli derived from the Chicxulub impact on the Yucatan Platform. The Cretaceous-Paleogene (K-Pg) boundary sedimentary succession is found at the El Guayal, Bochil, and Chilil outcrops of Tabasco and Chiapas, and offshore Campeche, 300-500 km (186-311 mi) west of the Chicxulub structure center. From base to top, this succession consists of four subunits: (1) carbonate breccia, 40-300 m (131-984 ft) thick, without ejecta; (2) fine- to medium-grained carbonate breccia, 10-20 m (33-66 ft) thick, mixed with sparse ejecta; and (3) siltstone, shale, and carbonate sand facies, 9-30 m (2998 ft) thick, containing abundant ejecta (altered glass and shocked quartz). This unit culminates in a nearly pure clay layer (∼2 cm [∼0.7 in.] thick) with the well-known iridium anomaly at the top. Unit 4 is a conglomeratic breccia ranging from 10 to 20 m (33 to 66 ft) thick containing ejecta that is interbedded with or overlays subunit 3 (the ejecta layer) in some wells. Subunits 1, 2, and 3 are highly dolomitized in offshore Campeche, and the glass in subunit 3 is altered to clay minerals (smectite). Subunits 1 and 2 constitute hydrocarbon reservoir facies, whereas subunit 3 corresponds to the sealing layer of these reservoirs. Regionally, this sequence displays a gradational structure that represents a large debris flow followed by ballistic and clastic sedimentation with materials reworked by currents. Moreover, well logs, areal distribution, and stratigraphic relationships suggest that the thick K-Pg boundary sedimentary succession is a base-of-slope apron deposit. Based on the stratigraphy, sedimentology, and distribution of impact materials in the carbonate sedimentary succession, the following sequence of events can be inferred: megaseismic shaking that induced the collapse of the platform margin and produced the lower breccia facies (subunits 1 and 2); ballistic emplacement of ejected material (carbonate fragments, shocked minerals and glass) that supplied components to subunit 2 and formed the ejecta layer (subunit 3), the latter acting as the seal for Cantarell and neighboring oil fields; and reworking of the ejecta layer and coarser-grained carbonate fragments by the effect of one or more impact-generated tsunami waves to form a conglomeratic breccia (subunit 4) within subunit 3.
    No preview · Article · Jan 2009 · AAPG Memoir
  • S. Xu · Á.F. Nieto-Samaniego · S.A. Alaniz-Álvarez · J.M. Grajales-Nishimura
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    ABSTRACT: We document that the direction of fault traces and the long axis of volcanic domes show a similar distribution, which indicates that the normal faults controlled in some way the location of volcanic rocks. In this study we analyze the evolution of the faults from a geometric point of view, without considerations about the volcanic processes. Bed tilt was controlled by fault block rotation with continuous fault activity. Multi-peak profiles of bed tilt along the fault strike and evident corrugation of the fault traces in the study area should be partly due to segment linkage during fault evolution. Some normal faults are associated with mode I fracture mechanism, whereas some other faults are due to mode II fracture mechanism according to the calculated initial dips. The plot of maximum fault displacement (D) versus trace length (L) is very scattered. Faults with D/L ratios larger than 0.1 and smaller than 0.1 can be distinguished; these two fault groups are produced by the effects of fault evolution and sampling. The principal factor influencing D/L ratios is the interaction and linkage among the faults. In addition, fault block rotation, fault initial mechanism, lithology of volcanic rocks, and denudation are other factors.
    No preview · Article · Jan 2008 · Boletin de la Sociedad Geologica Mexicana
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    ABSTRACT: The true bed thickness (t) is the actual thickness of a given formation perpendicular to the bedding plane. The value of t depends on the angle and the direction of the dip of the measured formation, as well as the drift angle and azimuth of the bore-hole. The traditional methods to calculate the parameter t consider only the case of monoclinal beds but not the case of a folded bed, which will cause deviations when the bed dip on the top is different from mat on the bottom. To avoid these deviations, this paper shows an approach to calculate the values of t using a folded bed model. The deviations for the monoclinal bed model are positively related to the bed dip, the dip difference and the deviated angle of the wells. A case study from the Cantarell oil field complex in the southern Gulf of Mexico (offshore Campeche) is used to test the folded bed method. The results indicate that this model can yield more uniform spatial change of the values of t, whereas the monoclinal bed model will overestimate the average value of t. Compared to the folded bed model, the maximum relative deviation off from the monoclinal bed model reaches 22.3% and the maximum absolute deviation of t reaches 34.5 m.
    Full-text · Article · Nov 2007 · Journal of Canadian Petroleum Technology
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    ABSTRACT: Fault slip and fault separation are generally not equal to each other, however, they are geometrically related. The fault slip (S) is a vector with a magnitude, a direction, and a sense of the movement. In this paper, a series of approaches are introduced to estimate quantitatively the magnitude and direction of the fault slip using fault separations. For calculation, the known factors are the pitch of slip lineations (γ), the pitch of a cutoff (β), the dip separation (Smd) or the strike separation (Smh) for one marker. The two main purposes of this work include: (1) to analyze the relationship between fault slip and fault separation when slickenside lineations of a fault are known; (2) to estimate the slip direction when the parameters Smd or Smh, and β for two non-parallel markers at a place (e.g., a point) are known. We tested the approaches using an example from a mainly strike-slip fault in East Quantoxhead, United Kingdom, and another example from the Jordan Field, Ector County, Texas. Also, we estimated the relative errors of apparent heave of the normal faults from the Sierra de San Miguelito, central Mexico.
    Full-text · Article · Oct 2007 · Journal of Structural Geology
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    ABSTRACT: Problems with measuring fault slip in the subsurface can sometimes be overcome by using subsurface structural contour maps constructed from well logs and seismic information. These maps are useful for estimating fault slip since fault motion commonly causes the dislocation of structural contours. The dislocation of a contour is defined here as the distance in the direction of fault strike between two contours which have the same value on both sides of a fault. This dislocation can be estimated for tilted beds and folded beds as follows: Similarly, for an asymmetric fold, the dislocation of contours due to the vertical slip component is Scb= (Smax - Smin)/(n + 1), and the strike-slip component is Ss= Scs= (nSmin+ Smax/(n + 1), where n is the ratio between the values of interlines of the two limbs, and Scb is the dislocation of contours due to the vertical slip component for either of the two limbs (here it is for limb b). In all cases, three conditions are required for the calculation of contour dislocation: These methods for determining fault slip from the dislocation of structural contours are discussed using case studies from the Cantarell oilfield complex, Campeche Sound (southern Gulf of Mexico), the Jordan-Penwell Ellenburger oilfield in Texas, and the Wilmington oilfield in California.
    Full-text · Article · Jun 2004 · Journal of Petroleum Geology
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    ABSTRACT: The main oil reservoir in the Cantarell Field, offshore Campeche, consists of a dolomitized carbonate breccia with an ejectsseal on top, considered to have been formed during the Chicxulub impact event. Two different dolomitization events have been identified associated with the reservoir. The first generation (D1) is a bright-red luminescent saddle dolomite while the second generation is a minute, non-luminescent dolomite (D2). Brine fluid inclusions show an evolution from D1 to D2 to higher temperatures (from 80–120 to 100–120 °C) and salinities (from 2–8 to 6–8 wt.% eq. NaCl). Hydrocarbon-bearing fluid inclusions evolved from heavy oils to light oils in D1 (from core to rim), while in D2, all inclusions appear to be formed by heavy oil with an 'API similar to the oil contained in the present reservoir. These facts suggest that the end of the dolomitization process was closely related with the beginning of the main accumulation of oil into the reservoir, displacing the aqueous fluids and precluding the precipitation of carbonates.
    Full-text · Article · May 2003 · Journal of Geochemical Exploration

  • No preview · Article · Feb 2002
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    Martinez-Ibarra R · Tritlla J · Cedillo-Pardo E · Grajales-Nishimura J.M

    Full-text · Conference Paper · Jan 2002
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    J. Smit · B. Roep · J. M. Grajales-Nishimura · J. Bermudez
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    ABSTRACT: The K/T boundary in marine deposits in and around the Gulf of Mexico at a dis- tance of
    Full-text · Article · Jan 1996 · Special Paper of the Geological Society of America
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    Full-text · Article · Jan 1994
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    ABSTRACT: 40Ar/39Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 ± 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from 40Ar/39Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 ± 0.08 Ma (mean plateau age for Beloc) and 65.07 ± 0.10 Ma (mean total fusion age for both sites). The 40Ar/39Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.
    Full-text · Article · Sep 1992 · Science

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