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Honduras Geology June, 1997
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El mapeo geológico del cuadrángulo de San Francisco de Becerra se efectuó intermitentemente durante el período de febrero a noviembre de 1988. El trabajo fué iniciado con el propósito de entender las estructuras asociadas con fallas mayores, estudiar la naturaleza de la formación Agua Fria, y para evaluar los recursos minerales de la zona.
Afloramientos del basamento metamórfico del Paleozoico se encuentran en la parte sur del cuadrángulo y están compuestos de filitas y esquistos grafíticos y sericíticos. También hay vetas gruesas de cuarzo que tienen un rumbo paralelo con la foliación (generalmente N60E). Estas rocas pertenecen al miembro superior (Las Marias) de la formación Cacaguapa y tienen una edad superior al Jurásico.
Encima del Paleozoico descanza la formación Agua Fria del Jurásico compuesta de capas delgadas de areniscas, limolitas, y lutitas negras. En muchos sitios esta roca está muy deformada y alterada con aparencias filíticas. Vetas finas de cuarzo sin orientación preferida también abunden tal como los cuerpos masivos de cuarzita.
En la parte suroeste del cuadrángulo hay un conglomerado de cuarzo en capas rojas. Se cree que estas rocas pertenecen a la formación Valle de Angeles inferior que se ha visto en otras partes de Honduras. Solo hay un sitio donde se encuentran fósiles en los clastos de caliza (81.3,03.7).
Al norte, por los alrededores de Juticalpa, hay una abundancia de tobas y brechas líticas. Los fragmentos líticos incluyen fenocristales de feldespato y cuarzo, fragmentos de lavas félsicos, y basalto. Al sur de San Francisco de Becerra hay afloramientos de tobas soldadas de un color rosado. Se supone que todo este material es de edad Terciario. La gente de esta zona usa la roca volcanica como material de construcción.
Cubriendo el suelo del valle de Catacamas hay una capa de aluvión y terrazas Quaternarios. Es en esta zona (por el Río Jalán y Río Guayape) donde se ha trabajado la zona en busca de oro de placer a principios de los años setenta. También se há trabajado la Quebrada del Oro y zonas al sur. Solo hay una mina en el cuadrángulo que se trabajó hace 20-30 años, la mina Anderson Rey del Oro, y está situado en rocas de la formación Agua Fria.
La estructura regional está complicada por los desplazamientos que han ocurrido en la falla Guayape, 35 km al este. Pliegues, juntas, fracturas, cizallas, y fallas de varios tipos son productos de las fuerzas tectónicas producidas por esta falla. Las dos orientaciones preferidas de fallas menores mapeados en el cuadrángulo tienen rumbos de N35E (aproximadamente paralelo con la falla Guayape) y de N35W.
Mapping of the San Francisco de Becerra quadrangle was initiated at the request of the Instituto Geografico Nacional in collaboration with the Direccion General de Minas e Hidrocarburos and the Peace Corps. The successful completion of this project would not have been possible without the generous contributions and encouragement offerred by the following organizations and individuals.
First of all, I would like to thank Jorge Betancourt and the Peace Corps for providing the financial resources and enthusiastic support for my work as a volunteer. Considering the bureaucratic process of any government agency, the Peace Corps has almost always pulled through in a timely fashion for my urgent requests.
The Instituto Geográfico Nacional has been most helpful through Ing. Juan Jose Guevara in providing me with the necessary maps, air photos, and indispensible travel expenses. Rodney Saubers and Emory Phlegar, both with the Inter-American Geodetic Survey at the Instituto Geográfico Nacional, have also been extremely helpful in providing me with obscure or hard to find information and maps. In addition, the logistics of shipping my rock samples to the United States could not have been possible without their assistance.
I wish to extend my thanks to the Dirección General de Minas e Hidrocarburos for providing the necessary vehicles and drivers to carry out the field work. The use of their rock cutting facilities is also most appreciated.
My special thanks go to Ric Finch (Tennessee Technological University) for providing me with relevant literature that got me started on Honduran geology and how to proceed with my field work here. His useful comments and suggestions through timely correspondence and a weeklong field visit were invaluable to me.
I would also like to acknowledge the very active participation of various individuals at the University of Texas at Austin who assisted me with different aspects of the project and who all made useful contributions to the interpretation of my rocks. First and foremost, I am grateful to Mark Gordon, who is working on the Santa Maria del Real quad for his doctoral dissertation, for his suggestion of mapping the San Francisco de Becerra quadrangle. Mark provided enormous amounts of relevant literature, free thin-sectioning services, and many useful discussions and insights into aspects and problems in Honduran geology. I am also grateful for his invitation to UT inorder to pursue my Honduran geology research. The final form of this report could not have been made possible without their resources.
Numerous faculty members at UT also provided a lot of support including: Bill Muehlberger, for his structural suggestions and use of personal resources while at UT; Keith Young, for his time and efforts in identifying the fossils; Dan Barker, for his comments and insights on the volcanic thin-sections; and Sally Sutton and Bob Folk, for their comments on the meta-sedimentary thin-sections.
Last, and certainly not least, I thank the people of those outlying communities of Olancho who provided guide services and good company during my long strenuous hikes into the remote mountain areas. Their hospitality and that of the people of San Francisco de Becerra was truly exceptional and will always be remembered.
I might add that any errors or inaccuracies in this report are the sole responsibility of the author. This open-file report is meant to accompany the Geologic Map of San Franciso de Becerra (1:50,000 scale) which is being published by the Instituto Geografico Nacional.
The geographic setting of Honduras in Central America lends itself to a unique opportunity to study a variety of geological and tectonic problems. Only until recently has enough attention been devoted to this area inorder to deceifer it's complex series of geological events.
The geologic investigation of the San Francisco de Becerra quadrangle was performed at the request of the Instituto Geografico Nacional in collaboration with the Direccion General de Minas e Hidrocarburos and the U.S. Peace Corps. The information gathered in this study is intended to contribute to the understanding of the previously poorly documented Agua Fria Formation and to the general understanding of Honduran geology.
Of all the countries in Central America Honduran geology remains the least understood due in part to the lack of access to many regions, it's topographic terrain, and the heavy vegetative cover. Considering these circumstances, Mills et al. (1967) published a remarkable paper which was the first attempt to describe the geology of this country in any detail. Over the years this work has been augmented by even more detailed field mapping projects performed by graduate students from the University of Texas at Austin and the University of Wesleyan, Peace Corps volunteers, and workers from private companies and other universities (see table 1). The location of these mapped quadrangles appears in figure 1.
The United Nations has also been actively involved for the past twenty years in detailed mapping of potential mining areas, namely Yuscaran, Quitagana, El Mochito, and others. In addition, from 1969-1972 they carried out a regional geological survey and geochemical exploration in the northwestern part of the country. This data was used in the compilation of the national geologic map (Elvir, 1974). In 1977, further detailed mapping of this region was carried out by the government of Honduras in collaboration with the government of Japan. A highly detailed series of reports was then published by the Japan International Cooperation Agency in 1978 which presented the results of their effort.
An inventory of at least 250 mines and potential mining areas is currently under way at the Direccion General de Minas e Hidrocarburos (DGMH). Their work will result in maps which outline the metalic and non-metalic mineral resources as well as a new version of the geologic map of Honduras. This information is expected to be available towards the end of 1989.
Geophysical data has also been collected in Honduras though the resolution is frequently inadequate for detailed work. The Defense Mapping Agency has computer contoured Bouguer and Free-Air gravity anomaly maps which were compiled using data from various sources. Areas in central and eastern Honduras lack adequate coverage to rely too heavily on the contouring interpretation. There is also a magnetic anomaly map (1:250,000 scale) which was produced in 1985 by Sunmark Aeroservices, Inc. as part of a project sponsored by World Bank and DGMH. This map, however, is not available to the public at the present time.
Honduras lies in the northern portion of Central America with Guatemala bordering it to the northwest, El Salvador to the southwest, and Nicaragua to the south. It is the second largest and most mountainous country of Central America and encompasses 112,088 square kilometers. Highlands and mountains make up 81.7% of this area and more than 75% of the land has slopes exceeding 25% (JRB Assoc., 1982). The location of the map area is shown in figure 2 along with the breakdown of the morphotectonic units in the entire region.
Two principal geographic features characterize the area encompassed by the San Francisco de Becerra quadrangle. The northern half of the quadrangle is dominated by a portion of the Valle de Catacamas (Catacamas Valley) which is roughly 15-20 km wide by 50 km long in it's entirety and runs southwest to northeast. This broad flat valley is surrounded by high relief topography on all sides, especially to the north and east. Only a portion of the southern range, called the Cerro de Azacualpa, is included in the map area.
The San Francisco de Becerra quadrangle lies in the central portion of the department of Olancho between latitudes 14o30'N and 14o40'N and longitudes 86oW and 86o15'W. It covers approximately 500 square km at a scale of 1:50,000 (which is roughly equivalent to a 15 minute quadrangle). A major town in the northwest corner of the map, Juticalpa, provides the only direct link to the capital city, Tegucigalpa.
Most of the area within the quadrangle is easily accessible with the exception of the mountainous southeast corner. A southwest-northeast trending highway runs through the upper central portion of the quadrangle paralleling the Guayape River. From this arterial highway numerous unpaved roads branch off to the north or south. The network of roads and 4-wheel drive access is rather good, but becomes limited in the rainy season. Mule trails and footpaths comprise the remaining access into the southeastern mountain areas (see figure A4 in appendix).
The Guayape River is the main river which cuts through the Catacamas Valley. The Guayape then feeds into the Patuca River (off the map) which eventually empties into the Atlantic Ocean. In the southwest corner of the quadrangle, the Jalan River runs north into the Guayape. Figure 3a illustrates the drainage pattern of all of the streams and tributaries that empty into the Guayape and Jalan rivers. The direction of flow of these minor streams is generally perpendicular to that of the two major rivers (see fig. 3b).
Figure 4 illustrates the topographic patterns for the Cerro de Azacualpa range. Shading and outlines distinguish the different elevation ranges as indicated in the key. The figure extends into the quadrangle to the south, the Azacualpa-Rio Guayambre quad, inorder to include both the northwest and southeast sides of the range.
Patterns in this type of illustration, such as the truncation or offsets of mountain ranges, are helpful in identifying faults and lineations which may not be apparent when viewing air photographs. Numerous branches on the north side appear to be truncated suggesting normal faulting. Similarly, there is a slight offset in the trend of the range near it's midpoint suggesting the possibility of strike slip faulting.
A preliminary and now outldated geological map of Honduras was prepared by the Direccion General de Minas e Hidrocarburos in 1974 (Elvir, 1974), and is the only recent published source of information available for the quadrangle area. Earlier work by Helbig (1953) produced a sketchy geologic map of eastern Honduras which included the San Francisco de Becerra region. Finally, numerous field investigations have also been carried out by the personnel at DGMH, however, none of their data has ever been published.
Detailed geological studies are currently under way on an adjacent quadrangle to the northeast, Santa Maria del Real, as part of Mark B. Gordon's doctoral thesis. His work has spilled over into the entire region in order to gain better structural control of his map area. Apart from this work, there are no other mapped quadrangles in this region.
Topographic quadrangles of Honduras are published by the Instituto Geografico Nacional at a scale of 1:50000. The Universal Transverse Mercator grid (1 km per side) is superimposed on the map thus fascillitating reading of the ordinate and abscissa coordinates of one's location. Due to the scale used, a location accuracy of no better than one tenth of a kilometer is necessary, therefore, the mapping resolution is good to within about 50 m from a given point. For example, the church in the central park of San Francisco de Becerra is located at (96.3, 19.2).
The climate in this part of Honduras generally consists of a dry season (the verano) which lasts from roughly December through May and a rainy season (invierno) from June through November. Some of the most torrential rains usually occur anytime from July through September and contribute to the 180-250 cm of anual rainfall depending on the elevation. Temperatures are also dependent on the elevation. For zones with elevations lower than 500m such as the Catacamas Valley the median anual temperature is 26-28oC while zones above 500m experience temperatures from 16-24o C (JRB Associastes, 1982).
The combination of temperatures, precipitation, topography, and soil types give rise to a variety of ecosystems in Honduras. According to Holdridge's (1978) ecological classification scheme for Honduras, the Catacamas Valley is classified as a 'dry tropical forest'. However, due to extensive deforestation for the development of agriculture, only small patches of forest remain along the Guayape river. The higher elevations to the south, in turn, still maintain the 'subtropical humid forest' as defined by Holdridge (1978). This vegetation primarily consists of oak (Quercus) and pine (pinus oocarpa is found at lower elevations, and pinus pseudodostrobus at the higher elevations). Only along some of the highest ridges and peaks (over 1200m) does one find vestiges of cloud forest where the dense, broadleaf vegetation thrives under the low rate of evaporation. These peaks are frequently cloud covered.
Extensive land use is threatening much of this biological habitat as heavy deforestation is continuously encroaching on the mountains. Slash and burn practices are the most common method used in clearing land for grazing and agriculture. Corn, coffee, and bean fields are frequently seen in the mountains, while the valley farmers usually cultivate cotton, rice, corn, and beans.
In order to grasp the geologic complexities with the San Francisco de Becerra quadrangle it is necessary to understand the regional setting and the conditions which gave rise to the local geology. A vast amount of research effort has been devoted to the task of piecing together a picture that describes the tectonic and geologic evolution of the area.
The Cacaguapa schist is the rock unit which is thought to underly all of the rocks in Honduras and is considered to be the basement rock of the Chortis block. This basement complex and the suite of rocks that lie on it are considered by many to be a geologic terrain which is independent of the northern Guatemala (the Mayan block) and southern Central America terrains. The Paleozoic basement in northern Guatemala shows a higher degree of metamorphism than that of the Cacaguapa Schist in Honduras.
Ross and Scotese (1988) and Gose (1985) have performed some of the most recent modeling of the tectonic evolution of the Caribbean region. A summary of their models with occassional references to others is as follows:
Beginnning with the reconstruction of Pangea 180 million years ago during the mid-Jurassic (fig. 5A) spreading centers appeared north and southeast of the Yucatan and southeast of the Chortis block. These spreading centers and associated transform faults evolved in response to the splitting up of three major plates, namely the North American, South American, and African plates (fig. 5B). Paleozoic and Mesozoic plate motions gave rise to the Honduras Intracontinental Basin which includes a thick sequence of sediments found in the present day Ulua Basin. By mid-Cretaceous, Yucatan was in it's present position (attached to Mexico) and a new subduction zone appeared just north of the Greater Antilles (fig. 5C). This subduction zone migrated east while enhancing a major transform fault feature, the Hess Escarpment, in the process (fig. 5D). By late Cretaceous, plate motions along the northern boundary of the Chortis had created parallel tectonic fold belts with generally east-west trends. These mountains make up the "nuclear fold belt" which is described in detail by Mills et al (1967). At 60 ma. Ross and Scotese (1988) estimate that another subduction zone appeared which once again continued the trend of the trench off Mexico (fig. 5E). With a closure of boundaries, the Caribbean plate was thus born and moved according to the stresses imposed on it by the surrounding plates Gose (1985). During the Eocene the orogenic process creating the northern Central American sierras ("nuclear fold belt") had climaxed and by the Oligocene most of Central America was emergent (Dengo and Bonenberger, 1969). In all, almost 20,000 feet of Mesozoic sediments had been faulted and folded into the east-west anticlinoria. Throughout the Tertiary, Honduras continued it's eastern migration toward it's present position while at the same time active volcanism extruded magmas and thick tuffaceous deposits across the western, central, and southern Honduras. Much of this activity is thought to be associated with the subducting Cocos plate beneath the Chortis block. This period also roughly coincides with the opening of the Cayman trough (Rosencrantz et al., 1988) (see figure 5F). The Cayman trough is a small rift zone with associated left lateral transform faults to the east and west. The complex series of splayed faults in northwestern Honduras and southern Guatemala (Motagua fault, Polochic fault, and others) are believed to be part of an intraplate deformation process which is accommodating the large displacements created by the Cayman trough (Rosencrantz and Sclater, 1986). Another significant structural feature in Honduras is the apparent extensional environment which extends from the northcoast in the Sula Valley down to the Gulf of Fonseca. This series of north-south trending disjointed grabens is known as the Honduras Depression (Muehlberger, 1976). The eastern migration of the Caribbean plate is the most likely explanation for this localized extension (Mann and Burke, 1984). Finally, figure 5G is a representation of the Caribbean plate margins at the present time.
The Cacaguapa Schist is the oldest exposed rock unit in the San Francisco de Becerra quadrangle area. This unit is composed of Paleozoic sericitic and graphitic schists which make up most of the foothills in the southern portion of the quadrangle. The initial deposits probably consisted of sandstones and shales that were metamorphosed into low-grade high-relief metamorphic rocks. Several intrusives pushed their way into these rocks which were later metamorphosed by one of possibly several episodes of deformation (Horne et al, 1976).
Around the mid-Jurassic, sandy, shaley and coaly sediments were deposited in a relatively passive deltaic environment. Cycad and fern fossils in the black shales suggest a swampy or wet tropical environment . Transgressing water during the Cretaceous lead to a marine environment which accounts for the thick sequence of limestones (Yojoa Group carbonates) which appear in the ranges to the north of the quadrangle. Subsequent uplift and folding eventually brought these limestones to the surface where exposure to the elements lead to a complete erosion of these rocks in the southern part of the valley and mountains. Later, left lateral motions along the Guayape fault 35 km to the east contributed to extensive faulting and folding in the Catacamas Valley region. These motions also lead to river offsets and the progressive change in bedding attitudes as one approaches the fault from west to east.
By the end of the Cretaceous, the net result of continued uplifting and erosion was the deposition of thick redbed sediments produced by streams and flood plains. These consisted of red limestone/sandstone/quartz pebble conglomerates which remained in areas of relatively low relief.
Tertiary volcanism brought about the extensive maroon lithic tuffs and ashfall deposits seen to the north near Juticalpa. These deposits most likely covered the entire area and originated from volcanic centers to the west.
Finally right lateral faulting in the area by the Guayape fault lead to the formation of the Catacamas Valley which resembles either a normal pull apart basin or a fault wedge basin as proposed by Gordon and Muehlberger (1988).
Figure 6 compares the stratigraphic columns by Mills et al (1967), Horne et al (1974), Finch (1981), and Kozuch (this report). The most significant change in stratigraphic nomenclature that this report proposes is to drop the formation name of "El Plan" in favor of "Agua Fria" based on current work by Dr. R.C. Finch (personal communication).
Comparison of Finch's (1981) fairly complete stratigraphic column with that of Kozuch's (this report; see figure 6) demonstrates the extent to which the complex structure and erosion of the Catacamas valley and surrounding mountains have affected the exposed geology. Essentially, the mountains south of the valley consist of mid-Jurassic Agua Fria sediments resting unconformably on the metamorphic Paleozoic basement complex (Cacaguapa Schist). Exposures are good when found, however, no sizeable outcrop was ever encountered that could be used as a measured section. In the southwest, the redbed sediments of the Valle de Angeles Group also appear to rest unconformably on the basement. They may, in fact, be fault bound against the basement. These redbed conglomerates are thought to be Upper Cretaceous based on their resemblance to dated rocks in other parts of the country, however, an exact stratigraphic position cannot be assigned to these rocks until fossils within the redbeds themselves are found. Next, one finds volcanic tuffs and pyroclastics which are also faulted up against the basement. These rocks are thought to be Tertiary in age based on field relations in adjacent quadrangles. The upper and lower age limit of this unit is still in question until it can be properly dated. Finally, the Quaternary terraces and stream alluvium blanket the valley floor and generally consist of unconsolidated flood plain deposits.
The follow section describes the characteristics of these formations in more detail.
Horne et al (1976) describes the basement as a widespread sequence of metamorphic rocks consisting of dominantly low grade phyllite and mica schists with subordinate quartzite and marbles (which are prevalent at the top). Carpenter (1954) first studied the sequence of graphitic and sericitic schists at San Juancito. He describes them as well foliated and containing numerous pods of milky white quartz up to a foot in length. Occassionally pyrite casts anywhere from 1/4 - 1" in diameter may be found. This unit is probably similar to the phyllitic Palacaguina found in Nicaragua (Zoppis Bracci, 1957; del Giudice, 1960). It also appears equivalent to Fakundiny's (1970) upper member of the Cacaguapa Schist (the Las Marias Member) which consists of greenschist facies pelitic strata with minor marble and quartzite. The schist found in the San Francisco de Becerra quadrangle and in surrounding quadrangles fits all of these descriptions and will thus be considered to be equivalent to the upper member of the Cacaguapa Schist.
Outcrops of the Cacaguapa schist lie along a 4-5 km wide stretch of foothills which run along the south side of the Catacamas Valley. The only interuption in this band of rock occurs in an area west of Potrerillos where the valley floor abruptly runs up against the Agua Fria rocks. Rolling hills and relatively smooth erosional surfaces make up the characteristic topography of the Cacaguapa Schist in this area. Should the Cacaguapa Schist have very irregular topography of it's own, then it is quite possible that these basement rocks may also surface within the Azacualpa range (Montaña Chagüiton, Cerro Capiro, etc.). Dense vegetation, however, renders mapping of these outcrops nearly impossible at the present time.
The most common schists encountered in the quadrangle area are generally sericitic and graphitic in nature. At many outcrops, the rock resembled a phyllite rather than a schist due to the characteristic gray or silvery phyllitic sheen present on the surfaces. Inspection with a hand lens, however, usually revealed the very fine (1 mm or less) alternating layers of quartz lenses and micas. Where good clean schist is found, distinct micaceous flakes of muscovite and biotite are seen in alternating layers with quartz rich minerals and other accessory minerals. Thin stringers of milky white quartz also permeate the rock and generally run parallel to foliation.
Thin sections revealed fine lepidoblastic textures with white micas constituting the prominant minerals. Crenulation cleavage was a common structural feature which often revealed the sense of shear. Many rocks contained strained quartz in the form of subangular to rounded grains or as fine ribbons. In rocks which resembled meta-shales, chlorite was a prominent constituent with minor quantities of graphite scattered throughout the rock as irregular blebs.
A very common weathering feature to the basement rocks is their resemblance to dried out tree bark. Black, silvery, brown, and rusty orange streaky patterns on the irregular and ripply surfaces are usually quite unique to these rocks. Another sign of being in the vicinity of Cacaguapa schists is the remarkable amount of quartz fragments found in the surface float.
Occassionally, large (up to 1 cm) cubic pyrite casts with limonite coatings were found randomly scattered throughout the rock mass, the limonite most likely being the alteration product of pyrite. These casts are one of the characteristic features of this formation which distinguishes it from others.
In addition to the schists, outcrops of a bluish gray quartzite were not uncommon. These quartzites did not contain the quartz veins that were present in the schists. No stratigraphic relation could be determined for any of these rocks due to the vegetative cover.
No marble was ever found in the quadrangle area, however, small outcrops do exist 3-4 km to the west of the Río Jalán in the southeast corner of the adjacent Lepaguare quadrangle.
Metamorphism of the original Cacaguapa sediments probably took place sometime before the mid-Jurassic Agua Fria sediments were deposited. Radiometric dating by Williams and McBirney (1969) suggests an early Paleozoic date, however, the data has been inconclusive. Pushkar et al (1972) determined a Sr87/Sr86 ratio from which Horne et al (1976) calculated a maximum age of 412 million years (mid-Silurian) for a phyllite sample. Further age dating is necessary on these rocks in central and eastern Honduras.
A fairly thick sequence of sedimentary rocks which rest on top of the Paleozoic basement are widespread throughout much of Central Honduras and only until recently is a reasonable picture of their nature, thickness, age, and distribution beginning to emerge. The name Honduras Group was first proposed by Finch (1985) to distinguish two distinct sedimentary sequences of roughly Jurassic age.
Beginning with the lower member of the Honduras Group, the interbedded black shale and sandstone unit exposed near San Juancito, was called the El Plan Formation by Carpenter (1954). Similarly, several other investigators (Simonson, 1977 and others) have assigned the El Plan name to the thin bedded sandstone and shale strata which is thought to lie directly and nonconformably on the Paleozoic basement rocks.
A problem soon arose with the name "El Plan". The rocks that Carpenter (1954) described do not lie exactly in El Plan, and they appear to encompass only a portion of the complete lithology seen elsewhere. In fact, the El Plan sediments may represent just one facies of the more widespread sediments present in other parts of Honduras. Based on recent field studies, R.C. Finch and A. Ritchie (personal communication) propose changing the name to "Agua Fría Formation", after a small mining town in southern Honduras. They have measured the thickest section of sediments yet (1570 m), and in light of their work, this report will use the name Agua Fría Formation to refer to the lower member of the Honduras Group.
The upper member of the Honduras Group is a siliclastic unit (occassionally associated with redbeds) which has commonly been called the Todos Santos Formation after a similar looking unit in northwest Guatemala. Paleomagnetic investigations by Gose (1985) and Gose and Swartz (1977) however, have shown that the sediments found on the Honduran Chortis Block were deposited with a different magnetic orientation than those on the western Guatemalan Mayan Block. Therefore, usage of the Todos Santos name for sediments south of the Motagua fault is technically inappropriate and should be abandoned as suggested by Gose and Finch (1987). Since no outcrops of this formation were encountered in the quadrangle area, however, no further reference to this portion of the Honduras Group will be necessary.
An extensive deposit of Agua Fría sediments covers the lower portion of the quadrangle which essentially blankets the highlands of the map area. They extend from just east of the Río Jalán to the easternmost edge of the quadrangle, and from the latitude of Potrerillos down to the southernmost edge of the quadrangle. There appear to be no other formations in this area except for the few intrusives which may penetrate the Agua Fría rocks.
Though the Agua Fria sediments are characterized in the broadest sense as thin bedded tan sandstones and black shales, there is a great deal of variation in their appearance in the San Francisco de Becerra quadrangle. Local metamorphism caused by intrusives or intense shearing resulting from faulting could be the predominant causes of this variation. These factors, in addition to the similarity of weathering appearances with the Cacaguapa Schist often created difficulties in distinguishing these two rock formations from one another. Many times only a gradational transition from the basement to the "meta-Agua Fría " sediments occurred instead of a clear cut contact between the two units. The lack of good outcrops also hampered the search for a reasonable contact.
Characteristics of good clean undeformed Agua Fría sediments consisted of three main varieties. These included: 1) thin bedded (< 1cm to 5 cm) tan silty sandstones with interbedded shales, 2) thin bedded shales with interbedded sandstones, and 3) thick portions (several meters thick) of massive sandstone. Fine laminations and cross-bedding are some of the structural features occassionally seen in the siltstones. Thin quartz veining and deformed or wavey beds are other characteristics. These rocks are slightly porous with tightly packed angular grains (90% quartz, 5% feldspars, plus others) and are usually very hard.
The metasediments are principally composed of fine bluish to white quartzite in the form of thin beds. These beds are also on the order of 1-5 cm thick and are usually quartz veined. Veining does not occur necessarily along a bedding surface, but rather at random orientations. These veins are usually on the order of 1-5 mm thick. Large siliceous zones also exist. A highly resistive north-south trending ridge southwest of Potrerillos is almost entirely silicified. A similar but smaller zone lies just south of Quebrada de la Danta up on the ridgeline.
There are also many outcrops of very deformed metasediments which almost resemble the phyllitic schists of the Cacaguapa formation. They sometimes exhibit a silvery gray phyllitic sheen on the bedding surface which can cause a great deal of confusion with the Cacaguapa phyllites. Some examples include the deformed shales found near Laguna del Guineo (96.3,08.8) where thick (1-2 cm) veins appear to have sweat out of the quartz and swirled around in response to the surrounding stresses. Other deformed shales can be found near the village of Los Planes in the Montaña Chagüiton area and at the foot of Cerro Capiro.
The thickness of this formation is still in question. The combination of deformations, faulting, and lack of a continuous exposed section makes the thickness difficult to calculate. However, considering the general trend of the bedding and the ample surface coverage, there may be up to 3000 meters of Agua Fría sediments.
In reviewing the stratigraphy of Honduras and the fossils identifications made by previous workers, Mills et al (1967) assigned a late Triassic - mid Jurassic age to the El Plan Formation. More recently, Delevoryas and Srivastava (1981) suggested confining the age to mid-Jurassic based on the cycad and fern fossils that they identified from the same area as El Plan. Ammonite fragments collected by Finch have also been dated as mid-Jurassic (personal communication).
No fossil localities were found for the Agua Fría rocks in the quadrangle area. However, two very good sites were found just 2 kilometers south of the San Francisco de Becerra quadrangle in the Azacualpa-Río Guayambre quad (localities (87.1,01.2) and (90.2,02.0)). The plant fossils collected resemble the cycads and ferns reported by Delevoryas and Srivastava (1981), however, accurate identifications of these fossil samples remains to be performed.
The Valle de Angeles Group is a thick sequence of predominantly redbed siliclastic strata with four major subdivisions: the lower redbeds, the Jaitique formation, the Esquías formation, and the upper redbeds. Some brief remarks about each unit are worth mentioning here even though the only member found in the quadrangle area was the lower redbed unit.
In essence, a quartz pebble conglomerate with a high percent of coarse clastic strata makes up the lower Valle de Angeles. The Ilama formation, as it was originally defined by Mills et al. (1967), was thought to be associated with the Yojoa Group carbonates, and they depicted the formation as having a variable stratigraphic position. However, further field investigations by UN geologists and Finch (1972) found that the "Ilama" conglomerates appeared in different statigraphic positions in the Valle de Angeles Group instead. Gallo and VanWagoner (1978) also placed these sediments in the Valle de Angeles Group. Because of the lack of continuous strata that can be used as a map unit and seeing that the original definition of this formation name was in error, Finch (1981) proposed dropping the name "Ilama Formation" .
Above the quartz pebble conglomerates lies a limestone unit called the Jaitique Formation which is made up of two members. The lower member is an unnamed thick bedded limestone unit overlain by the Guare member which consists of thin bedded shaly limestones. Finch (1972) assigned a Cenomanian age to the Jaitique carbonates.
The Esquias formation is another limestone unit which is also considered to be Cenomanian, "though somewhat younger" (Finch, 1981). This blue-gray limestone has been described in detail by Horne et al. (1974).
Finally, the upper Valle de Angeles consists of fine grained, locally gypsiferous, red clastic strata (Finch, 1981).
For the time being, the rocks found in the quadrangle area will be considered as lower Valle de Angeles redbeds based on the descriptions presented above. However, until fossils that were found in some of the limestone clasts can be identified, the true stratigraphic position cannot be known with certainty.
The only part of the quadrangle which contains any Valle de Angeles rocks is a narrow strip (2-4 km wide) which runs along both sides of the Jalán river. Following the river north to where it empties into the Guayape, the distribution of these redbeds tends to fan out into the Catacamas Valley. The northwestern most limit of the Valle de Angeles becomes increasingly difficult to map because it exhibits a transitional gradation into the Quaternary terraces.
In this quadrangle the most common rock type within the Valle de Angeles redbeds is a quartz pebble conglomerate. From a distance the beds appear to have a reddish brown color and often take on a black staining where weathered. Subangular to rounded quartz and quartzite pebbles are usually found poorly sorted in a well indurated fine red matrix. In the matrix are unevenly distributed fine interstitial sands, silts, and clay particles bound by a hematite cement and silica. Porosity seems to vary with the hardness of the rock. When the rock is not very porous, it it usually well indurated and contains significant amounts of silica. Small (10 cm) to large scale (1m or more) bedding is often determined by the weathering profiles in addition to the occassional presence of graded beds. Sharp indentations usually are a good indication of the contact between beds. Cross bedding is also a very common feature in these rocks.
In addition to the quartz and quartzite pebble clasts, rounded and sometimes broken pebbles of light gray siltstone were found. Other clasts included angular to rounded limestone pebbles which varied in size from 1-20 cm. These were only encountered at one locality (81.0,03.6) and were found to contain a variety of fossils including oysters, gastropod, mollusk, and bivalve fragments, stromatoporoids, orbitolinas, radiolitids, chambered forams (choffafella sp.), rudists (?), and algal forms. Frequently the clasts were noted to be fractured and filled with calcite.
Mills et al. (1967) dated the redbed quartz conglomerate sediments as Latest Albian - Cenomanian. Finch (1972) assigned an Albian - Cenomanian age to these rocks which is roughly equivalent to the Mid-Albian - Early Cenomanian age determined by Gallo and VanWagoner (1978). To the author's knowledge, no one in the past has ever dated the fossils in the clasts, and although the Mid-Albian - Early Cenomanian may be a reasonable age, the true age cannot be known with certainty since previous claims are based only on field relationships. Keith Young at the University of Texas at Austin is currently working on the fossil identifications.
Of all the rocks in Honduras, perhaps the most difficult to classify are the volcanics. With so many varieties of volcanic rocks, and so very little which has been done to differentiate them in Honduras, an enormous task lies ahead to identify and explain the events that produced them. Williams and McBirney (1969), Dupre (1970), Everett (1970), Fakundiny (1970), Horne et al. (1970), Curran (1980), and Anderson (1985) each made valuable contributions to the understanding of Honduran volcanics by mapping out and differentiating the various Tertiary and Quaternary flows in central Honduras. Unfortunately, large portions of western and eastern Honduras still contain volcanic rocks which have not been studied in any detail and remain classified simply as Tertiary volcanics (Tv). The volcanic tuffs found in the San Francisco de Becerra quadrangle do not resemble the Padre Miguel tuffs nor any others which have been described by the previously mentioned authors. Therefore, not until the tuffs are dated and mapped out in other quadrangles nearby can they be assigned to a specific stratigraphic unit and be named.
The vast majority of tuffs in the quadrangle outcrop in the northwestern portion of the quad in and around Juticalpa. Though a continuation of volcanic exposures was expected east of the Rîo Juticalpa, none were found. The only other mapable outcrop was a small hill just south of the town of San Francisco de Becerra.
Only in one small spot near Cerro Capiro (97.7,05.3) were fragments of a very white tuff encountered, however, this material was only in the float and no outcrop was ever found.
The bulk of the volcanic rocks in the quadrangle area are reddish or maroon lithic tuffs. Several outcrops along the highway southwest of Juticalpa showed colorful signs of alteration which might have resulted from nearby thermal activity. At least two outcrops in the same vicinity, also demonstrated inverse graded bedding within the coarse tuffaceous layers. Koch and McLean (1975) state that this phenomenon may indicate a progressive increase with time in the intensity of eruptions.
Several varieties and textures of tuff were identified in outcrop and in thin section. Rocks near Juticalpa were very brecciated and contained numerous joint sets. At times the number of joint sets made the bedding surface indistinguishable. Samples collected near the northern edge of the quadrangle were usually crystal-lithic breccias with fragments consisting of pumice and intermediate felsic lavas and vesicular basalt lavas. There was also a minor presence of calcite and sericite visible in thin section. Almost all of the samples had lithic fragments which were poorly sorted and very angular suggesting very little transport. No glass shards were seen in the northernmost rocks. Other samples collected in the northwest vicinity but closer to the fault bound valley (80.8,17.0) included lithic airfall tuffs which were fine grain, non porphyritic, and which contained many poorly sorted angular lithic fragments.
Several outcrops on the small hills south of San Francisco de Becerra exhibit lithophysal zones which are easily identified by gas formed vugs up to 2 cm in diameter. Rocks in this area generally had a pinkish color. Thin sections revealed these to be crystal vitric welded ashflows. These densely welded pyroclastic flow rocks contained a sizeable amount of glass shards exhibiting fluvial features which wrapped around large feldspar phenocrysts (some albitized plagioclase) and completely flattened pumic fragments.
The age of these rocks is thought to be Tertiary based on field relations of other rocks in nearby quadrangles. However, until the rocks can be properly dated, the upper and lower age limits will remain in question. It is assummed that the volcanic rocks south of San Francisco de Becerra are somehow related to those near Juticalpa, however, since they appear to lie unconformably on the basement, this relation is only an assumption at best. It is the general appearance of the rocks which allows one to correlate them with those to the north.
A variety of sedimentary structures are present in the Quaternary deposits which cover the Catacamas valley floor. The oldest sediments are found in the terraces (Qt1,2,3..). These flood plain deposits consist of poorly to moderately sorted gravels and sands with an overall brown to rusty orange color. From some of the dry stream beds that feed into the Guayape river, some spectacular stream cut terraces depict crossbedding and graded bed structures. Angular to rounded quartz fragments, schist fragments, and siltstone pebbles are also found in the terrace cuts. Several terrace levels can be identified by their knobby terrain with flat tops or broad, flat, and very extensive surfaces. Thickness of the layers rarely exceeded 20 meters. Air photographs were most helpful in mapping out the various terrace levels.
Quaternary alluvium deposits (Qal) are generally confined to areas on either side of the Jalán and Guayape rivers. They consist of unconsolidated sands, gravels, and pebbles made of schist, shales, or sandstones. One site near the Guayape River (94.5, 19.8) actually had some very large embedded boulders of highly weathered, semi-rounded, fine sandstone. However, boulder size clasts are uncommon within the alluvium.
Several intrusions are present in the San Francisco de Becerra region which are too small to be mapped. These include rocks found at Quebrada de la Danta [(98.7,07.5), (98.0,08.7), (99.9,07.0)] and Quebrada Santa Fe (98.1,05.1). Two others, however, are fairly sizeable and the contacts are relatively easy to follow. These will be the focus of my attention.
The largest intrusion situated in Laguna del Guineo is actually a metamorphozed granite. Generally composed of medium grained quartz (which was the dominant mineral), feldspar, and minor quantities of sericite and altered biotite, it is the deformed nature of the quartz which betrays it's metamorphosed state. Significant quartz grain size reduction permeated the rockmass. An interesting feature that was found in a stream bank near Laguna del Guineo was a large chill zone (?) roughly 10 meters long by 30 cm wide which resembled xenolithic slab of tan sandstone floating in the intrusive. Very small pyrite crytals in a fine grained matrix were found scattered throughout this chill zone material.
The other large intrusion was spotted just northwest of El Ocotillal on the south side of the Azacualpa range. This rock appeared to be very fresh in outcrop, however, thin section revealed some minor weathering. The large hornblende crystals (up to 2 mm in diameter), in addition to the quartzo-feldspathic matrix, would render this rock a diorite.
The age of these intrusions is difficult to establish. However, since the Laguna del Guineo intrusion is fairly metamorphosed, it might have deformed contemporaneously with the basement and Agua Fría rocks, thus rendering it post-Agua Fría .
The structure of the San Francisco de Becerra quadrangle appears to be dominated by faults and intrusive bodies, though it is not clear just how large of a role the intrusives may play. Extensive folding may also have taken place in this region, though outcrops revealed only a few small scale folds. The largest structural feature by far is the southwest-northeast trending Catacamas Valley which opened as a result of roughly N-S extensional forces.
Figure 7 is an attempt to structurally resolve the series of complex contacts encountered in the field. From section A-A' the most recent normal faulting which gave rise to the valley is evident. These faults are strikingly apparent in the field. Previous to the normal faulting episode, overthrusting of the Cacaguapa schists onto the Agua Fría rocks must have occurred to the south to resolve the apparent problem of Agua Fría beds dipping under the basement. Thrusting must have also occurred to the north to elevate the Mesozoic sediments far enough to where they could be stripped away by erosion. It is possible that two different styles of faulting on the north side of the valley may have used the same fault surfaces.
The main features to section B-B' are the faults in the Jalan river area that bring the Valle de Angeles redbeds up against the basement. These faults most likely combine normal and right lateral strike-slip displacements and may be related to the strike slip motions expected along the edge of a pull-apart basin or wedge (see figure A5 in the appendix). These and all of the faults produced in the cross-sections can be identified from the topographic sheet, air photo linears, or they may be seen in the field.
Generally speaking, the fault trends shown in figure 8a appear to be controlled by the Guayape fault. While many faults and linears follow the general trend of the Guayape (roughly N35E), others tend to align at N35W (see fig. 8b). Though it was not always observed nor mapped as such, it is believed that most of the major streams which drain off of the Cerro de Azacualpa correspond to fault locations (compare with the drainage map in fig. 3).
There is a strong tendency for the Cacaguapa foliations to dip 60-70 degrees to the northwest with a northeasterly strike (figure 9). This compares rather closely with the poles to bedding data for the Agua Fría rocks (see figure 10). This suggests that at least one episode of uplift and deformation is common to both rock units, and that it occurred after the Agua Fría rocks were in place (e.g. post mid-Jurassic). No attempt was made to plot the volcanic bedding data due to insufficient data points.
It is evident that more work is needed in the Catacamas valley to grasp the nature of the complex structures in the region and the role that the Guayape fault. Geologic mapping and regional neotectonic studies in surrounding quadrangles are currently in progress in hope to shed some light on these problems.
There is only one mine present in the quadrangle area, the Anderson Rey del Oro mine, which was in operation from 20 to 30 years ago. Unfortunately, no detailed information exists as to the nature or time of operations there. Recent sampling and analyses by the personnel at DGMH has indicated the presence of minor quantities of gold, silver, lead, zinc, and copper.
Apart from the Anderson mine, there is also a presence of placer gold in the southwestern streams and rivers. Panners are frequently seen working the Quebrada de Los Lirios (near 93.3,04.5) and Quebrada del Gallo o del Oro (near 91.0,03.5), however results are usually tenuous at best.
In an unpublished report for DGMH, Glover (1978) discusses the placer gold mining activity performed along the Quebrada Danto (off the quad) and Río Jalán. He states that in 1971, Russel International Mining Company (RIMCO) worked several concessions along these rivers. They used a 1 million lempira (approx. 1/2 million dollars) dredge to work the area, but failed after 1 day due to inadequacies in the separation-classification-concentration system for dredge capacity. Samples which were assayed in Canada revealed 0.01 and 18.0 oz/ton gold, and those which were assayed in the United States revealed 7.6 oz/ton gold, 32.3 SiO2, 3.3% Fe2O3 , 34.3 TiO2 from 15 cubic yards of material.
In 1974, Corporacion Minera Mayan, S.A. also worked concessions on the Jalán downstream to where it joins the Guayape River (Glover, 1978). Results of their work prooved inconclusive since their Boddensen dredge sank after a short period of time.
A visual confirmation of platinum was made from samples collected by RIMCO during their dredging operations in 1971 on the Río Jalán (Glover, 1978). It is not known from where on the river the samples were collected.
Occassional outcrops of graphite were encountered, one of which lies near (00.7,13.1). Associated with the metamorphic basement rocks, the occurrence of graphite is rare in the quadrangle area and the quantity is minimal.
The red lithic tuffs found near (97.2,18.0) are actively quarried for use as building stones in the construction of houses in San Francisco de Becerra and surrounding towns. The rock is also quarried in the vicinity of Juticalpa.
Along Quebrada San Felipe, the Guayape River, and the Jalán River people collect sands and gravel for use in road and construction purposes. This material is usually poorly sorted and requires sifting and sorting prior to use.
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Delevoryas, T. and S.C. Srivastava, 1981. Jurassic plants from the Department of Francisco Morazán, Central Honduras: Rev. Paleobot. Palynol., Vol. 34, pp. 345-357.
del Giudice, D., 1960. Apuntes sobre la geologia del Departamento de Nueva Segovia: Boletín Servicios Geológicos Nacional Nicaragua, No. 4, pp. 17-37 (in Spanish).
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Dupré, W.R., 1970. Geology of the Zambrano quadrangle, Honduras, Central America [unpublished M.A. thesis]: University of Texas, Austin, Texas, 128 pp.
Elvir, A.R., 1974. Mapa Geológico de la Republica de Honduras: Instituto Geográfico Nacional, Tegucigalpa, Honduras, scale 1:500,000, 4 sheets.
Everett, J.R., 1970. Geology of the Comayagua quadrangle, Honduras, Central America [Ph.D. Diss.]: University of Texas, Austin, 234 pp.
Finch, F.C., 1972. Geology of the San Pedro Zacapa quadrangle, Honduras, Central America [Ph.D. Diss.]: University of Texas, Austin, Texas, 238 pp.
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Finch, R.C., 1985. Mapa Geológico de Honduras, Santa Barbara Sheet: Instituto Geográfico Nacional, Tegucigalpa, Honduras, scale 1:50,000.
Folk, R.L., (1968). Petrology of sedimentary rocks: Austin, Texas, Hemphills, 170pp.
Gallo, J., and J.C.VanWagoner, 1978. Stratigraphy and facies analysis of Honduras: Exxon Production Research Company, Special Report. (on open-file at Dirección General de Minas e Hidrocarburos, Tegucigalpa, Honduras).
Glover, J., 1978. Summary of information extracted from annual reports submitted by mining entities holding exploration/exploitation rights pertaining to placer-mineral mines, deposits, and showings: Internal report, Proyecto DGMH-ACDI, Honduras, Tegucigalpa.
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Description of Thin Sections Descriptions of the thin sections will be subdivided into several sections corresponding to the various formations to which the rocks belong. Beginning with the Cacaguapa Formation and working our way up the stratigraphic column, the format of the descriptions will vary according to the type of rock which is being described.
For the metamorphic rocks of the Cacaguapa Schist I will use the following format:
Rock name:
Sample number:
Location: grid number and description of location.
Description: fresh surface color (F:), weathered surface color (W:), texture,
composition, remarks, metamorphic facies.
----------------------------------------------------------
Rock name: phyllite
Sample number: SF-26T
Location: (01.2,13.5) 1 km west of Sabana Larga
Description: F: light brown or tan, W: reddish or rusty brown; augen-mylonitic
texture; large well rounded to angular quartz grains and meta-clasts molded
in a fine grained matrix; contains sheared quartz grains and ribbon quartz;
minor quantities of white mica are present along the folia. Very similar
to SF-74.
Rock name: schist
Sample number: SF-27T
Location: (01.5,13.6) 1 km west of Sabana Larga
Description: F: W:; fine lepidoblastic texture, strong foliation shows
development of crenuation cleavage, largely composed of sericite and white
micas, long dark minerals (pyhrotite or other sulfide) cut across foliation,
very porous.
Rock name: chlorite schist mylonite
Sample number: SF-29T
Location: (02.9,15.5) 1 km north of Sabana Larga
Description: F: olive green, W: dark green; strong foliation shows fine
banded granoblastic matrix with folia containing substantial sericite and
graphite, ribbon quartz is strained.
Rock name: phyllite
Sample number: SF-33T
Location: (04.9,18.5) about 3 km south of Tres Ceibas
Description: good crenulations developed in the folia to determine sense
of shear, large rounded grains of both strained and unstrained quartz scattered
throughout the rock; contains white micas, limited biotite, and minor chlorite;
regular and widely spaced foliation bands in a poorly sorted matrix.
Rock name: phyllitic schist
Sample number: SF-37T
Location: (94.6,10.6) in stream north of Santa Fé
Description: F: tan, W: dark brown; irregular but generally elongated phenocrysts
of biotite and muscovite are set in a fine grained matrix with a schistose
fabric.
Rock name: phyllite
Sample number: SF-74T
Location: (99.3,11.6) on Cerro del Sombrero
Description: F: tan, W: reddish or maroon brown; augen-mylonitic texture;
large sand grains of sedimentary origin are well rounded to angular; also
contains rip-up clasts that are metamorphic in nature; dissolution of grain
boundaries is common; plenty of sericite present within folia as well as
throughout. This sample is very similar to SF-26T.
Rocks from the Agua Fria formation will roughly follow the classification
scheme of Folk (1968) for clastic sedimentary rocks:
Rock name:
Sample number:
Location:
Description: general rock classification; 5-fold name (grain size: prominent
cements, textural maturity, prominent transported consituents, main name);
hardness; color (F: fresh, W: weathered); weathering character and bedding,
porosity; permeability; sorting; rounding of clasts; homogeneity of clasts
throughout specimen; packing; orientation of grains; grain shape; cements:
(in order of age, volumetrically largest cement given in 5-fold name above);
clasts and percentages; environment of deposition.
------------------------------------------------------------
Rock name: fine meta-sandstone
Sample number: SF-25T
Location: (88.8,04.6) in Quebrada San Felipe
Description: fine meta-sandstone; medium hard; F: tan, W: rusty brown;
slightly porous; large, poorly sorted rounded to subangular (but mostly
elongated) quartz grains are packed in a fine grained matrix of sheared
quartz, plagioclase and sericite are also present in minor quantities.
Rock name: deformed shale
Sample number: SF-42T
Location: (97.5,05.9) 4 km south of Laguna del Guineo
Description: terrigenous; hard; poor bedding definition (slight lineation
to matrix minerals is only clue to bedding plane); contains 15% graphite
in irregular blebs in a predominantly choritic matrix; cement is chlorite
and minor calcite (?); low energy environment of deposition.
Rock name: meta-greywacke
Sample number: SF-43T
Location: (97.5,05.9) 4 km south of Laguna del Guineo
Description: F: tan, W: rusty brown; contains a lot of rounded to subangular
sandsize quartz grains set in a fine matrix; biotite and sericite present
along foliation bands; phenocrysts may be hematite.
Rock name: quartz-biotite schist
Sample number: SF-54T
Location: (93.3,08.7) Potrerillos
Description: F: gray, W: red, orange, white or tan; 10% small biotite crystals
set in a lepidoblastic matrix of similar grain size to that of biotite;
foliated matrix contains sericite and fine zone quartz; rock has sedimentary
origin appearance though it has been strongly altered.
Rock name: mylonite
Sample number: SF-59T
Location: (97.5,07.2) Quebrada de la Danta
Description: F:pink, white, and tan, W: orange and rusty brown; fine lepidoblastic
texture; rock has been strongly altered (or baked?); fine grained quartz
and sericite, there is a lot of hematite staining, and the sample is highly
fractured with plenty of quartz veining.
Rock name: deformed shale
Sample number: SF-83T
Location: (05.1,12.2) in Quebrada Escamile
Description: F: dark green or brown, W: black; very fine and silty texture;
contains biotite and 5% graphite in a deformed and foliated fine matrix
of probable chlorite and clay minerals; ample quartz veining.
The classification of the tuffaceous rocks presented here is adapted
from the format of Cook (1965) while the intrusives approximate that of
Streckeisen (1965) which is very similar:
Rock name:
Sample number:
Location: grid location, and location description
Description: color (F: fresh, W: weathered); texture; composition; remarks;
classification.
-------------------------------------------------------
Rock name: metagranite
Sample number: SF-1D
Location: (95.0,10.3), Laguna del Guineo.
Description: F: light gray, W: rusty orange to brown; aphanitic porphyritic;
phenocrysts consist of % quartz and K-feldespar (orthoclase?) with minor
white mica and biotite; quartz is highly sheared, extensive grain size
reduction.
Rock name: crystal lithic breccia
Sample number: SF-22T
Location: 4 km west of Juticalpa
Description: F: maroon or gray, W: dark maroon to dark gray; plagioclase
phenocrysts have sericite on surfaces as well as penetrating the crystals;
lithics are intermediate felsic lavas and basalt lavas; evidence of calcite;
no glass shards.
Rock name: lithic airfall tuff
Sample number: SF-23T
Location: 4 km southwest of Juticalpa
Description: F: maroon or gray, W: dark maroon to gray; fine grained; non-porphorytic;
angular lithic fragments of pumice and lavas; no shards visible.
Rock name: crystal-vitric welded ashflow
Sample number: SF-36T
Location: foothills south of San Francisco de Becerra
Description: F: pink, W: light gray or dark pink; large amount of glass
shards; completed flattened pumice shows wispy fluvial structures around
isolated plagioclase phenocrysts and lithic fragments.
Rock name: chill zone (?) xenolith
Sample number: SF-38T
Location: (95.0,10.3), 1km north of Laguna del Guineo.
Description: F: gray, W: light rusty brown or white; contains a lot of
irregular blebs of biotite (20% maximum); sheared feldspar, minor pyrite,
and skeletal opaque minerals; entire rock exhibits extensive alteration.
Rock name: diorite
Sample number: SF-87T
Location: (05.2,05.5), 3 km northwest of El Ocotillal.
Description: F: dark gray, W: black; major minerals include quartz and
feldspar with minor hornblende crytals up to 2 mm in diameter; other minor
constituents include chlorite, sphene, and secondary pyroxenes; lots of
alteration is present.
Figure 1. Location of geologic quadrangle maps published to date in Honduras. The maps which are in progress (LU-La Union, D-Danli,SMR-Santa Maria del Real) are also included. The key to the quadrangle abbreviations is given in Table 1.
Figure 2. Morphotectonic units of Central America (after Dengo and Bohnenberger, 1969). The location of Honduras and the map area are shown relative to the rest of Central America.
Figure 3a. Watershed drainage map of the San Francisco de Becerra quadrangle. The two main rivers (Rio Guayape and Rio Jalan) are indicated with heavier lines.
Figure 3b. Rose diagram illustrating the general trend of all the streams and tributaries. The data was normalized by multiplying the number of streams of a particular azimuth by a weightling factor corresponding to the length of the stream. The weightling factors were the following : 1 for streams from 0-1 km in length, 2 for streams from 1.1-2.0 km, 3 for streams from 2.1-3.0 km, and so forth.
Figure 4. Topographic pattern map of both the San Franciso de Becerra and Azacualpa-Rio Guayambre quadrangles. Shaded area corresponds to elevations over 900 meters; the blank outlined area corresponds to elevations from 700-900 meters.
Figure 5(a, b, c, d, e, f, g). Tectonic plate evolution of the Caribbean (adapted from Ross and Scotese, 1988).
Figure 6. Stratigraphic column used in this report and those of previous authors.
Figure 7. Geologic cross-sections of the San Francisco de Becerra quadrangle from points A (85.2,20.3) to A' (02.0,03.1) and from B (80.7,08.6) to B' (88.5,03.1). Symbols correspond to the following: Qal = Quaternary alluvium and terraces, Tv = Tertiary volcanics, Kva = Cretaceous Valle de Angeles, Jaf = Jurassic Agua Fria, csp= Cacaguapa Schist, i = intrusive.
Figure 8a. Map of the San Francisco de Becerra quadrangle indicating the fault patterns. Solid lines are mapped faults, dashed lines are inferred or covered faults, dashed and dotted lines are air photo lineaments, and dashed/double dotted lines are topographic lineaments picked off the topographic sheet.
Figure 8b. Rose diagram illustrating the trend of all of the faults and lineaments in the San Francisco de Becerra quadrangle area. The weighting factors are the same as those used in the Watershed Drainage map (figure 3b).
Figure 9. Contour plot of the poles to foliation of the Cacaguapa Schist.
Figure 10. Contour plot of the poles to bedding of the Agua Fria Formation.
Figure 11. Conceptual illustration depicting the relative motions in the Catacamas Valley area due to the Guayape fault. Note the slip displacements that may occur where the Jalan River lies.
Figure A1. Sketch of thin sections of several samples collected in the San Francisco de Becerra quadrangle area.
Figure A2. Classification scheme for mechanical composition of ignimbrites (after Cook, 1965). Compositions are listed in order of increasing abundunce.
Figure A3a. Geologic map of the San Francisco de Becerra quadrangle, Honduras.
Figure A3b. Key to the symbols used on the geologic map in figure A3a. (Mapped Stratigraphic Units)
Figure A4. Map of the San Francisco de Becerra quadrangle showing principle routes of access and elevation points. All roads are unpaved except for the paved highway which runs northeast into Juticalpa.
Figure A5. Conceptual illustration depicting the sense of slip motions associated with various parts of the Catacamas valley due to the Guayape fault. Note the strike-slip motions in the vicinity of the Jalan River.
