Geologic Quadrangle-Boca Wampú (Special Edition)
GEOLOGY ALONG THE RíO PATUCA AND RíO WAMPú, LA MOSQUITIA,
HONDURAS
Robert D. Rogers
334 Williams Avenue North, Renton, WA USA 89004, Tele. 206-228-1592,
e-mail: rrogers@utig.ig.utexas.edu
The citation for this publication is: Rogers, R.D. 1995, Geology
along the Río Patuca and Rio Wampú. La Mosquitia, Honduras.
Open File Report, Instituto Geográfico Nacional, Tegucigapla, Honduras
21 pages. No Spanish version of this report was written. The report
accompanies the following map that is being prepared for publication by
the IGN: Rogers, R.D. in press, Mapa Geológico de Honduras: Hoja
de Boca Wampú (edición especial), Instituto Geográfico
Nacional, Tegucigalpa, Honduras, escala 1:50,000. (Several typographical
errors were corrected and a context error corrected
on 2/21/98).
Contents
ABSTRACT
INTRODUCTION
REGIONAL GEOLOGY
STRATIGRAPHY Honduras Group, Yojoa Group-Atima
Formation, Krausirpi beds, Valle de Angeles Group, Mafic volcanic rocks,
Tabacon beds, Alluvium.
STRUCTURE Compressional features, Strike-slip
faults, Patuca Lineament, Structural implications.
SUTAWALA WIND GAP
ECONOMIC AND ENVIRONMENTAL
GEOLOGY Minerals: Precious metals, Building materials. Hydrocarbons.
Environmental: Transportation, Hydropower.
CONCLUSIONS
REFERENCES
ACKNOWLEDGMENTS
EPS print file of geology map at true size (1:50,000) is available by e-mail
request to rrogers@utig.ig.utexas.edu.
This will print at size of standard Honduras geology sheet.
ABSTRACT
Recent 1:50,000 scale geologic mapping, at the confluence of the Río
Patuca and the Río Wampú of eastern Honduras, reveals new
details of the stratigraphy and structure.
Phyllite, slate, schist, and quartzite of the Jurassic-Cretaceous Honduras
Group form the northeast trending highlands north and east of the Río
Patuca. This unit appears to be a weakly metamorphic equivalent of the
Jurassic Aqua Fría Formation. Thick-bedded micrites and a few thin
sparry and biomicrite beds comprise the Cretaceous Atima Formation of the
Yojoa Group, which forms the Montañas de Colón south of the
Río Patuca. Thinly bedded shale, arenite, and graywacke with minor
limestone and quartz pebble conglomerate conformably overlie the Atima
limestone. This shale is found along the Río Patuca, east of the
Río Wampú, and in northeast striking valleys within the Montañas
de Colón. The Upper Cretaceous Valle de Angeles Group, consisting
of redbeds of fine-grained sandstone and lithic conglomerate, unconformably
overlies the shale. These redbeds are exposed in the Río Patuca
lowlands and flank the metamorphic highlands. Isolated basalt and andesite
flows occur in the redbeds in the Río Patuca lowlands and form thick
flows along the Río Wampú. K-AR chronology yield ages of
80.7±4.3 to 70.4±4.3 for the mafic flows (Weiland et al.
1993). The redbeds grade upward to a thick cobble and boulder breccia containing
clasts of the mafic volcanic rocks. This breccia flanks the southeast side
of the metamorphic highlands and forms the highlands south of the Río
Wampú.
South of the Río Patuca, northwest verging thrust faults place
Cretaceous Atima limestone over Upper Cretaceous Valle de Angeles redbeds
and repeats the Atima section in the Montañas de Colón. The
northeast trending metamorphic highland and the thick breccia north of
Río Patuca expose large folds. Small folds, thrust faults, and tear
faults within the redbeds express northwest-southeast compression. North-northeast
trending dextral strike-slip faults cross-cut the thrust faults of the
Montañas de Colón.
INTRODUCTION
Press for Location Map (93k)
Located in the Mosquitia region of the Departments of Olancho and Gracias
A Dios of the Republic of Honduras, the Ríos Patuca, Wampú,
and Sutawala intersect. The northeast striking Montañas de Colón
(>800 meters) form the southeastern margin of the map area. The Montañas
del Patuca (>500 meters) form the broken highlands to the north and west.
The lowlands of the Río Patuca, the largest river in Honduras, trends
northeast across the central portion of the map. Parallel to the Río
Patuca and 20 km to the south flows the Río Coco, the largest river
in Central America. The Montañas de Colón currently separates
these rivers.
Tropical rain forests cover the area with the exception of small fields
along the Ríos Patuca and Wampú, which were cleared by the
indigenous Tawahka. During the dry season from about January to April water
level along the rivers and streams is low exposing extensive outcropping
of bedrock.
The intersecting quarters of four 1:50,000 scale topographic maps served
as the base for the mapping. These maps are the NW 1/4 of the Confluencias
Ríos Patuca y Wampú (Hoja 3260 IV); the SW 1/4 of the Krausirpi
(Hoja 3261 III); the NE 1/4 of the Confluencias Ríos Patuca y Wasprasní
(Hoja, 3160 I); and the NW 1/4 of the Confluencias Ríos Wampú,
Aner y Pao (Hoja 3161 II). As their names indicate, these maps present
the unique occurrence of five navigable rivers and numerous tributaries
with exposed bedrock in the Mosquitia region of Honduras. The mapped area
is roadless, accessible only by dugout canoe (pipante) and on foot. Two
reconnaissance trips in January and October, 1991 preceded the field mapping
during January and February, 1992.
This area was selected for study because it is the most accessible place
in the Mosquitia region to conduct detailed mapping of the geology.
REGIONAL GEOLOGY
Honduras along with Nicaragua, El Salvador, and southern Guatemala form
the Chortis block of the Caribbean Plate (See Kozuch 1991, Donnelly et
al. 1991, for reviews of Honduran geology). The Chortis block, with its
lithologically and temporally distinct basement, is separated for the Maya
block of the North American plate by the Chixoy-Polochíc-Motagua
transform fault and from the Cocos plate by the Middle American Trench
subduction zone. The Chortis block has experienced rotation, shearing,
and stretching following Late Cretaceous-Early Tertiary collision with
the Maya Block to the north.
Honduras is cut by northeast and northwest trending shear zones presumably
active since Chortis collision (suturing) with the Maya block before the
Early Tertiary. Counterclockwise rotation of the Chortis resulting from
sinistral displacement relative to North America is believed to have resulted
in the opening of grabens and dextral motion on northeast and northwest
strike-slip faults on the Chortis block (Gordon and Muehlberger 1994).
East of the Guayape fault zone, structural and tectonic interpretations
suffer from a lack detailed mapping and are largely speculative.
The known stratigraphy of Honduras ranges from Paleozoic metamorphic
basement to Quaternary volcanic deposits. Gneiss, schist, phyllite, marble,
and meta-intrusive rock form the basement Cacaguapa schist. This sequence
has undergone at least three deformation episodes with the oldest being
at least 305 Ma (Horne et al. 1976).
The Jurassic-Cretaceous Honduras Group clastic strata composed of conglomerate,
sandstone, shale, coal, carbonate rock, and minor volcanic beds overlie
the basement and has experienced minor metamorphism in places (Gordon 1990,
Finch and Ritchie 1985, and Rogers 1992). The Honduras Group depositional
environment is varied and includes fluvial, coastal plain, and marine facies.
Deposition of a thick sequence of shallow marine carbonate rocks, the Yojoa
Group, occurred in Early Cretaceous Albian to Aptian time in central Honduras
(Donnelly et al 1991, Kozuch 1991). This marine transgressive sequence
is the thickest limestone unit exposed in Honduras.
The predominantly terrestrial redbed deposition of the Valle de Angeles
Group commenced in Late Cretaceous time interspersed by marine carbonate
deposition (the Jiatique and Esquías Formations of Cenomanian age)
in central Honduras (Finch, 1981). Quartz pebble conglomerate dominate
the lower Valle de Angeles Group, while fining to shale and sandstone in
upper redbeds. Based on the sedimentary structure of the Valle de Angeles
Group in the Tegucigalpa area, Rogers and O'Conner (1993) interpret this
group as proximal and distal tropical alluvial fans dominated by hyper-concentrated
fluid flows.
The Tertiary volcanic sequence rests unconformably on the Mesozoic strata.
Matagalpa mafic flows (Oligocene) have spotty exposure and may interfinger
with the thick sequence of predominantly ignimbrite tuffs of the Miocene
Padre Miguel Group. Padre Miguel deposition extends over most of central
and southern Honduras becoming thicker and younger to the south (R. Harwood,
pers. comm. 1992). Less extensive and presumably Tertiary-age tuff, andesite,
and pyroclastic deposits occur in central and northern Honduras. Late Tertiary-Quaternary
mafic flows cap the older volcanic sequence in places and appear related
to structural trends in central Honduras. Intrusives of varying ages and
compositions punctuate the stratigraphy. Eastern Honduras and especially
the Mosquitia region is poorly known geologically. Mills and Hughs (1974)
provide the only published record of the geology based on reconnaissance
transects along rivers courses and compilation of regional geologic information.
No mapping had been conducted in the region before this effort. Stratigraphic
and structural trends were based on regional extrapolation. Hydrocarbon
exploration in the region has produced a mixed bag of geologic results
with no coherent picture of the geology. This project was undertaken to
provide a level of investigation to serve as a basis for a broader understanding
of the geology of the region.
STRATIGRAPHY
Link to Geologic Map (403 K) Map size reduced
to load faster. EPS print file of map at true size (1:50,000) is available
by e-mail request to rrogers@utig.ig.utexas.edu.
This will print at size of standard Honduras geology sheet.
Link to Stratigraphic Column
HONDURAS GROUP (JKhg)
The metasedimentary rocks of the Jurassic-Cretaceous Honduras Group are
composed of dark (fresh exposure) to light gray, pink and tan phyllite,
tan to gray quartzite, minor black graphitic schist, and gray slate with
quartz veins increasing in frequency and size to the north, along the Río
Wampú. The rocks are weakly metamorphosed and form the rugged northeast
trending highlands of the north-central map area.
These rocks are correlated with the Honduras Group. They are the likely
equivalent to the Jurassic Agua Fría strata of the Honduras Group
east of the Guayape fault based on similar appearance and deformation.
No fossils were observed, and the unit is assumed to be Jurassic-age as
are Agua Fría strata west of the Guayape fault. The contact between
the Honduras Group strata and the overlying redbeds (Valle de Angeles Group)
is unconformable and only locally faulted. The phyllite is often stained
pink near the contact with redbeds which show no sign of having been affected
by metamorphism. Honduras Group strata were noted in unconformable contact
below the Tertiary Tabacón beds and below mafic volcanic flows along
tributaries to the Río Wampú.
YOJOA GROUP-Atima Formation (Ky)
The Cretaceous Atima Formation of the Yojoa Group is composed of dark to
medium gray, thick-bedded micrites with a few sparry and biomicrite beds.
The Atima limestone forms the Montañas de Colón karst highlands
south of the Río Patuca. This unit is correlated with the Atima
Formation (Albian-Aptian) of central Honduras by its general appearance,
thickness, and the mapped stratigraphic relations. The Atima stratigraphic
contact with underlying beds was not found. The upper Atima contact appears
conformable with the thin-bedded sandstone and shale of the Krausirpi beds
in the Sutawala valley. Along the Quebrada Kahkatingni south of Cerro Wampú,
Atima limestone with epikarst development was found immediately below Valle
de Angeles redbeds. Paleontological studies released by the Dirección
General de Minas e Hidrocarburos support this interpretation and indicates
an upward shoaling from Albian to lowermost Cenomanian (IBI, 1985). This
suggests continued deposition of Atima limestone in eastern Honduras following
cessation of Atima deposition in central Honduras. The Yojoa Group carbonate
rock are absent north of the Río Patuca in the project area.
KRAUSIRPI BEDS (Kk)
These strata are composed of light gray to tan shale and gray thin and
planar-bedded arkosic, lithic arenite, and graywacke that weather to a
red-brown orange. Both the sandstone and shale are calcareous in places.
Thin limestone beds appear in this unit as well as a limestone breccia
near the contact with the Atima limestone. A minor lithic pebble conglomerate
was found. The clastic rocks contain alternating coarse-fine layers and
rare wood fragments. Calcareous rocks are typically finer grained, and
one limestone bed contains algal stromatolites. The Krausirpi beds are
found within the strike valleys of the Montañas de Colón
and are exposed along the Río Patuca during low flow. The Krausirpi
beds are in conformable contact with the underlying Atima limestone in
the Sutawala valley. At Krausirpi, these beds are in contact with the overlying
Valle de Angeles redbeds and are separated from the redbeds by a minor
unconformity. This unit contains upper Albian-lower Cenomanian marine fossils
(IBI, 1985). The change from marine carbonate deposition to marine clastic
deposition, with terrestrial carbonaceous material unconformably below
terrestrial redbeds, indicates a marine regression. The Krausirpi beds
may be prodeltaic.
The Krausirpi beds were distinguished by their mappable occurrence and
stratigraphic position below the Valle de Angels redbeds at Krausirpi and
above the Atima limestone in the Sutawala valley. Supporting paleontological
data was divulged after the field-based decision to map the Krausirpi beds
as a separate unit. It is possible that the Krausirpi beds are a local
unit of the Yojoa Group. However, mapping relations suggest that it is
a separate unit that should not be correlated with other mapped units in
Honduras.
VALLE DE ANGELES GROUP (Kva)
The Valle de Angeles redbeds in the project area contain maroon to red
fine-grained sandstone, matrix- and clast-supported pebble to boulder subangular
to subrounded poorly sorted conglomerate of quartz, limestone, and minor
volcanic fragments. Bedding is generally planar, but a few fluvial cross-beds
were observed. The unit is exposed in the lowlands along the Río
Patuca, as the moderate topography flanking the Honduras Group highlands,
in the valleys north of the highlands, and as fault slivers among Atima
limestone in the Sutawala valley.
The lower contact of the Valle de Angeles redbeds is unconformable with
the Honduras Group and the Krausirpi beds. Southeast of Cerro Wampú,
along Quebrada Kahkatingni, redbeds rest unconformably on epikarst developed
on the Atima limestone which was subaerially exposed before Valle de Angeles
deposition. The upper contact is transitional with the extremely coarse
Tabacón beds, gradually coarsening up section, and displaying a
loss of sandy material in the Tabacón beds (the matrix material
changes from sand to silt). In places, mafic volcanic flows occur at the
upper contact separating the Valle de Angeles redbeds from the Tabacón
beds. The age of the Valle de Angeles redbeds is constrained by lower Cenomanian
limestone clasts (Atima -see above) found within the conglomerates and
ages between 80.7±4.3 to 70.4±4.3 Ma for the mafic volcanic
flows above the redbeds (Weiland et al. 1993). The Valle de Angeles strata
have planar beds, lack basal scour, contain few channels, and have matrix-supported
clasts; features indicating deposition by hi-viscosity and hyper-concentrated
fluid flows. A few cross-beds were observed. Deposition occurred as debris
flows with minor fluvial facies on a tropical alluvial fan.
MAFIC VOLCANIC ROCKS (Kv)
The dark gray, green and reddish basalt and andesite flow rock contains
plagioclase phenocrysts and a biotite rich groundmass. Flow banding, scoria,
and autobrecciated flows were observed. Calcite and zeolote filled cavities
appear in the mafic flows. The flows are found extensively in the low relief
north of the Río Wampú between the Ríos Pao and Aner
and as isolated flows interbedded with the Valle de Angeles redbeds. K-AR
whole rock and plagioclase dating obtained ages of 80.7±4.3 to 70.4±4.3
Ma for the flow rock (Weiland et al. 1993). These isotopic ages and the
presence of the volcanic rock interbedded within the Valle de Angeles redbeds
are the reasons for assigning both the mafic volcanic rock and the generally
underlying redbeds a Cretaceous age. The mafic flows separate the Tabacón
beds and the Valle de Angels redbeds on Crique Malawás. Mafic flows
unconformably overlie the Honduras Group metasedimentary strata north of
the map area.
TABACóN BEDS (Tt)
The Tabacón beds are composed of maroon to green, cobble to boulder,
subangular to angular breccia and conglomerate of quartzite, volcanic rock,
quartz, and minor red sandstone clasts. Tabacón beds flank the southeast
side of the Honduras Group highlands and appear as a rugged ridge-former
(with numerous waterfalls) to the northwest of the Honduras Group highland.
Angular clasts of the Tabacón beds are generally supported in a
fissile mud matrix, and the sand size fraction of the matrix is minor.
Bedding is exclusively planar with the excellent exposure along the Quebrada
Tabacón.
The lower contact of the Tabacón beds with the Valle de Angeles
redbeds is gradational. Minor fluvial cross-beds occur within this transitional
zone. The lower contact of the Tabacón beds with the mafic volcanic
rocks and the Honduras Group is unconformable where observed along tributaries
to the Río Wampú. The Tabacón beds are assigned an
Early Tertiary age based on the Late Cretaceous ages obtained for the underlying
volcanic rock and presumably the clasts which comprise the Tabacón
deposit. The Tabacón beds were deposited in hi-viscosity debris
flows rich in fines. Based on the angularity of the clasts within this
deposit, it is not likely that the material traveled far from its source,
presumably a fault bounded uplift. It is possible that the Tabacón
beds are a local unit of the Valle de Angeles Group. However, mapping relations
suggest that it is a local basin fill that should not be correlated with
other mapped units in Honduras.
QUATERNARY ALLUVIUM (Qal)
Unconsolidated silt, sand, and gravel deposited at the confluence of the
Río Patuca and the Río Sutawala were mapped as Quaternary
alluvium. Additional alluvium occurs along the Río Patuca, Río
Wampú, and other rivers and streams in the project area. No attempt
was made to systematically map the surficial deposits of the project area.
STRATIGRAPHIC IMPLICATIONS
-
The Yojoa and Valle de Angeles Groups appears to be younger stratigraphically
(10-15 my) than in Central Honduras. This indicates a depositional basin
that is younger to the east.
-
The mafic volcanic rock and Tabacón beds define a local(?) Late
Cretaceous-Early Tertiary basin fill and is evidence for tectonic activity.
-
A limestone boulder breccia and mafic volcanic rock occur along the Río
Coco between Tilba and Awasbila south of the Montañas de Colón.
These may correlated genetically with the Tabacón beds found north
of the Montañas de Colón, defining the southern margin of
a depositional basin during the Late Cretaceous-Early Tertiary.
-
Krausirpi beds thin and disappear to the southwest along the Río
Patuca. This may define the margin of the marine depositional basin (Yojoa
Group) during Albian/Cenomanian.
-
The Valle de Angeles strata and the basal transitional Tabacón redbeds
appear to have a northern source, based on the few paleocurrent indicators
found.
-
The limestone clast conglomerate of the Valle de
Angeles Group was always found south of and distal from the exposed Honduras
Group highlands. No Yojoa Group limestone was found
eastnorth
of the Río Patuca in the map area. It is questionable whether Yojoa
Group limestone was deposited east north
of the Río Patuca.
STRUCTURE
(see Montañas de Colón Fold Thrust
Belt, Eastern Honduras for additional documentation of structural geology
and cross-section)
Link to NW-SE geological cross-section (150k)
COMPRESSIONAL FEATURES
The dominant structural features of the map area are northwest verging
thrusts in the Montañas de Colón and folding east of the
Río Patuca. Evidence for this is the predominate northeast strikes
and southeast dips that are maintained across lithologic boundaries south
of the metamorphic highlands and the presence of Lower Cretaceous Atima
limestone over Upper Cretaceous Valle de Angeles redbeds. At Siquiapisne
on the Río Patuca and along Quebrada Kahkatingni, interleaved Atima
and Valle de Angeles strata were observed with bedding attitudes consistent
across contacts and with the older Atima over the younger Valle de Angeles.
This relation was seen along the northwest front of the Montañas
de Colón and interpreted as southeast dipping reverse faults. Valle
de Angeles strata occurs as fault slivers within the Atima limestone at
three localities along the Río Sutawala, indicating fault repetition
of the thick Atima limestone in the Montañas de Colón. The
prominent Cerro Wampú appears to have a thrust contact on its northwest
face while the southeast face is a demonstrable dip slope evidenced by
epikarst at the contact between the Atima limestone and the overlying Valle
de Angeles redbeds.
Deviation from southeast dips exists in the thin-bedded Valle de Angeles
and Krausirpi beds defining small-scale thrusts and folds consistent with
northwest-southeast compression. Small northwest trending (perpendicular
to the northeast structural trend) right and left lateral shears were observed
in the Valle de Angeles and Krausirpi beds in association with compressive
features and are interpreted as compression related tear faults. A large
(1.5 km displacement) northwest trending sinistral tear fault exists west
of the map area based on air photo and topographic map interpretation.
A northeast trending fold belt is exposed across the map area northwest
of the Río Patuca. The northeast trending Honduras Group highland
has Valle de Angeles strata exposed unconformably on its northwest and
southeast sides defining a large anticline. Attitudes of the Valle de Angels
strata dip away from the highland. Synclinal folding of the Tabacón
beds southeast of the Honduras Group highlands is less well defined by
bedding attitudes. However, the gradational contact between the Valle de
Angeles and the Tabacón strata on both margins of the Tabacón
exposure supports a syncline.
Northeast trending folds within Atima limestone are seen on air photos
of the Montañas de Colón east of the map area, and one small
fold was mapped in the Sutawala drainage. South of the crest of the Montañas
de Colón stratigraphic dips remain to the southeast, ruling out
the possibility of a flower structure.
Compressional folding and faulting affects all Mesozoic units, indicating
the compression occurred during the Cenozoic. It is not apparent that the
Tabacón beds experienced the degree of folding as the Honduras Group
highlands or the Yojoa strata, which leaves open the possibility the Tabacón
beds are coevel with the deformation.
STRIKE-SLIP FAULTS
In addition to the tear faults associated with compression, a series of
north-northeast trending dextral strike-slip faults cut the older compressional
features of the Montañas de Colón. These large faults have
displacements of about 1 km based on aerial photography interpretation.
Several small faults were found showing both dextral and sinistral slip
indicators (slickensides) that do not match orientations expected for compressional
induced tear faults. These structures evidence shearing not related to
compression.
PATUCA LINEAMENT
The Río Patuca is unusually straight as it crosses the project area
and flows to the northeast. Several workers have defined a northeast trending
lineament through this area extending en echelon to the Caribbean (Finch
and Ritchie 1991, and Kozuch 1991). A major reason for this field work
was to define this feature and to investigate its relation to other northeast
trending features of the Chortis block, i.e. the Guayape Fault and the
Coco lineament. The physical presence of the Patuca lineament could not
be demonstrated based on this field work.
STRUCTURAL IMPLICATIONS
A complete discussion of the tectonic implications of the mapped structures
are beyond the scope of this presentation. However, a few points can be
made.
-
The Montañas de Colón overthrust and fold-belt with associated
folds to the northwest are a regional northeast trending feature extending
at least 150 km in length. These features can be seen from aerial photography
and LANDSAT imagery to the southwest through the Cordillera Entre Ríos.
To the northeast, compressional features can be seen on the surface to
Wampusirpi and Sierra Warunta. A well drilled near Awaus, 100 km to the
northeast, passed through thousands of feet of Honduras Group strata before
re-encountering Valle de Angeles strata in a thrust structure.
-
North-northeast trending dextral strike-slip faults that cut the compressional
features of the Montañas de Colón may relate to a still unconfirmed
Patuca lineament. Further work is needed to determine the relation of northeast
trending structures in La Mosquitia with similar structures to the west.
SUTAWALA WIND GAP
Mills and Hughs (1974) and Finch (pers. comm., 1992) noted that the Sutawala
valley (a wind gap) through the Montañas de Colón contains
quartz pebble and cobble bedload and terrace deposits. The Montañas
de Colón is almost exclusively limestone. No possible bedrock source
for the quartz clasts was found in the Montañas de Colón.
The quartz clasts are restricted to the main valley and are not present
in the tributaries of the strike valleys. The Río Sutawala is noticeably
underfit with its spring fed headwaters in the existing valley. The upper
Río Patuca and the Río Wampú are the probable source
for the quartz clasts. The Río Sutawala and Río Wampú
have very similar trends, and it is proposed that the Río Wampú
and the upper Río Patuca flowed through the Sutawala valley to the
Río Coco to form the paleo-Coco-Patuca-Wamp· river flowing
on to the Mosquitia plains. The highest elevation of the Sutawala valley
is less than 100 meters above the level of the Río Patuca indicating
that the paleo-Patuca-Wampú· river flowed during and after
the Montañas de Colón uplift and has been captured by the
lower Río Patuca recently. Only minor uplift could have occurred
following the capture. The presence of the paleo-Coco-Patuca-Wamp·
river may help explain the alluvial deposits of the plains of La Mosquitia.
Present deposition of these rivers consist of mostly fine grained suspended
load with little coarse bedload. Deposits of the Mosquitia plains are composed
of lithic pebble and cobble clasts in a sandy matrix. A large river system
draining uplifting highlands could have deposited these clasts.
CONCLUSIONS
Detailed mapping at the confluence of the Río Patuca and the Río
Wampú of eastern Honduras revealed a stratigraphy significantly
different from central Honduras and previous work in eastern Honduras.
The oldest mapped unit are the phyllite, slate, schist, and quartzite of
the Jurassic-Cretaceous Honduras Group. This unit appears to be a weakly
metamorphic equivalent of the Jurassic Aqua Fría Formation. Thick-bedded
micrites and a few thin sparry and biomicrite beds comprise the Cretaceous
Atima Formation of the Yojoa Group. Thinly bedded shale, arenite, and graywacke
with minor limestone and quartz pebble conglomerate of the Krausirpi beds
conformably overlie the Atima limestone. The Upper Cretaceous Valle de
Angeles Group, consisting of redbeds of fine-grained sandstone and lithic
conglomerate, unconformably overlies the Krausirpi beds. Isolated basalt
and andesite flows occur in the redbeds and as thick flows blanketing underlying
units. The redbeds grade upward to the thick cobble and boulder breccia
of the Tabacón beds containing clasts of the mafic volcanic rocks.
Northwest verging thrust faults place Cretaceous Atima limestone over
Upper Cretaceous Valle de Angeles redbeds and repeats the Atima section
in the Montañas de Colón. The northeast trending metamorphic
highland and the Tabacón beds north of Río Patuca express
large folds. Small folds, thrust faults, and tear faults within the redbeds
are expressions of northwest-southeast compression. These features are
part of a regional fold and thrust belt extending approximately 150 km
along a northeast trend.
North-Northeast trending dextral strike-slip faults cut the thrust faults
and folds of the Montañas de Colón. These features may relate
to postulated northeast trending linears which are younger than the thrust
and fold belt in the Mosquitia region.
ECONOMIC AND ENVIRONMENTAL
GEOLOGY
This section provides an overview of the potential for mineral and hydrocarbon
exploitation in the Project Area and provides a brief discussion of the
environmental geology concerns.
MINERALS Precious Metals
The Ley de Minerales identifies the area along the Río Patuca as
an exclusive zone of mineral extraction by the local population. The Dirección
General de Minas e Hidrocarburos is prohibited from granting mineral or
mining claims in this zone. Indigenous and Ladino Hondurans pan and use
small dredges to extract placer gold along the Río Patuca upstream
of its confluence with the Río Wampú. This generally occurs
during the dry season from January to May. Placer gold extraction also
occurs to a lesser extent along the Río Wampú and its tributaries.
The source of the placer gold appears to be local vein deposits that
are associated with the pervasive quartz veins in the metamorphosed Agua
Fría Formation of the Honduras Group. The metamorphosed Agua Fría
strata occurs extensively along the course of the Río Patuca upstream
of the Project Area and in the highland of the Montañas de Patuca.
No intrusive body of rock which might indicate a massive deposit was discovered
during the field mapping. The quartz veins, at this level of investigation,
is believed to result from a regional low-grade metamorphic event and subsequent
tectonic deformation. While locally rich gold producing vein deposits may
occur, no such deposits of this type were observed nor have any been reported
in the region. Placer gold along the Río Patuca is mobilized and
redeposited annually during the peak floods of the rainy season. Continued
extraction at current levels are expected to continue indefinitely without
"playing out" the resource.
Environmental impacts from placer gold extraction takes several forms.
While not inherently damaging to the river, continued disruption of the
bed material adds fine sediment to the flow and disrupts bottoms dwelling
aquatic organisms during periods of low flow. These changes may work through
the ecosystem and impact fish and aquatic reptiles which feed the indigenous
communities. Baseline and monitoring data are not available to assess environmental
impacts. Changes in the annual river hydrograph and annual sediment transport
are not expected to result from small scale placer mining. The use of mercury
to separate the gold from other heavy minerals does occur, however the
extent of the use and exposure in the environment is not documented. Release
of mercury into the environment from placer gold extraction warrants additional
study to determine the net use and extent of release to the environmental.
Impacts are expected from the migration of upwards of 40,000 people
into the gold producing regions of the Río Patuca during the dry
season every year. Lack of sanitation, potable water, health care and civil
order impact the people extracting the gold as well as frontier communities
and probably downstream communities along the Río Patuca. Sporadic
hunting and fishing by these people may affect the local wildlife population.
Anecdotal data, however, suggest that the miners do not hunt or fish extensively
as this takes daylight time away from gold extraction operations.
Building Materials
Non-precious minerals used for building material such as sand, gravel,
and limestone exists in the Project Area. Alluvial sand and gravel occurs
along the Río Patuca in limited quantities, often hidden under a
dense cover of vegetation. Colluvial sand from weathered deposits of the
Valle de Angeles Group occurs extensively along the heavily vegetated lowlands
of the Río Patuca. The gravel and cobble clasts Tabacón beds
could be used for building material but would require processing to wash
the rock. Exploitation of these materials would be limited by access, their
spotty occurrence and a current lack of need. Extensive alluvial sand and
gravel deposits exists in the easily accessible plains of the savannas
of La Mosquitia towards the coast. Barge transport of the alluvial deposits
from the Mosquitia plains would provide the most cost effective source
should large quantities of building materials be needed near the Project
Area.
Limestone of the Atima Formation of the Yojoa Group forms the prominent
Montañas de Colón. These massive bedded limestones could
be economically quarried for cut building stone or crushed for building
aggregate. Should the chemical makeup of the deposit be of cement grade,
processing of the lime into cement could be economical. Use of this deposit
depends entirely upon the proximity of a demand for lime. No such need
is envisioned in the foreseeable future.
In general, the development and extraction of either precious minerals
or common building material requires the development of a transportation
network to bring equipment in and to extract the resources. The exception
to this may be the development of barge transport along the Río
Patuca or the Río Coco. The current nonregulated nature of these
rivers would limit barge transport to a few months of the year during seasonal
high flow. Water levels during other times of the year are too shallow
to permit barge transport. Without accurate information on river depths
or flow, further study of the feasibility of even light barge traffic on
these rivers is needed.
The karst and cave systems of the Montañas de Colón are
entirely unexplored. An unknown amount of biological and cultural information
may exist in this area. Considering the recent discovery of the remains
of two hundred humans placed in a cave in central Olancho 3,000 years ago,
it is not unimaginable to speculate that similar cultural artifacts may
exist in the Montañas de Colón. For these reasons, extreme
care and consideration must be given to protect these resources during
any exploitation of the mineral resources of the region.
HYDROCARBONS
La Mosquitia has been a target for hydrocarbon exploration and speculation
for decades. The source of this speculation appears to be the observation
that the massive limestone of Yojoa Group is similar to the oil producing
Coban Formation of the Peten Region of Guatemala. Subsequent research in
the geology of Central America conclusively demonstrates that these deposits,
although similar in appearance, formed in different areas and at different
times and the Yojoa Group has no predisposition as oil bearing strata.
As recently as 1992, oil exploration by the Cambria Oil Company in Awaus
drilled through 17,000 feet of Mesozoic strata before "coming up dry" in
metamorphic rocks. The apparent target of this exploration was the limestone
of the Yojoa Group which was never encountered during drilling.
Based on field work in the Boca Wampú area, there are several
factors that limit the possibility that the Yojoa Group limestones could
host hydrocarbons:
First, surface exposure the limestone is extremely dense with little
primary or secondary porosity. This severely limits the limestone's ability
to store hydrocarbons that may have been trapped.
Second, the only strata with the potential to serve as a hydrocarbon
source that has been identified in Honduras are the shales the Guare Member
of the Valle de Angeles Group. While, Mills and Hugh (1967 and 1974) place
the Guare shales in the Yojoa Group, Finch (1981) has shown that the correct
stratigraphic location for the Guare Member is in the Valle de Angeles
Group in central Honduras. Mills and Hugh (1974) mistakenly identify the
calcareous shales present in the Montañas de Colón as "Guare",
whereas I designated them as the Krausirpi beds, a new stratigraphic unit.
Terminology aside, geologic mapping places the shale "source" stratigraphically
above the "host" Yojoa Group limestone, a situation which precludes any
trapping of hydrocarbons in the lower limestone regardless of the quality
of the host or source beds.
Third, the lack of Yojoa Group limestone in the Awaus dry well confirms
a mapping relation reviled in the Project Area - that the Yojoa strata
is regionally non-existent north of a northeast trending line delineated
by the northwest flanks of the Montañas de Colón. When this
trend is extended northeast toward Awaus, the recent drilling site lies
to the north of the limit to the Yojoa Group. The chance of finding a Yojoa
Group "host" is very low over a large area of La Mosquitia.
In the Project Area itself, the prospect for exploitable hydrocarbons
are even less than for La Mosquitia as a whole. In addition to the limiting
factors listed above and assuming that the Yojoa limestone is the target,
the extensive surface exposure of the limestone would have breached any
hydrocarbon trap that may existed. Hydrocarbons tend to migrate upward
along fractures or bedding plains until trapped by overlying impermeable
strata. The predominant southeast dipping strata in the Project Area would
have allowed hydrocarbon migration to the surface.
A story among the Tawahka tells of burning ground in the Cerro Asanbugna
which some have attributed to burning hydrocarbons ignited by lighting.
Upon inquiring about this with several people, similar features of the
story reoccurred, that the fires only occur in the karst limestone mountains
and only during the dry season and only every few years. This is consistent
with forest litter or "duff" fires that may burn several feet below the
surface of a layer of organic forest litter. This phenomenon has been reported
in the rain forests of Southeast Alaska and in peat deposits in North Carolina.
This explanation seems more probable than lighting striking a tar seep
which no one has ever seen.
ENVIRONMENTAL Transportation
Cartographers have crisscrossed the maps of La Mosquitia with roads for
decades. The lack of a population of sufficient size to invest in overland
transportation has prevented these road from being build. The region's
waterways have served the population's transportation needs for centuries.
However, Ladino migration into La Mosquitia, the opportunity for resource
extraction, and the "Contra" war has kept alive the possibility of a road
linking La Mosquitia with central Honduras.
Road building in La Mosquitia must be examined in context with the history
of overland transportation in the frontier regions of Honduras. Trails
made by homesteaders eventually become roads by use and need without design
from planners or engineers. Alternatively, roads are advanced into a region
during timber harvest, followed closely by settlers who gradually expand
the road network. Transportation planning is not typically involved in
these efforts. Natural barriers of rivers and mountains have, in part,
prevented road from being advanced into La Mosquitia.
There are several obvious overland routes into La Mosquitia based on
starting and ending destinations and the intervening topography. Routes
near the Project Area from Olancho include existing overland trails down
the Río Aner and along the Río Wampú to Boca Wampú
or, alternatively, passage down the Quebrada Tabacón from near the
Wampú-Aner confluence. Either of these options would require bridge,
fording or ferry crossing of the Río Wampú and several of
its large tributaries. Without an all-weather road and bridge crossings
of the major tributaries the route could provide assess only during the
dry season.
Two routes options exist upon reaching the Río Patuca near Boca
Wampú. The first is to construct a road along the north side of
the Río Patuca to near Krausirpi and then cross (by bridge or ferry)
the river to the south side in order to access the southern communities,
eventually extending the road to Wampusirpi and then Awaus and finally
to connect with the Mocoron-Puerto Lempria Road. This would be the longer
route but would access more communities. The second route upon reaching
the Río Patuca near Boca Wampú is to cross the Montañas
de Colón along the Río Sutawala trail to reach Awasbila along
the Río Coco. This would tie more directly into the existing La
Mosquitia road network.
Any planned road building effort in this region would be formidable
in respects to engineering, expense, environmental and cultural concerns.
River crossings by bridge of the Río Patuca and Río Wampú
would be expensive and require extensive design work in order to withstand
the annual peak flood. A permanent all-weather road into this region could
not be constructed of native soil material but would generally require
full-bench rock construction to prevent road failure. Again, this would
necessitate expense and design and require quarries to supply road aggregate.
The need for full-bench road construction with stone applies especially
to any proposed road through the Río Sutawala valley. Clays weathered
from the Yojoa limestone makes the route virtually impassable with sticky
mud during the rainy season. Yojoa limestone would make a good road surfacing
material as would the Tabacón breccia, however the Valle de Angeles
and Honduras Group rocks are heavily weathered, easily erodible and would
be a poor source for road-grade rock.
Hydropower
Plans and studies exist for the development of hydropower near and within
the Project Area. These include sites on the Río Patuca near Pimineta,
near the confluence with the Río Wampú and near Valencia
upstream along the Río Patuca. Any hydroelectric development along
the Rio Patuca, whether a storage type project or a run-of-river operation
would be the largest hydroelectric facility in Central America. The limiting
factor for any mainstem dam along the Río Patuca, expense and design
aside, would be controlling upstream sediment sources. The Patuca river
system drains the largest area of any river in Honduras and this includes
the agricultural Valle de Catacamas, Valle de Jamastrán, and large
portions of Olancho experiencing accelerated erosion due to deforestation.
The river currently carries a large sediment load in suspended and bedload
transport. A mainstem dam would effectively trap all but the smallest fraction
of the sediment load for the Río Patuca. The useful life span of
any dam would be limited.
Development of proposed damsites along the Río Wampú would
be a massive undertaking, although it may not suffer sedimentation problems
to the extent that a dam would on the Río Patuca. The narrow steep
canyon of the Río Wampú where it cuts the rocks of the Honduras
Group provide the most reasonable damsite location. Land use changes within
the Wampú drainage that would occur with hydroelectric and agrarian
development would result in accelerated erosion and reservoir sedimentation
reducing life of any project. Similar to the Patuca watershed, the Wampú
basin land use changes are the limiting factor for hydroelectric development.
These land use changes would affect the annual and instantaneous peak flow,
impacting the ability of any hydroelectric project to function. Considering
the history of hydropower in Honduras, effective watershed management should
be first issue addressed and resolved before proceeding with hydropower
design and construction.
Any hydropower development along the Río Sutawala or any river
draining from the Montañas de Colón is not feasible because
the extensive karst terrain that would limit reservoir storage.
The above discussion includes only some the technical issues involved
with hydropower development in the Project Area. Obviously, before any
project advances, feasibility and impact studies would be required. This
is intended only to serve as a starting point and basis for future studies.
It can be stated that the associated environmental, land use and cultural
impact of any hydropower development in the Project Area would be severe,
altering dramatically and forever the identity of the indigenous people
who depend on the rivers and the nature of the flora and fauna of their
environment.
REFERENCES
Donnelly T.M., G.S. Horne, R.C. Finch, and E. López Ramos 1991,
Northern Central America: The Maya and Chortis Blocks: in The Geology of
North America, H: The Caribbean Region, (Dengo, G. and J.E. Case, eds.)
p. 37-76. Geol. Soc. Am., Boulder, Co. USA.
Finch R.C. 1981, Mesozoic Stratigraphy of Central Honduras: AAPG Bull.,
v. 65, p. 1320- 1333.
Finch R.C. and A.W. Ritchie 1985, Mapa Geológico de Honduras,
Danlí sheet, scale 1:50,000, Inst. Geogr. Nac., Tegucigalpa, Honduras.
Finch and Ritchie 1991, The Guayape Fault System, Honduras, Central
America, J. S. Am. Earth Sci., v. 4, p.43-60.
Gordon M.B. and W.R. Muehlberger 1994, Rotation of the Chortís
block causes dextral slip on the Guayape fault, Tectonics, v. 13, n. 4,
p. 858-872.
Gordon M.B. 1990, Strike-slip faulting and basin formation at the Guayape
fault-Valle de Catacamas intersection, Honduras, Central America, Ph.D.
dissertation, 260 pp. Univ. of Tex., Austin.
Horne G.S., S.G. Clark, and P. Pushkar 1976, Pre-Cretaceous rocks of
northwestern Honduras: Basement terrane in Sierra de Omoa, AAPG Bull.,
v. 60, p. 566-583.
IBI 1985, (unpub. report) Biostratigraphy and Source Potential of East
Honduras Surface Samples, Houston, Texas: released by DGMH Tegucigalpa,
Honduras.
Kozuch M.J. 1991, Mapa Geológico de la República de Honduras,
scale 1:500,000, Inst. Geogr. Nac., Tegucigalpa, Honduras.
Mill R.A. and K.E. Hughs 1974, Reconnaissance Geologic Map of Mosquitia
Region, Honduras and Nicaragua Caribbean Coast, AAPG Bull., v. 58, n. 2,
p. 189-207.
Rogers R.D. 1992, Geology of the Valle de Jamastrán Quadrangle,
open file report, 56 pp., Inst. Geogr. Nac., Tegucigalpa, Honduras.
Rogers R.D. and E.A. O'Conner 1993, Mapa Geológico de Honduras,
Tegucigalpa sheet, (2nd ed) scale 1:50,000, Inst. Geogr. Nac., Tegucigalpa,
Honduras.
Weiland T.J., Suayah, I.B. and R.C. Finch 1993, Mesozoic volcanic rocks
of the Río Wampú, eastern Honduras: Chronology, Geochemistry
and Petrology. GSA Annual Meeting Abst w. Prog., p. A-97.
ACKNOWLEDGMENTS
Tinki Pali!: Dionisio Cruz, Benjamin Dixon, Larro, Edgardo Benitez and
all the Tawahka of Krausirpi, Krautara, and Yapuwás. Your help cannot
measured or repaid. Federation Indienous de Tawahka provided quarters in
Krausirpi.
Thanks to the Richards: Ric Finch, Richard Harwood, Richard Markey,
Dick Mills, and the non-Richards: Mike Kozuch, Mark Gordon, Bill Muelhberger,
Paul Mann, and Staci Tyberski for the aid, help, conversations, discussions,
reprints, preprints and all around support in understanding the geology
of the Chortis.
The field mapping was undertaken as part of the geological mapping effort
of the Honduran Government aided by the Peace Corps. This effort has led
to or is leading to the publication of 32 geologic sheets, 15 of which
were mapped by Peace Corps Volunteer geologists.
Thanks greatly to Peace Corps Honduras-APCD Jorge Betancourt and PCV's
for support. Dirección General de Minas e Hidrocarburos provided
hard to find reports and lab equipment. Instituto Geográfico Nacional
provide field support, maps, and aerial photography. Emory Phleger (DMA)
also aided with maps and support of the mapping program. Cambria Oil Company
provide lodging and access to well cuttings in Awaus. MOPOWI and Cultural
Survival assisted with reconnaissance of the map area in 1991.
Foster Wheeler Environmental Corporation provided support and materials
for preparation of this presentation. Pat Allan provided web page assistance
and graphic conversion.
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