,. . , SOTANITO D,E AHUACAYLAN Sierra Madre Oriental Jalpan
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ASSOCIATION FOR MEXICAN CAVE STUDIES
,y. CAVE REPORT SERIES
Number 1 t r
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ASSOCIATION FOR MEXICAN CAVE STUDIES
CAVE REPORT SERIES Number 1
SOTANITO DE AHUACATLAN Sierra Madre Oriental; Jalpan; Ahuacatlan
by TERRY W. RAINES
The Speleo Press • Austin • 1972 The Association for Mexican Cave Studies is a non-profit, volunteer organization whose goals are the collection and dissemination of infor mation concerning Mexican caves. The AMCS publishes a Newsletter, Bulletin, and Cave Report Series which are available to any sincerely interested, conservation-minded person. Prices are available by writing. Some of the persons responsible for the continued success of the Association's endeavours are the following: Publications Editor Terry W. Raines Cave Files . William H. Russell Secretary-Treasurer Jan E. Lewis Coordinating Biologist James R. Reddell Photo Editor . Carl E. Kunath Production Manager. Ronald G. Fieseler ASSOCIATlON FOR MEXICAN CAVE STUDIES P. O. Box 7672, Austin, Texas 78712
Frontispiece: Craig Sainsott views the entrance of the 288.3 m (946 ft) drop within Sotanito de Ahuacatlan.
Copyright ©1972 by the Association for Mexican Cave Studies Printed in the United States of America
The Spe1eo Press P. O. Box 7037 Austin, Texas 78712
ASSOCIATION FOR MEXICAN CAVE STUDIES P. O. Box 7672, University Station Austin, Texas 78712 USA
Price of this issue - $2.50 US INTRODUCTION the mid 1960's this right-of-way consisted solely of a single lane road paved with cob Of the 18 physiographic provinces in bles which was built in 1910. Branching off Mexico (Russell, 1969, Assoc. Mex. Cave the highway at innumerable points is a com Stud. News., 3: 27), the Sierra Madre Oriental plex network of both primary and secondary has been the most productive in terms of trails which provide the really basic means caves and other karst features to date. For the of travel. These trails date from the 1500's past ten years the AMCS has been conducting and even earlier, and can lead one to almost field investigations in this rugged terrain of any point desired. Access to the Sotanito is thick limestone sequences. The Sierra Madre by way of one of these primary routes that is extensive, measuring roughly 200 km by leaves Ahuacatlan and continues to the north 550 km, with few roads to allow access. These west indefinitely. Presently, this particular logistics problems, coupled with the lack of trail is being widened to road-size which will manpower, have limited extensive detailed ex allow passage of trucks to Puerto Guilotla and ploration and certainly in many locations then on to Santa Agueda, a small village west large caves only a few minutes' hike from the of the Area. road have not been entered. As a result, To reach the Sotanito, follow the main AMCS cavers have directed their efforts from trail, which trends generally northwest, out of one area of concentrated karst development town. It roughly parallels the arroyo in the to another. Most recently initiated has been valley below but climbs continuously. Less the Ahuacatlan Area, located within the Jal than 1 km from Ahuacatlan the first hillside pan Region of the SMO Province. The Jalpan arroyo is crossed. Continue on, up over a Region lies almost entirely within the state of broad ridge, until reaching a second arroyo. Queretaro and to the northwest of Jalpan, From this point the cave entrance is directly Qro. The small town of Ahuacatlan gives its up the arroyo, requiring a steep, one hour name to the Area, which consists primarily of hike. It would be impossible to describe ex the Cerro de la Tinaja north of the highway actly where the entrance can be found from (see map, p. 7 ). It is within this area that here as it is so small and insignificant. The Sotanito de Ahuacatlan is situated. upper photograph on page 16 is a view from For the most part, volunteer manpower the cave which may give some aid. This field to produce this report was supplied by the is crossed immediately before arrival at the ever-present, hard-core group of Austin cavers, entrance, located in an area of undergrowth. with, of course, help from our friends. Per Also, the town of Ahuacatlan lies hidden in sons who should be recognized are: Chuck the main valley directly above the caver. The Bryan, Arthur Cleaves, de de Esparza, Ronnie last leg of the journey is most comfortably Fieseler, Blake Harrison, Roy Jameson, James traversed under the direction of a local guide, Jasek, Orion Knox, Carl Kunath, Jan Lewis, who would be more than willing to help out Neal Morris, James Reddell, Olga Reyes, Jim if approached in a friendly manner. The eleva and Julie Rodemaker, Bill and Carol Russell, tion gained between Ahuacatlan and the cave Craig Sainsott, Joe Simo, Richard M. Smith, is about 400 m over a distance of 2.5 km. The Bob Stockton, and Hugo Victoria. Undoubt weather is usually hot and the trail steepens as edly, others will appear in the latter stages of one nears the cave. There is absolutely no wa production who can not be credited at this ter once you get there, so be prepared. time. As mentioned before, the Ahuacatlan Area and Cerro de la Tinaja are essentially one GEOGRAPHY and the same. Extending to the north beyond the map, the range is ultimately terminated Primary vehicular travel through the by the Rio Ayutla. Total dimensions are 5 km Ahuacatlan Area is via a hard-surfaced high by 20 km. To the southeast of the Sotanito, way which borders the southern edge. Until the greatest elevation difference is 500 to 600 m. It is measured between the crest of necessarily contemporaneous, they are said to the Cerro de la Tinaja and the base level at be homotaxial, and therefore rock-stratigraph Ahuacathln. The crestal area is broad, giving ical units. However, on the basis of fossil evi way on the southwestern flank to a dip slope dence, certain time intervals can be assigned of 30°. In the vicinity of the linear peak a at specific locations. number of shallow stream courses head. These channels are in general oriented directly down LAS TRANCAS FORMATION slope and coalesce with a base level arroyo The lower-most formation exposed in the which is parallel to the range. Because of in Ahuacatlan Area is a splintery-weathering, ternal drainage, the channels very rarely carry slightly phyllitic gray shale interbedded with a water and are consequently poorly developed. dark-gray argillaceous limestone. These thin On the other hand, the usually dry base level beds contain small quartz grains and the for arroyos do flood after intensive summer rains, mation has scattered beds of impure calcare in this case conducting the torrent through nite. Ahuacatlan into the RIO Jalpan drainage sys The photograph on page 9 is a good ex tem. ample of the splintery-weathering exhibited The climate of the AhuacaWm Area is by the Las Trancas formation, while on page rather harsh on visitors as well as local resi 10 is iJlustrated the characteristic thin bed dents. The winter and spring months are quite ding. A small thrust fault can also be seen in dry, receiving only 10% of the annual 600 mm this photograph with accompanying drag folds. rainfall. Then, during the summer months, Fossil evidence found by Segerstrom heavy rains erode quantities of loose topsoil 1961 indicates the Las Trancas formation in from bare corn fields. At all times good water the immediate Ahuacatlan area is considered for drinking can usually only be found along to be late Callovian to late Oxfordian age. the base level arroyos because the above lime These, of course, are stages of the Late Juras stone terrain readily consumes all precipita sic System. tion quickly. EL DOCTOR FORt\1AnON The El Doctor is the principal rock unit GEOLOGY OF THE AHUACATLAN AREA exposed in the area. To the west of the region, the EI Doctor overlies the Las Trancas with by Richard M. Smith great disconformity, however, the exposed contact between these two formations near LOCATION Ahuacatlan is extremely gradational as can be The author, aided by several other mem seen on page 11 . The lithologic characteristics bers of AMCS, mapped the area during 1971 change from slightly phyllitic gray shale and 1972. It should be noted that the mapping dark-gray argillaceous limestone in the upper was reconnaissance in nature and because of Las Trancas to shaly limestone interstitially the difficulty of access and poor exposures, bedded with calcareous shales. These beds much reliance was placed on the geologic map range from 15 em to 20 em thick. compiled by Segerstrom in 1961. The few mi In turn, these beds grade into a thick nor errors found in the remarkable Segerstrom bedded, fine grained, dove micrite. Further work were corrected on the included map. in the section, a rudistid facies appears turning the hitherto unfossiliferous micrite into a vir LITHOSTRATIGRAPHIC UNITS tual coquina. The extent of this facies could The rocks exposed in the Ahuacatlan not be determined, but certainly constitutes area have been subdivided into formations on a major portion of the middle El Doctor. the basis of lithologic characteristics. Since The middle EI Doctor quickly changes these formations have a similar order of ar within a few feet from massive limestone to rangement in different locations, but are not thin-bedded limestone with some interbeds of
2 brown calcareous shale. been intensely folded with the axial plane Along the highway, just south of Esca trend from northwest to southeast. It is evi nelilla, an attempt was made to measure a sec dent from lithologic considerations that the tion through the El Doctor, but due to inten EI Doctor is the competent unit while the Las sive parasitic folding and some faulting, the Trancas and Soyatal-Mexcala act as the in extent of repetition of the section could not competent units. Parasitic folds, boudinage, be determined. tension fractures, shear zones and minor fault Again from fossil evidence gathered by ing are related to this folding episode. Segerstrom 1961, the El Doctor formation, All folding and related structures are a in the Ahuacat!
3 All boudens observed were in the lower a topography peculiar to and dependent upon unit of the El Doctor. Boudens (sausage underground solution and the diversion ofsur shaped structures) are common on the limbs face waters to underground routes. The anti of folds where medium to thick limestone clines are a mature to old karst terrain. Al beds alternate with thin limestone beds. They though lapies are common, the most promi probably formed at the time of folding since a nent karst feature visible in the area to the tensional force was then exerted on the limbs average person is sinkholes or dolinen. They of the folds causing the more plastic units to are numerous in the region, occuring in two fracture and flow. The photograph on page 15 types of localities: in upland interfluvial areas shows the result of flowage on the limbs of a and at the heads of arroyos. Both are areas of fold in the El Doctor. Unfortunately, these imminent integration ofa surface drainage sys features are not true boudens, but the author tem. The two dolinen immediately to the west had no better photograph at his disposal. of the Sotanito are in an upland interfluvial Associated with the boudens and having area. The larger of the two is named Joya del a similar history are tension fractures. These Durazno (see photograph on page 12) and fractures are most obvious in the more mas measures 500 m by 650 m. The sinkholes sive El Doctor and are recognizable as calcite through the region were much more numerous veinlets or often as a network of en echelon in the past than they are now; their number fissures filled with calcite. The latter type of has been reduced by headwater erosion of sur deformation was due to shearing, while the face streams. former was generally simple tension. As the Between AhuacaWin and Jalpan the Rio tensional or shearing forces opened up the Jalpan flows through a natural tunnel 1.5 km fractures, calcite was deposited in them. long and emerges at a place called Puente de Only a few small faults were mapped in Dios. The tunnel was formed by subterranean the area. Because of the terrain, it was diffi stream piracy, which diverted surface waters cult to ascertain their lateral extent much less from about 1050 m above sea level on the vertical displacement. Several zones were map west side of the limestone anticlinal ridge of ped that mayor may not be faults but are EI Doctor to about 900 m above sea level on definitely shear zones on a large scale. the east side. A classical example of this sort Although jointing of the more massive of feature is the Natural Tunnel of Virginia. El Doctor limestone was noted, a thorough GEOLOGIC HISTORY investigation was not conducted. It was ob served that the thick-bedded limestone had a Marine deposition of clastic materials pronounced vertical jointing pattern with a took place during the latter part of Middle strike orientation parallel and perpendicular Jurassic or the early part of Late Jurassic to the major fold trends. It is assumed by the time. The existing sedimentary and metamor author that this joint pattern provided the phic rocks were eroded where there was local pathway for the water that formed the Sota emergence. General submergence followed, nito. and graywacke, arkose, chert, calcareous shale, and argillaceous limestone were deposited in GEOMORPHOLOGY the sea during the Callovian, Oxfordian, Kim The Ahuacatlan Area is a combination of meridgian, and Portlandian stages of Late Ju two geomorphic terrains. The Soyatal-Mexcala rassic time. synclines that appear as topographic highs re Owing to a withdrawal of the sea and to flect the geomorphic patterns one generally differential uplift, the Ahuacatlan area was finds on a shale formation. All drainage is a only slightly underwater during much of Early bove ground and parallels the fall line of the Cretaceous time. The area to the west was a slope. Irregularities are few due to the homo landmass and erosion in this part was so deep geneity of the formation. locally, as at Bernal, that the Las Trancas In contrast, the El Doctor anticlines pose clastic beds and impure limestone were com-
4 pletely removed. followed by minor faulting, erosion, and local A general submergence began in the east terrestorial deposition. The deepening of the ern part of the area probably in middle Albian Rio Jalpan valley has been the latest observ time and progressed westward during late Al able geologic change and this is still going on bian time. The submergence continued prob today. ably into early Cenomanian time and was fol lowed by uplift and emergence that lasted un REFERENCES til late Turonian. Renewed submergence in Segerstrom, Kenneth. 1961. "Geology of the late Turonian time continued into Maestrich Bernal-Jalpan Area, Estado de Queretaro, tian. Toward the close of the Cretaceous per Mexico." Ceol. Surv. Bull., 1104-B. iod the entire region was uplifted and has con Johnson, Arvid. 1970. Physical processes in tinued to be emergent. geology. Freeman, Cooper & Co. The Cenozoic history of the region began Pettijohn, F. J. 1957. Sedimentary rocks. Har with the folding of all rocks that had been de per & Row. posited in Cretaceous and earlier times. Fold Thornberry, W. D. 1954. Principals ofgeomor ing continued until late Eocene time and was phology. Wiley & Sons, Inc.
5 GEOLOGIC AP D SECTIO OF THE AHUACATL AREA, QUERETARO, EXICO 1 7
Ro k- trati raphi nit
ala and oyatal formation undiffer ntiated Overturned ed
octor lime tone
heer zon howing trik di onformity ..... La ranca formation "-.... ? ault movement unknown
ymbol Boudinage ------ontact· ob erved and inf rred Para itic fold howin angl of plung
Overturned anticline howing trac of hing ro ection line urface and dir ction of plunge
Overturned yncline howing trace of hinge trike and dip of bed) howing dip angle urface and dir ction of plung Ked
.. ( . .. Kms ( ..
Kms
o 2
The middle section of the Las Trancas formation exposed in a road cut one-half way up Cuesta de Huasmazontla. The upper Las Trancas formation near its contact with the EI Doctor. This road cut is located at the west edge of the Ahuacatlan Area Map.
10 Contact between the Las Trancas formation and the El Doctor at a point 100 m to the right (east) of the previous photograph.
11
Parasitic folding of the El Doctor limestone in a road cut