http://dx.doi.org/10.18268/BSGM2019v71n3a# P. ###‒ VOL. 71NO. 3 BOL. SOC.GEOL.MEX.2019 Cincinnati, OH,45221,USA. ment, 401 Braunstein Hall, 2600 Clifton Ave. Cincinnati, GeographyDepart Universityof Nicholas P. Dunning Roo C.P. 77524,. No. 39,Mza.29,SM64,Cancún,Quintana A.C., UnidaddeCienciasdel Agua, Calle 8, CentroInvestigación de Científica de Yucatán, [email protected] Rosa M.Leal-Bautista tana Roo. C.P. 77580,Mexico. Mza. 9,Lote 1, Local F, , Quin Desarrollo Sustentable, Javier Rojo Gómez, Centro de Innovación eInvestigación para el Gudalupe Velazquez-Oliman Illinois 60115,USA. vironmental Geosciences, Emeritus, DeKalb, IllinoisUniversity,Northern andEn Geology Eugene C. Perry Eugene C. Peninsula, Mexico hydrogeochemistry andgeomorphologyofthenorthernYucatán The IcaicheFormation:Majorcontributortothestratigraphy, Manuscript accepted: Corrected manuscript received: Manuscript received: Perry , Gudalupe Velazquez-Oliman - - - karst. stratigraphy,sum, hydrogeochemistry, Keywords: Yucatan Peninsula, gyp fresh water lensoverlying asalineintrusion theYucatán Peninsulation of thata pervasive host the Mexican por the more northerly lowlands of of rockshave markedly than rocks lower permeability the Peninsula. resulting The southeast margin of Puerto Formation, the Carrillo onthe formed of rocks,sedimentary perhapsincludinglocalfacies post-Eocene marine of the permeability affected from deposits the ChicxulubImpact may have impact haps mixed with siliceouscomponentsof the Icaiche Formation, per during weathering of ). Argillaceous sediment released Lake Chichancanaband Felipe Puerto, Carrillo the EIR (between marginthe area of at the eastern rock,watervarying and highly quality in ciation of irregular terrains, extensive brec of the formation innorthcentral Yucatán karst deep state; and 3) the EIR; 2)the development of west marginsof and interior drainage) along theeastand floors with flat basins partly or completely enclosed karst of was important in: 1) the formation overlying rock,dissolution, followed by collapse of groundwater. Inthisstudy, we propose that gypsum ticularly thoseplaceswhere flowing it encounters Peninsula wherepresent itis inthesubsurface, par the Yucatánwhere itcrops out andintopartsof features geochemistry beyond andgroundwater on hydrologicoutsize influence andgeomorphic theIcaiche Formation gypsum, had an has of therelativelysolubility high transport. Because of fordams andingenioussystems water storage and local claysin constructionof dant impermeable water supply and,somewhat later, by usingabun and adapting natural depressions(called unpalatable by groundwater using in this region of tenure, the Maya survived and at times prospered pletely abandoned by about 950 CE. During their fortwo almost millenniaandfinallyalmostcom thatterrain the Mayasuccess occupiedwithvarying the Yucatán Peninsula,of whicha encompasses area known asthe Elevated Interior Region (EIR) the physiographic a considerableoccupies part of Icaiche The Formation inthe formation. deposits the gypsum during weathering and dissolutionof the sulfate-contaminated water that is produced of activity. Low population densityis a consequence with limited access, fewpeople, andlittle economic been little studied because itcropsan areaout in Campeche andQuintana Roo. has formation The the Mexicanstates Yucatan,parts of in the southern 10000km estimated minimum area of thatdeposits covercontains bedded gypsum an Paleogene-EoceneThe Icaiche Formation, which ABSTRACT Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín , Rosa M. Leal-Bautista 2 poljes , islocated bajos . (large, ) for ------, Nicholas P. circunstancias están directamente relacionadas con la presencia limitada población y reducida actividad económica. Estas que elafloramiento sepresentaáreaun en conlimitado acceso, de yeso.de depósitos ha sido poco estudiada ya Esta formación Roo. Abarca más de 10000km de Yucatán,de los estados mexicanos Campeche yQuintana La Formación Icaiche Paleoceno-Eoceno aflorala zona en sur RESUMEN carst. yeso, hidrogeoquímica, estratigrafía, Palabras clave: Península de Yucatán, salina. dulce que se superpone a la intrusión presencia del lente deagua la permite comparada con la zona norte cuya permeabilidad la zona de la península de Yucatán sur de la parte mexicana para Lo anterior resultó en unmaterial con baja permeabilidad Puerto que sepresentansureste el margen en dela Península. incluyendo las facies locales de la Formación Felipe Carrillo sedimentarias de origen marino del post-Eoceno, posiblemente de las rocas del Chixchulub pudieron afectar la permeabilidad Icaiche ysuposible mezcla de sílice del impacto condepósitos durante los procesos de erosión de la Formación llosos formados Quintana Roo. Así mismo, sesugiereque los sedimentos arci Chicancanab y laFormación FelipeLago Puerto en Carrillo este dela EIR (entre en la margen de los flujos subterráneos rock brecciation of ( Yucatán; de las irregularidades y 3)laformación profundas que sepresentanla zona en norte-central delestado de kársticas degeoformas la formación este yoestedelaEIR;2) que aparecen enlas márgenes se presentan como valles cerrados) kársticas de poljes (depresiones elongadas que 1) la formación por los procesos (yeso)kársticos de colapsos seguida generaron: En este trabajo se propone que la disolución del sulfato de calcio la Península en presentar los flujos subterráneos de Yucatán. tancia no ha sido reconocida ni la hidrogeoquímica que puede secciones no afloradas de la Formación. Sin embargo, su impor hidrogeológicas y geomorfológicas tanto en superficie como en las de la zonalas yen características terísticas de permeabilidad influencia tiene Formación Icaiche.las carac en Esta formación solubilidad del yeso quepredominalos afloramientosen de la Sin embargo,del agua. esto no fueconstante debido a la alta de sistemas de almacenamiento y de transporte la construcción aprovechamiento de los sedimentos arcillosos de la zona permitió Incluso“bajos”, como los principales suministros de agua. el kársticasadaptaron las depresiones de la zona, denominadas sedieron cuando los mayasesta región en usaronde apogeo y CE. Estudios arqueológicos han señalado que las condiciones dos mil años y quefueron finalmenteabandonados para el950 incluye ocupados por los Mayas, terrenos con cierto éxito por casi de la [EIR]) PenínsulaInterior Region de Yucatán, la cual (Elevated Interior Elevada conocida como Región fisiográfica La Formación Icaiche ocupa una zona considerable del área poco interés delapoblación por establecerseesta zona. en que afectanútil, generando las condiciones químicas del agua erosiónde yeso y disolución de los depósitos de la Formación consecuencia de la subterránea, de sulfato disueltoel agua en Dunning ), así como la variación hidrogeoquímica /2019 2 ysecaracteriza por capas extensive 1 - - -

The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology ABSTRACT INTRODUCTION / STRATIGRAPHIC The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology RELATIONS 1. Introduction MEMBER 2.1. THEICAICHEFORMATION ANDITSGYPSUM the YucatánPeninsula withinMexico 2. Stratigraphicrelationsinthepartof 2 2 the Icaiche FormationGuate existnorthern in noting that rocksequivalent or similartothoseof Yucatán southernmost state, Mexico.worth Itis Campeche, Quintana Roo,southern southern and little-studied IcaicheThe Formation crops out in was establishedwas byJacques Butterlin and Federico framework stratigraphic The for Yucatán geology except at low pH. calcite, severalis sum times greater than that of gyp weathering because, occurs the solubility of et al. annual1100-1600 mm/year rainfall is (Dunning Yucatán,cipitation like southern where average moderate to high pre rapid weathering in areas of Abundant cancontribute gypsum to especially insoluble interbedded argillite. den by release of unconsolidated overbur can produce ablanket of abundance canbeobscured becauseitsdissolution and limited road access. Furthermore, gypsum tropical thick vegetation, intense weathering, of tions (Figure 1) are incompletely known because sparse, andthe contact relationswith other forma of the state indicate IcaicheYucatán. Formation rocksis Exposure of to qualified is word that henceforth referred to simply as“Yucatán” unless the subsurface (Figure inclusive 1). This region is Formation is present either at the surface orin the three states where the Icaiche ing all parts of the Yucatán Peninsula,Mexican portion of includ the on the influence present hydrogeologyof and geomorphology outsize an exerted have may that formation probably argillaceous material of paper examinesThis waysin which and gypsum correlated. formally Belize,mala andnorthern but these have notbeen / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín , 2012; Dunning , 2012;Dunning et al., 2016). This enhanced 2016).This ------/2019 BASAL PALEOGENE ALBION FORMATION 2.2. CRETACEOUS BARTON CREEKFORMATION AND Eocene lagoonal rockswhose detailed stratigraphy Paleocene-lower IcaicheThe Formationof consists 1952). continue south into Belize and Guatemala (Flores, 2017). Note thatprobable itis that Icaiche rocks de Campeche, Quintana Roo y Yucatán the tothoseinthe map of ure 1,conform Icaiche Formation withinMexico, shown inFig the emphasized here. outcrop The boundariesof thischaracteristic will be importance of The Formation. Icaiche the of characteristic defining bedded evaporite the as theyused the presence of correlation, for fossils identifiable Lacking 1960). area between 1958 and1960(Butterlin andBonet, Bonet who ma Cretaceous Chicxulub bolide impact that rests cemented air-fall material fromthe terminal partially athinblanket of mation,of consisting transitional Cretaceous-Paleogene Albion For (Viniegra-O., 1981; Peterson, 1983)and2)the Cretaceous shallow carbonates and evaporites theYucatán Upper Group part of of formation by1) theBarton Creek two older formations: In Yucatán, the Icaiche Formation is underlain cussed inthispaper. columnthatstratigraphic includes the rocksdis below.m asdiscussed Figure 2 isa generalized at least 25–35 an estimated minimumof thickness region where it is exposed inoutcrop, the GM has the Icaiche Formation. Inthe member (GM) of asthe gypsum bedsinformally to these gypsum Member” inFigure Gypsum 1. We shall refer of shown by the rectangle labelled “Outcrop Area Yucatán.within bedded gypsum area is This Paleocene-Eocene surfaceexposure of area of Xpujil, Campeche to approximate the minimum about 10000 km area of outcrop an define to (2017) SGM of map the on poor Despite exposure, symbols it is possible to use the quarry difficult. correlation fossil made because recrystallization has is indeterminate ea xesv il td fthe of study field extensive an de 2 , which iscentered on , 2007(SGM, Estados - - - Figure 1 is a small outcrop beneath weakly consolidated other exposure,1). The near Ramonal (Figure 1) block uplifted along the Río HondoFault (Figure in a 88.485° W), about west20 km of these includes the Johnson (18.516°N,quarry two outcrops(Pope only study area (and thus inMexico)of consists the in theBarton Creek formation Exposure of che Formation. Icai the with correlated definitively been not has at Agua Dulce(Figure 1), but that Paleogene unit by identified Pope been has limestone mite overlyingand tan, thin-bedded, pink micritic with weathered, white, micriticPaleogene dolo Formation theAlbion contactof single 2005). A dolomite (Pope Barton Creek formation of atop weathered ahighly disconformably surface GeologicalMap of theMexicanYucatán Peninsula(modified fromSGM,2017). et al. 05.Telreto largest, 2005).The of et al. (2005) et al Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ., - - Creek inFigure 1)(Pope in Belize (labeled Barton the Albion Islandquarry the Río HondoFault at along the projection of andthe Albion FormationCreek formation occurs boththe Barton A large additional outcrop of to be present at shallow along the highway. depth can also be inferredthe Barton Creek formation coincident Belize border) (Pope (which parallels the Río HondoFault and the places alongthe Ucum-Álvaro Obregón highway Albion Formationexposed is innumerousother abundant solution cavities” (Pope mite with iron oxide staining, calcite veins, and stronglyis altered weathered “deeply [...]dolo the Barton Creek formation the upper surface of that shows clearly it because significant is outcrop Albion Formation rocks. Although small, this et al ., 2005). et al., et al /2019 2005).Thus, ., 2005). The ., 2005). The 3 3 -

The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology STRATIGRAPHIC RELATIONS The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology STRATIGRAPHIC RELATIONS OVERLYING ROCKS 2.3. ICAICHEFORMATION STRUCTURE AND Figure 2 4 4 2011; Tankersley 2008, Cabadas-Baez ran dust, andNorth American loess(Sedov Central American andMexican volcanoes, Saha for the latter material include ash from various the Peninsula throughout the Quaternary. Sources contributed parent material to the soil cover across that aeolian deposition has gradual product of and the the formation may be both a residuum of soilandsmectitic clay that variably thicklayer of mapped, the Icaiche Formation is blanketed by a ternary. Even whereunconsolidated no material is Miocene rocks, andby alluviummapped as Qua Puerto Formation,Pliocene Carrillo bybits of by the Eocene Formation, by the outcrop, the Icaiche Formation is overlain directly its mainarea of On the north, east, and west of state (Figure 1). the part of in the the southernmost surface only almost entirely inthesubsurface;itcropsout on Yucatán the stateIcaiche of Formation is present Quintana Roo;southwestern however, inthe Campeche and southern crops out over much of that Formation plungesgently to the north. The ananticline IcaicheThe Formationpart of forms / Ageneralizedincludescolumn thattherocks stratigraphic discussed inthispaper. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et al. , 2015,2016). et al ., 2010;Bautista et. al. et al. - - /2019 , , MAYA LOWLANDS AREA TO THE ELEVATED INTERIOR REGIONOFTHE 2.4. CORRESPONDENCEOFTHEICAICHEOUTCROP combined to create, land, inthe EIR, a harsh with the ocean” (Perry accessible fresh water lens inhydraulic equilibrium area” (Gunn the over gypsum much of soiland of dance of Yucatán the EIRfromnorthern are the“abun the geologic features that most readily distinguish ogy. humanoccupation, From the perspective of to constraints imposedbyhumans regional geol emphasize theunusuallyclever adaptation here by focus for thisstudy.region of We dothisinpart to EIRto designate the major will adopt the term tion (Figure 1).Therefore, for convenience, we the Icaiche Forma or shallow subcrop of pattern is, inmanycases, closelyrelated to the outcrop and water agriculture management that style of andsoil types dictated adistinctivegeology Maya marksan area which in practical reasons related to Maya Lowlands (Dunning the to as the Elevated Interior Region (EIR) of a somewhat larger physiographic region referred above mean sealevel (msl) andisincludedwithin elevationout rangesin from about50to300m areaThe over which the Icaiche Formation crops et al., 20) adteasneo an 2002), “and the absence of et al. , 2011). These features, 2011).These et al. , 2012). The EIR , 2012).The - - - GEOMORPHOLOGY ANDHUMANACTIVITY IN THEELEVATED INTERIORREGIONTO 3.1. IMPORTANCE OFGYPSUMANDARGILLITE 3. Discussion rsn tt fgeologic/hydrologic knowledge. present state of given our possibleis good as about as todetermine developednology in the EIR isimperfect, it is tech and culture Maya and geology between fit further discussed in Section As 5.1, although the et al perennial water supplies around areas with except Maya leftanddid not return needs (Dunning organized to meet collective water management ancient urbanization inthe EIR, aspopulations challenges arguably were adrivingforce behind tellanos and Foias, environmental 2017). These Preclassicto Late Terminalperiods (Cas Classic 1000 BCE and about 925 CE,from the Middle environment for nearly two millennia —between Maya survived andsometimesprospered inthis and variablethis bad groundwater climate, the Despite fields. desiccate and flood alternately can arises from wide variation in precipitation that Afurther problem gypsum. dissolving for farming bywater contaminated with sulfate derived from whose soil,although arable, iseasilypoisoned mation, have influenced the geomorphology and geomorphology the influenced have mation, itsrocks, especially the Icaiche for of the geology is adequate to draw usefulinferences about how about the EIR, we think the knowledge available geological information Despite the paucity of geologic/hydrologic explanations. limiting specific offer currently can we which for 4.3), fall comfortably into environmental patterns (section 5.1)andsub-region 10,a the 7, encompassing Puuc cities and these regions, onlysub-region Quintana Roo. Of Yucatán, Campeche,within the states of and sub-regions that outlines some 16geomorphic to afigure review 1 of paper by Beach limiting knowledgeThis is illustrated by reference ., 2015a). et al. (Dunning (Dunning , 2016). By about 950 CE the et al. , 2012;Beach polje et al. (section (2015a) Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - ieotrpifrainaotteaudneo tive outcrop about the abundance information of lowlands); 3)the qualita present in the northern able argillaceous clay (much greater than what is imperme that required a thickresidual cover of storage, usedinClassicalMaya successfully times, water of systems by provided evidence definitive the GM; 2)the the extensive sizeof and thickness tigation. We will draw onseveral observations: 1) be tentative but may be useful for further inves data arewill necessarily limited, ourconclusions weathering. Because available of ing conditions argillite can haveunder landscapesvary in forming and interbedded into the importance that gypsum hope this study will provide some general insight the Peninsula. Furthermore, we hydrogeology of at least directly, local bedrock, from weathering of mentioned in section 2.2.Much probably came, as clay surficial this for sources multiple probably as Lake Silvituk (Perry natural aquitards for shallow perched lakes such claythe regionin alsoserve as Abundant layersof et al. et al. water (Matheny, 1976;Matheny potable ground reliable sources of the region of reservoirsto compensate for absencethroughout canals, dams, and construct extensiveof systems Classical times to able clay required by Mayas of on abundant depended EIR agriculture imperme and Cejudo, 2017). argillaceous sediment to the coast (Leal-Bautista Quintana Roo, possibly related to transport of eastern 7) the facies changes in younger rocksof (Socki gypsum buried deeply areof with dissolution consistent Peninsularthe northern coast inYucatán state that present near 2011); 6) the distinctive forms karst on the SGM (2017)(Perry interior drainage thatsystems are labeled poljes of 5)the distinctive che formation; mapped patterns devitrifiedglass (Pope of quantity significant a containing ejecta impact 2006) that weaklyconsolidated AlbionFormation 4) the knowledge from drill core (Lefticariu argillaceous material in the Icaiche Formation. , 2012;Beach , 2002; Domínguez and Folan, 1996; Dunning et al. et al. , 2002;Perry et al, , 2017;Dunning et al., 2005)underlies the Icai et al., 2011). There are et al 2009; Perry et al. /2019 ., 1983;Gunn , 2009);and et al. , 2016). et al., et al. 5 5 ------,

STRATIGRAPHIC RELATIONS / The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology DISCUSSION The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology DISCUSSION GYPSUM WITHGROUNDWATER 3.2. MOREACTIVE WHENWET: INTERACTION OF 6 6 mation is an important source of surficial clay surficial of source important an is mation One argument that suggesting the Icaiche For (section 5.1). are located on the Eocene Chichen Itza Formation ing important archeological sites such asUxmal, Icaiche Formation, the northwest corner, includ the area is the but, whereas bedrock over most of ouini h diino sulfate and calciumions the addition of solution is dis zone vadose of effect chemical outcrops.The contributing to local relief, anddisappearing from to water from rain merely by dissolving, thus over which the GM cropsresponds out, gypsum Within the vadose zone, ciated soils. changes produced by decaying vegetation in asso pH the by affected little is solubility,it carbonate magnitude) and that, unlike (often byan order of sum solubilityisgreater than carbonate solubility that, as noted above, except in acid water, gyp its environment. of hydrology on the depends as a geological agent gypsum the behavior of to the water table is important because gypsum a layer of of beneath the water table farther north. outcrop,present is the vadose zoneits area in of state) and therefore that the GM, which in occurs Yucatánoutcrop (all the way to the north coastof the present area of the subsurface to the north of evidenceis continuous that in bedded gypsum present Yucatán,first in shall processeswe logical geo surface the on influence disproportionate a To that advance oursuggestion had the GM has GM, asdiscussedinsection3.3. materialsiliceous is and beneathboth within the argillite content. Anotherpossible argillite source increased the north, presumably asa result of of thanthe carbonate lesspermeable nificantly rocks the Icaiche Formation are sig that carbonates of indicatesfurther as discussed in section5.This the EIR (Perry of fringes the northern etratesslightly southof only source) is that the pervasive saline intrusion pen in the region (and perhaps the ultimate primary / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et al. , 2009;Perry It is worth emphasizing i.e. primarilyinthe area et al., The relation The 2011), ------/2019 GYPSUM MEMBER 3.3. OUTCROP EXTENTANDTHICKNESSOFTHE produce subsurface erosion and collapse. They argillite. processes, These working together, can silicates, especially for transport of in suspension calcite, gypsum, dolomite, andother minerals and feedback for further subsurface dissolutionof those channels, enlarge voids, andprovide positive will obviously channelsopen inbedded gypsum through flowing water saturated, initially not If flowing. is groundwater if important particularly behavior gypsum below the water table can be related to commonionprecipitation. However, important only for chemical secondary reactions calciumislikelyto be bonate terrains, addition of car in environmental haveeffects, but, important groundwater. and runoff to sulfate added The can 4), blocks of gypsum rock (more gypsum than ameter in 4), blocksof fragments. Inasecondnearby outcrop (Figure an argillite matrix supporting much rock coarser a very poorly sorted siliciclastic rockof consisting there are what appear to be twoof “intrusions” at thisoutcroptheDisplacing bedded gypsum clay.are outlined bygypsum thinner beds of crystalline, coarsely gently folded a meter thick) of 3). There, stacked beds (each individualbed about coordinates 18.530° N, 89.576°W(Figures 1and outcrops along the athighway occurs and near verses. the most informative For example, oneof tra highway in identified be readily can outcrops Earth “Street View”where prominent gypsum the well-known website Google application of several apossible novel suggests kilometers. This beds, makingthem easy to identify and follow for left distinctive impressionsin these softgypsum equipment the highway(used in construction) have excavating beds. massive teeth of gypsum The of theGM,exposingimportant new outcrops area of mately 18.5° Nandessentiallybisects the outcrop the Yucatáncrosses Peninsulamost of at approxi the Mexicanroad Highway186 occurred.This significantly improved in 2009when wideningandpartial levelling of geology EIR to Access discharge. may alsoaddsedimentat the pointof - - - argillite. At 18.530° N, 89.576° W.Labeledargillite. At “ProminentGypsum Outcrop” inFigure 1. Figure 3 Formation. the Icaiche tion 4.2, we correlate with the GM of by Lefticariu in drill massive core UNAM6 gypsum described of and 3)thesubsurface occurrence 35mthick ness; thick a general in stagesgivingonly impressionof similar size in which excavation has proceeded of face inFigure exposed 5;2)aquarry inthe quarry 25 m m based on the following: 1) an estimate of ing. 25–35 We estimate a minimumof thickness not possible, because complete outcrops are lack the GM is the thickness of A definitive estimate of been removed by quarrying.) bywater. structureslump subsequently has (This movement mass probablylubricated indication of that outcrop, outlined in red clay, are a further bedsin (Figuredeformed to view highly 6).The that wall was exposed a slump onthe west side of (Figure 5). In2008, gypsum crystalline coarsely of about 25 m in Figure 3, there is anexposed wall of the hill from the exposure shown opposite side of thatsiliciclastic material. is onthe In a quarry the of fluidity the emphasizing intrusion, clastic silici asimilar in “float” dimension) maximum Roadcut in massivelybedded gypsum Roadcut layer of theIcaiche Formationalong Highway“intrusions” of 186.Note poorlysorted et al. ( 2006), which, asnoted in sec Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - - SULFATE-CONTAMINATED WATER CONSTRAINTS ONHUMANACTIVITY FROM 4.1. LIVINGONAGYPSIFEROUS SUBSTRATE: gypsum oftheGypsumMember surface orsubsurfaceweatheringof 4. Regionsarguablyaffectedby developing facilitiesfor capturingandstoring once have accommodated to local conditions by It is quite remarkable that a large population could foryears about a thousand after abandoned. it was whyregionthis remained has almostunpopulated the major reasons EIR isprofound.is oneof This the of groundwater the on gypsum of effect The Roo. The clays cover the floor of shallow karst ( depressions shallow of floor the cover clays The Roo. Campeche, Yucatánarea of state, andQuintana layersthat donotexistthe better in knowncoastal clay impermeable the presence of ter because of these storage and distribution facilities for rainwa Maya, living inthe EIR, were able to develop rainwater during the Maya Classic period. The bajos ), which the Maya extended and /2019 7 7 -

DISCUSSION / REGIONS AFFECTED The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology BY WEATHERING OF GYPSUM REGIONS AFFECTED BY The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology WEATHERING OF GYPSUM Earth “StreetView.” can beused fora virtualfield tripalong Highway 186inGoogle andgypsum ductile soft, identifies that excavatingequipment outcrop. Note distinctivetoothmarksof50 meastofthat the about and in Figure3 as outcrop same the of part argillite, Figure 4 8 8 lakes (and by extension modified are presented in Table 1 and show that shallow byZoh Wagner (Wagner, 2009;Perry water from Lake Silvituk and Lake of Analyses Dunning ervoirs(Matheny large res (and alsoimitated)deepened to form layer has similarly low sulfate, whereas underlying mala), water held in a lake (Cival) above a clay margin (at ElPalmarsouthern inPetén, Guate acrossthe Mexico-Guatemala border. Near its high for EIR extendsThe human consumption. thatwater pumps with asulfate concentration too a town well is withinonlya few hundred of meters specialinterest becauseit (TableLake Zoh of 1)is can store remarkably ion-free water. Water from / BlocksofmassiveGMcaught up in poorly bedded Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín et al ., 2012). et al. , 1983;Gunn bajos ftheMaya) of et al et al ., 2002; ., 2011) - - /2019 MEMBER ROCKS AREA PROBABLY AFFECTEDBYBURIED GYPSUM 4 .2. THEPOCKMARKEDTERRAIN:ADISTANT KARST (Table 1). Near this well, there is aspringin standardsfor (SDWA,1996)consumption human which the sulfate about content 6 timesUS-EPAis Olmedo,a hand-dugtown 2016),has well in 282people (Navarro- Guadalupe, consistingof to this area. One resettlement community, La Mexico were brought densely populated parts of (Ericson in the 1960s program, initiated bythe Mexican government potable water. Ina resettlement the lack of of Yucatán,because mostly least populated parts of the to resettle the EIR, the area remains oneof federal Mexican Campeche government and by the government of the by efforts despite Today, layer hashighsulfate (Beach clay the by confined aquifer an in groundwater it occurs far from it occurs thenearest Icaiche outcrop. Itis Yucatánnorthern Peninsula isnot obviousbecause ofthe hydrogeology and geomorphology affects A second way inwhich the Icaiche Formation through theAlvarado pipeline. inated water, andsendingthe water to Xpujil contam in the southeast, just outside the area of CONAGUA responded by drilling a supply well dried up causingreal hardshipin the region. et al., the Classic period (Dunning was for the Maya of County,the 28000inhabitantsof it as that wateralmost astenuous is supply today for A drought in 2005 (Proceso, 2005) demonstrated Constitución. the other (100 km long) brings water from (57 km long) brings water from Lake Alvarado, the region, through two pipelines:one center of the municipality Xpujil, the major population of also supplies water (obtained outside the region) to Mexico, and brought by tank trucks. CONAGUA CONAGUA, the National Waterof Commission by La Guadalupe rely water ondrinking furnished chemistryto thetown well (Table 1). Residents of spring water. Water fromsimilar in thisspringis whichcrops out indirect gypsum contact with 2016). In that year, rain-fed Lake Alvarado et al., 1999), farmers from 1999),farmers et al. , 2015b). - thickness: 25m.Photograph takenin2008. Figure 5 rbbeta h Mo the Icaiche Formation is probable that the GM of bodies that are perched lakes not in equilibrium water neighboring from distinctly differ latterweCenotes Ocom andNohbec. The discuss this sectionandparticularly insection6,where Cenotes Ucil andXcolak in of ant in discussion table controlled byimport distinctionis The msl. and witheachother, tappinginto aregional water hydraulicsubsurface with the ocean connection cenotes havecondition that all these northern a ically invoke the implied but generally unstated innorthern common Yucatán (Schmitter-Soto sinkhole water-filled of (from the Maya be ambiguous. Here, we usetheword somewhat depressionsis karst variable and can Please note that the regional nomenclature for nearest Icaiche outcrop. state (Perry the Pockmarked northcentral Yucatán Terrain of cenotes and deep tion of characterized karst, by a dense popula of form the distinctive responsible for the development of Awallofmassivelybeddedgypsum oftheGMIcaicheFormationexposed inaquarry 500mwestofFigure 3.Estimated et al. 02,aot10k ot fthe , 2002),about north of 160 km tzonot ) to refer to a specific type specific a to refer to ) et al. aguadas , 2002). We specif , that constitute Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - - - was inferred by Gmitro (1986), Perry m beneath the surface inthe Pockmarked Terrain more than 100 the GM gypsum presenceThe of this usagemay differ. the EIR, partsof southern of other discussions direct connection tothe regional water table. In its blocks that sediment with filled partially is that with the ocean. We use also supporte the Pockmarked Terrainsum of with the GM is in the subsurface gyp water.sinkhole matter Correlation of organic by sulfide to reduced readily ate-saturated groundwater, or sulfate, which is either calcium, which isubiquitousincarbon (CaSO tracer element for gypsum marine origin, is a better groundwater of gypsum ing that strontium, aminorelement present in spelled worthXcolak andXkolac.Itis mention m inCenote Xcolac (20.909º N, 88.857ºW),also in Cenote Ucil (20.990º N, 88.600ºW)and120 the water column 100m-deep water at the base of the sulfateon high and strontium ioncontent of and Socki et al. ytepeec f 5mlyro a35mlayer of d by the presence of (2002). This assumptionwasbased (2002). This aguada to specify a sinkhole to specify /2019 4 •2(H et al. 2 O)) than (2002) 9 9 - - -

REGIONS AFFECTED BY The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology WEATHERING OF GYPSUM REGIONS AFFECTED BY The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology WEATHERING OF GYPSUM 10 10 (2008): leogene basement faultsreported byGulick that in environment.karst shallowpre-Pa The limestone saline intrusionthandevelopment of opment of how Perry lower sea-stand. Here is especially duringtimesof provide a pathway for movement, groundwater by Perry e Gulick measurements of by seismic offshore Impact Chicxulub the of edge ring fractures along the eastern a set of covery of the Pockmarked Terrainof is provided by the dis A mechanismfor producing sinkholes the deep tion outcrop (Lefticariu thenearest Icaiche Forma Peto,north of 50km fromUNAM6, anobservation well drilled near overlying Paleocene collapse breccia inrockcore recrystallized massive Paleocene/Eocene gypsum / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín fboth carbonates andevaporites. However,of incon dissolution subsurface produce to sufficient been have itself, may penetration. enhanced permeability, The of opment, opening this zone to extensive groundwater ...may have devel resulted inexceptional permeability and Perry of theEIR.the easternpartTable 1.Waterbodiesand DatafromWagner wellswithinorat (2009) et al Chichancanab La Guadalupe La Guadalupe aeSliu 86 03 0.2 18.63/90.31 Lake Silvituk Nuevo Israel et al. gypsum o ae1.9/8.20.23 18.59/89.42 Zoh Lake o el1.9/8.27.9 18.59/89.42 Zoh Well Sample Spring . (2009), these deep fractures. (2009), these deep may Lake Well Well (2009)explained why develkarst et al. would be more likely inadeep, (2011). et al Longitude (ºW) t al Latitude (ºN)/ ., 2006). 83 94 16.29 18.33 /89.48 98 87 7.4 19.84 /88.76 9.93 18.33 /89.48 90 85 6.1 19.00 /88.57 . (2008). As set forth. (2008).As et al - - Chloride (mEq/L) - - - - /2019 . DISSOLUTION OFGYPSUM 4.3. POLJES the GM d the A third geomorphic/hydrogeology result of outcrop. rain developedfrom 160km the nearest Icaiche mechanismby which the unique Pockmark Ter buried Icaiche Formationthe most likely gypsum in the subsurface, we consider the dissolution of and ourabilitytotrace theGM it northward of In summary, given the extensive surface exposure collapse features inthe area. to produce the subsurface erosion that contributed to associated with impact ejecta [ormore probably GM] gypsum have preceded andaccelerated dissolution of anhydrite may expansion accompanying hydration of circulation groundwater deep occurs. Inthat case, the salineintrusion, well below the water table, if and thus isperhaps more likely to take place within anhydrite, andcelestite isnot directly pHdependent gypsum, trast to carbonate dissolution, solubility of poljes (mEq/L) Sulfate 36.46 32.41 31.49 souinmyhv entefraino issolution may have of been the formation , PROBABLY FORMEDBYSUBSURFACE 52.9 25.1 0.03 0.04 of Southern Campeche andQuintana Southern of 100xSO 224 712 326 414 400 13 20 4 /Cl - h aeo oeo the most extensive poljes: “ one of the name of vegetation canimpede access, afact made clear by et al. were exploited with intensive cultivation (Dunning created zones withhighproductive potential that and toeslopes bordering manylow lands( soil erosion onadjacent uplands onthe footslopes cumulic, base-richderived soils from apronsof of Dunning and desiccation duringdrought periods (Gunn rainy during flooding toward tendency oftenbecause counterbalancedit is by the seasonal this potential not been exploitedhas everywhere age (although and thick nutrient-poor) soil. But water stor of potential in the form agricultural offer surface.They the anywhere,” on “go least at that do not seem to drainage patterns internal limestone weathering. They alsohave complicated aeolian inputsandinsoluble residues of ering of weath the from derived clays residual by floored (Figuredimension 1) (SGM, 2017). They are thatbasins areor more 40km intheir longest Roo. are These closed,often interconnected associated with evaporites (Doğan, and Yesilyurt,and (Doğan, evaporites with associated Europe andthe Middle EastareEastern commonly holes.sink The above creating something analogous to enormous rocks theEIRregion,followed bycollapse of of dissolvedout siliciclastics limestoneandsuspended water, passagewaysopened subterranean carrying which gypsum, by underground dissolutionof We gypsum. submit that the of Icaiche Formation with itsnear-horizontal beds the located on oradjacent to the outcrop area of a coincidencethat the large what is their plumbing system? We it is not suggest eachquestion thatA basin. arisesis out of pension material were transported in solutionandsus of the requiredepressions thatform large amounts to lost mass the and floor valley the on sediment accumulated residual and both the volume of these Except for what evaporates, rainwater falling on Si Puedes , 2002,2006,2015).Swampyareas andthick poljes (e u fyou can)”(Figure 1). (getoutif et al ms ev hog oesr fdrain, must leave throughsort of some ., 2012).However, the development poljes o Turkeyand elsewhere of in poljes poljes o the region are of were formed were formed et al ., 2002; bajos Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Sal - - - ) POLJE FORMATION 4.3.1 POSSIBLEFATE OFSILICICLASTICRESIDUES Becak-Morocoy isbecomingextended. drainage processby which the joint Poljes Nuevo acontinuing subsurface lake drainagepart is of Bautista is investigating the possibility that this secting Poljes Nuevo BecakandMorocoy. Leal- inter Roo. junctionof It is at the southwestern Quintana paralleling or less southeastern faults in lakes about 10 km long, trending NNE-SSW, more shallow a chain of andispart of quarries gypsum anorth-southlineof east Om liesaboutof 2 km observation).2018 (Leal-Bautista, personal Lake August, in refilled quickly then and unexpectedly Om (18.49°N, 89.08°W)drained rapidly and thismechanism,Laguna 2004). Insupportof erosion that formed subsurface residues removed duringthe processof siliciclasticinsoluble 4 may be representative of material in the intrusions shown inFigures 3and support perched water tables. We that suggest the Puerto Formation the Carrillo all ability facies of and, in particular what may be a local, low-perme Miocene Estero Franco andBacalar Formations relativelyargillite high content. For example, the these younger carbonate rocksindicative of of theEIR?Section 6 describescharacteristics of marine rockssedimentary to the east deposited clay inpost-Eocene impermeable is the source of answer toanapparently unrelated question: What Formation (Pope argillite derived from devitrified theglass Albion of in Figure 6 andthe dark layer inFigure 3); and2) (redin theGM layersinterbedded with gypsum Probable source materials include: 1)argillite fluids. water-rich mobile, as emplaced been have the GM (Figures 3and4) must ded evaporite of materialinantly siliciclasticsedimentary into bed unsorted,dom We assertthatof the “intrusions” sediments being deposited offshore.sediments being deposited were into carbonate subsequently incorporated et al. poljes , 2005). This suggests an suggests , 2005). This andthat these sediments /2019 11 11 - - - -

REGIONS AFFECTED BY The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology WEATHERING OF GYPSUM The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology THE TICUL FAULT MARKER OFHYDROGEOLOGICAL REGIONS 5.1. THETICULFAULT, AUSEFULBUT INEXACT 5. TheTiculFault the photograph ofFigure 5wastaken. Figure 5.Thefeature hadbeenexcavated,henceremoved,before Figure 6 12 12 the Yucatán Peninsula as fitting a variation of a variation fitting as Peninsula Yucatán the theentire Mexicanpart of the hydrogeologyof Perhapsreflexively, envision to easy become has it remains generallyvalid. investigatorsous the ensuing47years;in but it and hasbeen tweaked many timesby numer Hanshaw and Back,(1980) and Backet al. (1986) carbonate aquifer. That model was developed by on adenser saline intrusion withina permeable floatingwaterfresh of lens a Peninsulaof consists Yucatán the northernmost aquifer of system In 1970BackandHanshaw proposed that the / A slump structure in the same quarry as shown in as quarry same in the structure slump A Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín - /2019 GROUNDWATER FLOW 5.2. THETICULFAULT ASACONDUIT FOR h al,Uml(4k ot fthe fault), and the fault, south of Uxmal (14 km impressive cities, includingOxkintocright on the EIR. These of occupies the northwest corner noted foris distinctivestyle architecture, Puuc Maya citiesthat agroup of of ruins 2017). The valid dividerfor archeological(Beach, purposes for the boundary EIR, andthata is northern Dun to establish. ning difficult is it) support not do saline intrusion)andthe rocksin the south (that rocksin the north (thatthe permeable support a al., the Iaiche Formation (Perry beneath outcrops of wrong. the Hanshaw andBack(1980) model, but that is 2.0ºN 920 ) 0k otes fTicul (20.206º N,southeast of 89.290ºW),60km to dominate the landscape as far as Tzucacab the EIR, continues blockand of the southern of boundary scarp, the northern whichThis forms northern Yucatán. of plain lowland flat dropped, almost 100 mabove the down- W), to a height of Ticul(20.40° N, 89.535º eponym, the town of in south central Yucatán its state, risingdirectly south of landmark well-defined conspicuous, a Eocene age (McClain, 1997)is Ticul Fault of the normal block of up-thrust southern The 2002). 92m(Perry Ticul Fault) lies at of a depth the table in nearbyof Santa south Elena (10 km Sayil (Perry wells to deep atsupplies groundwater Uxmal and to be accessible by pre-Colonial technology, now has anaquifer, which, although it was too deep Formation that does support a saline intrusion and theChichen Itza the porous, rocksof permeable rainwater. However, the Puuc cities were built on were utterly on capturing and storing dependent the EIR and citiesof cities were likethe southern to groundwater,access andinthat sensethese residents700 and950CE.Their didnothave the fault) Sayil flourished(21 between km south of 2011). However, the betweenprecise boundary et al. Thereno evidence is for asalineintrusion (2012)have usedtheTiculFault the as et al. , 2002).For reference, the water et al. et - , EVOLUTION OFACOMPLEXGEOMORPHIC REGION TABLE: ASIMPLEMODELTO EXPLAINONGOING 5.3. DISSOLUTION OFGYPSUMBELOW THEWATER quently, field.Conse the fault trace markedis inthe map of the in to discern difficult becomes the Ticul Fault (Figure 1), the exact position of 89.050º W)andCatmis(19.960º N, 88.950ºW) betweenIn the 16 km, Tzucacab (20.070ºN, Chichancanab. the region around Lake been transported out of which sulfate (a proxy forhas dissolved gypsum) show inthe next section, it is the majorconduitby the GM because, aswe importance of morphic the geo Fault of is important to an understanding et al. Mexico(Perry of and theGulf Celestun Estuary roundsthe Chicxulub impactandthence into the 88.760º W) westward to the fault thatsystem sur LakeChichancanab (19.840ºN, of the vicinity movement,groundwater water from carrying (Figure1). fault is an important conduit for The ae rmtevcnt fLake Chichancanab water from the of vicinity elevationfor asabasis postulating that ground Perry et al. (Perry with respect togypsum canab, whosewater approximatelyis saturated LakeChichan fault bypasses endof the southern the N, 88.210ºW)andbeyond.section of This Ticul Fault forto Cenote Nohbec (19.100º 120km show a dashed trace (denoting uncertainty) for the SGM(2017) continues to Catmis, the map of of contact withasulfate sourceSoutheast (gypsum). ratios, are high andstronglygroundwater suggest Both, these sulfate concentrations andSO and 19.7mEq/L,respectively (Perry sponding SO whereas the ratio at Catmis is1.8,with corre Tzucacab hasaSO chemistry.in groundwater Groundwater from that, within that distance, significant there is also a notable change is it think We line. dashed a as onFigureSGM (2017) (and correspondingly 1) , 2005). , 2002;Perez-Ceballos et al. (2002)usedwater chemistry andlake 4 euvln ocnrtoso 12.1 equivalent concentrations of 4 C qiaetrtoo 1.03, /Cl equivalent ratio of et al. et al , 2012). The Ticul , 2012). The . 2002;Hodell et al. , 2002). 4 /Cl Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------omnocrec fcalcareous breccia noted occurrence of common by gypsum dissolutioncanexplain the Removal of to regional characteristics summarized in Table 2. aforementioned can be best evaluated by referring Evidenceformining”. “solution the analog of natural a performing effect —in it removing and thisunit Fault of is actively gypsum dissolving that moving 2)groundwater through the Ticul Peninsula, the northern andalso it is inmuch of thisarea as present in the shallow subsurfaceof statements:probablehighly 1) Itis thatis GM geochemical data, we cannow makestronger SGM (2017) with these previouslyreported of Mexico. on the map Combining information of moves west through the Ticul Fault into the Gulf variability is documented (Perry water. well This of quality the in differences local observation,lished personal 2013) reported wide whereJMM residents queried byPerry (unpub in the subsurface inthe of vicinity gypsum of heterogeneous distribution additional evidence of byWaterdissolution. gypsum chemistryprovides are collapsed breccias above cavernsproduced in road-cuts near the town. We that suggest these José María Morelos (JMM)and within the town of Calcareous brecciaalso abundant is inoutcrops down-dropped side). northern the TiculFault trace (muchmore abundantthe on flanking quarries in (2017) SGM of map the on n f h ihs esrdi aeso Yucatán. the highest measured in waters of one of ing water (SDWA,1996), andthehighervalue is ( crops. lower The value exceeds Mexican ber of and highsulfate values are deleterious to anum It is worth noting that sulfate is a strong laxative, active, ongoingprocess. by gypsum dissolutionisan gests that removal of sulfate sug in groundwater the concentration of local variabilityhigh in and 18.93mEq/L.This respectiveThe sulfate concentrations were 7.29 a nearby well station at was 9.01. an agricultural town well was 1.74,whereas the ratio for water in Cl ratio measured for water inthe meter apart at(Figure SO Chunhuhub 1).The wells nearthefault trace and aboutakilo pair of NOM- 127 SSA-1994 ) and US standards for drink et al /2019 ., 2002)ina 13 13 4 / - - - - -

The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology THE TICUL FAULT The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology THE TICUL FAULT Table 2. Features related to the transitional hydrology of the eastern “Ticul Fault Zone”.Table 2.Featuresrelatedtothetransitionalhydrologyof theeastern“TiculFault 14 14 Carrillo Puerto Fm. Puerto Carrillo of a meander, sitting on the form the in acenote Nohbec: within about 4 above msl. water level elevation Surface Breccia” “Calcareous Nohbec. into Cenotes Ocom and Channels for overland flow lake elevation. of and climate of record 9000-year meandering stream.meandering of channel Ocom, occupying the shore. Gypsum precipitating on saturated with gypsum. nearly or Water saturated Chain of cenotes, including Fault is a strong transport agent removing gypsum why divide andsuggests a groundwater the Ticul 4 m)as (elevation Chichancanab Lake confirms Earth(accessed28/02/2018).That to Google 1–2maboveaccording msl a water elevation of jected to runthrough Cenote Nohbec,which has the Ticul Fault is proAs noted above, the trace of / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín a “fossil” “fossil” a Feature is on the Ticul Fault trace. Fault Ticul the on is Nohbec arm Cenote One of 19.142º N, 88.168º W. Ocom and Nohbec. Ocom and Cenotes Chichancanab, Lakes Esmeralda and Fm. Puerto Carrillo exclusively in not but predominantly, are Quarries Catmis. of south and trace Fault Ticul of west and east (2017) for quarries in a band Noted on the map of SGM Earth Can be observed in Google 19.840º N, 88.760º W Lake Chichancanab 19.470º N, 88.100º W 19.840º N, 88.760º W Lake Chichancanab Location or Entity or Location - /2019 dissolution. subsurface gypsum to related collapse Suggests surface movementsurface low over Image PIA03379. Indicates Show clearly NASA on msl. above flow supported perched stream Fm once Puerto Carrillo impermeable the of facies relatively a that Suggests change. level sea to response scale) years) but regular (longer (months, slow Indicates (msl). is controlled by the ocean level whose aquifer with an hydraulic contact Indicates permeability rocks. msl. msl. meter a of within is Ocom gypsum. with contact direct Water in Possible Significance Possible rso funderlying gypsum. erosion of subsurface jected up to the surface asaresult of the fault here is visible precisely because it is pro of path diffuse the that suggesting region, this in rillo Puerto Formation that overlies the fault divide is considerably older than the 5 m.y. Pliocene Car from the region. In fact, the 50 m.y. Eocene fault of the Carillo Puerto Fm. Puerto Carillo the of south the in change (facies) on Google Earth the map of SGM (2017) and on evident stream channels “fossil” several of One Hodell Perry in measurement reported Lake Esmeralda Earth. Google on Measured town José María Morelos. road cuts in and around the Also notable in street and aquifer. by level base (msl)captured Best example stream of (2002). Reported by Perry al. et Illustrate permeability Illustrate et al et et al et . (2002). Notes . (2005) - - eastern Yucatán complex landformsandhydrologyof 6. Furthersuggestionsaboutthe eodn h itr fa perched stream that has recording of the history Earth.We Google in assemblage this as interpret resembles astream meander as canbe seen clearly Ocom” inFigure 1 (19.47º N, 88.07º W), that cenotes all occupya sinuous basin, labeled “Lake approximately 1-2 m above msl . These vations of eight cenotes that have water ele which isone of landscape, isoccupiedby Cenote Ocom (Table 2), particularly an evolving helpful in interpreting ever, one apparent fossil stream channel, that is How processes. karst by influenced be to appear these do not ormoremeters aboveMost of msl. open water, several bodies of nent or ephemeral perma by filled are that channels stream “fossil” includemeander-likeThese features, resembling aquitards. toconstitute as impermeable ficiently cene rocksbordering the EIR onthe east are suf precipitation, thatpre-modern suggest post-Eo which probably developed during a period of Several features regional (Table geomorphic 2), variations. lated by Pleistocene and perhapsearlier sea level observed in the region, may have been stimu erratic, incomplete subsidence thatpresently is from below.transport, followedmass This bythe dissolutionanderosion Ticul Fault as aresult of channels developed relatively recently along the in thisregion until subsurface gypsum layers of aquitardsabove the GM mayhave protected of these observations isnificance that of the presence sig The studies couldusefullytest this suggestion. as the younger rockswere Provenance deposited. eroded from the EIR andtransported eastward rockscontain considerable argillaceous material post-Eocene section 4.3.1, is that these eastern, Yucatán than here. One possibility, proposed in mation, which innorthwestern more is permeable Puerto For the Carrillo rocks, includingrocksof expanding clay are in local common layers of that confirmed 2017) Cejudo, and (Leal-Bautista local quarries A reconnaissance inspectionof been letdown by baselevel. erosion tomodern Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ------down-dropped FaultBlock dissolution ofgypsumintheeastern 7. settlement 8. Effectofgypsumkarstonregional Ad hoc ing through theTiculFault, that we postulate, is Our provisional answer is that the solution min SGM(2017). upthrust fault block onthe map of canab, calcareousbreccia not shown is on the LakeChichan exceptthe immediate in of vicinity in occurring the down-dropped blocknear the fault, whereas, erosion is why Specifically, here. ence andsubsurfaceerosionmodel we propose north. That may poseaproblem for the subsid Ticul Fault anddown-dropped to the is normal Where it is well exposed in the northwest, the regionoccupied by was bycolonials.Spanish the 1840s, Beginningin the (Chamberlain, 1948),the area was largely ignored and, after earlywith Mayas bloody skirmishes on the south (Witscheyand Brown, 2010); Lake Chichancanab and extending to Lake of sitesinthe area that lies east and south pation of 1521,thereextensive was Maya occu invasionof Therelittle is evidence that, before the Spanish meability increase. per and brecciation cause to sufficient probably almost40%, would involve volume changes of more buried deeply down-dropped fault block and anhydrite would preferentially occur inthe tion of et al. at drite lowtransition occurs temperature (Jowett (Rosencrantz, 1990) and that the gypsum-anhy Peninsula was once a tectonically active region may alsobe worth mentioning that the Yucatán experienced repeated large changes insea level. It above, particularlynear this coastalarea that has than table water the below effective more much during a massive uprising. Until the mid–20 vegetation andfew roads, after theywere defeated dense foundhere asaferefuge,a wildplace of in , 1993). Dehydration of gypsum andrehydra gypsum , 1993).Dehydration of explanationsforselective indios rebeldes /2019 : Mayas who th cen 15 15 ------

FURTHER SUGGESTIONS / EXPLANATIONS The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology / EFFECT OF GYPSUM KARST EFFECT OF GYPSUM/ CONCLUSIONS / The Icaiche Formation: stratigraphy, hydrogeochemistry and geomorphology ACKNOWLEDGMENTS / REFERENCES Acknowledgements 9. Conclusions 16 16 renamed Felipe Puerto 1930. Thus,in Carrillo Chan Santa Cruz, rebel Mayaformer townof a lished as capital of largest towns are José María Morelos, not estab Manilkara zapota Mayas, itinerant th tury ose epfo ubro researcherswho to seekhelp from anumber of topics from geochemistry to archeology, has led us this paper,state. addressing broad The scope of the part of aquifer in the south-easternmost deep Quintana Roo. Part II willfocusa proposedon southeast andaqueousgeochemistry of geology the hydro a two-part study of isPartThis I of theGMonsurrounding areas. the effectsof the EIR andof rocks, sediments, and waters of of emphasizes the need for adetailed geological study the region are tentative about the hydrogeology of ourconclusions scarce. factthat The manyof a valuable resource likelytobecomeincreasingly Quintana Roo. southern Potable water is and of the EIR edly bring pressure for development of Quintana Roogrowth innorthern will undoubt the Yucatán Peninsula.tion of Rapidpopulation the Mexicantopography, por andhabitability of hydrogeology, the influenced strongly have GM little-studied Icaiche Formationand especiallyits the relativelyWe submit that the characteristicsof relatively unattractive settlement. for permanent aquifer) may have combined to make the region the GM exposed within adynamic to groundwater and poorwater quality (resulting fromof gypsum Irregular topography, variable soil development, the region. the distinctive characteristics karst of development may have been, in part, a functionof the mid-1970s. We that suggest this late and slow tourism that in began was overtaken by awave of regionthis remained largely undeveloped until it / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín e area was occupiedlargely by rebellious trees) and loggers. Today the chicleros municipio (avseso chicle from (harvesters of until 1974, and the - - - - /2019 References zadder-Beach, Timothy Beach, David King, and acknowledge Luz gratefully their help: Sheryl them and criticism. We have from each learned of (through variousiterations) andprovided valuable the manuscriptalphabetically, read parts orallof listed researchers, following The for his field. the in help Yucatán) de Científica Investigación de We are to Dr. grateful Eduardo Cejudo (Centro Técnico from CONAGUA inQuintana Roo. Yucatán, and Eng. Iván Gamboa Rosas Secretario guez, Director Técnicofrom CONAGUA in especially from M.Eng. José LuisAcostaRodrí Mexico (CONAGUA)Water and of Commission acknowledge institutional help fromthe National haveresponded. It is apleasure graciously to Bautista, F., Palacio-Aponte, G., Quintana,P., Back, W., J.S., Hanshaw B.B., Herman, Van W.,Back, Hanshaw, B.B.,of 1970,Comparison this manuscript. de Yucatán. We take responsiblity for any errors in Científica Investigación de Centro the from port availability forstudy theregion. received This sup addressed asfar as possible due to the limited data reviewer for constructive thatcriticisms we have Mihai Lefticariu. 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