Pliocenemicrofossils from the Monticello point maar, SierraGounty, New Mexico

NewMexico Museum o,rn,"ft lJiff?if ,ifl?XXlli {f it!!,{^;{i{#n NM87104

Abstract sp. A and Chara sp. B; the foraminiferan Introduction Ammonia becarri; the ostracods Potnmo- Two fossil localities in the Monticello A series of maar deposits of late Ce- Point maar on the western shore of El- nozoic age are present along the shores of Elephant Butte Lake, Sierra County, New l\4exico(Fig. 1). Volcanologicaland petrologicalstudies of thesemaars have been undertakenby Aubele et al. (1976), sistent with a Pliocene age assignment Warren (1978),and Kelly (1988);however, for the Monticello Point maar diposits, ejecta. there has been no attempt to It produces fossils of the charo- which formed in three study the stages. The first paleontologyof these stage was explosive forniation of the maar maars.Here, we re- basin, and a second stage of erosion of port the resultsof studiesof microfossils the eiecta and stabilization of the maar from the maar at Monticello Point. This surface soon followed. During the third maar produced an extensive sample of and final stage, formation of a maar lake charophytes, foraminiferans, ostricods, produced a saline, diatom-rich water- and gastropodsfrom two NMMNH (New crater. It yields the charophytes Cftara body in the Monticello Point maar. Mexico Museum of Natural History and Science)localities in the SWV4NEI1+SEtl+ sec. 35 T11SR4W (Fig. 1). Thesefossils are now in the NMMNH collection. Their paleoecological significance leads us to proposea three-stagemodel of maar and maar-deposit formation at Monticello Point. Mitchell Polnt maar diatomite

NMMNHtocatity 27108 Alsoin this issue LargeExogyra from Dakota 1,, Sandstone p.49 ChristinaLochman Balk NMMNH locality 2Z1OA honoredby NMGS p. 54 NMGS1995 news p. 55 NMGS1994 abstracts p. 56

Black Mesa maar Upcomingmeetings p. 58

t u"-* Service/News p.62 Staffnotes p. 63 ..""**" Black Blufls maar Gomingsoon f-tl;--r Climaticinferences from rock glaciers

FIGURE l-Maars near Oil andgas discovery wells drilled Elephant Butte Lake, including the Monticello point maar (after warren, stratigraphic column oi ^uui a"porits at Monticello point (see in 1993 description).1?1?,:l1s*sured Table 1 for (Bachman Meh- Geology and age beds at White Cliffs maar, immediately in the 2-3 Ma range and east of the Monticello Point maar across nert, 1978; Kelly, 1988). This places a min- A maar is a volcanic crater created by a Elephant Butte Reservoir, as "chalk," but imum age of about 2 Ma on the maar violent explosion. It is characterized by they are mostly siliceous in composition. deposit at Monticello Point. Fossil mam- pyroclastic deposits that dip into the cra- This diatomite represents a period of per- mals indicate a Blancan (2-4 Ma) age for ter and by a lake(s) that occupies that cra- manent saline lake deposition within the the axial facies of the Palomas Formation ter (Ollier, 7967).The maars in the Elephant stable maar lake. Fossils from the basal southwest of the Monticello Point maar Butte Lake area were formed by phrea- bed of the diatomite (NMMNH locality (Lucas and Oakes, 1986; Repenning and tomagmatic eruptions when rising basal- 27108) are the charophytes Lamprothanium May, 7986). Mack et al. (7993), using mag- tic magma interacted with groundwater sp., Chara sp. A and Chara sp. B; the for- netostratigraphy, bracketed the Palomas associated with the ancestral Rio Grande aminiferan Ammonia becarri; the ostracods Formation south of Truth or Conse- drainage (Warren, 1978). Potamocyprisuniawdata, Candonainopinata, quences, New Mexico at 0.73 to 0.80 Ma The strata studied here are the inward- Cyprideis salebrosa, and Limnocythere sta- for the top of the formation and2.9 to 3.I dipping maar ejecta deposits and deposits plini; and the diatoms Campylodiscusclyp- Ma for the formation base. We therefore of a lake that filled the maar crater, which eus, Anomoeneis spharophora, Cyclotella sp. conclude the Monticello Point maar is of occupied an area of about 10 hectares (al- cf. C. caspia, Denticula elegans, and Am- Iate Pliocene age, an age assignment con- mosf 25 acres).The baseof the maar ejecta phora coffaeiformis. sistent with the fossils reported here. deposits is not exposed, and they are di- The Monticello Point maar deposit is rectly overlain by piedmont facies of the thought to be closely related to other maar Paleontology Pliocene-Pleistocene Palomas Formation deposits to the north, east, and southeast (Lozinsky and Hawley, 1986). The maar (across the reservoir) of Monticello Point deposits exposed at Monticello Point (Figs. (Fig. 1). This complex of maars is similar Lamprothaniuffi sp. 7, 2) ate of three types: to what OIIier (7967\ referred to as the This charophyte (Fig. 3A-B) has elon- 1. Ejecta sandstones and sedimentary "Red Rocks" type, caused by a number of gate gyrogonites, a rounded base, five breccias are trough-crossbedded or wavy closely spaced multiple eruptions. In Vic- spiral cells meeting around a pentagonal laminar (Fig. 2B-C). Clasts are scoria- toria, Australia, the Red Rocks maar com- plate, an apex with five extended and ceous basalt in a sandstone matrix. This plex contains salt lakes that have been slightly inflated spiral cells forming a dis- matrix is primarily the eroded rim eiecta studied ecologically and found to be char- tinct neck, and 9-11 spirals in side view. and in places contains volcanic bombs. acterized by very rapid and short-term Lamarothanium is bv far the most abun- 2. Lacustrine charophytic limestone (Fig. changes in thermal and chemical charac- 2C) is a thin (0.1 m thick), localized unit teristics (Walker, 7972). that contains NMMNH locality 27104. This The maar deposits in the Elephant Butte material represents a small pond and area are overlain by a series of basalts that spring deposit intercalated in the re- erupted subsequent to maar formation. worked maar eiecta. Fossils from this To the north of Monticello Point, the New AAexnc@ limestone are the charophvte Lamprothan- Mitchell Point maar is overlain by the ium sp., the ostracods llyoiypris bradyi and Mitchell Point basalts, which have yielded Candona elongalactoides,and the gastropod a K-Ar age of 2.9 + 0.3 Ma (Bachman and GEOLOGV Physa sp. Mehnert, 1978). The White Cliffs maar, 3. A thick diatomite, with numerous ir- across Elephant Butte Lake, is overlain by o Scienceand Service regular nodules of white opal and trans- the Black Mesa basalt, which has not been lssN 0196-948X lucent quartz, forms the prominent white dated. However, dates of other basalts and volume 16, No. 3, August 1994 beds at Monticello Point (Fig. 2A, D). of basaltic dikes that overlie maar deposits Editor:Carol A. Hjellming Warren (7978, p.24) referred to the white to the southeast of Monticello Point are Published quarterly by New Mexico Bureau of Mines and Mineral Resources a division of New Mexico lnstitute of Mining & Technology TABLE 1-Measured section of strata in the Monticello Point maar, SW'/+NE1/+SE1/+sec. 35 T11S R4W, Sierra County, New Mexico. See Fig. 1 for stratigraphic column. BOARD OF REGENTS Ex-Officio Bruce King, Goaernorof New Mexico Thickness Alan Morgan, Superintendentof Publiclnstruction Unit Lithology (m) Appointed Diane D. Denish, Pres.,7992-1997,Albuqueruue J. Michael Kelly.sec. Treas..1992-1e97. Rosuetl 7. Sandy siltstone; light-brown and reddish-brown. Not measured Lt. Cen. Leo Marqtez, 1989 1995,Albuquuque 6. Diatomite; white (N 9) and very pale orange (10 YR 8/2); clayey; 4-7 Steve Torres, 1991 1997,Albuquerque Zimmerly, 1991 1997, calcareous; finely laminated. NMMNH locahty Charles Suono 27708. New Mexico Institute of Minin8 & Technology 5. Sandstone and mudstone in thin interbeds; grayish-yellow (5 Y 8/4) 0.8 President...... DanielH.L6Dez and grayish-orange (10 YR7l4). Sandstone is very fine grained, New Me\ico Bureauof Mines& MineralResoures Directorand StateGeologist. . . CharlesE. Chapin subrounded, well sorted, quartzose, calcareous, and ciayey. Sub{iptiore: Issued quarterly, February, May, August, 4. Sandstone and conglomerate; same color and lithology as unit 3; November; subscription price $6.00/calendaryear. trough crossbedded. Editorial matter: Articles submitted for oublication 3. Charophytic limestone; very pale (10 8/2) to should be in the editor's hands a minimum of five orange YR pale 0.1 (5) months before date of publication (February, yellowish-orange (10 YR 8/6); weathers pale yellowish-brown (10 YR May, August, or November) and should be no longer 612) and dusky yellowish-brown (10 YR 2/2). NMMNH locality than 20 typewritten, double-spacedpages. All 27104. scientific papers will be reviewed by at least two people in the appropriate field of study. Address 2. Sandstone and conglomerate; same color and lithology as unit 1; 4.0 inquides to Carol A. Hjellming, Editor of Nru Me,@ trough crossbedded. Geolo3y,New Mexico Bureau of Mines & Mineral Resources,Socorro, NM 87801-4796. 1. Sandstone and conglomerate; grayish-orange (10 YR 7/4) to 26.0t Publisherlas publicdomqin, therefore reproducible uithout yellowish-gray (5 Y 712)with brownish-biack (5 YR 2/1) clasts of permission.Source credit requested. vesicular basalt. Sandstone is very fine grained, angular, poorly Cbculation:1,6N sorted, silty, and calcareous litharenite; laminar to wavey iaminar P/intel; University of New Mexico Printing Seilices bedded.

August 1994 NewMexico Geology FIGURE 2-strata exposed at the Monticello Point maar. A, Overview of prominent white beds of diatomite. B, View ofrravy-bedded unit 1 (Fig' 1) C, View of unit 3, light-colored limestone that contains charophytes u.rd oth". fossils (NMMNH locality 2770A). D, Close-up of finely laminar beds of diatomite, unit 6 (NMMNH locality27108).

dant charophyte in the Monticello Point sin-Protelphidium orbiculare (Brady) and maarsample. Studies in Australiaindicate Cribroelphidium selseyense(Heron-Allen members of this genus are particularly and Earland) (Bachhuber and McClel- adapted to highly saline environments lan, 1977)-and the Lucero Basin-Cri- (Burneet al., 1980;Brock and Lane, 1983). broelphidium selseyense (Kietzke, They have also been reported associated unpublished data). Ammonia beccarrihas with foraminiferansand eusalineto me- The internal structure of the gyrogonite is alsb been reported from several south- lake sediments and cores tasalineostracods and molluscsin the Ho- rounded rhombohedral Platelets ar- east California locene of Algeria (Plaziat, 199t). ranged in slightly fan-shaped patterns (Arnal, 1954; Smith, 1960; Patterson, originating on the inner wall and spread- ing to the outer wall. Platelet size is re- Chara sp. A. duced near the origin and along the outer This charophyte(Fig. 3C-G) has a round wall. to slightly oval gyrogonite, poorly devel- oped ridges, five-six spiralsin side view, Ammonia beccarri (Linnaeus, 1758) a pentagonalbasal plate defined by the five spiral cells,multiple pentagonalplates The test of specimens of A. beccarri(Fig' aborally, and a poorly developed neck. 3J-L) is trochospiral, inflated, and has eight Chnrasp. A from MonticelloPoint appears chambers in the outer whorl. The wall to be the same speciesillustrated by For- structure is calcareous and finely perfo- from other Sahara saline lakes (PIaziat, ester (1991,fig. 9.15) from the Pliocene rate. The wall of the Monticello Point 1991), nonmarine saline ponds in Man- Glenns Ferry Formation(3.1 Ma) at Sand specimens is often covered with clay ro- itoba, Canada (Patterson et al., 1990;Pat- Point, Idaho. settes of diagenetic origin (Fig. 3L). terson and McKillop, 1991), wells in Foraminifera are only occasionally re- central Asia (Brodsky, 1928), and a lake ported in nonmarine environments ot in Hawaii (Resig, 7974). Foraminifera, Chara sp. B Pleistocene and Holocene age. Pleisto- including Ammonia beccarri, have also This charophyte (Fig. 3H-I) has an cene occurrences in New Mexico are from asymmetricallyoval gyrogonitewith 9-11 pluvial/playa lakes of the Estancia Ba- [?

New Mexico Geology Atgrst 7994 ,.,::,,.ia,a.{&

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FIGURE 3-Charophytes and foraminiferans from the Monticello Point maar A-8, ktmphrothaniumsp., side view of upper end of worn gyrogonite with P_rominentapical neck (A) and side view of a more-typical elongate, flask-shapedgyrogonite (B). C-D, Charn sp. A, side views of gyrogonite. E-F, Charasp. A, side (E) and basal (F) views of gyrogonite; note pentagonal base plate in F. G, Charasp. A, side view of gyrogonite. H-I, Chara sp B, side views of gyrogonite. l-K, Ammoniabeccarii, basal (f) and side (K; views o] test. L, Ammoniabeuarii, basal view of heavily encrusted test. Barscales:1micron. been reported from several Quaternary al. (1990)thought these foraminiferans that point a supply of foraminiferans and Recentlakes in Australia(Lud- were from marine fish introduced to carried by migrating waterfowl would brook, 1953,1,965;Cann and DeDeckker, nearby Red Bluff Reservoir.This is cer- quickly occupy the newly availableniche. 1981;DeDeckker et aI.,1982). tainly possiblefor the extant population Ammonia beccaniis a valuable paleo- A Recent New Mexico occurrenceof but does not account for the Pliocene salinity indicator, particularly when re- foraminiferans has been noted in the in- and Pleistoceneoccurrences. More likelv, producing populations are present. testinal contents of the Pecospupfish, as outlined by Bachhuberand McCle[in Bradshaw (1957)demonstrated that al- Cyprinodonpecosensis (Echelle and Echelle) (7977),at a critical point the playas and though this speciescan survive in salin- from a saline spring in the lower Pecos springs reached a ities 2%oto 70%o,thev can only salinity at which the of 'l.37oo Valley (Subletteet al., 1990).Sublette et foraminiferansare able to reproduce.At reproduce in the range of to 40%o'.

August 1994 Nan MexicoGeology .- {

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FIGURE 4-Ostracods from the Monticello Point maar. A-B , Ilyocypris bradyi,left side view of carapace (A) and interior view of right valve (B). C- D, Potamocypris unicaudata, side view of left valve (C) and interioiview of ieft valve (D). E-F, Cnndona inopinata, left (E) and riSht (F) side views of adult femaies. G-H, Candona elongalactoides,left side view of adult female (G) and right side view of adult female (H). I-K, N, Cyprideis salebrosa,left side view of adult male (I), left side view of adult female (J), interior view of adult fimale right valve (K) and interior view right male valve (N) t- M, Limnocytherestaplini,left side view adult male (L) and right side view of unusually reticulated adult male (M). Bar scales : 10 microns.

Ilyocypris bradyi Sars, 1890 longer than the posterior; both sulci trend and ventrally (except at the ventra), con- This ostracod (Fig. aA-B) has large valves about 5'posterior of vertical. The valves cave where it is narrow, and moderately that are rounded rectangular in outline are also marked by three pits correspond- wide along the posterior margin. The and punctate. The left valve overlaps the ing to the larger adductor field and two muscle scars are somewhat obscured by right. The dorsal margin is straight, mandibular scars on the valve interior. The diagenetic recrystallization. The adductor rounded at the ends, and has slight in- surface is marked by moderate but even- scar field is nearly circular and is com- dentations at the sulci. The ventral mar- sized punctae, obscured and distorted posed of four elongate scars and a larger, gin is moderately convex near the slightly in the sulci and muscle scar field rounded posterior scar. The other scars midpoint, and the anterior and posterior pits. The posterior marginal surface has are difficult to resolve, although their gen- margins are evenly rounded. The anterior many small spines, and the edge of the eral shapes and positions are marked by margin is slightly larger than the posterior anterior ventral margin also has scattered raised areas corresponding to surface Pits margin, and the greatest height is slightly spines. These spines are probably the seti and sulci. (0.23 of length) posterior of the anterior tubercules of Carbonnel and Ritzkowski This species is large, llke Ilyocypris bi- margin. The valve surface is marked by (1969). The interior has a well-developed plicata (Koch), but it has posterior spines, two prominent sulci, the anterior one inner lamella, which is widest anteriorly

Nm Mexico Geology Augttst 7994 unlike that species.Its lack of lateral and these species in having a more highly This species has been described from posterior tuberclesseparates it from most arched dorsal margin, lower lengthftreight many Pliocene, Pleistocene, and Holo- other membersof the genus. The Mon- ratio, and a much more pointed posterior cene deposits (e.9., Gutentag and Ben- -1.952; ticello Point specimens'areslightly more margin. The Monticello Point specimens son, Benson, L969; Lister, 1975; angular anteriorly than is typical of most do not have the apparently compressed Swain, 1976; Stout, 1981;van den Bold, modern examples,but this may be within anterior seen in some of the specimens 1990).It is often cited as being character- the variation of this species. from the Verde Formation in Arizona istic of brackish(e.g., van den Bold, 1990) Hoff (1942) considered this species (Forester, 1991, frg. 6.5-6). Candonaino- and salineconditions (e.g., Lister, 1975). characteristicof running waters as well as pinatahaspreviously been reported from The nodes sometimesseen on this species temporary waters; he indicated that it tol- the Pliocene Verde Valley and the 111 are absent on the Monticello Point spec- eratessalinities up to 4.5%o.Healso noted Ranch locality, both in Arizona (Forester, imens, and the surface ornamentation that it prefers high-bicarbonatewaters and 1991).Both these localitieshave faunas ranges from strongly reticulated to nearly crawls on the surface. Bronshtein (1988, suggestiveof spring or seepdeposition. smooth. Noding hasbeen observed to vary p. 95) reported that in the former Soviet with differencesin the salinity, with higher- Union this species is "found in various Candona elongalactoiilesDickinson and salinity specimens showing fewer nodes types of waters:seasonal water holes,ox- Swain, 1967 (Vesper, 1975).The total lack of node de- bow lakes,and rivers, . . . [but] undoubt- This speciesof Candona(Fig. 4G-H) has velopment in the Monticello Point speci- edly maybe consideredcrenophilous, since smooth, elongate valves that are subel- mens thus suggestssaline conditions. its favorite habitatis springs." Regarding liptical to slightly reniform in side view. Plioceneoccurrences, Forester (799I, p. The greatest height is slightly anterior of Limnocythere staplini Gutentag and 1.40) reported this speciesfrom the Verde the midpoint. The dorsal margin is evenly, Benson, 1952 Valley,Arizona (4.5-4.0 Ma) and consid- slightly convex to nearly straight, and the This speciesof ostracod(Fig. 4L-M) has eredit to be part "taxa of an assemblageof ventral margin is slightly concave. The small, subquadrate valves with an ob- in fliving] ground-water discharge set- anterior and posterior margins are broadly scure to faintly reticulated surface. It is tings." Forester (L991,, p. 142) also re- and subequally rounded. The left valve is distinctly sexually dimorphic with fe- ported this species from Flatiron Butte, larger than the right and overlaps all mar- males proportionally shorter, more arched Idaho (2.8 Ma), with an assemblageof gins exceptthe dorsal margin. dorsally, and deeper valved, particularly "ordinary taxa Ithat were] eutropic, living This specieshas been reported from a anteriorly, than males. The dorsal margin in shallow, permanent to ephemeral,fresh number of Pliocenelocalities: Hay Ranch is nearly straight in malesand slightly but to slightly saline lakes or ponds domi- Formation, Elko County, Nevadi (Dick- distinctly arched in females. The ventral nated by groundwater discharge." inson and Swain, 196f; GlennsFerry For- margin is sinuate with a concave surface mation, Owyhee County, Idaho (Swain, extending past the duplicature at the valve Potamocypis unicaudata Schafer, 1943 1986a);and the Cache Valley Formation, center. The anterior and posterior mar- This ostracod (Fig. aC-D) has smooth, Franklin County, Idaho (Swiin, 1986b). gins are rounded, the anterior more so rounded triangular valves with a highly than the posterior. The valves have a dis- arched dorsal margin and ventral margin Cypideis salebrosavan den Bold, 1963 tinct sulcus,ending in a subcentralpit over nearly straight to very slightly convex.The The valves of this ostracod (Fig. 4I-K, the muscle scar area, and a small node anterior and posterior margins are N) are medium to large, subovate, and anterior of the sulcus, followed by an- rounded. The anterior is larger, with its have a distinct but not deep sulcus.The other faint sulcus anterior of that. The greatestheight slightly posterior (0.26of left valve overlaps the right, and the dor- surface is marked with faint to obscure length) to the anterior margin and its sal margin is straight to slightly arched at reticulations arranged in a vaguely con- greatest length near the ventral margin. its greatest height, which is slightly an- centric fashion centered on the muscle scar Potamocyprisunicaudata is similar to Po- terior of the adductor muscle scar field. area. tamocyprissmargdina (Vavra) but differs in The ventral margin is slightly convex, and Males of this speciesresemble males of being proportionally higher, especially the the anterior and posterior margins are Limnocythere friabilis Benson and MacDon- right valve, and in having greater dorsal rounded, the anterior slightly more so than ald, but differ in being proportionally and ventral overlap. It differs from mod- the posterior. The posterior margin of deeper valved, less distinctly reticulated, ern representatives of the speciesin mi- males is more pointed than that of fe- and lacking postero-marinal spineson the nor ways: being slightly more pointed males. The valve surface has numerous left valve. In New Mexico, this specieshas posteriorly, being slightly more elongate, rounded pits arranged in a somewhat been reported from Pleistocene pluvial and having greater ventral overlap. concentric fashion centered around the Lake Estancia.Lister (1975)noted that this anterior hinge area and the muscle scar speciesis often associatedwlth Cyprideis Candona inopinata field. The muscle scarshave a set of four salebrosain samples from the Quatemary This ostracod (Fig. aE-F) has moder- adductor scarsarranged in a vertical row of the Salt Lake Basin.This speciesis char- ately large, smooth valves. The left valve and two antennular scars slightly above acteristic of saline environments (De- and anterior of the adductor scars.The lorme, 1969, 1989).Forester (1986)found anterior scar is larger and "u" shaped; a L. staplini particularly characteristicof al- single, elongate mandibular scar is just kaline-depleted saline environments. Lister anterior and ventral of the adductor field (1975) suggested that variations in the and is somewhat "," shaped.Three or four prominence of reticulations in this species dorsal scarsare abovethe adductor field, may be environmentally controlled. and one is anterior near the anterior hinge margin is rounded, the posterior margin area. The hingeline has anterior and pos- Diatoms is p_ointed,and the anterior dorsal margin terior dental areas of the right valve di- We submitted a sampleof the diatomite is flat. In dorsal view, the valves are ln- vided by a bladelike selvagearea that fits from NMMNH locality 27108 to f . Platt flated with their greatest width at about into the tooth socketsand a groove in the Bradbury of the U. S. Geological Survey the same point as greatestheight. left valve. Sexual dimorphism is distinct, for analysis. Dr. Bradbury (etter to Lucas, This speciesclosely resemblesCandona with males larger, more elongate propor- 13 April 1989,with permission) reports: truncataFurtos, Canilornacutula Delorme, tional to height, and with a sharper pos- The MonticelloPoint sample has abun- andC.andonnrawsoniTessler but di_ffersfrom terior angle than females. dantdiatoms, although they are not es-

August 1994 Nao MexicoGeology pecially well preserved-as often ometry of the lake basin. Anadon (L992, terminated lacustrine deposition at Mon- happens in saline, alkaline aquatic en- p. 6) noted that in playa lakes in Spain, ticello Point maar. vironments. The sample is dominated ephemeral lakes lacked "marine-like or- This model of the formation of Monti- by Campylodiscus clypeus and Anomoeneis ganisms" even though they had favorable cello Point maar may have general appli- sphaerophora(type costata). Cyclotella sp. water chemistry. Anadon (7992, p.6) listed cabilitv to manv-Butte or all the maars exposed ct. C. caspia, Denticula elegans, and Am- five interactive factors that determine near Elephant Lake. However, no phora coffaeiformisare rare. There is some of the sedimentary deposits or fine-grained marl in the material. . . .it whether "marine organisms" could suc- studies indicates. . .salinity probably between 3 ceed in a particular saline lake: (1) per- fossils of these maars are available. Until and \Woo, comparatively high pH and ennial waters, (2) chloro-sulphate water such studies take place, the Monticello alkaliniw. and shallow water environ- composition (CVSO4ratios between 3 and Point maar remains the only one of the ments al that site (the diatoms are ben- 26), (3) salinity range (13%o ro 4W^), (4) many maars in this area for which we have thic and require sunlit substrates). possibilities of colonization, and (5) suc- documentation of the stratigraphy and cessful competition against saline-toler- paleontology. Physa sp. ant limnic biota. The Ostracoda of the AcrNowr-ppcMENrs-Paul Knight first Silicified specimens of this gastropod, Monticello Point maar are saline-tolerant brought the paleontological potential of identified for us by R. Smartt, are com- limnic species. These species probably the Monticello Point maar to our atten- mon in the charophyte limestone precluded successful colonization by ma- tion. Bruce Allen and Steve Hayden pro- (NMMNH locality 27704). rine ostracod species. The Foraminifera, vided field assistance. J. Platt Bradbury on the other hand, apparently find in sa- identified and interpreted the diatoms, and Paleoecology line lakes a niche not occupied by com- Richard Smartt identified gastropods. J. Lozinsky Two microfossil assemblagesare found peting limnic thalassicorganisms. Platt Bradbury and Richard version of in the sediments from the Monticello Point carefully reviewed an earlier maar. The samples immediately associ- Evolution of the Monticello Point maar this article. ated with the Chara beds are rich in char- We envision a three-stage evolution of ophyte gyrogonites but have only two the Monticello Pont maar and its associ- species of ostracods, llyocypris bradyi and ated deposits: References Candonaelongalactoides. The sediments are 1. The first stage was explosive for- Anadon, P, 1992, Composition of inland waters with sandy, containing poorly sorted sand mation of the maar basin. Rising magma marine-like fauna and inferences for a Miocene lake in Spain: Palaeogeography, Palaeoclimatology, Pa- grains of worn sedimentary and granitic contacted ground water, producing an ex- laeoecology, v 99., pp. 1-8. rocks mixed with euhedral to slightly plosive ejection of debris, creating the maar Aranda-Gomez, J. J., Luha J. F., and Pier, G.,1'992, rounded basaltic volcanic rocks. This sed- basin. This Surtseyan stage was one in The La Brena-El Jaguey maar complex, Durango, iment is considerably coarser than that which sand wave and surge beds were Mexico: I. Geological evolution: Bulletin of Volca- v. 54, pp.393-404. the nology, found in the clays associated with ov- built up around the maar crater. No Arnal, R. E., L954, Preliminary rePort on the sedi- erlying diatomites. The microfossils in this Strombolian emptions seem to have taken ments and Foraminifera of the Salton Sea, southern sequence suggest a movrng water, pos- place, as no cinder cones or air-fall ash California: Geological Society of America, Bulletin, sibly spring environment. This is indi- beds appear to be associated with the v. 65, pp. 1.227 1.228. Crumpler, L. S., Loeber, K. N., and fronds Aubele, J. C., cated by the oriented charophyte Monticello Point maar. This stage of the Kudo, A. M., 1976, Maare and tuff rings in New found on the limestone surfaces and the development of the Monticello Point maar Mexico: New Mexico Geological Society, Special presence of Ilyocypris bradyi, a species fre- is the "hydromagmatic surge" phase de- Publication 6, pp. 709-71.4. quently found in springs and other lotic scribed in some other maar depositional Bachhuber, F. W, and McClellan, W. A.,7977, Pale- oecology of marine Foraminifera in the pluvial Es- environments. 1979; models (e.g., Wohletz and Sheriden, tancia Valley, central New Mexico: Quaternary The second microfossil assemblage is Aranda-Gomez et al., 1992). Sand wave Research, v. 7, pp. 254)67. found in the basal clays associated with and surge deposits of the Monticello Point Bachman, G. O., and Mehnert, H. H.,7978, New K- the diatomite (NMMNH locality 27108). maar contain fluvial lithic material full of Ar dates and the late Pliocene to Holocene geo- history of the central Rio Grande region, This more morphic assemblage contains a somewhat scoria and volcanic bombs (unit 1 in Fig. New Mexico: Geological Society of America, Bul- diverse ostracod fauna, including several 1). letin, v. 89, pp.283292 saline indicator species (i.e., Cyprideissal- 2. The second stage involved erosion of Benson, R. H., 1969, Ostracodes of the Rita Blanca ebrosa,Limnocythere staplini). The charo- the ejecta and stabilization of the maar lake deposits: Geological Society of America, Mem- oir 113, pp. 107-115. phytes also include Lamprothanium,a stage, the maar surface. After the explosive Bradshaw, J.5.,1957, Laboratory studies on the rate saline-tolerant genus, and the foramini- crater becomes a small sedimentary basin. of growth of the foraminller "Steblusbeccarri (Linne) feran Ammonia beccari. This environment Erosion of the ejecta in and around the var. tepida (Cushman)": Journal of Paleontology, v is interpreted as a saline lake with per- crater tends to produce a generally uP- 31, pp. 7138-1.1!7. Brock, M. A., and Lane, J. A. K , 1983, The aquatic manent water. A very similar association ward-fining sequence of sediments in the macrophyte flora of saline wetlands in western of Ammonia becurii and Cvprideis tlrosa was closed drainage basin of the maar crater. Australia in relation to salinity and permanence; lz reported by Anadon (1992) from a Mio- The maar surface erodes and is stabilized. Hammer, U. T. (ed.), Proceedings of the interna- cene lacustrine sequencein the Ebro Basin Fluvial deposition in the maar basin pro- tional symposium on athalassic (inland) saline lakes, The Hague, pp.53-76. of northeastern Spain. Anadon consid- v. 16: Junk, duces crossbedded sandstones and con- Brodsky, A. A.,1928, Foraninifera (Polythalamia) in ered this fauna particularly characteristic glomerates (units 2 and 4 in Fig. 1). Springs the wells of the Kara-Kum desert: Tashkent Uni- of perennial, saline waters with a salinity develop along the maar walls and provide versity, Central Asiatic State Transactions, v. 8, Zo- range of 1,3%oto 40%aand a CVSO* ratio habitats for charophytes, gastropods, and olog, pp. 1.-1.6. 1988 Freshwater Ostracoda: between Bronshtein, Z. 5., [1947], 3 and 26. a few ostracods (NMMNH locality 27101'). Fauna of the USSR, Crustacea, v. 2, no. 1: A. A. Direct comparison of the fossil assem- 3. Maar lake formation culminates the Balkema [Russian Translation Series 54], Rotter- blages from the Monticello Point maar with second phase. Provided the crater rim is dam, 470 pp. other saline-lake faunas is hampered by not ruptured or otherwise dissected dur- Burne, R. V., Bauld, J., and DeDeckker, P., 1980, Sa- line lake charophytes and their geological signifi- the fact that most previously described ing the first or second stages, a lake forms cance: Journal of Sedimentary Pehology, v. 50, pp. assemblages of this type come from playa in the crater. This lake was a saline, dia- 281.-293. lakes, not maars. Their similarity to the tom-rich waterbody in the Monticello Point Cann, J. H., and DeDeckker, P., 7981, Fossil Quater- Monticello Point assemblages, however, maar. A diverse biota of saline-tolerant nary and living Foraminifera from athalassic (non- saline lakes, southern Australia: of indicates marine) foumal that water chemistry is more im- charophytes, foraminiferans, ostracods, Paleontology, v 55, pp. 660-670. portant to a particular salinelake biota and diatoms lived in this lake until chang- Carbonnel, G., and Ritzkowski, S., 1969, Ostracodes than is the mode of formation and ge- ing paleohydrology filled in or otherwise lacustres de l'oligocene (Melanienton) de la Hes

NewMexico Geology August L994 (Allemagne): Archives Science (Soc. Phys. Hist. Na- Mexico: New Mexico Geological Society, Guide- Schafer, H. W-, 7943, Uber zwei neue deutsche Arten tur Geneva), v.22, pp.55-78. book to 37th Field Conference , pp. 239-247. der Susswasser-Ostracoden: Zoolosisches An- Conrad, C., and Lappartient, J-R., 1,991,,The ap- Lucas, S. G., and Oakes, W., 1986, Pliocene (Blancan) zeiger, v. 143, pp.2-10-2-16. pearance of Cardium fauna and foraminifers in the vertebrates from the Palomas Formation, south- Smith, P 8., 1960, Fossil Foraminifera from the south- great lakes of the early Quaternary period in the central New Mexico: New Mexico Geoloqical So- eastern California deserts: U. S. Geological Suruey, Algerian Central Sahara Desert: Journal of African ciety, Guidebook to 37th Field Conference, pp. 249- Professional Paper 4C0B, pp. 278t79. Earth Sciences, v.12, pp.375-382. 255. Stout, L. N., 1981, An unusual occurrence of the DeDeckker, P, Bauld, J., and Burne, R. V, 1982, Pillie Ludbrook, N. H., 1953, Foraminifera in sub-Recent brackish-water ostracode, Cyprideis salebrov in cen- Lake, Eyre Peninsula, South Aushalia: modern en- sediments at Lake Epe, South Aushalia: Australian tral Missouri: Journal of Paleontology, v. 55, pp. vironment and biota, dolomite sedimentation, and Journal of Science, v. 16, pp. 108-109. 898-900. Holocene history: Transactions of the Royal Socieiy Ludbrook, N. H., 1965, Occurrence of Foraminifera Sublette, J. E., Hatch, M. D., and Sublette, M.,1990, of South Aushalia, v. 105, pp. 769-1,81,. in salt lakes: Geological Suruey of South Australia, The Fishes of New Mexico: University of New Mex- Delorme, L. D.,1.969, Ostracodes as Quaternary pa- Quarterly Geological Notes, v. 74, pp. 6-7. ico Press, Albuquerque, 393 pp. leoecological indicators: Canadian Journal of Eaith Mack, G. H., Salyards,S. L., andJames, W.C.,7993, Swain, F. M., 1976, Paleoecological implications of Sciences,v. 6, pp. l47l-1476. Magnetoshatigraphy of the Plio-Pleistocene Camp Holocene and late Pleistocene Ostracoda, Lake La- Delorme, L. D., 1989, Methods in Quaternary ecology Rice and Palomas Forrnations in the Rio Grande rift honton Basin, Nevada (abs.); in lnternational Sym- no. 7: Freshwater ostracodes: Geoscience Canada, of southern New Mexico: American fournal of Sci- posium on Ecology and Zoogeogtaphy of Recent v. 16, pp. 85-90. ence, v.293, pp.49-77. and Fossil Oshacoda: Austrian Academy of Sci- Dickinson, K. A., and Swain, F. M., 1967, Late Ce- Olliea C. D., 7967, Maars: their characteristics, va- ences, Limnological Institute, Vienna, p. 35. nozoic freshwater Ostracoda and Cladocera from rieties, and definition: Bulletin Volcanologique, v Swain, F. M., 7986a, Late Cenozoic non-marine Os- northeastern Nevada: Journal of Paleontology, v. 31., pp. 45-73. tracoda from southern Idaho: Revista Espanola de 41, pp. 335-350. Patterson, R. T., 1987, Arellaceans and Foraminifera Micropaleontologia, v. 18, pp. 85-114. Forester, R. M., 1985, Determination of dissolved an- from Pleistocene Lake Tocopa, California: Journal Swain, F. M., 1986b, Freshwater Ostracoda from the ion composition of ancient lakes from fossil ostra- of Foraminiferal Research, v.17, pp.333-j43. Cache Valley Formation (Pliocene) of southeastem codes: Geology, v. 14, pp. 796-798. Patterson, R. T., and McKillop, W. B., 1991, Distri- Idaho: Revista Espanola de Micropaleontologia, v. Forester, R. M., 1991, Pliocene climate history of the bution and possible paleoecological significance of 18, pp. 353-385. western United States derived from lacustrine os- Annectina airiosa, a new species of agglutinated For- van den Bold, W 4.,1990, Stratigraphical distribution tracodes: Quaternary Science Reviews, v. 10, pp. aminifera from nonmarine salt oonds in Manitoba: of fresh and brackish water Ostracoda in the late 1.33-1.46. Journal of Pafeontology, v. 65, pp. 33. 37. Neogene of Hispaniola; in Whatley, R., and May- Gutentag, E. D., and Benson, R. H, 1962, Neogene Patterson, R. T., Scott, D. B., and McKillop, W B., bury, C. (eds.), Ostracoda and Global Events: (PliePleistocene) freshwater Ostracoda from the 1990, Recent marsh-type agglutinated Foriminifera Chapman Hill, London, pp.221-229. central High Plains: Kansas Geological Suwey, Bul- from inland salt springs, Manitoba, Canada: NATO Vesper, B., 1975, To the problem of noding on Cypri- letin 157, 60 pp. Advanced Study Institute, Series C, Mathematical deis torosa (Jones, 1850); in Swain, F. M. (ed.), Bi- Hoff, C. C.,1,942, The ostracods of Illinois, their bi- and Physical Science, v. 327, pp.765-781,. ology md palobiology of Oshacoda: Paleontological ology and taxonomy: Illinois Biological Mono- PlaziaL J.-{J., 1991, Paleogeographic significance of Research Institute, Ithaca, New York, pp.205J1,6. graphs, v. 19,196 pp. the Cardium, potamids, and Foraminifera living in Walker, K. F., 1972, Studies on a saline lake ecosystem: Kelly, f. C., 1988, Petrology and perrogenesis of alkali inha-continental salt lakes of North Africa (Sahara Australian ]oumal of Marine and Freshwater Re- basalts and their associated inclusions from Ele- Quaternary, Egypt Present lakes): Journal of Afri- search, v. 24, pp.2l-71. phant Butte area, Sierra County, New Mexico: Un- can Earth Sciences, v. 12, pp.383-389. Warren, R. G., 1978, Characterization of the lower published MS thesis, University of New Mexico, Repenning, C. A. and May, S. R., 1986, New evidence crust-upper mantle of the Engle Basin, Rio Grande Albuquerque, 172 pp. for the age of the lower part of the Palomas For- rift, from a petrochemical and field geologic study Linnaeus, C., 7758, Systema naturae per regna tria mation, Truth or Consequences, New Mexico: New of basalts and their inclusions: Unpublished-Albuquerque, MS nafurae, secundum classes, ordines, genera, spe- Mexico Geological Society, Guidebook to the 37th thesis, University of New Mexico, cies, cum characteribus, differntiis, synonymis, lo- Field Conference, pp. 257-2ffi . 156 pp. cis: G. Engelman, Lipsiae, Edition I0, v.'l',824 pp. Resig, J. M., 1974, Recent Foraminifera from a Ha- Wohletz, K. H., and Sheriden, M. F., 1983, Hydro- Lister, K. H., 1975, Quaternary freshwater Ostracoda waiian lake: ]ournal of Foraminiferal Research, v. volcanic exolosions. II. Evolution of basaltic tuff from the Great Salt Lake Basin, Utah: University of 4, pp.69J6. rings and tuff cones: American Journal of Science, Kansas, Paleontological Contributions Paper 78, 34 Sars, G. O., 1890, Oversegt af Norges crustaceer, med v.283,pp.385-413. tr pp. forelobige Barnaekninger over de nye eller nimdre Lozinsky,R. P.,and Hawley,J. W., 1986,Upper Ce- bekjendte: Arter Forh Selsk. Christian, v. 1, pp. 1- nozoic Palomas Formation of south-central New 80.

August 1994 Nan MexicoGeology