LOMITA, "Series"

MESOZOIC (UPPER TRASSIC AND JURASSIC ?)

State of Mérida, Venezuela

Synonym of LA QUINTA FORMATION

Author of name: P. Christ, 1927.

Original reference: P. Christ, 1927, p. 406.

Original description: ibid.

A series of conglomerates, red sandy shales and red sandstones named after the Quebrada Lomita, in the State of Mérida, is considered by Christ as the youngest formation of the Andean massif, sensu stricto. According to this author (p. 406) the age is considered to be lower Cretaceous, partly probably lower and middle Mesozoic and its base probably Permian. The Lomita series is transgressive on the older formations.

Lomita series is an obsolete name and according to Sutton (1946, p. 1639), they definitely belong to the La Quinta formation which is belived to be Upper Triassic and ? Jurassic in age.

(See also LA QUINTA FORMATION)

LA QUINTA, Formation

UPPER TRIASSIC and JURASSIC

State of Táchira, Venezuela

Author of name: E. Kündig, 1938.

Original reference: E. Kündig, 1938, p. 31, 32.

Original reference: ibid.

The name, La Quinta "series" (in the Spanish edition, "formación") was published by E. Kündig (1938, p. 31, 32) to designate predominantly redcolored non-marine, clastic beds of lower Mesozoic age, extensively distributed in the Venezuelan Andes. While Kündig's name is by no means the first that had been proposed for this formation, his designation of an excellent and accessible type section, and his complete description (including the first report of fossils) have led to the general adoption of his name, in preference to earlier but less well defined ones (Lagunillas conglomerate of Sievers, 1888; Lomita series of P. Christ, 1927; Old Red series of Liddle, 1928, Red formation of Oppenheim, 1937, and others to be mentioned.)

These red clastic sediments had long been observed both in Venezuela and Colombia, but until around 1938 they were not always clearly distinguished from basal Cretaceous sandy beds which generally overlie them, often without apparent unconformity. Thus the "Lagunillas conglomerate" of Sievers (1888, p. 8-16) included basal Cretaceous conglomerates in places (according to Gerth, 1935, p. 221; Sutton, 1946, p. 1637). In addition, the type locality is not considered satisfactory, so the name is not at present in use. It was mentioned by Engleman (1935), Schuchert (1935), Gerth (1935) and Liddle (1928); but since the publication of Kündig's name, the only author who has attempted to revive the name Lagunillas seems to be Rutten (1940, 1942). Even if the name were better defined, any attempt to revive it would be inconvenient on account of the well established use for a Tertiary formation of the Maracaibo basin (see LAGUNILLAS Formation). The term "Lomita series" of P. Christ (1927) is a prior synonym, as modern authors (Sutton, 1946, p. 1639; González de Juana, 1951, p. 196) have recognized, but they have not attempted to substitute it for Kündig's better defined name.

The term "Old Red series" of Liddle (1928, p. 101-104), although in general use in Venezuela between 1928-1938, is entirely undesirable as a nongeographic term; in addition, Liddle (1946, p. 124) admits that it included some older beds. The same objections hold for Oppenheim's (1937) "Red Formation". (See "OLD RED Series" and RED Formation.)

R. Englemann (1935, p. 780-783) gave an interesting discussion of "PermoTrias? Red-beds" in the Andes; he suggested that the beds were equivalent to the "Jiron" (Giron) of Colombia, and also suggested a possible correlation with the Roraima beds of the Gran Sabana. He noted the occurrence of cobbles of Paleozoic limestone in the basal red-beds near Mucuchachí; a possible discordance between the red-beds and Cretaceous sandstones in Río Canaguá (or Libertad); and states that the Red-beds outcrop northwest of Maracaibo, where locally they have been called the "Peñocira" (only published reference to this name). He also reports that the Red-beds had been cored in wells some 20 km. SE of the outcrop in Manantiales, lying normally below the Cretaceous.

H. Gerth (1935, p. 221-223) has section on "terrestrial deposits of probably Triassic age in the northern Cordillera", in which he uses the term "intermediate beds" ("Zwischenschichten") to designate the red-beds, with reference to their position between Paleozoic basement rocks in the Serranías of Mérida and Perijá and the overlying Cretaceous. He recapitulates the work of Sievers, Christ and Liddle, stressing Sievers's (1888) description of the red-beds on the Colombian side of the Perijá range, which brought out that these rocks overlie tuffs, breccias and flows of quartz-porphyry and melaphyre, and have similar volcanics intercalated in them. On account of the similarity to beds referred in Argentina to the Triassic (Paganzo series), Gerth believes the red-beds to be Triassic. - The "Jiron beds" of Colombia, however refers tu the Cretaceous (p. 352).

The name Girón (often spelled Jirón), first applied by Hettner (1892) to beds near the town of that name in Colombia, Department of Santander, is the only term that has offered serious competition to the name La Quinta. Schuchert (1935, p. 670), in connection with the Girón group of Colombia, states that it is represented in Venezuela by "the Lagunillas conglomerate of Sievers, the Palmarito and Lomita of Christ, and the Old Red series of Liddle". On p. 689, he quotes Stappenbeck (1927) (a publication we have not seen) as considering the Girón to be represented by the Lagunillas conglomerate. Schuchert reflects accurately the contemporary uncertainty on the age and correlation of the Colombian Girón, noting that some geologists correlate it with the Villeta group (Cretaceous), others believe it older Mesozoic or possibly even Paleozoic. This uncertainty is also reflected by Schuchert's mention (1935, p. 689) of the Lagunillas conglomerate under his discussion of the Lower Cretaceous in Venezuela.

L. Kehrer (1937, fig. 1) used the term Girón, and gives reasons for preferring the name to Lagunillas or Old Red (p. 55). Although in his 1938 paper he uses the designation "La Quinta (Girón)" throughout, in the discussions of the papers presented at the 1938 Venezuelan Geologic Congress, he states that he would prefer to retain Girón rather than introduce a new name (p. 240).

It is fortunate for Venezuelan geologists that the name La Quinta has replaced Girón, since the latter has had a long and tangled history in literature. (See for instance Oppenheim, 1940). Although various authors have separated Cretaceous beds from the Girón, apparently it is still not very well defined, as brought out by the recent discovery of Carboniferous and Permian fossils in part of the Girón by Brückner (1954).

A few others synonyms of the La Quinta formation should be mentioned: The Río Masparro formation of Mackenzie (1937, p. 276) (see article). Hedberg and Sass (1937, p. 75) proposed the name Macoita formation for red beds "well exposed in the Macoita River" and which had been referred to the "Old Red series"; however, Liddle (1946, p. 118) states that within the section mentioned by these authors, there are no beds which had been referred to the "Old Red", but only shales and sandstones of the Devonian Campo Chico formation (See article MACOITA Formation). The Seco conglomerate of Sutton (1946, p. 1639) is also a synonym of the La Quinta formation (see article).

The term "Formación La Quinta" (in the English edition, La Quinta series) was given by Kündig in allusion to the small town of La Quinta, about 3.5 kilometers west of La Grita in Táchira. The type section is exposed along a road which, leaving the Trans-Andean Highway near La Quinta (elevation 1,130 m.), leads to the town of Seburuco, 7 km. distant. Following this road downstream along the La Grita river, a section of the La Quinta formation, some 2,300 meters thick in total, is exposed, the beds resting with strong angular unconformity on phyllites and "epi-schists" referred to the Mucuchachí formation. The Mucuchachí beds dip 30-50° SE, while the La Quinta dips 60-70° WNW. The La Quinta section can be divided here into a lower conglomeratic portion (400 m), a middle predominantly shaly portion, (500 m.) and an upper sandy portion (1,300 m.) The beds are overlain by white sandstones of the "Tomón" (Cretaceous) with apparent conformity. Kündig's detailed description of the three divisions (which are not suggested to be formal members) is as follows:

Lower division: Conglomerates, dark (greenish) red, hard, poorly sorted, with pebbles up to fist-size, well rounded and strongly cemented. Some finer-grained beds "contain tuffaceous material and especially much biotite". The conglomerates are interstratified with brick-red, soft, heavy bedded clayey sandstones. Total, 400 m.

Middle division (exposed near the bridge of La Grita), begins with the following detailed section:

a) 5 m. dark red and greenish shales.

b) 2 m. conglomeratic sandstones, cross bedded, white, redstained, has pebbles of quartz only.

c) 10 m., like (a), on top of red sandy shales.

d) 1 meter bed, like (b).

e) 4 meters red shales, which contain in the upper part fish scales and bones, and greenish-white coprolites.

f) 1 meter bed like (b), but red in color.

g) 5 m. micaceous sandy shales with scattered fish-remains.

h) 2 m., like (b).

A repetition of similar beds (except that the white conglomeratic beds disappear) occurs for 150 meters or more; Kündig estimates the total thickness as 500 meters. A talus zone marks an interval, then there follows the upper division, of well-stratified, soft red cross-bedded sandstones, interbedded (in a narrow zone) with a hard white coarse quartz sandstone. This upper sandy division is said to be 1,300 meters thick.

The fish remains found in horizons (e) and (g) were studied by A. Smith Woodward, who determined them as consisting of plates, premaxillas, teeth, palatal bones and scales "of a genus of fish indistinguishable from the genus Lepidotus". (For the systematic classification of this fish, see Romer, 1945, p. 97, 580). Romer gives the geologic range of Lepidotus as Upper Triassic to Lower Cretaceous, perhaps even Upper Cretaceous in Europe. Woodward believed the remains to indicate a rather primitive form of the genus which would suggest an age of Upper Triassic or Lower Jurassic.

From Romer's discussion (1945, p. 537) it would appear that Lepidotus was a marine denizen (although he notes that little is known of fresh-water fish of the lower Mesozoic). However, Dr. Royo y Gómez informs us that the genus has also been found in brackish and fresh-water sediments. It was suggested in Kündig's paper that the coprolites associated with the fish remains were formed by sharks. There is thus a suggestion of a marine environments for the fish-bearing beds, but the evidence is by no means conclusive. Kündig did not discuss the problem. One might speculate on the possibility of a marginal marine incursion from a sea normally far to the west; such an incursion, perhaps, as suggested by the marine fossiliferous horizon in the predominantly red Payand‚ formation of Colombia (see Trumpy, 1943). On this supposition, Kehrer's report (1938) of an unidentified ammonite and a Halobia ? from supposed "Mucuchachí" beds, which as Sutton (1946, p. 1638) suggested, might really be La Quinta, could fit into the picture.

A different, non-marine, environment is indicated by the fossils cited by Sutton (1946, p. 1638), found in black shales in the La Quinta formation in the state of Mérida. These fossils were found by Olsson and Dallmus, along the trail from Potosí to Canaguá near the Hacienda Montaña, at a locality called Celensio. Olsson identified the fossils as fresh-water ostracods, and abundant specimens of the conchostracan phyllopod Estheria. (In the recent text of Moore, Lalicker and Fischer, the name of this genus is changed to Cyzicus). This genus is fairly common as a fossil in fresh and brackishwater sediments from the Devonian onward, but Olsson considered the Celensio specimens to be most similar to species found in Upper Triassic formations of India, Argentina and Colombia.

The La Quinta formation has an extensive but somewhat irregular distribution in the Venezuelan Andes, and has been recognized in limited areas, on the east flank of the Sierra de Perijá. In the Andes, it occurs on the southwest flank, towards the Táchira depression, and in southeast Mérida; but it appears to be missing over the central, highest part of the Cordillera, as pointed out by González de Juana (1951, p. 196) and Bucher (1952, p. 15). The latter notes that two lines on the map, one from Ciudad Bolivia to Mérida, the other from Barinas to Valera, delimit a belt at right angles to the present Andean axis, where La Quinta sediments are missing. These authors believe, therefore, that this belt represents an old Paleozoic uplift and that the continental sediments of the La Quinta were accumulated principally on the flanks of this uplift. With reference to this apparent absence of La Quinta in the Andean knot, however, it may be mentioned that according to Sievers, 1888 (as quoted by Engleman, 1935, p. 783) almost all the crest of the Sierra Culata or Sierra del Norte near Mérida, is made up of "red-beds". Engleman did not visit this region, but states that "his experience with Sievers's judgement in other parts of the mountains" inclines him to believe that this might be so. The undersigned does not know whether sufficiently detailed studies have been since made in this region, to disprove Sievers' findings.

Northeast of this belt, the La Quinta sediments again appear on the flanks of the Andes. Bucher's map shows an irregularly V-shaped belt which appears to follow the general line of the Mucuchachí outcrops near Ciudad Trujillo. On the opposite or southern flank the beds are brought to the surface in anticlines in western Portuguesa and Barinas (see Bucher's map, south center of quadrangle D: 9-10°).

Liddle (1946, p. 141) states that "the most northeasterly outcrop of definitely known La Quinta series is in the southwestern part of the State of Lara" and that "it is possible that partly metamorphosed shales and slates around Quibor in the south-central part of the State of Lara were derived from sediments of La Quinta series rather than from the Barranquín formation." No La Quinta is shown in Lara on Bucher's map, however.

The possibility that La Quinta sediments might exist or have existed far to the north of the present outcrops, however, is suggested by the presence of red-beds in a well (Manuel N° 1) in the represent La Quinta. (S. E. Aguerrevere, 1938, p. 250). Hedberg (1942, p. 201) has also suggested the possible equivalence of the Hato Viejo-Carrizal formations of the subsurface in Guárico-Anzoátegui. The thickness of the La Quinta formation in the Andes is said to be extremely variable, with the figure of 3,600 meters reported by Kündig for the section in El Zumbador, as a probable maximum. It should be noted that in some places (e.g. near Trujillo, as reported by Schaub, 1944) the base of the La Quinta is a conglomerate formed by pebbles of the Palmarito formation.

In the Sierra de Perijá, the La Quinta is considered to be represented by the "Seco conglomerate" (Sutton, 1946, p. 1639), found in the quebrada Aponcito Seco, NW of Machiques, where it is some 670 meters thick. (See SECO Conglomerate). Similar conglomerates are reported towards the south in the Macoíta river, where La Quinta beds are said to overlie the upper Devonian (?) Macoíta formation, with unconformity that is not readily apparent (see MACOITA Formation). Towards the north, however, the La Quinta seems to disappear; at least, Liddle did not recognize it in the Río Cachirí section (Liddle, 1943, 1946). González de Juana (1951, p. 196) reports that it outcrops northwest of Maracaibo, in the Manantiales ridge (this is shown in Bucher's map.) The same author believes that red beds occurring on Toas island, referred by Sutton (1946) to the "Palmarito", are more probably La Quinta.

Hedberg (1942, p. 197-200), in an interesting discussion of the La Quinta-Girdn beds of Colombia and Venezuela, notes that the contact between these and overlying basal beds of the Cretaceous frequently appears to be transitional, but that in some cases there is visible unconformity; he believes that this indicates weak orogenic movements that followed the deposition of the La Quinta beds and preceded the Cretaceous transgression. Bucher (1952, p. 16) agrees with this interpretation. Hedberg believed that this orogenesis occureed in late Jurassic time, but Bucher does not commit himself to a definite date.

Kündig (1938) reported that basic igneous intrusions, in the form of small lenses and sills up to 80 meters thick, are locally developed in the La Quinta formation (e.g., west of Mérida in the Carvajal valley and north of Lagunillas in the valley of Aguadura). Petrographic types represented are porphyritic diabases, porphyritic quartz-diorites and vitriophyric diabases. The rocks are believed to be in part superficial flows, in part intrusions. There is no indication of metamorphism, and the intrusions (at least in the region of Mérida) do not affect younger rocks.

Frances de Rivero