Back-reef Environments Research Articles

Foraminiferal Biofacies on a North Coast Fringing Reef (1-75 m), Discovery Bay, Jamaica

Recent foraminifera inhabiting Jamaican north coast fringing reefs exhibit variation in distribution patterns that are related to bathymetry and reef morphology. Parallel traverses were run from the back reef (depth 1-4 m) across the reef crest, fore-reef terrace (5-14 m), escarpment (24 m), slope (30-55 m), and upper (75 m) deep fore-reef zones at Discovery Bay, Jamaica. Approximately 150 species belonging to 80 genera were identified. Diversity indices (S, H', J') are lowest on the fore-reef terrace, increase toward the back-reef andfore-reef escarpment and slope, and tend to be highest on the mid-lower slope and deep fore reef. Major operational taxonomic groups of foraminifera (suborders Textulariina, Miliolina, benthic and planktonic Rotaliina) exhibit distinct bathymetric trends, with the Miliolina occurring most abundantly in the back reef, and Textulariina and planktonic Rotaliina being most abundant below 30 m. Benthic rotaliines are prominent across the entire reef environment and may compose >60% of foraminiferal sediment assemblages. Among the largest and most common species, Amphistegina gibbosa (benthic Rotaliina) dominates fore-reef assemblages, whereas Archaias angulatus (Miliolina) is most abundant in back-reef environments. Individual fore-reef zones are poorly delineated in Q-mode cluster analysis of foraminiferal species abundances (2 5% of foraminiferal assemblages at any site) based on standard counting procedures (300 foraminifera from all size-fractions >0.125 mm). Reef zones are, however, clearly defined when the standard countingprocedures are applied to individual size-fractions (1-2, 0.5-1.0, 0.25-0.5, and 0.125-0.25 mm) and species abundances determined from total counts of all four size-fractions combined ('sieve method). Based on the sieve method, Q-mode cluster analysis of common (3% of foraminiferal assemblages at any site) species delineates back reef, fore-reef terrace, and fore-reef slope and upper (75 m) deep fore-reef zones. The alternative counting procedure appears to compensate for operator bias in specimen counts introduced by large and unusually abundant species (e.g., Amphistegina gibbosa) and by small but colorfulforms (e.g., Discorbis rosea), which appear to mask the zonation when using standard counting procedures.

Information loss in the transition from life to death assemblages of foraminifera in back reef environments, Key Largo, Florida

Despite numerous distributional studies of foraminifera in modern shallow-water carbonate environments, information loss and taphonomic bias in the transition from life to death assemblages of foraminifera in these environments have not previously been examined in detail. Surface sediment and vegetation samples were collected along six nearshore traverses and one traverse across the back reef lagoon off Key Largo, Florida. Living foraminifera are found in abundance on algae and the marine angiosperm,Thalassia testudinum, while foraminifera in sediment assemblages are represented primarily by empty tests. Q-mode cluster analysis of living assemblages onThalassiadelineates inshore (depth 0.4–2.7 m) and offshore (3.0–9.0 m) back reef biofacies. Calcareous imperforate (suborder Miliolina) species thrive in quiet waters of the inshore biofacies, in which biotic interactions appear to be the prime factor in determining small-scale species distributions of living foraminifera. Fragile species are most susceptible to test destruction, and, therefore, sediment assemblages are dominated by more robust forms (e.g.,Archaias angulatus, Valvulina oviedoiana, thick-walled species ofQuinqueloculina).Water turbulence primarily determines species composition of living populations of the offshore biofacies. These assemblages are dominated by the calcareous perforate (suborder Rotaliina) speciesPlanorbulina acervalisandRosalina bahamaensis. These species resist transport by encrustingThalassiablades and having a test which fits flush with grass blades, respectively. However, sediment assemblages of the offshore biofacies are also dominated by typical inshore, robust species (Archaias angulatus, thick-walled miliolids). Thus, inshore and offshore biofacies are not readily differentiated by Q-mode cluster analysis of sediment assemblages. Robust species are wide ranging and often abundant in sediment because of differential preservation and time-averaging of sediment assemblages. The resultant taphonomic bias may interfere with paleoecologic interpretations concerning intensity of water energy and distance from shore.

Information loss in the transition from life to death assemblages of foraminifera in back reef environments, Key Largo, Florida

Despite numerous distributional studies of foraminifera in modern shallow-water carbonate environments, information loss and taphonomic bias in the transition from life to death assemblages of foraminifera in these environments have not previously been examined in detail. Surface sediment and vegetation samples were collected along six nearshore traverses and one traverse across the back reef lagoon off Key Largo, Florida. Living foraminifera are found in abundance on algae and the marine angiosperm, Thalassia testudinum, while foraminifera in sediment assemblages are represented primarily by empty tests. Q-mode cluster analysis of living assemblages on Thalassia delineates inshore (depth 0.4–2.7 m) and offshore (3.0–9.0 m) back reef biofacies. Calcareous imperforate (suborder Miliolina) species thrive in quiet waters of the inshore biofacies, in which biotic interactions appear to be the prime factor in determining small-scale species distributions of living foraminifera. Fragile species are most susceptible to test destruction, and, therefore, sediment assemblages are dominated by more robust forms (e.g., Archaias angulatus, Valvulina oviedoiana, thick-walled species of Quinqueloculina).Water turbulence primarily determines species composition of living populations of the offshore biofacies. These assemblages are dominated by the calcareous perforate (suborder Rotaliina) species Planorbulina acervalis and Rosalina bahamaensis. These species resist transport by encrusting Thalassia blades and having a test which fits flush with grass blades, respectively. However, sediment assemblages of the offshore biofacies are also dominated by typical inshore, robust species (Archaias angulatus, thick-walled miliolids). Thus, inshore and offshore biofacies are not readily differentiated by Q-mode cluster analysis of sediment assemblages. Robust species are wide ranging and often abundant in sediment because of differential preservation and time-averaging of sediment assemblages. The resultant taphonomic bias may interfere with paleoecologic interpretations concerning intensity of water energy and distance from shore.

Effects of the Caribbean threespot damselfish, Stegastes Planifrons (Cuvier), on algal lawn composition

Algal lawn communities within territories of herbivorous threespot damselfish, Stegastes planifrons (Cuvier) were studied in a shallow back-reef environment at La Parguera, Puerto Rico. Caging exclusion experiments, monitoring of non-manipulated lawns and gut content analyses were used to determine the effect of S. planifrons on algal species composition of the lawn. An average of 40 algal species per sampling period were found in naturally occuring lawns, with a total of 53 species being recorded throughout the course of study. Examination of algal species found in damselfish guts and comparison with natural lawns indicate that damselfish feed primarily on their algal lawns and graze the algae present in proportion to abundance. Caged algal lawns showed significant decline in algal species number and abundance over time. Non-selective feeding by Stegastes planifrons within their territorial lawns appears to result in an “intermediate disturbance” which maintains a greater algal species richness than is found in their absence.

Lower Devonian Carbonate Facies and Platform Margin Development, East-Central Alaska and Yukon Territory: ABSTRACT

Pragian to Emsian (mid-late Early Devonian) sedimentation on the southwestern portion of the Yukon stable block, east-central Alaska and Yukon Territory, is represented by a package of intergradational carbonate facies, each characteristic of its relative position on or off the carbonate platform and the platform's stage of development. End_Page 658------------------------------ In Pragian time, crinoid thickets were extensive across the platform. By Emsian time, an east-west-trending rugosan coral-stromatoporoid reef complex, cored by Renalcis-bound mudstone, had developed along the platform margin. This reef complex was composed of large colonial corals, often capped by stromatoporoids, with framework cavities filled with skeletal wackestone to rudstone matrix. A pelletal and intraclastic wackestone to packstone facies was deposited in the slightly protected back-reef environment to the north. Concurrently, sediments and blocks were shed from the fore reef southward into the foreslope environment dominated by a Thamnopora-crinoid floatstone to rudstone facies. Slope failures produced bioclastic debris flow and turbidite sedimentation of shelf-carbonate detr tus into the coeval shale of the adjacent basin situated to the south and west. Pelagic sedimentation of clay-size carbonate material also deposited thin, dark, lime mudstone beds within this basin. Toward the end of Emsian time, a rapid marine transgression inundated the shallow shelf area, and deeper water open marine carbonate sedimentation occurred, represented by a tentaculitid-rich whole-fossil bioclastic wackestone to mudstone facies. As the waters continued to deepen, basinal siliceous oozes and clays were deposited over the entire region through the Middle Devonian. End_of_Article - Last_Page 659------------

Sedimentology of the middle Eocene Minia and Samalut Formations, West Beni Mazar, Western Desert, Egypt

The petrography of the middle Eocene Minia and Samalut Formations is discussed. The formations are subdivided into lithofacies denoting lateral as well as vertical facies changes. An environmental interpretation for these two formations is proposed. The lower portion of the Minia Formation was deposited in a shoal environment whilst the upper portion was deposited in a back reef environment. The Samalut Formation can be differentiated into the following subenvironments from south to north: shelf edge, shelf break mounds and fore slope talus.

Stratigraphy, Petrography, and Paleoenvironmental Interpretation of Mississippian-Pennsylvanian Amsden Formation South of La Barge Guard Station, Salt River Range, Western Wyoming: ABSTRACT

The Amsden Formation, named by N. H. Darton in 1904 during mapping of the Bighorn Mountains, Wyoming, consists of red shales, limestones, sandstones, and cherty beds. The Amsden was later subdivided into four members (in ascending order): the Darwin Sandstone (E. Blackwelder, 1918), the Horseshoe Shale (W. W. Mallory, 1967), the Moffat Trail Limestone (W. J. Sando and others, 1975), and the Ranchester Limestone (W. W. Mallory, 1967). All members crop out in the study area. The Darwin Sandstone Member is up to 88.4 m (290 ft) thick, disconformably overlies the Mississippian Mission Canyon Limestone, and is conformably overlain by the Horseshoe Shale Member. It is a quartzarenite with minor amounts of feldspar interpreted as being deposited in a nearshore or beach environment. The Horseshoe Shale Member is 25.9 m (85 ft) thick and conformably overlies the Darwin Member. The Horseshoe Shale Member contains fine-grained terrigenous sediment interpreted to have accumulated in a lagoon or back-reef environment. The lower part is a white to red siltstone with localized areas of pisolitic hematite; the upper part is organic-rich black shale containing palynomorphs. The Moffat Trail Limestone Member is 29.0 m (95 ft) thick and conformably overlies the Horseshoe Shale Member. The Moffat Trail consists of biomicrites, pelmicrites, and silty micrites. It is interpreted to represent open-marine, low-energy carbonate-shelf deposition. The Ranchester Limestone Member is 9.4 m (31 ft) thick and conformably overlies the Moffat Trail Member. The Ranchester contains silty dolomite, carbonate, and red siltstone, representing the maximum transgression of the Pennsylvanian sea. The Pennsylvanian Wells Formation conformably overlies the Ranchester Member. End_of_Article - Last_Page 932------------

Extensive Coniatolite-Pelagosite Diagenetic Sedimentation in Marine Limestones, Tansill Formation (Permian), New Mexico: ABSTRACT

Pelagosites (calcareous crust formed in splash zone) and coniatolites (supratidal tufa) composed of inorganic precipitates of aragonite and some high-Mg calcite have been described from Holocene deposits along the western Persian Gulf and elsewhere. Such diagenetic deposits are believed to be restricted to intertidal and supratidal environments, and are only rarely encountered in ancient carbonate rocks. Laminated encrustations, coated grains, and pseudostromatolites of presumed former aragonite mineralogy, all associated to some extent with encrusting marine fossils, are the dominant if not exclusive components of shallow-marine limestones in the Tansill Formation (back-reef facies of the Capitan) in New Mexico. These deposits occur in shallow back-reef environments of possible hypersaline character. In landward directions, they are replaced by peritidal dolomites. The vertical and lateral occurrence of particular coniatolite-pelagosite structures is related to the hydraulics of the depositional environment in a manner somewhat similar to that which controls algal laminite and stromatolite distributions in modern and ancient deposits. Internally, the laminae of crystalline calcite in these deposits are interlayered with the alga Archaeolithoporella and encrusted by Tubiphytes. Petrographically, this crystalline calcite consists of square-tipped crystal ghosts and divergent fan-druses in neomorphic sparry mosaics identical to altered aragonites described from other ancient carbonates. These deposits are similar to the coniatolites and pelagosites described from the Holocene, but represent the first reported occurrence of extensive diagenetic sedimentation of this type in ancient shallow-marine carbonate rocks. End_of_Article - Last_Page 602------------

An Analysis of Competitive Interactions in a Patch Back‐Reef Environment

Manipulative field experiments were used to test for the existence of competitive interactions between three abundant herbivore species in a shallow back—reef zone. Densities of the territorial threespot damselfish, Eupomacentrus planifrons, and two sea urchins, Diadema antillarum and Echinometra viridis, were altered through addition and removal experiments conducted within patches of staghorn coral, Acropora cervicornis. Removals of each urchin species resulted in population increases of the other urchin. Additions of each urchin species tended to inhibit increases of the other species. Removals of damselfish resulted in increases of the other species. Removals of damselfish resulted in increases in Diadema density within 24 h, while Echinometra density increased during the 3rd d following the perturbation. Dry biomass of algae on ceramic tiles in the lower strata of damselfish removal patches was reduced by 62% as compared with algal biomass in these strata in the presence of damselfish. Wire mesh cages were utilized over a 2—mo period to test the effect of predation on competition at the herbivore level. No significant alteration of species numbers was observed in the absence of predation. Therefore, predation did not appear to affect significantly the distributions and abundances of the adult members of the community. Low predation levels on adults within this system do not appear to alter the competitive interactions between these herbivores. Interference competition by the threespot damselfish appears to mediate competition between the two echinoids, allowing coexistence of all species. The presence of damselfish may reduce destructive echinoid grazing pressure on the coral substrate.

PHYSICAL PROCESSES AND SEDIMENT FLUX THROUGH REEF-LAGOON SYSTEMS

Studies of physical processes in reef-lagoon systems continue to emphasize the importance of waves and wave-induced currents at the reef crest as agents of sediment transport to backreef environments. These across-the-reef currents are also largely responsible for driving backreef lagoon circulation. Rapid energy transformations associated with the process of wave breaking at the reef crest are responsible for strong reef-normal surge currents. Estimates of energy loss, as determined by wave height changes caused by wave breaking, can be as high as 70-80%' for discontinuous reefs and >90% for continuous examples. The amount of energy loss is related to depth of water over the reef crest, a function of reef topography and tidal regime. Low-tide conditions promote the greatest incident wave modification and attenuation as a result of increased breaking-wave intensity. Under trade-wind conditions found in the Caribbean, surge currents of 50-80 cm/sec for durations of 2-6 sec are common in a low to moderate wave-energy setting (4-6 sec input waves, 40- 50 cm average heights). Sediments through the sand sizes up to pebbles are easily transported lagoonward by these periodic bursts of energy. Flow in shallow backreef lagoons (generally

Interference behavior and ecology of threespot damselfish (Eupomacentrus planifrons).

Interference behavior by threespot damselfish directed at the sea urchins, Diadema antillarum and Echinometra viridis, differed in levels of aggression and discrimination. Higher aggression towards and recognition of Diadema by threespots was correlated with the distribution of Diadema along edges of coral patches. Lower aggression levels combined with lower recognition levels of Echinometra were correlated with a distribution of Echinometra closer to damselfish algal lawns. Differences in behavior of the urchins stimulated differing levels of aggression by the damselfish directly affecting the distribution of the urchins in the back-reef environment.

Stratigraphy and depositionalenvironments of the lower cretaceous in the Karst region of the outer Dinarides (yugoslavia)

A detailed study of four geological columns and numerous data obtained from other localities in the Karst region of the Dinarides has been used as the base for a discussion of the stratigraphic range of determined taxa, revealing considerable differences from earlier listings. Of the stratigraphic subdivisions the biostratigraphic one seems preferable. An uniformity of biostratigraphic subdivision for the narrower Mediterranean region is proposed. A lithofacial analysis has determined that the sedimentation of the inner part of the carbonate bank (platform) occurred through alternating supratidal, intertidal, subtidal, lagoon and back-reef environments.

Geology of the Fletcher Mine, Viburnum Trend, Southeast Missouri

Fletcher mine is situated on a buried Precambrian ridge that stood as a topographic high during Upper Cambrian Bonneterre deposition. After deposition of the Lamotte Sandstone that surrounds and pinches out against the ridge, algal reefs grew and formed a barrier to open marine shelf deposition. This created offshore, reef, and back reef environments. Clastic carbonates of the Bonneterre Formation were then deposited over the area and became the host for base metal mineralization.Sulfide mineralization, principally galena, sphalerite, and chalcopyrite, follows a pronounced north-south trend within the Fletcher area. The ore zone reaches its widest distribution around the Precambrian ridge that protrudes into the Bonneterre. Ore distribution is facies related, and local emplacement is influenced by porosity, fracturing, brecciation, and the shape of the buried Precambrian high. Most of the mining to date occurs in the middle of the upper clastic grainstone unit. Where the Sullivan Siltstone is brecciated, mineralization extends into the overlying mudstones and grainstones and intothe Davis Formation. Two north-south, narrow, linear breccia trends extend the full length of the mine and contain good sulfide mineralization.The mineralization occurs mainly as open-space and fracture fillings, with minor replacement of dolomite. Dissolution of galena is common and is associated with ore zones that show second-stage enrichment.

Ökologie und systematische stellung der foraminiferen im gebankten dachsteinkalk (obertrias) des nördlichen toten gebirges (oberösterreich)

Statistical analysis reveals the strong facies dependence of foraminifera of the backreef environment in the Upper Triassic sedimentary limestones. Six facies are distinguished on the basis of counted allochems: 1.(1) Oolite facies. Ooids indicate strong water turbulence and normal marine salinity. Vagile foraminifera with great adherence dominate (Tetrataxis, Duostomina, etc.). Glomospirella indicate the allochthonous position of ooids.2.(2) Oolitic facies. Ooids have been transported and redeposited. The heterogeneous composition of foraminifera reflects the close association with the oolite, grapestone and pellet-mud facies.3.(3) Grapestone facies. Subtidal algal mats and strong water turbulence caused the formation of grapestones. The sligjtly raised salinity affords optimum conditions for vagile miliolids (Miliolipora, Quinqueloculina).4.(4) Calcareous algal-foraminiferal-detritus facies. Undamaged Dasycladaceae indicate low turbulence. Salinity may have reached higher levels in which highly variable involutinids with big shells were developed. Their association with calcareous algae corresponds to that of Recent larger foraminifera.5.(5) Pellet-mud facies. Pellets and micritic matrix indicate the least water movement and high salinity. Strongly adapted foraminifera, such as Trochammina, Agathammina, Palaeospiroplectammina and Frondicularia, predominate.6.(6) Mud facies. The absence of pellets, because of their destruction, confirms stronger water currents than in the pellet—mud facies; salinity reaches high levels. Foraminifera with thin shells (Involutina, Nodosaria) preferred this environment.

Subtidal Algal Stromatolites from the Florida Backreef Environment

ABSTRACT Blue-green algae form potential stromatolite structures in the Holocene subtidal Florida Backreef environment. The stromatolite structures are domal and circular to elliptical in plan view. The stromatolites occur randomly scattered among Thalassia sp. grass flats in about 3 m of water. The stromatolite structures are similar to many found in the Geologic record. Growth forms of the blue-green algae stromatolites (Schizothrix?) and their environmental occurrence are important when interpreting ancient depositional environments in terms of the water depth and relative position to the shoreline.

Oil Occurrence and Lower Cretaceous Carbonate-Evaporite Cyclothems in South Florida: GEOLOGICAL NOTES

Most of the Lower Cretaceous of south Florida was deposited in carbonate-evaporite cyclothems typical of a backreef environment. Lithologic constituents of these cyclothems include cap, reservoir, and source rock necessary for oil accumulation. Reservoir calcarenite is formed in the middle of the cylothem. The nature of horizontal and vertical changes in facies suggests that fluctuating sea level was the cause of cyclic deposition. A cyclothem should be 125 ft (40 m) thick to provide sufficient source rock for a commercial accumulation.

EXPLORATION OF THE SOUTHWEST FLANK OF THE PAPUAN SASIN

Since 1965, Tenneco Australia and Signal Pacific have been exploring three tenements totalling 30,082 square miles off the eastern coast of the Cape York Peninsula Queensland. The area is relatively unexplored but the recent drilling of the Anchor Cay well, along with seismic mapping, provides a vital link between the Papuan Basin and the Laura and other basins of the Queensland coast.The primary objective of the exploration venture was initially and remains, the Mesozoic age sandstones believed to exist in a near shore environment in the subject area. Carboniferous pyroclastics and Permian granites form the positive Cape York-Oriomo Platform. Mid-Mesozoic age sediments, are found east of this ridge, becoming thicker and more basinal regionally eastward. Tension faulting along the southwest flank of the basin has created several closed structures. Tertiary sediments are primarily carbonates and exist in a shelf, reef, forereef arrangement with petroliferous pinnacle reefs being located on bathymetrically favored structures.Seismic mapping directed at the northern portion of the tenements located several structures worthy of testing. The one with the maximum sedimentary column, the Anchor Cay structure, was chosen for a stratigraphic test and drilled in early 1969. No severe drilling problems were found at shallow depths but below 10,700 feet sloughing of cobbles into the borehole became a problem. The well was abandoned at 11,888 feet, still in sediments, where continued drilling became impracticable. The lithology encountered in this stratigraphic test was similar to that anticipated. A reef core of Pliocene rock was penetrated. Miocene rocks in a near back reef environment, and a thin Eocene carbonate section were penetrated. At approximately 7,000 feet an unconformity separated the Tertiary carbonates from the Mesozoic elastics. Immediately beneath the unconformity were reservoir quality sandstones of lower Cretaceous age. Volcanic and/or intrusive exotics became increasingly common in the Jurassic.Based on the facies encountered in the Anchor Cay stratigraphic test, it seems apparent that the most favored fairway for sandstone reservoir development is to the west where seismic shooting has indicated several structures. The initial basic concepts regarding this exploration venture are still valid and much more effort is required before a thorough evaluation can be made.

Reef Petrography in the Beaverhill Lake Formation, Upper Devonian, Swan Hills Area, Alberta, Canada

ABSTRACT Statistical measurements of organic and inorganic parameters in thin sections reveal that the Swan Hills Member of the Beaverhill Lake Formation in the Shell Swan Hills 10-17 well is made up by the rhythmical alternation of eight carbonate microfacies. These rock-types are closely related and interpreted as a continuous sequence representing fore-reef, reef and back-reef conditions. The fore-reef environment shows dark-colored calcarenites whereas the reef itself consists of dark-colored bio-constructed limestones made up by cabbage-type stromatoporoids followed in shallower water by branching colonies of Amphipora. With these two organically constructed deposits are associated several types of biocalcarenites. The back-reef environment is represented by light-colored calciluti es containing scattered colonies of Amphipora and of mat-type stromatoporoids. The vertical superposition of these microfacies displays seven rhythms of sedimentation during which an Amphipora-stromatoporoid reef community was established over a carbonate platform, developed and eventually disappeared. The rhythms seem to correspond to tectonically controlled phases of depth decrease.

Ecology of Recent Foraminifera in Northern Florida Keys

Foraminifera live in the following environments in the Florida Keys area: Florida Bay, water 0-10 feet deep; the back-reef, water mostly 15-30 feet deep but ranging from 0 to 40 feet deep; the reef, locally awash at low tide but extending seaward to a depth of about 60 feet; and the fore-reef, water deeper than 60 feet. The boundaries between the back-reef and the reef and between the reef and the fore-reef environments are transitional. The Florida Bay environment is characterized by great variations in the abundance of the Miliolidae, Peneroplidae, Nonionidae, and Rotaliidae, and by the absence of the Amphisteginidae, Textulariidae, Lagenidae, and Buliminidae. Variations in the Florida Bay fauna suggest sorting. The Amphisteginidae and Buliminidae represent families present in the back-reef environment which are not found in Florida Bay. The Peneroplidae and Amphisteginidae are most abundant and the Nonionidae are least abundant on the outer reef patches. The fore-reef environment is characterized by the appearance of the Cassidulinidae and the rise of the Anomalinidae to a position of minor abundance. Angulogerina, Bulimina, Uvigerina, and Reusella do not occur at depths much shallower than 150 feet. These environments may be recognized and differentiated by noting the relative abundance of individuals belonging to the various families without regard to the species or genera involved.

Nummoloculina in Lower Cretaceous of Texas and Louisiana

Several occurrences of the miliolid Nummoloculina in the Lower Cretaceous of Texas (lower Glen Rose through upper Devils River limestones) and one occurrence in the Lower Cretaceous of northern Louisiana (lower Glen Rose limestone) are reported for the first time. The geologic range of Nummoloculina as ascertained by the writers is Lower Cretaceous to Recent. Nummoloculina limestones in Texas are here reported from the upper Devils River limestone (Georgetown limestone equivalent) in Val Verde County and the Edwards limestone in La Salle and Maverick counties. Nummoloculina occurring in the Devils River limestone in Val Verde County is figured and discussed. Nummoloculina from the El Abra miliolid member of the El Abra formation of northern Mexico (Lower Albian through Lower Cenomanian) is figured for comparison. The uppermost Devils River limestone and the upper El Abra miliolid member are compared, but no correlation is implied. Following Norton's zonation of foraminifers, miliolid limestone environments would correspond most closely with his Zone A where the water is 0-5 fathoms deep and the temperature is 21°-32°C. Miliolids occurring in abundance are facies foraminifers characteristic of back-reef and inter-reef environments; therefore, they are useful in paleoecology. Although miliolid limestones in Texas vary in age within, but are restricted to the Lower Cretaceous (Sligo through upper Devils River limestones), they may be of local or regional value in the differentiation of large stratigraphic units within the Sligo through upper Devils River limestones. Miliolid limestones are used successfully in parts of southwest and central Texas to mark the faunal top of the Edwards limestone. However, in the Devils River area, or in any other area where reefs were formed in Washita as well as Fredericksburg limestones, such differentiation based on miliolids is unsatisfactory.