Northwestern Cuba Research Articles

A diversity baseline of benthic macrofauna along the northwestern slope of Cuba (Gulf of Mexico)

The Gulf of Mexico (GoM) is a unique ecosystem due to its physical characteristics, being influenced by the Mississippi River in the north and the Loop Current from the south, resulting in a gradient of organic to carbonate sediment composition from north to south. The continental slope of the northern and southwestern portions of the GoM are generally well studied; however, less is known about the southeastern GoM along the slope of Cuba. To fill this knowledge gap, sediment cores were collected in 2017 at nine stations (974–1580 m depth) to determine abiotic controls on the deep-sea benthic macrofauna community. Oceanographic data indicated a stratified water column typical of an oligotrophic ocean and no evidence of hypoxia. Sediment texture and composition indicated a west-east gradient likely determined by downslope transport of terrigenous material in the eastern part with a high proportion of carbonate in the west. Heavy metals (Cu, Hg, Pb, and Zn) at concentrations known to cause adverse benthic effects were present in the east near the city of Havana, with the macrofauna community showing characteristics indicative of environmental stress. Overall, this region supported a diverse community of macrofauna families of low abundance, typically only 1–2 animals, and high variability among replicates within stations. Rarefaction curves revealed higher biodiversity per number of individuals in the samples from Cuba compared to those from the nGoM at similar depths, though more samples would be needed to better reveal the true diversity. The major factors influencing macrofauna communities in the continental slope off northwestern Cuba are most likely the lack of organic-rich sediment and low sediment deposition rates, both of which can be attributed to the strong currents and lack of major terrigenous input, along with the regular natural disturbances which prevents domination.

Setting an Environmental Baseline for the Deep-Sea Slope Offshore Northwestern Cuba (Southeastern Gulf of Mexico) Using Sediments and Nematode Diversity

Deep-sea offshore northwestern Cuba is the less studied zone of the Gulf of Mexico (GoM). Our study aimed to set an environmental baseline and investigate a potential west-east gradient of sediment properties and nematode diversity along the northwestern Cuba. Sediments were collected by multicorer at nine sites in the insular slope between 974 and 1682 m depth. Sediment texture and composition showed a west-east gradient caused likely by narrowing of shelf width and increasing of downslope transport of terrigenous material. We found clear signatures of heavy metal pollution likely derived from Havana City but also from open-sky mining (Castellanos mining complex) and port dredging operations (Mariel). Nematode assemblages were dominated by the deep-sea genera: Acantholaimus, Metadasynemella, Desmodorella, Cervonema, Daptonema, Halalaimus, and Pselionema. α-diversity was about 20–50 genera and γ-diversity of about 100 genera. The β-diversity was substantial likely because small-scale patchiness of resources and heavy metals stress that increased assemblage variability. Individual weight decreased with depth indicating food-supply limitation in the deep sea; also, heavy metals were negatively correlated with weight suggesting deleterious effects on the growing. Our findings indicate that heavy metal pollution has reached deep-sea sediments and corroborate the long-range effects of anthropogenic activities on deep sea. Taxonomic diversity and biological traits (life strategy and trophic composition) constituted a powerful bioindicator of benthic health and benchmark for future potential disturbances in the region. Northwestern Cuba slope is still an understudied portion of the GoM and more research is needed to fully understand its biodiversity and biogeochemical patterns.

New fossil Cetaceans from the Middle Miocene of Cuba

Remains of cetaceans, particularly odontocetes, are scarce in the Cuban fossil record. Here we describe the second odontocete (toothed whale) record from the Neogene of Cuba and extends the temporal distribution of this group in the Insular Caribbean into the Middle Miocene. This account is based on two isolated teeth found in limestones of the Güines Formation that crop out in a quarry near the town of Guanábana, Matanzas City, northwestern Cuba. The specimens are referred to the superfamily Physeteroidea incertae sedis. These findings, along with other fossils recovered from other Early and Middle Miocene localities in the region support the hypothesis of a complex, diverse marine vertebrate fauna on the formerly called “Habana-Matanzas channel” and circum-Cuban waters during the Neogene.

Mollusk death assemblages from the deep slope off northwestern Cuba (Gulf of Mexico)

We evaluated the mollusk death assemblages along seven sites in a deepsea expedition off northwestern (NW) Cuba. We aimed to (1) provide the first baseline of mollusk diversity in sediments of the NW region, and (2) test if there were west-east gradients of α- and β-diversities. We found 141 species in sediments: 68 deepsea benthic, 43 shelf benthic, and 30 pelagic species. The richness of pelagic species was similar along the NW region indicating significant settlement of pteropod shells to the seabed. The occurrence of shelf species in the deepsea suggested a downslope transport of shells enhanced by the slope steepness and dredging in two ports. β-diversity of deepsea benthic mollusks showed a high turnover at local scales explained by habitat heterogeneity. β-diversity of pelagic species was extremely low suggesting that the planktonic assemblage was evenly distributed. In contrast, high β-diversity of shelf benthic species occurred likely due to downslope transportation of materials. Deepsea gastropods were mostly detritivores, while bivalves were mostly suspension feeders. These dominant biological traits indicated oligotrophic conditions in sediments likely coupled with an intense hydrodynamic regime in the deepsea. The NW Cuban region seems to be a hotspot for mollusk diversity because of the discovery in a single expedition of seven new species, 12 new records, and 36% endemism relative to the entire Gulf of Mexico. Our findings revealed a complex and diverse mix of deep/pelagic/shelf species but did not indicate a west-east gradient in the mollusk assemblage structure.

Seasonal Abundance and Size Structure of Sharks Taken in the Pelagic Longline Fishery off Northwestern Cuba

AbstractThe Straits of Florida comprise an important migratory route for apex predators moving among the Gulf of Mexico, Atlantic Ocean, and Caribbean Sea. Off Cuba’s northwestern coast, various gear types are used by Cuban fishers, including small‐scale pelagic longlines. We report here the results of a 2011–2019 monitoring program for the longline fleet based in Cojímar, Cuba. This fleet comprises 134 small vessels targeting mostly swordfish (family Xiphiidae), billfishes (family Istiophoridae), tunas (family Scombridae), and sharks (class Chondrichthyes) within 20 km of Cuba’s coast. Most operations are nocturnal with 11–12‐h sets comprising an average of 56 hooks on 6,643 m of mainline. Five orders, eight families, and 18 species of sharks were documented in this fishery. Two carcharhinids (Silky Shark Carcharhinus falciformis and Oceanic Whitetip Shark C. longimanus) and two lamnids (Longfin Mako Isurus paucus and Shortfin Mako I. oxyrinchus) were the most abundant shark species caught, with shark CPUE averaging 1.98 sharks/trip (SD = 0.938). Catch abundance showed seasonal differences, with Silky Sharks and Longfin Makos more common in winter and Oceanic Whitetip Sharks more common in summer and autumn. Bimodal size structure in some species suggests multiple life stages utilizing the area, while the predominance of young sharks in species including the Oceanic Whitetip Shark suggests the importance of the area as juvenile habitat, possibly as a pupping and/or nursery ground. This characterization of the Cuban longline fishery is an important step forward for Cuba’s National Plan of Action for Sharks and demonstrates the potential impacts that small‐scale fisheries can have on vulnerable sharks.

The Role of Mesoscale Dynamics over Northwestern Cuba in the Loop Current Evolution in 2010, during the Deepwater Horizon Incident

The Loop Current (LC) system controls the connectivity between the northern Gulf of Mexico (GoM) region and the Straits of Florida. The evolution of the LC and the shedding sequence of the LC anticyclonic ring (Eddy Franklin) were crucial for the fate of the hydrocarbons released during the Deepwater Horizon (DwH) oil spill in 2010. In a previous study, we identified LC-related anticyclonic eddies in the southern GoM, named “Cuba anticyclones” (“CubANs”). Here, we investigate the relation between these eddies and LC evolution in 2010, focusing on the DwH period. We use high-resolution model results in tandem with observational data to describe the connection between the LC system evolution within the GoM (LC extensions, Eddy Franklin and LC Frontal Eddies—LCFEs) and the mesoscale dynamics within the Straits of Florida where CubANs propagate. Five periods of CubAN eddy activity were identified during the oil spill period, featuring different formation processes under a combination of local and regional conditions. Most of these cases are related to the retracted LC phases, when the major LC anticyclone (Eddy Franklin in 2010) is detached from the main body and CubAN eddy activity is most likely. However, two cases of CubAN eddy presence during elongated LC were detected, which led to the attenuation of the eastward flows of warm waters through the Straits (Florida Current; outflow), allowing the stronger supply of Caribbean waters through the Yucatan Channel into the Gulf (inflow), which contributed to short-term LC northward extensions. Oceanographic (LCFEs) and meteorological (wind-induced upwelling) conditions contributed to the release of CubANs from the main LC body, which, in tandem with other processes, contributed to the LC evolution during the DwH oil spill incident.

Macrophytobenthos biomass in the Northwestern Cuban shelf, almost 50 years ago

Abstract This study presents for the first time a comprehensive review of the macrophytobenthos on the Northwestern Cuban shelf using data collected almost 50 years ago, and can be considered as a baseline for present and future studies. During 1972−1973 the total estimated fresh biomass was 1.88 million tons (686 tons km−2). Compared with seagrasses, seaweeds were 1.40 times more frequent but had a total biomass 2.86 times smaller. Frequency wise, 90 % of all seaweeds were Chlorophyta, while Phaeophyta, and Rhodophyta were 5 % each. Six Bryopsidales genera (Avrainvillea, Caulerpa, Halimeda, Penicillus, Rhipocephalus, and Udotea) comprised 73 % of 16 Chlorophyta species collected, and 80 % of their total fresh biomass. Turtle grass (Thalassia testudinum) leaves fresh weight was 96 % of all seagrasses biomass, and 71 % of the total macrophytobenthos biomass. The combined biomass of five Halimeda species and that of turtle grass leaves were 88 % of the total regional macrophytobenthos fresh biomass. Species presence was greatest on sand substrate, and least on reef rubble, with a total biomass greater at 1 m depth on organic mud mixed with sand. Of all species, only Halimeda spp. showed seasonal changes in biomass. The total biomass of macrophytobenthos was higher in the western larger and deeper Gulf of Guanahacabibes than in the eastern smaller and shallower Buenavista cays to La Mulata Port section of the shelf. The total macrophytobenthos biomass and that of some species showed significant correlations with depth. The eight most frequent macrophytes in the Northwestern Cuba shelf had similar Caribbean presence.

DNA barcoding of fish eggs collected off northwestern Cuba and across the Florida Straits demonstrates egg transport by mesoscale eddies

AbstractIdentifying spawning sites for broadcast spawning fish species is a key element of delineating critical habitat for managing and regulating marine fisheries. Genetic barcoding has enabled accurate taxonomic identification of individual fish eggs, overcoming limitations of morphological classification techniques. In this study, planktonic fish eggs were collected at 23 stations along the northwestern coast of Cuba and across the Florida Straits to United States waters. A total of 564 fish eggs were successfully identified to 89 taxa within 30 families, with the majority of taxa resolved to species. We provide new spawning information for Luvarus imperialis (Louvar), Bothus lunatus (Plate Fish), Eumegistus illustris (Brilliant Pomfret), and many economically important species. Data from most sites supported previously established patterns of eggs from neritic fish species being found on continental shelves and oceanic species spawning over deeper waters. However, some sites deviated from this pattern, with eggs from reef‐associated fish species detected in the deep waters of the Florida Straits and pelagic species detected in the shallow, continental shelf waters off the coast of northwestern Cuba. Further investigation using satellite imagery revealed the presence of a mesoscale cyclonic eddy that likely entrained neritic fish eggs and transported them into the Florida Straits. The technique of combining DNA‐based fish egg identification with remotely‐sensed hydrodynamics provides an important new tool for assessing the interplay of regional oceanography with fish spawning strategies.

Connectivity and larval dispersal pathways of Panulirus argus in the Gulf of Mexico: A numerical study

The connectivity among subpopulations of Panulirus argus in the Gulf of Mexico is evaluated using a particle-tracking model coupled to a realistic hydrodynamic simulation generated with the Hybrid Coordinate Ocean Model. In 12 potential subpopulations of the Gulf of Mexico, virtual larvae were released daily from March 21 to June 18, 2006–2010. Virtual propagules were tracked for a maximum of 198 days and programmed to undergo vertical migrations and to eventually “die” according to an exponential decay function. The subpopulations that were the most inter-connected and had the highest values of self-settlement were those from the Bay of Campeche (Campeche, Southern Veracruz, Central Veracruz, and Northern Veracruz). This pattern can be explained by the recirculation resulting from the semi-permanent cyclonic gyre in the Bay of Campeche and the back and forth behaviour of the shelf currents at Veracruz. Self-settlement was low at Quintana Roo, Southern Florida, and Northwestern Cuba, because the Loop Current quickly transported the larvae away from those areas. Southern Florida received a considerable number of settlers coming from almost all other subpopulations mainly by means of the Loop Current. Larvae from Yucatan may be transported to subpopulations in the Bay of Campeche by means of both westward Loop Current Eddies and the westward inner-shelf current in the Campeche Bank. The continental shelf of the Bay of Campeche, particularly the islands and cays in the western edge of the Campeche Bank, emerged as both important settlement areas and larval dispersal pathways. A program for the protection of the species in these areas may help increase the population size of P. argus in the Gulf of Mexico, potentially favouring local fisheries.

Nuevos registros de distribución de Gambusia rhizophorae (Teleostei: Poeciliidae) en el archipiélago cubano

El complejo de especies Gambusia punctata está representado en Cuba por dos especies: G. punctata Poey, 1854, endémica de Cuba y G. rhizophorae Rivas, 1969, la que ha sido reportada en los cayos de Florida, en el sur Estados Unidos, y la costa norte del occidente de Cuba. En el presente trabajo se reportan nuevos sitios de distribución de G. rhizophorae a lo largo del archipiélago cubano, tanto en la costa norte como en la costa sur. Se dan a conocer, además, los valores de salinidad de los cuerpos de agua donde habita la especie.

Rivulus berovidesi, a new killifish species (Teleostei: Rivulidae) from western Cuba.

Rivulus berovidesi, a new killifish species, is described from a small stream in Sierra de Cajalbana, northwestern Cuba. It is readily distinguished from Rivulus cylindraceus Poey by the combination of an exclusive color pattern and meristic characters such as a d-type frontal scalation pattern (versus e-type pattern in Rivulus cylindraceus). The current diagnosis of Rivulus berovidesi based on chromatic, morphological and meristic characters is consistent with a recent molecular analysis of this genus in Cuba.

230Th/U-dating of a late Holocene low uranium speleothem from Cuba

We present 22 U-series ages for a stalagmite from north-western Cuba based on multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionisation mass spectrometry (TIMS). Our results reveal that the stalagmite continuously grew within the last ~1400a. Low uranium content of the sample and thus, extremely low 230Th concentrations limit the precision and accuracy of 230Th/U-dating by TIMS. Samples measured by MC-ICPMS show a high variability of 232Th content along the growth axis with some sections significantly affected by initial 230Th from a detrital phase. An a-priori bulk earth ratio for (238U/232Th) cannot be used to accurately account for this initial 230Th. Using an age model based on the 230Th/U ages determined on samples with low or negligible 232Th concentration, we find that the (238U/232Th) activity ratio of the detrital phase is an order of magnitude larger than the bulk earth value, indicating the importance of an accurately determined correction factor.

Late Holocene Fauna from a Cave Deposit in Western Cuba: post-Columbian occurrence of the Vampire BatDesmodus rotundus(Phyllostomidae: Desmodontinae)

Abstract. Here I report a fossil microvertebrate fauna from a late Holocene cave deposit in northwestern Cuba. This study provides new chronological data for the understanding of the post-Pleistocene survival of some of Cuba's rarest extinct bats, and a post-Columbian record of Desmodus rotundus. Remains were excavated from a superficial, mound-like deposit with no dicernible stratigraphy. The bones of 13 bat species, one owl, one rail, a small colubrid snake, one frog, a nesophontid shrew, a rat, a mouse, and two capromyid rodents were extracted from the assemblage. The chiropterans were the most abundant and included the extinct taxa Desmodus rotundus and Artibeus anthonyi, the rare Lasiurus insularis,and the endangered Natalus primus. The mixed assemblage originated from accumulated owl pellets and carcasses of roosting bats. Three Artibeus jamaicensis scapulae from the same level and bone coloration as the Desmodus material yielded a modern radiocarbon content indicative of post-thermonuclear testing ...

Caribbean Lower Tithonian ammonites from central-east Mexico

Imlay's ammonite species Paradontoceras butti and Paradontoceras antilleanum are first reported from central-east Mexico under precise stratigraphic control. Mexican and Cuban ammonites referred to these species have been studied and proved to have been gathered from a relatively limited area within the southern paleomargin of the north American Plate, which embraces eastern Mexico and north-western Cuba. The palaeontological examination, the multivariate analysis conducted on Mexican and Cuban data, the precise biostratigraphic and biogeographic control support the reinterpretation of Imlay's species P. antilleanum and P. butti. The latter has been designated the single, valid nominal species-level taxon which comprises the two species proposed by Imlay. The new genus Housaites has been created since the taxon Butticeras Houša is not available for taxonomic nomenclature. Housaites butti (Imlay) is upper Lower Tithonian (Semiforme/Verruciferum Zone of the Tethyan standard) in Mexico. The stratigraphic range in Cuba is not conclusively known.

Late Jurassic continental flood basalt doleritic dykes in northwestern Cuba: remnants of the Gulf of Mexico opening

Abstract Accreted terranes, comprising a wide variety of Late Jurassic and Early Cretaceous igneous and sedimentary rocks are an important feature of Cuban geology. Their characterization is helpful for understanding Caribbean paleo-geography. The Guaniguanico terrane (western Cuba) is formed by upper Jurassic platform sediments intruded by microgranular dolerite dykes. The geochemical characteristics of the dolerite whole rock samples and their minerals (augitic clinopyroxene, labradorite and andesine) are consistent with a tholeiitic affinity. Major and trace element concentrations as well as Nd, Sr and Pb isotopes show that these rocks also have a continental affinity. Sample chemistry indicates that these lavas are similar to a low Ti-P2O5 (LTi) variety of continental flood basalts (CFB) similar to the dolerites of Ferrar (Tasmania). They derived from mixing of a lithospheric mantle source and an asthenopheric component similar to E-MORB with minor markers of crustal contamination and sediment assimilation. However, the small quantity of Cuban magmatic rocks, similarly to Tasmania, Antarctica and Siberia differs from other volumetrically important CFB occurrences such as Parana and Deccan. These dolerites are dated as 165-150 Ma and were emplaced during the separation of the Yucatan block from South America. They could in fact be part of the Yucatan-South America margin through which the intrusive system was emplaced and which was later accreted to the Cretaceous arc of central Cuba and to the Palaeogene arc of eastern Cuba. These samples could therefore reflect the pre-rift stage between North and South America and the opening of the gulf of Mexico.

Spatial Variation in Stable Isotopes (δ13C and δ15N) in Marine Fish along the Coast of Havana City: Evidence of Human Impacts from Harbor and River Waters

Abstract We examined the hypothesis that nutrients from land sources are enhancing the food supply for fish in coastal reefs of northwestern Cuba. Spatial variation in stable isotope ratios (δ13C and δ15N) was investigated at two sites heavily impacted by mixed pollution sources in Havana City, Cuba, and two reference sites. Significant differences in isotope signatures were found among sites for territorial species, e.g., δ15N was consistently enriched at impacted sites. The most plausible explanation is enriched nitrogen and carbon sources in the food web derived from organic pollution of the coastal zone by human wastewaters. This supports earlier findings that fish were larger in the vicinity of the harbor because of nutrient additions due to sewage that can increase ecosystem productivity and enhance growth of fish. It is also evidence of the direct land-to-water linkage in coastal zone food webs and illustrates how additional nutrients may affect marine food web functions.

Lateral lithological and compositional variations of the Cretaceous/Tertiary deep-sea tsunami deposits in northwestern Cuba

Lateral lithological, compositional, and grain size variations in the Peñalver Formation in northwestern Cuba, which is a Cretaceous/Tertiary (K/T) boundary deposit accumulated on the northwestern slope of the extinct Cretaceous Cuban arc and distributed over an area of 150 km, are examined in order to investigate the influence of a tsunami on the deep-sea bed. The lower part of the Peñalver Formation is composed of calcirudite containing grains derived from a shallow platform. It is considered to have been deposited by debris flows from the shallow carbonate platform triggered by the impact of the seismic wave. The upper part of the formation is composed of calcarenite to calcilutite hemipelagic to pelagic sediments. This has a distinctly different source to the lower part and is considered as having been formed under the influence of tsunami waves, judging from its regional homogeneity and the presence of serpentine lithic grains that were probably transported from central to eastern Cuba by a westward flowing water mass. An erosional surface between the two parts, together with sedimentary structures in the upper part indicative of current influence is more common with decreasing presumed depositional depth, which can be interpreted as stronger tsunami effect at the shallower depths. In addition, compositional and grain size oscillations that repeated >6 to 10 times are observed in the upper part, which may reflect repeated lateral injection of the sediments eroded from the shelf to the upper slope of the depositional basin by backwash of successive tsunami waves into the dense sediment suspended cloud that was formed by the first tsunami.

Tramas tróficas de peces de arrecifes en la región noroccidental de Cuba. I. Contenido estomacal

Trophic webs of reef fishes in northwestern Cuba. I. Stomach contents. Studies on the reef fishes of Cuba are not rare, but most have two basic limitations: small sample sizes and exclusion of small species. Our study sampled more species and larger samples in the sublitoral region of Havana city (23 degrees 7.587' N, 82 degrees 25.793' W), 2-18 m deep. We collected fish weekly from October 2004 through February 2006 with traps and harpoon. Overfishing has modified the fish communities. We used the relative importance index to describe the diets of carnivore and omnivore species, and a modification of the relative abundance method for the herbivores and sponge-eating species. The main food items are benthonic crustaceans (crabs, shrimp, copepods) and bony fish (mainly demersal species). Most species are eurifagous and thus, less affected by anthropic disturbance than specialist feeders.

Origin of the Peñalver Formation in northwestern Cuba and its relation to K/T boundary impact event

Abstract The uppermost Maastrichtian Penalver Formation and its equivalents in northwestern Cuba are characterized by thick, normal-graded calcarenite with distinct basal conglomerate, and have been suspected as deposits related to the Cretaceous–Tertiary boundary (K/T) impact. However, its depositional mechanism is not well understood and clear evidence for its association with the impact has never been presented. In this study, detailed field survey and petrographic observations were carried out on the Penalver Formation in order to clarify its sedimentary processes and to test its relation to the K/T impact. The Penalver Formation at the type locality near Havana is approximately 180 m thick and is subdivided into the Basal, Lower, Middle, Upper and Uppermost Members based on its lithology. The Basal Member consists of massive, poorly sorted, calcirudite with grain-supported fabric, which contains abundant macrofossils of shallow-marine origin and occasional large intraclasts of the underlying strata, suggesting that it was formed by a grain flow from a carbonate platform on the Cretaceous Cuban Arc. The Lower to Uppermost Members consist of massive calcarenite and calcilutite that show upward fining. Composition of the calcarenite is distinctly different from that of the Basal Member. The homogeneous appearance, coarse-tail normal grading, abundant water escape structures, and abundant reworked fossils in these members are consistent with those of the Mediterranean “homogenite”, a deep sea tsunami-induced deposit that was formed by settling from a high density suspension. Repetition of thin conglomerate beds in the Lower Member that contain well-sorted, well-rounded mud clasts and shallow marine fossils is considered to reflect intermittent lateral flow possibly induced by a series of tsunami waves during an early stage of settling of grains from a high density suspension. Altered vesicular glass of probable impact origin and shocked quartz are discovered in the Basal and the Lower to Upper Members, respectively. Together with the biostratigraphically constrained age of the Penalver Formation, this evidence suggests that the Penalver Formation has a genetic relation to the K/T impact. Distribution of altered vesicular glass and shocked quartz grains can explain the sequence of the initial grain flow and the following tsunami waves.

Mineralogical and chemical variations, Castellanos shale-hosted Zn-Pb-Ba deposit, northwestern Cuba

The shale-hosted Castellanos sedimentary exhalative Zn-Pb-Ba deposit of Jurassic age in northwestern Cuba consists of pyrite, sphalerite, and galena in a hydrothermal quartz-carbonate-barite matrix with very little clastic or shale matrix. The northeastern end of the Zn-Pb-Ba lens overlies a transgressive Cu stringer zone which is interpreted as the vent or feeder channel for the exhalative mineralization. Abundance patterns in the sulfide assemblage define layering within the deposit. In the southwestern part of the deposit sphalerite and galena increase and pyrite decreases stratigraphically upward within individual layers. To the northeast, near the vent, sphalerite and galena decrease upward, parallel to pyrite. In the area of the vent the basal carbonate is exclusively dolomite; however, calcite abundance increases rapidly upward. Remote from the vent, dolomite is the dominant carbonate from the base to the top of the deposit. Carbonate and barite are the main gangue minerals near the discharge site; quartz is the major gangue mineral in the southwestern section. These and other variations result from differences in a Ca (super 2+) , f OH2 , temperature, and Sigma S relative to sulfide-forming cations, especially Fe (super 2+) , at the discharge site and in the depositional basin some distance from the vent.