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C. K. Paull W. Ussler III T. Lorenson W. Winters J. Dougherty 《Geo-Marine Letters》2005,25(5):273-280
Gas hydrates are common within near-seafloor sediments immediately surrounding fluid and gas venting sites on the continental
slope of the northern Gulf of Mexico. However, the distribution of gas hydrates within sediments away from the vents is poorly
documented, yet critical for gas hydrate assessments. Porewater chloride and sulfate concentrations, hydrocarbon gas compositions,
and geothermal gradients obtained during a porewater geochemical survey of the northern Gulf of Mexico suggest that the lack
of bottom simulating reflectors in gas-rich areas of the gulf may be the consequence of elevated porewater salinity, geothermal
gradients, and microbial gas compositions in sediments away from fault conduits. 相似文献
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This paper focuses on the analyses of the clastic sedimentary infill of the Coastal Plain of Eastern Mexico, which initiated synchronously with the Laramide orogeny in the vicinity of the Golden Lane. Results of these analyses are used as boundary conditions for calibrating/interpreting seismic profiles across more distal depocenters in the offshore of the Gulf of Mexico, from the sea shore and continental slope in the west to the abyssal plain in the east. The objective of the study is to better predict the reservoir distribution in the Deep offshore Basin of the Gulf of Mexico (DBGM), in order to explore for petroleum. 相似文献
5.
Consideration of the oasis analogy for chemosynthetic communities at Gulf of Mexico hydrocarbon vents 总被引：4，自引：0，他引：4
Robert S. Carney 《Geo-Marine Letters》1994,14(2-3):149-159
The analogy between desert oasis and deep-sea chemosynthetic community arose from the biomass contrast between vents and the relatively depauperate background benthic fauna. Fully developed, the analogy helps pose questions about interactions with the background fauna with respect to resources, colonization, and persistence. The chemosynthetic sites of the Gulf of Mexico provide an opportunity to consider possible interactions between vent and nonvent fauna over a 3000-m depth range. It is postulated that deep chemosynthetic communities require the operation of geochemical transporting and concentrating processes to overcome low levels of in situ methane and sulfide production. Clathrate reservoirs may serve these functions. A few chemosynthetic species at the Gulf of Mexico upper slope sites are related to shallow-water sulfide species, but it can be speculated that the dominant chemosynthetic fauna may have originated in a wide spread deep sulfide biome of the Cretaceous. Generic endemism of consumers is low in Gulf of Mexico sites, suggesting a high level of colonization from the surrounding benthos. Chemosynthetic communities may avoid excessive colonization by predators in spite of the apparent food limitation of the surrounding benthos due to toxicity or an evolutionary mechanism selecting against specialized predators. The abundance of large predators is related to the composition of the surrounding benthos and is high at the Gulf of Mexico upper slope sites. Exclusion of chemosyntheic communities from shallower depths may be due to excessive predation by generalists. 相似文献
6.
Magnesian calcites are the most abundant authigenic minerals associated with hydrocarbon vents at 25 sites, in water depths ranging from 100 to 600 m in the Green Canyon area and about 2200 m in the Alaminos Canyon area on the Continental Slope of the northern Gulf of Mexico. The most frequently encountered magnesian calcites have 10–15 mol% MgCO3 and the apparent structural disorder revealed by XRD peak widths increases with Mg substitution. There are no systematic variations in Mg content with respect to water depth or geographic location. The calcite saturation state of the precipitating fluid is primarily determined by the nature of the fluids escaping from the vents, not the ambient seawater. 相似文献
7.
Lesley D. Nixon Barbara J. Bascle David A. Marin 《Marine Georesources & Geotechnology》2013,31(2-3):211-212
The Offshore Atlas Project (OAP) grouped 4,325 Miocene and older and 5,622 Pliocene and Pleistocene productive sands in the Gulf of Mexico into 91 chronostratigraphic hydrocarbon plays to aid the oil and gas industry with regional hydrocarbon exploration and field development. OAP has produced a two-volume atlas series entitled Atlas of Northern Gulf of Mexico Gas and Oil Reservoirs. Volume 1 comprises Miocene and older reservoirs, while volume 2 comprises Pliocene and Pleistocene reservoirs. Chronozones (Reed et al., 1987) were used to define geologic ages in the Gulf of Mexico. A chronozone is a time-stratigraphic unit defined by a particular benthic foraminifera biostratigraphic zone. The 26 chronozones identified by Reed et al. (1987) were further grouped into 14 Cenozoic and 2 Mesozoic chronozones for OAP. A composite type log (CTL), which shows the chronostratigraphic relationship of all productive sands in a field, was constructed for each of the 876 proved federal fields in the Gulf of Mexico. Depositional facies (retrogradational, aggradational, progradational, and submarine fan)were next identified on each CTL. The four facies were identified primarily according to characteristic SP-curve shapes, paleoecozones, and sand content. The chronozones and depositional facies identified on each CTL were then correlated among fields across the Gulf of Mexico. All productive sands correlated to the same chronozone and depositional facies were then identified as a unique play. Both federal and state fields in the Gulf of Mexico contain original proved reserves (sum of cumulative production and remaining proved reserves) estimated at 12.481 Bbbl of oil and condensate and 156.466 Tcf of gas (40.322 Bboe [sum of liquids and energy equivalent gas]). Of this, 9.943 Bbbl of oil and condensate and 122.263 Tcf of gas (31.698 Bboe) have been produced. Miocene plays contain the most total original proved reserves with 41.9 %, followed by Pleistocene plays (36.2 %), Pliocene plays (18.6 %), Mesozoic plays (2.9 %), and Oligocene plays (0.4 %). Miocene plays have produced the largest amount of total hydrocarbons, as well, at 43.5 % followed by Pleistocene plays (36.5 %), Pliocene plays (19.1 %), Oligocene plays (0.5 %), and Mesozoic plays (0.4 %). Just over two-thirds of the Gulf of Mexico's total original proved reserves are contained in progradational facies (67.4 %),with the remainder comprising submarine-fan facies (18.5 %), aggradational facies (9.9 %), retrogradationalfacies (2.4 %), combination facies (1.7 %), and caprock and reef reservoirs (0.1 %). Total cumulative production from the different facies closely mimics the distribution of original proved reserves. Of the 91 plays, the lower Pleistocene progradational play (LPL P.1) contains the most original proved gas reserves (10.5 %) and has produced the most gas (11.4 %). However, the upper upper Miocene eastern progradational play (UM3 P.1B) contains the most original proved oil and condensate reserves (18.9 %) and has produced the most oil and condensate (21.4%). Several technical studies resulting from OAP have been published. Hunt and Burgess (1995) described the distribution of OAP plays deposited by the ancestral Mississippi River delta system in the north-central Gulf of Mexico over the past 24 million years. The lower Miocene plays are restricted to the westernmost portion of the Louisiana shelf. In the late middle Miocene, the depocenter migrated east of the present-day Mississippi River delta. During the late upper Miocene, the depocenter began migrating back to the west and prograded basinward, and it continued to do so throughout the Pliocene and Pleistocene. Lore and Batchelder (1995) discussed how OAP plays can be used to find exploration targets and assess undiscovered resources. As an exploration tool, OAP play maps can be used to identify conceptual submarine-fan plays downdip of established shallow water producing facies, and to identify wells where a known producing facies or chronozone has not yet been reached. As an assessment tool, the extensive data sets associated with each OAP play can be used to infer statistically the size of undiscovered resources in a play to determine if exploration in that play is economically justifiable. Lore et al. (1995) estimated the amount of undiscovered conventionally recoverable resources in the Gulf of Mexico, basing their assessment on previous work performed for OAP. Mean level estimates show that, by far, submarine-fan plays have the greatest potential for additional oil and gas in the Gulf of Mexico, with 75.1 % and 70.4 % of the total oil and gas resources, respectively. Mean level estimates for the 13 OAP Miocene, Pliocene, and Pleistocene chronozones show that upper Pleistocene plays have the most oil resource potential (24.3 %), while lower Pleistocene plays have the most gas resource potential (20.6 %). 相似文献
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墨西哥及墨西哥湾盆地构造单元及其演化 总被引：2，自引：0，他引：2
墨西哥及墨西哥湾盆地中生代以来可划分为两个一级构造单元,分别是墨西哥造山带和墨西哥湾盆地,进一步可划分二级构造单元6个,其中在墨西哥造山带划分了3个二级构造单元,分别是下加里福尼亚造山带、西马德雷—南马德雷岛弧带和东马德雷逆冲挤压带。在墨西哥湾盆地也划分了3个二级构造单元,分别是墨西哥湾盆地区、佛罗里达地块和尤卡坦地块。墨西哥造山带的形成是大洋板块和大陆板块相互作用的结果,但在不同构造单元上的表现不同。墨西哥湾盆地是一个中生代—新生代的裂谷盆地,包括内陆带、沿海带和洋壳带。根据墨西哥湾盆地构造地层幕将墨西哥湾盆地构造演化分为5个演化阶段,分别为晚三叠世到早侏罗世时期裂谷阶段,中侏罗世裂谷和地壳衰减阶段,晚侏罗世洋壳生成阶段,早白垩世下降阶段和晚白垩世至新生代陆源物质沉积和盐构造变形阶段。 相似文献
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评述了美国墨西哥湾深海油气储量、墨西哥湾原有的油气发现、墨西哥湾浅水和深水的油气发现统计、深水钻井重获许可后开发的新进展、墨西哥湾油田原油生产数据以及新发现开始生产石油的情况. 相似文献
10.
泰国湾区域经历了前裂谷期、裂谷期、裂后期的构造演化阶段,形成了多个裂谷盆地。泰国湾区域东北部在渐新世经历了一次明显构造反转,较泰国湾区域大部分地区强烈。通过对比区内钻井,结合地震解释,对该区的沉积特征和构造演化进行了分析,认为这次反转构造导致了反转构造带上构造、沉积特征与邻区有较大的不同。由于这次反转构造,泰国湾东北部在新层系发育新类型的油气系统,即深部的始新统油气系统:烃源岩为中始新统湖相泥岩,储层为上始新统-渐新统三角洲相砂岩,盖层为下中新统三角洲前缘相泥岩和上中新统以上的海相泥岩。该油气成藏系统已被钻井钻遇油气显示,是本区有效油气成藏系统。 相似文献
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《Marine and Petroleum Geology》2013,39(1):128-142
The northern Gulf of Mexico is dominated by salt tectonics, resulting fracturing and numerous seafloor seeps and vents. Woolsey Mound, site of the Gulf of Mexico Hydrates Research Consortium's seafloor observatory, has been investigated extensively via surveys, direct sampling and seafloor instrument systems. This study presents an innovative approach to seismic data interpretation, integrating three different resolution datasets and maximizing seismic coverage of the complex natural hydrocarbon plumbing system at Woolsey Mound.3D industry seismic data reveal the presence of a salt body at in the shallow subsurface that has generated an extended network of faults, some extending from the salt body to the seafloor (master faults). Higher resolution seismic data show acoustic wipe-out zones along the master faults with expulsion features – seafloor pockmarks and craters – located immediately above them and associated, in the subsurface, with high-amplitude, negative anomalies at constant depth of 0.2 s TWTT b.s.f., interpreted as free gas. Since pockmarks and craters provide pathways for hydrocarbons to escape from depth into the water column, related sub-surface seismic anomalies may indicate free gas at the base of the gas hydrates stability zone (GHSZ). Fluid flow and gas hydrates formation are segmented laterally along faults. Gas hydrates formation and dissociation vary temporally in the vicinity of active faults, and can temporarily seal them as conduits for thermogenic fluids. Periodic migrations of gases and other fluids may perturb the GHSZ in terms of temperature and pressure, producing the observed lack of classical BSRs. 相似文献
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Terry L. Wade Yousra Soliman Stephen T. Sweet Gary A. Wolff Bobby J. Presley 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2585
The concentrations of polycyclic aromatic hydrocarbons (PAHs) and trace elements were determined for surface (top 2 cm) sediment samples collected during the deep Gulf of Mexico benthos (DGoMB) study .These elements and compounds are known to be toxic to organisms at high concentrations and may affect biological communities. There is no indication of major anthropogenic input of the elements Be, Co, Cr, Fe, Si, Tl, V, K, Mg, Ca, Sr and Zn, based on normalization to Al. The concentrations of these metals in the sediment are a function of the relative amounts of trace-metal-rich Mississippi River-derived silicate material and trace-metal-poor plankton-derived carbonate. This is not true for the elements Ba, Ni, Pb, Cd, As, Cu and Mn, whose concentrations show considerable scatter when normalized to Al and a general enrichment. On a normalized basis, Mn is enriched 5–10 fold, Cu and Ni 2–3 fold and Pb 2 fold over Mississippi River-derived material. These enrichments are likely the result of remobilization of metals from depths in the sediment column where reducing conditions exist. The Ba concentrations at selected sites are higher than those of average clay-rich sediments, but are typical of sediments from near oil well platforms in the northern Gulf of Mexico. In the case of Ba, it seems likely that the enrichments, as high as a factor of 10, are due to disposal of oil well drilling mud. The Ba-enriched samples are from the three shallowest water sites in the Mississippi Trough (sites MT1, 2 and 3) and from site C1 and WC5. All are in an area of intense petroleum exploration and development. PAH concentrations are also elevated at MT1, MT3 and C1. The total PAH concentration ranged from not detected (ND) to 1033 ng/g with a mean of 140 ng/g. Even at the sites most enriched in PAHs and trace elements, the concentrations are not at the levels expected to adversely affect the biota. However, these predicted non-effects are based on research using mostly near-shore estuarine species, not on the indigenous species at the sampling sites. 相似文献
13.
Gulf of Mexico sediment sources and sediment transport trends from magnetic susceptibility measurements of surface samples 总被引：1，自引：0，他引：1
The magnetic properties from 200 trigger core-top and Van Veen grab sediment samples recovered from throughout the Gulf of Mexico have been analyzed and used to characterize sediment source and flow pattern distributions. Magnetic parameters included are anhysteretic remanent magnetism (ARM) and magnetic susceptibility (MS) measurements. Results from these measurements are compared to previously determined calcium carbonate percentages, and clay and hematite influx trajectories into the Gulf of Mexico for the same samples reported by Balsam and Beeson [Balsam, W.L. and Beeson, J.P., 2003. Sea-floor sediment distribution in the Gulf of Mexico, Deep-Sea Res. I, 50, 1421–1444.]. The ARM results give an estimate of magnetic grain size distributions, and by analogy, grain size distributions in general, whereas MS patterns show high detrital sediment accumulation zones within the Gulf. The dominant influx of modern high susceptibility sediment into the Gulf of Mexico appears to originate from the Red River, flow into Atchafalaya River Basin and out into the Gulf from Atchafalaya Bay, with significant additional contributions from the Mississippi River through the Southwest Pass of the Mississippi River Delta. This material then moves across the continental shelf and down through the Mississippi Canyon into the deep Gulf where it is redistributed at depths > 3600 m. The eastern shelf margins in the Gulf, offshore from Alabama and Florida, are accumulating calcite- or quartz-rich medium to fine-grained sediment that has a very low or diamagnetic MS signature. From the Louisiana to Texas Gulf coast margins, MS is moderate to high, suggesting a river influx of magnetic constituents from the volcanic fields in New Mexico, and from igneous and metamorphic sources in the Mississippi Basin. Offshore from western Mexico, the MS is high to moderate, but the Yucatan Shelf margin is characterized by low to diamagnetic MS values due to sediment dominated by calcite sands and oozes, a trend that continues to the east onto the West Florida Shelf. Additional measurements of samples collected in association with sites characterized by hydrocarbon seepage exhibit anomalously low MS values. The samples from the lower shelf and slope areas are typified by iron reduction by bacterial organisms in these samples. These results produce anomalous localized lows in the MS trends observed. 相似文献
14.
Two different and physically separated chemosynthetic communities of bacteria are responsible for the formation of the Beeri native sulfur deposit hosted in a Late Quaternary sandstone on the southern coastal plain of Israel. The enriched concentrations are distributed over an area of about 1 km2, within a zone 2–3 m thick at 1–13 m below surface. Two hundred fifty meters below the sulfur deposit, sulfur-reducing bacteria, thriving on methane generated in Neogene marls, reduced the Messinian gypsum to generate hydrogen sulfide, which subaqueously vented together with methane into the siliciclastic Quaternary sequence. Another, different chemosynthetic community ofBeggiatoa-like and unidentified bacteria oxidized the hydrogen sulfide into native sulfur and secondary gypsum, alunite, and iron sulfates. The coupled chemical and bacterial processes attributed to the formation of the sulfur deposit at Beeri are strikingly similar to the processes occurring today in the context of submarine hydrocarbon vents associated with the salt diapirs in the Gulf of Mexico. 相似文献
15.
A. Zabanbark 《Oceanology》2006,46(4):557-563
With respect of its structure, the Gulf of Mexico basin is heterogeneous. The following individual basins and subbasins can be distinguished; (1) Mississippi-Louisiana; (2) Gulf Coast within the boundaries of Texas and New Mexico; (3) Mexican Gulf Coast and adjacent system of foredeeps; (4) Yucatan subbasin; (5) Cuba-Bahamas system of foredeeps. Regional seismic studies reveal a close relationship between salt movements and sedimentation. Salt bodies represent excellent cap rocks for hydrocarbon fluids. Anticline folds termed “turtle” structures forming a system of belts appear in the deep parts of the gulf. These structures host large reserves of hydrocarbons, which are concentrated in the Paleogene-Miocene turbidite reservoirs with a porosity approximately 30% overlain by excellent cap rocks (salt, clay) with permeability exceeding 3 darcy. Three productive zones are defined: (1) the folds of the Mississippi River fan; (2) the Perdido belt of anticline folds; (3) Florida. The Paleogene and Miocene-Pliocene-Pleistocene sediments developed on the continental slopes of the Gulf of Mexico basin are the areas most promising with respect to hydrocarbon deposits. On January 1, 2006, the offshore oil production was 53 million tons and the gas production 40 billion cubic meters. Total prospective oil and gas reserves are estimated to be 5.5 billion tons and 4.7 trillion cubic meters, of which over 50% of oil and 1/3 of gas are expected to be discovered on the continental slope. 相似文献
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George Dellagiarino 《Marine Georesources & Geotechnology》2013,31(2-3):83-89
Since 1976, the Minerals Management Service (MMS) has administered its prelease geological and geophysical (G & G) data acquisition program through Title 30, Part 251, of the Code of Federal Regulations, which govern permitting, acquisitions, and data release. Leading indicators of offshore oil and gas activity are the number of permits issued to industry, associated mileage, and expenditures. Over the last 20 years, permit activity has indicated that most of the oil and gas surveying has been in the Gulf of Mexico, where 80 % of all permits have been issued, followed by Alaska (10 %), the Pacific (7 %), and the Atlantic (3 %). These statistics correlate with the dominant position of the central and western Gulf of Mexico areas in oil and gas activity. More than 95 % of all permits were issued for geophysical exploration, mostly for two-dimensional (2-D) common-depth-point (CDP) seismic data. However, over the last 10 years, permits for three-dimensional (3-D) seismic data have averaged 25 % of all geophysical permits and, by 1996, made up approximately half of all geophysical permits offshore-wide. Between 1976 and the early 1990s, industry shot approximately 500,000 linemiles of 2-D CDP data each year on the Outer Continental Shelf (OCS). Of that total, MMS acquired approximately50,000 line-miles annually. In the 1990s, parallel with industry, MMS increased its acquisition of 3-D seismic data in concert with the development and use of interactive workstations. The majority of 2-D and 3-D data have been acquired in the Gulf of Mexico by a ratio of 2:1 over Alaska, the next largest data inventory. With regard to MMS expenditures for G & G data, from 1976 through the 1980s, Alaska, having more offshore area than the other three regions combined, had the largest portion. However, in the 1900s, the vast majority of expenditures have been in the Gulf of Mexico. Over the years, permit totals, mileage acquired, and expenditures for data reflect trends of oil and gas pricing, limitations of offshore moratoria, and a shift of industry emphasis to foreign theaters. 相似文献
17.
《Marine and Petroleum Geology》2012,36(1):139-153
Future exploration in lower Miocene sandstones in the Gulf of Mexico will focus increasingly at depths greater than 4.5 km, and reservoir quality will be a critical risk factor in these deep to ultradeep reservoirs. The goal of this study was to understand the variation in reservoir quality of lower Miocene sandstones across the western Gulf of Mexico. To do this, we examined regional variation in detrital mineral composition, diagenesis, and reservoir quality in five areas: (1) Louisiana, (2) upper Texas coast, (3) lower Texas coast, (4) Burgos Basin, Mexico, and (5) Veracruz Basin, Mexico using petrographic and petrophysical data from depths of 0.9–7.2 km.There are strong variations in mineralogical composition within the study area. Lower Miocene sandstones from offshore Louisiana have an average composition of quartz = 86%, feldspar = 12%, and rock fragments = 2% (Q86F12R2). Feldspar and rock-fragment content increase southward as source areas shifted to include volcanic and carbonate rocks. Composition of samples from offshore Texas ranges from Q67F24R9 in the upper Texas coast to Q58F24R19 in the lower Texas coast. Lower Miocene sandstones from the onshore Burgos Basin, northern Mexico, have an average composition of Q54F22R23, whereas sandstones from the Veracruz Basin, southern Mexico, contain the highest proportion of rock fragments, Q33F12R55. Main diagenetic events in quartz-rich lower Miocene sandstones in Louisiana were mechanical compaction and precipitation of quartz cement. Compactional porosity loss increased to the south with increasing rock-fragment content. Calcite is the most abundant cement in the south and is strongly related to reservoir quality loss.At moderate burial depths, the best reservoir quality occurs in quartz-rich sandstones in Louisiana and decreases with increasing lithic content in Texas and Mexico. Porosity is higher in Louisiana and upper Texas than in lower Texas and Mexico at all depths and temperatures, but at depths >5 km and temperatures >175 °C, porosity differences are lessened. The lower Miocene sandstone trend in the western Gulf of Mexico from Louisiana to Mexico is an example of the importance of variation in detrital mineralogy as a control on diagenesis and reservoir quality. 相似文献
18.
George Dellagiarino 《Marine Georesources & Geotechnology》1999,17(2):83-89
Since 1976, the Minerals Management Service (MMS) has administered its prelease geological and geophysical (G & G) data acquisition program through Title 30, Part 251, of the Code of Federal Regulations, which govern permitting, acquisitions, and data release. Leading indicators of offshore oil and gas activity are the number of permits issued to industry, associated mileage, and expenditures. Over the last 20 years, permit activity has indicated that most of the oil and gas surveying has been in the Gulf of Mexico, where 80 % of all permits have been issued, followed by Alaska (10 %), the Pacific (7 %), and the Atlantic (3 %). These statistics correlate with the dominant position of the central and western Gulf of Mexico areas in oil and gas activity. More than 95 % of all permits were issued for geophysical exploration, mostly for two-dimensional (2-D) common-depth-point (CDP) seismic data. However, over the last 10 years, permits for three-dimensional (3-D) seismic data have averaged 25 % of all geophysical permits and, by 1996, made up approximately half of all geophysical permits offshore-wide. Between 1976 and the early 1990s, industry shot approximately 500,000 linemiles of 2-D CDP data each year on the Outer Continental Shelf (OCS). Of that total, MMS acquired approximately50,000 line-miles annually. In the 1990s, parallel with industry, MMS increased its acquisition of 3-D seismic data in concert with the development and use of interactive workstations. The majority of 2-D and 3-D data have been acquired in the Gulf of Mexico by a ratio of 2:1 over Alaska, the next largest data inventory. With regard to MMS expenditures for G & G data, from 1976 through the 1980s, Alaska, having more offshore area than the other three regions combined, had the largest portion. However, in the 1900s, the vast majority of expenditures have been in the Gulf of Mexico. Over the years, permit totals, mileage acquired, and expenditures for data reflect trends of oil and gas pricing, limitations of offshore moratoria, and a shift of industry emphasis to foreign theaters. 相似文献
19.
I. Rosman MacDonald Norman L. Guinasso Jr. James F. Reilly James M. Brooks W. Russell Callender Steve G. Gabrielle 《Geo-Marine Letters》1990,10(4):244-252
Communities of chemosynthetic fauna that depend on seeping oil and gas have been found in the Gulf of Mexico at approximately
45 sites between 88°W and 95°W and between the 350 and 2,200 m isobaths. Investigations suggest that the number of sites and
the range of occurrence will increase with additional exploration. The dominant fauna consist of species within four groups:
tube worms, seep mussels, epibenthic clams, and infaunal clams. These species co-occur to some degree, but tend to form assemblages
dominated by a single group. Community development is closely coupled to the geological and geochemical processes of seepage. 相似文献
20.
M. Taviani 《Geo-Marine Letters》1994,14(2-3):185-191
Recent suggestions that the Miocene-age calcari aLucina blocks scattered in the Apennine chain of the Italian peninsula are methanogenic in nature (paleo cold vents) calls for a reexamination of their macrofauna. Two Tortonian-age outcrops of such limestones (Case Rovereti and Montepetra) have been analyzed for their mollusk content and shown to host a diverse vent fauna. The paleoassemblages show remarkable similarities with modern counterparts associated with hydrocarbon venting on the Gulf of Mexico continental slope. Faunal data from both sites lend support to the hypothesis that methane/hydrocarbon venting was active during the Miocene and sustained specialized bathyal chemosynthetic communities in the ancient Mediterranean. 相似文献