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Idealized cross section of the Miami and Pourtales terraces, extracted from Malloy and Hurley (1970), and Miller (1986). A±D , G Depth (or elevation) of sinkholes in Figs. 1 and 4 (sinkhole A is not shown in Fig. 1). Because of the 50 ́ vertical exaggeration ( v.e. ), relative depths only can be compared. The gentle slope of the escarpment is characteristic of the extreme western end of the Pourtales Terrace where the NR-1 sinkhole ( G ) occurs near the base of the escarpment in a Quaternary sediment drape
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Nine submarine sinkholes have been surveyed and mapped with side-looking sonar and echo-sounder profiles in the Straits of
Florida. These structures are irregularly distributed across the surface of the South Florida Margin, forming a discontinuous
belt along the edge of the slope. The sinkholes occur in water depths too great to have ever been exp...
Contexts in source publication
Context 1
... sinkholes were surveyed on the Pourtales Terrace, about 50 km south of Vaca Key ( Fig. 1). The Jordan Sinkhole, so named because it was ®rst reported by Jordan et al. (1964), is located near the apex of the Pourtales Terrace. The Jordan East Sinkhole (our no- menclature) is located about 5 km east of the larger Jordan Sinkhole. Two additional sinkholes, referred to as the Marathon Sinkholes because of their location 60 km south of the town of Marathon on Vaca Key, were ®rst identi®ed by Malloy and Hurley (1970) in their bathymetric map of the southern Straits. In addition, at least half a dozen sinkhole-like depressions (not surveyed) were observed in OAS records at the margins of these survey areas and during transits between the sites. The NR-1 Sinkhole (Fig. 1) is located near the base of the Pourtales Escarpment about 40 km south of Marquesas Keys at the extreme western end of the southern Florida Straits (US Geological Survey and National Ocean Service 1989a). This sinkhole was originally surveyed in October 1994, and is described in Land et al. (1995). Data acquisition across the Jordan Sinkhole (Fig. 4D) was complicated by the size of the feature which is several hundred meters wider than the NR-1's side-scan sonar footprint ( 200 m). Because of the depth and steep interior walls of the hole, echo-sounder records taken during central crossings show numerous side echoes which obscure the actual bottom re ̄ections. Thus, the observed bathymetry of the sinkhole should be considered as representing minimum depths. The Jordan sink lies directly beneath the Gulf Stream and, coupled with powerful updrafts of 0.5 knots (25 cm/sec) from the hole (NR-1 ocers, personal communication), strong currents prevented operations being conducted closer than 50 m above the sea ̄oor. Preliminary observations suggest that the updrafts are probably a turbulence eect caused by current ̄ow across the mouth of the sinkhole. Thus, visual observations were impossible during most of the survey because of our inability to make a close approach to the sinkhole. However, some sea ̄oor lineations were observed oriented perpendicular to the margin on the west edge of the sinkhole complex. The general morphology of the Jordan Sinkhole, similar to a 1.2-km-long, E-W-oriented ®gure eight, indicates that it consists of two partially merged sinkholes (Fig. 4D). Within the broad outer depression are two roughly circular, steep-walled inner depressions, separated by a narrow ridge which rises to within 30 m of the surrounding sea ̄oor. The west lobe is narrower and deeper (Table 1), and has a more pronounced fun- nel shape than the east lobe. Side-scan sonar records indicate the presence of secondary ledges at intermediate depths within the west lobe. The Jordan complex includes a third sinkhole 500 m east of the main depression (Fig. 4D). Since it was crossed by one survey line only, its shape was not well established in the present study. The Jordan East Sinkhole has a shallow, bowl-shaped pro®le (Fig. 4E), contrasting strongly to the deep, steep- walled depressions of the Jordan Sinkhole complex. The margins slope gently down to a relatively ̄at bottom which is partially covered with rippled sand. Sediment cover is patchy and, in places, the sinkhole ̄oor consists of a rubbly pavement. The margin of the sinkhole consists of a <1-m-thick bed, presumed to be limestone, which has a weathered appearance and appears to be manganese-phosphate coated. The outcrop is covered in places by unconsolidated sediment. The North and South Marathon sinkholes (Fig. 4F) occur at the outermost edge of the Pourtales Terrace, near the slope break at 500 m water depth (US Geological Survey and National Ocean Service 1989b). The sea ̄oor at the southwest margin of the North Marathon Sinkhole is marked by a pronounced NW-SE fabric (Fig. 6) which probably represents outcropping strata on the outer edge of the terrace. Strong updrafts were again experienced during crossings, which caused erratic movements and degraded the quality of the side-scan sonar records. An abrupt loss of buoyancy occurred during the ®nal crossing over the South Marathon Sinkhole. During the transit to the Marathon site, another sinkhole was identi®ed 900 m west of North Mara- thon. Although there was insucient time to conduct a detailed survey, approximately four additional sinkholes were observed on the OAS screen as the NR-1 submarine lifted o bottom and prepared to surface. The NR-1 Sinkhole (Fig. 4G) is developed in a late- Quaternary drape of pelagic carbonate sediment 10 m thick on the gentle lower slopes of the Pourtales Escarpment (Figs. 1, 2; Brookes and Holmes 1989). The interior of the sinkhole consists of outcropping ledges, expressed as a series of concentric re ̄ectors on the side- scan sonar record (Land et al. 1995). Regional strati- graphic correlations (Maher 1971; Puri and Winston 1974) indicate that the NR-1 Sinkhole is probably rooted in Eocene strata of the lower Floridan Aquifer (Fig. 2). The southwest margin of the Pourtales Terrace is or- namented by a chain of sinkholes which extends for 100 km o the lower Florida Keys. The eastern end of the terrace is marked by a band of karst-like topography consisting of paired knolls and depressions extending an additional 55 km to the northeast (Jordan et al. 1964; Malloy and Hurley 1970). If the smaller sinkholes surveyed on the upper Miami Terrace are genetically related to the karst features on the Pourtales Terrace, their presence suggests that a discontinuous belt of submarine karst extends along the southeast margin of the Florida Platform for over 350 ...
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... Nine submarine sinkholes have been surveyed and mapped with side-looking sonar and echo-sounder pro®les in the Straits of Florida. These structures are irregularly distributed across the surface of the South Florida Margin, forming a discontinuous belt along the edge of the slope. The sinkholes occur in water depths too great to have ever been exposed above sea level, and some are several times larger than any known subaerial sinkholes in North America. Because most karst morphologies are the product of groundwater circulation, the distribution of submarine sinkholes in the Florida Straits may be directly related to the paleohydrology of the South Florida Platform. Sinkholes, or dolines, are circular depressions which typically range from 10 to 1000 m in diameter and which are about 2 to 100 m deep (Sweeting 1973). They commonly result from dissolution by meteoric groundwater in subaerially exposed carbonate strata (Esteban and Wilson 1993). For this reason sinkholes are often used as indices of subaerial exposure (e.g., Schlanger and Silva 1986; Lincoln and Schlanger 1987; Van Waasbergen and Winterer 1993). Thus, when Jordan (1954) ®rst reported submarine sinkholes on the Pourtales Terrace south of the Florida Keys (Fig. 1), he assumed that they formed during a Tertiary sea-level lowstand. Burnett and Gomberg (1977) concluded from petrologic and geochemical evidence that Tertiary limestones of the Pourtales Terrace had been subjected to freshwater diagenesis, and that submarine karst features observed there must have been caused by Miocene subaerial exposure. Although Malloy and Hurley (1970) proposed a marine origin for the South Florida submarine sinkholes, based on their interpretation of regional subsidence history, until recently most workers have accepted this subaerial interpretation. However, the origin of these features has been controversial since they were ®rst discovered, because they are at the maximum possible depth for exposure to have occurred given any combination of tectonic subsidence and eustatic sea-level fall (Fig. 2; Malloy and Hurley 1970; Mullins and Neumann 1979). Because the calcium carbonate saturation curve is non-linear, dissolution of carbonate rocks can occur when two ̄uids of dierent salinities combine even if both parent ̄uids are supersaturated with calcium carbonate (Runnells 1969; Plummer 1975; Hanshaw and Back 1979; Sanford and Konikow 1989a, b). Thus, submarine sinkholes may be the products of freshwater/ saltwater mixing. Limestone corrosion resulting from the mixing of fresh and saline waters is well documented at groundwater discharge sites in shallow-water areas (e.g., Back et al. 1984; Smart et al. 1988). The lack of unequivocal evidence for active carbonate dissolution in deeper submarine environments is the principal reason for the controversy over the origins of karst-like features in the Florida ...
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... continental slope o southeast Florida is inter- rupted by an intermediate-depth terrace, the surface of which coincides with a regional unconformity developed on Eocene±middle-Miocene strata. This erosional surface is exposed in the northern Straits of Florida as the Miami Terrace, and to the southwest as the Pourtales Terrace ( Fig. 1). A post-Miocene sediment drape separates the two terraces o Key Largo. Eocene/Oli- gocene strata beneath these terraces are oshore extensions of the Floridan Aquifer (Fig. 2), an important artesian aquifer in the southeastern United States which also hosts the sinkholes of the north central Florida karst terrane (String®eld 1966; Meyer 1989). The Miami Terrace occurs at 200±400 m water depths at the foot of a slope of post-Miocene sediment oshore Miami. The surface of the terrace consists of Oligocene±Miocene phosphatic limestone (Uchupi and Emery 1967), and is marked by a very irregular karst- like topography (Fig. 3; Malloy and Hurley 1970; Neumann and Ball 1970; Mullins and Neumann 1979). The Pourtales Terrace, in the southern Straits of Florida, is the drowned southern end of the Florida carbonate platform, located at 200±450 m water depths (Fig. 1; Jordan et al. 1964; Burnett and Gomberg 1977). Eocene limestones of the Floridan Aquifer system are presumed to crop out at the margin of the Pourtales Terrace, based on correlation with exploratory boreholes drilled on Marquesas and Big Pine Keys (Maher 1971; Puri and Winston 1974). Several submarine sinkholes occur along the southwest margin of the terrace (Jordan 1954; Jordan et al. 1964; Malloy and Hurley 1970). In the 1960s through 1980s, Kohout and others published a series of papers (Kohout 1965, 1967; Kohout et al. 1977, 1988) documenting evidence for a type of open-cycle thermal convection occurring within artesian aquifers of south Florida, now commonly referred to as Kohout convection (Simms 1984). Accord- ing to Kohout's model, cool seawater in the Florida Straits invades highly permeable limestones of the Tertiary Floridan Aquifer at its submarine outcrop and ̄ows inland. Geothermal heating increases the buoyancy of the encroaching seawater, causing it to migrate upwards where it becomes entrained with regional ̄ow of fresh groundwater toward the coast. The mixture of fresh and saline waters ultimately discharges from submarine springs on the shelf and along the shelf edge. Kohout hypothesized that submarine karst phenomena in the northern Straits of Florida are the result of mixing-zone dissolution at sites of groundwater discharge. However, Kohout's model is based primarily on negative geothermal gradients observed in onshore boreholes, and there is little hydrologic information available on the discharge end of his hypothetical circulation system. Land et al. (1995) identi®ed a sinkhole at the foot of the Pourtales Escarpment (now named the NR-1 Sinkhole) at water depths greater than 600 m ± too deep to have been subaerially exposed at any time during the Neogene. This discovery supports a marine origin and was the stimulus for additional surveys, the principal objective of which has been to investigate the role of submarine groundwater discharge in creating and maintaining these sinkholes. If submarine sinkholes in the Florida Straits are the product of groundwater ad- vection, they may provide fundamental information about the paleohydrology of the South Florida Platform. A series of sea ̄oor surveys were conducted in October 1994 and May 1995, using the US Navy NR-1 nuclear submarine. The NR-1 is equipped with 177.5 kHz side-scan sonar, 7 kHz seismic pro®ler and a 25 kHz narrow-beam echo-sounder which are displayed on a paper record produced by a Raytheon ̄at-bed recorder. The NR-1 also has an obstacle avoidance sonar (OAS) display which provides a detailed three-dimensional picture of the surrounding topography on a CRT screen. However, except for an occasional frame which is captured on video ®lm, the OAS data are not recorded. The NR-1 operates with an inertial navigation system but OAS images were used for reconnaissance. After a depression on the sea ̄oor was identi®ed with OAS (appearing as a circular or oval feature on the monitor), the NR-1 collected side-scan sonar, seismic and echo- sounder data in a grid, maintaining a constant depth along each pro®le of 50 m above the sea ̄oor adjacent to the sinkholes. The NR-1 is equipped with a large bow wheel which allows it to roll along the bottom in areas of moderate current and gentle topography. Visual observations of the sea ̄oor are made from the three forward viewports of the submersible, and documented with an electronic still camera, 8 mm ®lm and VHF videotape. Conductivity-temperature-depth (CTD) data were collected throughout the surveys. Because the CTD sensor is positioned on the sail of the NR-1, it records relatively low-resolution water-column data, and it is not well located or calibrated for making precise mea- surements of temperature or salinity near the sea ̄oor. No marked variations in temperature or salinity were observed during crossings over any of the sinkholes. Representative temperature and salinity values for each survey are given in Table ...
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Submarine slope failures are a likely cause for tsunami generation along the East Coast of the United States. Among potential source areas for such tsunamis are submarine landslides and margin collapses of Bahamian platforms. Numerical models of past events, which have been identified using high-resolution multibeam bathymetric data, reveal possibl...
Citations
... These submarine karst terranes were hypothesized to have been caused by groundwater discharge into the marine environment along the margins of the Florida platform [8]. Twelve sinkholes were imaged and described via side-scan sonar data, seismic profiles, and echosounder profilers aboard the U.S. Navy's submersible vehicle NR-1 [9,10]. The length of the largest sinkhole was 1.2 km, with a maximum vertical depth of 260 m. ...
... Our high-resolution multibeam bathymetric data showed well-developed submarine sinkholes on the Ganquan carbonate platforms (Figure 3). ROV Haima 2 imaged corals (Figure 5a,c), flow marks (Figure 5e), and corroded holes (Figure 5f) in the inner wall of submarine sinkhole No. 2, indicating that these submarine sinkholes show strong morphologic similarities (e.g., size, depth, and shape) with those developed on other carbonate platforms worldwide, such as the southern Florida Straits [8][9][10], southern Adriatic Sea [11], Abrolhos Bank of Australia [12,13], and the Bahamas and Caribbean Seas [7,14]. ...
... However, in areas where subsurface waters with different compositions mix, solution-collapse sinkholes in carbonate platforms may have never been subaerially exposed. Land and Paull [10] proposed that the collapse of carbonate rocks resulted from the mixing of deep freshwater and seawater near land in the Florida Straits because the sea level could not have dropped by 600 m to expose the surface. Michaud et al. [26] deduced that the dissolution of carbonate rocks was caused by underlying thermal convection derived from volcanic or basement hydrothermal systems. ...
Submarine sinkholes are unique and important geomorphological features with a typical cavity structure that are of great scientific value. Submarine sinkholes were discovered for the first time in the isolated Ganquan carbonate platform on the Xisha Islands, the northwestern South China Sea. Based on high-resolution multibeam bathymetric data and seismic profile data, we identified 37 submarine sinkholes at water depths ranging from 550 to 1267 m. They are subcircular to circular negative-relief features, and most of them are V- or compound V-shaped in the cross-section. Their average diameters range from 57 to 667 m, and the depth of the depression ranges from 2.5 to 241 m. By comparing submarine sinkholes in the Ganquan platform with those in other carbonate platforms worldwide, we can infer that the Ganquan platform submarine sinkholes are the largest sinkholes developed on an isolated carbonate platform. Remotely operated vehicle (ROV) “Haima 2” images revealed that the inner walls of submarine sinkholes are characterized by stalactite-like structures, possible dikes, flow marks, and corroded holes, which are typical karstic landscape features. The temperature within submarine sinkholes is 2 °C higher than that of the open ocean at the same water depth. Based on the results of the shallow formation profile and multichannel seismic profiles, we propose that the submarine sinkholes in the Ganquan platform probably formed via the dissolution of the carbonate platform via acidic hydrothermal fluids that originated from magmatic activity and migrated along faults.
... Around the Mediterranean, submarine palaeokarst features can occur much deeper than elsewhere in the world, because sea level in the Mediterranean at the end of the Miocene dropped over 1500 m (Fleury et al., 2007), much greater than the ~120 m decrease during the LGM. Dolines along the South Florida Margin, too deep to have ever been exposed subaerially, probably formed by enhanced dissolution due to freshwater/seawater mixing at the downgradient end of the groundwater flow system (Land and Paull, 2000). The seafloor dolines along the Bahama Escarpment, that lie at water depths of over 4 km, are interpreted to have formed by karstic processes at abyssal depths (Cavailhes et al., 2022). ...
Maps of seabed geomorphology derived from bathymetry data provide foundational information that is used to support the sustainable use of the marine environment across a range of activities that contribute to the Blue Economy. The global recognition of the value of the Blue Economy and several key global initiatives, notably the Seabed 2030 project to map the global ocean and the United Nations Decade of Ocean Science for Sustainable Development, are driving the proliferation and open dissemination of these data and derived map products. To effectively support these global efforts, geomorphic characterisation of the seabed requires standardised multi-scalar and interjurisdictional approaches that can be applied locally, regionally and internationally. This document describes and illustrates a geomorphic lexicon for the full range of coastal to deep ocean geomorphic Settings and related Processes that drive the formation, modification and preservation of geomorphic features on the seabed. Terms and Settings/Processes have been selected from the literature and structured to balance established terminology with the need for consistency between the range of geomorphic environments and processes. This document also presents a glossary of 406 geomorphic terms and identifies the insights that can be gained by mapping each unit type, from an applied perspective.
... Offshore Florida, Land et al. (1995) and Land and Paull (2000) showed that onshore aquifers likely contributed to or were wholly responsible for the formation of dissolution sinkholes/karst, although these were only found in shallow waters. In the eastern Mediterranean Sea, Bertoni and Cartwright (2005) imaged large (>1 km) circular depressions with "ring" faults similar to those observed in this study (Figure 7) and concluded evaporite dissolution driven by focused fluid-flow as the driving mechanism. ...
High-resolution bathymetry and 3D seismic data along the Cocos Ridge reveal a 245 km2 field of ~1 to 4 km in diameter seafloor depressions. The seafloor depressions are part of a two-tiered honeycomb pattern. The lower-tier depressions have steep faults that truncate strata with chaotic internal reflections consistent with sediment collapse into the depression. These extend into a lens shaped interval just above igneous basement. Overlying these depressions is a second broader set with rough seafloor morphology with gently dipping boundaries defined by pinch-out stratigraphic patterns. Drilling results indicate that the lens-shaped zones that host the deeper depressions represent anomalous regions of high porosity, low velocity, and low density within calcareous rich sediment. Analysis of nannofossils from IODP Site U1414 suggests the collapse structures formed during the late Miocene, whereas the younger shallower depressions likely formed between the early Pliocene and the Pliocene-Pleistocene boundary. Geochemical and petrological analysis at Site U1414 suggests that hydrothermal circulation during the late Miocene led to carbonate dissolution and collapse. Following collapse, focused fluid-flow and bottom current scouring resulted in formation of the overlying set of depressions and a honeycomb seafloor morphology. Similar sets of depressions along the Carnegie Ridge to the south support the hypothesis that two-tiered depressions formed in response to processes that occurred broadly across the Panama Basin between the late Miocene and the Pliocene-Pleistocene transition. Geochemical results at Site U1414, combined with geophysical data, suggest this two-tiered system of depressions currently guides ongoing fluid outflow.
... In the Bahamas or in Belize, several landforms belong to this category (Mylroie et al., 1995). Sinkholes can be found in the submarine environment (Land et al., 1995;Land and Paull, 2000), however, sinkholes discovered at a water depth of greater than 200 m cannot be explained by classical karstic dissolution, i.e., corrosion by meteoric waters. Deep-sited sinkholes in the Bahamas are related to brine-rich deepfluid circulation (Paull and Neumann, 1987;Cavailhes et al., 2022). ...
... Their inferred formation process is density cascading of dense water at the bank edge. Deep-sea sinkholes have been described along the Florida Escarpment (e.g., water depth of ∼450 m, Land and Paull, 2000; ∼ -575 m water depth, Land et al., 1995). They were formed by carbonate dissolution under the action of brines circulating inside the drowned platform. ...
... This represents the mean slope between the edge and the middle of the depression. The asymmetry is 2.73, slightly higher than values published by Land and Paull (2000) ( 1.1-2.15). ...
Submarine depressions are common features on the eastern Bahamian seafloor but the genesis of the deepest ones (>4000 m in water depth) is not well understood. We conducted a morphometric analysis and compared them to a worldwide database of rounded depressions, whatever their genesis is. The deep Bahamian depressions are large elongated structures, among the largest on Earth, with a width greater than 1000 m and a depth sometimes greater than 200 m. They extend at the toe of the Blake Bahama Escarpment (BBE), one of the tallest escarpments on Earth. Some of them align parallel to the BBE. Other depressions align along large submarine canyon axes. When aligned along canyon axes, the depressions closest to the canyon head are flanked by a topographic high interpreted as a slope-break deposit, i.e., sediment deposited after flow expansion following a hydraulic jump. Turbidity currents in the carbonate canyon system are not permanent processes, but are rather triggered during sea-level highstands when the carbonate platform is flooded. In addition, some depressions are not located in canyon axes. Consequently, the size and location of the depressions are not likely explained by a simple plunge pool mechanical erosion. Rather, our data suggest that all depressions could be initiated by giant karstic dissolution structures (dolines or sinkholes). Under interpretation, those located in canyon axes are sporadically refreshed by carbonate-laden turbidity currents. The height of the outsized chutes marking the crossing of the BBE by the canyon mouth generates a hydraulic jump allowing sediment deposition toward the bottom of the depression. Large depressions observed at this location in the Bahamas were the result of an initial dissolution phase related to retreat of the BBE and the more recent sediment-laden flow activity. The depressions orientated along canyon axes facilitated the regressive erosion that formed the canyons. At present, the depressions located at canyon mouths act as regular plunge pools.
... The submarine groundwater discharge (SGD) study plays a major play role in the coastal aquifer and water resources management. Taniguchi and Makoto (2002), Robb (1990), Peng et al. (2008), Land and Paull (2000). Studying the SGD discharge with flux rate estimation is essential one for coastal zones monitoring of freshwater environment. ...
Submarine groundwater discharge (SGD) study is essential for groundwater in coastal terrace at Tiruchendur. The famous Murugan Temple is located in the area and around 25,000 people who visit this temple use the SGD well water at NaaliKinaru (a small open well) as holy water and drink it. The rock and soil type are sandy clay, silt, beach sand, calcarenite, kankar, gneissic rock and charnockite in base rock. Megascopic identification method was used to identify the porous and permeable rocks such as calcarenite, sandstone and kankar to support to increase SGD flux. Grain size study was used to identify the paleo-coastal estuarine environment with sediment deposits in the terrace. The square array electrical resistivity method was used to study the subsurface geology and aquifer depth. The 2d ERT technique was used to identify the subsurface shallow perched aquifer of freshwater. The magnetotelluric survey method was used to scan the entire subsurface geological and tectonic uplift, coastal ridges, rock folded subsurface structural features of continental and oceanic tectonism. Darcy’s law was used to calculate the SGD flux rate in the above study area.
... Focusing on fluid circulation in carbonate margins allows scientists to interestingly trace and discuss the supply, the storage and the release of chemical elements implied in carbonate platform diagenetic reactions (Staudigel et al., 2021) as well as document their geomorphologic consequences, leading to surprising submarine karstic landscapes (e.g. Land and Paull, 2000). ...
... Backshall et al., 1979;Rosenberg, 2019), (ii) Dissolution derived crater-like features that originate from an underlying thermal convection of volcanic or basement-hydrothermal systems (e.g. Yubko and Lygina, 2015;~−2300 m;Michaud et al., 2018); (iii) Submarine dolines related to the subsurface mixing of fresh and/or saline waters that dissolve limestones in coastal zones (e.g.~−450 m, Land and Paull, 2000;~−575 m, Land et al., 1995). ...
... The studied abyssal depressions show strong morphologic similarities (size, depression depth and shape) with the submarine karstic structures described by Land and Paull (2000) along the carbonate continental slope of Florida (Fig. 6b). In addition, the morphologic sharpness of the studied depressions appears related to seafloor collapse ( Fig. 5a and c). ...
This study reports the discovery of abyssal giant depressions located at the toe of the Bahamian carbonate platform, along the Blake Bahama structurally-controlled Escarpment (BBE) that exhibits up to 4 km of submarine elevation above the San Salvador Abyssal Plain (SSAP). Analysis of seismic reflection and bathymetric data collected during the CARAMBAR 2 cruise revealed the presence of 29 submarine depressions; their water depths range from 4584 m to 4967 m whereas their negative reliefs are elliptical in shape, range in diameter from 255 m to 1819 m, and in depth from 30 m to 185 m. The depression alignment trends are parallel to the BBE as well as to structural lineaments of the area, exclusively between 2200 and 5000 m from its toe, and overlies a buried carbonate bench in which a high-amplitude seismic anomaly has been detected. The depression density interestingly increases where the recognized structural lineaments intersect the BBE. Based on their physical attributes (i.e. location, jagged morphologies, water depths), we interpret these depressions as collapse sinkholes rather than pockmarks or plunge pools. The aforementioned observations suggest an atypical relationship between the spatial occurrence of the giant abyssal sinkholes, the carbonate platform tectonic structures, the buried carbonate bench that underlies the hemipelagites in the SSAP and the geomorphology of the area. According to the wider literature that reports fluid seepages along submarine carbonate escarpments, we propose that the ground water entrance during low sea-level stands, the dissolution of evaporites by meteoric water, the platform-scale thermal convection and the seawater entrance at the platform edge most probably collectively act in concert to favor the circulation of brines and therefore the corrosion within the Bahamian carbonate platform. These mechanisms are particularly efficient along the structural heterogeneities (e.g. the Sunniland Fracture Zone, SFZ) which act as fluid conduits localizing the dissolution and control the physiography of the area by maintaining the location of the sedimentary pathways. The dense fluids would migrate along the faults towards the BBE free edge and are subsequently trapped into the buried carbonate bench that laterally disappears below the low-permeability deep-sea hemipelagites of the SSAP. In consequence, the trapped corrosive fluids dissolve the carbonates preferentially along the tectonic structures such as the SFZ. They are this way at the origin of the BBE curvature and generate collapse-structures in the overlying fine-grained deposits finally resulting in the formation of giant abyssal sinkholes. This structurally-directed process of dissolution seems efficient to provide a brines density head to move out down to >4.5 km of water depth and is believed to have played a major role in the BBE 5–6 km erosional retreat.
... Previous studies of the Florida and Yucatan escarpments and the Straits of Florida by Deep Sea Drilling Project Legs 10 and 77, and traverses of the Florida escarpment in the Alvin manned submersible yielded some unexpected findings. Notable among them were recogni�on of the erosional origin of both the Florida escarpment (Paull et al., 1990a;Paull et al., 1990b) and that of Yucatan (Paull et al., 2014); sinkholes were documented on the outer Florida ramp (Land and Paull, 2000); the fresh water diagenesis of in situ carbonates from the lower Yucatan escarpment was recognized (Halley, Pierson and Schlager, 1984); and a par�ally buried paleocanyon was found in the western Straits of Florida (Denny, Aus�n and Buffler, 1994). At the �me that most of this work was done, subaerial exposure and erosion was not considered for features found at present day water depths between 500 and 3500 m. ...
... At the �me that most of this work was done, subaerial exposure and erosion was not considered for features found at present day water depths between 500 and 3500 m. Paull (1990a) proposed that the Florida escarpment canyons were caused by hypersaline water sapping; Land and Paull (2000) interpreted deep water sinkholes to be the result of brine and fresh water mixing; Halley et al. (1984) postulated that fresh water diagenesis of carbonates near the base of the Campeche escarpment was also due to brine-fresh water mixing; and Denny et al. (1994) ascribed excava�on of the Straits of Florida paleocanyon to oceanic currents. These explana�ons are incompa�ble with a) the low energy in the deep marine environment, and b) the difficulty of fresh water aquifers reaching the deep ocean without having a nearby elevated area to generate a hydraulic head. ...
... Evidence for extensive Paleocene-Eocene karst across much of Florida is the cavernous "Boulder bed" zone widely u�lized for urban wastewater injec�on (Winston, 1995). The kars�ng is also represented by sinkholes in present day water deeper than the 130 m Pleistocene lowstand (Land and Paull, 2000). ...
... The abundance of fine-grained sediment of shallow water carbonates successions which have low susceptibility to liquefaction hinders the development of soft-sediment deformation structure (Daley, 1972;Gibert et al., 2005;Alsop and Shumel, 2011;Moretti et al., 2016;Basilone et al., 2016a;Basilone, 2017). Nevertheless, the triggering mechanisms of soft-sediment deformation structure are various, including the instability of sediment floor (Daley, 1972) by the presence of local slope and chemical process which are related to evaporate and carbonate (desiccation and karstic features) (Handford, 1986;Demicco et al., 1994;Land and Paull, 2000;Michaud et al., 2005) and seismic activity (Kahle, 2002;Jewell and Ettenshon, 2004;Spalluto et al., 2007;Mastrogiacomo et al., 2012). ...
Soft-sediment deformation structure crops out in the Upper Triassic carbonate succession of Messaoudi Formation in the north eastern of Tataouine basin (south eastern Tunisia). The deformed interval is about 10 m thick and tack place between shallow-water limestone and stromatolitic bed. Soft-sediment deformation structures (slump), supareted by undeformed beds include boudins, pinch-and-swell structure, and normal faults and folded structures. Observations and measurements of the deformed structure and bed thickness of hinges and limbs indicate that all the deformed structures are related to slump structure, which affects unconsolidated sediment in the local paleo-slope. The internal mechanisms are ruled out due to the absence of features (high sediment rate, traction feature, chemical process). The slump was triggered by external mechanisms; tectonic effects related to the reactivation of EW faults during the opening movements of the paleotethys. These tectonic events generat a moderat seismic activity wich affected unconsolidated sediment.
... Gomberg (1976) distinguished three main physiographic sections: a Karst-like region on the eastern Terrace, a Central region, and a Lower region (Fig. 5). The karst-like topography of the eastern section (our East Terrace Community) exhibits sets of knolls and ridges reaching 50-120 m above and basins as deep as 135 m below the surrounding bottom, whereas the Lower region (our Lower Terrace Community) is characterized by numerous sinkholes and isolated mounds, or bioherms (Jordan et al., 1964;Land and Paull, 2000;Reed et al., 2005Reed et al., , 2006. Our analyses support these divisions in that the benthic communities on the East Terrace chiefly clustered separately from the ones in the West Terrace. ...
The Pourtalès Terrace is an exposed hard-bottom platform located south of the Florida Keys in 200–450 m depth with a diverse deep-sea coral ecosystem dominated by stylasterid hydrocorals, octocorals, and sponges that supports recreational and commercial fisheries. Portions of the Terrace have been designated as managed areas in the absence of detailed habitat maps, which hampers identifying ecological benefits derived from such management actions. Here we report analyses of historic Terrace physiographic and geologic data with more recent high-resolution bathymetric and benthic data to statistically derive a benthic community characterization across the Terrace. Multivariate analyses of faunal density from 42 standardized sites showed spatially distinct communities: East Terrace, West Terrace, Upper Terrace Edge, Sinkholes and Lophelia Coral Mound (the southernmost record of this habitat in the continental U.S.). These corresponded to physiographic divisions into an Upper Terrace comprised of Central and Karst-like regions, and Lower Terrace. A detailed description of these communities is provided. This study presents new insights into the Terrace benthic community spatial arrangement and is a necessary step towards facilitating benthic mapping. Our recommendations highlight the information needed for benthic habitat map creation and collecting data to determine if current conservation boundaries match management goals.
... Dissolution of carbonates occurs predominantly in sub-aerial environments with meteoric diagenetic processes (Loucks, 2000;Santo et al., 2010) or in submarine conditions if related to ascending brines with a strong corrosive potential (Smart et al., 1988) or brackish fluid mixing, as documented offshore Florida (Land and Paul, 2000). Several studies have also described massive collapses associated with solution and development of karst in underlying evaporite layers (Broughton, 2017;Frumkin et al., 2011;Friedman, 1997). ...
Large discordant breccia bodies (LDBBs) are important record keepers of the tectonic and gravitational evolution in platform-to-basinal settings, and have important implications for fluid-flow migration and compartmentalization of tight carbonate reservoirs. In the Gargano Promontory of southern Italy, LDBBs occur within a Cretaceous slope and basinal carbonate succession. We use field mapping and Unmanned Aerial Vehicle (UAV) -based Structure from Motion (SfM) Photogrammetry to document otherwise inaccessible cliff-side exposures of seismic-to subseismic-scale vertical discordant breccias. LDBBs are up to 50 m in width, more than 80 m in height and display internal chaotic or aligned clast fabrics. The formation which generally contains the LDBBs is characterized by beds of cherty pelagic limestone intercalated with calcarenites, calciturbidites and horizons of mass transport deposits. The mass-transport deposits can be correlated across the chaotic breccia bodies, indicating only slight or no vertical displacement across the adjacent walls. The bases of the breccia bodies are always hidden below current sea level, while the rarely exposed tops are capped by bedded intervals of the host rock formation. Timing and origin of the studied breccias were determined using several lines of evidence, such as stratigraphic provenance of clasts in breccias, mutual relationships of structural and sedimentologic features, and previous studies which establish that the age of dolomitizing cements in the LDBBs formed at different times and by different processes (fault shearing and solution collapse). This work investigates the size, shape and geometry of these breccia bodies whilst also providing cm-scale detail of the textural features in otherwise inaccessible outcrops. We suggest that breccias formed as a result of solution exploiting a pre-existing fracture network characterized by large-scale vertical strike-slip or oblique-slip faults. Initial displacement along these faults created a wide fault damage zone, where fluid migration was later focused to create a zone highly susceptible to solution and subsequent periodic sidewall collapse.
