During the last interglacial (LIG) the volume of additional water in the world's oceans was large enough to raise global sea levels about 6–9 m higher than present levels. However, LIG sea levels vary regionally and those regional differences hold clues about the past distribution of ice sheets and local rates of subsidence and tectonic uplift. In this study, I used a standardized database template to review and summarize the existing constraints on LIG sea levels across the northern Gulf of Mexico and Caribbean shoreline of the Yucatán Peninsula. In total, I extracted 32 sea-level indicators including the insertion of 16 U-series ages on corals, 1 electron spin resonance age, 2 amino acid racemization ages, and 26 luminescence ages. Most dated sea-level indicators for the northern Gulf of Mexico are based on optically stimulated luminescence (OSL) ages of beach deposits of a mappable LIG shoreline. This shoreline extends from the Florida Panhandle through south Texas but is buried or removed by the Mississippi River across most of Louisiana. A similar feature is observed in satellite images south of the Rio Grande within the Mexican portions of the Gulf of Mexico but has yet to be dated. Elevations measured on portions of this feature close to the modern coast point to sea levels less than 1 m to
Across the Yucatán Peninsula, U-series dating of corals has provided the main index points for LIG sea levels. Other carbonate coastal features such as beach ridges and eolianites have also been described but rely on corals for their dating. The maximum elevation of the LIG coral-based relative sea-level (RSL) estimates decrease from around
The database described in this paper is available open access in spreadsheet format as Simms (2020), at this link:
During the last interglacial (LIG) Earth experienced global sea-surface temperatures on average
This work is part of the World Atlas of Last Interglacial Shorelines (WALIS), a community effort to construct a database of LIG relative sea-level indicators (
Map illustrating the location of the figures and locations mentioned in the text. LA: Louisiana; MS: Mississippi; AL: Alabama; FL: Florida.
The region of interest covered by this review contains two contrasting types of coastlines with respect to depositional settings and climate at the present and by extension during the LIG. Along the northern and western Gulf of Mexico, the coastline is dominantly siliciclastic with the LIG paleoshorelines marked by sandy paleo-raised beaches and potentially paleo-barrier islands (Price, 1933; Otvos, 1972b). Across the northern Gulf of Mexico, tides are diurnal and microtidal with tidal ranges generally 0.4 to 0.6 m but approaching 1 m within the Florida Panhandle (Stumpf and Haines, 1998; Livsey and Simms, 2013). Wave energy is generally low with wave heights averaging less than 1 m (Hwang et al., 1998), with the exception of during the passage of tropical cyclones, which enter the Gulf of Mexico on average every 1.6 years (Parisi and Lund, 2008), and winter cold fronts originating from North America. The climate across the northern Gulf of Mexico varies from arid to semi-arid along the US–Mexico border to humid temperate conditions along the eastern Gulf of Mexico (Thornthwaite, 1948).
The northern Gulf of Mexico is a passive margin, but, locally, Quaternary growth faults have been identified (Yeager et al., 2019). However, most known active growth faults are located seaward of the LIG shoreline, although anthropogenic activities such as groundwater and hydrocarbon withdrawal have potentially contributed to motion along faults landward of the modern shoreline (White and Morton, 1997 ; Qu et al., 2015). The passive margin is experiencing subsidence across most of the coastline. Attempts to quantify long-term subsidence usually rely on the elevation of the LIG (Paine, 1993; Simms et al., 2013) and are on the order of 0.05
Farther to the south along the Yucatán Peninsula and south to Honduras, the coastline is marked by increasingly more tropical climates as well as a mixed siliciclastic–carbonate coastline with LIG shorelines largely marked by fossil coral reefs and eolianites (Ward and Brady, 1979; Gischler and Hudson, 1998; Blanchon et al., 2009). The coastline is more carbonate-dominated at the northeastern tip of the Yucatán Peninsula with an ever increasing influence of siliciclastics to the south such that within Honduras the carbonate environments are restricted to the offshore islands of Roatán and the Swan islands (Fig. 1). This change is a reflection of the Maya Mountains and interior highlands that hug the shore across portions of southern Belize and Honduras, respectively, as the coastline leaves the stable platform of the Yucatán Peninsula and nears the orogenic belts marking the North American–Caribbean plate boundary (Pindell and Barrett, 1990). To the north, for most of its extent, the Gulf of Mexico and northern Yucatán shorelines are located along a passive margin except near the southwestern corner of the Gulf of Mexico where the Trans-Mexican Volcanic belt butts up against the Gulf (Ortega-Gutierrez et al., 1992). Like the northern Gulf of Mexico, the tidal range is relatively low, with values ranging from 0.1 to 0.8 m (Rankey et al., 2021). Trade winds drive the dominant wind direction from the northeast with average offshore wave heights of
Across the northern Gulf of Mexico, Price (1933) was one of the first to recognize the raised beach/barrier island shoreline across Texas now recognized as the Sangamon (LIG) shoreline. MacNeil (1949) mapped similar Pleistocene raised beach/barrier islands across western Florida. However, MacNeil (1949) separated features of similar age into more than one stage of Pleistocene shoreline development and potentially mixed others (Otvos, 1995). Over the next several decades discussion continued over the age of the raised beach/barrier island features mapped by Price (1933) and MacNiel (1949), with some suggestions of a mid-Wisconsin (
Across the Yucatán, most early work on the carbonate shorelines was conducted by graduate students of J. L. Wilson of Rice University in the 1960s and 1970s (Ward, 1985). Purdy (1974) was one of the first to describe in situ corals of
In the following discussion, I use “WALIS RSL ID” followed by a number to identify each of the RSL indicators discussed in the text that has been entered into the WALIS database. The number corresponds with the WALIS database identification numbers. Similarly, I use “WALIS U-series ID” followed by a number to identify each of the RSLs identified from a single coral discussed in the text that has been entered into the WALIS online database. I also use “WALIS LUM ID”, “WALIS ESR”, or “WALIS AAR ID” followed by a number to reference optically stimulated luminescence ages, electron spin resonance ages, or amino acid racemization ages, respectively, discussed in the text that have also been entered into the WALIS online database.
The LIG shoreline across most of the northern Gulf of Mexico formed what is locally known as the Ingleside shoreline across Texas (Price, 1933) and the Gulfport shoreline across Mississippi, Alabama, and the panhandle of Florida. Buried presumed LIG deposits have been identified beneath the Mississippi River (e.g., Prairie Terrace; Fisk, 1944), but their sea-level significance is not well constrained (Otvos, 2005), and their elevations are likely significantly contaminated by sediment-loading-induced subsidence.
Along the Texas coast, the Ingleside shoreline is composed of a
Aerial photographs illustrating well-preserved beach ridges on the LIG shorelines within
The elevation of the Ingleside shoreline varies across its expression in Texas. Paine (1993) provided one of the first attempts at a rigorous quantitative estimate of RSL change at the last interglacial based on the Ingleside shoreline in Texas. In order to quantify subsidence across the Gulf of Mexico at different timescales, Paine (1993) noted the maximum elevation of shell horizons in boring descriptions from a compilation of older geotechnical reports was 2 m above modern sea level (general definition), with the highest in situ oysters (
Map of the Texas coast of the northwestern Gulf of Mexico showing the locations of the LIG Ingleside shoreline segments (blue text) and modern barrier islands (red text) discussed in the text with their average elevations. Also shown as green stars and black text are the optically stimulated luminescence ages obtained from the Ingleside shoreline.
As it is difficult to assign a strict indicative meaning to the Ingleside deposits as presently described, Simms et al. (2013) took a different approach to estimate paleo-RSL from the Ingleside by mapping the feature in a geographical information system (GIS) software package using soil survey maps and determining its elevation from the United States Geological Survey's (USGS) National Elevation Dataset (NED) digital elevation model (DEM). The NED has a published 95th percentile confidence level of 3.0 m (Gesch et al., 2014) but is more accurate (1.94 m) along regions surveyed by lidar, which includes most of the coastal counties (Gesch et al., 2014). Assuming the Ingleside was a LIG barrier island (Price, 1933; Paine, 1993) similar to the modern barrier islands of the Texas Gulf Coast, which is still a matter of discussion (Otvos, 2018, 2020), Simms et al. (2013) subtracted the average elevation of the closest modern equivalent barrier island from the elevation of each of the Ingleside barrier island segments of the Texas coast. Assuming the preserved Ingleside deposits formed when RSLs reached their highest during the LIG, as many of them contained preserved beach ridges (Fig. 2b), and erosion led to little loss in elevation of the feature, the resulting calculations lead to a range of RSL differences at the LIG across the Texas coast from a high of 7.2 m for the Vidor segment (WALIS RSL ID no. 778) to a low of 0.2 m for the Hoskins Island segment (WALIS RSL ID no. 774) (Fig. 3). However, the Vidor segment (Orange of Otvos, 1997) and the Hoskins Island segments may not represent barrier islands (Otvos, 1997) and have yet to be dated. If the Vidor segment represents a different age or depositional environment, then the highest non-contested LIG barrier island in East Texas would be the Fannett segment, which has well-preserved beach ridge features, with an average elevation of
Simms et al. (2013) assigned an elevation error in their analysis of 1 standard deviation of the DEM pixel elevations of the Ingleside segment and modern islands. They also did not include an error term for the uncertainty in the DEM. Given the assumptions in their analysis of no erosion of the LIG features (either fluvial or eolian deflation), as well as similar wave and wind climates and coastal sediment supplies at the LIG compared to today (and thus average barrier island elevations), this study takes a more conservative approach to the error by increasing the error for each of the estimates of Simms et al. (2013) to 2 standard deviations plus an additional error term of
Topographic profiles through selected portions of the Texas coast illustrating the elevation and width differences between the Ingleside and modern barrier islands. See Fig. 3 for general locations.
The Gulfport shoreline, in some locations also known as the Pamlico shoreline, has a similar expression and elevation as the Ingleside shoreline of Texas (Otvos, 1972b). It rises between
The original publications of Blum et al. (2003) and Otvos (2005) provide little information about the elevations of the Gulfport segments dated. However, Rodriguez and Meyer (2006) did collect ground-penetrating radar (GPR) profiles through the beach ridges dated by Blum et al. (2003) on Fort Morgan Peninsula but do not show the lines collected over the LIG-aged deposits. However, they do report that the LIG (Sangamon in their original publication) beach ridges (sensu Otvos, 2020) were 4–5 m in height, while the modern beach ridges were 2–3 m in height. I thus assign a modern analogue value of
As many of the LIG sites along the northeastern Gulf of Mexico lack quantitative estimates of the elevation of RSL at the LIG, and assigning an indicative meaning to the deposits as currently described remains difficult, I followed the methods of Simms et al. (2013) to assign a RSL elevation for the LIG. This estimate was determined by subtracting the average elevations of the closest modern barrier islands from the average elevations of the six segments of the Gulfport shoreline dated with the assumption that they too represented barrier islands (Figs. 5 and 6; Table 1). Mapping the margins of the LIG features along the northeastern Gulf of Mexico using soil surveys is not as straightforward as it is along the Texas coast due to the sandier nature of much of the northeastern Gulf of Mexico coastal plain and shelf (the Gulfport shoreline is not bordered along its inland margins by a muddy unit as the Ingleside is in Texas). From this approach I obtained RSL estimates at the LIG for the English Lookout, Gulfport/Biloxi, Gautier, Fort Morgan Peninsula, Gulf Breeze (Florida), and Apalachicola sections of the Gulfport shoreline as
Last interglacial Gulf of Mexico shoreline elevations and relative sea levels.
Unlike many of the barrier islands in Texas, Fort Morgan Peninsula displays a morphology suggestive of a complex and multi-stage evolution. Its complex architecture reveals an additional potential pitfall in using the average elevation of the LIG and modern barrier islands to determine the RSL difference at the LIG (Fig. 7). Fort Morgan Peninsula experienced at least three phases of Holocene growth (Little Point Clear, Edith Hammock, and modern spit; Rodriguez and Meyer, 2006; Blum et al., 2003; Fig. 7). Their elevations vary more among the three Holocene phases than with the LIG (Fig. 7), likely reflecting the variability in sea levels and wave climates at the time of their formation (e.g., Rodriguez and Meyer, 2006; Donnelly and Giosan, 2008). In addition, the barrier island geomorphology is not as apparent for the Gulfport shoreline segments as it is for the Ingleside, nor are the analogue barrier islands as similar in width as the Ingleside segments from Texas. Thus using the larger error bars for this analysis seems warranted.
Topographic profiles through selected portions of the Mississippi–Alabama–Florida coast illustrating the elevation and width differences between the Gulfport and modern barrier islands. See Fig. 5 for general locations.
Digital elevation model and topographic profiles through the three Holocene (A–A
A feature similar to the Ingleside appears to continue south along the Gulf of Mexico south of the USA/Mexico border to Soto la Marina, Tamaulipas (Price, 1958), and possibly farther south into Veracruz-Llave but has yet to be dated (Wilhelm and Ewing, 1972; Hernandez-Santana et al., 2016; Figs. 1 and 2). Near Soto la Marina these features are dotted with small ponds similar to the blowout features common to the Ingleside across Texas (Price, 1933; Otvos, 2004; Simms et al., 2013). However, their LIG age has not been verified, and thus no data for these features have been input into the WALIS database. More work mapping and dating this potential LIG shoreline is warranted.
Dated LIG beach ridges and reefs have been identified and studied across many locations of the Yucatán coastlines of Mexico and neighboring Belize (Fig. 8). Additional constraints on LIG sea levels from the Yucatán have been reported based on speleothems within caves near the Mexican LIG beach ridges and coral reefs. These are the subject of a separate compilation within WALIS but are briefly discussed with reference to the other data reviewed in this study.
Map showing the location of LIG shoreline features of the Mexican Yucatán Peninsula. The red strip is the location of the LIG calcarenite beach ridge as mapped by Ward and Brady (1979), the green stars are the locations of the U-series ages collected by Szabo et al. (1978), and the yellow triangle is the location of the Blanchon et al. (2009) study. Also shown as a blue box is the general location of the speleothems studied by Mosey et al. (2013).
A prominent set of LIG calcarenite beach ridges extend across much of the northeastern portion of the Yucatán (Szabo et al., 1978; Ward and Brady, 1979). The calcarenite beach ridge plain extends 150 km from Cancún to Xel-Há with a width of 0.5 to 4 km and thicknesses ranging from 3 to 10 m (Ward and Brady, 1979) (Fig. 8). The strand plain is underlain by a caliche developed over older Pleistocene coral-bearing limestones (Fig. 9). In addition, a few isolated
Schematic cross section through the LIG coastline of the Yucatán Peninsula of Mexico (redrawn from Szabo et al., 1978). See Fig. 8 for a general location.
Although the calcarenite beach ridges reached elevations of 10 m (Szabo et al., 1978), they are capped by an eolianite facies (Fig. 9). The base of the calcareous beach facies with cross-bedding lies at elevations of
Ward and Brady (1979) also noted an extensive tract of Pleistocene coral reefs seaward of the calcarenite beach ridges. The reef tract contains in situ corals of
Schematic cross section through the LIG reef tracts located at Xcaret, Mexico, as composed by Blanchon et al. (2009). LRT is lower reef tract, URT is upper reef tract, and A.p. is
The well-documented framework of the ancient reef systems allowed for the identification of the different segments of the LIG reef at Xcaret (Jordán-Dahlgren, 1997; Blanchon et al., 2009; Blanchon, 2010) (Fig. 10). The LIG reef crest currently lies at an elevation up to
Inland and only a few tens of kilometers to the south of these LIG calcareous beach ridges and coral reefs, Moseley et al. (2013) surveyed and dated 10 subaerially formed speleothems from the cave networks south of Xel-Há in Quintana Roo, Mexico (Fig. 8). A total of 50 U-series ages were obtained from these speleothems. The ages ranged from
Within Belize, LIG corals have been found onshore at Ambergris Cay as well as within drill core beneath the Turneffe islands, Lighthouse Reef, and Glover's Reef (Gischler and Hudson, 1998; Gischler and Lomando, 1999; Gischler et al., 2000) (Fig. 11). These corals have been dated using U-series ages by Gischler et al. (2000) and Mazzullo (2006). In addition, Mazzullo (2006) obtained two additional amino acid racemization ages from the corals.
Map of the Belize and Honduras coastline showing the locations of U–Th (stars), amino acid racemization (shown as triangles), and electron spin resonance (shown as hexagons) ages discussed in the text. Ages in green denote the work of Gischler et al. (2000). Ages shown in yellow denote the work of Mazzullo (2006), and ages shown in red denote the work of Cox et al. (2008).
U-series ages obtained from Reef Point at Ambergris Cay dated to
The other 6 U-series ages of Gischler et al. (2000) were obtained from cores taken on Glover's, Lighthouse, and Turneffe reefs (Fig. 11). Neither of the two samples obtained from cores on Glover's Reef was considered reliable by Gischler et al. (2000) as they both appeared too old. One dates to
The elevation of the top of the Pleistocene section beneath the reefs is much lower in Belize than those farther north along the Yucatán Peninsula near Cancún, Mexico (Gischler et al., 2000). In addition, the top of the Pleistocene appears to deepen to the south and east (Gischler et al., 2000). Gischler et al. (2000) attribute this to tectonic subsidence as the margin trails off into the adjacent Cayman Trough. This interpretation is supported by evidence of neotectonic activity found within Holocene coastal successions (McClowsky and Liu, 2013) and deeper (Lara, 1993), but the accuracy of the ages of the corals from Gischler et al. (2000) is still a matter of discussion (MacIntyre and Toscano, 2004). MacIntyre and Toscano (2004) suggest the possibility that the ages are erroneously too old given their relatively low aragonite percentages and elevated
Only a handful of possible LIG deposits have been located in Honduras. Cox et al. (2008) obtained an ESR age (WALIS ESR ID no. 102) on an uplifted fossil reef on the western tip of Roatán island (WALIS RSL ID no. 450; Fig. 11). The poor preservation of the reef made it difficult to ascertain the elevation of RSL at the time of deposition, and the corals are of unknown species. Late Pleistocene limestones with in situ specimens of
With the exception of the new work in this study and the works of Burdette et al. (2012) and Simms et al. (2013), little detail is given as to the datums of the LIG shoreline elevations. This study, Burdette et al. (2012), and Simms et al. (2013) utilize the North American Vertical Datum of 1988 (NAVD88;
The rest of the studies defined mean sea level according to the generic definition and provided little detail as to how the elevations were physically measured. Moseley et al. (2013) used a depth gauge, while Burdette et al. (2012) and Simms et al. (2013) used high-resolution lidar with accuracies of 0.25 cm. However, within the entire region, the tidal range is less than 1 m, with some areas (e.g., the Yucatán) experiencing a tidal range of less than 0.15 m (Blanchon et al., 2009), and thus any errors associated with estimating the mean tide level are likely minimal and less than 1 m.
With the exception of the Honduran coast and possibly the eastern Gulf of Mexico (Otvos, 1981), the currently-dated LIG sites across the northwestern Gulf of Mexico and northwestern Caribbean are all subject to subsidence rather than tectonic uplift. Within the northwestern Gulf of Mexico subsidence appears to increase basinward (Simms et al., 2013), and along the Belize coast it appears to increase to the south and east (Gischler et al., 2000). However, constraining the magnitude of subsidence independent of the LIG elevations has remained problematic as most studies use the elevation of the LIG shoreline to determine subsidence (e.g., Paine, 1993; Gischler et al., 2000; Simms et al., 2013). Studies independent of the LIG shoreline elevation are needed to determine subsidence rates and hence correct LIG sea levels from its influence. GPS surveys provide some hope, but issues related to anthropogenic groundwater and hydrocarbon extraction are not always easy to correct for and likely dominate the subsidence signal at GPS timescales. Groundwater and hydrocarbon extraction are particularly relevant across the northern Gulf of Mexico (Paine, 1993; White and Morton, 1997; Morton et al., 2006; Chan and Zoback, 2007; Qu et al., 2015).
With the exception of the study by Blanchon et al. (2009) most of the studies of the LIG shoreline across the Gulf of Mexico and western Caribbean have been too coarse to test for fluctuations in LIG sea levels. Most ages have only been precise enough to establish a LIG age and not necessarily when during the LIG the feature was deposited. Neither have the deposits lent themselves to reconstructing fine-scale fluctuations in sea levels during the LIG, particularly within the siliciclastic shorelines of the northern Gulf of Mexico. The carbonate systems of the Yucatán Peninsula may provide more opportunities for testing for sea-level fluctuations during the LIG. The exception is the work of Blanchon et al. (2009). They found two distinct reef tracts that they argue represent an earlier, lower phase of LIG sea levels at
Shorelines and other coastal features from highstands in sea levels prior to the LIG have been reported from the northern Gulf of Mexico but have yet to be dated (Winker and Howard, 1977; Donoghue and Tanner, 1992). The most studied and best preserved are those within the panhandle of Florida near the Apalachicola delta, where Winker and Howard (1977) and Donoghue and Tanner (1992) describe two older terrace and shoreline sets – the Gadsden and Wakulla sequences, the former of which may correspond to multiple highstands (Winker and Howard, 1977). However, some discussion has arisen as to their origin, with some studies attributing these features to non-marine sources (Otvos, 1995) as very little detailed sedimentology has been conducted on the features to show their marine origins. In addition to the purported marine shorelines, the mapping of alluvial terraces suggests a progradational nature to much of the coastline, with earlier phases of transgression and regression leading to the development of multiple periods of coastal plain aggradation (Otvos, 2005). However, the alluvial terraces have only been preliminarily dated (e.g., Otvos, 2005), and more work is required to nail down their ages and relationship to former sea levels.
Older Pleistocene reefal units are present across the Yucatán Peninsula (e.g., Ward and Brady, 1979; Ferro et al., 1999; Gischler et al., 2010) but have not been well dated or been used to constrain the elevations of pre-LIG highstands. Speleothems that may help constrain older sea levels dating as far back as MIS11 have been identified within Quintana Roo (Steidle et al., 2020). Those results have yet to be published outside of meeting abstracts but are likely forthcoming.
Middle-to-late Holocene sea levels are well constrained in the region with several site-specific reconstructions and compilations available for the northern Gulf of Mexico (Tornqvist et al., 2004; Simms et al., 2007; Milliken et al., 2008; Livsey and Simms, 2013) as well as the Caribbean (Toscano and Macintyre, 2003; Gischler and Hudson, 2004; Khan et al., 2017). The records become sparser for the early Holocene and late glacial periods. One discussion that has repeatedly resurfaced within the northern Gulf of Mexico is the possibility of a mid-Holocene highstand (e.g., Tanner et al., 1989; Blum et al., 2002) but currently appears to have fallen out of favor (Otvos, 2001; Simms et al., 2009).
The amount of uncertainty in the age and elevation of the LIG sea-level indicators varies by location. The shoreline along the northern Gulf of Mexico is likely LIG in age but very few of the existing ages have the accuracy or precision to determine when within the generally accepted 115–129 ka time period it formed. The average error of the 24 OSL measurements thought to have been derived solely from LIG deposits is 10.4 ka, which is far too large to determine when within the LIG the feature(s) formed. Because few of the studies on the LIG shoreline to date have included detailed facies descriptions of the shoreline deposits, the elevations are probably accurate to within 2–3 m of the former highstand elevation and likely larger for the DEM-derived elevations given the assumptions related to analogous LIG and modern barrier islands. This latter assumption includes uncertainties related to post-depositional erosion, similarities in wave climate and sediment supply, differences in transgressive versus regressive architectures, the interpretation of the LIG shorelines as paleo-barrier islands, and specific timing of deposition with respect to the true highstand during the LIG. In addition, the lack of estimates of subsidence independent of the LIG elevation at each site also contributes to the uncertainty of LIG RSLs along the Gulf of Mexico. This uncertainty due to subsidence is likely on the order
The data from the northeastern Yucatán Peninsula probably provide the best estimates of RSL during the LIG for the region surveyed in this study. The analysis of Blanchon et al. (2009) includes the most detailed facies analysis of coral reef deposits within the region, leaving LIG RSL elevation estimates to
The Gulf of Mexico and northwestern Caribbean Sea last interglacial sea-level database is available open access, and updated as necessary, at the following link:
The LIG shoreline is well expressed over portions of the northern and western Gulf of Mexico and the eastern Yucatán Peninsula. The Gulf of Mexico shorelines are largely the remnant of sandy shorelines and barrier islands, while those of the Yucatán Peninsula are both coral reefs and calcarenite beaches. The elevation of these features suggests local LIG sea levels were between
The supplement related to this article is available online at:
ARS read the papers, compiled the data, conducted the ArcGIS analysis, and wrote the manuscript.
The author declares that there is no conflict of interest.
This article is part of the special issue “WALIS – the World Atlas of Last Interglacial Shorelines”. It is not associated with a conference.
I would like to thank Ian Baxter for taking an early look at the LIG elevations across the northeastern Gulf of Mexico and Paul Blanchon for sharing some of his original figures from Xcaret. John Anderson, Tony Rodriguez, and Regina DeWitt are thanked for their discussions regarding the LIG shorelines across the northwestern Gulf of Mexico. Paul Blanchon and Michael O'Leary provided insightful official reviews while Barbara Mauz also provided helpful comments. The data used in this study were compiled in WALIS, a sea-level database interface developed by the ERC Starting Grant WARMCOASTS (ERC-StG-802414), in collaboration with the PALSEA (PAGES/INQUA) working group. The database structure was designed by Alessio Rovere, Deirdre Ryan, Thomas Lorscheid, Andrea Dutton, Peter Chutcharavan, Dominik Brill, Nathan Jankowski, Daniela Mueller, Melanie Bartz, Evan Gowan, and Kim Cohen.
This paper was edited by Deirdre Ryan and reviewed by Paul Blanchon and Michael O'Leary.