Episodic postglacial deltaic pulses in the Gulf of Cadiz: Implications for the development of a transgressive shelf and driving environmental conditions

The postglacial sea-level rise after the Last Glacial Maximum provided ideal conditions to study the transgressive sedimentary response to sudden shelf flooding driven by different rates of sea-level rise. In this study, a high-resolution seismic stratigraphic interpretation and sedimentological analysis were conducted on data from the northern Gulf of Cadiz continental shelf (SW Iberian Peninsula), in order to: 1) understand the succession of sedimentary processes during each shelf flooding episode and 2) explore the significance of variable rates of sea-level rise, sediment fluxes, and climatic conditions on the development of postglacial deposits. Four backstepping seismic postglacial transgressive units (PTUs; 4 to 1 from oldest to youngest) that are linked to the retreating mouth of the Guadiana River were interpreted. Together, these seismic units display a wedge-shape geometry, are located over the inner to middle shelf, and overlie a regional unconformity formed during the Last Glacial Maximum. Each PTU can be divided into several sub-units with distinctive seismic facies that have a similar stratigraphic organization. Each PTU contains lower sub-units that are composed of low-angle tangential-oblique clinoforms. The clinoforms are locally topped by a channelized sub-unit. The distal and/or lateral parts of the clinoforms are occasionally buried by sheet-like semitransparent subunits. The uppermost sub-units are present over the proximal and central parts of each seismic unit and are also sheet-like. PTUs can also be subdivided and described sedimentologically. Fine-grained sands with intercalated silty layers dominate the lower part of each PTU (lower clinoform sub-units). The upper part of each PTU (upper sheet-like sub-units) is characterized by reworked facies, composed of highly fragmented bioclasts within a mixture of silt and coarse to medium sand. Finally, mud deposits occur as a sediment drape over the PTUs. The internal structure of each PTU reveals several phases of development under a general process of transgressive submergence in which both coastal and marine deposits were formed and eventually preserved. The initial phase involved the development of coarse-grained deltas in shallow water, which were locally eroded by a network of distributary channels. In a transitional phase, the infilling of distributary channels and the offshore export of fine-grained sediments is related to a change in sediment sources, possibly triggered by enhanced hydrodynamic processes. The final phase involved the reworking of fluvio-deltaic sediments by shoreface processes to generate a sediment sheet. Age correlation with a suite of postglacial sea-level curves indicates that the formation of the postglacial transgressive deposits is bracketed between 14 ka and 9 ka. The studied deposits are related to a period of reduced sea-level rise, culminating in the Younger Dryas event (two oldest PTUs), and to phases of enhanced sea-level rise, such as Meltwater Pulse (MWP) 1B (two youngest PTUs). In spite of high rates of sea-level rise over MWP-1B, each PTU exhibits progradation and preservation of much of the delta. The preservation of progradational deltaic units is likely caused by increased sediment supply during progradational pulses. We suggest that those pulses of enhanced sediment fluxes during MWP-1B were strongly driven by the overall climatic conditions in the southwest of the Iberian Peninsula, probably resulting from enhanced rainfall runoff during humid periods and scarce land vegetation cover.

[1]  J. Cooper,et al.  Response of a wave-dominated coastline and delta to antecedent conditioning and fluctuating rates of postglacial sea-level rise , 2021 .

[2]  M. Caldara,et al.  Transgressive Architecture of Coastal Barrier Systems in the Ofanto Incised Valley and Its Surrounding Shelf in Response to Stepped Sea-Level Rise , 2020 .

[3]  J. Cooper,et al.  Relict and contemporary influences on the postglacial geomorphology and evolution of a current swept shelf: The Eastern Cape Coast, South Africa , 2020 .

[4]  Stephen P. Phillips,et al.  Tidal estuarine deposits of the transgressive Naturita Formation (Dakota Sandstone): San Rafael Swell, Utah, U.S.A. , 2020 .

[5]  H. Vital,et al.  Terraces, reefs, and valleys along the Brazil northeast outer shelf: deglacial sea-level archives? , 2020, Geo-Marine Letters.

[6]  J. Cooper,et al.  Construction and evolution of submerged deltaic bodies on the high energy SE African coastline: The interplay between relative sea level and antecedent controls , 2020, Marine Geology.

[7]  A. López-Quirós,et al.  What feeds shelf‐edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil , 2020, Basin Research.

[8]  D. Rooij,et al.  Review of the late Quaternary stratigraphy of the northern Gulf of Cadiz continental margin: New insights into controlling factors and global implications , 2019, Earth-Science Reviews.

[9]  J. Cooper,et al.  Outer- to inner-shelf response to stepped sea-level rise: Insights from incised valleys and submerged shorelines , 2019, Marine Geology.

[10]  O. Catuneanu.  Model-independent sequence stratigraphy , 2019, Earth-Science Reviews.

[11]  R. Anderson,et al.  Vegetation and geochemical responses to Holocene rapid climate change in the Sierra Nevada (southeastern Iberia): the Laguna Hondera record , 2018, Climate of the Past.

[12]  J. O. Morais,et al.  Transgressive deposits and morphological patterns in the equatorial Atlantic shallow shelf (Northeast Brazil) , 2018, Regional Studies in Marine Science.

[13]  N. Glasser,et al.  Late Quaternary meltwater pulses and sea level change , 2018, Journal of Quaternary Science.

[14]  F. Lobo,et al.  Hazard potential of widespread but hidden historic offshore heavy metal (Pb, Zn) contamination (Gulf of Cadiz, Spain). , 2018, The Science of the total environment.

[15]  B. Valero-Garcés,et al.  Early Holocene humidity patterns in the Iberian Peninsula reconstructed from lake, pollen and speleothem records , 2018 .

[16]  D. Rooij,et al.  Morphology of the last subaerial unconformity on a shelf: insights into transgressive ravinement and incised valley occurrence in the Gulf of Cádiz , 2018, Geo-Marine Letters.

[17]  E. Toldo,et al.  Sandy barrier overstepping and preservation linked to rapid sea level rise and geological setting , 2016 .

[18]  R. Sánchez-Leal,et al.  Spatial distribution and intra-annual variability of water masses on the Eastern Gulf of Cadiz seabed , 2016 .

[19]  A. Aksu,et al.  Early Holocene age and provenance of a mid-shelf delta lobe south of the Strait of Bosphorus, Turkey, and its link to vigorous Black Sea outflow , 2016 .

[20]  P. Relvas,et al.  Characterisation of coastal counter-currents on the inner shelf of the Gulf of Cadiz , 2016 .

[21]  G. Fontolan,et al.  Early cementation and accommodation space dictate the evolution of an overstepping barrier system during the Holocene , 2015 .

[22]  N. Driscoll,et al.  Continental shelf morphology and stratigraphy offshore San Onofre, California: The interplay between rates of eustatic change and sediment supply , 2015 .

[23]  C. Pellegrini,et al.  Anatomy of a compound delta from the post-glacial transgressive record in the Adriatic Sea , 2015 .

[24]  R. Ramella,et al.  Recognition of a drowned delta in the northern Adriatic Sea, Italy: Stratigraphic characteristics and its significance in the frame of the early Holocene sea-level rise , 2015 .

[25]  L. Del Río,et al.  Variability in storm climate along the Gulf of Cadiz: the role of large scale atmospheric forcing and implications to coastal hazards , 2015, Climate Dynamics.

[26]  Yanyan Ma,et al.  Sedimentary system response to the global sea level change in the East China Seas since the last glacial maximum , 2014 .

[27]  Christophe Morhange,et al.  Human influence and the changing geomorphology of Mediterranean deltas and coasts over the last 6000 years: From progradation to destruction phase? , 2014 .

[28]  K. Lambeck,et al.  Sea level and global ice volumes from the Last Glacial Maximum to the Holocene , 2014, Proceedings of the National Academy of Sciences.

[29]  O. Catuneanu,et al.  High-resolution sequence stratigraphy of clastic shelves I: Units and bounding surfaces , 2013 .

[30]  J. Dorador,et al.  Digital image treatment applied to ichnological analysis of marine core sediments , 2013, Facies.

[31]  C. Ramsey,et al.  Rapid coupling between ice volume and polar temperature over the past 150,000 years , 2012, Nature.

[32]  N. Driscoll,et al.  Transgressive deposits along the actively deforming Eel River Margin, Northern California , 2012 .

[33]  P. Challenor,et al.  Sea-level probability for the last deglaciation: A statistical analysis of far-field records , 2011 .

[34]  S. Porębski,et al.  Pleistocene to Holocene transition in the central basin of the Gulf of Thailand, based on geoacoustic survey and radiocarbon ages , 2011 .

[35]  A. Kettner,et al.  High-frequency sea level and sediment supply fluctuations during Termination I: An integrated sequence-stratigraphy and modeling approach from the Adriatic Sea (Central Mediterranean) , 2011 .

[36]  G. Hampson,et al.  Stratigraphic Architecture of a Net-Transgressive Marginal- to Shallow-Marine Succession: Upper Almond Formation, Rock Springs Uplift, Wyoming, U.S.A. , 2011 .

[37]  J. Benavente,et al.  Storm thresholds for the Spanish Gulf of Cádiz coast , 2012 .

[38]  H. Lantzsch,et al.  Sediment recycling and adjustment of deposition during deglacial drowning of a low-accumulation shelf (NW Iberia) , 2010 .

[39]  J. Grimalt,et al.  The last glacial–interglacial transition (LGIT) in the western mid-latitudes of the North Atlantic: Abrupt sea surface temperature change and sea level implications , 2010 .

[40]  E. Bard,et al.  Deglacial Meltwater Pulse 1B and Younger Dryas Sea Levels Revisited with Boreholes at Tahiti , 2010, Science.

[41]  A. Voelker,et al.  Sediment instability on the Portuguese continental margin under abrupt glacial climate changes (last 60 kyr) , 2009 .

[42]  J. Goff,et al.  Shallow stratigraphy and complex transgressive ravinement on the New Jersey middle and outer continental shelf , 2009 .

[43]  Peter J. Bradbury,et al.  The Last Glacial Maximum , 2009, Science.

[44]  J. Gutiérrez-Mas,et al.  Evidence of high‐energy events in shelly layers interbedded in coastal Holocene sands in Cadiz Bay (south‐west Spain) , 2009 .

[45]  G. Benito,et al.  Palaeoflood and floodplain records from Spain: Evidence for long-term climate variability and environmental changes , 2008 .

[46]  J. Storms,et al.  Coastal dynamics under conditions of rapid sea-level rise: Late Pleistocene to Early Holocene evolution of barrier–lagoon systems on the northern Adriatic shelf (Italy) , 2008 .

[47]  M. Tesson,et al.  Variability of the transgressive stacking pattern under environmental changes control: Example from the Post-Glacial deposits of the Gulf of Lions inner-shelf, Mediterranean, France , 2008 .

[48]  Ó. Ferreira,et al.  Beach morphodynamic impact on a macrobenthic community along a subtidal depth gradient , 2007 .

[49]  M. Taviani,et al.  Late Glacial to Preboreal sea-level rise recorded by the Rhône deltaic system (NW Mediterranean) , 2007 .

[50]  T. Boski,et al.  Palynological evidence for environmental and climatic change in the lower Guadiana valley, Portugal, during the last 13 000 years , 2007 .

[51]  J. Woo,et al.  Development of depositional systems in the southeastern Yellow Sea during the postglacial transgression , 2007 .

[52]  M. Taviani,et al.  Sand bodies at the shelf edge in the Gulf of Lions (Western Mediterranean): Deglacial history and modern processes , 2006 .

[53]  W. Peltier,et al.  Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record , 2006 .

[54]  M. Field,et al.  Shallow stratigraphy and sedimentation history during high-frequency sea-level changes on the central California shelf , 2006 .

[55]  A. Maestro,et al.  The contourite depositional system of the Gulf of Cádiz: A sedimentary model related to the bottom current activity of the Mediterranean outflow water and its interaction with the continental margin , 2006 .

[56]  J. D. Río,et al.  Water mass circulation on the continental shelf of the Gulf of Cadiz , 2006 .

[57]  G. Benito,et al.  The Holocene fluvial chronology of Spain: evidence from a newly compiled radiocarbon database , 2006 .

[58]  P. Strat,et al.  High resolution stratigraphy and evolution of the Rhône delta plain during Postglacial time, from subsurface drilling data bank , 2005 .

[59]  G. Jouet,et al.  Seismic stratigraphy of the Deglacial deposits of the Rhone prodelta and of the adjacent shelf , 2005 .

[60]  H. Tur,et al.  Evidence and implications of massive erosion along the Strait of İstanbul (Bosphorus) , 2005 .

[61]  Hilary Clement Olson,et al.  Recent and modern marine erosion on the New Jersey outer shelf , 2005 .

[62]  J. Milliman,et al.  Holocene development of the Yellow River's subaqueous delta, North Yellow Sea , 2004 .

[63]  J. Dias,et al.  Contrasting styles of the Holocene highstand sedimentation and sediment dispersal systems in the northern shelf of the Gulf of Cadiz , 2004 .

[64]  R. Telford,et al.  The intercept is a poor estimate of a calibrated radiocarbon age , 2004 .

[65]  F. Lobo,et al.  Sedimentological and paleoenvironmental characterisation of transgressive sediments on the Guadiana Shelf (Northern Gulf of Cadiz, SW Iberia) , 2004 .

[66]  M. Tesson,et al.  Analysis of the postglacial deposits of the Rhône shelf (golfe du Lion). Implementation to the study of the late Quaternary depositional sequences , 2003 .

[67]  M. Siddall,et al.  Sea-level fluctuations during the last glacial cycle , 2003, Nature.

[68]  Kurt Lambeck,et al.  Links between climate and sea levels for the past three million years , 2002, Nature.

[69]  K. Lambeck,et al.  Sea Level Change Through the Last Glacial Cycle , 2001, Science.

[70]  K. Bergman,et al.  Isolated shallow marine sand bodies : sequence stratigraphic analysis and sedimentologic interpretation , 1999 .

[71]  E. Bard,et al.  Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge , 1996, Nature.

[72]  D. Stanley.  A GLOBAL SEA-LEVEL CURVE FOR THE LATE QUATERNARY: THE IMPOSSIBLE DREAM? , 1995 .

[73]  Y. Saito.  Shelf sequence and characteristic bounding surfaces in a wave-dominated setting: Latest Pleistocene-Holocene examples from Northeast Japan , 1994 .

[74]  E. Bard,et al.  U-Th ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years , 1990, Nature.

[75]  R. Fairbanks.  A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation , 1989, Nature.

[76]  Daniel F. Belknap,et al.  Influence of antecedent geology on stratigraphic preservation potential and evolution of Delaware , 1985 .

[77]  D. Swift,et al.  Barrier-island genesis: evidence from the central atlantic shelf, eastern U.S.A. , 1975 .

[78]  D. Swift.  Coastal Erosion and Transgressive Stratigraphy , 1968, The Journal of Geology.