Episodic postglacial deltaic pulses in the Gulf of Cadiz: Implications for the development of a transgressive shelf and driving environmental conditions
Author:
Carrión-Torrente Álvaro12, Lobo Francisco José1, Puga-Bernabéu Ángel2, Mendes Isabel3, Lebreiro Susana4, García Marga5, van Rooij David6, Luján María7, Reguera María Isabel4, Antón Laura4
Affiliation:
1. 1 Department of Marine Geosciences, Instituto Andaluz de Ciencias de la Tierra, Spanish Research Council and University of Granada, Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain 2. 2 Departmento de Estratigrafía y Paleontología, University of Granada, Granada, Spain 3. 3 Centre for Marine and Environmental Research, Universidade do Algarve, Faro, Portugal 4. 4 Instituto Geológico y Minero de España-Centro Nacional, Spanish Research Council, 28003, Madrid, Spain 5. 5 Oceanographic Centre of Cadiz, Spanish Institute of Oceanography, CSIC, Ministry of Science and Innovation, Cadiz, Spain 6. 6 Renard Centre of Marine Geology, Ghent University, Krijgslaan 281 (S8), 9000 Gent, Belgium 7. 7 Department of Earth Sciences, University of Cadiz, Puerto Real, Spain
Abstract
Abstract
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.
Publisher
Society for Sedimentary Geology
Reference121 articles.
1. Aksu,
A.E.
,
Hiscott,R.N., and
Yaltırak,C.,
2016,
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:
Marine Geology,
v.380,
p.113–137. 2. Anthony,
E.J.
,
Marriner,N., and
Morhange,C.,
2014,
Human influence and the changing geomorphology of mediterranean deltas and coasts over the last 6000 years: from progradation to destruction phase?:
Earth Science Reviews,
v.139,
p.336–361. 3. Baldy,
P.
,
1977,
Géologie du plateau continental portugaise (au sud du cap de Sines) [Thèse de 3ème Cycle] :
Université Paris VI,
113p. 4. Bard,
E.
,
Hamelin,B., and
Fairbanks,R.G.,
1990,
U-Th ages obtained by mass-spectrometry in corals from Barbados: sea-level during the past 130,000 years:
Nature,
v.346,
p.456–458. 5. Bard,
E.
,
Hamelin,B.,
Arnold,M.,
Montaggioni,L.,
Cabioch,G.,
Faure,G., and
Rougerie,F.,
1996,
Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge:
Nature,
v.382,
p.241–244.
Cited by
3 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|