- Email: [email protected]
Subaerially exposed continental shelves: Contributions from INQUA Project 0419
ARTICLE IN PRESS
Quaternary International 183 (2008) 1–2
Editorial
Subaerially exposed continental shelves: Contributions from INQUA Project 0419 The duration of time with high sea levels like the presentday level can be estimated using the Vostok ice core to occupy not more than 20% of the past 420,000 years. Consequently, the continental shelves are more often subaerially exposed. INQUA Project 0419, a project of the Sub-commission on Continental Shelves, Commission on Coastal and Marine Processes is devoted mainly to the study of the terrestrial record during this time period since the Middle Pleistocene climatic transition. The collection of papers in this volume is either presented at the Hong Kong workshop in 2005 or is contributed by participating project members. The papers are a contribution to the Commission on Coastal and Marine Processes, IGCP Project no. 464 ‘Continental shelves during the last glacial cycle’ and IGCP Project no. 526 ‘Risks, resources and record of the past on the continental shelf’. John Mylroie has used carbonate deposition and dissolution cycles to assess Late Quaternary sea-level changes in the Bahamas. Glacioeustatic sea-level highstand positions are recorded in aeolian and subtidal limestones, providing a depositional record of platform flooding and carbonate sediment production. Phreatic cave development also documents sealevel highstand positions. U/Th dating of Late Pleistocene fossil corals and cave stalagmites has produced an excellent record of the last interglacial (MIS 5e). Holocene aeolianite successions indicate platform flooding at 5000 BP, and sealevel stabilization at 3000 BP. Palaeosols, representing integrated aerosol dust deposition of 100 ka-long platform exposure events during glaciations, have been differentiated by paleomagnetic secular variation measurements. Previous interpretations of a beach unit to indicate a +20 m MIS stage 11 sea-level highstand, and of large boulders to represent a mega-tsunami, appear to be incorrect. The paper by Kim et al. describes a sequence of 12 uplifted marine terraces, up to 130 m elevation, on the southeast coast of Korea. The lower three terraces (8–25 m elevation) are dated by a combination of OSL and tephrochronology, and indicate correlation with high sea levels during MIS 5a, 5c and 5e. Calculated uplift rates are in the range 0.14–0.22 mm/year. The older terraces are undated, but based on extrapolation of uplift rate, they could range in age up to 1 million years.
Wyss Yim and colleagues have investigated the stratigraphy of subaerially exposed Quaternary deposits from Hong Kong, using OSL dating for chronological control. Rotary boreholes in Tai O Bay penetrated a succession of marine and terrestrial deposits formed during the last four interglacial–glacial cycles. The interglacial periods are represented by siliciclastic-dominated shallow marineestuarine deposits. Glacial periods are characterized by colluvial–alluvial fan deposits. OSL dating out has confirmed the last glacial age of the terrestrial unit unconformably overlain by Holocene intertidal–subtidal estuarine deposits. Density and moisture contents of the sediments reflect episodes of subaerial exposure of the preHolocene interglacial marine units. Desiccated crusts on the surfaces of interglacial units are marked by increased density and iron cementation, resulting from from acidsulphate soil development. Quaternary terrestrial deposits occurring on continental shelves can therefore be datable to a greater degree of certainty than can their subaerial counterparts. Jessica Reeves and colleagues reconstructed the environmental evolutionary record of the Gulf of Carpentaria region in northern Australia through the last glacial cycle using a series of six sediment cores. While the occurrence of palaeo-Lake Carpentaria has previously been identified, this study expands on the hydrological conditions of the lacustrine phases and extends the record through the Last Interglacial, detailing the previous sea-level highstand (MIS 5.5) and subsequent retreat. Comparisons are made both with global sea-level records and with local terrestrial records to determine environmental and climatic change through this period, including the occurrence and strength of the Austral monsoon. Ekaterina Taldenkova and colleagues used bivalves, ostracods and foraminifera to investigate sedimentary successions from the Laptev Sea. Past inflows of Atlanticderived waters are indicated by faunal evidence, whereas freshwater inputs, downslope sediment movements and icerafting are documented by the presence of euryhaline, brackish-water and freshwater ostracods. Atlantic-derived subsurface waters reached the Laptev Sea by ca. 16 cal. ka. The strongest Atlantic influence occurred prior to 12 cal. ka
1040-6182/$ - see front matter r 2008 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2007.10.027
ARTICLE IN PRESS 2
Editorial / Quaternary International 183 (2008) 1–2
and after 3 cal. ka. Subsequent changes in the benthic communities indicate a climate cooling characterized by intensified surface and bottom water circulation regimes. Massimo Caldara and colleagues discuss Holocene evolution and sea-level changes in the Battaglia basin area of Apulia. This former lake records a history of marine, lagoonal and lacustrine sedimentation from prior to 7000 cal. BP until it was drained in modern times. The sea-level curve shows continuous transgression from 7000 to 2730 cal. BP, followed by a short-lived abrupt drop. Sealevel rise has resumed in the past 2000 years. This pattern of transgression, punctuated by a short-lived regressive episode, mirrors that recorded elsewhere along the Apulian coast. Tectonic activity is believed to be a major factor governing sea-level history in Apulia. Using a climate simulation model, Hetherington et al. have investigated the impacts of climate change on two key human migrations, both of which are presumed to have occurred on exposed continental shelves during the last glaciation. The first migration was the migration of modern humans out of Africa across the Red Sea area into the Middle East and Asia around 100 ka. The second was the migration of humans from northern Asia to the Americas via Beringia around 13–14 ka. In both cases, Hetherington et al. argue that climate-controlled shifts in vegetation and reductions in net primary productivity may have pushed plants and animals (including humans) into more productive nearby areas on exposed continental shelves. Mastronuzzi and Romaniello analysed the factors influencing 14C dating of terrestrial gastropods in southern Italy, as a method of dating Holocene coastal aeolian deposits. Middle Holocene, Greek-Roman and Medieval morphogenetic phases were recognized using dating of subfossil terrestrial gastropods, archaeological data and OSL
analyses. Assessment of 14C dating results from terrestrial gastropods requires consideration of the effects of both micro-particles of calcite/aragonite in the shell structures, often derived from the local substratum; and the variation of CO2 content in the plants eaten by the gastropods. Terrestrial gastropods living in a coastal area were collected and 14C AMS dated. The results indicate that most living gastropods date up to 1500 years older than their real age. The aging effect on living gastropods is probably at least in part due to the Bomb Peak produced by the 1945–1955 nuclear tests. In addition to all our anonymous referees, the following referees are thanked for their assistance: Cecile Baeteman, David Bridgland, Lindsay Collins, Luigi Ferranti, Scott A. Elias and Jeremy Lloyd. Wyss W.-S. Yim Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China E-mail address: [email protected] Norm R. Catto Department of Geography, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3X9 Allan R. Chivas School of Earth and Environmental Sciences, University of Wollongong, NSW 2522, Australia Brad Pillans Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia
Quaternary International 183 (2008) 1–2
Editorial
Subaerially exposed continental shelves: Contributions from INQUA Project 0419 The duration of time with high sea levels like the presentday level can be estimated using the Vostok ice core to occupy not more than 20% of the past 420,000 years. Consequently, the continental shelves are more often subaerially exposed. INQUA Project 0419, a project of the Sub-commission on Continental Shelves, Commission on Coastal and Marine Processes is devoted mainly to the study of the terrestrial record during this time period since the Middle Pleistocene climatic transition. The collection of papers in this volume is either presented at the Hong Kong workshop in 2005 or is contributed by participating project members. The papers are a contribution to the Commission on Coastal and Marine Processes, IGCP Project no. 464 ‘Continental shelves during the last glacial cycle’ and IGCP Project no. 526 ‘Risks, resources and record of the past on the continental shelf’. John Mylroie has used carbonate deposition and dissolution cycles to assess Late Quaternary sea-level changes in the Bahamas. Glacioeustatic sea-level highstand positions are recorded in aeolian and subtidal limestones, providing a depositional record of platform flooding and carbonate sediment production. Phreatic cave development also documents sealevel highstand positions. U/Th dating of Late Pleistocene fossil corals and cave stalagmites has produced an excellent record of the last interglacial (MIS 5e). Holocene aeolianite successions indicate platform flooding at 5000 BP, and sealevel stabilization at 3000 BP. Palaeosols, representing integrated aerosol dust deposition of 100 ka-long platform exposure events during glaciations, have been differentiated by paleomagnetic secular variation measurements. Previous interpretations of a beach unit to indicate a +20 m MIS stage 11 sea-level highstand, and of large boulders to represent a mega-tsunami, appear to be incorrect. The paper by Kim et al. describes a sequence of 12 uplifted marine terraces, up to 130 m elevation, on the southeast coast of Korea. The lower three terraces (8–25 m elevation) are dated by a combination of OSL and tephrochronology, and indicate correlation with high sea levels during MIS 5a, 5c and 5e. Calculated uplift rates are in the range 0.14–0.22 mm/year. The older terraces are undated, but based on extrapolation of uplift rate, they could range in age up to 1 million years.
Wyss Yim and colleagues have investigated the stratigraphy of subaerially exposed Quaternary deposits from Hong Kong, using OSL dating for chronological control. Rotary boreholes in Tai O Bay penetrated a succession of marine and terrestrial deposits formed during the last four interglacial–glacial cycles. The interglacial periods are represented by siliciclastic-dominated shallow marineestuarine deposits. Glacial periods are characterized by colluvial–alluvial fan deposits. OSL dating out has confirmed the last glacial age of the terrestrial unit unconformably overlain by Holocene intertidal–subtidal estuarine deposits. Density and moisture contents of the sediments reflect episodes of subaerial exposure of the preHolocene interglacial marine units. Desiccated crusts on the surfaces of interglacial units are marked by increased density and iron cementation, resulting from from acidsulphate soil development. Quaternary terrestrial deposits occurring on continental shelves can therefore be datable to a greater degree of certainty than can their subaerial counterparts. Jessica Reeves and colleagues reconstructed the environmental evolutionary record of the Gulf of Carpentaria region in northern Australia through the last glacial cycle using a series of six sediment cores. While the occurrence of palaeo-Lake Carpentaria has previously been identified, this study expands on the hydrological conditions of the lacustrine phases and extends the record through the Last Interglacial, detailing the previous sea-level highstand (MIS 5.5) and subsequent retreat. Comparisons are made both with global sea-level records and with local terrestrial records to determine environmental and climatic change through this period, including the occurrence and strength of the Austral monsoon. Ekaterina Taldenkova and colleagues used bivalves, ostracods and foraminifera to investigate sedimentary successions from the Laptev Sea. Past inflows of Atlanticderived waters are indicated by faunal evidence, whereas freshwater inputs, downslope sediment movements and icerafting are documented by the presence of euryhaline, brackish-water and freshwater ostracods. Atlantic-derived subsurface waters reached the Laptev Sea by ca. 16 cal. ka. The strongest Atlantic influence occurred prior to 12 cal. ka
1040-6182/$ - see front matter r 2008 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2007.10.027
ARTICLE IN PRESS 2
Editorial / Quaternary International 183 (2008) 1–2
and after 3 cal. ka. Subsequent changes in the benthic communities indicate a climate cooling characterized by intensified surface and bottom water circulation regimes. Massimo Caldara and colleagues discuss Holocene evolution and sea-level changes in the Battaglia basin area of Apulia. This former lake records a history of marine, lagoonal and lacustrine sedimentation from prior to 7000 cal. BP until it was drained in modern times. The sea-level curve shows continuous transgression from 7000 to 2730 cal. BP, followed by a short-lived abrupt drop. Sealevel rise has resumed in the past 2000 years. This pattern of transgression, punctuated by a short-lived regressive episode, mirrors that recorded elsewhere along the Apulian coast. Tectonic activity is believed to be a major factor governing sea-level history in Apulia. Using a climate simulation model, Hetherington et al. have investigated the impacts of climate change on two key human migrations, both of which are presumed to have occurred on exposed continental shelves during the last glaciation. The first migration was the migration of modern humans out of Africa across the Red Sea area into the Middle East and Asia around 100 ka. The second was the migration of humans from northern Asia to the Americas via Beringia around 13–14 ka. In both cases, Hetherington et al. argue that climate-controlled shifts in vegetation and reductions in net primary productivity may have pushed plants and animals (including humans) into more productive nearby areas on exposed continental shelves. Mastronuzzi and Romaniello analysed the factors influencing 14C dating of terrestrial gastropods in southern Italy, as a method of dating Holocene coastal aeolian deposits. Middle Holocene, Greek-Roman and Medieval morphogenetic phases were recognized using dating of subfossil terrestrial gastropods, archaeological data and OSL
analyses. Assessment of 14C dating results from terrestrial gastropods requires consideration of the effects of both micro-particles of calcite/aragonite in the shell structures, often derived from the local substratum; and the variation of CO2 content in the plants eaten by the gastropods. Terrestrial gastropods living in a coastal area were collected and 14C AMS dated. The results indicate that most living gastropods date up to 1500 years older than their real age. The aging effect on living gastropods is probably at least in part due to the Bomb Peak produced by the 1945–1955 nuclear tests. In addition to all our anonymous referees, the following referees are thanked for their assistance: Cecile Baeteman, David Bridgland, Lindsay Collins, Luigi Ferranti, Scott A. Elias and Jeremy Lloyd. Wyss W.-S. Yim Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China E-mail address: [email protected] Norm R. Catto Department of Geography, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3X9 Allan R. Chivas School of Earth and Environmental Sciences, University of Wollongong, NSW 2522, Australia Brad Pillans Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia