Andrea D. Hawkes

Stratigraphic record of Holocene coseismic subsidence, Padang, West Sumatra

[1]xa0Stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of Padang, West Sumatra along the Mentawai segment (0.5°S–0.3°S) of the Sunda subduction zone. Each earthquake is marked by a sharp soil-mud contact that represents a sudden change from mangrove to tidal flat. The earthquakes occurred about 4000 and 3000 cal years B.P. based on radiocarbon ages of detrital plant fragments and seeds. The absence of younger paleoseismic evidence suggests that late Holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone. Our results point to a brief, few thousand year window of preservation of subsidence events in tidal-wetland stratigraphic sequences, a result that is generally applicable to other emergent coastlines of West Sumatra.

Attached benthic Foraminifera as indicators of past and present distribution of the coral Primnoa resedaeformis on the Scotian Margin

Benthic Foraminifera found attached to the deep-sea coral Primnoa resedaeformis may be used to establish paleo-coral locations long after the coral has disappeared. Recent coral research cruises have revealed that the coral on the Scotian Margin is in peril and in many cases no longer exists. Sea floor video footage suggests various fishing methods have destroyed much of the coral as it has in coastal areas off Norway and Alaska. To date deep-sea corals are sparse on the Scotian Margin; therefore evidence preserved in the sediment may establish whether corals were present and more abundant in the past. A representative assemblage of benthic foraminiferans found attached to the deep-sea coral Primnoa resedaeformis may be the evidence necessary to provide presence/absence indicators long after the coral has disappeared. Both foraminiferal species are known to be only associated with the coral, and distortion of the ventral side (attached) of common foraminiferal species found in the sediment, may provide a clue to past coral habitat. Identifying a deep-sea coral paleo-habitat indicator provides insight into the extent to which it existed. Video footage from coral cruises over the last three years indicates that coral and fish go hand in hand, an important observation for a region where fishing comprises 23 % of the local economy.