In November 2013, an artificial inlet was opened in the barrier island that separates the waters of the Setiu estuary-lagoon system of Terengganu, Malaysia, from the South China Sea. The inlet was opened to stabilize salinity and improve tidal flushing so that fish-farming could be expanded but, as a result, another inlet that was open in 2009 closed naturally by November 2015. These geomorphic changes caused salinity in the Setiu estuary to undergo significant increase from November 2013 to November 2015. To investigate the foraminiferal response to these salinity changes, 24 of 56 foraminiferal sampling stations occupied in 2009 were resampled in 2016. Salinity increased throughout the estuary from 2009 (mean 6.6, range 0–28.7) to 2016 (mean 33.3, range 23.3–34.8) and foraminiferal live communities and dead assemblages changed. Diversity of dead assemblages increased significantly (mean number of species/sample in 2009 = 10.9 versus 2016 = 25.8) as the result of transport of specimens of nearshore, neritic species into the estuary through the new inlet. Diversity of live populations increased slightly (2008 = 4.6 versus 2016 = 6.2). Dead assemblages and live populations dominated by agglutinated foraminifera in 2009 were co-dominated by calcareous hyaline foraminifera in 2016. Live calcareous porcelaneous foraminifera were rare in 2009 and 2016, but dead miliolids were more common and more widespread in 2016. Stations in higher energy environments immediately adjacent to the two different inlets of 2009 and 2016 were characterized by few live or dead foraminiferal tests. Changes in foraminiferal diversity, abundance, and distribution between the two sampling times of early June 2009 and late May 2016 were significant and took place within the 30-month interval between November 2013 (when the artificial inlet was opened) and May 2016 when samples were collected, but they most likely occurred over a shorter interval of time.
The distributions of modern foraminiferal species represent an important tool for petroleum geologists to characterize paleoenvironments. This paper documents the distribution of benthic foraminifera on the inner shelf (<40 m water depth) immediately offshore of the Terengganu River mouth, one of the three major drainages on the east coast of peninsular Malaysia. Sediment substrate type primarily controls the distribution of species; temperature, salinity, dissolved oxygen, and pH vary little in the study area and have little influence. Sandy substrates (mostly coarse and very coarse sand) from 20 to 40 m water depth are characterized by abundant specimens of the larger foraminifera Amphistegina spp. Muddy substrates immediately adjacent to the Terengganu River mouth from 12 to 20 m water depth are characterized by higher diversity assemblages dominated by several smaller calcareous taxa and the agglutinated species Ammobaculites exiguus. The latter species has been documented in muddy sediments at other river mouths on the east coast of peninsular Malaysia. Strong, seasonally reversing monsoon-driven currents affect sediment transport along the east coast of peninsular Malaysia and therefore indirectly influence the distributions of foraminiferal species. The results of this study add to the increasingly extensive database on modern foraminiferal distributions that provides a model for paleoenvironmental interpretations of hydrocarbon-bearing Neogene strata off the east coast of Thailand and peninsular Malaysia.
Recent research has shown that sedimentological information in barrier-island settings may provide more detailed interpretations of some past coastal environments than interpretations based upon foraminifera. This research investigates whether targeted documentation of modern foraminifera in specific coastal environments can result in higher resolution micropaleontology-based paleoenvironmental reconstructions. Bear Island, North Carolina, characterized by little human disturbance, was chosen for detailed documentation of foraminifera in modern barrier-island-related environments. Modern sediments in all subenvironments were predominantly siliciclastic (< 30 % clastic carbonate debris) in composition: clastic carbonate allochems (e.g., mollusk shell fragments, echinoid spines) were admixed with fine- to medium-grained quartz sand. The hypothesis that modern foraminiferal assemblages of 26 modern coastal subenvironments can be distinguished based upon their foraminiferal assemblages was tested by discriminant analysis and resulted in the recognition of four environmental supergroups: shoreface, ebb-tidal delta, flood-tidal delta/inlet channel, and “barrier-combined” (foreshore, washover, dune, sandflat, spit, longshore bar, and trough). Holocene paleoenvironments represented by foraminiferal assemblages in 16 vibracores collected from the modern inner shelf, shoreface, ebb-tidal delta, and inlet environments of Bogue Banks, immediately adjacent to Bear Island, were interpreted, via discriminant analysis, based upon the modern dataset. Holocene and modern foraminiferal assemblages were similar but variations in species abundance and species diversity allowed for alternative paleoenvironmental classification of core samples at varying levels of probability. The methodology of this research is widely applicable to other coastal environments.
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