Studies on settling, traction and entrainment of larger benthic foraminiferal tests: implications for accumulation in shallow marine sediments

Author(s)

Elza Hofmann, Johann Hohenegger

Abstract

Settling and traction velocities were measured on optimally preserved tests of

larger foraminifera using a settling tube and flume tank. Within larger

foraminifera with porcelaneous tests, the peneroplids, Peneroplis antillarum,

P. planatus, P. pertusus and Dendritina cf. D. zhengae, are distinguished by

low test densities (ca 1Æ2) that do not change with growth. Buoyancy is high

because of low Reynolds numbers and increases in large individuals because

of the allometric change of test shape. The fusiform Alveolinella quoyi, with

test densities ca 1Æ6, is characterized by high Reynolds numbers, inducing the

weakest buoyancy within porcelaneous larger foraminifera. The highest

buoyancy was recorded for the three soritids, Parasorites orbitolitoides,

Sorites orbiculus and Amphisorus hemprichii, because of their low test

densities (ca 1Æ25) and the extremely flat, biconcave, plate-like shape. Flat

tests, however, reduce traction and entrainment from smooth surfaces. Within

hyaline larger foraminiferat, the amphisteginids show thick-lenticular

(Amphistegina lobifera, A. radiata) to thin-lenticular tests (A. bicirculata,

A. papillosa), influencing buoyancy. Here, high test densities (ca 1Æ8) decrease

with growth in A. lobifera, A. lessonii and A. bicirculata, and remain constant

in A. radiata and A. papillosa. Minimum velocities required for entrainment

are lower for thick-lenticular tests and higher for thin-lenticular tests. Test

densities remain constant with growth in the calcarinid Baculogypsina

sphaerulata (q _ 1Æ78) and decrease slightly in Calcarina gaudichaudii and

Neorotalia calcar (starting at q _ 1Æ85), all living under extreme hydrodynamic

conditions. Density decreases the most in Baculogypsinoides spinosus

(starting at q _ 1Æ8), resulting in higher buoyancy through low Reynolds

numbers. Traction is promoted in spherical tests of Baculogypsina and

Baculogypsinoides. Within nummulitids, the thick-lenticular

Palaeonummulites venosus (test density decreasing with size; starting at

1Æ78) is less buoyant, expressed in high Reynolds numbers, but easily

entrained. Thick-lenticular juveniles and extremely flat adults distinguish

Operculinella cumingii, Heterostegina depressa and the giant Cycloclypeus

carpenteri. Test densities increase during growth, starting from ca 1Æ6 and

attaining a maximum of 1Æ8. Buoyancy is low in small tests and high in large

tests, while entrainment velocities are reduced as the tests flatten. High

buoyancy is also a characteristic of the entirely flat tests in Operculina

ammonoides (from deeper regions) and Planostegina operculinoides, which is

expressed in the lowest Reynolds numbers within larger foraminifera.

Organisation(s)

Department of Palaeontology

Journal

Sedimentology

Pages

1273-1306

No. of pages

34

ISSN

0037-0746

Publication date

2007

Peer reviewed

Yes

Austrian Fields of Science 2012

105121 Sedimentology, 1060 Biology, 105118 Palaeontology, 1051 Geology, Mineralogy

Sustainable Development Goals

SDG 14 - Life Below Water

Portal url

https://ucrisportal.univie.ac.at/en/publications/ed65cbd8-8b20-41b3-801f-0c73adadda29