DLA 35 (Arenal) (Ordovician of Argentina)

Also known as Are 21

Where: Jujuy, Argentina (23.5° S, 65.3° W: paleocoordinates 44.8° S, 128.8° W)

• coordinate based on unpublished field data

• small collection-level geographic resolution

When: Rupasca Member (Santa Rosita Formation), Tremadocian (485.4 - 477.7 Ma)

• bed-level stratigraphic resolution

Environment/lithology: transition zone or lower shoreface; lithified, silty, sandy siliciclastic sediments and lithified, muddy siliciclastic

• Offshore-transition deposits consist of regularly interbedded, yellowish green and grey, parallel-laminated mudstone, and thin to thick, light grey, erosive-based, fine- to very fine-grained sandstone with hummocky cross-stratification, combined-flow ripple cross-lamination and ⁄ or symmetrical to near-symmetrical ripples at the top. Sandstone beds are usually laterally extensive, although displaying thickness variation. Hummocky cross-stratification is the dominant structure in the thickest sandstone beds, while combined-flow ripple cross-lamination tends to dominate in the thinnest beds. In contrast to lower-shoreface deposits, amalgamation of hummocky beds is uncommon. Common shell lags and intraclast layers are present at the base of hummocky beds. Gutter casts, load casts, tool marks and wrinkle marks are common. These deposits reflect alternation of quiet-water sediment fall-out, and combined and pure oscillatory flows due to frequent storms (Buatois & Mangano 2003; Buatois et al. 2006). The presence of thin mudstone intervals separating hummocky beds indicates periods of low energy between storm flows and deposition immediately below fair-weather wave base.

Size classes: macrofossils, mesofossils

Preservation: cast, mold/impression

Collection methods: bulk,

Primary reference: D. Balseiro, B. G. Waisfeld, and L. A. Buatois. 2011. Unusual trilobite biofacies from the Lower Ordovician of the Argentine Cordillera Oriental: new insights into olenid palaeoecology. Lethaia 44:58-75 [D. Balseiro/D. Balseiro]more details

Purpose of describing collection: paleoecologic analysis

PaleoDB collection 136936: authorized by Diego Balseiro, entered by Diego Balseiro on 07.12.2012

Creative Commons license: CC BY (attribution)

Taxonomic list

 Phacopida - Pharostomatidae
Pharostomina sp. Sdzuy 1955 trilobite
 Asaphida - Asaphidae
Asaphellus sp. Callaway 1877 trilobite
 Asaphida - Remopleurididae
Apatokephalus sp. Brögger 1896 trilobite
 Ptychopariida - Olenidae
Leptoplastides sp. Raw 1908 trilobite
Parabolinella sp. Brögger 1882 trilobite