Monumento Natural Bosques Petrificados (Jurassic to of Argentina)

Where: Santa Cruz, Argentina (48.0° S, 68.0° W: paleocoordinates 44.8° S, 26.7° W)

When: La Matilde Formation (Bahia Laura Group), Bathonian to Bathonian (168.3 - 163.5 Ma)

Environment/lithology: fluvial-lacustrine; poorly lithified, tabular, burrowed, tuffaceous volcaniclastic sediments and breccia

• In the studied section at the Monumento Natural Bosques

•Petrificados locality, the pyroclastic deposits are the most important

•lithologic component; the preserved stratigraphic section is about

•125 m, affected at the upper portion by north–south normal faults

•(see Fig. 1.2). The succession begins with stratified siltstones and rare

•massive paleochannels. The lower fossiliferous level (“Barda Blanca”

•or “BB” in situ forest) developed on a lateral extended paleosol with

•abundant root traces and vegetal remains. The in situ stumps are

•covered by 12 m of pyroclastic deposits, with accretionary lapilli and

•laminated tuffs at the base (surge deposits?) and massive tuffs

•upwards (fallen ash deposits). It continues with massive intraformational

•breccias, deposited by debris-flow and hyperconcentrated

•flows during the reworking of pyroclastic sediments. These deposits

•are overlain by an upward coarsening interval of reworked tuffs (15–

•19 m), characterized by fine laminations, abundant burrows (Skolithos

•and Planolites), current ripples and impressions of herbaceous

•equisetaleans (Falaschi et al., 2009); these deposits are interpreted

•as a succession of shallow water bodies with important organic

•activity, with an increase of the terrigenous influence upwards. At the

•top of this shallow water succession the second fossiliferous level

•developed (“Bosque Principal” or “BP” in situ forest), over a mottled

•paleosol with abundant, unidentified vegetal remains. The stratigraphic

•section is interrupted by normal faults, but the upper deposits

•of the La Matilde Formation have more defined fluvial characteristics

•with paleochannels deposited by dilute flows.

Size class: macrofossils

Preservation: cast, mold/impression, trace, recrystallized, original silica, original carbon, replaced with silica

Primary reference: P. Falaschi, J. Grosfeld, A. B. Zamuner, N. Foix, and S. M. Rivera. 2011. Growth architecture and silhouette of Jurassic conifers from La Matilde Formation, Patagonia, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology 302(43):122-141 [P. Wilf/E. Stiles]more details

Purpose of describing collection: general faunal/floral analysis

PaleoDB collection 200039: authorized by Peter Wilf, entered by Elena Stiles on 26.02.2019

Creative Commons license: CC BY (attribution)

Taxonomic list

Pinopsida
 Pinales - Araucariaceae
 Pinales - Cheirolepidiaceae
Pararaucaria patagonica Wieland 1929
Wieland 1929
 Pinales -
Brachyphyllum indet. Brongniart 1828