Techniques of fossil hunting differs in different group of fossils, what are the best tips to find calcareus rocks rich in LBFs?
Calcareous rocks rich in LBFs are generally shallow marine rocks having been deposited in warm, shallow, calm ocean shelfs and often associated with reefal build-ups. They may be significant sediments in many geosynclinal setups and the LBFs are often visible to naked eyes in an outcrop sections. The fossils can be extracted from the sediments by mechanical chipping and cleaning or a normal wet processing technique involving use of mild detergents/ cleaning agents and studied both externally as well as in oriented sections.
In my opinion, the first thing is to get a good geological map of the study area.
May be trivial...not forget the lens when going for field work :-)
My Personal experience is, there are chances to find LBFs in any sort of rocks even clastics (Sandstone, Conglomerates, etc.) but in order to find well preserved LBFs, worth for systematic studies, then we need to take into account their Paleoecology.
As most LBFs host symbiont algae, they reside within photic range zones and oligotrophic part of sea water, which usually matches to middle to outer ramp, in ramp carbonate systems and slope and backshelves in shelf carbonates. Such locations are mostly low energy systems (except for turbiditic and gravity currents in highly inclined slopes) thus micrite is dominant in the rock groundmass, so there is a good chance to find well preserved LBFs (Nummulitids, Orthophragminids, Rotaliids, Loftusiids, Cyclamminids, etc) in such rocks. Other important groups of LBFs with porcelaneous wall such as Alveolinids & Soritids often reside in higher salinity areas such as restricted lagoons, still due to low energy systems of such places the rock matrix is almost micritic.
However, one should not neglect post diagenitic alterations which both affect grains and matrix. Most often it is not suggested to sample from intensly crystallized calcareous rocks mostly filled with crosscuts of sparitic veins and intensly dolomitized rocks. In such rocks there is a high risk that the wall structure of LBFs damaged by recrystallization which obscures accordingly their determination.
In my experince in high energy systems such as reefs there is low chance to hunt LBFs and sections from reefs are mostly dominated by macrofaunas (Corals, Spongs, etc).
Also in eutrophic sea waters (closer to coastlines) there are chances that smaller benthic forams are more abundant rather than LBFs.
In high enrgy coastal systems due to discharge of terrigenous materials, carbonate factories in general cannot function well , thus insitu calcitic biograins are mostly absent and accumulation of reworked shell fragments can be abundant instead, still low chances to find robust LBFs.
Additionally, in high energy systems usually grains including LBFs are broken, this in turn causes difficulty to determine them.
It depends in which LBF group are you focusing on, and on which kind of research are you carrying on. If you the aim of your research is a facies analysis and paleoenvironments, hard rock samples of swallow marine limestones shoud be your target. LBF genera can be easily indetified through the observance of thin sections or polished slabs. This kind of samples may be also adequate to find oriented section of Alveolinids and trematophore miliolids, since they can be in great numbres in shallow marine facies and by pure chance equatorialy oriented sections can be found, suitable for systematic purposes. Nevertheless, if your target is the systematic study of nummulitids, avoid hard-rock samples and look for marls where Nummulites and Assilina tests can be found loose of can be easily detached. Marly intervarls between shallow marine limestones are usually a good places to find them. To obtain a equatorially oriented sections in nummulitds, a heat treatment (see Schaub, 1981) is rather adequate, offering sections of greater quality than polishing.
Recently, as I was studying Nummulitic beds in the field, I found that the dominant lithology bearing Nummulites species is sandy limestone, it is not yet clear whether the insitu environment is a mixed siliciclastic carbonate environment or Nummulites are carried away from their original biotope off to a coastal environment, further microscopic studies may lead to a reliable answer.
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